Non-Genotoxic Anti-CD117 Antibody Conditioning Results in Successful Hematopoietic Stem Cell Engraftment in Patients with Severe Combined Immunodeficiency

Successful hematopoietic cell transplantation (HCT) requires vacating recipient hematopoietic stem cell (HSC) niches to permit transplanted HSC to engraft. Currently, DNA damaging radiation or chemotherapy are used to eliminate recipient HSC and achieve niche clearance. We have pursued a non-genotoxic approach to target and deplete HSC using a humanized monoclonal antibody, AMG 191, that binds human CD117 (c-Kit), a receptor tyrosine kinase expressed on the surface of HSC and progenitor cells (HSPC). We have shown that AMG 191 suppresses human hematopoiesis in vitro, depletes human HSC in mice xenografted with human cells, and safely depletes HSC of non-human primates. We have initiated a Phase I dose escalation trial to test AMG 191 as the sole conditioning agent to achieve donor CD34-enriched HSPC engraftment in patients undergoing HCT for severe combined immunodeficiency (SCID) (ClinicalTrials.gov: NCT02963064). SCID is a severe genetic immune disorder curable only by HCT. Because of toxicity concerns, infants with SCID often receive donor hematopoietic grafts without conditioning, resulting in a lack of donor HSC engraftment. Instead, mature T lymphocytes and possibly lymphoid progenitors engraft but support only donor T cell development. This approach is associated with incomplete and poorly sustained immune reconstitution, and many patients have either no donor B cells and/or poor B cell function requiring life-long immunoglobulin replacement therapy. Second unconditioned donor HSC "boosts" can be performed, but they do not result in HSC engraftment and immune defects may persist. The primary endpoint of our study is to assess the safety and tolerability of AMG 191 as a conditioning agent in SCID patients. Secondary endpoints include AMG 191 pharmacokinetics (PK), host HSC depletion, and the determination of the dose of AMG 191 that achieves adequate donor HSC engraftment, defined as >5% donor blood granulocyte chimerism in peripheral blood at 24 weeks. Seven patients have been treated to date who are >12 weeks post-HCT (Table 1): three in each of the first two dose cohorts (0.1 and 0.3 mg/kg AMG 191), and one patient in the third cohort (1.0 mg/kg). An eighth patient has been treated at the 1.0 mg/kg dose and is three weeks post-HCT. Patients have a mixture of SCID genotypes. All patients treated to date had prior HCT with lack of donor HSC engraftment as evidenced by 0% donor sorted granulocyte chimerism at study entry. AMG 191 administration and infusion of original donor CD34+-selected cells were uniformly well tolerated. Pre- and post-infusion marrow analyses in five evaluable patients demonstrated dose-dependent decline in CD117+HSPC following AMG 191 treatment. Table 1 shows that four of six patients, who are >24 weeks post-HCT, reached the predefined endpoint of >5% granulocyte chimerism at 24 weeks, demonstrating donor HSC engraftment. The two patients who did not show donor engraftment at 24 weeks had detectable, low level (<5%) engraftment at later time points. All patients with follow up of >36 weeks show the production of recent thymic emigrants and/or de novo production of naïve T and/or B cells. In addition to improved lymphocyte values, patients have demonstrated clinical improvement including resolution of chronic diarrhea, significant weight gain, and reduced IVIG requirements. Conclusion: This study is the first demonstration of HSC engraftment following monoclonal antibody-based conditioning of patients without chemo(radio)therapy. Specifically, this first-in-human HCT trial shows that an anti-CD117 antibody safely clears HSC niches and facilitates donor HSPC engraftment in patients with SCID. Clinical benefit has been observed with minimal to no toxicity. Four of six evaluable patients have sustained evidence of donor myeloid engraftment along with T and B lymphopoiesis, indicative of engraftment of multipotent HSC. These results suggest that antibody conditioning for HCT may be preferable to traditional chemo(radio)therapy conditioning, especially in patients with non-malignant diseases and/or increased risk of toxicities due to such agents, such as certain forms of SCID, Fanconi anemia and sickle cell disease. Anti-CD117 antibody conditioning may also be applicable to gene therapy with genetically corrected autologous HSC. The AMG 191 study is actively enrolling previously transplanted SCID patients and newly diagnosed SCID patients. Disclosures Dvorak: Alexion Inc: Consultancy; Jazz Pharmaceuticals: Consultancy. Prohaska:Forty Seven Inc: Equity Ownership, Patents & Royalties. Weissman:Forty Seven Inc.: Consultancy, Equity Ownership, Patents & Royalties. Cowan:Rocket Pharma: Consultancy; Homology Medicine: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; bluebird bio: Consultancy; California Institute Of Regenerative Medicine: Research Funding; UpToDate: Honoraria; Leadiant: Consultancy; NIH NIAD: Research Funding. Logan:Kadmon: Research Funding; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Kite: Research Funding; TeneoBio: Consultancy; Novartis: Consultancy; Astellas: Research Funding; Abbvie: Consultancy; Incyte: Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Research Funding; Kiadis: Consultancy; Jazz: Research Funding; Agios: Consultancy, Membership on an entity's Board of Directors or advisory committees. Weinberg:U.S. Patent Office: Patents & Royalties: patent pending - submitted for aldehyde dehydrogenase 2 (ALDH2) activators to expand hematopoietic stem cells. Shizuru:Forty Seven Inc: Equity Ownership, Patents & Royalties.

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Plerixafor (Mozobil ®)Plus G-CSF Is Effective in Mobilizing Hematopoietic Stem Cells in Patients with Concurrent Thrombocytopenia Undergoing Autologous Hematopoietic Stem Cell Transplantation.

Blood ◽

10.1182/blood.v114.22.3229.3229 ◽

2009 ◽

Vol 114 (22) ◽

pp. 3229-3229 ◽

Cited By ~ 1

Author(s):

Ivana N Micallef ◽

Eric Jacobsen ◽

Paul Shaughnessy ◽

Sachin Marulkar ◽

Purvi Mody ◽

...

Keyword(s):

Stem Cell ◽

Platelet Count ◽

Board Of Directors ◽

Research Funding ◽

Advisory Committees ◽

Hematopoietic Stem ◽

Platelet Counts ◽

Cd34 Cells ◽

Low Platelet Count ◽

Equity Ownership

Abstract Abstract 3229 Poster Board III-166 Introduction Low platelet count prior to mobilization is a significant predictive factor for mobilization failure in patients with non-Hodgkin's lymphoma (NHL) or Hodgkin's disease (HD) undergoing autologous hematopoietic stem cell (HSC) transplantation (auto-HSCT; Hosing C, et al, Am J Hematol. 2009). The purpose of this study is to assess the efficacy of HSC mobilization with plerixafor plus G-CSF in patients with concomitant thrombocytopenia undergoing auto-HSCT. Methods Patients who had failed successful HSC collection with any mobilization regimen were remobilized with plerixafor plus G-CSF as part of a compassionate use program (CUP). Mobilization failure was defined as the inability to collect 2 ×106 CD34+ cells/kg or inability to achieve a peripheral blood count of ≥10 CD34+ cells/μl without having undergone apheresis. As part of the CUP, G-CSF (10μg/kg) was administered subcutaneously (SC) every morning for 4 days. Plerixafor (0.24 mg/kg SC) was administered in the evening on Day 4, approximately 11 hours prior to the initiation of apheresis the following day. On Day 5, G-CSF was administered and apheresis was initiated. Plerixafor, G-CSF and apheresis were repeated daily until patients collected the minimum of 2 × 106 CD34+ cells/kg for auto-HSCT. Patients in the CUP with available data on pre-mobilization platelet counts were included in this analysis. While patients with a platelet count <85 × 109/L were excluded from the CUP, some patients received waivers and were included in this analysis. Efficacy of remobilization with plerixafor + G-CSF was evaluated in patients with platelet counts ≤ 100 × 109/L or ≤ 150 × 109/L. Results Of the 833 patients in the plerixafor CUP database, pre-mobilization platelet counts were available for 219 patients (NHL=115, MM=66, HD=20 and other=18.). Of these, 92 patients (NHL=49, MM=25, HD=8 and other=10) had pre-mobilization platelet counts ≤ 150 × 109/L; the median platelet count was 115 × 109/L (range, 50-150). The median age was 60 years (range 20-76) and 60.4% of the patients were male. Fifty-nine patients (64.1%) collected ≥2 × 109 CD34+ cells/kg and 13 patients (14.1%) achieved ≥5 × 106 CD34+ cells/kg. The median CD34+ cell yield was 2.56 × 106 CD34+ cells/kg. The proportion of patients proceeding to transplant was 68.5%. The median time to neutrophil and platelet engraftment was 12 days and 22 days, respectively. Similar results were obtained when efficacy of plerixafor + G-CSF was evaluated in 29 patients with platelet counts ≤ 100 × 109/L (NHL=12, MM=10, HD=3 and other=4). The median platelet count in these patients was 83 × 109/L (range, 50-100). The median age was 59 years (range 23-73) and 60.4% of the patients were male. The minimal and optimal cell dose was achieved in 19(65.5%) and 3(10.3%) patients, respectively. The median CD34+ cell yield was 2.92 × 106 CD34+ cells/kg. The proportion of patients proceeding to transplant was 62.1%. The median time to neutrophil and platelet engraftment was 12 days and 23 days, respectively. Conclusions For patients mobilized with G-CSF alone or chemotherapy ±G-CSF, a low platelet count prior to mobilization is a significant predictor of mobilization failure. These data demonstrate that in patients with thrombocytopenia who have failed prior mobilization attempts, remobilization with plerixafor plus G-CSF allows ∼65% of the patients to collect the minimal cell dose to proceed to transplantation. Thus, in patients predicted or proven to be poor mobilizers, addition of plerixafor may increase stem cell yields. Future studies should investigate the efficacy of plerixafor + G-CSF in front line mobilization in patients with low platelet counts prior to mobilization. Disclosures Micallef: Genzyme Corporation: Membership on an entity's Board of Directors or advisory committees, Research Funding. Jacobsen:Genzyme Corporation: Research Funding. Shaughnessy:Genzyme Corporation: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Marulkar:Genzyme Corporation: Employment, Equity Ownership. Mody:Genzyme Corporation: Employment, Equity Ownership. van Rhee:Genzyme Corporation: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding.

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Targeting CXCR4, VLA4, and CXCR2 for Hematopoietic Stem Cell Mobilization

Blood ◽

10.1182/blood-2019-124373 ◽

2019 ◽

Vol 134 (Supplement_1) ◽

pp. 1916-1916

Author(s):

Daniel Cancilla ◽

Haresh Thakellapalli ◽

Marvin J Meyers ◽

Michael P. Rettig ◽

Ezhilarasi Chendamarai ◽

...

Keyword(s):

Stem Cell ◽

Board Of Directors ◽

Hematopoietic Stem Cell ◽

Research Funding ◽

Patent Application ◽

Advisory Committees ◽

Hematopoietic Stem ◽

Hematopoietic Stem Cell Mobilization ◽

Equity Ownership ◽

Cell Mobilization

Background: Hematopoietic stem cell (HSC) transplant is an essential treatment for a variety of blood disorders and malignancies. A key step in this procedure is the mobilization of donor stem cells. The most commonly used regimen for donor mobilization is a 5-day course of G-CSF. The length of this regimen coupled with the associated side effects emphasizes a need for superior alternatives. In recent years, there has been a growing understanding of mechanisms governing stem cell retention within the bone marrow niche. This has led to the development of new mobilization drugs that specifically target these processes. Two examples of previously described drugs that target mechanisms of stem cell retention are Plerixafor (a CXCR4 inhibitor already in clinical use), and truncated Gro-Beta (tGroβ; a CXCR2 agonist). Another potential target for inducing mobilization is disruption of the interaction between the VLA-4 integrin and its ligand VCAM-1. In this study, we evaluate the efficacy of novel VLA-4 inhibitors (VLA4i) alone and in combination with Plerixafor and/or tGroβ for the purposes of hematopoietic stem cell mobilization. Methods: We synthesized over 15 novel VLA-4 inhibitor molecules and tested their potency using soluble VCAM-1 binding assays. The 5 inhibitors determined to be most potent were then tested in vivo in DBA mice for their ability to mobilize HSCs alone and in combination with tGroβ and/or Plerixafor (n=5). HSC mobilization was measured in wild-type and splenectomized mice via flow cytometry to quantify the proportion of LSK (Lineage- Sca+ cKit+) cells as well as via Colony Forming Unit (CFU) assays. For competitive transplant, mobilized CD45.1+ BALB/c mouse blood (10 uL) was injected into lethally irradiated CD45.2+ BALB/c recipients alongside 2.5x105 CD45.2+ BALB/c bone marrow cells (n=10 / cohort). HSC engraftment was monitored monthly via flow cytometry for ratio of 45.1+ vs. 45.2+ cells in peripheral blood. Results: Firetagrast and BIO5192 are previously characterized VLA4i that have been administered to humans for indications unrelated to HSC mobilization. Our best VLA4i to date, LGB-2019, exhibited similar potency as BIO5192 in preventing the binding of sVCAM-1 to VLA-4 (IC50: 1.7nM) and was >200-fold more potent than firategrast. LGB-2019 showed increased aqueous solubility and mobilized 1.5-fold more murine LSK cells for a longer time period (peak HSC mobilization maintained for 4 hours) than BIO5192 when administered alone. Simultaneous injection of C57BL/6 mice with LGB-2019 (VLA4i), Plerixafor (CXCR4i) and tGro-β (CXCR2a) resulted in a synergistic increase in circulating CFUs (Fig. 1A; 9.8 x 103 CFUs/mL) and LSKs (Fig. 1B; 12.8 LSKs/uL) at 4 hours post-injection. In contrast, 5 days of G-CSF treatment mobilized approximately 3-fold and 8-fold less CFUs and LSKs, respectively (Fig. 1A-B). We saw no significant difference in mobilization for splenectomized vs. wildtype mice (23.4 x 103 CFUs/mL vs. 23.0 x 103 CFUs/mL) when mobilizing DBA/2 mice via VLA4i+CXCR4i+CXCR2a. Three months after competitive transplantation, blood obtained from BALB/c mice mobilized with the triple combination engrafted significantly better than blood obtained from mice treated with G-CSF or the dual combinations (Fig. 1C). Summary: New insights about the stem cell niche have allowed for the development of targeted drugs for the purposes of mobilization. Here, we show that a novel VLA-4 receptor inhibitor in combination with two other known mobilizers induces mobilization of hematopoietic stem and progenitor cells (CFU/LSK) at levels superior to the standard of care G-CSF and in a dramatically shortened time frame. Mouse transplant data also show superior engraftment in lethally irradiated recipients when using the triple cocktail regimen compared to the G-CSF mobilized graft. Secondary transplants are ongoing and will provide a more complete picture of primitive HSC mobilization and serial engraftment properties of the cells. Disclosures Rettig: WashU: Patents & Royalties: Patent Application 16/401,950. Karpova:WashU: Patents & Royalties: Patent Application 16/401,950. Ruminski:WahU: Patents & Royalties: Patent Application 16/401,950. Morrow:Magenta Therapeutics: Employment, Equity Ownership, Patents & Royalties. DiPersio:Cellworks Group, Inc.: Membership on an entity's Board of Directors or advisory committees; RiverVest Venture Partners Arch Oncology: Consultancy, Membership on an entity's Board of Directors or advisory committees; Magenta Therapeutics: Equity Ownership; Incyte: Consultancy, Research Funding; Bioline Rx: Research Funding, Speakers Bureau; Macrogenics: Research Funding, Speakers Bureau; Karyopharm Therapeutics: Consultancy; Celgene: Consultancy; Amphivena Therapeutics: Consultancy, Research Funding; WUGEN: Equity Ownership, Patents & Royalties, Research Funding; NeoImmune Tech: Research Funding.

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Lower Hematopoietic Progenitor Cell Counts and Yields at Subsequent Donations Is Influenced By a Shorter Inter-Donation Interval between the First and Subsequent Mobilizations

Blood ◽

10.1182/blood-2019-123492 ◽

2019 ◽

Vol 134 (Supplement_1) ◽

pp. 1962-1962

Author(s):

Sandhya R. Panch ◽

Brent R. Logan ◽

Jennifer A. Sees ◽

Bipin N. Savani ◽

Nirali N. Shah ◽

...

Keyword(s):

Stem Cell ◽

Board Of Directors ◽

Peripheral Blood ◽

Research Funding ◽

Time Interval ◽

Advisory Committees ◽

Hematopoietic Stem ◽

Peripheral Blood Cd34 ◽

Cell Counts ◽

Cd34 Cells

Introduction: Approximately 7% of unrelated hematopoietic stem cell (HSC) donors are asked to donate a subsequent time to the same or different recipient. In a recent large CIBMTR study of second time donors, Stroncek et al. incidentally found that second peripheral blood stem cell (PBSC) collections had lower total CD34+ cells, CD34+ cells per liter of whole blood processed, and CD34+ cells per kg donor weight. Based on smaller studies, the time between the two independent PBSC donations (inter-donation interval) as well as donor sex, race and baseline lymphocyte counts appear to influence CD34+ cell yields at subsequent donations. Our objective was to retrospectively evaluate factors contributory to CD34+ cell yields at subsequent PBSC donation amongst NMDP donors. Methods. The study population consisted of filgrastim (G-CSF) mobilized PBSC donors through the NMDP/CIBMTR between 2006 and 2017, with a subsequent donation of the same product. evaluated the impact of inter-donation interval, donor demographics (age, BMI, race, sex, G-CSF dose, year of procedure, need for central line) and changes in complete blood counts (CBC), on the CD34+ cell yields/liter (x106/L) of blood processed at second donation and pre-apheresis (Day 5) peripheral blood CD34+ cell counts/liter (x106/L) at second donation. Linear regression was used to model log cell yields as a function of donor and collection related variables, time between donations, and changes in baseline values from first to second donation. Stepwise model building, along with interactions among significant variables were assessed. The Pearson chi-square test or the Kruskal-Wallis test compared discrete variables or continuous variables, respectively. For multivariate analysis, a significance level of 0.01 was used due to the large number of variables considered. Results: Among 513 PBSC donors who subsequently donated a second PBSC product, clinically relevant decreases in values at the second donation were observed in pre-apheresis CD34+ cells (73.9 vs. 68.6; p=0.03), CD34+cells/L blood processed (32.2 vs. 30.1; p=0.06), and total final CD34+ cell count (x106) (608 vs. 556; p=0.02). Median time interval between first and second PBSC donations was 11.7 months (range: 0.3-128.1). Using the median pre-apheresis peripheral blood CD34+ cell counts from donation 1 as the cut-off for high versus low mobilizers, we found that individuals who were likely to be high or low mobilizers at first donation were also likely to be high or low mobilizers at second donation, respectively (Table 1). This was independent of the inter-donation interval. In multivariate analyses, those with an inter-donation interval of >12 months, demonstrated higher CD34+cells/L blood processed compared to donors donating within a year (mean ratio 1.15, p<0.0001). Change in donor BMI was also a predictor for PBSC yields. If donor BMI decreased at second donation, so did the CD34+cells/L blood processed (0.74, p <0.0001). An average G-CSF dose above 960mcg was also associated with an increase in CD34+cells/L blood processed compared to donors who received less than 960mcg (1.04, p=0.005). (Table 2A). Pre-apheresis peripheral blood CD34+ cells on Day 5 of second donation were also affected by the inter-donation interval, with higher cell counts associated with a longer time interval (>12 months) between donations (1.23, p<0.0001). Further, independent of the inter-donation interval, GCSF doses greater than 960mcg per day associated with higher pre-apheresis CD34+ cells at second donation (1.26, p<0.0001); as was a higher baseline WBC count (>6.9) (1.3, p<0.0001) (Table 2B). Conclusions: In this large retrospective study of second time unrelated PBSC donors, a longer inter-donation interval was confirmed to be associated with better PBSC mobilization and collection. Given hematopoietic stem cell cycling times of 9-12 months in humans, where possible, repeat donors may be chosen based on these intervals to optimize PBSC yields. Changes in BMI are also to be considered while recruiting repeat donors. Some of these parameters may be improved marginally by increasing G-CSF dose within permissible limits. In most instances, however, sub-optimal mobilizers at first donation appear to donate suboptimal numbers of HSC at their subsequent donation. Disclosures Pulsipher: CSL Behring: Membership on an entity's Board of Directors or advisory committees; Miltenyi: Research Funding; Bellicum: Consultancy; Amgen: Other: Lecture; Jazz: Other: Education for employees; Adaptive: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Medac: Honoraria. Shaw:Therakos: Other: Speaker Engagement.

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Increased Early Mortality after Fludarabine and Melphalan Conditioning with Peripheral Blood Grafts in Haploidentical SCT with Post-Transplant Cyclophosphamide

Blood ◽

10.1182/blood-2019-129872 ◽

2019 ◽

Vol 134 (Supplement_1) ◽

pp. 4496-4496 ◽

Cited By ~ 1

Author(s):

Luke Eastburg ◽

David A. Russler-Germain ◽

Ramzi Abboud ◽

Peter Westervelt ◽

John F. DiPersio ◽

...

Keyword(s):

Bone Marrow ◽

Stem Cell ◽

T Cell ◽

Board Of Directors ◽

Research Funding ◽

Early Mortality ◽

Cell Transplant ◽

Advisory Committees ◽

Post Transplant ◽

Equity Ownership

The use of post-transplant cyclophosphamide (PTCy) in the context of haploidentical stem cell transplant (haplo-SCT) has led to drastically reduced rates of Graft-vs-Host (GvH) disease through selective depletion of highly allo-reactive donor T-cells. Early trials utilized a reduced-intensity Flu/Cy/TBI preparative regimen and bone marrow grafts; however, relapse rates remained relatively high (Luznik et al. BBMT. 2008). This led to the increased use of myeloablative (MA) regimens for haplo-SCT, which have been associated with decreased relapse rates (Bashey et al. J Clin Oncol. 2013). Most studies have used a MA total body irradiation (TBI) based regimen for haplo-SCT. Preparative regimens using fludarabine and melphalan (FluMel), with or without thiotepa, ATG, and/or low dose TBI have also been reported using bone marrow grafts. Reports on the safety and toxicity of FluMel in the haplo-SCT setting with PTCy and peripheral blood stem cell (PBSC) grafts are lacking. In this two-center retrospective analysis, the safety/toxicity of FluMel as conditioning for haplo-SCT was evaluated. We report increased early mortality and toxicity using standard FluMel conditioning and PBSC grafts for patients undergoing haplo-SCT with PTCy. 38 patients at the University of Rochester Medical Center and the Washington University School of Medicine underwent haplo-SCT with FluMel conditioning and PBSC grafts between 2015-2019. Outcomes were measured by retrospective chart review through July 2019. 34 patients (89.5%) received FluMel(140 mg/m2). Two patients received FluMel(100 mg/m2) and two patients received FluMel(140 mg/m2) + ATG. The median age at time of haplo-SCT was 60 years (range 21-73). 20 patients were transplanted for AML, eight for MDS, two for PMF, two for NHL, and five for other malignancies. The median Hematopoietic Cell Transplantation-specific Comorbidity Index (HCT-CI) score was 4 (≥3 indicates high risk). 11 patients had a history of prior stem cell transplant, and 16 patients had active disease prior to their haplo-SCT. Seven patients had sex mismatch with their stem cell donor. Median donor age was 42 (range 21-71). 20 patient deaths occurred by July 2019 with a median follow up of 244 days for surviving patients. Nine patients died before day +100 (D100, "early mortality"), with a D100 non-relapse mortality (NRM) rate of 24%. Median overall and relapse free survival (OS and RFS, respectively) were 197 days (95% CI 142-not reached) and 180 days (95% CI 141-not reached), respectively, for the entire cohort. The 1 year OS and NRM were 29% and 50%. The incidence of grades 2-4cytokine release syndrome (CRS) was 66%, and 52% of these patients were treated with tocilizumab. CRS was strongly associated with early mortality, with D100 NRM of 36% in patients with grade 2-4 CRS compared to 0% in those with grade 0-1. The incidence of acute kidney injury (AKI) was 64% in patients with grade 2-4 CRS, and 8% in those without (p < 0.001). 28% of patients with AKI required dialysis. Grade 2-4 CRS was seen in 54% of patients in remission prior to haplo-SCT and in 92% of those with active disease (p = 0.02). Of the 9 patients with early mortality, 89% had AKI, 44% needed dialysis, and 100% had grade 2-4 CRS, compared to 31%, 10%, and 55% in those without early mortality (p = 0.002, p = 0.02, p = 0.01). Early mortality was not significantly associated with age, HCT-CI score, second transplant, disease status at transplant, total dose of melphalan, volume overload/diuretic use, or post-transplant infection. In conclusion, we observed a very high rate of NRM with FluMel conditioning and PBSC grafts for haplo-SCT with PTCy. The pattern of toxicity was strongly associated with grade 2-4 CRS, AKI, and need for dialysis. These complications may be mediated by excessive inflammation in the context of allo-reactive donor T-cell over-activation. Consistent with this, multiple groups have shown that FluMel conditioning in haplo-SCT is safe when using bone marrow or T-cell depleted grafts. Based on our institutional experiences, we would discourage the use of FluMel as conditioning for haplo-SCT with PTCy with T-cell replete PBSC grafts. Alternative regimens or variations on melphalan-based regimens, such as fractionated melphalan dosing or inclusion of TBI may improve outcomes but further study and randomized controlled trials are needed. This study is limited in its retrospective design and sample size. Figure Disclosures DiPersio: WUGEN: Equity Ownership, Patents & Royalties, Research Funding; Karyopharm Therapeutics: Consultancy; Magenta Therapeutics: Equity Ownership; Celgene: Consultancy; Cellworks Group, Inc.: Membership on an entity's Board of Directors or advisory committees; NeoImmune Tech: Research Funding; Amphivena Therapeutics: Consultancy, Research Funding; Bioline Rx: Research Funding, Speakers Bureau; Macrogenics: Research Funding, Speakers Bureau; Incyte: Consultancy, Research Funding; RiverVest Venture Partners Arch Oncology: Consultancy, Membership on an entity's Board of Directors or advisory committees. Liesveld:Onconova: Other: Data safety monitoring board; Abbvie: Membership on an entity's Board of Directors or advisory committees.

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Blockade of PD-1 in Combination with Dendritic Cell/Myeloma Fusion Cell Vaccination Following Autologous Stem Cell Transplantation Is Well Tolerated, Induces Anti-Tumor Immunity and May Lead to Eradication of Measureable Disease

Blood ◽

10.1182/blood.v126.23.4218.4218 ◽

2015 ◽

Vol 126 (23) ◽

pp. 4218-4218 ◽

Cited By ~ 7

Author(s):

Jacalyn Rosenblatt ◽

Irit Avivi ◽

Noam Binyamini ◽

Lynne Uhl ◽

Poorvi Somaiya ◽

...

Keyword(s):

Stem Cell ◽

Dendritic Cell ◽

Stem Cell Transplantation ◽

Board Of Directors ◽

Research Funding ◽

Ex Vivo ◽

Advisory Committees ◽

Post Transplant ◽

Fusion Cell ◽

Equity Ownership

Abstract Autologous stem cell transplantation (ASCT) for multiple myeloma (MM) offers a unique setting to incorporate immunotherapy in an effort to target residual disease. Our group has developed a cancer vaccine in which dendritic cells (DCs) are fused to autologous tumor cells resulting in the presentation of multiple tumor antigens with the capacity to elicit a broad anti-tumor response. A fundamental challenge to developing a more effective tumor vaccine is overcoming the immunosuppressive milieu by which tumor cells evade host immunity. Up-regulation of the PD-1/PDL1 pathway represents a key element contributing to tumor-mediated tolerance, and potentially muting response to vaccination. We are conducting a clinical trial in which patients with MM are treated with an anti-PD1 antibody (Pidilizumab, MDV9300) in combination with a dendritic cell/myeloma fusion cell vaccine following autologous transplantation. 22 patients have been treated with post-transplant immunotherapy. Mean age was 64. MM cells were isolated from bone marrow and were identified by expression of CD38 or CD138. Mean tumor cell yield was 118x106 cells. Adherent mononuclear cells were isolated from leukapheresis collections and cultured with GM-CSF and IL-4 for 5-7 days, then exposed to TNFα for 48-72 hours to generate mature DCs. DCs expressed co-stimulatory (mean CD86 75%) and maturation markers (mean CD83 50%). DC and MM cells were co-cultured with PEG and fusion cells were quantified by determining the percentage of cells that co-express unique DC and myeloma antigens. Mean fusion efficiency was 41% and the mean cell dose generated was 4 x 106 fusion cells. Mean viability of the DC, myeloma, and fusion preparations was 92%, 89%, and 85%, respectively. As a measure of their potency as antigen presenting cells, DC/MM fusions potently stimulate allogeneic T cell proliferation ex-vivo (Mean stimulation index of 1.9, 9.2 and 7.1 for tumor, DC and DC/myeloma fusions respectively, n=21) Post-transplant immunotherapy was initiated after recovery from transplant-related toxicities. Median time from transplant to initiation of post-transplant immunotherapy was 80 days. Patients received 3 doses of Pidilizumab at 6-week intervals. DC/myeloma fusion cells vaccination is administered 1 week before each dose of Pidilizumab. To date, 22 patients have completed vaccinations and Pidilizumab. Adverse events judged to be potentially treatment related included grade 1-2 diarrhea, arthralgias, myalgias, fatigue, headache, nausea, chills, transaminitis, cytopenia, elevated TSH, and vaccine site reactions. A significant increase in circulatingtumor reactive lymphocytes was noted following post-transplant immunotherapy, as determined by T cell expressionof IFN-γ by CD8 cells following ex-vivo co-culture withautologous myeloma cell lysate. Mean percentage of tumor reactiveCD8 cells increased from 1.8% post-transplant to a peak of 9.16% following immunotherapy. In the post-transplant period, regulatory T cells fell to minimal levels and remained low throughout the period of immunotherapy. 6 patients achieved a best response of VGPR, 6 patients have achieved a nCR/CR, including 3 who converted to CR following immunotherapy. Median PFS from transplant is 19 months with ongoing follow up. In summary, DC/MM fusion cell vaccination in conjunction with PD1 blockade following ASCT was well tolerated, potently induced anti-tumor immunity, and in a subset of patients, resulted in the eradication of post-transplant measurable disease. Disclosures Richardson: Gentium S.p.A.: Membership on an entity's Board of Directors or advisory committees, Research Funding; Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Millennium Takeda: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Celgene Corporation: Membership on an entity's Board of Directors or advisory committees. Laubach:Novartis: Research Funding; Onyx: Research Funding; Celgene: Research Funding; Millennium: Research Funding. Anderson:Celgene: Consultancy; Millennium: Consultancy; BMS: Consultancy; Gilead: Consultancy; Oncopep: Equity Ownership; Acetylon: Equity Ownership. Rowe:BioSight Ltd.: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy; BioLineRx Ltd.: Consultancy. Kufe:Genus Oncology: Consultancy, Equity Ownership.

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The Abundance of Certain Bacteria in the Intestinal Flora Is Associated with Relapse after Allogeneic Hematopoietic Stem Cell Transplantation

Blood ◽

10.1182/blood.v126.23.744.744 ◽

2015 ◽

Vol 126 (23) ◽

pp. 744-744 ◽

Cited By ~ 2

Author(s):

Jonathan Peled ◽

Eric R. Littman ◽

Lilan Ling ◽

Satyajit Kosuri ◽

Molly Maloy ◽

...

Keyword(s):

Overall Survival ◽

Stem Cell ◽

Board Of Directors ◽

Research Funding ◽

Intestinal Flora ◽

Advisory Board ◽

Advisory Committees ◽

Hematopoietic Stem ◽

Streptococcus Anginosus ◽

Conditioning Intensity

Abstract The major causes of mortality after allogeneic hematopoietic stem cell transplantation (allo-HSCT) are relapse, graft-versus-host disease (GVHD), and infection. We have previously reported that changes in the intestinal flora can affect GVHD, bacteremia, and overall survival. As intestinal bacteria are potent modulators of systemic immune responses, and since GVHD is correlated with graft-versus-tumor activity, we hypothesized that components of the intestinal flora could be associated with relapse after allo-HSCT. We applied a biomarker-discovery approach and performed a retrospective observational analysis of 160 adults who received an unmodified (T-cell-replete) allograft. Patients were prospectively enrolled in a fecal biospecimen-collection protocol. For this analysis, we selected patients who had at least one specimen during the first 3 weeks following allo-HSCT. The primary diseases in this cohort were AML (37%), Non-Hodgkin's Lymphoma (33%), ALL (8%), MDS (7%), CLL (6%), Hodgkin's Lymphoma (6%), CML (2%), and myeloproliferative neoplasm (2%). The mean age of the patients was 52 years (range 21-75). They were conditioned with ablative (17%), reduced-intensity (64%), and nonmyeloablative (19%) regimens. They received grafts from cord blood (46%), unrelated adults (33%), or related adults (22%). Among adult grafts, 92% were from peripheral blood and 8% were from bone marrow. A census of the bacterial species in each stool sample was generated by 16S rRNA deep-sequencing as previously described (Jenq et al., BiolBone Marrow Transplant 2015). The area under the curve of bacterial abundance over time was used as a measure of each patient's cumulative exposure to each bacterial taxon. Bacterial taxa of each patient present at a frequency >1% were evaluated for association with the outcome of relapse or progression of disease within the first year after allo-HSCT using linear discriminant analysis of effect size (LEfSe), a common approach in microbiota studies (Segata et al., Genome Biology, 2011). Among the taxons most significantly associated with freedom from relapse were members of the human oral flora including Streptococcus anginosus. After stratifying the patients by median abundance, we found that those with higher abundance of this bacterium had less relapse after transplantation (Left figure, p = 0.0014). We also identified bacteria associated with increased risk of relapse, such as Enterococcus faecium (Right figure, p = 0.0103). We evaluated these bacteria as biomarkers in multivariate Cox models adjusted for three factors that were associated with relapse in this cohort: Refined Disease Risk Index (RDRI, Armand et al., Blood 2014), conditioning intensity, and graft source (cord blood vs. adult donor). Streptococcus anginosus predicted relapse in a multivariate model adjusted for all three factors (HR 0.39, 95% CI 0.16-0.96, p = 0.041). Enterococcus faecium predicted relapse in a model adjusted for RDRI and conditioning intensity but failed to do so in a model additionally adjusted for graft source. In this analysis there was no formal adjustment for multiple comparisons; these data are now being validated in an additional cohort of patients whose samples are being sequenced. Finally, although we have previously reported that low bacterial diversity is associated with decreased overall survival after allo-HSCT (Taur et al., Blood 2014), we did not find an association between bacterial diversity and relapse as assessed by reciprocal Simpson diversity index (p > 0.1). Thus, the results of this retrospective analysis have identified an association between relapse after allo-HSCT and the abundance of two bacteria in the intestinal flora. These might serve as potential novel diagnostics or therapeutic targets to prevent relapse and improve overall survival after allo-HSCT. Figure 1. Figure 1. Disclosures Peled: Merck: Research Funding. Giralt:SANOFI: Consultancy, Honoraria, Research Funding; TAKEDA: Consultancy, Honoraria, Research Funding; AMGEN: Consultancy, Research Funding; JAZZ: Consultancy, Honoraria, Research Funding, Speakers Bureau; CELGENE: Consultancy, Honoraria, Research Funding. Perales:Merck: Honoraria; Takeda: Honoraria; Amgen: Honoraria; Astellas: Honoraria; NMDP: Membership on an entity's Board of Directors or advisory committees. van den Brink:Boehringer Ingelheim: Consultancy, Other: Advisory board attendee; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Tobira Therapeutics: Other: Advisory board attendee; Regeneron: Honoraria; Merck: Honoraria.

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Genome-Wide RNA Tomography of the Hematopoietic Stem Cell Niche in Zebrafish Reveals Unexpected Functional Macrophage-Stem Cell Interactions

Blood ◽

10.1182/blood.v128.22.3882.3882 ◽

2016 ◽

Vol 128 (22) ◽

pp. 3882-3882

Author(s):

Elliott J Hagedorn ◽

Julie R Perlin ◽

Clara Mao ◽

Brian Li ◽

Christopher D'Amato ◽

...

Keyword(s):

Stem Cell ◽

Board Of Directors ◽

Cell Interactions ◽

Cell Populations ◽

Rna Seq ◽

Advisory Committees ◽

Hematopoietic Stem ◽

Equity Ownership

Abstract The challenges of visualizing the mammalian bone marrow have precluded a rigorous analysis of the dynamic cell-cell interactions that control hematopoietic stem and progenitor cell (HSPC) engraftment. The transparent zebrafish embryo provides an unparalleled opportunity to directly visualize HSPC-niche cell interactions in live animals. To identify genes expressed in the zebrafish caudal hematopoietic tissue (CHT) - an embryonic niche akin to the mammalian fetal liver - we employed a new technique called tomo-seq (RNA tomography). By pairing cryosectioning with RNA-seq, this technology permits spatial analysis of transcriptome-wide gene expression. Using tomo-seq we identified ~300 genes showing enriched expression in the CHT. In situ hybridization for 75 of 107 tested genes confirmed CHT expression. In parallel we performed RNA-seq on isolated cell populations, including endothelial cells, macrophages, neutrophils and erythrocytes, sorted from whole embryos. By cross-referencing these datasets we determined the cell types in which many of the 300 CHT-enriched genes were expressed. This analysis revealed several cell surface adhesion receptors enriched on macrophages in the CHT, including the integrin heterodimers itgam/itgb2, itgae/itgb7, itga4/itgb1b and itga4/itgb7. We examined whether known ligands for any of these integrins were present on HSPCs. In situ hybridization to vcam1 (ligand for itga4/itgb1b)showed punctate HSPC-like staining in the CHT. We then generated a vcam1:GFP promoter fusion, which we found was expressed in HSPCs. Using spinning disk confocal microscopy we imaged HSPCs and macrophages in the CHT and observed direct and specific physical interactions that preceded the engraftment of HSPCs. In a grooming-like behavior that lasts for 30-45 minutes, the HSPC is engaged by the macrophage, which moves all over the surface of the cell, before disengaging the HSPC, which then remains in the CHT. Between 48-72 hours post fertilization (hpf), 20% of HSPCs were engaged in this behavior with a macrophage. To evaluate the specificity of these interactions we established in vitro co-cultures using purified cell populations. In co-cultures between macrophages (mpeg1:mCherry) and HSPCs (cd41:GFP) we observed cell-cell interactions that were strikingly similar to those observed in vivo. In macrophage-HSPC co-cultures, 25% of cells were found to interact, whereas only 5% of cells were found to interact in macrophage-erythrocyte co-cultures. To functionally evaluate the macrophage-HSPC interactions in vivo, we depleted macrophages from zebrafish embryos at 55 hpf using clodronate liposomes and observed circulating HSPCs with a significant reduction in HSPC engraftment in the CHT (11/15 embryos, compared to the control where 14/14 embryos showed normal CHT engraftment). Together these studies establish a role for macrophages in promoting the niche engraftment of HSPCs. The results of this work could have important implications for the design of new therapies to improve engraftment during stem cell transplantation. Disclosures Zon: Scholar Rock: Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Other: Founder; Fate, Inc.: Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Other: Founder; Marauder Therapeutics: Equity Ownership, Other: Founder.

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CD200 Is a Stem Cell-Specific Immunosuppressive Target in AML

Blood ◽

10.1182/blood-2018-99-114818 ◽

2018 ◽

Vol 132 (Supplement 1) ◽

pp. 2768-2768

Author(s):

Shelley Herbrich ◽

Keith Baggerly ◽

Gheath Alatrash ◽

R. Eric Davis ◽

Michael Andreeff ◽

...

Keyword(s):

Gene Expression ◽

Flow Cytometry ◽

T Cells ◽

Stem Cell ◽

Board Of Directors ◽

Research Funding ◽

Advisory Committees ◽

Cd200 Receptor ◽

Blast Cells ◽

Equity Ownership

Abstract Acute myeloid leukemia (AML) stem cells (LSC) are an extremely rare fraction of the overall disease (likely <0.3%), largely quiescent, and capable of both long-term self-renewal and production of more differentiated leukemic blasts. Besides their role in disease initiation, they are also hypothesized as the likely source of deadly, relapsed leukemia. Due to the quiescent nature of the LSCs, they are capable of evading the majority of chemotherapeutic agents that rely on active cell-cycling for cytotoxicity. Therefore, novel therapeutic approaches specifically engineered to eradicate LSCs are critical for curing AML. We previously introduced a novel bioinformatics approach that harnessed publically available AML gene expression data to identify genes significantly over-expressed in LSCs when compared to their normal hematopoietic stem cell (HSC) counterparts (Herbrich et al Blood 2017 130:3962). These datasets contain gene expression arrays on human AML patient samples sorted by leukemia stem, progenitor, and blast cells (with normal hematopoietic cell subsets for comparison). We have since expanded our statistical model to identify targets that are both significantly overexpressed in AML LSCs when compared to HSC as well as LSCs compared to their corresponding, more differentiated blast cells. Instead of traditional methods for multiple testing corrections, we looked at the intersection of genes that met the above criteria in 3 independently generated datasets. This resulted in a list of 30 genes, 28 of which appear to be novel markers of AML LSCs. From this list, we first chose to focus on CD200, a type-1 transmembrane glycoprotein. CD200 is broadly expressed on myeloid, lymphoid, and epithelial cells, while the CD200 receptor (CD200R) expression is strictly confined to myeloid and a subset of T cells. CD200 has been shown to have an immunosuppressive effect on macrophages and NK cells and correlates with a high prevalence FOXP3+ regulatory T cells (Coles et al Leukemia 2012; 26:2146-2148). Additionally, CD200 has been implicated as a poor prognostic marker in AML (Damiani et al Oncotarget 2015; 6:30212-30221). To date, we have screened 20 primary AML patient samples by flow cytometry, 90% of which are positive for CD200. Expression is significantly enriched in the CD34+/CD123+ stem cell compartment. To examine the role of CD200 in AML, we established two in vitro model systems. First, we used CRISPR/Cas9 to knockout the endogenous CD200 protein in Kasumi-1. Further, we induced CD200 in the OCI-AML3 cell line that had no expression at baseline. Both cell lines did not express the CD200 receptor before or after manipulation, negating any autocrine signaling. In both systems, CD200 manipulation did not affect the proliferation rate or viability of the cells. To examine the immune function of CD200 in AML, we performed a series of mixed lymphocyte reactions. We cultured normal human peripheral blood mononuclear cells (PBMCs) with the CD200+ or CD200- cells from each line both. Cells were incubated in the culture media for 4-48 hours before being harvested and measured by flow cytometry for apoptosis or intracellular cytokine production. The presence of CD200 on the cell surface reduced the rate of immune-specific apoptosis among these leukemia cells. The difference in cell killing was most likely attributable to a CD200-specific suppression of CD107a, a surrogate marker or cytotoxic activity. In the OCI-AML3 model, PBMCs co-cultured with CD200+ cells produced approximately 40% less CD107a when compared to the CD200- co-culture. Additionally, we characterized our new cell lines using RNA sequencing. By comparing the CD200+ to the CD200- cells within each line, we observed that CD200+ cells significantly downregulate genes involved in defining an inflammatory response as well as genes regulated by NF-κB in response to TNFα. This indicates that CD200 may have an undiscovered intrinsic role in suppressing the immune microenvironment of AML LSCs. In conclusion, we have expanded our novel bioinformatics approach for robustly identifying AML LSC-specific targets. Additionally, we have shown that one of these markers, CD200, has a potential role as a stem cell-specific immunosuppressive target by reducing immune-mediated apoptosis and transcriptionally suppressing inflammatory cell processes. We are extending our study to explore CD200 in primary patient samples using a CD200-blocking antibody. Disclosures Andreeff: SentiBio: Equity Ownership; Amgen: Consultancy, Research Funding; Oncolyze: Equity Ownership; Reata: Equity Ownership; United Therapeutics: Patents & Royalties: GD2 inhibition in breast cancer ; Jazz Pharma: Consultancy; Astra Zeneca: Research Funding; Aptose: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Daiichi-Sankyo: Consultancy, Patents & Royalties: MDM2 inhibitor activity patent, Research Funding; Eutropics: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Oncoceutics: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy. Konopleva:Stemline Therapeutics: Research Funding.

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Prognostic Value of Cpss Cytogenetic Risk Classification in Patients with CMML after Allogeneic Hematopoietic Stem Cell Transplantation: A Retrospective Multicenter Study of the Chronic Malignancies Working Party of the EBMT

Blood ◽

10.1182/blood-2018-99-115981 ◽

2018 ◽

Vol 132 (Supplement 1) ◽

pp. 2182-2182

Author(s):

Christian Koenecke ◽

Dirk-Jan Eikema ◽

Sheree Hazelaar ◽

Dietrich W. Beelen ◽

Victoria Potter ◽

...

Keyword(s):

Stem Cell ◽

High Risk ◽

Hematopoietic Stem Cell Transplantation ◽

Stem Cell Transplantation ◽

Board Of Directors ◽

Cumulative Incidence ◽

Research Funding ◽

Advisory Committees ◽

Hematopoietic Stem ◽

Allogeneic Hsct

Abstract Introduction: The only curative treatment approach for patients with Chronic Myelomonocytic Leukemia (CMML) is allogeneic hematopoietic stem cell transplantation (HSCT), but disease relapse after transplantation is a major concern. Predictors for disease outcome after HSCT are limited. However, unfavorable cytogenetic abnormalities have been shown to serve as predictors for relapse after transplantation. The aim of this large multicentric, international study was to retrospectively determine the impact of cytogenetic information according to the CMML-specific prognostic scoring system (CPSS) on outcome after allogeneic HSCT. Patients and Methods: Patients were selected from the EBMT database who had received a first allogeneic HSCT for the treatment of CMML between 2000 and 2015. 268 centers participated into this study. In total, 1503 patients were included. Impact of CPSS-cytogenetic classification was analyzed regarding overall survival (OS) and cumulative incidence of relapse and non-relapse mortality after HSCT (gray test). Results: 488 female (32.5%) and 1013 male (67.5%) patients were included to the study. Median age at HSCT was 57.6 years (range 0.3-75.4). At time of HSCT, only 422 (28.1%) patients were in complete remission, whereas 1004 (66.8%) had active disease (77 missing). Matched related donor HSCT was performed in 35.7% of the patients, matched unrelated donor HSCT in 57.6%, mismatched related in 3.3% and mismatched unrelated in 3.4%. Bone marrow (12.6%), peripheral blood (84.3%), or both (0.3%) served as the stem cell graft. Cord blood was used as a graft in 2.8%. Myeloablative preparative regimens wereused in 223 patients (15.0%), and less intensive regimens were given to 1268 patients (85.0%). Median survival of patients included into this study was 52.2 months. 637 patients had sufficient cytogenetic information according to CPSS (866 missing), complete relapse information was available in 1385 patients. 143 patients could be categorized into CPSS-high, 85 in intermediate and 375 in low risk cytogenetics, respectively. In univariate analysis high risk CPSS cytogenetic information was found to be strongly associated with OS (low 38% (32-44%), intermediate 41% (30-53%), high 26% (18-34%)), and higher cumulative incidence of relapse (low 40% (35-46%), intermediate 42% (30-54%), high 48% (39-56%)), but not with non relapse mortality (low 28% (23-33%), intermediate 25% (16-35%), high 30% (22-38%)) at 60 months (Figure 1). Conclusion: In this international, multicentric analysis we show that CMML patients with high-risk cytogenetics had significantly worse OS after HSCT than patients with intermediate or low risk cytogenetics according to CPSS. New therapeutic strategies to prevent relapse after HSCT in CMML patients with high-risk cytogenetics are needed. Disclosures Koenecke: Amgen: Consultancy; abbvie: Consultancy; BMS: Consultancy; Roche: Consultancy. Beelen:Medac: Consultancy, Other: Travel Support. Finke:Novartis: Consultancy, Honoraria, Other: travel grants, Research Funding; Riemser: Consultancy, Honoraria, Research Funding; Medac: Consultancy, Honoraria, Other: travel grants, Research Funding; Neovii: Consultancy, Honoraria, Other: travel grants, Research Funding. Niederwieser:Novartis: Research Funding; Miltenyi: Speakers Bureau. Chalandon:Roche: Membership on an entity's Board of Directors or advisory committees, Other: Travel costs. Ganser:Novartis: Membership on an entity's Board of Directors or advisory committees. Kobbe:Amgen: Honoraria, Research Funding; Roche: Honoraria, Research Funding; Celgene: Honoraria, Other: Travel Support, Research Funding.

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AVID200, a Potent Trap for TGF-β Ligands Inhibits TGF-β1 Signaling in Human Myelofibrosis

Blood ◽

10.1182/blood-2018-99-116474 ◽

2018 ◽

Vol 132 (Supplement 1) ◽

pp. 1791-1791 ◽

Cited By ~ 7

Author(s):

Lilian Varricchio ◽

John Mascarenhas ◽

Anna Rita Migliaccio ◽

Maureen O'Connor-McCourt ◽

Gilles Tremblay ◽

...

Keyword(s):

Stem Cell ◽

Board Of Directors ◽

Research Funding ◽

Type I Collagen ◽

Normal Donor ◽

Type I ◽

Cell Transplant ◽

Dependent Manner ◽

Advisory Committees ◽

Hematopoietic Stem

Abstract Myelofibrosis (MF) is caused by driver mutations which upregulate JAK/STAT signaling. The only curative treatment for MF is hematopoietic stem cell transplant. Ruxolitinib alleviates many of the symptoms in MF but does not significantly alter survival. There is, therefore, an urgent need for additional rational therapies for MF. Bone marrow fibrosis and collagen deposition are hallmarks of MF which have been attributed to megakaryocyte (MK) derived TGFβ, which also plays a role in myelo-proliferation. There are three isoforms of TGFβ (TGFβ1, β2, and β3). AVID200, which was constructed by fusing TGFβR ectodomains to IgG Fc regions, is a potent TGFβ trap with pM potency against two of the three TGFβ ligands, TGFβ1 and β3 (IC50 values of ~ 3 pM ). AVID200's IC50 for TGFβ2 is ~4,000-fold higher indicating that it has minimal activity against TGFβ2, which is desirable since TGFβ2 is a positive regulator of hematopoiesis. We explored the therapeutic potential of AVID200 by culturing MF or normal donor (ND) mononuclear cells (MNCs) first in the presence of stem cell factor and thrombopoietin (TPO) and then TPO alone in order to generate MK-enriched populations. Although the percentage of mature MKs from ND and MF MNCs was similar, the absolute number of CD41+/CD42+ MKs generated from MF MNCs was two-fold greater than ND MNCs. To determine the levels of TGFβ secreted by the MKs we screened MF and ND MNC conditioned media (CM). We observed significantly higher levels of TGFβ1 but not TGFβ2 and TGFβ3 in MF MK CM. The effects of AVID200 on MKs were then evaluated by measuring the levels of phosphorylated SMAD2. Treatment with 0.001 - 0.1 nM AVID200 decreased phosphorylation of SMAD2, suggesting that AVID200 blocks autocrine MK TGFβ signaling. The increased levels of TGFβ in MF patients promote the proliferation and deposition of collagen by mesenchymal stem cells (MSCs). Cellular proliferation of MSCs was evaluated following treatment with either recombinant TGFβ1 or ND/MF CM in the presence or absence of AVID200. In the absence of AVID200, both recombinant TGFβ1 and MK-derived CM increased the proliferation of MSCs by 1.4- and 1.6-fold respectively, which returned to basal levels with the addition of increasing concentrations of AVID200. These data indicate that AVID200 directly blocks the effect of TGFβ1 on MSCs. MF stroma is characterized by an increase in Type I collagen. We therefore examined if treatment with AVID200 interferes with the ability of TGFβ1 to induce collagen expression by MSCs. MSCs were cultured in presence of recombinant TGFβ1 alone or in combination with varying concentrations of AVID200 for 72 hours. Recombinant TGFβ1 alone induced an increase in COL1A1 mRNA expression as compared to untreated controls (p<0.01). Addition of AVID200 eliminated the TGFβ-mediated increase in COL1A1 expression in a dose dependent manner. ND and MF MK-derived CM also increased COL1A1 expression by MSCs as compared to un-treated controls (p<0.01) and that effect was eliminated by AVID200 treatment (p<0.01). We next demonstrated that TGFβ1 activated pSMAD2 in MSCs without affecting total SMAD2/3 expression and that SMAD2 phosphorylation was reduced by adding AVID200. Furthermore, AVID200 treatment decreased pSTAT3 which is associated with the ability of TGFβ to induce fibrosis. We next investigated the effect of AVID200 on MF hematopoiesis. Briefly, MNCs (which produce TGFβ) from two JAK2V617F+ MF patients were incubated with or without 50 nM of AVID200 and plated in semi-solid media. Treatment with AVID200 did not affect the overall number of colonies generated, but reduced the numbers of JAKV617F+ colonies while increasing the numbers of WT colonies: for PT1, there were 32% JAKV617F+ CFUs in untreated cultures (11 JAKV617F+/34 total colonies) versus 16% JAKV617F+ CFUs (7 JAKV617F+/42 total CFUs) in AVID200 treated cultures; for PT2 there were 100% JAKV617F+ CFUs in untreated cultures (37 JAKV617F+/37 total CFUs) versus 94% JAKV617F+ CFUs (49 JAK2V617F+/52 total CFUs) in AVID200 treated cultures. The in vivo effects of AVID200 on the development of MF in GATA1 low mice will be presented at the meeting. These data indicate that AVID200 selectively suppresses TGFβ1 signaling associated with the proliferation of MSCs and type I collagen synthesis, and depletes MF MNCs of JAK2V617F+progenitor cells. We conclude that AVID200 is a promising agent for treating MF patients which will be evaluated in a phase 1 clinical trial. Disclosures Mascarenhas: Novartis: Research Funding; CTI Biopharma: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees; Roche: Research Funding; Janssen: Research Funding; Promedior: Research Funding; Merck: Research Funding; Incyte: Membership on an entity's Board of Directors or advisory committees, Research Funding. Iancu-Rubin:Incyte: Research Funding; Merck: Research Funding; Summer Road, LLC: Research Funding; Formation Biologics: Research Funding. Hoffman:Incyte: Research Funding; Summer Road: Research Funding; Merus: Research Funding; Janssen: Research Funding; Formation Biologics: Research Funding.

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