Effect of oseltamivir phosphate versus placebo on platelet recovery and plasma leakage in adults with dengue and thrombocytopenia; a phase 2, multicenter, double-blind, randomized trial

Background Thrombocytopenia, bleeding and plasma leakage are major complications of dengue. Activation of endogenous sialidases with desialylation of platelets and endothelial cells may underlie these complications. We aimed to assess the effects of the neuraminidase inhibitor oseltamivir on platelet recovery and plasma leakage in dengue. Methods We performed a phase 2, double-blind, multicenter, randomized trial in adult dengue patients with thrombocytopenia (<70,000/μl) and a duration of illness ≤ 6 days. Oseltamivir phosphate 75mg BID or placebo were given for a maximum of five days. Primary outcomes were the time to platelet recovery (≥ 100,000/μl) or discharge from hospital and the course of measures of plasma leakage. Results A total of 70 patients were enrolled; the primary outcome could be assessed in 64 patients (31 oseltamivir; 33 placebo). Time to platelet count ≥100,000/μl (n = 55) or discharge (n = 9) were similar in the oseltamivir and placebo group (3.0 days [95% confidence interval, 2.7 to 3.3] vs. 2.9 days [2.5 to 3.3], P = 0.055). The kinetics of platelet count and parameters of plasma leakage (gall bladder thickness, hematocrit, plasma albumin, syndecan-1) were also similar between the groups. Discussion In this trial, adjunctive therapy with oseltamivir phosphate had no effect on platelet recovery or plasma leakage parameters. Trial registration ISRCTN35227717.

Efficacy of Recombinant Human Thrombopoietin for the Treatment of Secondary Failure of Platelet Recovery After Allogeneic HSCT

Secondary failure of platelet recovery (SFPR) is a life-threatening complication that may affect up to 20% of patients after allogeneic hematopoietic stem cell transplantation (HSCT). In this study, to evaluate the efficacy of recombinant human thrombopoietin (rhTPO), we retrospectively analyzed 29 patients who received continuous rhTPO for the treatment of SFPR. Overall response and complete response were observed in 24 (82.8%) patients and 10 (34.5%) patients, at a median time of 21.5 days (range, 3-41 days) and 39.5 days (range, 7-53 days) after initiation of rhTPO treatment, respectively. Among the responders, the probability of keeping overall response and complete response at 1 year after response was 77.3% and 80.0%, respectively. In multivariate analysis, higher CD34+ cells (≥3 × 106/kg) infused during HSCT (HR: 7.22, 95% CI: 1.53-34.04, P = 0.01) and decreased ferritin after rhTPO treatment (HR: 6.16, 95% CI: 1.18-32.15, P = 0.03) were indicated to associate with complete response to rhTPO. Importantly, rhTPO was well tolerated in all patients without side effects urging withdrawal and clinical intervention. The results of this study suggest that rhTPO may be a safe and effective treatment for SFPR.

Room for Improvement: A 20-Year Single Center Experience with Allogeneic Stem Cell Transplantation for Myelodysplastic Syndromes

Allogeneic stem cell transplantation (allo-SCT) remains the only curative therapeutic approach for patients with myelodysplastic syndromes (MDS). The aim of the study was to assess the efficacy/safety of allo-SCT as well as to identify factors influencing post-transplant survival. One hundred and two MDS patients (median age: 48 years; 57 males) who underwent allo-SCT were retrospectively evaluated. Twenty seven patients were transplanted from HLA-matched sibling and 75 patients received grafts from unrelated donors. Peripheral blood was a source of stem cell for 79 patients. Reduced intensity conditioning was used in 64 subjects. Acute and chronic graft versus host disease (GvHD) developed in 61 and 19 of patients, respectively. In total, 61 patients have died. The causes of deaths included infectious complications (n = 30), steroid-resistant GvHD (n = 17), MDS relapse (n = 9) and transformation to AML (n = 5). Non-relapse mortality and cumulative incidence of relapse at 2 years were 49.8% and 9%, respectively. 41 patients are alive at last contact and present full donor chimerism. 38 patients remain in complete hematological remission (CHR), 3 patients had CHR with incomplete platelet recovery. Median follow-up from diagnosis of MDS and transplantation are 27.1 months and 7 months respectively. Overall survival and relapse-free survival were 41% at 2 years. Increased serum ferritin level > 1000 ng/ml, presence of acute GvHD, grades III–IV acute GvHD and high hematopoietic cell transplantation-comorbidity index were found to negatively influenced survival. Allo-SCT for MDS is feasible procedure with a proportion of patients to be cured.

Immunomodulatory and immunosuppressive drug protocols in the treatment of canine primary immune thrombocytopenia, a scoping review

Primary immune thrombocytopenia (ITP) is a cause of severe thrombocytopenia in dogs. Immunosuppressive corticosteroid drugs are frequently used in the management of ITP, but treatment failure may occur. Immunomodulatory and non-corticosteroid immunosuppressive drugs might improve outcomes from therapy either alone or in combination with corticosteroids. The objectives of this scoping review were (1) to evaluate the current evidence relating to immunomodulatory and immunosuppressive drug protocols in the treatment of canine ITP, and (2) to answer the clinical question, whether or not therapy with immunomodulatory or non-corticosteroid immunosuppressive drugs alone or in combination with corticosteroids could improve outcome, compared to therapy with corticosteroids alone. A literature search was performed in the electronic databases of Agricola, CAB Abstracts, Embase, Medline and Web of Science for publications in November 2019 and again February 1, 2021. Selection criteria were relatively strict and included peer-reviewed research papers reporting outcome measures from immunomodulatory and immunosuppressive drug protocols in the treatment of canine ITP with a pre-therapeutic mean or median platelet count < 50,000/µL as a strict criterion for inclusion. Studies were evaluated if they had an appropriate diagnostic work up to exclude underlying conditions. Outcome measures and adverse events were compared between drug protocols both within studies and between studies. The search identified 456 studies, with six studies being eligible for inclusion. The studies were mostly case series while two were randomized controlled trials. Level of evidence varied with an overall uncertain subject enrollment, small groups, inadequate description and variable use of drug protocols or outcome measures. For outcomes such as platelet recovery time and duration of hospitalization, an improvement was observed using adjunctive therapy (human intravenous immunoglobulin) compared to therapy with corticosteroids alone. For outcomes of complete platelet recovery time, survival (6-month), mortality and relapse, no improvement was observed using adjunctive drugs compared to corticosteroids alone. Specifically, therapy with mycophenolate mofetil alone and adjunctive azathioprine were associated with more severe adverse events compared to other drug protocols. Evidence relating to immunomodulatory and immunosuppressive drug protocols in the treatment of canine ITP was of variable quality. Future larger case-controlled trials are required for determination of optimal treatment protocols in canine ITP.

Results of Hematopoietic Stem Cells Transplantation with Tcrαβ and CD19-Depletion from Matched Related Donors and Infusions of CD45RA Depleted Donor Lymphocytes in Pediatric Severe Aplastic Anemia

Introduction HSCT from matched family donors results in most favorable outcomes among children with severe aplastic anemia (SAA). Despite overall success, morbidity, associated with acute and chronic graft-versus-host disease (GVHD) is not completely prevented with current standard of pharmacologic prophylaxis. Depletion of ab T cells from the graft prevents GVHD, and improves outcome of hematopoietic stem cell transplantation from haploidentical donors, while infusions of donor memory lymphocytes (mDLI) (CD45RA-depleted) are able to transfer pathogen-specific immunity without the risk of GVHD. We evaluated the outcomes of ab T cell depletion and add-back of intermediate-dose mDLI among the pediatric SAA recipients of matched related grafts. Materials and methods A total of 16 children with SAA (8 female, 8 male, median age 10,9 y) underwent allogenic HSCT from matched family donors (MFD) between february 2015 and may 2021. For 15 (94%) pts it was the first allo HSCT, for 1 pts it was the second HSCT. TCR αβ+/CD19+ depletion of HSCT with CliniMACS technology was implemented in all cases. The median dose of CD34+ cells was 7,1 x10 6/kg (range 2,6-13), αβ T cells - 28x10 3/kg (range 5,6-184). All pts received an additional injection of memory T-cell (CD45RA-depleted) on day 0 at 1 million T cells per kg. All patients received cyclophosphamide at 100 mg/kg, fludarabine at 100 mg/m 2, rituximab 100mg/m 2 and serotherapy with either rabbit ATG at 5 mg/kg (n-2) or horse ATG at 100 mg/kg (n-14). Post-transplant GVHD prophylaxis included calcineurin (CNI)-based regimen and abatacept 10mg/kg on days -1, +7, +14 and +28. All pts received a graft from a 10/10 HLA-matched sibling. Median time of follow-up for survivors was 1,1 years (range: 0.14 - 6.38). Results Primary engraftment was achieved in all evaluable patients (100%) with full donor chimerism, and the median time to neutrophil and platelet recovery was 11 (10-20) and 14 (11-20) days, respectively. One patient had aGVHD grade I, there were no incidence of grade II-IV aGVHD and TRM. Event-free and overall survival were 100%. CMV viremia was detected among two patients after a median of 40 (35-73) days after HSCT. No cases of ADV and Epstein-Barr virus (EBV) viremia and EBV disease were recorded. The median recovery of T cells on day+60 was 0,26 (0,04-0,9). Conclusion ab T cell-depleted transplantation with intermediate dose memory T cell add-back definitively prevents GVHD and provides a platform for safe HSCT from matched family donors in patients with SAA. Disclosures Maschan: Miltenyi Biotec: Speakers Bureau.

Iadademstat in Combination with Azacitidine Generates Robust and Long Lasting Responses in AML Patients (ALICE Trial)

Introduction: Acute Myeloid Leukemia (AML) is an aggressive hematological malignancy. Elderly patients were historically treated with chemotherapy, with ORRs below 30%. Despite treatment improvements with the recent approval of the combination venetoclax plus azacitidine, with 64% of ORR and overall survival of 14.7 months, 25% of patients continue to be refractory and 50% are estimated to relapse. The management of AML, especially in elderly or unfit patients, remains a major challenge. Lysine-specific histone demethylase 1 (LSD1) contributes to the malignant transformation event in AML. Iadademstat (iada) selectively inhibits LSD1 and has shown efficacy in preclinical models, including promoting differentiation in AML. Iada has been administered so far to +100 oncology patients in different clinical trials, showing good safety. With a favorable ADME profile and high bioactivity allowing low dosing regimens, a low DDI risk is anticipated, making iada suitable for different drug combinations and offering additional therapeutic options for patients. This is a 36-month update of the ongoing Phase II ALICE clinical trial of iadademstat plus azacitidine in front-line AML patients. Methods: ALICE (EudraCT 2018-000482-36) is an open-label, single arm, Phase IIa clinical trial to assess the safety, tolerability, dose finding and efficacy of iadademstat in combination with azacitidine for the treatment of adult AML patients. ALICE includes AML patients, who have not received prior treatment other than hydroxyurea and are considered by the investigator as ineligible for intensive chemotherapy or have refused this treatment option. Secondary end points of the study address the anti-leukemic activity of the combination (overall response rate, time to response and duration of response) along with PK/PD measures. Results: Current unaudited data corresponds to 34 patients enrolled, including 22 evaluable patients (with at least 1 bone marrow disease evaluation). Evaluable patients achieved an 73% objective response rate (ORR): 5 complete remissions (CR), 6 CR with incomplete hematological recovery (CRi) and 5 Partial Remissions (PR). The current median Time to Response is 30 days, with some durable responses, extending for more than one year in five patients, with the longest CR up to date above 930 days (still ongoing, with CR and MRD negative). Moreover, 5 patients became transfusion independent and MRD negative. The number of adverse events (AEs) reported is in line with the usual evolution of the disease and with other AML trials. Only 2 AEs (in 2 patients) were deemed as serious reactions, probably related to treatment: one differentiation syndrome (G3) and one intracranial hemorrhage (G5). The most frequent reported adverse reaction was thrombocytopenia, observed in almost half of patients (47%), although 63% of patients had presented with grade ≥3 thrombocytopenia at baseline, making difficult to unequivocally attribute observed cytopenias to treatment. Of note, patients that showed response experienced platelet recovery within the first 3 cycles of treatment. Other than the hematological events, the iada-azacitidine combination appears to be safe and well tolerated. We have not observed other significant non-hematological toxicities or other organ-related toxicities. We expect to achieve full patient recruitment of the ALICE study (36 subjects) in October 2021 and will report updated safety and efficacy results based on an October data cut-off. Conclusions: Data to date indicate that iadademstat has a good safety profile and produces robust, fast and in some cases durable responses. Iadademstat appears to be an active candidate for combination with azacitidine and other agents. Drug-related toxicity appears to be predictable, manageable, and restricted to hematologic events. Considering the novel mechanism of action of iadademstat, a pro-differentiating agent, combination strategies with iadademstat might increase therapeutic options for AML patients in first line treatment, as well as for refractory, intolerant, or relapsed patients. Disclosures Salamero: Pfizer: Consultancy; BMS/Celgene: Consultancy, Honoraria; Novartis: Consultancy, Honoraria. Somervaille: Novartis: Consultancy, Honoraria. Molero: AbbVie: Honoraria; Jansen: Honoraria; BMS-Celgene: Other: Travel, accommodation expenses. Pérez-Simón: Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Gutierrez: Oryzon Genomics: Current Employment. Buesa: Oryzon Genomics: Current Employment, Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties. Bosch: Roche: Membership on an entity's Board of Directors or advisory committees, Other: Travel; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Research Funding; AbbVie: Membership on an entity's Board of Directors or advisory committees, Other: Travel; Gilead: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel; TAKEDA: Membership on an entity's Board of Directors or advisory committees, Other: Travel. Montesinos: Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Tolero Pharmaceutical: Consultancy; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Sanofi: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Teva: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Stemline/Menarini: Consultancy; Forma Therapeutics: Consultancy; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Incyte: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Daiichi Sankyo: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Karyopharm: Membership on an entity's Board of Directors or advisory committees, Research Funding; Glycomimetics: Consultancy; Agios: Consultancy; AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Astellas Pharma, Inc.: Consultancy, Honoraria, Other: Advisory board, Research Funding, Speakers Bureau.

Effect of Daratumumab-Containing Induction on CD34+ Hematopoietic Stem Cells before Autologous Stem Cell Transplantation in Multiple Myeloma

Introduction: Daratumumab (Dara) is an anti-CD38 monoclonal antibody representing a novel treatment agent for multiple myeloma (MM). Nonetheless, several studies have reported a Dara-related impairment of CD34+ hematopoietic stem cell (HSC) mobilization and post-autologous stem cell transplantation (ASCT) complications, including low yields of mobilized HSCs and delayed neutrophil engraftment. Impact of Dara on the mobilization process and HSCs remains poorly understood even though sufficient yields of CD34+ cells are necessary for a successful ASCT and subsequent patient recovery. Aims: To compare the effect of the Dara-containing (Dara-Bortezomib-Dexamethasone [D-VCd]) and conventional (Bortezomib-Thalidomide-Dexamethasone [VTd]) therapy on CD34+ HSCs. Methods: Transplant eligible MM patients were treated with D-VCd or VTd induction regimen followed by a cyclophosphamide + G-CSF mobilization and a high-dose melphalan D -1 before ASCT. Flow cytometry (FCM) screening of CD34+ subsets was performed in the bone marrow (BM) or apheresis product (AP) at three consecutive time points: 1) diagnostic BM (DG), 2) mobilization AP (MOB), 3) a day prior ASCT BM (D-1). Furthermore, RNA sequencing (RNAseq) of sorted CD34+ cells was performed on total RNA with ribo-depletion protocol in AP after the induction. D-VCd samples had lower RNA yields thus the D-VCd or VTd groups were processed as independent batches. Results: Clinical data revealed no significant differences in mobilization (p &gt;0.050) likely due to a small cohort sizes (D-VCd n=5 vs VTd n=9), though a trend towards worse performance in D-VCd was observed. Median CD34+ cell yield was 3.08 vs 10.56 x 10 6/kg. Platelet recovery of &gt;20x10 9/L was D+14 vs D+12 (range: 11-18 vs 10-16). Neutrophil recovery of &gt;0.5x10 9/L was D+12 in both groups (range: 11-17 vs 11-12). In FCM analysis, DG (n=14), MOB D-VCd (n=5) vs VTd (n=9), D-1 D-VCd (n=7) vs VTd (n=15) were compared. CD34+ frequency (Fig. 1A) difference in MOB D-VCd vs VTd was insignificant (median: 1.15% vs 1.89%), whereas CD34+ fraction dropped in D-1 D-VCd (median: 0.52% vs 0.72%, p=0.027), albeit there was no significant reduction in D-1 D-VCd vs initial DG (median: 0.52% vs 0.45%). Differences in the distribution of certain HSC subsets were detected in the CD34+ pool (Fig. 1B-E). Frequency of multipotent progenitors (MPPs) (Fig. 1B) was increased in MOB D-VCd (median: 82.1% vs 66.2%, p=0.004). Frequency of lympho-myeloid-primed progenitor + granulocyte-monocyte progenitor (LMPP+GMP) (Fig. 1C) subset was reduced in D-VCd in both MOB (median: 1.7% vs 16.9%, p=0.042) and D-1 (median: 5.3% vs 14.0%; p=0.026). Erythro-myeloid progenitors (EMPs) (Fig. 1D) were reduced in MOB D-VCd (median: 10.7% vs 19.5%, p=0.042), while the frequency of EMPs increased in D-1 D-VCd (median: 20.8% vs 12.4%, p=0.045). No considerable differences were found in the expression of adhesion molecules CD44/HCAM or CD184/CXCR4. CD38 was strongly diminished in the whole D-VCd CD34+ fraction of MOB and D-1. To understand whether the differences in the mobilization efficacy after D-VCd induction were reflected in the expression profile of mobilized CD34+ cells, differential expression analysis was performed. Overall 133 significantly deregulated genes (p&lt;0.05; log fold change &gt;(-)1) between cohorts (D-VCd n=5 vs VTd n=5) were revealed (Fig. 2). Pathway analysis showed cellular response and localization as the most deregulated categories. The list of deregulated genes contained 25% of non-coding RNAs, some of which were linked to a protein localization in the cell (RN7SL1/2). The expression of adhesion molecules was inspected independently. Out of 59 HSC hallmark genes, only 8 were significantly altered in D-VCd. Interestingly, the main homing molecule CXCR4 seemed to be downregulated in D-VCd, while integrins A3 and B4 were upregulated. Conclusions: Despite the limited cohort sizes, a prospective trend of delayed neutrophil and platelet recovery was observed after D-VCd therapy. FCM analysis revealed a significant reduction of CD34+ subsets responsible, among others, for a reconstitution of neutrophils and megakaryocytes. A strong signal in transcriptome data which would potentially explain differential mobilization in D-VCd cohort was not detected, nevertheless, several genes with adhesive/homing and stem cell differentiation function were indeed altered. The results warrant further investigation. Figure 1 Figure 1. Disclosures Hajek: BMS: Consultancy, Honoraria, Research Funding; AbbVie: Consultancy, Honoraria; Novartis: Consultancy, Research Funding; Janssen: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pharma MAR: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding.

Hematologic Recovery after Allogeneic Transplantation: Risk Factors and Its IMPACT on Transplant Related Mortality

Introduction. Hematologic recovery is often not satisfactory in patients undergoing an allogeneic stem cell transplantation (HSCT). A significant proportion have been reported to have low peripheral blood counts, despite full donor chimerism. This condition can be related to several factors including: number of CD34+ cells infused , stem cell source, underlying disease, conditioning regimen, GvHD and viral infections. Recently transplant platforms have changed, including the use of haploidentical transplants and modified GvHD prophylaxis. Aim of the study: to investigate factors associated with hematological recovery following an allogeneic HSCT in current transplant years. Methods: We included 1311 patients, with hematological diseases, undergoing an allogeneic HSCT, between year 2000 and 2020, in two transplant center: Genova and Roma. The main diagnoses were acute leukemia (54%), lymphoproliferative disorders (13%) , myelodysplastic syndromes (9%) and myelofibrosis (9%). 1108 patients aged &lt;60 years and 203 aged &gt;60 years. Platelet counts were taken as a surrogate marker of hematologic recovery. Results: We first ran a multiple regression analysis on factors influencing platelet counts between 50 and 100 days post-transplant. These factors were patients age &gt;60 years, GvHD grade II-IV, non sibling donor and a diagnosis of myelofibrosis. Platelet recovery at different time points, up to over 4 years post-transplant, is shown in Figure 1a in patients stratified according to an age cut off of 60 years. Patients younger than 60 years showed significantly improved platelet recovery , at each time point, when compared to patients over 60 years ; the difference persisted beyond 4 years. There was no difference in platelet recovery in patients aged 18-40 and 41-60. Donor age and year of transplant had no effect on platelet recovery. Figure 1b shows platelet recovery according to risk factors (age, GvHD, myelofibrosis, non sib donor). Transplant related mortality (TRM). We then asked whether low platelet counts predicted TRM. Patients with a platelets count higher than 20 and 50x10^9 on days 50-100 post-HSCT, showed a reduced transplant related mortality (TRM) as compared to patients with a lower platelet count (13%vs 39%: p&lt;0.000001; 11% vs31%, p&lt;0.000001) (Figure 1 c,d). Conclusions: Platelet recovery post-HSCT seems to be strongly influenced by patient's age, together with GvHD, a diagnosis of myelofibrosis and donor type. Slow recovery in older patients remains statistically significant beyond 4 years after HSCT. Hematologic recovery after HSCT has not improved over the past 2 decades. Low platelet counts are a strong risk factor for mortality after allogeneic HSCT. Clinical trials with TPO agonists post HSCT are warranted to assess whether hematologic recovery can be improved, and whether this will translate in reduced mortality. Figure 1 Figure 1. Disclosures Sica: Pfizer: Honoraria. Laurenti: AstraZeneca: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria; Roche: Honoraria, Research Funding; Gilead: Honoraria; BeiGene: Honoraria. Metafuni: Jazz: Other: Invited Clinical case presentation at meeting. Angelucci: Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene BSM: Honoraria, Other: DMC; Blue Bird Bio: Honoraria, Membership on an entity's Board of Directors or advisory committees; Menarini-Stemline: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: steering commitee, Speakers Bureau; Vertex Pharmaceuticals: Honoraria, Other: DMC; Crispr therapeutics: Honoraria, Other: DMC; Glaxo: Honoraria, Membership on an entity's Board of Directors or advisory committees; Gilead: Honoraria, Membership on an entity's Board of Directors or advisory committees.

Preliminary Safety and Efficacy Results from Precizn-1: An Ongoing Phase 1/2 Study on Zinc Finger Nuclease-Modified Autologous CD34+ HSPCs for Sickle Cell Disease (SCD)

Introduction Sickle cell disease (SCD) is caused by pathologic variants in both alleles of the β-globin gene, affecting ~100,000 patients in the US (Strouse. Handb Clin Neurol 2016;138:311-24). Elevated fetal hemoglobin (HbF) levels ameliorate symptoms and improve survival in patients with SCD (Hebert. Am J Hematol 2020;95:1235-45). SAR445136 (BIVV003) is a novel therapeutic product comprising autologous CD34+ HSPCs modified ex vivo by zinc finger nucleases (ZFN) and targeting the BCL11A gene erythroid-specific enhancer (ESE) to increase endogenous HbF production. Methods PRECIZN-1 (NCT03653247) is an ongoing first-in-human, open label, single arm, multi-site study evaluating safety and tolerability of SAR445136 (n=8; aged 18-40 years), with severe SCD across 6 US sites. Eligible subjects underwent mobilization and apheresis with plerixafor 240 ug/kg/day for up to 3 days to collect autologous CD34+ HSPCs to achieve a minimum of 10 × 10 6 CD34+ HSPC/kg for manufacturing of the SAR445136 dose. Additional apheresis cycles were allowed to achieve the minimum cell dose and rescue aliquots. Autologous HSPCs were transfected ex vivo with ZFN mRNAs targeting the ESE region of the BCL11A locus to manufacture SAR445136. A single IV infusion of 3-20 × 10 6 CD34+ HSPC/kg was administered at least 72 hours after the final busulfan myeloablation dose. Subjects were monitored for stem cell engraftment and hematopoietic recovery, adverse events (AEs), clinical and laboratory hemolysis markers, total Hb and HbF, percentage of F cells and sickle-cell related events post-SAR445136 infusion. Health-related quality of life (HRQoL) was assessed via the PROMIS-57 survey at screening, Weeks 26 and 52, and early termination visit. Results Of the 7 subjects that underwent mobilization and apheresis to date (25 June 2021), 5 achieved successful target yields ranging from 3.4-13.8 x 10 6 CD34+ HSPC/kg per apheresis day (mean: 6.49 x10 6 CD34+ HSPC/kg per apheresis day) in one apheresis cycle (4.45-10.9 x 10 6 CD34+ HSPC/kg per 2-day cycle). One subject failed to mobilize; one discontinued due to intercurrent cholangitis. Baseline patient characteristics of the 4 patients infused are in Table 1. Pre-apheresis peripheral blood WBC ranged from 23.2-36.9 x 10 3/μL (mean: 28.7 x 10 3/μL) and % CD34+ was 0.09-0.36% (0.22%) with absolute CD34+ counts of 20-80/μL (mean: 60/μL). Four of the mobilized subjects were successfully infused with SAR445136 at a single dose ranging from 3.2-9.7 x 10 6 CD34+ HSPC/kg (mean: 5.17 x 10 6 CD34+ HSPC/kg). All 4 subjects engrafted with a median time to neutrophil and platelet recovery of 21.5 and 24.5 days, respectively. No rescue doses were required. All 4 patients improved clinically since SAR445136 infusion, with no recurrence of previous vaso-occlusive crises (VOCs). Total Hb stabilized at 9-10 g/dL by week 26 post SAR445136 infusion along with improvements in the clinical markers of hemolysis in all 4 subjects. Percent HbF levels were 1-11% at screening, increasing to 15-29% by Week 13 in all 4 subjects, to 14-39% by Week 26 in the 3 subjects with at least 26 weeks follow up; and persisting at 35% in 1 subject with 65 weeks follow up (Figure 1). Percent F cells increased to 49-94% in 3 subjects with at least 26 weeks follow up, persisting at 90% in 1 subject with 65 weeks follow up. The fourth subject had 87.5% F cells at 13 weeks follow up. Although preliminary, a trend of improvement exceeding the proposed minimally clinically important difference in all PROMIS-57 HRQoL domains except sleep disturbance was observed in the 3 subjects with 26 weeks follow up, whose scores were "worse" than the norm at baseline (≤2 points per domain). SAR445136 was generally well tolerated with no infusion related reactions. The AEs reported were consistent with plerixafor mobilization and busulfan myeloablation therapy. No AEs or SAEs were reported as related to SAR445136. Conclusions As of 25 June 2021, these preliminary proof-of-concept efficacy and safety results confirm the potential therapeutic value of ZFN-mediated modification of the BCL11A ESE region and SAR445136 infusion to address current unmet needs of patients with SCD. All 4 infused patients had no SCD related events including VOCs following SAR445136 infusion, as well as increases in total Hb, HbF, and %F cells, and clinical improvements in PROMIS-57 domains. SAR445136 is generally well tolerated in the 4 subjects infused to date, with no related AEs or SAEs reported. Figure 1 Figure 1. Disclosures Abedi: BMS/Celgene: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Seattle Genetics: Speakers Bureau; Abbvie: Speakers Bureau. Galeon: Sanofi: Current Employment. Reiner: Sanofi: Current Employment. Smith: Sanofi: Current Employment. Wang: Sanofi: Current Employment. Ramezi: Sanofi: Current Employment. Rendo: Sanofi: Current Employment, Other: May hold shares and/or stock options . Walters: AllCells, Inc: Consultancy; Vertex pharmaceuticals: Consultancy; Ensoma, Inc.: Consultancy; BioLabs, Inc: Consultancy.

Lintuzumab-Ac225 in Combination with CLAG-M Yields High MRD (-) Responses in R/R AML with Adverse Features: Interim Results of a Phase I Study

Background: Lintuzumab-Ac225 (Actimab-A) is a humanized CD33 antibody, lintuzumab, conjugated to an alpha emitting isotope, actinium (Ac225), with potent single agent activity against AML. We hypothesized that a low dose infusion of lintuzumab-Ac225, after salvage chemotherapy, would effectively eliminate residual leukemia and improve remission rates, and depth of remission. Patients and Methods: Adult patients with relapsed/refractory AML (RR-AML), and with adequate organ function and performance status were eligible for screening. On screening, we assessed CD33 expression, greater than 25% of leukemic blasts must have expressed CD33 antigen by flow cytometry for inclusion. Induction consisted of G-CSF, 300mcg/d, given D1-6, cladribine 5mg/m2, given D2-6, cytarabine 2g/m2, given D2-6, and mitoxantrone 10mg/m2, given D2-4. Lintuzumab-Ac225 was administered as a single dose on either day 7, 8, or 9. This trial enrolled to 4 cohorts, administering lintuzumab-ac225 at a dose of 0.25uCi/kg, 0.50uCi/kg, 0.75uCi/kg, and 1.0uCi/kg. Treatment consisted of one induction cycle. Disease assessment, including MRD assessment by flow, was performed between Days 29-42. Results: Sixteen patients with a median age of 64 yrs were evaluable for toxicity and response. Three pts were treated in cohort 1 (0.25uCi/kg), nine pts were treated in cohort 2 (0.5uCi/kg), three pts were treated in cohort 3 (0.75uCi/kg), and one pt was treated in cohort 4 (1.0uCi/kg). Patient characteristics include 63% (n=10) pts with adverse cytogenetics, mutations involving TP53 in 44% (n=7) pts, and secondary/therapy-related AML in 50% (n=8) of patients. Patients received a median 2 lines of therapy, and 50% (n=8) received a venetoclax combination regimen prior to enrollment. Table 1 summarizes patient characteristics. No undue non-hematologic toxicities were observed in this trial. Commonest AEs were neutropenic fever and infection. Among responders, an ANC&gt;1000 was achieved in 9/10 patients, at a median of 33 days, and a platelet count &gt;50k was achieved in 6/10 patients at a median of 37 days. Of note, two patients proceeded to HCT prior to platelet recovery. Overall, among patients enrolled in cohorts 1-3, CR/CRi was observed in 67% (n=10) pts. One patient enrolled in cohort 4 achieved an aplastic marrow by D+42, with subsequent stem cell boost and neutrophil recovery. Of responders, 70% (7/10) had no measurable disease (MRD(-)) by flow cytometry. Among patients receiving &lt;4 lines of prior therapy, 71% (n=5) pts with adverse cytogenetics, 80% (n=4) pts with TP53 mutation, and 80% (n=4) pts receiving a prior venetoclax combination achieved a remission. Estimated 6-month OS was 60%. Conclusions: Lintuzumab-Ac225 at a low dose appears to be safe in combination with the salvage chemotherapy regimen CLAG-M. Furthermore, this combination has demonstrated promising efficacy results among high risk RR-AML patients, namely patients with adverse molecular/cytogenetic features and patients previously receiving venetoclax. Updated Cohort 4 results will be presented at ASH. Upon determination of MTD, we plan to explore the combination of lintuzumab-Ac225 with other salvage regimens (e.g. FLAG, FLAG-Ida, MEC) to determine whether adding this novel agent can generally improve salvage outcomes in hard to treat patients. Figure 1 Figure 1. Disclosures Abedin: Helsinn: Research Funding; Agios: Honoraria; AltruBio: Research Funding; Pfizer: Research Funding; Amgen: Honoraria; Actinium: Research Funding; Astellas Pharma Inc.: Research Funding. Guru Murthy: Guidepoint: Consultancy; Cancerexpertnow: Honoraria; Techspert: Consultancy; Qessential: Consultancy; Cardinal Health Inc.: Honoraria; TG therapeutics: Other: Advisory board. Hamadani: Sanofi, Genzyme, AstraZeneca, BeiGene: Speakers Bureau; Takeda, Spectrum Pharmaceuticals and Astellas Pharma: Research Funding; Janssen, Incyte, ADC Therapeutics, Omeros, Morphosys, Kite: Consultancy. Atallah: Pfizer: Consultancy, Research Funding; BMS: Honoraria, Speakers Bureau; Takeda: Consultancy, Research Funding; Abbvie: Consultancy, Speakers Bureau; Amgen: Consultancy; Novartis: Consultancy, Honoraria, Research Funding.