How to Monitor Immune Reconstitution Following Allogeneic Hematopoietic Stem Cell Transplantation: A Survey from the EBMT- Cellular Therapy & Immunobiology Working Party

Blood ◽  
2016 ◽  
Vol 128 (22) ◽  
pp. 4581-4581
Author(s):  
Raffaella Greco ◽  
Fabio Ciceri ◽  
Maddalena Noviello ◽  
Attilio Bondanza ◽  
Luca Vago ◽  
...  
Keyword(s):  
Stem Cell ◽  
T Cell ◽  
Immune Reconstitution ◽  
Cellular Therapy ◽  
Working Party ◽  
Standard Of Care ◽  
Hematopoietic Stem ◽  
Post Transplant ◽  
Molecular Tests ◽  
Routine Basis

Abstract Background: Post transplant immune reconstitution plays a major role in determining the outcome of allogeneic hematopoietic stem cell transplantation (allo-HSCT), and is currently monitored with different techniques in different Centers, with the aim of identifying clinically relevant immunological biomarkers. However, it is unclear which and how many of these immunological tests are currently performed on a routine basis, and which ones have the potential to predict patient outcome, and possibly guide patient care after allo-HSCT. Methods: The EBMT Cellular Therapy & Immunobiology Working Party (CTIWP) conducted a survey to identify current policies to monitor immune reconstitution in patients undergoing allo-HSCT and possibly reach a general consensus. This study followed the EBMT study guidelines. All EBMT Centers were invited to participate. Each participating Center received a questionnaire on the availability of specific immunomonitoring assays, specifying the use in clinical practice and/or within investigational trials. Assays were based on relatively simple and readily available parameters such as absolute lymphocyte counts (ALC) to more complex cellular and molecular tests. Moreover, the Centers were asked to define the transplant platform (HLA-identical sibling, matched unrelated donor, haploidentical and/or cord blood) on which each test is generally performed. Results: Policies for post-transplant immunomonitoring have been reported by 35 participating EBMT Centers active in 14 Countries and performing allo-HSCT from HLA identical related (35 centers), matched unrelated (33), haploidentical (34), unrelated cord blood (27). Complete blood counts and immunoglobulins are routinely tested for patients' care by all centers. Relative proportions of T cell subsets are currently tested by flow-cytometry as "standard of care" or "investigational" by 82% and 17% of centers respectively. B cell and NK cell counts are quantified routinely by 46% and 23% of Centers, and investigationally by 40% of Centers. The availability of molecular tests (STR, qPCR, Fish) to measure post-transplant engraftment are reported by all Centers, except two, as a standard of care measure. T cell receptor-expressing circles (TRECs) and/or K-deleting recombination excision circles (KRECs) are quantified within selected clinical trials by 37% of Centers. Interestingly, 60% of Centers evaluate, mostly as an investigational measure, antigen specific T cell responses by: proliferation assays (49%), interferon-gamma enzyme-linked immunospot-Elispot (49%), intracellular cytokine staining (46%) and tetramer/dextramer staining (37%). Most of these Centers test responses to Cytomegalovirus and Epstein Barr Virus, and 5 Centers use at least one of these assays on a routine basis. About half of the participating Centers (43%) commonly test antigen-specific antibodies, mainly as responses to vaccines, and not routinely. T-cell receptors (TCR) and B-cell receptors (BCR) repertoires are measured by spectratyping in 14 out of 35 Centers (4 as clinical practice and 10 in selected trials), or, in selected trials, by next generation sequencing (in 11 out of 35 the participating Centers). Conclusions: Results of this survey indicate that country- and center expertise are associated with heterogeneous and distinct protocols, and underline the clinical need to harmonize methods and to provide practical recommendations for monitoring post-transplant immune reconstitution, both for routine purposes and investigational studies. Adequate reporting and connection between individual Centers exploiting these data will foster collaborative and comparative research studies, with the ultimate goals of improving patient care and refining our understanding of the immunological correlates to clinical outcome. Acknowledgments: R. Ram, M. A. Diaz, G. McQuaker, D. Russo, E. Faber, P. Chiusolo, C. Rössig, S. M. Martin, A. Anagnostopoulos, M. Stelljes, K. Orchard, P. Jindra, A. Sampol, K. Patrick, M. A. Bekadja, J. Gayoso, A. Olivieri, J. Passweg, E. Jost, H Labussiere-Wallet, Y Koc, A. Lange, I. Garcia Cadenas, N. Kröger, A. Biondi, N. Milpied, D. Olive, E. Lanino, G. Stuhler, J.H. Dalle, J.R. Cabrera Marín, F. Ciceri, D. Uckan-Cetinkaya, R. Parody Porras, G. Kriván. Disclosures Ciceri: MolMed SpA: Consultancy. Bonini:TxCell: Membership on an entity's Board of Directors or advisory committees; Molmed SpA: Consultancy.

Higher Prevalence But Similar Infectious Profile Overtime After Haploidentical Transplantation Compared With HLA-Identical Transplantation For Hematological Diseases

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 4528-4528
Author(s):  
Roberto Crocchiolo ◽  
Luca Castagna ◽  
Andrea Vai ◽  
Barbara Sarina ◽  
Stefania Bramanti ◽  
...  
Keyword(s):  
Stem Cell ◽  
T Cell ◽  
Immune Reconstitution ◽  
Viral Infections ◽  
Conflicts Of Interest ◽  
Fungal Infections ◽  
Infectious Complications ◽  
Hematopoietic Stem ◽  
Post Transplant ◽  
Haplo Group

Introduction a major limitation of hematopoietic stem cell transplantation (HSCT) from haploidentical donor is the impaired immune reconstitution due to extensive immunosuppression necessary to overcome HLA disparity. Recently, a platform for T-cell repleted HSCT from haploidentical donor (haplo-HSCT) using post-transplant cyclophosphamide (CTX) has been reported, with low TRM and high reproducibility. However, little has been reported so far about immune reconstitution and, in particular, incidence of infections after this type of transplantation. Aims of the study to describe infectious complications after T-cell replete haplo-HSCT after NMA conditioning performed at our center and to compare them with HLA-identical transplantations performed at the same center. Patients and Methods data on patients with hematological malignancies who underwent haplo-HSCT were collected and compared with RIC/NMA-HSCT from HLA-identical donors. Transplants included were those performed up to 31st December 2012. Infections were classified as FUO, bacterial, micotic or viral and prevalence over five post-transplant intervals was estimated: days 0-30, 31-100, 101-180, 181-365, >365. Prevalence for each time period was defined as the number of infectious events/patients at risk. Results we identified a total of 72 and 40 patients transplanted from HLA-identical or haploidentical donor respectively. Median follow-up was longer in HLA-identical vs. haploidentical (34 vs. 15 months, p<0.0001). Among 38 out of 40 haplo-HSCT patients, a total of 96 infectious events occurred, with a median of 3 events/patient (range: 0-6). Etiologies were as follows: 39 bacterial, 6 fungal and 51 viral. Bacterial infections occurred mostly between day 0 and +30, whereas viral infections/reactivations between +30 and +100 (see Figure 1a). In the HLA-identical cohort, 166 events occurred among 64 out of 72 patients, with a median of 2 events/patient (range: 0-8); etiologies were: 84 bacterial, 9 fungal and 73 viral. FUO events were 19 and 34 among haplo- and HLA-identical transplants respectively. Prevalence of infections was lower in HLA-identical compared with haplo-HSCT group, but subdistribution of etiologies was similar overtime (see Figure 1b), with bacterial and FUO mostly before day+30 and viral events mostly between +30 and +100. Importantly, no fungal infections occurred beyond day +180 in haplo group, probably due to the low incidence of chronic GVH. Conversely, higher prevalence of bacterial events observed in HLA-identical group may be due to chronic GVH. Deaths due infection were 25% in haplo group (10/40, occuring between +13 and +152) and 11% (8/75) among HLA-identical transplants. Conclusion RIC haplo-SCT with post-transplant CTX shows a slightly higher rate of infectious complications compared with HLA-identical ones. Subdistribution of etiologies is similar, with the highest prevalence of viral infections between +30 and +100 and no fungal events after +180. Thus, in haplo-SCT, immunological recovery appears to be satisfactory after +180. Future comparisons with other alternative stem cell sources (i.e. cord blood) are warranted. Disclosures: No relevant conflicts of interest to declare.

IL-15 Administration Increases Graft Versus Leukemia Activity in Recipients of Haploidentical Hematopoietic Stem Cell Transplantation,

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 4027-4027
Author(s):  
Christopher Sauter ◽  
Chandra Biswas ◽  
Cavan Bailey ◽  
Michelle Panis ◽  
Tulin Budak-Alpdogan ◽  
...  
Keyword(s):  
T Cells ◽  
Stem Cell ◽  
T Cell ◽  
Immune Reconstitution ◽  
Low Dose ◽  
Nk Cell ◽  
Hematopoietic Stem ◽  
Cell Numbers ◽  
Post Transplant ◽  
Graft Versus Leukemia

Abstract Abstract 4027 The success of haploidentical (HI) hematopoietic stem cell transplantation (HSCT), suggests that graft-versus-leukemia (GVL) effect might have a substantial role in this transplant modality. Rigorous T-cell depletion (TCD) of the graft decreases the occurrence of graft-versus-host disease (GVHD) in HI-HSCT, however this results in immunodeficiency and high disease relapse rate, especially in patients with resistant or residual leukemia. Therefore, enhancing GVL activity of HSCT without increasing GVHD is crucial for improving the outcome of haploidentical transplant. Post-transplant IL-15 administration is shown to enhance immune reconstitution, particularly donor-derived NK and CD8+ T cell populations in murine models. We evaluated the efficacy of IL-15 for enhancing GVL effect in recipients of HI-HSCT. For developing clinically relevant haploidentical transplant models, different hybrid mice with B6 background that share the same haplotype (H2Kb) are used for our murine haploindentical transplant experiments. Lethally irradiated B6D2F1/J (H2Kb/d) mice are transplanted with B6CBAF1/J (H2Kb/k) TCD bone marrow (BM) and T cells at varying doses. Some animals were also given P815 tumor cells on the day of transplant. Administration of IL-15 significantly increased the numbers of CD8+ T and NK cells in the spleen and BM in the T cell depleted model at post-transplant day 28. Infusion of very low dose haploidentical T cells (1×104) with TCD-BM resulted in a conflicting effect on immune reconstitution, i.e. increased T cell numbers, and decreased NK cell population. Post-transplant IL-15 administration also changed this immune reconstitution pattern and significantly increased both T and NK cell numbers in recipients of HI-HSCT. In P815 challenged mice that were transplanted with very low dose T cell added TCD-BM, IL-15 administration significantly increased anti-tumor activity of the graft and improved survival (Figure 1) without increasing GVHD. This effect was observed when IL-15 administration was given at a later time point rather than immediately following transplantation, possibly allowing for more donor cell engraftment and T cell proliferation to take place. IL-15 administration without T cell infusion did not result in any survival improvement. We conclude that in our experimental HI transplant models, IL-15 administration augments anti-tumor effect of the HI-HSCT without increasing GVHD risk, and this effect requires presence of donor derived T cells. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Impact of Different T Cell Depletion Protocols on Immune Reconstitution Following Allogeneic Hematopoietic Stem Cell Transplantation

Blood ◽  
2020 ◽  
Vol 136 (Supplement 1) ◽  
pp. 43-44
Author(s):  
Amandine Pradier ◽  
Adrien Petitpas ◽  
Anne-Claire Mamez ◽  
Federica Giannotti ◽  
Sarah Morin ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Immune Reconstitution ◽  
Cell Depletion ◽  
Unrelated Donor ◽  
T Cell Depletion ◽  
Hematopoietic Stem ◽  
Post Transplant ◽  
The Impact

Introduction Allogeneic hematopoietic stem cell transplantation (HSCT) is a well-established therapeutic modality for a variety of hematological malignancies and congenital disorders. One of the major complications of the procedure is graft-versus-host-disease (GVHD) initiated by T cells co-administered with the graft. Removal of donor T cells from the graft is a widely employed and effective strategy to prevent GVHD, although its impact on post-transplant immune reconstitution might significantly affect anti-tumor and anti-infectious responses. Several approaches of T cell depletion (TCD) exist, including in vivo depletion using anti-thymocyte globulin (ATG) and/or post-transplant cyclophosphamide (PTCy) as well as in vitro manipulation of the graft. In this work, we analyzed the impact of different T cell depletion strategies on immune reconstitution after allogeneic HSCT. Methods We retrospectively analysed data from 168 patients transplanted between 2015 and 2019 at Geneva University Hospitals. In our center, several methods for TCD are being used, alone or in combination: 1) In vivo T cell depletion using ATG (ATG-Thymoglobulin 7.5 mg/kg or ATG-Fresenius 25 mg/kg); 2) in vitro partial T cell depletion (pTCD) of the graft obtained through in vitro incubation with alemtuzumab (Campath [Genzyme Corporation, Cambridge, MA]), washed before infusion and administered at day 0, followed on day +1 by an add-back of unmanipulated grafts containing about 100 × 106/kg donor T cells. The procedure is followed by donor lymphocyte infusions at incremental doses starting with 1 × 106 CD3/kg at 3 months to all patients who had received pTCD grafts with RIC in the absence of GVHD; 3) post-transplant cyclophosphamide (PTCy; 50 mg/kg) on days 3 and 4 post-HSCT. Absolute counts of CD3, CD4, CD8, CD19 and NK cells measured by flow cytometry during the first year after allogeneic HSCT were analyzed. Measures obtained from patients with mixed donor chimerism or after therapeutic DLI were excluded from the analysis. Cell numbers during time were compared using mixed-effects linear models depending on the TCD. Multivariable analysis was performed taking into account the impact of clinical factors differing between patients groups (patient's age, donor type and conditioning). Results ATG was administered to 77 (46%) patients, 15 (9%) patients received a pTCD graft and 26 (15%) patients received a combination of both ATG and pTCD graft. 24 (14%) patients were treated with PTCy and 26 (15%) patients received a T replete graft. 60% of patients had a reduced intensity conditioning (RIC). 48 (29%) patients received grafts from a sibling identical donor, 94 (56%) from a matched unrelated donor, 13 (8%) from mismatched unrelated donor and 13 (8%) received haploidentical grafts. TCD protocols had no significant impact on CD3 or CD8 T cell reconstitution during the first year post-HSCT (Figure 1). Conversely, CD4 T cells recovery was affected by the ATG/pTCD combination (coefficient ± SE: -67±28, p=0.019) when compared to the T cell replete group (Figure 1). Analysis of data censored for acute or chronic GVHD requiring treatment or relapse revealed a delay of CD4 T cell reconstitution in the ATG and/or pTCD treated groups on (ATG:-79±27, p=0.004; pTCD:-100±43, p=0.022; ATG/pTCD:-110±33, p&lt;0.001). Interestingly, pTCD alone or in combination with ATG resulted in a better reconstitution of NK cells compared to T replete group (pTCD: 152±45, p&lt;0.001; ATG/pTCD: 94±36, p=0.009; Figure 1). A similar effect of pTCD was also observed for B cells (pTCD: 170±48, p&lt;.001; ATG/pTCD: 127±38, p&lt;.001). The effect of pTCD on NK was confirmed when data were censored for GVHD and relapse (pTCD: 132±60, p=0.028; ATG/pTCD: 106±47, p=0.023) while only ATG/pTCD retained a significant impact on B cells (102±49, p=0.037). The use of PTCy did not affect T, NK or B cell reconstitution when compared to the T cell replete group. Conclusion Our results indicate that all TCD protocols with the only exception of PTCy are associated with a delayed recovery of CD4 T cells whereas pTCD of the graft, alone or in combination with ATG, significantly improves NK and B cell reconstitution. Figure 1 Disclosures No relevant conflicts of interest to declare.

New Developments in Allotransplant Immunology

Hematology ◽  
2003 ◽  
Vol 2003 (1) ◽  
pp. 350-371 ◽  
Author(s):  
A. John Barrett ◽  
Katayoun Rezvani ◽  
Scott Solomon ◽  
Anne M. Dickinson ◽  
Xiao N. Wang ◽  
...  
Keyword(s):  
T Cells ◽  
Stem Cell ◽  
T Cell ◽  
Stem Cell Transplantation ◽  
Cell Transplantation ◽  
Immune Reconstitution ◽  
Cytokine Gene ◽  
Post Transplant ◽  
Cytokine Milieu ◽  
Cytokine Gene Polymorphisms

Abstract After allogeneic stem cell transplantation, the establishment of the donor’s immune system in an antigenically distinct recipient confers a therapeutic graft-versus-malignancy effect, but also causes graft-versus-host disease (GVHD) and protracted immune dysfunction. In the last decade, a molecular-level description of alloimmune interactions and the process of immune recovery leading to tolerance has emerged. Here, new developments in understanding alloresponses, genetic factors that modify them, and strategies to control immune reconstitution are described. In Section I, Dr. John Barrett and colleagues describe the cellular and molecular basis of the alloresponse and the mechanisms underlying the three major outcomes of engraftment, GVHD and the graft-versus-leukemia (GVL) effect. Increasing knowledge of leukemia-restricted antigens suggests ways to separate GVHD and GVL. Recent findings highlight a central role of hematopoietic-derived antigen-presenting cells in the initiation of GVHD and distinct properties of natural killer (NK) cell alloreactivity in engraftment and GVL that are of therapeutic importance. Finally, a detailed map of cellular immune recovery post-transplant is emerging which highlights the importance of post-thymic lymphocytes in determining outcome in the critical first few months following stem cell transplantation. Factors that modify immune reconstitution include immunosuppression, GVHD, the cytokine milieu and poorly-defined homeostatic mechanisms which encourage irregular T cell expansions driven by immunodominant T cell–antigen interactions. In Section II, Prof. Anne Dickinson and colleagues describe genetic polymorphisms outside the human leukocyte antigen (HLA) system that determine the nature of immune reconstitution after allogeneic stem cell transplantation (SCT) and thereby affect transplant outcomethrough GVHD, GVL, and transplant-related mortality. Polymorphisms in cytokine gene promotors and other less characterized genes affect the cytokine milieu of the recipient and the immune reactivity of the donor. Some cytokine gene polymorphisms are significantly associated with transplant outcome. Other non-HLA genes strongly affecting alloresponses code for minor histocompatibility antigens (mHA). Differences between donor and recipient mHA cause GVHD or GVL reactions or graft rejection. Both cytokine gene polymorphisms (CGP) and mHA differences resulting on donor-recipient incompatibilities can be jointly assessed in the skin explant assay as a functional way to select the most suitable donor or the best transplant approach for the recipient. In Section III, Dr. Nelson Chao describes non-pharmaceutical techniques to control immune reconstitution post-transplant. T cells stimulated by host alloantigens can be distinguished from resting T cells by the expression of a variety of activation markers (IL-2 receptor, FAS, CD69, CD71) and by an increased photosensitivity to rhodamine dyes. These differences form the basis for eliminating GVHD-reactive T cells in vitro while conserving GVL and anti-viral immunity. Other attempts to control immune reactions post-transplant include the insertion of suicide genes into the transplanted T cells for effective termination of GVHD reactions, the removal of CD62 ligand expressing cells, and the modulation of T cell reactivity by favoring Th2, Tc2 lymphocyte subset expansion. These technologies could eliminate GVHD while preserving T cell responses to leukemia and reactivating viruses.

The Use of Clinical Grade Magnetic Beads to Deplete Immune Suppressive Elements from Autologous Peripheral Blood Hematopoietic Stem Cell Grafts Enhances T Cell Immune Responses.

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 2311-2311
Author(s):  
Zaid S Al-Kadhimi ◽  
Haider Mahdi ◽  
Moshrik Abdalamir ◽  
Elyse Paul ◽  
Voravit Ratanatharathorn ◽  
...  
Keyword(s):  
Immune Response ◽  
Stem Cell ◽  
T Cell ◽  
Hematopoietic Stem Cell ◽  
Magnetic Beads ◽  
T Cell Proliferation ◽  
Clinical Grade ◽  
Hematopoietic Stem ◽  
Post Transplant ◽  
Autologous Grafts

Abstract Background: Despite the demonstrated efficacy of high dose chemotherapy and autologous hematopoietic stem cell transplantation in Myeloma and relapsed Lymphoma, relapse continues to be a problem. Improving post transplant immune reconstitution in general and tumor specific immune response can reduce relapse rates. Pre-clinical and clinical data suggest that the abundance of CD4+/CD25+ regulatory T-cells (T-regs) and CD14+ monocytes in the autologous graft can contribute to the well described immune suppression state in the early months post transplant. We hypothesized that it is feasible to deplete both of these cellular inhibitory elements from the autologous grafts using clinical grade CD25 and CD14 magnetic beads from Miltenyi. We also hypothesized that the depletion of these populations would improve the proliferative capacity of T-cells in these grafts. Methods: Samples of peripheral blood hematopoietic stem cell grafts from 9 patients (4 lymphomas and 5 myelomas) undergoing autologous stem cell transplantation, with G-CSF mobilized grafts. We depleted T regs and monocytes, using CD25 and CD14 beads from these graft samples. Then we compared T cell reactivity between the manipulated graft versus the unmanipulated graft samples, in a mixed lymphocyte reaction. Results: We show that it is feasible to deplete both populations based on phenotype analysis that confirmed selective depletion of CD4+/CD25+/CD127-T reg population (70–80%) and CD14 population (74%.). The positively selected population was enriched for T regs CD4+CD25+CD127-(50–85%) and monocytes CD14+ (75%+). Furthermore in 9 out of 9 patients T cell proliferation measured by 3H thymidine uptake was close to two fold or higher in the double depleted grafts compared to the unmanipulated grafts (P=0.004 Wilcoxon Signed Rank Test). Conclusion: Double depletion of T regs and monocytes from autologous grafts using clinical grade magnetic beads, leads to enhanced T cell proliferation. This work will lay the ground for a subsequent clinical trial of regulatory T-cell/Monocyte depleted autologous transplantation using the same strategy, to enhance immune recovery post transplant and achieve better anti-lymphoma, or anti-myeloma immune response. Figure Figure

A Novel Chemotherapy-Based Allogeneic Hematopoietic Stem Cell Transplant Regimen for Very Young Children with Leukemia.

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 3149-3149
Author(s):  
Susan E. Prockop ◽  
Nancy A. Kernan ◽  
Elizabeth G Klein ◽  
Rachel Kobos ◽  
Andromachi Scaradavou ◽  
...  
Keyword(s):  
Stem Cell ◽  
T Cell ◽  
Young Children ◽  
Cord Blood ◽  
Chronic Gvhd ◽  
Disease Free Survival ◽  
Cell Transplant ◽  
Hematopoietic Stem ◽  
Free Survival ◽  
Post Transplant

Abstract Abstract 3149 Young children in need of allogeneic hematopoietic stem cell transplant (HSCT) are at increased risk of unacceptable side effects from total body irradiation (TBI) and have historically been considered candidates for non-TBI containing regimens. However, disease free survival (DFS) has been poorer in cohorts of very young patients transplanted without TBI and novel chemotherapy based regimens are needed. We report results in a cohort of 14 children all under three years of age at the time of transplant (6 – 32 months; median 19.8 months) using a clofarabine-based ablative regimen. Fourteen patients in this age group have undergone transplant with a regimen consisting of clofarabine 20 mg/m2/day × 5, thiotepa 10 mg/Kg/day × 1 and melphalan 70 mg/m2/day × 2. All patients had high risk disease. Seven (7) pts were transplanted for ALL, 6 for AML and 1 for JMML. Patients with ALL or AML in first remission (CR1) or CR2, were categorized as patients with good risk disease while all other pts were considered as poor risk irrespective of all other factors. Transplant risk was good for 6/7 with ALL, and 3/6 with AML. The patient with JMML had stable disease. Stem cell grafts consisted of unmodified bone marrow (BMT) (N=6), double cord blood (dCBT) (N=7) and T cell depleted PBSCT (N=1). Donors were matched unrelated (N=5) or mismatched unrelated (N=9) including 7 double umbilical cord blood grafts, and one T cell depleted graft. Graft versus host disease (GvHD) prophylaxis was with tacrolimus and methotrexate for unmodified BMT, tacrolimus and mycophenolate for dCBT or T cell depleted HSCT. Two patients died early post transplant of infection (1) and acute GvHD (1). Neutrophil engraftment for the 13 evaluable patients was at a median of 13 days (10 –29 days) for PBSC and BM grafts and 17.5 days (12 –23 days) for recipients of CB grafts. Platelet engraftment for the 12 evaluable patients was at a median of 23 days (16 – 36 days) for recipients of PBSC and BM grafts and 43.5 days (36 –66 days) for recipients of CB grafts. In all five patients developed grade II-IV GvHD, and two patients chronic GvHD. Seven patients developed transaminitis which resolved in all cases. No patients developed Grade IV mucositis. One patient (AML) died after relapsing 5.5 months post transplant. Two patients are alive after relapsing at 1.3 months (AML) and 10.8 months (JMML) post-transplant. Nine of the 14 patients are alive in continuous complete remission seven of whom are greater than 36 months from transplant (40.2 – 71 months). The seven patients without chronic GvHD have had robust immune reconstitution, have responded to vaccination, and continue to meet growth and developmental milestones. Only one patient (transplanted at 14 months of age) has mild neurocognitive deficits. This novel chemotherapy based regimen is associated with durable engraftment of unmodified and cord blood HSCT grafts and promising disease free survival in very young children with leukemia. Based on the low toxicity profile in this cohort of patients higher dosing of clofarabine will be explored as a possible way to improve leukemia remission in the highest risk patients. Disclosures: Off Label Use: Clofarabine.

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