cGy Total Body Irradiation Research Articles

Effect of ABO Mismatch and Red Blood Cell Alloimmunization on the Outcome of Hematopoietic Cell Transplantation for Sickle Cell Disease

Hematopoietic stem cell transplantation (HCT) remains the sole well-established curative option for patients with sickle cell disease (SCD). Nonmyeloablative conditioning has been used to improve outcomes and reduce toxicities in adult SCD patients. However, recipient-donor ABO incompatibility and alloimmunization may be significant impediments to successful outcomes of HSCT in SCD patients owing to risks of hemolysis, delayed engraftment, poor graft function, and graft failure (GF). Here we report our experience with allogeneic HCT for SCD and the effects of RBC group mismatch and alloimmunization on the outcome of transplant recipients. We conducted a retrospective analysis of all SCD patients age >14 years who underwent HCT between January 2015 and February 2022 at our center. All patients received i.v. alemtuzumab (1 mg/kg divided over 5 days on days -7 to -3) and 300 cGy total body irradiation on day -2 or -1 for conditioning. Pretransplantation preparation consisted of hydroxyurea at the maximum tolerated dose for 2 to 3 months and 1 session of exchange transfusion. Peripherally mobilized CD34 stem cells targeting 10 × 106 /kg of recipient weight were used. For graft-versus-host disease prophylaxis, sirolimus was started on day -1 and continued for 1 year with tapering if lymphoid chimerism was >50%. For patients with major ABO incompatibility, we administered 2 doses of rituximab (375 mg/m2) and 3 sessions of plasmapheresis before starting the conditioning regimen, targeting an isohemagglutinin titer <1/32. The primary objective was to determine the impact of RBC group mismatch and alloimmunization on the outcomes of the HCT recipients. The secondary objective was to assess the impact of GF on overall survival (OS). Logistic regression was done to evaluate predictors for GF. The Kaplan-Meier method was used for survival analysis. A total of 194 patients were included, with a median age of 26 years. Their median baseline hemoglobin and hemoglobin S values were 93 g/L and 71.3%, respectively. Indications for HCT included recurrent vaso-occlusive crisis in 52.5% of the patients, central nervous system events in 19.6%, and acute chest syndrome in 17%. After a median follow-up of 28.8 months (range, 5 to 83 months), 16 patients (8%) experienced GF (3 with primary GF and 13 with secondary GF). On univariate analysis, ABO minor incompatibility and RBC alloantibodies against donor non-ABO antigens were predictive of GF. On multivariate analysis, RBC alloantibodies against donor non-ABO antigens (odds ratio, 8.29; 95% confidence interval, 2.01 to 34.05; P = .0033) was the sole factor predictive of GF. None of the 16 patients with major ABO incompatibility developed GF. The 2-year OS for all patients was 95%. The 2-year OS was 98% in patients without GF, compared to 74% in patients with GF (P < .0001). In our SCD patients who underwent HSCT, the presence of RBC alloantibodies against donor non-ABO antigens was an independent risk factor for GF. Patients with GF had inferior survival, and strategies for decreasing the risk of GF are needed.

The effects of substituting cladribine for fludarabine on outcomes of a reduced intensity conditioning regimen.

e18518 Background: Drug shortages may be encountered especially in times of pandemics and war. The extrapolation of data focusing on different diseases may provide clinical clues for substituting two chemotherapeutic drugs of the same class. The substitution of cladribine for fludarabine in a reduced intensity conditioning (RIC) regimen composed of fludarabine, melphalan and total body irradiation (TBI) may yield similar side effect profile and outcomes. Methods: Consecutive patients undergoing an allogeneic stem cell transplant in our center between November 2019 to December 2022 were included. Within this period cladribine had to be substituted for fludarabine during a drug shortage. All patients received intravenous melphalan 75 mg/m2/day on day -2, and 200 cGy TBI on day -1. The regimen included either subcutaneous cladribine 10 mg/m2/day on days -5 to -2, or intravenous fludarabine 40 mg/m2/day on days -5 to -2. Graft versus host disease (GvHD) prophylaxis included a calcineurin inhibitor (CNI) + mycophenolate mofetil (MMF) for matched related donor transplants; and post-transplant cyclophosphamide + CNI + MMF for matched unrelated (MUD) and haploidentical donors. The distributions and medians of studied parameters in two cohorts were compared with non-parametric methods. Overall survival (OS), progression-free survival (PFS) and transplant-related mortality (TRM) were estimated by the Kaplan-Meier Method. The cut-off for statistical significance was defined as p&lt;0.05. Results: A total of 70 patients (27 in cladribine and 43 in fludarabine cohort) were included. Median age was 59 (22 to 76) and 64.3% constituted males. Median follow-up was 10.2 months (0.1 to 44.7). Acute leukemia diagnosis, intermediate to high disease risk index (DRI) and intermediate to high Charlson comorbidity index (CCI) constituted 45.7%, 60.0% and 58.1% respectively. Haploidentical donors were used in 28.6%. The distribution of gender, diagnosis, DRI and CCI scores, donor type, total CD34 dose given, panel reactive antibody (PRA) positivity were similar. Median days to neutrophil engraftment was shorter with fludarabine (19 vs 16, p=0.01), however, median duration of in-unit stay was similar (27 vs 28 days, p=0.73). TRM, nausea and acute GvHD frequency was lower with cladribine (p=0.35, p=0.001 and p=0.02, respectively). Typhilitis and perianal infections were more common with cladribine (p=0.07 and p=0.04, respectively). OS and PFS were similar (p=0.81 and p=0.66, respectively). When cladribine was compared to fludarabine on day +90, OS was 78,0% (95% CI: 62.3-93.7) vs 65,0% (95% CI: 51.3-78.7); PFS was 70.0% (95% CI: 52.4-87.6) vs 65.0% (95% CI: 51.3-78.7); TRM was 19.0% (95% CI: 3.3-34.7) vs 24.0% (95% CI: 10.3-37.7). Conclusions: Cladribine may be safely constituted for cladribine in a RIC regimen and may yield similar, even some favorable, outcomes when compared to fludarabine.

Low Disease Relapse and High Survival in Non-Myeloablative Two-Step Haploidentical Transplant, Results of a Prospective Trial

Introduction We previously developed a two-step approach that separates the lymphoid and myeloid portions of the graft, allowing a consistent T cell dosing and sparing the stem cells from the effect of cyclophosphamide. The two-step approach demonstrated safety and efficacy in patients treated with a myeloablative conditioning protocol. Here, we extended our 2-step platform to older and less fit patients and explored the effects of using a high dose of T cells on disease relapse and transplant outcomes. Methods Patients received fludarabine 30mg/m 2 IV daily for 3 days, from day -10 to day -8. Two hundred cGy total body irradiation (TBI) was given on day -7. This was increased to 400 cGy TBI in 2 doses after 13 patients had been treated. A fixed dose of 2 x 10 8/kg CD3+ T cells was given on day -6, followed 2 days later by cyclophosphamide 60mg/kg IV daily on day -3 and day -2. Tacrolimus and mycophenolic acid were started on day -1, followed by infusion of CD34-selected stem cells on day 0. Results Thirty-three patients with hematologic malignancies were treated (Table 1). Majority were haploidentical transplants (91%), and the rest were matched related donors. Median age was 68 (range, 33-76) years, with 64% patients &amp;gt;65 years old. Median follow-up was 31 months (range, 0-76 months). Median HCT-comorbidity score was 4 (range, 0-9). Forty-seven percent had high or very high-risk disease risk index. Twenty-seven percent had prior autologous transplant. Overall survival was 75% at 1 year and 50% at 3 years. The cumulative incidence (CI) of non-relapse mortality (NRM) and relapse were 22% and 31% at 3 years. However, the CI of relapse was much lower for patients treated with 400 cGy TBI versus those treated with 200 cGy TBI (6% vs 54%, p = 0.017) (Figure 1), while NRM was similar (25% vs 15%, p = 0.348). This contributed to a very high survival of 69% in patients who received the higher dose of TBI at 3 years, with median OS not reached. The median time to neutrophil and platelet recovery was 11 and 17 days, respectively. The median donor CD3+ T cell chimerism at day +28 was 100% (range, 71% to 100%). The CI of grade II acute graft-versus-host-disease (GVHD) was 23% and 27% at 100 days and 6 months, respectively. The CI of chronic GVHD was 8% at 3 years. There were no grade III or IV acute GVHD, no severe chronic GVHD and no deaths attributable to acute or chronic GVHD. There were 13 deaths in the study, of which 7 died from disease relapse, 3 died from toxicity related to treatment regimen, and 2 died from infection. Conclusions The NMA two-step approach allo-SCT showed a low disease relapse rate and high survival in patients treated with 400 cGy TBI, despite a generally older and more medically compromised patient population.

Early cessation of calcineurin inhibitors is feasible post–haploidentical blood stem cell transplant: the ANZHIT 1 study

AbstractHaploidentical hematopoietic stem cell transplant (haplo-HSCT) using posttransplant cyclophosphamide (PTCy) is appropriate for those who lack matched donors. Most studies using PTCy have been retrospective making conclusions difficult. ANZHIT-1 was a phase 2 study conducted at 6 Australian allogeneic HSCT centers. The primary end points were disease-free and overall survival at 2 years after HSCT. The reduced-intensity conditioning (RIC) included fludarabine, cyclophosphamide, and 200 cGy total body irradiation, and the myeloablative conditioning (MAC) was IV fludarabine and busulfan. PTCy, MMF and a calcineurin inhibitor (CNI) were used for graft-versus-host disease (GVHD) prophylaxis. CNIs were weaned and ceased by day +120 in eligible patients on day 60. Patients (n = 78) with hematological malignancies were included in the study, with a median follow-up of 732 days (range, 28-1728). HSCT was RIC in 46 patients and MAC in 32 patients. Disease-free survival probability at 2 years was 67.5% (95% [CI], 53.2-85.6) for MAC recipients and 68.3% (95% CI, 56.3-83.01) for RIC recipients. Transplant-related mortality (TRM) on day 100 and year 1 was 4.9% (95% CI, 1.6-15.3) and 17.9% (95% CI, 8.8-36.5), respectively, in the MAC group compared with 3.1% (95% CI, 0.8.1-12) and 11.6% (95% CI, 6-22.4), respectively, in the RIC group. The median time for elective cessation of CNI was day 142.5 days, with no excess chronic GVHD (cGVHD) or mortality. Of the evaluable patients, 71.6% discontinued immunosuppression 12 months after transplant. This prospective haplo-HSCT trial using PTCY demonstrated encouraging survival rates, indicating that early CNI withdrawal is feasible and safe.

Alternative donor BMT with posttransplant cyclophosphamide as initial therapy for acquired severe aplastic anemia

AbstractSevere aplastic anemia (SAA) is a marrow failure disorder with high morbidity and mortality. It is treated with bone marrow transplantation (BMT) for those with fully matched donors, or immunosuppressive therapy (IST) for those who lack such a donor, which is often the case for underrepresented minorities. We conducted a prospective phase 2 trial of reduced-intensity conditioning HLA-haploidentical BMT and posttransplantation cyclophosphamide (PTCy)-based graft-versus-host (GVHD) prophylaxis as initial therapy for patients with SAA. The median patient age was 25 years (range, 3-63 years), and the median follow-up time was 40.9 months (95% confidence interval [CI], 29.4-55.7). More than 35% of enrollment was from underrepresented racial/ethnic groups. The cumulative incidence of grade 2 or 4 acute GVHD on day 100 was 7% (95% CI, not applicable [NA]-17), and chronic GVHD at 2 years was 4% (95% CI, NA-11). The overall survival of 27 patients was 92% (95% CI, 83-100) at 1, 2, and 3 years. The first 7 patients received lower dose total body irradiation (200 vs 400 cGy), but these patients were more likely to have graft failure (3 of 7) compared with 0 of 20 patients in the higher dose group (P = .01; Fisher exact test). HLA-haploidentical BMT with PTCy using 400 cGy total body irradiation resulted in 100% overall survival with minimal GVHD in 20 consecutive patients. Not only does this approach avoid any adverse ramifications of IST and its low failure-free survival, but the use of haploidentical donors also expands access to BMT across all populations. This trial was registered at www.clinicaltrials.gov as NCT02833805.

Outcomes of Busulfan, Fludarabine, and 400 cGy Total Body Irradiation Compared With Busulfan and Fludarabine Reduced-Intensity Conditioning Regimens for Allogeneic Stem Cell Transplantation in Adult Patients With Hematologic Diseases: A Single-Center Experience

Reduced intensity conditioning (RIC) regimens decrease the risk for nonrelapse mortality (NRM) in adult patients undergoing allogeneic hematopoietic stem cell transplantation for hematologic malignancies but increase the risk for relapse. The aim of this study was to compare the outcomes of fludarabine-total body irradiation (TBI) with fludarabine among patients with hematologic diseases. This retrospective study of 137 patients with different hematologic malignancies compared the outcomes of 63 patients who received a conventional RIC regimen with 2 days of IV busulfan (3.2 mg/kg/d×2 days) and fludarabine with 74 patients who received the same regimen plus 400 cGy of fludarabine and busulfan (FB)-TBI divided in 2 doses over 1 day (200 cGy BID). Median follow-up was 4.62 years. The donors were either HLA-matched siblings (36%) or HLA-matched unrelated donors (64%). The FB-TBI showed trends toward improvement in progression-free survival (PFS) and overall survival (OS) over FB (5-year PFS rates 50% vs 34%, P=.06, and 5-year OS rate 53% vs 39%, P=.13). Acute graft-vs-host disease (aGVHD), relapse, and NRM were similar between the 2 groups. The 5-year cumulative incidence of chronic GVHD (cGVHD) was lower in the FB-TBI group compared with the FB group (29% vs 52%, P=.003). Multivariable analysis revealed that grade III-IV aGVHD was the only independent risk factor for worse OS (P=.001) in both groups. A high disease risk index was possibly associated with inferior OS (P=.07) in both groups. The FB-TBI is a safe and effective intensified RIC regimen for adult patients with hematologic malignancies. It predicted a lower risk for cGVHD and showed possibly improved PFS and OS compared with FB.

Allogeneic haematopoietic cell transplants as dynamical systems: influence of early-term immune milieu on long-term T-cell recovery.

Immune recovery following haematopoietic cell transplantation (HCT) functions as a dynamical system. Reducing the duration of intense immune suppression and augmenting antigen presentation has the potential to optimise T-cell reconstitution, potentially influencing long-term outcomes. Based on donor-derived T-cell recovery, 26 patients were adaptively randomised between mycophenolate mofetil (MMF) administered for 30-day post-transplant with filgrastim for cytokine support (MMF30 arm, N = 11), or MMF given for 15 days with sargramostim (MMF15 arm, N = 15). All patients underwent in vivo T-cell depletion with 5.1 mg kg-1 antithymocyte globulin (administered over 3 days, Day -9 through to Day -7) and received reduced intensity 450 cGy total body irradiation (3 fractions on Day -1 and Day 0). Patients underwent HLA-matched related and unrelated donor haematopoietic cell transplantation (HCT). Clinical outcomes were equivalent between the two groups. The MMF15 arm demonstrated superior T-cell, as well as T-cell subset recovery and a trend towards superior T-cell receptor (TCR) diversity in thefirst month with this difference persisting through the first year. T-cell repertoire recovery was more rapid and sustained, as well as more diverse in the MMF15 arm. The long-term superior immune recovery in the MMF15 arm, administered GMCSF, is consistent with a disproportionate impact of early interventions in HCT. Modifying the 'immune-milieu' following allogeneic HCT is feasible and may influence long-term T-cell recovery.

Allogeneic Blood or Marrow Transplantation with Post-Transplantation Cyclophosphamide for Peripheral T Cell Lymphoma: The Importance of Graft Source

The use of post-transplantation cyclophosphamide (PTCy) for graft-versus host-disease (GVHD) prophylaxis has revolutionized allogeneic blood or marrow transplantation (alloBMT), but there is limited published experience in peripheral T cell lymphoma (PTCL). We sought to assess outcomes in patients with PTCL who underwent alloBMT with PTCy. We reviewed the charts of all adult patients age ≥18 years who underwent alloBMT with nonmyeloablative conditioning and PTCy-based GVHD prophylaxis at the Sidney Kimmel Comprehensive Cancer Center between January 2004 and December 2020. Sixty-five patients were identified. The median age was 59 years (range, 24 to 75 years). Lymphoma histology included PTCL not otherwise specified (n=24), anaplastic lymphoma kinase-negative anaplastic large cell lymphoma (n=14), angioimmunoblastic T cell lymphoma (n=7), enteropathy-associated T cell lymphoma (n=6), hepatosplenic T cell lymphoma (n=4), and others (n=10). Eleven patients were in first complete remission (17%); the remaining patients were in first partial remission or underwent salvage therapy to at least PR prior to transplantation. Forty-eight patients underwent alloBMT from a haploidentical related donor (74%), 10 from a fully matched donor (15%), and 7 from a mismatched unrelated donor (11%). All patients received fludarabine, cyclophosphamide, and total body irradiation (TBI). The graft source was bone marrow (BM) in 46 patients (71%) and peripheral blood (PB) in 19 patients (29%); all patients in the BM cohort received 200 cGy TBI, and most patients in the PB cohort (15 of 19) received 400 cGy TBI. GVHD prophylaxis comprised PTCy, mycophenolate mofetil, and a calcineurin inhibitor or sirolimus. With a median follow-up of 2.8 years (range, 290 days to 14.2 years), the 2-year progression-free survival (PFS) for the entire cohort was 49% (95% confidence interval [CI], 38% to 64%), and the 2-year overall survival (OS) was 55% (95% CI, 44% to 69%). Outcomes were significantly improved in those receiving PB compared to those receiving BM, including a 2-year PFS of 79% (95% CI 63% to 100%) versus 39% (95% CI, 27% to 56%), 2-year OS of 84% (95% CI, 69% to 100%) versus 46% (95% CI, 33% to 63%), and 1-year cumulative incidence of relapse of 5% (95% CI, 0 to 16%) versus 33% (95% CI, 19% to 46%), with no difference in GVHD and nonrelapse mortality. AlloBMT with PTCy is safe and well-tolerated in patients with PTCL. Our data suggest that increasing the TBI dose to 400 cGy and using PB allografts may offer improved disease control and better survival outcomes, though additional studies are needed to confirm these findings.

Donor HLA mismatch promotes full donor T-cell chimerism in the allogeneic stem cell transplant with reduced-intensity conditioning and post-transplant cyclophosphamide GVHD prophylaxis.

Full donor T-cell chimerism (FDTCC) after allogeneic stem cell transplant (allo-SCT) has been associated with improved outcomes in hematologic malignancy. We studied if donor human leukocyte antigen (HLA) mismatch improves achievement of FDTCC because mismatched HLA promotes donor T-cell proliferation where recipient T-cells had been impaired by previous treatment. Patients (N = 138) received allo-SCT with reduced-intensity conditioning (RIC) from 39 HLA mismatched donors (16 unrelated; 23 haploidentical) with post-transplant cyclophosphamide (PTCy) or 99 matched donors (21 siblings; 78 unrelated) with PTCy (N = 18) or non-PTCy (N = 81). Achievement of FDTCC by day 100 was higher with HLA mismatched donors than matched donors (82.1% vs. 27.3%, p < 00,001), which was further improved with 200cGy total body irradiation (87.9%) or lymphoid (versus myeloid) malignancy (93.8%). Since all mismatched transplants used PTCy, FDTCC was higher with PTCy than non-PTCy (68.4% vs. 25.7%, p < 0.00001), but not in the matched transplant with PTCy (38.9%), negating PTCy as the primary driver. Lymphocyte recovery was delayed with PTCy than without (median on day + 30: 100 vs. 630/µL, p < 0.0001). The benefit of FDTCC was not translated into survival outcomes, especially in myeloid malignancies, possibly due to the insufficient graft-versus-tumor effects from the delayed lymphocyte recovery. Further studies are necessary to improve lymphocyte count recovery in PTCy transplants.

Radiation Sparing Reduced Intensity Conditioning for Allogeneic Cell Transplantation in Patients with Dyskeratosis Congenita Comparable to Standard of Care: A Phase III Single Institution Trial

Introduction Dyskeratosis congenita (DKC) is a rare form of inherited multiorgan disease caused by mutations affecting telomere maintenance. Complications include bone marrow failure (BMF), pulmonary and liver fibrosis, and predisposition to malignancy. Allogeneic hematopoietic cell therapy (alloHCT) can rescue affected individuals from hematologic complications. However, toxicity from alkylator and radiation exposure can be lethal or potentially expedite DKC-specific organ complications. In this single institution phase III clinical trial, we aimed to demonstrate non-inferior short-term alloHCT outcomes with a radiation sparing reduced intensity conditioning (RIC) regimen while monitoring for long-term reductions in systemic toxicity. Methods We compared two consecutive cohort of patients with DKC requiring alloHCT for BMF or myelodysplastic syndrome (MDS). Both received RIC with fludarabine 200 mg/m2, cyclophosphamide 50 mg/kg, and alemtuzumab 1 mg/kg. The earlier cohort (4/2006-8/2012) additionally received 200 cGy total body irradiation ("TBI"), while the latter (11/2015-2/2021) "Non-TBI" cohort did not. We restricted our analysis to bone marrow (BM) and peripheral blood stem cell (PBSC) recipients. AlloHCT milestones including neutrophil engraftment, graft failure, disease progression, acute and chronic graft-versus host disease (GvHD), serious infections, and overall survival were prospectively recorded. The cumulative incidence of time-dependent events was compared between cohorts using the Fine-Gray test with death as a competing risk. Infection density over the first 100 days after alloHCT was calculated using the Mantel-Haenszel chi-square test for incidence density. Estimates of overall survival were calculated by Kaplan-Meier curves. Results The TBI cohort included 12 patients aged 2.2-52.2 years (median 20.5), 11 with SAA and 1 with MDS. Stem cell sources were unrelated donor BM in 8, sibling donor PBSCs in 2, and sibling BM in 1, with a median follow-up of 1531 days (range 83-3960). The comparable Non-TBI group included 10 patients aged 1.7-65.9 years (median 9.8), 8 with SAA and 2 with MDS/RAEB. Stem cell donor sources were unrelated donor BM in 8 and sibling BM in 2, with a median follow-up of 870 days (range 303-2420). Neutrophil engraftment occurred at a median of 13 days in the TBI cohort and 8.5 days in the Non-TBI cohort (p<0.001; Fig 1a). Cumulative incidence of acute GvHD by day 100 for the TBI cohort was 0.08 (95% CI <0.01, 0.32) compared to 0.1 (95% CI <0.01, 0.37) for the Non-TBI cohort (p=0.74). Cumulative incidence of chronic GvHD by 3 years for the TBI cohort was 0.17 (95% CI 0.02, 0.43) compared to 0.1 (95% CI <0.01, 0.37) for the Non-TBI cohort (p=0.7). With regard to serious infections the first 100 days after alloHCT, there were no fungal infections in either group and infection density of viral infections, bacteremia, and pneumonia episodes was equivalent between cohorts. In the TBI cohort, one case was recorded as a late graft failure at day +1371, however upon retrospective review, this patient maintained 10% BM cellularity with 100% donor chimerism and experienced cytopenias and death likely resulting from Epstein-Barr viremia and possible post-transplant lymphoproliferative disease. In the Non-TBI cohort, one patient experienced non-neutropenic graft failure/rejection at day +28. A second Non-TBI patient demonstrated graft failure in the form of MDS recurrence at day +359. There was no statistically significant difference in overall survival between the two groups (p=0.4; Fig 1b, Table 1), with the 5.5 years median survival of the TBI cohort and the median survival not achieved for the Non-TBI cohort. Conclusions A successful alloHCT conditioning regimen for DKC must provide myeloablation to allow for sustained donor engraftment and immunosuppression to decrease GvHD risk, while limiting an unfavorable toxicity profile to which DKC patients are more susceptible. Elimination of TBI from the RIC regimen demonstrated equivalent overall survival, acute and chronic GvHD incidence, and day +100 infection density with an expedited neutrophil engraftment and no increase in graft failure risk. While there appears to be a trend toward less lethal DKC late effects like pulmonary failure and secondary malignancy, definitive assessment of such outcomes requires further longitudinal follow-up of both cohorts. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Outcomes of Patients with TP53-Mutated Myeloid Neoplasms (TP53-MN) and the Role of Allogenic Blood or Marrow Transplantation (alloBMT)

Background: TP53 mutations are present in up to 20% of patients with myeloid malignancies and are frequently associated with a complex karyotype (CK) and poor responses to therapy. Even though overall response rates have improved significantly with less intensive induction modalities such as hypomethylating (HMA) agents alone or in combination with venetoclax, most patients succumb to their disease. AlloBMT remains the only curative option and even though the outcomes after alloBMT are disappointing, some patients achieve long-term survival. In the current study, we aimed to determine the clinical outcome of patients with TP53-MN and the impact of therapies including alloHCT on outcomes. Methods: We performed a single-center retrospective review of adult patients with TP53-MN evaluated at Johns Hopkins between November 2015 and February 2020. The analysis of somatic mutations was performed using a 59-gene targeted next-generation sequencing (NGS) assay. Cytogenetic analysis was performed on bone marrow or peripheral blood using standard methods including G-banding by trypsin with Giemsa staining. Results: We identified a total of 93 patients with TP53-MN. Disease subtypes included de novo AML (n = 22), AML arising from MDS/MPN (n = 15), MDS (n = 23), therapy-related myeloid neoplasm (n = 29), MDS/MPN overlap syndrome (n = 2) and MPN (n = 2). The median (Q1, Q3) age was 67 years (59 - 73 years). Cytogenetics was available for 89/93 (95.7%) patients. Of those, 73 (82.0%) patients had complex karyotype (CK). The median maximum TP53 variant allele frequency (VAF) per patient was 42.5%. Sixty-two (66.6%) patients had TP53 null phenotype: 14 (15.1%) patients had multiple TP53 mutations, 37 (41.6%) had deletion 17p and 11 (12.0%) had copy-neutral loss-of-heterozygosity (CnLOH). Overall, 79/93 (85%) patients received therapy: 20 (25.3%) were treated with HMA alone, 30 (38.0%) with HMA+venetoclax, 10 (12.7%) with HMA+others, 15 (19.0%) with intensive chemotherapy, 2 (2.5%) with an immunomodulatory drug, 1 (1.3%) with ivosidenib and 1 (1.3%) with a JAK2 inhibitor. Of those, 29 (36.7%) patients received non-myeloablative alloBMT with post-transplant cyclophosphamide (10 (34.5%) bone marrow and 19 (65.5%) mobilized peripheral blood grafts (PBSCT)). Median overall survival (OS) in patients receiving alloBMT, any therapy, or supportive care was 18.9, 4.1, and 2.5 months respectively (p < 0.001, Figure 1). Among patients in the alloBMT group, there was a significant OS difference between TP53-MN CK vs. non-CK (median OS 13.7 months vs not reached, p = 0.01, Figure 2). Also, patients with TP53-MN CK demonstrated better OS when treated with alloBMT compared to any therapy or supportive care. However, most TP53-MN CK patients ultimately succumbed to their disease regardless of the therapeutic modality. Therapeutic modalities prior to alloBMT did not appear to affect post-alloBMT outcomes but among patients who received PBSCT, OS was significantly better in patients receiving 400cGy vs 200 cGy total body irradiation (median OS 8.9 vs. 21 months, p=0.01). Conclusions: TP53-MN appears to be a heterogeneous disease with a variable prognosis. While OS of patients with TP53 mutations and non-CK who underwent alloBMT resembled that of intermediate-risk AML, patients with TP53 null phenotype associated with CK had a worse outcome. Even though OS appears to be significantly improved with alloBMT, particularly patients receiving PBSCT+400cGy TBI, most patients eventually relapse. Novel therapeutic strategies are urgently needed to improve the outcomes of TP53 CK patients. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Alternative Bone Marrow Transplantation with Post-Transplant Cyclophosphamide (PTCy) As Initial Therapy for Acquired Severe Aplastic Anemia (SAA)

Immunosuppressive therapy (IST) is standard front-line treatment for SAA, except for patients aged <20 years with a suitable HLA-matched sibling donor (MSD) for BMT. The hematopoietic response after IST, even with the addition of eltrombopag, is ~ 70%-80% and 5-year survival is 60% to 85%. Failure-free survival (alive and in remission without clonal disease) beyond 10 years after IST is ~50%. In contrast, long-term survival after BMT is ~90% in patients aged < 20 years, and 75% in older patients. Currently, BMT with an unrelated or HLA-haploidentical (haplo) donor is reserved for failure of IST because of morbidity and mortality concerns. PTCy improves the safety and efficacy of haplo BMT by facilitating engraftment and decreasing graft-vs-host disease (GVHD), with survival comparable to MSD BMT. Here we review the outcomes of alternative donor BMT and PTCy in treatment-naïve (TN) SAA patients. Eligible patients met criteria for SAA and were TN. Fanconi anemia and telomere biology disorder patients were excluded. Non-myeloablative (NM) conditioning included rabbit antithymocyte globulin (0.5 mg/kg day-9 and 2 mg/kg on days -8,-7), fludarabine (30mg/m2/day on days -6 to -2), low dose CY (14.5 mg/kg on days -6, -5) and total body irradiation (TBI) (200cGy or 400 cGy day -1). After the marrow graft was infused on day 0, cyclophosphamide 50 mg/kg/day IV was administered on days 3 and 4 post-transplant. All received mycophenolate mofetil (MMF) from day 5-35 and tacrolimus from day 5 through 1 year. Neutrophil recovery was defined as occurring on the first of three consecutive days of an ANC >1.0 x109/L. Red cell recovery was defined as days from transplant to the last red blood cell transfusion. Platelet recovery was defined as the first day of a platelet count >50,000 without transfusion in the preceding 7 days. Thirty-two eligible patients were treated at Johns Hopkins between 9/2016 and 5/2022. Median follow-up for all patients is 40 months (range 2-78). Table 1 shows demographics. The median age was 25 years (range 3-63) with 24 patients age >20 years, and 56% were males. Median time to neutrophil recovery was 20 days (range 14-88). Median time to red cell recovery was 25 days with 90% transfusion independence by day 60. Median time to platelet recovery was 25 days with 90% transfusion independence by day 100. TBI dose was increased from 200 to 400 cGy to reduce graft failure after graft loss in 3 of the first 7 patients; 2 of these 3 died (from infection and graft failure) and one has been re-transplanted and is now 100% donor. Overall survival at 3 years post-transplant is 93%. (Figure 1) All 24 consecutive patients who received 400 cGy are alive and well with engraftment. CMV reactivated in 13 patients, and 6 required therapy. Rates of acute and chronic GVHD were both 7%, none developed grade 3-4 acute or extensive chronic GVHD, and all patients beyond day 365 are off treatment for GVHD. No secondary malignancies have been observed. NM BMT with PTCy, using mostly haplo donors, can cure SAA. Increasing TBI dose from 200 to 400 cGy improves engraftment. Rates of infection and mortality are not increased compared to standard upfront IST. Historical data show that >50% of patients in this age range require transplantation subsequent to IST. Upfront BMT, as described here, allows patients to come off immunosuppression by 6-12 months post-BMT, prevents the morbidity of prolonged IST, and may reduce healthcare costs. Most patients receiving 200 cGy TBI maintain fertility; we are monitoring fertility rates after 400cGy. This approach forms the basis for the upcoming Bone Marrow Transplant Clinical Trials Network multicenter study in TN acquired SAA. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Incidence of Radiation Pneumonitis after a Single 550 cGy Fraction of Total Body Irradiation: Single Institutional Experience

<h3>Purpose/Objective(s)</h3> Total body irradiation (TBI) is an important component of the conditioning regimen prior to allogeneic stem cell transplant. While a variety of TBI dose and fractionation schemas have been studied, the optimal regimen is unknown. The American College of Radiology (ACR) suggests that relatively low dose rates of less than 10-20cGy per minute may provide the optimal outcome and reduce the risk of interstitial pneumonitis. However, there are no reported outcomes of patients treated with dose rates higher than 20cGy per minute to the best of our knowledge. The objective of the study is to investigate the incidence of radiation pneumonitis after a single fraction of 550 cGy TBI delivered at a high dose rate (∼30cGy per minute) at a single institution, where this regimen has been used as a component of the conditioning regimen for patients with hematological malignancies undergoing hematopoietic stem cell transplantation over the past 25 years. Radiation pneumonitis (RP) is an important potential toxicity associated with TBI and its incidence has not been previously reported for this regimen. <h3>Materials/Methods</h3> A retrospective chart review was performed for 183 consecutively treated patients (61% male, 39% female, aged 24 to 71) treated with single fraction 550 cGy TBI delivered at a high dose rate at our institution from 2010-2021 for a wide range of hematological malignancies including ALL (n=55), AML (n=49), CLL (n=7), CML (n=4), various forms of lymphoma (n=49), MDS (n=8), multiple myeloma (n=7), T-PLL (n=2), and B-PLL (n=2). Patients received one of the following conditioning regimens: 550 cGy single fraction TBI with cyclophosphamide, 550 cGy single fraction TBI with cyclophosphamide and thymoglobulin, or 550 cGy single fraction TBI with cyclophosphamide and fludarabine. Patients were treated on a stretcher with opposed lateral fields. Patients were evaluated for the development of radiation pneumonitis at 12 months based on CTCAE v5.0. <h3>Results</h3> Of the 183 patients, 96 patients survived until the 12-month time point. The cause of death includes sepsis, GVHD, and multi-organ failure, among others. The incidence of grade 2 or greater RP was 9.4% (9/96 patients) at 12 months in these patients. Only 1 patient developed grade 3 RP and 1 patient developed grade 4 RP. <h3>Conclusion</h3> The institutional regimen of 550 cGy TBI delivered in a single fraction at a high dose rate is associated with a low incidence of radiation pneumonitis at 12 months; however, the analysis was limited by competing transplant-related mortality in this patient population.

P1312: FORODESINE AMPLIFIES HOST INNATE IMMUNE RESPONSE THROUGH TOLL-LIKE RECEPTOR 7 ACTIVATION WHILE PREVENTING EXPERIMENTAL GRAFT-VERSUS-HOST DISEASE

Background: Forodesine, a novel inhibitor of purine nucleoside phosphorylase (PNP), causes nucleotide pool imbalances by accumulating intracellular deoxyguanosine, thereby resulting in selective apoptosis of T-cells. Recent evidence indicates that specific types of nuclear acids including guanosine and its derivatives act as natural ligands for toll-like receptor 7 (TLR7). So far, it is unclear whether and how forodesine can modulate host innate immunity, including antigen-presenting cells (APCs) such as macrophages and dendritic cells (DCs), which express TLR7 abundantly. Aims: The aim of this study is to investigate the role of forodesine in host APC function as well as donor T-cell activation both in vivo graft-versus-host disease (GVHD) models and in vitro cell assays. Methods: NOG mice were subjected to 250 cGy total body irradiation followed by intravenous injection of human isolated T-cells. Mice were treated with forodesine (20 mg/kg) or vehicle daily after transplantation. Results: Despite the mice without treatment developing severe GVHD after transplantation, guanosine and deoxyguanosine were hardly detected in the plasma, suggesting that purine nucleosides released from damaged tissues were rapidly degraded by PNP. In fact, inhibition of PNP activity by forodesine markedly increased plasma guanosine levels, whereas deoxyguanosine was still undetectable. This was also the case in GVHD target organs, including liver and lungs. At the same level of guanosine in the liver, forodesine promoted TNF-a production from in vitro alveolar macrophage cultures. Preincubation with a TLR7 antagonist, ODN20958, attenuated the TNF-a production from macrophages stimulated by guanosine and forodesine. Nuclease treatment did not reduce macrophage TNF-a production, suggesting that single-strand RNA, a well-known TLR7 ligand, is not involved in this response. Similar results were observed in Flt3-ligand-induced plasmacytoid DCs. Not only TNF-a but also IL-12 production was induced by the combination of guanosine and forodesine, and was comparable to that in pDCs pulsed with R848, a potent agonist of TLR7/8. These observations suggest that a sustained high level of guanosine caused by forodesine treatment lead to continuous activation of TLR7 signaling, resulting in cytokine production from APCs. Meanwhile, as reported previously, forodesine inhibited the proliferation of human T-cells activated with CD3 and CD28 antibodies in the presence of deoxyguanosine. Of note, however, this combination did not impair but rather stimulated IFN-g production from activated T-cells cocultured with pDCs. This suggests that T-cell priming capacity mediated by the interaction with pDCs is conserved through TLR7 activation. Finally, we investigated the in vivo effects of forodesine on survival, body weight change, and disease severity of GVHD mice. Forodesine treatment significantly prolonged survival of the mice compared with control mice, with a median survival of 17.5 days vs 14 days, respectively (p = 0.029). The mean body weight loss percentage at day 9 was 11.5% vs 19.0% in the forodesine group and control, respectively (p = 0.003). Furthermore, the clinical GVHD scores were also lower in the forodesine group vs control (4.9 vs 0.6 points, p = 0.001). Image:Summary/Conclusion: This study demonstrates that forodesine amplifies host innate immune response through TLR7 signaling, while ameliorating T-cell GVH reaction. Further studies are needed to investigate whether forodesine can provide host protection against infections in a transplant setting.

Non-myeloablative allogeneic blood or marrow transplantation (AlloBMT) with post-transplant cyclophosphamide (PTCy) for peripheral T-cell lymphoma (PTCL): Improved outcomes with peripheral blood (PB) allografts and increased total body irradiation (TBI) to 400 cGV.

7047 Background: The use of PTCy for graft-versus host-disease (GVHD) prophylaxis has revolutionized alloBMT, but there is limited published experience in PTCL. Methods: All patients with PTCL who received a non-myeloablative alloBMT using PTCy-based GVHD prophylaxis between January 2004 and December 2020 at Johns Hopkins Hospital were analyzed. Standard population statistics were used. Results: Sixty-five patients were identified. The median age was 59 years (range, 24-75 years). Lymphoma histology included PTCL-not otherwise specified (n=24), ALK-negative anaplastic large cell lymphoma (n=14), angioimmunoblastic T-cell lymphoma (n=7), enteropathy-associated T-cell lymphoma (n=6), hepatosplenic T-cell lymphoma (n=4), and other (n=10). Eleven patients were in first complete remission (CR1, 17%). The remaining patients were in first partial remission (PR1) or underwent salvage therapy to at least PR prior to transplant. Forty-eight patients received an alloBMT from a haploidentical related donor (74%), 10 from a fully matched donor (15%), and 7 from a mismatched unrelated donor (mMUD, 11%). All patients received non-myeloablative conditioning with fludarabine, cyclophosphamide, and TBI. The graft source was bone marrow (BM) in the first 46 patients (71%). Because of relatively high relapse rates, in 2018 we began using PB and increased TBI from 200 to 400 cGy; the remaining 19 patients (29%) received this regimen. GVHD prophylaxis was PTCy, mycophenolate mofetil, and a calcineurin inhibitor or sirolimus. With a median follow up of 2.8 years, the 3-year progression-free survival (PFS) for the entire cohort was 39% (95% confidence interval [CI] 28-54%), and the 3-year overall survival (OS) was 43% (95% CI 31-58%). The cumulative incidence (CuI) of relapse and non-relapse mortality (NRM) at 1 year was 25% (95% CI 14-35%) and 12% (95% CI 4-20%), respectively. Among 29 cases of GVHD (45%), 2 were grade 3-4 acute GVHD (3%) and 3 were severe chronic GVHD (5%). Univariate analysis including age, histology, mMUD, PB/400cGy, and CR1 revealed only PB/400 cGy TBI as a significant predictor of survival, relapse, or NRM. Outcomes by source. Conclusions: AlloBMT with non-myeloablative conditioning and PTCy is safe and well-tolerated in patients with PTCL. Our preliminary data suggest increasing TBI dose to 400 cGy and using PB allografts may offer improved disease control and better survival outcomes, though additional studies are needed to confirm these findings. [Table: see text]

Cumulative incidence of subsequent malignancy after allo-HCT conditioned with or without low-dose total body irradiation

AbstractSubsequent malignancies (SMs) present a significant burden of morbidity and are a common cause of late mortality in survivors of allogeneic hematopoietic cell transplant (allo-HCT). Previous studies have described total body irradiation (TBI) as a risk factor for the development of SMs in allo-HCT survivors. However, most studies of the association between TBI and SM have examined high-dose TBI regimens (typically ≥600 cGy), and thus little is known about the association between low-dose TBI regimens and risk of SMs. Our goal, therefore, was to compare the cumulative incidence of SMs in patients of Alberta, Canada, who received busulfan/fludarabine alone vs busulfan/fludarabine plus 400 cGy TBI. Of the 674 included patients, 49 developed a total of 56 malignancies at a median of 5.9 years' posttransplant. The cumulative incidence of SMs at 15 years' post-HCT in the entire cohort was 11.5% (95% confidence interval [CI], 8.5-15.6): 13.4% (95% CI, 9.1-19.3) in the no-TBI group and 10.8% (95% CI, 6.6-17.4) in the TBI group. In the multivariable model, TBI was not associated with SMs, whereas there was an association with number of pre-HCT cycles of chemotherapy. The standardized incidence ratio for the entire cohort, compared with the age-, sex-, and calendar year–matched general population, was 1.75. allo-HCT conditioning that includes low-dose TBI does not seem to increase risk of SMs compared with chemotherapy-alone conditioning.

Allogeneic Blood or Marrow Transplantation with Nonmyeloablative Conditioning and High-Dose Cyclophosphamide-Based Graft-versus-Host Disease Prophylaxis for Secondary Central Nervous System Lymphoma

Secondary central nervous system (CNS) lymphoma is a rare and often fatal complication of non-Hodgkin lymphoma (NHL). Treatment options include radiation therapy, high-dose systemic chemotherapy, intrathecal chemotherapy, and high-dose chemotherapy with autologous stem cell rescue, but outcomes remain poor. Allogeneic blood or marrow transplantation (alloBMT) is widely used in patients with relapsed/refractory systemic NHL. We sought to understand whether a graft-versus-lymphoma effect could maintain remission in CNS disease. We reviewed outcomes in 20 consecutive patients with secondary CNS lymphoma who underwent alloBMT with nonmyeloablative conditioning using fludarabine, cyclophosphamide, and 200 cGy total body irradiation. For graft-versus-host disease prophylaxis, all patients received post-transplantation cyclophosphamide, mycophenolate mofetil, and a calcineurin inhibitor. With a median follow up of 4.1 years, the median overall survival for the entire cohort was not reached. Median progression-free survival was 3.8 years (95% confidence interval [CI], 5.3 months to not reached). The cumulative incidence of relapse was 25% (95% CI, 5% to 45%), and nonrelapse mortality was 30% (95% CI, 5% to 54%) at 4 years. Of the 5 patients who relapsed, 2 were CNS only, 1 was systemic only, and 2 were combined CNS/systemic. The use of alloBMT in CNS lymphoma merits further investigation.

Engraftment of Double Cord Blood Transplantation after Nonmyeloablative Conditioning with Escalated Total Body Irradiation Dosing to Facilitate Engraftment in Immunocompetent Patients

To improve accrual to a randomized clinical trial of double unrelated cord blood (dUCB) versus HLA-haploidentical bone marrow (haplo-BM) transplantation, patients with less previous therapy and potentially greater immunocompetence were enrolled. To reduce the risk of graft rejection, patients randomized to receive dUCB received a higher dose of total body irradiation (TBI) (300 cGy versus 200 cGy). In this study, we investigated whether the inclusion of recipients of 300 cGy TBI influenced the trial outcomes. This was a secondary analysis of dUCB recipients, 161 who received TBI 200 cGy and 18 who received TBI 300 cGy. Fine and Gray regression was used to evaluate the effect of TBI dose on relapse and nonrelapse mortality (NRM). Cox regression was used for evaluation of neutrophil engraftment and overall survival. Patient characteristics were similar in the 2 TBI dose subgroups. The probability of neutrophil engraftment was 100% for patients who received TBI 300 cGy versus 91% (95% confidence interval, 86% to 95%) for those who received TBI 200 cGy (P=.64), which was similar after regression analysis adjusting for age, total infused nucleated cell dose, HLA matching to the patient, and comorbidity score. We also investigated whether the lower survival probability and higher cumulative incidence of NRM observed in the dUCB arm of BMT CTN 1101 could be influenced by the TBI 300 cGy patient subset. There was no significant difference in the 1-year incidences of NRM and relapse or in 1-year survival, even after adjustment in multivariate analysis. Patients in BMT CTN 1101 who received TBI 300 cGy and 200 cGy had similar engraftment and early mortality. We conclude that inclusion of a modified regimen for dUCB transplantation had no demonstrable influence on this large randomized trial.

Inducible SBDS Deficiency and Germline FANCC/FANCG Deficiency Differentially Impact the Capacity of Bone Marrow Niches to Engraft Hematopoietic Stem Cells after Transplantation

Strategies to optimize interactions between the recipient bone marrow (BM) microenvironment and donor hematopoietic stem cells (HSC) could improve hematopoietic stem cell transplantation (HSCT) outcomes by reducing graft failure rates, improving blood and immune reconstitution efficiency, and reducing intensive cytotoxic conditioning requirements. Such methods are particularly relevant for patients with inherited bone marrow failure syndromes (iBMFs), rare genetic disorders for which HSCT is required to cure bone marrow failure (BMF), but for which HSCT is also associated with a high incidence of delayed donor engraftment, graft failure and morbidity due to chemotherapy and radiation sensitivity.In previous studies of the MPL-/- model of congenital amegakaryocytic thrombocytopenia, we discovered that decreased numbers of megakaryocytes and/or long-term (LT)-HSC caused by absent thrombopoietin/MPL signaling resulted in diminished capacity of the MPL-/- BM niche microenvironment to efficiently engraft wildtype (WT) donor HSC after HSCT. This observation led us to hypothesize that pre-existing BMF, regardless of cause, may generally alter HSC niche elements critical for engraftment after HSCT. We now present data testing this hypothesis in mouse models of Fanconi Anemia (FA) and Shwachman-Diamond Syndrome (SDS).To model FA, we used double mutant FANCC-/-;FANCG-/- mice, which have previously been demonstrated to develop manifestations of BMF. In our facility, FANCC-/-;FANCG-/- mice did not develop evidence of BMF, as measured by blood counts, BM cellularity, and HSC quantitation out to 1 year of age even with induction of HSC cycling by polyinosinic-polycytidilic acid (pIpC). Using SCT assays in which GFP+ WT donor BM was transplanted into FA recipients (FANCC-/-, FANCG-/-, FANCC-/-;FANCG-/-) or WT controls after 800-1100 cGy total body irradiation (TBI), efficiency and durability of donor engraftment was assessed at 3 weeks and 5 months, respectively, after primary SCT by competitive secondary HSCT. Unexpectedly, all FA recipients demonstrated more rapid BM reconstitution and enhanced early hematopoietic progenitor engraftment of WT donor BM compared with WT controls. However, there was no significant difference in LT-HSC engraftment efficiency or durability in the FA recipient groups versus WT controls.To model SDS, we first attempted to generate a model of osteoblast-specific SBDS deletion by crossing Col1A1Cre mice with mice carrying floxed SBDS alleles (SBDSfl/fl). However, this Col1A1CreSBDSExc model proved to be embryonic lethal at E12-E15 due to profound developmental abnormalities. We thus generated an inducible model by crossing SBDSfl/fl mice with Mx1Cre+ mice, and inducing SBDS deletion in Mx1-inducible BM hematopoietic and osteolineage niche cells by pIpC administration. SBDS deletion induced by pIpC was confirmed with PCR methods.Within 4 weeks of pIpC induction, Mx1CreSBDSExc mice show evidence of BMF, including a 40% reduction in platelet counts, inverted myeloid/lymphoid cell ratio in blood, and up to 80% reduction in immunophenotypic BM LT-HSC. When we attempted HSCT with GFP+ WT donor BM in Mx1CreSBDSExc and littermate control recipients following 1100 cGy TBI, 90% of Mx1CreSBDSExc recipients died by day 9 after HSCT, whereas all littermate controls survived. BM sections from Mx1CreSBDSExc recipients demonstrated persistent aplasia out to 1 week post-HSCT, suggesting that Mx1CreSBDSExc died from primary graft failure. Competitive secondary HSCT performed from BM harvested 1 week after primary HSCT demonstrated severe deficits in GFP+ WT donor HSC engraftment in Mx1CreSBDSExc recipients. Our initial studies as to why donor engraftment fails in Mx1CreSBDSExc recipients have identified that compared to WT, Mx1CreSBDSExc mice show significantly reduced expansion of osteolineage niche cells after TBI, a response that we have previously shown to be critical for efficient donor engraftment after HSCT.Taken together, our data demonstrate that pre-existing BMF and SBDS deficiency in BM osteolineage cells, but not FANCC or FANCG deficiency without co-existent BMF, significantly reduce the capacity of the BM niche to engraft donor HSC. Future studies defining specific niche deficits in our inducible SBDS deficiency model will provide critical insights into cellular and molecular pathways required for efficient engraftment after HSCT. DisclosuresNo relevant conflicts of interest to declare.

Allogeneic Hematopoietic Stem-Cell Transplantation for GATA2 Deficiency Using a Busulfan-Based Regimen

Background: GATA2 deficiency is an increasingly recognized bone marrow failure syndrome responsible for: MonoMAC, monocytopenia with atypical mycobacterial infection (MAC); DCML, dendritic cell, monocyte and lymphoid cell deficiency; Emberger syndrome with lymphedema and monosomy 7; and familial myelodysplastic syndrome (MDS)/acute myelogenous leukemia (AML). GATA2 deficiency can be reversed by hematopoietic stem cell transplantation (HSCT). However, the intensity of conditioning required to ensure engraftment and reverse the myelodysplastic syndrome (MDS) characteristic of the disease remains controversial.Methods: We carried out a prospective study of allogeneic HSCT in 22 patients (mean age 26 years; range 17 to 45 years) with GATA2 deficiency, or the MonoMac syndrome, using a myeloablative, busulfan-based conditioning regimen. All 22 patients had MDS and two had AML. Eleven patients had clonal cytogenetic changes in the bone marrow. There were two matched related donor (MRD) recipients, 13 matched unrelated donor (URD) recipients, and 7 haploidentical related donor recipients. MRD and URD recipients received conditioning with 4 days of busulfan (days -6 to -3) to target an AUC between 3600 and 4800 min*microm/L and 4 days of fludarabine 40 mg/m2/day (days -6 to -3). Haploidentical related donor recipients received low-dose cyclophosphamide for two days (days -6 and -5), fludarabine 30 mg/m2/day for 5 days (days -6 to -2), 2-3 days of busulfan depending upon cytogenetics, along with 200 cGY total body irradiation (TBI) on day -1. MRD and URD recipients received tacrolimus and short course methotrexate for post-transplant graft-versus-host disease (GVHD) prophylaxis, whereas haploidentical recipients received high-dose post-transplant cyclophosphamide (PT/CY) followed by tacrolimus and mycophenolate mofetil for GVHD prophylaxis.Results: Nineteen of the 22 patients are alive with resolution of the clinical phenotype and correction of the bone marrow MDS with eradication of the cytogenetic changes at a median follow-up of 23 months (range, 6 to 48 months) giving an overall disease-free survival of 86 percent. The three deaths all occurred in the URD group. Of the three deaths, one resulted from refractory acute myelogenous leukemia (AML), and two from complications related to treatment for GVHD. There was a 26 percent incidence of grade III-IV acute GVHD (aGVHD) in the MRD and URD groups, and no grade III-IV aGVHD in the haploidentical related donor cohort. Similarly, there was a 46 percent incidence of chronic GVHD (cGVHD) in the MRD and URD cohort, whereas two of the 7 (28 percent) of the haploidentical related donor recipients had cGVHD.Conclusions: Despite overall disease-free survival of 86 percent with eradication of the clonal cytogenetic abnormalities in the bone marrow, GVHD remains a limitation in the MRD and URD cohorts treated with standard post-transplant tacrolimus/methotrexate prophylaxis for GVHD. We are currently de-escalating the busulfan dosing based on the AUC in all cohorts and incorporating PT/CY in the MRD and URD cohorts to decrease toxicity and reduce the incidence of aGVHD and cGVHD. Together with our previous studies using a nonmyeloablative regimen, it appears that when GATA2 deficiency patients are transplanted when they have a hypocellular bone marrow with MDS and without cytogenetic changes, a nonmyeloablative regimen results in reliable engraftment in GATA2 deficiency since the GATA2 deficient marrow has a proliferative disadvantage. However, with clonal progression and unfavorable cytogenetic changes and/or a hypercellular marrow, where the malignant clone has a proliferative advantage, a higher dose regimen results in more reliable engraftment and eradication of the clone. Studies to identify the precise level of conditioning for the stages of the disease are ongoing. DisclosuresNo relevant conflicts of interest to declare.