HLA-haploidentical Donors Research Articles

Comparison of HLA-haploidentical donors with post-transplant cyclophosphamide versus HLA-matched unrelated donors in peripheral blood stem cell transplantation for acute myeloid leukaemia.

HLA-haploidentical haematopoietic cell transplantation with post-transplant cyclophosphamide (PTCy-haplo) is emerging as an effective alternative due to donor availability and safety. We conducted a nationwide retrospective study comparing the outcomes of PTCy-haplo with both anti-thymocyte globulin (ATG)-free and ATG-administered matched unrelated donors (MUD) transplantation, using peripheral blood stem cells as the first transplantation for acute myeloid leukaemia (AML). Our study showed a lower and slower haematopoietic recovery and a higher incidence of infection-related deaths after PTCy-haplo than after MUD transplantation. In addition, we revealed an increased risk of acute and chronic graft-versus-host disease (GVHD) in ATG-free MUD transplantation in comparison to PTCy-haplo. For grades III-IV acute GVHD, the hazard ratio (HR) was 2.71 (95% CI, 1.46-5.01), and for extensive chronic GVHD, the HR was 3.11 (95% CI, 2.07-4.68). There was no significant difference regarding overall survival amongst the groups. In addition, GVHD-free relapse-free survival (GRFS) was lower in ATG-free MUD transplantation than in PTCy-haplo (HR, 1.46; 95% CI, 1.17-1.82). Notably, ATG-administered MUD transplantation showed no significant difference in GRFS from PTCy-haplo, negating the advantage of PTCy. Our results suggest that PTCy-haplo could be viable for AML patients without an HLA-matched related donor.

Mucosal-associated invariant T cells are functionally impaired in pediatric and young adult patients following allogeneic hematopoietic stem cell transplantation and their recovery correlates with clinical outcomes.

Mucosal-associated invariant T (MAIT) cells are innate-like T cells implicated in the response to fungal and bacterial infections. Their contribution to restoring T-cell immunity and influencing hematopoietic stem cell transplant (HSCT) outcomes remains poorly understood. We retrospectively studied MAIT-cell recovery in 145 consecutive children and young adults with hematologic malignancies undergoing allogeneic (allo)-HSCT between April 2019 and May 2022, from unrelated matched donor (MUD, N=52), with standard graft-versus-host-disease (GvHD) prophylaxis, or HLA-haploidentical (Haplo, N=93) donor after in vitro αβT/CD19-cell depletion, without post-HSCT pharmacological prophylaxis. With a median follow-up of 33 months (range, 12-49 months), overall survival (OS), disease-free survival (DFS), and non-relapse mortality (NRM) were 79.5%, 72%, and 7%, respectively; GvHD-free relapse-free survival (GRFS) was 63%, while cumulative incidence of relapse was 23%. While αβT cells were reconstituted 1-2 years post HSCT, MAIT cells showed delayed recovery and prolonged functional impairment, characterized by expression of activation (CD25, CD38), exhaustion (PD1, TIM3) and senescence (CD57) markers, and suboptimal ex vivo response. OS, DFS, and NRM were not affected by MAIT cells. Interestingly, higher MAIT cells at day +30 correlated with higher incidence of grade II-IV acute GvHD (19% vs. 7%, P=0.06). Furthermore, a greater MAIT-cell count tended to be associated with a higher incidence of chronic GvHD (cGvHD) (17% vs. 6%, P=0.07) resulting in lower GRFS (55% vs. 73%, P=0.05). Higher MAIT cells also correlated with greater cytomegalovirus (CMV) reactivation and lower late blood stream infections (BSI) (44% vs. 24%, P=0.02 and 9% vs. 18%, P=0.08, respectively). Future studies are needed to confirm the impact of early MAIT-cell recovery on cGvHD, CMV reactivation, and late BSI.

Peripheral blood stem cell transplantation using HLA-haploidentical donor with post-transplant cyclophosphamide versus HLA-matched sibling donor for lymphoma.

Data comparing HLA-haploidentical donors and HLA-matched sibling donors (MSDs) in peripheral blood stem cell transplantation (PBSCT) for lymphoma are scarce. We retrospectively analyzed 465 patients with lymphoma aged 16 years or older who underwent PBSCT using haploidentical donors with post-transplant cyclophosphamide (PTCy-haplo) (n = 166) or MSDs with calcineurin inhibitor-based graft-versus-host disease (GVHD) prophylaxis (n = 299). Two-year overall survival (OS), progression-free survival (PFS), and GVHD-free, relapse-free survival (GRFS) in the PTCy-haplo and MSD groups were 49.2% versus 51.9% (P = 0.64), 38.0% versus 39.9% (P = 0.97), and 27.7% versus 18.5% (P = 0.006), respectively. In multivariable analyses, PTCy-haplo recipients had slower neutrophil recovery (hazard ratio [HR], 0.62; P < 0.001) and platelet recovery (HR, 0.54; P < 0.001), lower risk of chronic GVHD (HR, 0.64; P = 0.038) and extensive chronic GVHD (HR, 0.45; P = 0.008), and better GRFS (HR, 0.66; P = 0.003) than MSD transplant recipients. OS, PFS, relapse or progression, and non-relapse mortality were similar between the groups. The difference might be mainly due to PTCy use rather than donor type; however, the results suggested that PTCy-haplo could be a possible option as an alternative to conventional MSD transplantation for lymphoma in PBSCT.

Sequential haplo-identical conditioning transplant regimen for pediatric patients with relapsed or refractory hemophagocytic lymphohistiocytosis.

Allogeneic hematopoietic stem cell transplantation (HSCT) currently stands as the sole remedy for individuals afflicted with hemophagocytic lymphohistiocytosis (HLH). In this study, we retrospectively evaluated how pediatric patients with relapsed or refractory (R/R) HLH responded to our institution's cocktail conditioning regimen. The disease was diagnosed according to criteria applicable to patients with familial/genetic, relapsing, or severe/persistent HLH. All donors were HLA haplo-identical family donors. In our cohort, sixty-five patients (P-HLH), including 28 with familial/genetic HLH, 36 with secondary HLH, and 1 with an unknown cause, underwent haplo-identical family donor HSCT. The conditioning regimen consisted of intravenous administration of etoposide (VP-16), busulfan, fludarabine, rabbit anti-human thymocyte globulin (r-ATG), and cyclophosphamide (Cy). Tacrolimus and mycophenolate mofetil were used for graft-versus-host disease (GvHD) prevention. We observed that the median time for neutrophil recovery was 11 days (range, 8-24), and for platelet counts to exceed 20 × 109/L, it was 14 days (range, 7-130). There were 5 patients (7.7%) who experienced grades III to IV acute GvHD, and 6 patients (9.2%) developed extensive chronic GvHD. The estimated 3- and 5-year overall survival rates were 78.1% (95% CI, 65.8-84.6%) and 74.9% (95% CI, 61.2-84.4%), respectively. The estimated 3- and 5-year event-free survival rates were 73.5% (95% CI, 60.8-82.6%) and 70.3% (95% CI, 56.4-80.5%), respectively. Our findings demonstrate that our innovative conditioning regimen is both effective and safe, offering valuable insights for healthcare professionals evaluating the merits of existing therapies.

HLA haploidentical stem cell transplantation from HLA homozygous donors to HLA heterozygous donors may have lower survival rates than haploidentical transplantation from HLA heterozygous donors to HLA heterozygous donors: a retrospective nationwide analysis.

In HLA haploidentical stem cell transplantation, patients and donors usually share one HLA haplotype and have one different HLA haplotype (hetero-to-hetero). However, there are rare cases of transplantation from HLA homozygous donors to heterozygous recipients (homo-to-hetero), resulting in mismatches only in the graft-versus-host direction. We previously reported that homo-to-hetero transplants have a lower survival rate in a mouse model than hetero-to-hetero transplants due to stronger graft-versus-host disease (GVHD) but inferior graft-versus-leukemia effect. To examine whether homo-to-hetero transplant effects also occur in humans, we retrospectively compared the results of 59 homo-to-hetero and 4,539 hetero-to-hetero cases in the Japanese transplant registry data. The results showed no statistical difference between the homo-to-hetero and hetero-to-hetero groups in the cumulative incidences of neutrophil engraftment (83.1% vs 89.0%), acute GVHD II-IV (36.8% vs 38.8%), III-IV (16.8% vs 17.4%), chronic GVHD (32.7% vs 30.7%), relapse (52.9% vs 49.0%), and non-relapse mortality (31.6% vs 28.2%). In contrast, overall survival was significantly lower in the homo-to-hetero group than in the hetero-to-hetero group (12.6% vs 26.2%, p = 0.0308). The inferior effect of homo-to-hetero transplantation on overall survival remained significant in multivariate analyses.

Pyogenic spondylitis after Corynebacterium striatum blood stream infection following allogeneic hematopoietic stem cell transplantation for malignant lymphoma

Patient 1 was a 70-year-old woman with refractory diffuse large B-cell lymphoma who received allogeneic peripheral blood stem cell transplantation from an HLA-haploidentical related donor. Upper back pain appeared on day63, and Th8-Th9 pyogenic spondylitis was diagnosed based on magnetic resonance imaging (MRI). Blood culture on day14 identified Corynebacterium striatum as the causative bacteria of blood stream infection (BSI). The pyogenic spondylitis resolved after treatment with daptomycin for 2 months. Patient 2 was a 65-year-old man with relapsed angioimmunoblastic T-cell lymphoma who received bone marrow transplantation from an HLA-DR single-antigen-mismatched unrelated donor. Lower back pain appeared on day30, and L4-L5 pyogenic spondylitis was diagnosed based on MRI. Blood culture was negative. Daptomycin and clindamycin were selected for treatment based on the drug susceptibility of bacteria that had caused pre-engraftment BSI (Escherichia coli on day3 and Corynebacterium striatum on day9), and the pyogenic spondylitis resolved after 6 months of this treatment. Pyogenic spondylitis should be considered in the differential diagnosis of back pain accompanied by BSI before engraftment in allogeneic hematopoietic stem cell transplant recipients.

Mismatched Unrelated Donor Transplantation with Ptcy-Based Gvhd Prophylaxis Is Associated with Better Survival Than Double Unit Umbilical Cord Blood Transplantation in Patients with AML in First CR: A Study from the ALWP of the EBMT

Background: The best donor option for acute myeloid leukemia (AML) patients lacking an HLA-matched donor has remained unknown. The recently reported BNT CTN 1101 trial observed higher non-relapse mortality (NRM) and lower overall survival (OS) in patients randomized to double-unit unrelated umbilical cord blood transplantation (dCBT) in comparison to those randomized to HLA-haploidentical bone marrow transplantation with post-transplant cyclophosphamide (PTCy)-based graft-versus-host disease (GVHD) prophylaxis 1. In addition, recent registry studies observed at least as good transplantation outcomes in AML patients given grafts from 9/10 HLA-matched unrelated donor (UD 9/10) with PTCy-based GVHD prophylaxis as those given grafts from HLA-haploidentical donors 2,3. These observations prompted us to perform a retrospective registry study comparing hematopoietic cell transplantation (HCT) outcomes between UD 9/10 and dCBT. Methods: Inclusion criteria consisted of adult patient, AML in CR1 at transplantation, either peripheral blood stem cells (PBSC) from UD 9/10 with PTCy as GVHD prophylaxis or dCBT, transplantation between 2013 and 2021, and no in vivo T-cell depletion. Results: A total of 208 dCBT patients and 270 UD 9/10 allo-HCT were included. The 180-day cumulative incidence of grade II-IV acute GVHD was 29% in UD 9/10 versus 44% in dCBT recipients (P=0.001). The 2-year cumulative incidences of relapse and of NRM were 23.5% and 12.5%, respectively, in UD 9/10 recipients versus 27% (P=0.39) and 18% (P=0.07), respectively in dCBT recipients. Two-year OS and LFS were 70% and 64%, respectively, in UD 9/10 recipients versus 60% (P=0.016) and 55% (P=0.028), respectively in dCBT recipients. In multivariate analyses, in comparison with UD 9/10 recipients, dCBT patients had a higher non-relapse mortality (HR=2.35, 95% CI: 1.23-4.48; P=0.01), comparable relapse incidence (HR=1.12, 95% CI: 0.67-1.86; P=0.66), lower leukemia-free survival (HR=1.5, 95% CI: 1.01-2.23; P=0.047), and lower overall survival (HR=1.66, 95% CI: 1.08-2.55; P=0.02). Conclusions: In summary, our results suggest that transplantation outcomes are better with UD 9/10 with PTCy-based GVHD prophylaxis than with dCBT for AML patients in CR1. These data might support the use of UD 9/10 with PTCy-based GVHD prophylaxis in AML patients lacking an HLA-matched donor. References Fuchs, E. J. et al. Double unrelated umbilical cord blood vs HLA-haploidentical bone marrow transplantation: the BMT CTN 1101 trial. Blood 137, 420-428 (2021).Baron, F. et al. Comparison of HLA-mismatched unrelated donor transplantation with post-transplant cyclophosphamide versus HLA-haploidentical transplantation in patients with active acute myeloid leukemia. Bone Marrow Transplant. 57, 1657-1663 (2022).Battipaglia, G. et al. Post-transplant cyclophosphamide in one-antigen mismatched unrelated donor transplantation versus haploidentical transplantation in acute myeloid leukemia: a study from the Acute Leukemia Working Party of the EBMT. Bone Marrow Transplant. 57, 562-571 (2022).

T-Cell Depletion with Both Reduced Dose Anti-Thymocyte Globulin and Reduced Dose Post-Transplant Cyclophosphamide in Haploidentical Peripheral Blood Stem Cell Transplantation for Acute Leukemia and Myelodysplatic Syndrome

Graft-versus-host disease (GVHD) prophylaxis in allogeneic hematopoietic stem cell transplantation from HLA haplo-identical familial donor (haplo-HSCT) is based on in vivo T-cell depletion with either anti-thymocyte globulin (ATG) or post-transplant cyclophosphamide (PTCy). ATG has made significant contributions to enabling haplo-HSCT. However, the benefit of ATG may be often mitigated by higher risk of viral reactivation, including cytomegalovirus (CMV) and Epstein-Barr virus (EBV) due to a slower immune reconstitution. PTCy revolutionized HLA-mismatched HSCT and rapidly became the standard-of-care. However, it also has problems due to a cytokine release syndrome (CRS) -like symptoms and excessive cytotoxicity leading to the risk of acute cardiotoxicity and the possibility of alleviated graft-versus-leukemia effect. Considering a demand for more optimal in vivo T-cell depletion, we tried to combine both ‘lower-dose’ ATG and ‘lower-dose’ PTCy before and after stem cell infusion, respectively, hoping they can mitigate their individual limitations while maintaining the effectiveness of in vivo T-cell depletion. We retrospectively included 60 adults with acute leukemia or myelodysplastic syndrome who underwent haplo-HSCT following busulfan (3.2 mg/kg/day for 4 days as myeloablative and for 2 days as reduced intensity conditioning) and fludarabine (a total of 160 mg/m 2) between January 2019 and June 2023. Among them, 32 received a novel combination of ATG (a total of 3.0, 3.5, or 4.0 mg/kg depending on the absolute lymphocyte count level on days -3) and PTCy (50mg/kg on day +3 and 30mg/kg on day +4) compared to 28 patients who received ATG only (2.5 mg/kg/day from days -3 to -1, a total of 7.5 mg/kg) as in vivo T-cell depletion. Most patients received cyclosporine and mycophenolate mofetil as GVHD prophylaxis. The median follow-up duration for all patients was 8 months (median 9 months in the ATG/PTCy group and 7.5 months in the ATG group, respectively; P = 0.744). Baseline characteristics including age, sex, disease status, modified EBMT score, and the intensity of conditioning, were well-balanced except slightly higher infused CD34+ cells in the ATG/PTCy group (median 5.2 vs. 4.7 x 10 6/kg, P = 0.042). The cumulative incidence of acute GVHD at day +100 and moderate to severe chronic GVHD at 1 year were significantly lower in the ATG/PTCy group compared to the ATG group, respectively [grades II-IV acute GVHD: 20.4% (95% confidence interval [CI], 4.3-33.8%) vs. 48.4% (95% CI, 25.2-64.4%), P = 0.014; grades III-IV acute GVHD: 7.5% (95% CI, 0-17.1%) vs 31.1% (95% CI, 10.5-46.9%), P = 0.019; and moderate to severe chronic GVHD: 9.5% (95% CI, 0-21.2%) vs. 60% (95% CI, 23.3-79.1%), P = 0.007]. The ATG/PTCy group had a tendency of less incidence and severity of the haplo-fever. Multivariate analysis showed a significantly higher GRFS (hazard ratio 0.35, P = 0.002) and OS (hazard ratio 0.4, P = 0.014) for an ATG/PTCy group. The use of dual T-cell depletion with the reduced dose ATG in combination with the reduced dose PTCy showed a significantly superior early transplant outcome over with ATG of 7.5 mg/kg in terms of both GVHD and survival outcomes.

Reconstitution Dynamics and Impact on Clinical Outcomes of Mucosal-Associated Invariant T-Cells in Pediatric Patients Receiving Allogeneic Hematopoietic Stem Cell Transplantation

Background Understanding the reconstitution of all immune system components after allogeneic hematopoietic stem cell transplantation (HSCT) is crucial to optimize the prevention of infections, leukemia relapse and graft-versus-host disease (GvHD), thus improving patient's outcome. Mucosal-associated invariant T (MAIT) cells have received major interest in the field for their ability to respond to fungal and bacterial infections and control mucosal homeostasis in the GvHD context. However, the impact of MAIT cell recovery on T-cell immunity and on patient outcomes after HSCT remains not fully characterized. Patients and study design We retrospectively analyzed 156 consecutive patients (median age 8.5 years, range 0.6-24.7) affected by malignant hemopathies undergoing HSCT between April 2019 to May 2022, fully engrafted at day+30 after receiving the graft from an unrelated matched (MUD) or mismatched (mMUD) donor (n=52 and n=11, respectively) or from an HLA-haploidentical (Haplo) donor (n= 93) after alpha-beta T-/CD19-cell depletion. Conditioning regimen was myeloablative, TBI- (n=120) or chemo-based (n=36) in all patients. GvHD prophylaxis included short course methotrexate, anti-thymocyte globulin, cyclosporin with or without abatacept 10mg/kg at day -1,+5,+14,+28,+42,+60 for patients transplanted from mMUD or MUD, respectively. Haplo-HSCT patients did not receive any post-HSCT pharmacological prophylaxis. Patient characteristics are listed in Table 1. We investigated T and, in particular, MAIT cell recovery up to 2 years after HSCT and their correlation with clinical outcomes. Results With a median follow-up of 27 months (range 2-49), the overall survival (OS), disease-free survival (DFS) and non-relapse mortality (NRM) of the entire cohort were 78,5% (95%CI 70-84), 70% (95%CI 62-77) and 6% (95%CI 3-11), respectively. The cumulative incidence (CI) of relapse was 23% (95%CI 17-31). CI of grade II-IV acute GvHD (aGvHD) was 19.7% (95%CI 14-27), while CI of chronic GvHD (cGvHD) was 15% (95%CI 10-22) with a CI of moderate-severe cGvHD of 10% (95% CI 6-16), resulting in a cGvHD-free, relapse-free survival (GRFS) of 63% (95%CI 54-69). CI of post-HSCT CMV reactivation was 35% (95%CI 28-43); 13 and 22 patients experienced pre-engraftment or late blood stream infections (BSI) (CI 8%, 95%CI 5-13 and 14%, 95%CI 9-20, respectively). While total abT cells reached normal levels between 1 and 2 years post-transplantation, MAIT cells showed prolonged impaired reconstitution up to 2 years post-HSCT. Compared to UD-HSCT, MAIT cell recovery after Haplo-HSCT was significantly delayed. Interestingly, across all time points analyzed, we observed that a large fraction of MAIT cells were negative for CD161, a marker canonically expressed on MAIT cells. We also found that MAIT cells showed prolonged functional impairment as demonstrated by the increased expression of the activation (CD25, CD38), exhaustion (PD1, TIM3) and senescence (CD57) markers, as well as by the suboptimal response to ex vivo T-cell activation 1 year post HSCT. OS, DFS and NRM were not influenced by the absolute number and proportion of MAIT cells when assessed 30 days post-HSCT. Interestingly, higher absolute count of MAIT at +30 was associated with higher CI of aGvHD (27% vs 11%, p=0.04) in univariate analysis. Furthermore, an higher proportion of MAIT cells at the same time point, as well as the use of mMUD as donor, were associated as independent factors with a higher CI of all grades of cGvHD (25% vs 8%, p=0.01 and 74% vs 12%, p&amp;lt;0.001, respectively) and moderate-severe cGvHD (17% vs 4% p=0.024 and 59% vs 8% p=0.017, respectively), resulting in lower GRFS in patients with an higher proportion of MAIT cells at +30 (72% vs 52%, p=0.019) (Fig. 1). Univariate analysis also showed that patients with higher absolute values of MAIT had a lower CI of late BSI (17% vs 35%, p=0.05) but experienced more frequently CMV reactivation (44% vs 26%, p= 0.029) which occurred more in Haplo- and mMUD-recipients compared to MUD-patients (41.2% and 45.4% vs 21.2%, p=0.029). Conclusions Our study shows that MAIT cell recovery is significantly impaired in terms of absolute number and function in patients receiving HSCT. Evaluation of MAIT cells at early time points after HSCT may represent a useful parameter to identify patients at risk of late BSI, cGvHD and CMV reactivation. Additional studies are needed to further assess the biological function of MAIT cells.

Conditioning Intensity in Patients Aged > 50 Years Undergoing Allogeneic Hematopoietic Cell Transplantation for Myelodysplastic Syndrom: A Study on Behalf of the Chronic Malignancies Working Party of the EBMT

Introduction Myelodysplastic syndromes (MDS) affect mainly older individuals, with a median age &amp;gt; 70 years. Reduced intensity conditioning (RIC) is usually used for MDS patients undergoing allo-HCT to balance the toxicity of myeloablative conditioning (MAC), particularly in the more elderly or those with multiple comorbidities. In addition, the clinicians subjective opinion/ experience remains a major guide in choosing the intensity of conditioning. The majority of studies comparing RIC and MAC reported a higher cumulative incidence (CI) of relapse (RP) and lower non-relapse mortality (NRM) in the RIC groups. However, the impact of conditioning intensity on outcome after allo-HCT remains controversial. To gain more insight into the impact of conditioning on outcomes following allo-HCT for MDS, we evaluated RIC versus MAC in MDS patients aged &amp;gt; 50 years in a large EBMT cohort. Patients and methods This was a registry-based retrospective multicenter study that included MDS patients above 50 years, who received a first allo-HCT following RIC or MAC conditioning between 2014 - 2018 and had data on IPSS-R at allo-HCT and RIC/MAC conditioning available. Data collected included disease features, patient, donor and transplantation characteristics. Patients with ex vivo T-cell depletion were excluded. Variables with missing values ≤35% were handled with multiple imputation. OS, DFS, RP and NRM were compared using the Log-rank and Gray's test for CI, and (cause-specific) Cox proportional hazard models for multivariable analyses (MVA). A conditional logistic regression after propensity score matching (PSM) was also performed for potential risk confounders. Results Among the 1393 included patients (from 121 centres), 922 (66%) were men and the median age at allo-HCT was 62.8 (IQR:58.2-66.9) years. The majority of patients (n=884; 64.3%) had RAEB. The IPSS-R was recorded as very low/low (n=598, 43%), intermediate (n=352, 25%) and high/very high (n=443, 32%). Cytogenetic risk score was very good/good (n=932, 66.9%), intermediate (n=250, 17.9%) and poor/very poor (n=211, 15.1%). Karnofsky index was ≥ 90 in 916 pts (69.3%) and HCT-CI ≥ 3 in 292 pts (27.3%). Disease status at transplant was recorded as complete remission (n=486, 34.9%), untreated/stable disease (n=544, 39.0%), and progressive disease (n=310, 22.3%). Donor was HLA-matched (related/unrelated) (n=989, 71.1%), unrelated HLA-mismatched (n=286, 20.5%) or familial HLA haplo-identical donor (n=153, 10.9%). Source of SC was BM (n=112, 8.0%) and PB (n=1255, 90.0%). A RIC regimen was used in 1053 (75.5%) patients. In vivo T-cell depletion with anti-thymocyte globulin (ATG) was used in 941 pts (67.5%). Median time of follow up was 27.9 months (IQR: 26.4-30.6). Median rate of OS in RIC vs MAC group was 54.2(95% CI: 33.5-NA) vs 46.2(95% CI: 32.6-69.4), p=0.84; median rate of DFS was 28.4(95% CI: 19.4-58) vs 28.0 (95% CI: 22.5-39.1), respectively, p=0.64. Cumulative incidence rate of RP and NRM for RIC vs MAC regimen at 36 months were 31.2% vs 29.7% and 29.9% vs 30.4%, respectively (Figure 1). Both in univariable and MVA we did not observe a significant (&amp;gt; 0.05) association between the conditioning regimen on the outcomes. Similar results were obtained using PSM to control potential confounders (such as age, source of SC, stage of disease, HCT-CI, cytogentic risk score, neutrophile and platelet counts and sAML) and conditional logistic regression analysis (Table1). Conclusion To our knowledge, this is the largest retrospective cohort study that highlights a lack of association between RIC/MAC regimen and outcomes in MDS patients undergoing allo-HCT. Our results are in line with the recent published systematic review and metanalysis where evidence for using a one conditioning regimen over another remains weak [1,2]. 1) Rashidi et al. Biology of Blood and Marrow Transplantation. 2020; 26:138-141. 2) Akbar et al. Blood.2020; 136:40-41.

TCRαβ +/CD19 + - Depleted HLA-Haploidentical Hematopoietic Stem Cell Traansplantation in Pediatric Patient with Fanconi Anemia

Background Allogeneic hematopoietic stem cell transplantation (HSCT) currently represents the only proven treatment able to rescue bone marrow failure and prevent the occurrence of clonal evolution in patients with Fanconi Anemia (FA). If HSCT from HLA-identical related donor (MRD) is reported to be associated with better outcomes, this is not available for most patients. On the other hand, the identification of a fully matched unrelated donor (MUD) may be unsuccessful, or require times incompatible with a prompt treatment of the haematological condition. For patients who lack a MRD or MUD, the preferred donor choice is debated. HLA partially matched haploidentical donor (haplo) is virtually immediately available for all patients and haplo-HSCT has been reported over the last few years as a promising alternative for those patients. Following the favorable results already reported from our group of a cohort of pediatric and young adult FA patients underwent haplo-HSCT, based on the selective depletion of TCRαβ + and CD19 + cells graft manipulation, here we present the outcome of an enlarged cohort of patients who received HSCT in 3 different centers. Methods Patients diagnosed with FA and eligible for an allogeneic transplantation, but lacking a MRD or MUD, and with a suitable HLA-haploidentical donor were eligible to this study. The conditioning regimen included intravenous fludarabine, cyclophosphamide and single-dose total body irradiation for most patients. Pretransplant anti-T-lymphocyte globulin was administered in all patient to control in vivo bidirectional donor-recipient alloreactivity. Apheresis and graft manipulation were performed as previously reported (Li Pira, Biol Blood Marrow Transplant 2016). Results Thirty-five patients (19 males and 16 females) underwent haplo-HSCT between September 2011 and April 2023 in 3 different centers (Bambino Gesù Children's Hospital, Rome, Italy; Policlinico San Matteo, Pavia, Italy; Tokyo; National Center for Child Health and Development, Children's Cancer Center, Tokyo, Japan). Twenty-four patients have been previously reported (Strocchio, Blood Adv 2021). Details on patients and donor characteristics, graft composition and conditioning regimen are listed in table 1. One patient with clonal evolution and 1 with AML received fludarabine and AraC 3 weeks before the start of the conditioning. Primary engraftment was achieved in 33 patients (94.3%), with median time for neutrophil and platelet recovery of 12 days (range, 9-20 days) and 10 days (range, 7-14 days), respectively. Primary graft failure occurred in 2 patients and both were successfully transplanted from the other haploidentical parent. The monitoring of chimerism analysis confirmed a stable engraftment of donor hemopoiesis in all engrafted patients. Within 33 evaluable patients, 9 (27.3%) experienced grade 1-2 aGvHD (7 with stage I-II skin-only involvement, 1 with stage I lower gastrointestinal involvement) at a median time of 35.5 days (range, 16-67 days) after HSCT. One patient developed late-onset skin only grade 2 aGvHD at day +211 after HSCT. One patient (3%) experienced grade IV aGvHD (liver and gastrointestinal involvement) at day + 100 from HSCT, 4 weeks after the infusion of adenoviral-specific donor T cells; he is currently receiving ruxolitinib and the complete resolution of GvHD was obtained. Only one patient (3%), developed cGvHD with mild skin involvement. Thirteen patients (39.4%) experienced one or more viral infections or reactivations (6 cytomegalovirus, 4 herpesvirus-6, 2 adenovirus, 1 parainfluenzae); the specific antiviral treatment was administered with a complete resolution of infection in all cases. With a median follow up of 5.5 years (range, 0.6-11.4 years) all the patients are alive and with resolution of hematological complications. Except for the already reported vulvar intraepithelial neoplasia, no additional posttransplant malignancy was observed Conclusions Our data obtained from enlarged cohort of patients previously reported, confirm excellent results in terms of survival and a good rate of engraftment also in a multicenter setting. The low incidence of acute and chronic GvHD, a particularly detrimental complication in patients with DNA repair disorder, makes this approach attractive in this patient population. In FA patients lacking a standard donor, TCRab +/CD19 + haplo-HSCT is confirmed to be a promising strategy.

Analysis of Post-Transplant Clinical Outcomes and Prognostic Factors in FLT3-ITD Mutated Acute Myeloid Leukemia Patients Under ELN 2022 Risk Stratification

Background In 2022 European LeukemiaNet (ELN) recommendations for diagnosis and management of acute myeloid leukemia (AML), one of the most important changes made to the genetic risk classification of AML is that the FLT3-ITD allelic ratio (AR) is no longer considered in the risk classification; consequently, AML with FLT3-ITD (without adverse-risk genetic lesions) are now categorized in the intermediate-risk group, irrespective of the allelic ratio or concurrent presence of NPM1 mutation. Aims To investigate the survival outcomes of FLT3-ITD mutated AML patients underwent allogeneic hematopoietic stem cell transplantation (allo-HSCT), based on prognostic stratification defined by the 2017 and 2022 ELN guidelines, and to analyze the risk factors affecting transplant prognosis. Methods A total of 163 FLT3-ITD mutated AML patients underwent allo-HSCT were enrolled in this study. Bone marrow aspirates were obtained, cytogenetic and molecular characteristics were collected at the time of diagnosis. Genetic risk category was classified according to the 2017 and 2022 edition of the European LeukemiaNet (ELN) recommendations. HLA-haploidentical donor transplants were performed if no HLA matched sibling or unrelated donor was available. Patients received myeloablative conditioning with a modified Bu/Cy/Flu/Ara-c (busulfan/cyclophosphamide/fludarabine/cytarabine) or MCBC (melphalan/cladribine/busulfan/cyclophosphamide) preparative regimen. The therapeutic process and clinical outcomes were retrospectively analyzed. Results We assessed 163 adults with FLT3-mutated AML (median age 37 years) allografted between 2017 and 2022 in our clinical center. The median follow-up of alive patients was 24.9 months. The 2-year relapse-free survival (RFS) and overall survival (OS) were 67.2% and 71.9%, respectively. The 2-year incidences of relapse and non-relapse mortality were 27.9% and 12.5%, respectively. There was no significant difference in survival outcomes between the intermediate and high-risk groups after transplantation, both defined by the 2017 and 2022 ELN guidelines. High FLT3-ITD allelic ratio (≥0.5) at initial diagnosis was associated with elevated WBC counts ( P&amp;lt;0.001), but did not affect the response ratefollowing induction chemotherapy ( P=0.059) . Patients with high allelic ratio were more likely to benefit from maintenance therapy after transplantation ( P=0.048 for OS). In univariate analysis, presence of NPM1 mutation and the allelic ratio of FLT3-ITD did not affect any of the transplant outcomes. In multivariate analysis, MRD-negative at transplantation, occurrence of chronic GVHD and posttransplant maintenance therapy improved OS and RFS. Conclusion Allo-HSCT can overcome the poor prognosis in patients with FLT3-ITD mutated AML. Neither the presence of NPM1 mutation nor the FLT3-ITD allelic ratio affected survival. Prevention of disease relapse after transplantation remains a challenge. The main prognostic factors affecting transplant outcomes included pre-transplant MRD status and the application of maintenance therapy. Thus, introduction of FLT3 inhibitors as post-transplant maintenance therapy and the development of highly sensitive MRD assays will further reduce disease recurrence and improve survival.

Reduced Intensity Haploidentical Bone Marrow Transplantation in Adults with Severe Sickle Cell Disease: BMT CTN 1507

Background: Allogeneic hematopoietic stem-cell transplantation has curative potential for sickle cell disease (SCD). Event-free survival (EFS) in children with SCD is &amp;gt;90% after a bone marrow transplant (BMT) from a myeloablative matched sibling donor (MSD). Unfortunately, &amp;lt;15% of patients with SCD have MSD, and myeloablative conditioning can be prohibitively toxic in adults with SCD. Reduced intensity HLA-haploidentical BMT with post-transplant cyclophosphamide (PTCy) has been shown in small studies to expand the donor pool with encouraging results. Still, concerns about graft failure and graft-versus-host disease (GVHD) persist. We present the results of a Blood and Marrow Transplant Clinical Trials Network (BMT CTN) 1507, multi-center single-arm, phase-II, prospective clinical trial (clinicaltrials.gov #NCT03263559) of haploidentical-BMT with PTCy to estimate EFS at 2-years in adults with severe SCD. Pediatric stratum data is not included in the data presentation and will be available in 2-years. Study Design and Methods: Eligibility: SCD patients aged 15.00-45.99 years with prior stroke, recurrent ACS or pain, chronic transfusion regimen, or tricuspid valve regurgitant jet velocity (TRJV) ≥2.7 m/sec were eligible. Participants were required to have an HLA-haploidentical first-degree relative donor, willing and able to donate bone marrow. The primary objective was EFS (survival without primary or secondary graft failure or second infusion of stem cells) at 2 years after haploidentical-BMT. Secondary objectives included determining the impact on clinical and laboratory manifestations of SCD and other transplant outcomes at 2 years post haploidentical-BMT. The protocol was opened for enrollment on 10/5/2017, completed accrual on 01/6/2021, and data are current as of 8/2023. Preconditioning with hydroxyurea (HU) 30mg/kg/day (Day-70 to Day-10); Conditioning regimen included Thymoglobulin (rATG), Thiotepa, Fludarabine, Cyclophosphamide, and Total Body Irradiation (TBI). GVHD prophylaxis included PTCy, sirolimus, and mycophenolate mofetil, figure. Results: A total of 54 eligible participants enrolled from 19 sites; 42 (78%) proceeded to transplant. Amongst enrolled participants, 59.3% are male, 92.6% are Black, and 3.7% are Hispanic. 10 participants started HU but did not proceed to BMT, and 2 did not start HU or proceed to BMT. Reasons included donor issues (n=4), withdrawal of consent (n=2), insurance coverage (n=2), death (n=1), and other (n=3). 38/42 (90%) participants completed the study as planned; 2 participants withdrew consent, and 2 were lost to follow-up. The median age was 22.8 years at enrollment; 47/54 (87%) of enrolled participants had Hemoglobin SS disease, 40/54 (74.1%) had a Lansky/Karnofsky score of 90-100 at baseline, and 41/54 (75.9%) had an HLA match score of 4/8. Recurrent vaso-occlusive pain episodes (38.9%), acute chest syndrome (16.8%), and overt stroke (16.7%) were the most common indications for transplant. Only 13 (31%) participants achieved the intended 30 mg/kg/day dosing of HU preconditioning. Estimated 2-year EFS is 88% (95% CI: 73.5%, 94.8%); all except one qualifying event occurred within 12 months. The 2-year overall survival (OS) post-HU was 93.0% (95% CI: 79.8%, 97.7%), and the 2-year OS post-transplant was 95.0% (95% CI: 81.5%, 98.7%); 2 (4.8%) participants had primary graft failure, and 1 (2.4%) had secondary graft failure before day +100. The cumulative incidence of grades II-IV acute GVHD at day 100 was 26.2% (95% CI: 14.0%, 40.2%), and grades III-IV acute GVHD at day 100 was 4.8% (95% CI: 0.9%, 14.4%). There were two deaths in the first year post-BMT (1 -organ failure; 1-ARDS), none in the second year; 33 (78.6%) participants reported at least one re-admission post-BMT, mainly due to either bacterial infection (n=41) or viral reactivation (n=36), table. Conclusion: This multi-center phase-II trial of a reduced intensity haploidentical-BMT in adults with SCD shows durable donor engraftment at 2-years with low mortality. The 2-year EFS and OS are comparable to that reported after MSD myeloablative BMT. These results support haploidentical BMT with PTCy as a suitable and tolerable curative therapy for adults with SCD and severe end-organ toxicity such as stroke and pulmonary hypertension, a population typically excluded from participating in myeloablative gene therapy and gene editing trials.

Allogeneic, donor-derived, second-generation, CD19-directed CAR-T cells for the treatment of pediatric relapsed/refractory BCP-ALL

AbstractAutologous CD19-directed chimeric antigen receptor (CAR)-T cells have shown unprecedented efficacy in children with relapsed/refractory B-cell precursor acute lymphoblastic leukemia (BCP-ALL). However, patients either relapsing after allogeneic hematopoietic stem cell transplantation (allo-HSCT) or displaying profound lymphopenia and/or rapidly progressing disease often cannot access autologous products. These hurdles may be overcome by allogeneic, donor-derived CAR-T cells. We tested donor-derived T cells transduced with a second-generation (4.1BB) CD19-directed CAR for treatment of patients with BCP-ALL in a hospital-exemption setting. Two constructs were tested: a retroviral construct incorporating the suicide gene inducible caspase-9 (CD19-CAR–Retro_ALLO) first and then a lentiviral construct and an automated, Prodigy-based manufacturing process (CD19-CAR–Lenti_ALLO). Thirteen children/young adults received ALLO–CAR-T cells between March 2021 and October 2022. Doses ranged between 1.0 × 106 and 3.0 × 106 CAR-T cells per kg. The toxicity profile was comparable with that of autologous CAR-T cells, characterized mainly by cytopenia, cytokine release syndrome (maximum grade 1), and grade 2 immune-effector cell–associated neurotoxicity syndrome. One case of acute graft-versus-host disease (GVHD) occurred and was rapidly controlled with steroids and ruxolitinib. None of the other patients, including 3 given ALLO–CAR-T cells from an HLA-haploidentical donor, experienced GVHD. Two patients received ALLO–CAR-T cells before HSCT and showed a significant expansion of CAR-T cells without any sign of GVHD. All patients obtained complete remission (CR) with absence of minimal residual disease in the bone marrow. With a median follow-up of 12 months (range, 5-21), 8 of 13 patients maintained CR. Allogeneic anti-CD19 CAR-T cells can effectively treat highly refractory BCP-ALL relapsing after allo-HSCT without showing increased toxicity as compared with autologous CAR-T cells.

Cost-Effectiveness of Unrelated Umbilical Cord Blood Transplantation versus HLA-Haploidentical Related Bone Marrow Transplantation: Evidence from BMT CTN 1101

BMT CTN 1101 was a Phase III randomized controlled trial comparing reduced-intensity conditioning followed by double unrelated umbilical cord blood transplantation (UCBT) versus HLA-haploidentical related donor bone marrow transplantation (haplo-BMT) for patients with high-risk hematologic malignancies. Here we report the results of a parallel cost-effectiveness analysis of these 2 hematopoietic stem cell transplantation (HCT) techniques. In this study, 368 patients were randomized to unrelated UCBT (n=186) or haplo-BMT (n=182). We estimated healthcare utilization and costs using propensity score-matched haplo-BMT recipients from the OptumLabs Data Warehouse for trial participants age <65 years and Medicare claims for participants age ≥65 years. Weibull models were used to estimate 20-year survival. EQ-5D surveys by trial participants were used to estimate quality-adjusted life-years (QALYs). At a 5-year follow-up, survival was 42% for haplo-BMT recipients versus 36% for UCBT recipients (P=.06). Over a 20-year time horizon, haplo-BMT is expected to be more effective (+.63 QALY) and more costly (+$118,953) for persons age <65 years. For those age ≥65 years, haplo-BMT is expected to be more effective and less costly. In one-way uncertainty analyses, for persons age <65, the cost per QALY result was most sensitive to life-years and health state utilities, whereas for those age ≥65, life- years were more influential than costs and health state utilities. Compared to UCBT, haplo-BMT was moderately more cost-effective for patients age <65 years and less costly and more effective for persons age ≥65 years. Haplo-BMT is a fair value choice for commercially insured patients with high-risk leukemia and lymphoma who require HCT. For Medicare enrollees, haplo-BMT is a preferred choice when considering costs and outcomes.

Donor selection for adoptive immunotherapy with NK cells in AML patients: Comparison between analysis of lytic NK cell clones and phenotypical identification of alloreactive NK cell repertoire.

Natural killer (NK) cell-based adoptive immunotherapy in leukemia patients is an emerging field of interest based on clinical evidence of efficacy and safety. Elderly acute myeloid leukemia (AML) patients have been successfully treated with NK cells from HLA-haploidentical donors, especially when high amounts of alloreactive NK cells were infused. The aim of this study was comparing two approaches to define the size of alloreactive NK cells in haploidentical donors for AML patients recruited in two clinical trials with the acronym "NK-AML" (NCT03955848), and "MRD-NK". The standard methodology was based on the frequency of NK cell clones capable of lysing the related patient-derived cells. The alternative approach consisted of the phenotypic identification of freshly derived NK cells expressing, as inhibitory receptors, only the inhibitory KIR(s) specific for the mismatched KIR-Ligand(s) (HLA-C1, HLA-C2, HLA-Bw4). However, in KIR2DS2+ donors and HLA-C1+ patients, the unavailability of reagents staining only the inhibitory counterpart (KIR2DL2/L3) may lead to an underestimated identification of the alloreactive NK cell subset. Conversely, in the case of HLA-C1 mismatch, the alloreactive NK cell subset could be overestimated due to the ability of KIR2DL2/L3 to recognize with low-affinity also HLA-C2. Especially in this context, the additional exclusion of LIR1-expressing cells might be relevant to refine the size of the alloreactive NK cell subset. We could also associate degranulation assays, using as effector cells IL-2 activated donor peripheral blood mononuclear cells (PBMC) or NK cells upon co-culture with the related patient target cells. The donor alloreactive NK cell subset always displayed the highest functional activity, confirming its identification accuracy by flow cytometry. Despite the phenotypic limitations and considering the proposed corrective actions, a good correlation was shown by the comparison of the two investigated approaches. In addition, the characterization of receptor expression on a fraction of NK cell clones revealed expected but also few unexpected patterns. Thus, in most instances, the quantification of phenotypically defined alloreactive NK cells from PBMC can provide data similar to the analysis of lytic clones, with several advantages, such as a shorter time to achieve the results and, perhaps, higher reproducibility/feasibility in many laboratories.

Outcome after allogeneic stem cell transplantation with haploidentical versus HLA-matched donors in patients with higher-risk MDS

Allogeneic hematopoietic stem cell transplantation remains the best curative option for higher-risk myelodysplastic syndrome. The presence of monosomal karyotype and/or complex karyotype abnormalities predicts inferior survival after allo-SCT in MDS patients. Haploidentical allo-SCT has been increasingly used in acute leukemia (AL) and has similar results as using HLA-matched donors, but data on higher-risk MDS is sparse. We compared outcomes in 266 patients with higher-risk MDS after HLA-matched sibling donor (MSD, n = 79), HLA-matched unrelated donor (MUD, n = 139) and HLA haploidentical donor (HID, n = 48) from 2010 to 2019. Median donor age differed between the three groups (p < 0.001). The overall survival was significantly different between the three groups with a better OS observed in the MUD group (p = 0.014). This observation could be explained by a higher progression-free survival with MUD (p = 0.014). The cumulative incidence of grade 2–4 acute GvHD was significantly higher in the HID group (p = 0.051). However, in multivariable analysis, patients transplanted using an HID had comparable mortality to patients transplanted using a MUD (subdistribution hazard ratio [sHR]: 0.58 [0.32–1.07]; p = 0.080) and a MSD ([sHR]: 0.56 [0.28–1.11]; p = 0.094). MUD do not remain a significant positive predictor of survival, suggesting that beyond the donor-recipient HLA matching, the donor age might impact recipient outcome.

HLA-haploidentical hematopoietic stem cells transplantation with regulatory and conventional T-cell adoptive immunotherapy in pediatric patients with very high-risk acute leukemia.

Allogeneic hematopoietic stem cell transplantation (HSCT) is still needed for many children with very high-risk acute leukemia. An HLA-haploidentical family donor is a suitable option for those without an HLA-matched donor. Here we present outcomes of a novel HLA-haploidentical HSCT (haplo-HSCT) strategy with adoptive immunotherapy with thymic-derived CD4+CD25+ FoxP3+ regulatory T cells (Tregs) and conventional T cells (Tcons) performed between January 2017 and July 2021 in 20 children with high-risk leukemia. Median age was 14.5 years (range, 4-21), 15 had acute lymphoblastic leukemia, 5 acute myeloid leukemia. The conditioning regimen included total body irradiation (TBI), thiotepa, fludarabine, cyclophosphamide. Grafts contained a megadose of CD34+ cells (mean 12.4 × 106/Kg), Tregs (2 × 106/Kg) and Tcons (0.5-1 × 106/Kg). All patients achieved primary, sustained full-donor engraftment. Only one patient relapsed (5%). The incidence of non-relapse mortality was 15% (3/20 patients). Five/20 patients developed ≥ grade 2 acute Graft versus Host Disease (aGvHD). It resolved in 4 who are alive and disease-free; 1 patient developed chronic GvHD (cGvHD). The probability of GRFS was 60 ± 0.5% (95% CI: 2.1-4.2) (Fig.6), CRFS was 79 ± 0.9% (95% CI: 3.2-4.9) as 16/20 patients are alive and leukemia-free. The median follow-up was 2.1 years (range 0.5 months-5.1 years). This innovative approach was associated with very promising outcomes of HSCT strategy in pediatric patients.

Allogeneic Hematopoietic Cell Transplantation in Patients with Relapsed or Refractory Acute Leukemia

Introduction: Current guidelines support allogeneic hematopoietic cell transplantation (allo-HCT) in patients with acute leukemia who achieve complete remission (CR) and are at high risk for relapse. Patients with primary refractory disease or those refractory to re-induction therapy after relapse have a poor prognosis in the absence of allo-HCT. While several studies have addressed the role of allo-HCT in those settings, the measurable benefit of allo-HCT has not been defined in such patients. Most previous studies have included patients who received myeloablative conditioning and did not address the possible impact of molecular genetic risk factors. Objective: The present study assessed outcomes of allo-HCT in patients with refractory or relapsed (R/R) acute leukemia receiving myeloablative (MAC) or reduced intensity conditioning (RIC) regimens. Our goal was to identify novel risk factors associated with improved outcomes to aid patient selection in the setting of R/R acute leukemia. Methods: Patients with R/R acute leukemia undergoing allo-HCT at Memorial Sloan Kettering Cancer Center (MSK) between 2009 and 2020 were included. Patients had a marrow blast count of 5% or more at the time of allo-HCT and were classified into one of the following categories: primary induction failure (PIF), at least 2 lines of induction therapy; not in CR (NCR), no more than one line of induction therapy; untreated relapse (UR); and refractory relapse (RR), no remission after at least one line of re-induction therapy for relapse. Results: We identified 101 patients with acute myeloid leukemia (AML; n=94), acute lymphoblastic leukemia (ALL; n=3), biphenotypic acute leukemia (n=2), and plasmacytoid dendritic cell leukemia (n=2). Table 1 depicts patient and transplant characteristics. Median blast count at the time of allo-HCT was 8% (IQR, 5%,15%). 37 patients had at least one genomic alteration, and 30 patients had circulating blasts at the time of transplant. Grafts were from HLA-identical siblings in 30 patients, from HLA-matched unrelated donors in 51 patients and from HLA-mismatched or HLA-haploidentical donors in 20 patients. 61 and 40 patients received MAC and RIC, respectively. Graft source was unmodified bone marrow (n=8), unmodified peripheral blood stem cells (PBSC; n=80), or CD34+ cellselected peripheral blood stem cells (n=7). Overall survival (OS) at 4 years was 25% (95% CI: 18%, 35%). In univariate analysis, RIC (HR 1.71, p=0.035), presence of circulating blasts (HR 2.21, p=0.002), and high pre-transplant ferritin levels (HR 1.43, p=0.049) were associated with inferior OS. In multivariate analysis, RIC was associated with reduced OS. The 4-year cumulative incidence of relapse/disease progression and non-relapse mortality (NRM) was 54% (95% CI: 43%, 63%) and 24% (CI, 16%, 33%) respectively. In univariate analysis, RIC, presence of circulating blasts, and elevated pre-transplant ferritin levels were associated with increased NRM. In multivariate analysis, RIC and elevated pre-transplant ferritin levels were associated with high NRM. The cumulative incidence of acute graft-vs-host disease (aGVHD) was 45% (95% CI: 35%, 54%) at day 100. There was no statistically significant effect of genomic and molecular parameters on NRM and OS. However, high risk molecular mutations (TP53, RUNX1, ASXL1 or FLT3-ITD) had borderline association with relapse/disease progression (HR 1.7, p=0.073). Conclusion: Allo-HCT provides durable remission in a select group of patients with relapsed or refractory acute leukemia with an OS of 25% at 4 years. The presence of circulating blasts and elevated ferritin levels at the time of allo-HCT was associated with increased NRM and inferior OS in this retrospective analysis. Known high-risk gene mutations did not affect outcomes in this population. The impact of these parameters should be evaluated in a larger cohort of 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