T-cell Replete Research Articles

Mother Vs Father Haploidentical Donor for T Cell-Replete HCT with Ptcy Prophylaxis

Background: When several haplo donors of similar ages are available, which factors should be prioritized remains a matter of debate. This is a frequent clinical question for recipients who are undergoing haplo hematopoietic cell transplantation (HCT) from a parent donor. Although conventionally a female donor is avoided for a male recipient due to the high risk of graft-versus-host disease (GVHD), gender-mismatch (female-to-male) has not been identified as an independent predictor of worse outcomes in the setting of T cell-replete haploidentical HCT with post-transplant cyclophosphamide (PTCy) prophylaxis. On the other hand, certain (mis)matches at specific HLA loci with haplo HCT are now being recognized as predictors of survival. Thus, it has become even more ambiguous whether HLA or non-HLA factors should be prioritized for a haploidentical donor selection. Whether HLA factors trump non-HLA factors (e.g female-to-male, donor age, relationship) remains an area of active investigation. As patient and donor ages and relationships are important predictors of outcomes and are very tightly correlated to each other, we studied the effects of HLA and non-HLA factors stratified by donor relationship (mother vs father). Objective: We sought to compare the outcomes of T-cell replete haplo HCT using a mother vs father donor with PTCy prophylaxis, after accounting for (mis)matching at individual HLA loci and patient/donor age. Results: We included 57 patients with a mother (n=29) vs father (n=28) donor. Median age at HCT (23 yrs vs 27 yrs, p=0.1) and donor age (50 yrs vs 52 yrs, p=0.9) were similar in both groups. Most received RIC (79% vs 86%, p=0.5), BM graft (83% vs 75%, p=0.5), had HCT-CI >3 (46% vs 64%, p=0.2), and low/intermediate DRI (45% vs 54%, p=0.8), were CMV seropositive (86% vs 79%, p=0.04), and B-leader matched (51% vs 48%, p=0.9) and ABO matched with the donor (76% vs 64%, p=0.4). The recipient was male in 59% (mother donor) vs 61% (father donor). The median follow-up was 54 vs 28 months. Graft failure occurred in 0% vs 4%, p=0.3; the median time to neutrophil engraftment was 18 days in both groups. The cumulative incidence of grade II-IV aGVHD (65% vs 56%, p=0.3) and grade III-IV aGVHD at day 180 (31% vs 15%, p=0.2), 3-yr cGVHD (31% vs 15%, p=0.2); NRM (35% vs 26%, p=0.5), relapse (21% vs 32%, p=0.4), PFS (39% vs 36%, p=0.9) and OS was (53% vs 41%, p=0.3) in mother vs father donor, respectively. In multivariate analysis, no statistically significant differences were noted in any outcome between mother vs father donors, likely due to small number of events. However, B-leader mismatch was associated with a significantly higher risk of NRM (HR 2.7, 95% CI 1.03-7.02, p=0.04), and HLA-A mismatch was associated with a lower risk of NRM (HR 0.3, 95% CI 0.1-0.8, p=0.02), better PFS (HR 0.2, 95% CI 0.1-0.4, p<0.001) and OS (HR 0.1, 95% CI 0.05-0.4, p<0.001). HCT-CI >3 was associated with inferior PFS (HR 3.5, 95% CI 1.5-7.6, p=0.002) and OS (HR 4.1, 95% CI 1.7-9.8, p=0.002). Conclusion: HLA factors, such as B-leader mismatch (high NRM) and HLA-A mismatch (low NRM and high PFS and OS) may have a stronger prognostic impact on mortality than donor-relationship. Recognizing the limitations of the small sample size, our data suggest that among parent haplo donors, in cases where both father and mother are B-leader matched and/or HLA-A mismatched with the recipient, father should be preferred due to a 2-fold higher risk of grade III-IV aGVHD and cGVHD (although statistically non-significant) with maternal donors. However, it remains unclear whether a B-leader mismatched (and/or HLA-A matched) father be selected over a B-leader matched (and/or HLA-A mismatched) mother. Further large-scale studies are needed to comprehend these complex immunobiological relationships. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Son Vs Daughter Haploidentical Donor for T Cell-Replete HCT with Ptcy Prophylaxis

Background: A younger haplo donor is usually preferred over an older donor. However, when several donors of similar ages are available, which factors should be prioritized remains a matter of debate. This is a frequent clinical question for older recipients who are undergoing haplo hematopoietic cell transplantation (HCT) from a child donor. Although conventionally a female donor is avoided for a male recipient due to the high risk of graft-versus-host disease (GVHD), this has not been consistently seen in the setting of T cell-replete haploidentical HCT with post-transplant cyclophosphamide (PTCy) prophylaxis. Additionally, there is increasing recognition of the impact of (mis)matches at specific HLA loci with haplo HCT. Whether HLA factors trump non-HLA factors (e.g female-to-male, donor age, relationship), or vice-a-versa, is unclear. As patient and donor ages and relationships are important predictors of outcomes and are very tightly correlated to each other, we studied the effects of HLA and non-HLA factors stratified by donor relationship (son vs daughter). Objective: We sought to compare the outcomes of T-cell replete haplo HCT using a son vs daughter donor with PTCy prophylaxis, after accounting for (mis)matching at individual HLA loci and patient/donor age. Results: We included 298 consecutive patients with a daughter (n=96) vs son (n=202) donor. Median age at HCT (56 yrs vs 58 yrs, p=0.05) and donor age (27 yrs vs 29 yrs, p=0.1) were similar in both groups. Most received RIC (78% vs 76%, p=0.5) and had HCT-CI >3 (52% vs 54%, p=0.6). Fewer patients with a daughter donor received BM graft (56% vs 74%, p=0.002) and had high/very high DRI (20% vs 41%, p<0.001). Most patients were CMV seropositive (83% vs 81%, p=0.09) and ABO matched with donor (60% vs 61%, p=0.9). Significantly more patients with a daughter donor had HLA-C mismatch (97% vs 88%, p=0.01); other mismatches were similar in both groups: A (91% vs 96%, p=0.2), B-leader (43% vs 37%, p=0.6), DRB1 (92% vs 94%, p=0.5), DQB1 (86% vs 90%, p=0.3), DPB1 (76% vs 80%, p=0.4). The median follow-up was 24 vs 27 months. Graft failure occurred in 2% vs 4%, p=0.5; the median time to neutrophil engraftment was similar (20 vs 19 days). The cumulative incidence of grade II-IV aGVHD (39% vs 34%, p=0.5) and grade III-IV aGVHD at day 180 (12% vs 6%, p=0.1), 2-yr cGVHD (18% vs 12%, p=0.4); NRM (28% vs 33%, p=0.5), relapse (24% vs 29%, p=0.4), PFS (47% vs 38%, p=0.2) and OS (50% vs 46%, p=0.4) were similar in daughter vs son, respectively. In multivariate analysis, daughter donors were associated with similar risk of grade II-IV aGVHD (HR 1.2, 95% CI 0.8-1.9, p=0.3), cGVHD (HR 1.03, 95% CI 0.5-2.3, p=0.9), and NRM (HR 0.9, 95% CI 0.6-1.4, p=0.7) as sons. For survival, significant interactions were noted between donor gender and DRI. In patients with low DRI, there was no impact of donor gender, but in patients with high/v high DRI, daughter donors were associated with improved PFS (HR 0.5, 95% CI 0.2-0.9, p=0.03) and OS (HR 0.5, 95% CI 0.3-0.9 p=0.04) as compared to sons. Relapse rate was highest with son-to-mother (HR 1.7, 95% CI 1.02-2.7, p=0.04). PB graft was associated with a significantly higher risk of cGVHD (HR 3.1, 95% CI 1.5-6.4, p=0.003). High/very high DRI was associated with a high risk of relapse (HR 2.4, 95% CI 1.5-3.9, p<0.001). Patient age >50 yrs had high NRM (HR 2.03, 95% CI 1.1-3.7, p=0.02), poor PFS (HR 1.5, 95% CI 1.02-2.3, p=0.04) and OS (HR 1.6, 95% CI 1-2.5, p=0.05). There was no significant impact of specific HLA mismatches on any of the outcomes. Having 3 class II HLA (vs <3) mismatches was associated with a high risk of cGVHD (HR 3.3, 95% CI 1.3-8.7, p=0.01), with no impact on survival. Conclusion: Among child haplo donors, our data suggest that female donors do not result in any inferior outcomes as compared to male donors. A daughter may even be a preferred donor for patients with high/very-high DRI as it conferred survival benefit as compared to a son donor. This may partly be related to a higher risk of relapse seen in son donor to mother recipient. Also, certain HLA mismatches (e.g. B-leader), which have prognostic implications in haplo HCT in general, did not appear to be of significance when accounted for donor relationship and age in patients with a child donor. Further large-scale studies are needed to comprehend these complex immunobiological relationships. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Irradiation-free, T-cell replete haploidentical transplant for Fanconi anaemia, weighing the benefits.

The optimal haploidentical haematopoietic cell transplant approach for Fanconi anaemia (FA) patients is not well established, given the rarity of the disease, the increased sensitivity to DNA-damaging agents and the high risk of severe graft-versus-host disease (GVHD). The report by Xu et al. suggests that excellent engraftment and short-term survival can be achieved in FA patients without irradiation, but their retrospective cohort was plagued by a high rate of severe GVHD. Our commentary explores the outcomes in T-cell replete haploidentical haematopoietic cell transplantand ponders whether elimination of total body irradiation in FA patients is the best method if it limits the ability to safely administer post-transplant cyclophosphamide. Commentary on: Xu et al. Unmanipulated haploidentical haematopoietic cell transplantation with radiation-free conditioning in Fanconi anaemia: A retrospective analysis from the Chinese Blood and Marrow Transplantation Registry Group. Br J Haematol. 2022;199:401-410.

Human leukocyte antigen-haploidentical transplantation for relapsed/refractory acute myeloid leukemia: Better leukemia-free survival with bone marrow than with peripheral blood stem cells in patients ≥55 years of age.

The best stem cell source for T-cell replete human leukocyte antigen (HLA)-haploidentical transplantation with post-transplant cyclophosphamide (PTCy) remains to be determined. In this European Society for Blood and Marrow Transplantation retrospective study, we analyzed the impact of stem cell source on leukemia-free survival (LFS) in adult patients with primary refractory or relapsed acute myeloid leukemia (AML) given grafts from HLA-haploidentical donors with PTCy as graft-versus-host disease (GVHD) prophylaxis. A total of 668 patients (249 bone marrow [BM] and 419 peripheral blood stem cells [PBSC] recipients) met the inclusion criteria. The use of PBSC was associated with a higher incidence of grade II-IV (HR=1.59, p=.029) and grade III-IV (HR=2.08, p=.013) acute GVHD. There was a statistical interaction between patient age and the impact of stem cell source for LFS (p < .01). In multivariate Cox models, among patients <55 years, the use of PBSC versus BM resulted in comparable LFS (HR=0.82, p=.2). In contrast, in patients ≥55 years of age, the use of PBSC versus BM was associated with higher non-relapse mortality (NRM) (HR=1.7, p=.01), lower LFS (HR=1.37, p=.026) and lower overall survival (HR=1.33, p=.044). In conclusions, our data suggest that in patients ≥55 years of age with active AML at HLA-haploidentical transplantation, the use of BM instead of PBSC as stem cell source results in lower NRM and better LFS. In contrast among younger patients, the use of PBSC results in at least a comparable LFS.

Mixed T cell CHIMERISM in bone marrow at day+30 after allogeneic stem cell transplantation: Correlation with acute GVHD grades III-IV and no impact on relapse and overall survival.

Early chimerism analysis is important to assess engraftment in allogeneic hematopoietic stem cell transplantations. We retrospectively investigated the impact of T-cell chimerism at day 30 in bone marrow on acute graft-versus-host disease (aGVHD), relapse, and overall survival in 142 adult allo-transplanted patients. The majority of patients (89%) received myeloablative conditioning and 90% have undergone T-cell replete donor graft. At day 30, 103 patients showed T-complete chimerism with prevalence in haploidentical transplants, whereas 39 cases had CD3+ mixed chimerism, including 30 patients transplanted with HLA identical donors, and 21 with T-cell donors<90%. T-cell chimerism at day 30 was weakly inversely related to aGVHD grades II-IV (p=.078) with no cases of grades III-IV aGVHD in patients with CD3+ <95%. Mixed T-cell chimerism did not impact on relapse (p = .448) and five of the seven patients who relapsed had T-cell chimerism ≤90%. Older age and active disease at transplant had a statistically significant negative effect on overall survival (p = .01 and p = .0001, respectively), whereas mixed CD3+ chimerism did not. T lymphocyte chimerism analysis at day +30 in bone marrow could identify allo-transplanted patients at major risk of aGVHD grades III-IV (CD3+ donors >95%) mainly post-myeloablative conditioning regimen.

Feasibility and Efficacy of Partially Replacing Post-Transplantation Cyclophosphamide with Bendamustine in Pediatric and Young Adult Patients Undergoing Haploidentical Bone Marrow Transplantation

Post-transplantation cyclophosphamide (PT-CY) is the most widely applied graft-versus-host disease (GVHD) prophylaxis regimen in T-cell replete haploidentical bone marrow transplantation (haplo-BMT). Although PT-CY has met with great success in the haplo-BMT arena by suppressing GVHD, patients without acute GVHD have high relapse rates. One strategy to reduce relapse rates being explored by others is a dosage reduction of PT-CY. We have taken a different approach in evaluating whether partially replacing PT-CY with post-transplantation bendamustine (PT-BEN) would be advantageous, an idea based on our preclinical research identifying several beneficial immunomodulatory properties of BEN. We therefore initiated and completed a Phase Ia trial to evaluate the progressive substitution of PT-CY with PT-BEN (ClinicalTrials.gov identifier NCT02996773). We compared outcomes between 13 patients with high-risk hematologic malignancies who received PT-CY/BEN and 31 contemporaneous haplo-BMT recipients treated with the same myeloablative conditioning regimens but receiving only PT-CY. We found that partial replacement of PT-CY with PT-BEN (PT-CY/BEN) on day +4 was well tolerated and associated with significantly earlier trilineage engraftment. We also report favorable trends toward significant improvements on univariate and multivariate analyses with PT-CY/BEN compared with PT-CY with respect to rates of chronic GVHD (hazard ratio [HR], .08; 95% confidence interval [CI], .005 to 1.11; P=.06), and GVHD-free relapse-free survival (GRFS) (HR, .22; 95% CI, .05 to .86; P=.039). Our human trial has now transitioned to Phase Ib, which will further evaluate the safety and potential benefits of PT-CY/BEN. Herein we also expand our pediatric, adolescent, and young adult experience to 31 patients, demonstrating overall survival, progression-free survival, and GRFS at 3 years of 85.6%, 76.1%, and 58.2%, respectively, in a largely racial/ethnic minority cohort. PT-CY/BEN appears to be a promising treatment option that requires further evaluation.

Assessment of Patient-Specific Human Leukocyte Antigen Genomic Loss at Relapse After Antithymocyte Globulin–Based T-Cell–Replete Haploidentical Hematopoietic Stem Cell Transplant

Patient-specific human leukocyte antigen (HLA) genomic loss (HLA loss) is one of the reputed mechanisms of leukemia immune escape and relapse after haploidentical hematopoietic stem cell transplant (HSCT). However, clinical characteristics and prognosis of this distinct relapse type in the setting of haploidentical HSCT based on antithymocyte globulin (ATG) T-cell-replete conditioning are still unknown, especially for patients with lymphoid leukemia. To identify the incidence of and patient characteristics associated with HLA loss at hematologic cancer relapse after ATG-based haploidentical HSCT and to assess overall survival after HLA loss at relapse. This retrospective and multicenter case series study used data from medical records to identify patients who experienced relapse of hematologic cancer after receipt of ATG-based haploidentical HSCT. The study included 788 consecutive patients aged 8 to 70 years with lymphoid or myeloid leukemia who received ATG T-cell-replete haploidentical HSCT at the Zhejiang Cooperative Group for Blood and Marrow Transplantation between May 1, 2012, and May 31, 2021. Relapse after ATG-based haploidentical HSCT. Incidence, risk factors, and postrelapse overall survival among patients with HLA loss at hematologic cancer relapse after receipt of haploidentical HSCT. Logistic regression analysis was used to identify characteristics associated with the likelihood of HLA loss, and Kaplan-Meier and Cox regression analyses were performed to evaluate postrelapse survival. A total of 788 patients who received haploidentical HSCT for hematologic cancer were identified, 180 of whom experienced relapse after HSCT. Of those, 106 evaluable patients (median age, 30.9 years [range, 8.3-64.6 years]; 54 female [50.9%] and 52 male [49.1%]) were screened for HLA loss, which was detected in 54 patients (50.9%). Patients with HLA loss experienced relapse later than those without HLA loss (lymphoid group: median, 323 days [range, 98-2056 days] vs 151 days [range, 57-2544 days]; P = .01; myeloid group: median, 321 days [range, 55-1574 days] vs 223 days [range, 68-546 days]; P = .03). Among patients with lymphoid leukemia, those with minimal residual disease positivity before hematologic relapse (odds ratio [OR], 28.47; 95% CI, 1.99-407.98; P = .01), those with chronic graft-vs-host disease (OR, 27.68; 95% CI, 1.40-546.88; P = .03), and those with more than 180 days between HSCT and relapse (OR, 6.91; 95% CI, 1.32-36.22; P = .02) were more likely to lose unshared HLA at relapse, whereas male patients (OR, 0.03; 95% CI, 0.003-0.32; P = .04) were more likely to preserve their HLA genome at relapse. Patients with myeloid leukemia had different factors associated with HLA loss, including underweight status (OR, 0.10; 95% CI, 0.02-0.60; P = .01) and acute graft-vs-host disease (OR, 4.84; 95% CI, 1.14-20.53; P = .03). The receipt of preemptive donor lymphocyte infusion among patients with minimal residual disease recurrence did not postpone hematologic cancer relapse in those with HLA loss (median, 322 days [range, 204-1030 days]) compared with no receipt of donor lymphocyte infusion (median, 340 days [range, 215 days to not available]; P > .99). In this study, HLA loss at leukemia relapse occurred frequently after receipt of ATG-based haploidentical HSCT. The identification of risk factors associated with HLA loss would help to prompt screening, avoid potentially harmful infusions of donor T cells, and develop alternative therapeutic strategies.

49 - The Effect of Post-Transplant Bendamustine on Immune Reconstitution in Young Patients Undergoing T-Cell Replete Haploidentical Bone Marrow Transplantation: A Phase Ia/Ib Clinical Trial

49 - The Effect of Post-Transplant Bendamustine on Immune Reconstitution in Young Patients Undergoing T-Cell Replete Haploidentical Bone Marrow Transplantation: A Phase Ia/Ib Clinical Trial

Value of the Assessment of Interleukin 6 level in Allogenic T-cell Replete Haploidentical peripheral blood haematopioetic stem cell transplantation using post-transplant cyclophosphamide as a predictor for the occurrence of acute Graft versus Host Disease

Value of the Assessment of Interleukin 6 level in Allogenic T-cell Replete Haploidentical peripheral blood haematopioetic stem cell transplantation using post-transplant cyclophosphamide as a predictor for the occurrence of acute Graft versus Host Disease

T-replete HLA-matched grafts vs T-depleted HLA-mismatched grafts in inborn errors of immunity

AbstractHematopoietic cell transplantation (HCT) has become standard-of-care for an increasing number of inborn errors of immunity (IEI). This report is the first to compare transplant outcomes according to T-cell–replete (ie, T-replete) HLA-matched grafts using alemtuzumab (n = 117) and T-cell–depleted (ie, T-depleted) HLA-mismatched grafts using T-cell receptor-αβ (TCRαβ)/CD19 depletion (n = 47) in children with IEI who underwent first HCT between 2014 and 2019. All patients received treosulfan-based conditioning except patients with DNA repair disorders. For T-replete grafts, the stem cell source was marrow in 25 (21%) patients, peripheral blood stem cell (PBSC) in 85 (73%), and cord blood in 7 (6%). TCRαβ/CD19 depletion was performed on PBSCs from 45 haploidentical parental donors and 2 mismatched unrelated donors. The 3-year overall survival (OS) and event-free survival for the entire cohort were 85% (77%-90%) and 79% (69%-86%), respectively. Analysis according to age at transplant revealed a comparable 3-year OS between T-replete grafts (88%; 76%-94%) and T-depleted grafts (87%; 64%-96%) in younger patients (aged <5 years at HCT). For older patients (aged >5 years), the OS was significantly lower in T-depleted grafts (55%; 23%-78%) compared with T-replete grafts (87%; 68%-95%) (P = .03). Grade III to IV acute graft-versus-host disease was observed in 8% of T-replete marrow, 7% of T-replete PBSC, 14% of T-replete cord blood, and 2% of T-depleted PBSC (P = .73). Higher incidence of viremia (P < .001) and delayed CD3 reconstitution (P = .003) were observed after T-depleted graft HCT. These data indicate that mismatched donor transplant after TCRαβ/CD19 depletion represents an excellent alternative for younger children with IEI in need of an allograft.

T-Cell-Replete Versus ex vivo T-Cell-Depleted Haploidentical Haematopoietic Stem Cell Transplantation in Children With Acute Lymphoblastic Leukaemia and Other Haematological Malignancies.

Allogeneic haematopoietic stem cell transplantation (HSCT) represents a potentially curative option for children with high-risk or refractory/relapsed leukaemias. Traditional donor hierarchy favours a human leukocyte antigen (HLA)-matched sibling donor (MSD) over an HLA-matched unrelated donor (MUD), followed by alternative donors such as haploidentical donors or unrelated cord blood. However, haploidentical HSCT (hHSCT) may be entailed with significant advantages: besides a potentially increased graft-vs.-leukaemia effect, the immediate availability of a relative as well as the possibility of a second donation for additional cellular therapies may impact on outcome. The key question in hHSCT is how, and how deeply, to deplete donor T-cells. More T cells in the graft confer faster immune reconstitution with consecutively lower infection rates, however, greater numbers of T-cells might be associated with higher rates of graft-vs.-host disease (GvHD). Two different methods for reduction of alloreactivity have been established: in vivo T-cell suppression and ex vivo T-cell depletion (TCD). Ex vivo TCD of the graft uses either positive selection or negative depletion of graft cells before infusion. In contrast, T-cell-repleted grafts consisting of non-manipulated bone marrow or peripheral blood grafts require intense in vivo GvHD prophylaxis. There are two major T-cell replete protocols: one is based on post-transplantation cyclophosphamide (PTCy), while the other is based on anti-thymocyte globulin (ATG; Beijing protocol). Published data do not show an unequivocal benefit for one of these three platforms in terms of overall survival, non-relapse mortality or disease recurrence. In this review, we discuss the pros and cons of these three different approaches to hHSCT with an emphasis on the significance of the existing data for children with acute lymphoblastic leukaemia.

Effect of Donor Characteristics on T Cell Replete Haploidentical Stem Cell Transplantation: Over the Last 10 Years at a Single Institution

Background: Owing in part to the development of T-cell-replete strategies such as PTCy based graft versus host disease (GVHD) prophylaxis, colony-stimulating factor (G-CSF), and anti-thymocyte globulin (ATG) approach, it increases donor availability for almost all patients in need, which was associated with survival outcomes comparable to those of human leukocyte antigen (HLA)-matched hematopoietic stem cell transplantation (HSCT). So there has been a rapid expansion in Haploidentical stem cell transplantation (haplo-SCT). One of the most complex issues with haplo-SCT is donor selection, given that multiple haploidentical donors are often available for a given recipient.Methods: To develop evidence-based guidance for donor selection in the setting of ATG-based T-cell-replete haplo-SCT, we performed a prospective cohort study of 512 consecutive hematologic malignancies patients accepting haplo-SCTs at a single center to determine which donor variables were most important in favoring transplant outcomes when applied in the uniform G-CSF mobilized peripheral blood stem cell (PBSC) source, myeloablative conditioning regimen, and low-dose ATG based GVHD prophylaxis.Results: In our low dosage ATG based T-cell replete Haplo-SCT and PBSC donor source protocol, increasing donor age was the only donor characteristic that influenced overall survival (OS). Donor age increasing by five years was associated with poorer OS (HR, 1.08 [1.00, 1.17; P =0.044]). Female donor to the male recipient, ABO incompatibility, increasing patient age, and HLA genotype did not influence OS in multivariable analyses. Female donor to the male recipient was significantly associated with higher non-relapse mortality (NRM) (HR, 2.05 [1.23, 3.41; P =0.006]). Increasing donor age by five years had the trend of higher NRM (HR, 1.11 [0.98, 1.25; P =0.094]). ABO incompatibility, increasing patient age, HLA genotype, disease, disease risk index (DRI) did not impact NRM. No donor-related variables had a significant influence on Relapse. Besides, increasing donor age (per 5 yr) had a higher risk for grade 3 to 4 acute GVHD (aGVHD) (HR, 1.17 [1.05, 1.30; P= 0.005]), female donor to the male recipient was associated with higher risk for grade 2 to 4 aGVHD (HR, 1.50 [1.06, 2.11; P= 0.022]). Sibling donors had superior OS(79.3% vs 63.8%, P=0.003), Disease-free survival (DFS) (76.9% vs 62.2%, P=0.009), and NRM (5.1% vs 13.8%, P=0.048) than parental donors in the group of patients age <35. However, sibling donors had higher NRM (32.4% vs. 11.1%, P=0.008) than offspring donors in the group of patients age ³35. Maternal donors appeared higher risk of developing cumulative incidence of 100-day grade 2 to 4 aGVHD than paternal donors (HR, 1.95 [1.25, 3.03; P= 0.003]). But no significant differences of OS, DFS, NRM, Relapse, 3 to 4 aGVHD, and chronic GVHD (cGVHD) were observed between maternal and paternal donors.Conclusion: We found that younger donors were associated with superior OS, lower NRM and lower risk for the cumulative incidence of grade 3 to 4 aGVHD, a female donor to a male recipient was associated with higher NRM and higher risk for the cumulative incidence of grade 2 to 4 aGVHD, sibling donors had superior outcomes than parental donors in younger recipients (yr<35), whereas offspring donors had superior results than sibling donors in older recipients (yr³35). Paternal donors are preferred than maternal donors. ABO incompatibility didn't affect transplant outcomes as PBSC derived grafts used. These data strongly suggest that a younger donor, usually a young sibling or a young offspring, generally avoid female donor to a male recipient, should be preferred when multiple haplo donors are available. DisclosuresNo relevant conflicts of interest to declare.

Alphabeta T and B-Cell Depleted HLA-Haploidentical Hematopoietic Stem Cell Transplantation (TBdepl-haploHSCT) in Children with Myelodysplastic Syndromes

Background: Pediatric myelodysplastic syndromes (MDSs) are a heterogeneous group of clonal disorders, accounting for less than 5% of childhood hematologic malignancies. Usual indications to HSCT are: MDSs with excess of blasts, MDSs secondary to previously administered chemoradiotherapy and RCC associated with monosomy 7, complex karyotype, severe neutropenia, or erythrocyte/platelet transfusion dependence [Locatelli & Strahm, Blood 2018]. We previously demonstrated that TBdepl-haploHSCT is a suitable option for children with acute leukemia, with outcomes comparable to those reported in studies using either an HLA-identical sibling or an unrelated volunteer as donor. Here we present the results of this approach in children with MDSs.Patients and methods: Between February 2013 and February 2021, 23 children with MDSs other than juvenile myelomonocytic leukemia received TBdepl-haploHSCT from an HLA-partially matched relative at Ospedale Pediatrico Bambino Gesù, Rome, Italy or at IRCCS Fondazione Policlinico San Matteo, Pavia, Italy as part of a prospective study (#NCT01810120). All patients were prepared to the allograft using a fully-myeloablative conditioning regimen including a combination of cytotoxic drugs and/or total body irradiation (TBI). Anti-T-lymphocyte globulin (ATLG) was used before transplantation (12 mg/kg total dose, from days -5 to day -3) to modulate bi-directional donor/recipient alloreactivity. Rituximab (200 mg/sqm) was administered on day -1 to prevent post-transplantation EBV-induced lymphoproliferative disorders (PTLD). No patient received any post-transplant pharmacological GvHD prophylaxis.Results: Characteristics of patients enrolled in the study are shown in Table 1 (which reports also donor and graft characteristics). Median follow-up of surviving patients is 4.2 years (range: 0.5 - 8.5 years). Seventeen children were affected by refractory cytopenia of childhood (RCC) (2 cases occurring in the context of inherited bone marrow failure syndromes: one had GATA2 deficiency and the other SAMD9L mutation), while 1 and 5 were affected by MDS with excess of blasts 1 (EB1) and EB2 (one had GATA2 deficiency), respectively. Median time to neutrophil and platelet recovery was 14 (range 10-19) and 11 (range 9-14) days, respectively, with four patients (3 with RCC and 1 with EB2) experiencing primary graft failure, the cumulative incidence of this complication being 17.3% (95% CI 0.3-31.5). All these 4 patients were rescued with a second TBdepl-haploHSCT from the same or the other parent. Cumulative incidence of grade II-III acute GvHD was 11.4% (95% CI 0-25.2). One patient developed skin and gut GvHD after the second TBdepl-haploHSCT, while for all other patients skin was the sole organ involved; no case of grade IV GvHD was observed. One patient developed moderate chronic GvHD [cumulative incidence 5.2% (95% CI 0-14.8)], which completely resolved with low-dose steroids and ruxolitinib. Notably, no patient died for transplant-related complications. Six patients experienced CMV, 2 HHV-6 and 1 adenoviral infection/reactivation; one patient developed lung aspergillosis, which resolved with specific treatment. One patient affected by EB2, not in remission at time of transplant, relapsed 27 months after HSCT, the 5-year cumulative incidence of relapse being 7.1% (95% CI, 0-19.7); she eventually died after failing a second HSCT. The 5-year probability of overall and event-free survival were 92.3% (95% CI 56.6 -98.9) and 76.3% (95% CI 51.3-89.6) (Figure 1A and B), respectively. Five-year disease-free-survival was 90% (95% CI 47.3-98.5). Because of the low number of events, no prognostic factor related to OS and EFS was found. In particular, the MDS variant did not influence the patient's outcome. The median CD3+ cell count on day +30, +90, +180 and +360 were 113, 171, 558 and 1307/mcl, respectively.Conclusions: These data indicate that TBdepl-haploHSCT is a safe and effective transplant option also in children with MDS. Indeed, the low risk of both non-relapse mortality and acute/chronic GvHD makes this approach particularly attractive in the pediatric setting. Moreover, this haplo strategy compares favorably with T-cell replete approaches [Suo et al., 2020]. [Display omitted] DisclosuresMerli: JAZZ: Consultancy; SOBI: Consultancy. Locatelli: Miltenyl: Honoraria; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Bellicum: Consultancy, Membership on an entity's Board of Directors or advisory committees; bluebird bio, Inc.: Consultancy; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees.

Letermovir Is Effective for Prevention of Cytomegalovirus Reactivation in HLA-Haploidentical Peripheral Blood Stem Cell Transplantation with Post-Transplant Cyclophosphamide

[Introduction] Cytomegalovirus (CMV) infection is a common viral infection in recipients of allogeneic hematopoietic stem cell transplantation (allo-SCT). Early CMV reactivation after allo-SCT is associated with worse non-relapse mortality (NRM) and overall survival (OS). Recently, T-cell replete HLA-haploidentical SCT using post-transplant cyclophosphamide (PTCy-haplo SCT) has been developed and spread rapidly worldwide. Rationale of this strategy is assumed to be selective and cytotoxic depletion of alloreactive T cells which are responsible for graft-versus-host disease (GVHD), while preserving non-alloreactive T cells which can contribute to fight infections. However, recent studies showed that PTCy-haplo SCT was associated with the increased incidence of CMV infection. Letermovir (LET), a novel anti-CMV agent, which inhibits the CMV DNA terminase complex, was approved for the prevention of CMV reactivation in allo-SCT recipients in 2018 in some countries including Japan based on the result of a phase 3 trial. Our facility performs LET prophylaxis in allo-SCT recipient if either donor or recipient is seropositive CMV. Although LET is effective for the prevention of CMV reactivation in allo-SCT recipients, the clinical effectiveness of LET prophylaxis in PTCy-haplo SCT is not well elucidated. Based on these things, we retrospectively evaluated the efficacy of LET prophylaxis in PTCy-haplo SCT.[Methods] We retrospectively analyzed consecutive 99 recipients who received PTCy-haplo SCT at Hokkaido University Hospital from March 2013 to March 2021. We compared the cumulative incidence of CMV reactivation between the LET prophylaxis group (LET group, 33 patients) and LET non-prophylaxis group (non-LET group, 66 patients). LET was initiated on the day 0 at a dosage of 480mg daily. All patients were monitored for CMV reactivation by using the anti-CMV pp65 monoclonal antibody HRP-C7 assay at least once a week from the time of engraftment. CMV reactivation was defined as the detection of CMV antigen positive cells per 50000 white blood cells, whereas CMV disease was defined by organ dysfunction attributable to CMV.[Results] As baseline patient's characteristics were summarized in Table1, there were no difference between LET and non-LET group in terms of age, sex, underlying disease, disease risk at transplantation, prior transplantation, conditioning intensity, and CMV serostatus. All patients received peripheral blood stem cell transplantation. GVHD prophylaxis consisted of Cy (40-50 mg/kg on day 3 and 4), tacrolimus (from day 5), and mycophenolate mofetil (from day 5). The cumulative incidence of CMV reactivation at 150 days after transplantation in LET group was significantly lower than that in non-LET group (30.3% versus 69.7%; P <.001, Figure1A). Importantly, CMV disease were occurred in three patients without LET prophylaxis (gastritis, enteritis, and retinitis), but not in the patients with LET prophylaxis. The cumulative incidence of NRM at 1 year was similar between the patients with and without LET prophylaxis (17.6% versus 9.2%; P=0.366, Figure1B), as was OS at 1 year (71.5% versus 69.4%; P=0.801, Figure1C). Neutrophil engraftment was achieved in 32 patients (97%) at a median of 15 days in LET group and 64 patients (97%) at a median of 14.5 days in non-LET group (P=0.243). Furthermore, platelet engraftment was achieved in 26 patients (79%) at a median of 34 days in LET group and 57 patients (86%) at a median of 31 days in non-LET group (P=0.282). These findings suggest that LET does not affect engraftment. Interestingly, the length of hospitalization in the LET group was significantly shorter than that in non-LET group (the median, 59.5 days versus 71 days; P=0.0488), suggesting that LET suppresses CMV reactivation leading to early discharge.[Conclusion] To our best knowledge, this is the largest retrospective study about the efficacy of LET in PTCy-Haplo SCT. LET is effective for prevention of CMV reactivation in PTCy-haplo SCT. Further studies focused on the long term effect of LET prophylaxis in PTCy-haplo SCT, such as the incidence of relapse and chronic GVHD, is warranted. [Display omitted] DisclosuresNakagawa: AbbVie GK: Research Funding; Takeda Pharmaceutical Company: Research Funding. Teshima: Gentium/Jazz Pharmaceuticals: Consultancy; Merck Sharp & Dohme: Membership on an entity's Board of Directors or advisory committees; Pfizer Inc.: Honoraria; Nippon Shinyaku Co., Ltd.: Research Funding; CHUGAI PHARMACEUTICAL CO., LTD.: Research Funding; Fuji pharma CO.,Ltd: Research Funding; Takeda Pharmaceutical Company: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis International AG: Membership on an entity's Board of Directors or advisory committees, Other, Research Funding; TEIJIN PHARMA Limited: Research Funding; Astellas Pharma Inc.: Research Funding; Bristol Myers Squibb: Honoraria; Janssen Pharmaceutical K.K.: Other; Kyowa Kirin Co.,Ltd.: Honoraria, Research Funding; Sanofi S.A.: Research Funding.

Bacterial Prophylaxis in Patients with Acute Gvhd; Who Is at Risk for Bloodstream Infections?

Consensus on the need for antibacterial prophylaxis in patients with acute graft-vs.-host disease (AGVHD) has not been established with practices varying across centers. The aim of this study was to determine the risk for bacterial bloodstream infections (BSI) from neutrophil engraftment through day 100 post-hematopoietic cell transplant (HCT) in patients with AGVHD and whether organ involvement and severity impact this risk.Methods: The cause-specific hazards for developing BSI after-engraftment by day 100 was compared between patients with and without grade II-IV AGVHD by treating AGVHD as a time-dependent variable.Results: A total of 4064 adult patients who underwent a matched related, matched unrelated, or mismatched unrelated T-cell replete, marrow or blood HCT for AML, ALL, or MDS from 2008-2012 within the CIBMTR registry were analyzed. Grade II-IV AGVHD occurred in 1607 (39.5%) patients, 62% of which had lower GI involvement and 70% had skin involvement. In multivariate analysis (MVA), the hazard ratio for BSI was 1.83 (95% CI: 1.53-2.18; p<0.0001) in those with grade II-IV AGVHD vs. those with grade 0/I. Patients with grade III/IV AGVHD had the highest risk for BSI (HR 2.45; 95% CI 1.99-3.0; p <0.0001) with a borderline risk for those with grade II (HR 1.35; 95% CI 1.03-1.77; p=0.0275). Patients with lower GI involvement had higher risk when compared to those with grade II-IV AGVHD without GI involvement (HR 1.54; 95% CI 1.17-2.02; p=0.0019) with risk being incrementally higher with each lower GI stage (1-4). Patients with isolated stage 3 skin AGVHD (n=214) did not have significantly higher risk for BSI (HR 1.25; 95% CI 0.82-1.91; p= 0.3); however, those with isolated stage 4 (n=27) had higher risk (HR 3.30; 95% CI 1.74-6.27; p=0.0003) when compared to those with grade 0/I AGVHD. In MVA, patients who developed a BSI between engraftment and day 100 post-transplant had worse survival (HR 1.64, 95% CI 1.43-1.87; p <0.001) and higher non-relapse mortality (NRM), HR 2.22; 95% CI 1.91-2.59; p <0.001). When evaluating type of infections: Gram negative bacteremia was seen in a higher proportion of patients (7%) with lower GI involvement vs. 4% in those without lower GI involvement and 4% in those with grade 0/1 AGVHD (p <0.01). Staphylococcus aureus bacteremia was seen in a higher proportion of patients with grade 2-4 AGVHD with skin involvement (4%) vs. 2% in those without skin involvement and 1% in those with grade 0/1 AGVHD (p <0.01).Conclusions: Patients with grade II-IV AGVHD are at higher risk for BSI compared to patients with grade I AGVHD or no AGVHD. Those with lower GI involvement or with stage 4 skin AGVHD are at highest risk. The development of BSI is associated with worse survival and higher NRM. Strategies for the lowering the risk for BSI in high risk patients are needed. [Display omitted] DisclosuresGulbis: EUSA Pharma: Other: Advisory board participation. Kitko: Vanderbilt University Medical Center: Current Employment; Co-investigator on two NIH grants as part of the cGVHD consortium: Research Funding; Horizon: Membership on an entity's Board of Directors or advisory committees; PER: Other: PER - CME educational talks about GVHD. MacMillan: Equilium: Other: DSMB member; Incyte: Consultancy; Jazz Pharmaceuticals: Consultancy. Pidala: CTI Biopharma: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Clinical trial support; Syndax: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Clinical trial support; Regeneron: Consultancy; Pharmacyclics: Other: Clinical trial support, Research Funding; Incyte: Consultancy; Takeda: Other: Clinical trail support; Novartis: Other: Clinical trail support; BMS: Other: Clinical trial support, Research Funding; Johnson and Johnson: Other; Jannssen: Other: Clinical trial support; BMS: Other; AbbVie: Other. Riches: Jazz Pharmaceuticals: Other: Payment; BioIntelect: Membership on an entity's Board of Directors or advisory committees; ATARA Biotherapeutics: Other: Payment. Arora: Kadmom: Research Funding; Syndax: Research Funding; Pharmacyclics: Research Funding.

Selective Targeting of Immune Modulatory Proteins to Mitigate Fibrosis and Inflammation in Sclerodermatous Graft-Vs-Host Disease

Chronic graft-vs-host disease (cGVHD) is a major obstacle to the success of allogeneic hematopoietic stem cell transplantation (HCT) in patients. This debilitating condition is characterized by chronic inflammation, cell-mediated and humoral immunity, and ultimately tissue fibrosis. There is currently little or no understanding of the molecular pathogenesis of chronic cGVHD resulting in poor effective treatment strategies. Sclerodermatous GVHD (sclGVHD) is one of the more severe forms of cGVHD associated with poor prognosis and low sensitivity to immune suppressive therapy.Methods: To address the current gap in knowledge pertaining to the underlying pathophysiology of sclGVHD we used single cell RNA sequencing analyses on fresh patient biopsy specimens. In vivo studies were carried out by sub lethal irradiation of BALB.k recipients which underwent HCT from miAg-mismatched AKR/J donors. Recipient sclerodermatous-tissues were analyzed using FACS, IHC and IF staining. Human studies were conducted on (i) Primary samples from patients with severe sclGVHD using tissue microarrays (TMA) by Immuno-histofluorescence (IHF) and IF. (ii) Dermal fibroblasts from sclGVHD samples were subjected to ATACseq and ChiPseq CRISPR-Cas9 JUN deletion. (iii) Also, dermal fibroblasts from human scl-GVHD were implanted under the kidney capsule of NSG mice to study the effects of inhibiting pro-fibrotic pathways in vivo.Results: We show for the first time that in a mouse model of sclGVHD (male), recipients of female T-cell replete grafts developed severe scleroderma with massive skin thickening and collagen deposition. Fibroblasts strongly expressed JUN, which is part of AP-1, a transcription factor involved in the acute phase response that regulates gene expression in response to stimuli from cytokines, growth factors and pathogens. We have previously demonstrated JUN as a key player in the molecular pathogenesis of other fibrotic diseases (Wernig G et al. PNAS 2017, Cui et al. Nature comm. 2020, Lerbs et al. JCI i 2020). Likewise, CD47, an immune checkpoint protein that prevents removal of Mϕ, was strongly co-expressed in fibroblasts in sclGVHD - but not in the control mice (Fig A+B). Here we show that (i) In humans, (n = 45 sclGVHD patients), there is a strong expression and activation of JUN and CD47 in dermal fibroblasts which was not observed in control samples. Mixed inflammatory infiltrates were dominated by Mϕ and granulocytes. (ii) Isolated primary fibroblasts from fresh human sclGVHD skin biopsies analyzed for chromatin accessibility across the genome by ATAC-seq showed wide open accessibility to the JUN promoter, IL-6 promoter and CD47 enhancer and promoter indicating that they play a critical role in regulating the pathogenesis of sclGVHD. In contrast, normal fibroblasts displayed only minimal accessibility to the JUN promoter. We further validated our data using CRISPR-Cas9 knock-down studies on sclGVHD fibroblasts and show that the IL-6 promoter, enhancer and promoter of CD47 are regulated by JUN, with JUN deletion resulting in significant decrease in the promoter binding accessibility to IL-6 and CD47 (Fig C). Further, JUN activity appears to regulate key members of the Hh signaling pathway (GLI1, PTCH1 and PTCH2), as their chromatin accessibility was decreased with JUN deletion. These correlative findings were confirmed by JUN ChIP seq, an assay that identifies binding sites of DNA-associated proteins. (iii) To test our findings in vivo we established xenograft models of primary human sclGVHD by implanting cells under the kidney capsule of NSG mice.All treatments (except placebo) resulted in decreased fibrosis (Fig D), presumably by blocking the activation of JUN (pJUN) and its profibrotic downstream pathway members IL-6 and pSTAT3, as assessed by phospho flow. Conclusion: In our studies we demonstrate that in established SclGVHD, combinatorial therapy consisting of anti-CD47 antibody together with IL6 blockade has the highest potential to translate into a therapeutic intervention given its ability to be more effective than currently used antifibrotic and anti-inflammatory agents in clinic. The findings from our study are significant because we show an important mechanism underlying SclGVHD onset, identify a novel genetic signature that can be targeted, describe a new mouse model and a clinical assay that has a high throughput readout and suggest a treatment regimen for patients. [Display omitted] DisclosuresArai: Magenta Therapeutics: Research Funding. Shizuru: Forty seven Inc: Other: Inventor on a patent licenses by Forty Seven. Forty seven was acquired by Gilead in 2020; Jasper Therapeutics, Inc.: Current holder of stock options in a privately-held company, Membership on an entity's Board of Directors or advisory committees, Other: Chair of scientific advisory board.

Haploidentical Versus Cord Blood Stem Cell Transplantation As the Second Transplant for Relapsed Acute Myeloid Leukemia Patients after the First Stem Cell Transplantation

Haploidentical Versus Cord Blood Stem Cell Transplantation As the Second Transplant for Relapsed Acute Myeloid Leukemia Patients after the First Stem Cell Transplantation

Effectiveness of T-Cell Replete Haploidentical Hematopoietic Stem Cell Transplantation for Refractory/Relapsed B Cell Acute Lymphoblastic Leukemia in Children and Adolescents.

Background: The prognosis of refractory/relapsed B-cell precursor acute lymphoblastic leukemia (BCP-ALL) remains dismal owing to acquired resistance to chemotherapeutic agents. This study aimed to evaluate the efficacy of T-cell replete HLA haploidentical hematopoietic stem cell transplantation (TCR-haplo-HSCT) for pediatric refractory/relapsed BCP-ALL (RR-BCP-ALL).Methods: Nineteen pediatric patients with RR-BCP-ALL underwent TCR-haplo-HSCT between 2010 and 2019 at the Fukushima Medical University Hospital. The disease status at TCR-haplo-HSCT included complete remission (CR) in eight patients and non-CR with active disease in 11 patients. Total body irradiation-based, busulfan-based, and reduced-intensity conditioning regimens were employed in 11, 6, and 2 patients, respectively. Low-dose anti-thymocyte globulin (thymoglobulin, 2.5 mg/kg) was used in all patients. Graft-vs.-host disease (GVHD) prophylaxis was administered with tacrolimus, methotrexate, and prednisolone.Results: All patients received peripheral blood stem cells as the stem cell source. The HLA disparities in graft vs. host directions were 2/8 in one, 3/8 in five, and 4/8 in 13 patients. Among 18 patients who achieved primary engraftment, acute GVHD occurred in all 18 evaluable patients (grade II, 9; grade III, 8; grade IV, 1), and chronic GVHD was observed in 10 out of 15 evaluable patients. Three patients died because of transplant-related mortality. The 3-year overall survival (OS) and leukemia-free survival rates were 57.4 and 42.1%, respectively. Compared to patients older than 10 years in age (N = 10), those younger than 10 years in age (N = 9) showed an excellent OS rate (3-year OS rate: patients < 10 years old, 100%; patients > 10 years old, 20% [95% confidence interval, 3.1–47.5]; p = 0.002).Conclusions: We suggest that TCR haplo-HSCT with low-dose ATG conditioning has the potential to improve the transplantation outcomes in patients with RR-BCP.

Activation status dictates the function of unlicensed natural killer cells in mice and humans

Natural killer (NK) cells are involved in innate defense against viral infection and cancer. NK cells can be divided into subsets based on the ability of different receptors to bind to major histocompatibility (MHC) class 1 molecules, resulting in differential responses upon activation in a process called “licensing” or “arming.” NK cells expressing receptors that bind self-MHC are considered licensed due to an augmented effector lytic function capability compared with unlicensed subsets. However, we demonstrated that unlicensed NK subsets instead positively regulate the adaptive T-cell response during viral infections that are related to localization and cytokine production. In this study, the differential effects of the two types of NK subsets were contingent on the environment in viral infection and hematopoietic stem cell transplantation (HSCT) models. Infection of mice with high-dose (HD) murine cytomegalovirus (MCMC) led to a loss of licensing-associated differences, as compared with mice with low-dose (LD) infection: the unlicensed NK subset no longer localized in lymph nodes (LNs), but instead remained at the site of infection. Similarly, the patterns observed during HD infection paralleled the phenotypes of both human and mouse NK cells in an HSCT setting where NK cells exhibit an activated phenotype. However, in contrast to the effects of subset depletion in T-cell replete models, the licensed NK cell subsets still dominated antiviral responses after HSCT. Overall, our results highlight the intricate tuning of NK cells and how it affects overall immune responses with regard to licensing patterns and their dependency on the level of stimulation and activation status.

CT-255: Progressive Substitution of Post-Transplant Cyclophosphamide with Bendamustine as GVHD Prophylaxis Reduces GVHD while Preserving GVL

Context Post-transplant cyclophosphamide (PTCy) is approved in haploidentical stem cell transplant setting. However, disease relapse and CMV or BK/JC viral reactivation veno-occlusive disease of the liver (VOD) remains a major challenge with the use of PTCy. Progressive substitution of PTCy with bendamustine (PT-BEN) may be a suitable option as evidenced by murine models. Objective To compare the outcomes for patients receiving PTCy with PT-BEN compared to historical cohorts receiving PTCy alone. Design This is a single arm, retrospective and prospective, single centre study in which all the patients undergoing allogeneic stem cell transplantation with a T-cell replete graft were recruited. Patients or Other Participants All patients received T-cell replete stem cells followed by PTCy 50mg/kg on day +3 and bendamustine 90mg/m2 on day +4. Calcineurin inhibitors with mycophenolate mofetil was given. Main Outcomes Measures The main outcome measures included myeloid and platelet engraftment, viral reactivations, disease status, incidence and severity of acute GVHD, incidence of veno-occlusive disease until D+28 post-transplant. Results Five patients have been recruited, all males, median age being 17 years. Two patients had relapsed/refractory (R/R) ALL after 2 lines of therapy, 1 had R/R AML, 1 had very severe aplastic anemia, 1 was high risk ALL in CR1. 3 fully matched a sibling, whereas 2 had haplomatched donors from mother. All the donors and recipients had seropositivity for CMV. Two patients received FluCyTBI, 2 received FluCyATG, and 1 received FluTreoTBI as conditioning. One patient expired due to neutropenic septic shock on D+8 and has been excluded from analysis. The median day for myeloid engraftment was 12 and platelet engraftment was 14. No patient had VOD, thrombotic microangiopathy, or culture positive bacterial infections. All the patients were in CR, 100% donor chimerism at D+28. Three patients had CMV reactivation, controlled with antivirals. One patient had Gr1 skin GVH and 1 patient had Gr1 gut GVH managed with topical and oral steroids respectively. Conclusions Progressive substitution of PT-BEN may ameliorate the toxicities associated with PT-Cy in post-transplant setting.