HLA-haploidentical Hematopoietic Stem Cell Research Articles

Incremental Eligibility Criteria for the BMT CTN 1507 Haploidentical Trial in Children with Sickle Cell Disease

The Blood and Marrow Transplant Clinical Trials Network (BMT CTN) 1507 leadership and the Data Safety Monitoring Board (DSMB) established incremental entry criteria for children aged 5-14.99 years with sickle cell disease (SCD) enrolling on a phase 2 trial of HLA-haploidentical hematopoietic stem cell transplantation (clinicaltrials.gov #NCT032635590). First, enrollment was limited to overt stroke in the first 10 participants (Stage 4). Subsequently, the DSMB reviewed the interim results and expanded eligibility to include children with silent cerebral infarcts or abnormal transcranial Doppler velocities with magnetic resonance angiography-defined cerebral vasculopathy (Stage 3). A third cohort was enrolled after the DSMB reviewed the clinical outcomes in these cumulative initial enrollments (n=18). Additions to the entry criteria included non-neurologic morbidities (Stage 2). Eligibility criteria included: a) life-threatening acute chest syndrome requiring exchange transfusion, b) right heart catheterization confirmed pulmonary hypertension, c) persistent systemic hypertension despite maximum medical therapy, d) acute pain despite maximum medical therapy in the absence of psychosocial factors and unmanaged asthma after adjudication, or e) 2 major priapism episodes in 12 months or 3 in 24 months. Children with SCD who did not meet the criteria for stages 4, 3, and 2 were not eligible. For the first time, we introduce a staged strategy to eligibility for a curative therapy trial for children with SCD concordant with 45 CFR § 46.405(b). The research governance-mandated eligibility strategy used within the BMT CTN 1507 phase 2 study may apply to future pediatric SCD curative therapy trials.

Prediction model for EBV infection following HLA haploidentical matched hematopoietic stem cell transplantation

AimsAllogeneic hematopoietic stem cell transplantation (allo-HSCT) is an effective treatment for hematological malignancies. However, viral infections, particularly EBV infection, frequently occur following allo-HSCT and can result in multi-tissue and organ damage. Due to the lack of effective antiviral drugs, these infections can even progress to post-transplant lymphoproliferative disorders (PTLD), thereby impacting the prognosis. In light of this, our objective is to develop a prediction model for EBV infection following allo-HSCT.MethodsA total of 466 patients who underwent haploidentical hematopoietic stem cell transplantation (haplo-HSCT) between September 2019 and December 2020 were included in this study. The patients were divided into a development cohort and a validation cohort based on the timing of their transplantation. Our aim was to develop and validate a grading scale using these cohorts to predict the risk of EBV infection within the first year after haplo-HSCT. Additionally, single-cell RNA sequencing (sc-RNAseq) data from the bone marrow of healthy donors were utilized to assess the impact of age on immune cells and viral infection.ResultsIn the multivariate logistic regression model, four predictors were retained: donor age, female-to-male transplant, graft MNC (mononuclear cell) dose, and CD8 dose. Based on these predictors, an EBV reactivation predicting score system was constructed. The scoring system demonstrated good calibration in both the derivation and validation cohorts, as confirmed by the Hosmer–Lemeshow test (p > 0.05). The scoring system also exhibited favorable discriminative ability, as indicated by the C statistics of 0.72 in the derivation cohort and 0.60 in the validation cohort. Furthermore, the clinical efficacy of the scoring system was evaluated using Kaplan–Meier curves based on risk ratings. The results showed significant differences in EBV reactivation rates between different risk groups, with p-values less than 0.001 in both the derivation and validation cohorts, indicating robust clinical utility. The analysis of sc-RNAseq data from the bone marrow of healthy donors revealed that older age had a profound impact on the quantity and quality of immune subsets. Functional enrichment analysis highlighted that older age was associated with a higher risk of infection. Specifically, CD8 + T cells from older individuals showed enrichment in the pathway of “viral carcinogenesis”, while older CD14 + monocytes exhibited enrichment in the pathway of "regulation of viral entry into host cell." These findings suggest that older age may contribute to an increased susceptibility to viral infections, as evidenced by the altered immune profiles observed in the sc-RNAseq data.ConclusionOverall, these results demonstrate the development and validation of an effective scoring system for predicting EBV reactivation after haplo-HSCT, and provide insights into the impact of age on immune subsets and viral infection susceptibility based on sc-RNAseq analysis of healthy donors' bone marrow.

Effect of Immunopeptidome Gap Caused By Recipient-Donor HLA Mismatch in Umbilical Cord Blood Transplantation and HLA-Haploidentical Hematopoietic Stem Cell Transplantation

Introduction The immune response by alloreactive T cells plays a crucial role in allogeneic hematopoietic stem cell transplantation (allo-HCT), causing not only graft-versus-leukemia but also harmful graft-versus-host disease (GVHD). Human leukocyte antigens (HLA), which are highly polymorphic and differ widely among individuals, are the key molecules that present antigens to T cells. This individual variation in antigen-presenting capacity, the immunopeptidome, is thought to be assessable as HLA evolutionary divergence (HED) between alleles. Several autoimmune diseases are explained by HED, and HED is reported to be associated with outcome in HLA-matched allo-HCT. Thus, HED can be a useful indicator of potential immune reactivity. HLA-mismatched allo-HCT, including umbilical cord blood transplantation and HLA-haploidentical allo-HCT (Haplo-HCT), has been increasing in recent years. The combination of HLA mismatch alleles varies from case to case, thus speculating that it causes individual differences in immune responses is easy. HLA mismatches have long been known to be associated with recurrence and GVHD, but a few risk assessment studies have focused on the immunopeptidome gap due to each HLA mismatch in individual cases. Aim This study aimed to examine the prognostic impact of the gap of immunopeptidome in mismatched HLA between recipient and donor in HLA-mismatched allo-HCT. Methods Allo-HCT was performed on 317 patients at our institution from 2006 to 2022. Of the 272 patients with evaluable allele data, 123 patients who underwent more than 3 alleles HLA-mismatched allo-HCT were retrospectively analyzed. Graft sources included cord blood (n=69, 56.1%) and haploidentical stem cells derived from peripheral blood (n=54, 43.9%). The median age at allo-HCT was 44 (range: 16-67) years and the median observation period was 545 [8-5551] days. Diagnoses include acute myeloid leukemia (n=61, 49.6%), acute lymphoblastic leukemia (n=24, 19.5%), malignant lymphoma (n=24, 19.5%), myelodysplastic syndrome (n=10, 8.1%), and others (n=4, 3.2%). The conditioning regimens was non-myeloablative (n=89, 72.4%). GVHD prophylaxis for 54 Haplo-HCT was anti-thymocyte globulin in 27 (50%) and post-transplant cyclophosphamide in 27 (50%) patients. The immunopeptidome gap of HLA mismatch (HED-mis) was evaluated between each mismatched allele. Grantham distance, which predicts amino acids from HLA allelic information and attempts to measure evolutionary distance based on the chemistry of the two amino acids, was used to calculate HED-mis. HLA allele data were drawn from clinical records. Tobias Lenz et al. produced the calculator program (https://hladiv.net/). HED-mis for each HLA class I: HLA-A (HED-mis A), HLA-B (HED-mis B), and HLA-C (HED-mis C) were calculated to evaluate acute and chronic GVHD (aGVHD and cGVHD), cumulative relapse rate (CIR), and overall survival (OS). Result The median [range] of HED-mis for 123 patients was 0.13 [0.00-13.70] for HED-mis A, 7.15 [0.00-11.25] for HED-mis B, and 4.19 [0.00-7.58] for HED-mis C. Patients were divided into 4 groups at each HED-miss value quartile: Q1, Q2, Q3, and Q4. Non-Q4 (Q1, Q2 and Q3 with the lower gaps) and Q4 with the highest gap of HED-mis A, B, and C were compared to confirm the effect of gap size. Univariate analysis revealed that non-Q4 of HED-mis B was associated with increased aGVHD 2-4 up to 100 days after all-HCT, compared to Q4 (non-Q4 49.8% vs. Q4 25.0%, p=0.017), but was unrelated to the incidence of severe aGVHD 3-4 ( p=0.58). Q4 of HED-mis A demonstrated no difference in aGVHD 2-4 compared to non-Q4 ( p=0.20) but was associated with increased severe aGVHD 3-4 (non-Q4 of 0.06% vs. Q4 of 20.7%, p=0.019, Table and Figure). Similarly, multivariate analysis adjusted for each HED-mis, graft, and conditioning revealed that Q4 of HED-mis A was a risk factor for severe aGVHD 3-4 (hazard ratio [HR]: 3.85, p=0.015), and non-Q4 of HED-mis B was a risk factor for developing aGVHD 2-4 (HR: 3.64, p=0.017). HED-mis C was unrelated to any grade aGVHD, but Q4 of HED-mis C may have a better 2-year CIR in univariate (20.3%, vs. in non-Q4, 46.2%, p=0.055) and multivariate analyses (HR: 0.34, p=0.051). No association was found with each HED gap and each quartile for cGVHD and OS. Conclusion Gaps in the immunopeptidome of HLA-mismatched alleles, especially in HLA-A, should be considered in severe aGVHD development during donor selection.

Efficacy and safety of allogeneic hematopoietic stem cell transplantation in the treatment of 28 patients with hepatitis-related aplastic anemia

Objective: To evaluate the efficacy and safety of HLA-haploidentical hematopoietic stem cell transplantation (allo-HSCT) for hepatitis-related aplastic anemia (HRAA) patients. Methods: Retrospective analysis was performed on hepatitis-associated aplastic anemia patients who received haplo-HSCT at our center between January 2012 and June 2022. October 30, 2022 was the final date of follow-up. Results: This study included 28 HRAA patients receiving allo-HSCT, including 18 males (64.3% ) and 10 females (35.7% ), with a median age of 25.5 (9-44) years. About 17 cases of severe aplastic anemia (SAA), 10 cases of very severe aplastic anemia (VSAA), and 1 case of transfusion-dependent aplastic anemia (TD-NSAA) were identified. Among 28 patients, 15 patients received haplo-HSCT, and 13 received MSD-HSCT. The 2-year overall survival (OS) rate, the 2-year failure-free survival (FFS) rate, the 2-year transplant-related mortality (TRM) rate, the 100-day grade Ⅱ-Ⅳ acute graft-versus-host disease (aGVHD) cumulative incidence rate, and the 2-year chronic graft-versus-host disease (cGVHD) cumulative incidence rate were 81.4%, 81.4% (95% CI 10.5% -20.6% ), 14.6% (95% CI 5.7% -34.3% ), 25.0% (95% CI 12.8% -45.4% ), and 4.2% (95% CI 0.6% -25.4% ), respectively. After transplantation, all patients had no significant liver function damage. Compared with the MSD-HSCT group, only the incidence of cytomegaloviremia was significantly higher in the haplo-HSCT group [60.0% (95% CI 35.2% -84.8% ) vs 7.7% (95% CI 0-22.2% ), P=0.004]. No statistically significant difference in the Epstein-Barr virus was found in the 2-year OS, 2-year FFS, 2-year TRM, and 100-day grade Ⅱ-Ⅳ aGVHD cumulative incidence rates and 2-year cGVHD cumulative incidence rate. Conclusion: Allo-HSCT is safe and effective for HRAA, and haplo-HSCT can be used as a safe and effective alternative for newly diagnosed HRAA patients who cannot obtain HLA-matched sibling donors.

Updated Analysis on the Outcomes of Children with Acute Leukemia (AL) Receiving an Alpha/Beta T and B-Cell Depleted HLA-Haploidentical Hematopoietic Stem Cell Transplantation (TBdepl-haploHSCT)

Background: We previously reported (Locatelli et al., Blood 2017) that TBdepl-haploHSCT is a suitable and effective option for children with AL lacking an HLA-compatible donor and/or needing an urgent allograft. This type of transplant is characterized by a low incidence of both acute and chronic graft-versus-host disease (GvHD) and by low non-relapse mortality (NRM), translating into survival outcomes comparable to those of patients transplanted from an HLA-compatible donor. Here we report an update on a cohort of 213 children with AL of our study, with a minimum follow-up of 180 days after the allograft. Patients and methods: Between October 2010 and January 2022, 213 children with AL received TBdepl-haploHSCT from an HLA-partially matched relative at Ospedale Pediatrico Bambino Gesù in Rome, Italy. All patients were in morphological complete remission (CR) and were prepared to TBdepl-haploHSCT using a fully-myeloablative conditioning regimen including a combination of total body irradiation (TBI) and/or cytotoxic drugs. All patients received also anti-T-lymphocyte globulin (ATLG) before transplantation (12 mg/kg total dose, from days -5 to day -3) to modulate bi-directional donor/recipient alloreactivity and rituximab (200 mg/sqm) on day -1 to prevent post-transplantation EBV-induced lymphoproliferative disorders (PTLD). No patient received any post-transplant pharmacological GvHD prophylaxis. Data were analyzed as of July 15, 2022. Results: Table 1 reports details on characteristics of patients included in the analysis. The median follow-up of surviving patients is 47.6 months (range: 6 months - 11.7 years). Two hundred and eight patients (98% of the total number) engrafted with a median time to neutrophil and platelet recovery of 13 (range 9-24) and 11 (range 7-23) days, respectively. Only 5 patients experienced graft failure; all were rescued with a second allograft. Eleven out of the 213 patients (5%) died of transplant-related complications (4 because of idiopathic pneumonia, 2 each because of disseminated adenovirus infection and thrombotic microangiopathy and 1 each of cardiac insufficiency, combined CMV/rhinovirus pneumonia and sepsis from Pseudomonas aeruginosa), the 5-year cumulative incidence of NRM being 5.2% (95% CI, 2.8-8.8). Forty-four patients relapsed at a median time of 192 days (range 56-1711) after HSCT, the 5-year cumulative incidence of relapse being 22.7% (95% CI, 16.9-29.2). Cumulative incidence of grade II-III acute GvHD was 14.7% (95% CI 10.6-20.3). Three patients and 1 developed gut and liver GvHD, respectively, while for all other patients skin was the sole organ involved. Fourteen out of the 193 patients at risk developed chronic GvHD, in all cases of limited severity, the cumulative incidence of this complication being 8.1% (95% CI 4.8-13.3). The 10-year probability of overall and leukemia-free survival (LFS) were 75.4 (95% CI 68.6-80.9) and 71.6% (95% CI 64.4-77.6), respectively. In univariate analysis, disease status at transplantation (CR1 vs CR2 vs CR>3), use of TBI during the preparative regimen and age at transplant above the median value (9.5 years) were associated with better patient's outcome, mainly because of a reduced incidence of relapse. Notably, among TBI-based regimens, the use of thiotepa and fludarabine was associated with an improved DFS as compared to other combinations (82.4% vs 63.9%, p=0.01). In a multivariable model for LFS including also gender and type of disease, only TBI (hazard ratio (HR) 0.38 (95% CI, 0.17-0.85, p=0.01) and disease status at HSCT (HR 1.72 (95% CI, 1.05-2.79, p=0.02) remained statistically significant. The 10-year GvHD/relapse-free survival was 65.1% (95% CI 57.7-71.4). The median CD3+ cell count on day +30, +90, +180 and +360 were 140, 185, 533 and 1058 /mcl, respectively. Conclusions: TBdepl-haploHSCT is becoming a widespread haplo platform for pediatric patients affected by both malignant and non-malignant disorders. This cohort of homogeneously treated patients, the largest reported so far with a median follow-up of almost 4 years, confirm once more the effectiveness and safety of this approach. Furthermore, this analysis identified subgroups of patients (e.g., those in CR>3) for whom post-transplant strategies aimed at reducing the risk of relapse (the main cause of treatment failure) are desirable. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Severe acute interstitial lung disease after BNT162b2 mRNA COVID-19 vaccination in a patient post HLA-haploidentical hematopoietic stem cell transplantation

Severe acute interstitial lung disease after BNT162b2 mRNA COVID-19 vaccination in a patient post HLA-haploidentical hematopoietic stem cell transplantation

Comparison of porcine ALG and rabbit ATG on outcomes of HLA-haploidentical hematopoietic stem cell transplantation for patients with acquired aplastic anemia

ObjectiveTo evaluate the efficacy and safety of P-ALG (porcine anti-lymphocyte globulin) and R-ATG (rabbit anti-thymocyte globulin) in the conditioning regime for patients with acquired aplastic anemia who underwent HLA-haploidentical hematopoietic stem cell transplantation (halpo-HSCT).MethodsA total of 91 patients with acquired aplastic anemia who received haplo-HSCT at our center between January 2014 and December 2020 were retrospectively reviewed. Twenty-eight patients were in the P-ALG group while sixty-three patients were in the R-ATG group.ResultsThe median time was 11 versus 13 days (P = 0.294) for myeloid engraftment and 12.5 versus 15 days (P = 0.465) for platelet engraftment in the P-ALG and R-ATG groups, respectively. There were no significant difference in 5-year overall survival (74.83% ± 8.24% vs 72.29% ± 6.26%, P = 0.830), GVHD-free, failure-free survival (71.05% ± 8.65% vs 62.71% ± 6.22%, P = 0.662), failure-free survival (74.83% ± 8.24% vs 66.09% ± 5.84%, P = 0.647) and transplantation-related mortality (25.17% ± 8.24% vs 26.29% ± 6.22%, P = 0.708) between the two groups. The incidence of aGVHD (acute graft versus host disease) (65.39% ± 9.33% vs 62.71% ± 6.30%, P = 0.653), II–IV aGVHD (38.46% ± 9.54% vs 35.64% ± 6.24%, P = 0.695), III–IV aGVHD (19.23% ± 7.73% vs 10.53% ± 4.07%, P = 0.291), cGVHD (chronic graft versus host disease) (22.22% ± 12.25% vs 22.31% ± 6.30%, P = 0.915), and moderate to severe cGVHD (5.56% ± 5.40% vs 9.28% ± 4.46%, P = 0.993) were not significantly different. Similar outcomes were observed between the P-ALG and R-ATG groups for severe bacterial infection (17.9% vs 25.4%, P = 0.431), invasive fungal diseases (3.6% vs 9.5%, P = 0.577) and graft rejection (0% vs 9.5%, P = 0.218). However, the incidence of cytomegalovirus infection and Epstein-Barr virus infection was significantly lower in the P-ALG group (46.4% vs 71.4%, P = 0.022; 3.6% vs 25.4%, P = 0.014).ConclusionThe efficacy and safety of P-ALG were similar with R-ATG in the setting of haplo-HSCT for patients with acquired aplastic anemia patients. P-ALG could be an alternative for R-ATG.

Post-Transplantation Cyclophosphamide After HLA Identical Compared to Haploidentical Donor Transplant in Acute Myeloid Leukemia: A Study on Behalf of GETH-TC

Post-transplantation cyclophosphamide (PTCY) effectively prevents graft-versus-host disease (GVHD) after unmanipulated HLA-haploidentical hematopoietic stem cell transplantation (HSCT) and achieves low rates of GVHD in HLA-identical transplantation. To compare the outcomes of haploidentical versus HLA identical HSCT in patients undergoing HSCT for acute myeloid leukemia (AML) using PTCY. We conducted a retrospective study of 229 patients undergoing first HSCT for AML using PTCY with additional immunosuppression, 99 from matched sibling or unrelated donor (MSD/MUD) performed in 3 hospitals and 130 from haploidentical donors (haplo group) performed in 20 hospitals within the Spanish Group of Hematopoietic Stem Cell Transplantation and Cellular Therapy. Peripheral blood stem cells were used as graft in 89% of patients; myeloablative conditioning was used in 56%. There were significantly more patients with active disease (5% versus 20%, P = .001), high/very high disease risk index (DRI) (32% versus 67%, P = .000) and prior auto-HSCT (2% versus 11%, P = .010) in the haplo group. Median follow-up was 27 and 62.5 months for MSD/MUD and haplo, respectively. At 2 years, no significant differences were observed in overall survival (OS) (72% versus 62%, P = .07), event-free survival (EFS) (70% versus 54%, P = .055), cumulative incidence of relapse (19% versus 25%, P = .13), non-relapse mortality (14% versus 19%, P = .145), and the composite endpoint of GVHD and relapse-free survival (49% versus 42%, P = .249). Multivariate analysis identified only age and active disease as significant risk factors for OS and EFS; reduced-intensity conditioning, high/very high DRI, and haplo donor were nearly statistically significant for these outcomes. Grade II-IV acute GVHD was lower in MSD/MUD (14% versus 47%, P = .000). Cumulative incidences of grade III-IV acute GVHD (4% versus 9%, P = .14) and moderate-severe chronic GVHD (22% versus 19%, P = .28) were similar. Limitations of our study include limited sample size, differences between haplo and MSD/MUD groups and heterogeneous additional immunosuppression and PTCY timing in MSD/MUD. The use of an HLA-identical donor with PTCY in patients with AML showed lower incidence of clinically significant grade II-IV acute GVHD compared to haplo donors. Further studies with larger sample sizes should be performed to establish a possible benefit of HLA-identical donor on survival.© 2022 American Society for Blood and Marrow Transplantation. Published by Elsevier Inc. All rights reserved.

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.

Post-Transplant Cyclophosphamide after HLA Identical Compared to Haploidentical Donor Transplant in Acute Myeloid Leukemia: A Study on Behalf of Geth-TC

Introduction: High-dose post transplant cyclophosphamide (PTCY) effectively prevents graft-versus-host disease (GVHD) after unmanipulated HLA-haploidentical hematopoietic stem cell transplant (HSCT) and offer low rates of GVHD in the setting of HLA identical transplant. The objective of our study was to compare the outcomes of haplo vs HLA identical HSCT in patients undergoing HSCT for acute myeloid leukemia (AML) using PTCY.Patients and methods: We conducted a retrospective study of 229 patients undergoing a first HSCT for AML using PTCY, 130 from an haploidentical donor between 2013 and 2018 (median follow up 62.5 months) and 99 from a matched sibling (MSD) (n=38) or unrelated donor (MUD) (n=61) (median follow up 27 months) between 2013 and 2019, in 20 centers in Spain. Last update of the cohort was performed in March 2021.Results: Baseline characteristics are summarized in Table 1. There were more patients with active disease at transplant (5% MSD/MUD vs. 20% haplo, p=0.001), high/very high DRI (32% vs. 67%, p=0.000) and prior autologous HSCT (2% vs. 11%, p=0.010) in the haplo group. Mobilized peripheral blood stem cells was the most frequent stem cell source in both groups. Most patients received myeloablative conditioning (55% vs. 64%, p=0.170). All Patients in the haplo group received PTCY days +3+4 followed by a calcineurin inhibitor (CNI) and MMF from +5. In the MSD/MUD group, 37% received both CNI+MMF, 33% only CNI and 30% PTCY with sirolimus+MMF (this group included only MUD donors). None of the patients received ATG. Cumulative incidence of neutrophil recovery at day 28 was 97% in both groups, with a median of 16 and 17 days respectively (p=0.948). Both 2-year overall survival (OS) (72% vs. 62%, p=0.07) and event-free survival (EFS) (70% vs. 54%, p=0.055) were higher in the MSD/MUD group, but the difference was not statistically significant (Figure 1). Multivariate analysis only identified age and pre-transplant status as independent risk factors for OS, and pre-transplant status for EFS. No differences were found in the cumulative incidence of relapse at 2 years (19% vs. 25%, p=0.13) and non-relapse mortality (14% vs. 19%, p=0.145). Cumulative incidence of grade II-IV acute GVHD was lower in MSD/MUD (14% vs. 47%, p=0.000, Figure 2), while III-IV aGVHD was similar (4% vs. 9%, p=0.14). Cumulative incidence of chronic GVHD and moderate-severe cGVHD at 2 years was similar for both groups (42% vs. 33% (p=0.051); 22% vs. 19% (p=0.28)). No differences were found in GRFS (48% vs. 46% (p=0.506)). Most frequent cause of death in the early post-transplant period was non-GVHD related infection in both groups.Conclusions: in our experience, PTCY as GVHD prophylaxis in both MSD/MUD and Haplo transplant in AML using mostly PBSC effectively prevents GVHD and offers similar NRM, relapse and survival rates. Poor control of the disease before transplant was the only factor affecting OS and EFS in this setting. Prospective studies are needed to confirm our results. [Display omitted] DisclosuresBailen: Pfizer, Kite-Gilead, Gilead: Honoraria. Guerreiro: Novartis, Gilead: Consultancy, Honoraria. Oarbeascoa: Gilead: Honoraria, Speakers Bureau. Kwon: Novartis, Celgene, Gilead, Pfizer: Consultancy, Honoraria.

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.

Salvage HLA-haploidentical hematopoietic stem cell transplantation with post-transplant cyclophosphamide for graft failure in non-malignant disorders

Graft failure requires urgent salvage HSCT, but there is no universally accepted approach for this situation. We investigated T-cell replete haploidentical HSCT with post-transplantation cyclophosphamide following serotherapy-based, radiation-free, reduced intensity conditioning in children with non-malignant disorders who had rejected their primary graft. Twelve patients with primary or secondary graft failure received T-cell replete bone marrow grafts from haploidentical donors and post-transplantation cyclophosphamide. The recommended conditioning regimen comprised rituximab 375 mg/m2, alemtuzumab 0.4 mg/kg, fludarabine 150 mg/m2, treosulfan 20–24 g/m2 and cyclophosphamide 29 mg/kg. After a median follow-up of 26 months (7–95), eleven of twelve patients (92%) are alive and well with complete donor chimerism in ten. Neutrophil and platelet engraftment were observed in all patients after a median of 18 days (15–61) and 39 days (15–191), respectively. Acute GVHD grade I was observed in 1/12 patients (8%) and mild chronic GVHD in 1/12 patients (8%). Viral reactivations and disease were frequent complications at 75% and 42%, respectively, but no death from infectious causes occurred. In summary, this retrospective analysis demonstrates that a post-transplantation cyclophosphamide-based HLA-haploidentical salvage HSCT after irradiation-free conditioning results in excellent engraftment and overall survival in children with non-malignant diseases.

Immune reconstitution after T-cell replete HLA haploidenticalhematopoietic stem celltransplantation using high-dose post-transplant cyclophosphamide.

As HLA haploidentical related donors are quickly available, HLA haploidentical hematopoietic stem cell transplantation (haploHSCT) using high-dose post-transplant cyclophosphamide (PTCy) is now widely used. Recent basic and clinical studies revealed the details of immune reconstitution after T-cell replete haploHSCT using PTCy. T cells and NK cells in the graft proliferate abundantly at day 3 post-haploHSCT, and the PTCy eliminates these proliferating cells. After ablation of proliferating mature cells, donor-derived NK cell reconstitution occurs after the second week; however, recovering NK cells remain functionally impaired for at least several months after haploHSCT. PTCy depletes proliferating cells, resulting in the preferential accumulation of Treg and CD4+ T cells, especially the memory stem T cell (TSCM) phenotype. TSCM capable of both self-renewal and differentiation into effector T cells may play an important role in the first month of immune reconstitution. Subsequently, de novo T cells progressively recover but their levels remain well below those of donor CD4+ T cells at the first year after haploHSCT. The phenotype of recovering T cells after HSCT is predominantly effector memory, whereas B cells are predominantly phenotypically naive throughout the first year after haploHSCT. B cell recovery depends on de novo generation and they are not detected until week 4 after haploHSCT. At week 5, recovering B cells mostly exhibit an unconventional transitional cell phenotype and the cell subset undergoes maturation. Recent advances in immune reconstitution have improved our understanding of the relationship between haploHSCT with PTCy and the clinical outcome.

Outcome of Children with Different Non-Malignant Disorders Given Alphabeta T and B-Cell Depleted HLA-Haploidentical Hematopoietic Stem Cell Transplantation (TBdepl-haploHSCT)

Background: allogeneic HSCT is the only potentially curative treatment for many non-malignant diseases (NMD), either inherited or acquired. However, many patients lack an HLA-matched donor (familiar (MFD) or unrelated (MUD)) and the outcome of children transplanted from an HLA-haploidentical relative (haplo) was historically inferior to that of transplants from a MFD or a MUD. We previously published promising results in a cohort of 23 children with NMD given this type of allograft (Bertaina et al., Blood 2014), demonstrating a low transplant-related mortality (TRM) and high cure rates. Here, we report the outcome of a large cohort of children affected by NMD who received a TBdepl-haploHSCT at our Center (NCT01810120). Patients and methods: Between February 2011 and June 2020, 80 consecutive patients affected by NMD received TBdepl-haploHSCT from an HLA-partially matched relative at Ospedale Pediatrico Bambino Gesù in Rome, Italy. Patients had many different disorders (see Table for details on patient- and transplant-related characteristics). Median time from diagnosis to transplant for the whole cohort was 12 months (range 1-177), while it was 2.5 months (range 1.3-11.2) for SCID patients. All patients, including children with SCID, received a conditioning regimen, which varied according to the original disease. Pre-transplant anti-thymocyte globulins (from day -4 to day -2) were given to modulate bi-directional donor/recipient alloreactivity, while rituximab (on day -1) was administered to prevent PTLD. Moreover, no post-transplant pharmacological GvHD prophylaxis was given. Results: fifty-eight patients (72.5%) achieved primary donor cell engraftment, while 3 patients experienced secondary graft failure (GF); the cumulative incidence of either primary or secondary GF was 27.8% (95% CI 17.2-37.0). Median time to neutrophil and platelet recovery was 13.5 (range 9-33) and 10 days (range 7-51), respectively. As expected, GF occurred more frequently in children with disorders known to be associated with an increased GF risk (i.e., HLH, thalassemia, SAA or osteopetrosis) (see also Figure 1A). Three children (4%) experiencing GF died because of infectious complications before retransplant. Sixteen of the 22 patients with either primary or secondary GF were successfully retransplanted (2 with a mismatched unrelated cord blood unit, the other having received a second TBdepl-haploHSCT from either the same donor or the other parent). Since 3 other patients died [all because of infectious complications, 2 due to disseminated adenovirus infection and 1 to CMV pneumonia)], TRM is 7.8% (95% CI 1.6-13.7). Eighteen patients experienced acute GVHD of any grade, the cumulative incidence of this complication being 22% (95% CI 13.5-31.8); 10/18 patients developed grade II acute GVHD (no patient developed grade III or IV aGVHD), this resulting into a cumulative incidence of 12.9% (95% CI 6.6-21.4). Only one patient at risk developed mild chronic GVHD. Twenty-two and 7 patients developed clinically-relevant (i.e., with a viral load &amp;gt; 1000 copies/ml and/or requiring specific antiviral-treatment) CMV and adenovirus infection, respectively, at a median time of 4 (range 0-16) and 1 (range 1-4) weeks from HSCT. Time averaged area under the curve (i.e., viral burden under the curve/weeks at risk for infection) for CMV and ADV are reported in Figure 1B. With a median follow-up of 36 months (range 2 - 110), the 5-year probability of overall survival and event-free survival for the entire cohort of patients is 92.1% (95% CI 83.3-96.4) (Figure 1C) and 68.1% (95% CI 56.4-77.2), respectively. Considering the 16/22 given a successful 2nd allograft, the 5-year disease-free survival is 88.4% (95% CI 78.9-93.8). Details on reconstitution of CD3+, CD4+ and CD8+ lymphocytes are reported in Figure 1D. Conclusions: TBdepl-haploHSCT is an effective option for children with different NMD. GF (either primary or secondary) is a challenging problem in a sub-group of patients at risk (i.e., those with HLH, thalassemia, SAA or osteopetrosis): thus, new strategies to overcome this problem are desirable. However, a second transplant is able to rescue most of these patients. Prompt availability of this type of transplant, limiting infectious risk, low incidence of both acute and chronic GvHD preserving a good quality of life in patients makes this strategy an attractive choice in patients with NMD. Figure 1 Disclosures Merli: Bellicum Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees; SOBI: Consultancy, Membership on an entity's Board of Directors or advisory committees; Jazz: Honoraria; Sanofi-Genzyme: Honoraria; Atara Therapeutics: Honoraria. Algeri:BlueBird Bio: Membership on an entity's Board of Directors or advisory committees; Atara Therapeutics: Membership on an entity's Board of Directors or advisory committees. Locatelli:Jazz Pharmaceeutical: Speakers Bureau; Medac: Speakers Bureau; Miltenyi: Speakers Bureau; Bellicum Pharmaceutical: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Amgen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau.

Phenotypic and Functional Characterization of NK Cells in αβT-Cell and B-Cell Depleted Haplo-HSCT to Cure Pediatric Patients with Acute Leukemia.

NK cells can exert remarkable graft-versus-leukemia (GvL) effect in HLA-haploidentical hematopoietic stem cell transplantation (haplo-HSCT). Here, we dissected the NK-cell repertoire of 80 pediatric acute leukemia patients previously reported to have an excellent clinical outcome after αβT/B-depleted haplo-HSCT. This graft manipulation strategy allows the co-infusion of mature immune cells, mainly NK and γδT cells, and hematopoietic stem cells (HSCs). To promote NK-cell based antileukemia activity, 36/80 patients were transplanted with an NK alloreactive donor, defined according to the KIR/KIR-Ligand mismatch in the graft-versus-host direction. The analysis of the reconstituted NK-cell repertoire in these patients showed relatively high proportions of mature and functional KIR+NKG2A−CD57+ NK cells, including the alloreactive NK cell subset, one month after HSCT. Thus, the NK cells adoptively transfused with the graft persist as a mature source of effector cells while new NK cells differentiate from the donor HSCs. Notably, the alloreactive NK cell subset was endowed with the highest anti-leukemia activity and its size in the reconstituted repertoire could be influenced by human cytomegalovirus (HCMV) reactivation. While the phenotypic pattern of donor NK cells did not impact on post-transplant HCMV reactivation, in the recipients, HCMV infection/reactivation fostered a more differentiated NK-cell phenotype. In this cohort, no significant correlation between differentiated NK cells and relapse-free survival was observed.

Immune Modulation Properties of Zoledronic Acid on TcRγδ T-Lymphocytes After TcRαβ/CD19-Depleted Haploidentical Stem Cell Transplantation: An analysis on 46 Pediatric Patients Affected by Acute Leukemia.

TcRαβ/CD19-cell depleted HLA-haploidentical hematopoietic stem cell transplantation (haplo-HSCT) represents a promising new platform for children affected by acute leukemia in need of an allograft and lacking a matched donor, disease recurrence being the main cause of treatment failure. The use of zoledronic acid to enhance TcRγδ+ lymphocyte function after TcRαβ/CD19-cell depleted haplo-HSCT was tested in an open-label, feasibility, proof-of-principle study. Forty-six children affected by high-risk acute leukemia underwent haplo-HSCT after removal of TcRαβ+ and CD19+ B lymphocytes. No post-transplant pharmacological graft-versus-host disease (GvHD) prophylaxis was given. Zoledronic acid was administered monthly at a dose of 0.05 mg/kg/dose (maximum dose 4 mg), starting from day +20 after transplantation. A total of 139 infusions were administered, with a mean of 3 infusions per patient. No severe adverse event was observed. Common side effects were represented by asymptomatic hypocalcemia and acute phase reactions (including fever, chills, malaise, and/or arthralgia) within 24–48 h from zoledronic acid infusion. The cumulative incidence of acute and chronic GvHD was 17.3% (all grade I-II) and 4.8% (all limited), respectively. Patients given 3 or more infusions of zoledronic acid had a lower incidence of both acute GvHD (8.8 vs. 41.6%, p = 0.015) and chronic GvHD (0 vs. 22.2%, p = 0.006). Transplant-related mortality (TRM) and relapse incidence at 3 years were 4.3 and 30.4%, respectively. Patients receiving repeated infusions of zoledronic acid had a lower TRM as compared to those receiving 1 or 2 administration of the drug (0 vs. 16.7%, p = 0.01). Five-year overall survival (OS) and disease-free survival (DFS) for the whole cohort were 67.2 and 65.2%, respectively, with a trend toward a better OS for patients receiving 3 or more infusions (73.1 vs. 50.0%, p = 0.05). The probability of GvHD/relapse-free survival was significantly worse in patients receiving 1–2 infusions of zoledonic acid than in those given ≥3 infusions (33.3 vs. 70.6%, respectively, p = 0.006). Multivariable analysis showed an independent positive effect on outcome given by repeated infusions of zoledronic acid (HR 0.27, p = 0.03). These data indicate that the use of zoledronic acid after TcRαβ/CD19-cell depleted haploHSCT is safe and may result in a lower incidence of acute GvHD, chronic GvHD, and TRM.

Reference guide for the treatment of aplastic anemia

Aplastic anemia is a syndrome characterized by the decrease in hematopoietic stem cells along with bone marrow hypoplasia and pancytopenia, which is likely to be a T cell-mediated autoimmune disease. Since the response rate to immunosuppressive therapy is higher if started ahead of time, early initiation of treatment is recommended even in non-severe cases. Among treatment approaches in severe cases, immunosuppressive therapy with anti-thymocyte globulin (ATG) plus cyclosporin is the basic approach. However, the effectiveness of thrombopoietin receptor agonists has also been reported, with recovery of hematopoiesis in three blood lineages observed in some patients. Despite no evidence of increased incidence of genetic mutations with thrombopoietin receptor agonist treatment, bone marrow testing is recommended after three to six months of long-term treatment to detect the presence of chromosomal abnormalities. With regard to hematopoietic stem cell transplantation for aplastic anemia, cyclophosphamide is reduced as a pretreatment therapy, and instead, fludarabine is used in combination in order to reduce cardiotoxicity. Since HLA haploidentical hematopoietic stem cell transplantation has been developed and is being reportedly used in patients with no suitable donors, this transplantation approach might also be extended to aplastic anemia patients who were not considered eligible for transplantation in the past.

HLA-Matched and HLA-Haploidentical Hematopoietic Stem Cell Transplantation for Acute Myelogenous Leukemia with t (16;21) (p11.2;q22)

HLA-Matched and HLA-Haploidentical Hematopoietic Stem Cell Transplantation for Acute Myelogenous Leukemia with t (16;21) (p11.2;q22)

Long-Term Outcome of Children with Acute Leukemia (AL) Given Alphabeta T and B-Cell Depleted HLA-Haploidentical Hematopoietic Stem Cell Transplantation (TBdepl-haploHSCT)

Background: TBdepl-haploHSCT is a suitable option for children with AL in need of an allograft, lacking an HLA-compatible donor. We previously published promising results in a cohort of 80 children with AL, given this type of allograft (Locatelli et al., Blood 2017), demonstrating a low incidence of acute and chronic graft-versus-host disease (GvHD) and low non-relapse mortality (NRM), translating into a final outcome comparable to that of patients transplanted from an HLA-compatible donor. We present the long-term follow-up analysis of this study (NCT01810120), now including 134 patients, with a minimum observation time of 100 days after the allograft. Patients and methods: Between October 2010 and April 2019, 134 children with AL in morphological complete remission (CR) received TBdepl-haploHSCT from an HLA-partially matched relative (a parent in 97% of cases) at Ospedale Pediatrico Bambino Gesù in Rome, Italy. 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 GvHD prophylaxis. Results: Characteristics of patients enrolled in the study are shown in Table 1. Median follow-up of surviving patients is 60 months (range: 3 months - 8.7 years). Only 3 patients did not achieve engraftment (all affected by acute myeloid leukemia and who did not receive TBI during conditioning regimen); median time to neutrophil and platelet recovery was 13 (range 9-22) and 11 (range 8-23) days, respectively. Cumulative incidence of grade II-III acute GvHD was 16.5% (95% CI 9.9-22.6). One patient developed gut GvHD, while for all other patients skin was the sole organ involved; no case of grade IV GvHD was recorded. Eight out of the 123 patients at risk developed chronic GvHD, in all cases of limited severity, the cumulative incidence of this complication being 7.6% (95% CI 2.3-12.6). Six patients died for transplant-related complications (2 because of idiopathic pneumonitis and 1 each of disseminated adenovirus infection, cardiac insufficiency, combined CMV/rhinovirus pneumonia and sepsis from Pseudomonas aeruginosa), the 5-year cumulative incidence of NRM being 4.5% (95% CI, 1.8-9.0). Since 25 patients relapsed at a median time of 173 days (range 59-1012) after HSCT, the 5-year cumulative incidence of relapse is 21.1% (95% CI, 14.2-29.1). The 5-year probability of overall and leukemia-free survival (LFS) were 74.6 (95% CI 65.1 -71.9) and 74.4% (95% CI 65.4-81.4) (Figure 1A), respectively. Use of TBI during the preparative regimen, age at transplant above the median value (Figure 1B) and disease status at transplantation (CR1 and CR2, Figure 1C) were associated with better patient's outcome, because of a reduced incidence of relapse (Figure 1D for TBI). All these 3 factors remained statistically significant in multivariable analysis for LFS: hazard ratio (HR) for TBI was 0.16 (95% CI, 0.06- 0.37, p&amp;lt;0.001, HR for age at HSCT was 0.27 (95% CI, 0.11-0.65, p=0.003), while that for disease status was 0.49 (95% CI, 0.26-0.91, p=0.02), respectively. The 5-year GvHD/relapse-free survival was 69.9% (95% CI 60.8-77.3). The median CD3+ cell count on day +30, +90, +180 and +360 were 187, 215, 660 and 1260/mcl, respectively. Conclusions: These data confirm in a larger population and with a longer follow-up that TBdepl-haploHSCT is a safe and effective transplant option, being associated with a low risk of both NRM and acute/chronic GvHD, resulting into a 5-year LFS comparable or even better with that reported in studies using either an HLA-identical sibling or an unrelated volunteer as donor. In particular, the low incidence of chronic GvHD preserves a good quality of life in patients with long life-expectancy. Leukemia recurrence represents the main cause of treatment failure and strategies based either on the use of a titrated number of donor T cells transduced with a safety switch or ex-vivo depleted of the alloreactive component could further improve patient's outcome. Figure 1 Disclosures Merli: Novartis: Honoraria; Sobi: Consultancy; Amgen: Honoraria; Bellicum: Consultancy. Algeri:Miltenyi: Honoraria; Atara Biotherapeutics: Consultancy, Honoraria; Bluebird bio: Consultancy, Honoraria. Locatelli:Amgen: Honoraria, 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: Consultancy; Miltenyi: Honoraria; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees.

CongenitalSTAT3mutation Mediates Primary Persistent Polymorphic Inflammatory Activation and T Cell Leukemogenesis

Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathways play a pivotal role in inflammation and immunity, among which, JAK/STAT3 pathway is the most potent and leads the crosstalk of immunity and oncogenesis. Somatic STAT3 activatingmutations have been found in about 40% of T cell large granular lymphocytic leukemia (T-LGLL) patients, most of which are located in exon 21 which encodes Src homology 2 (SH2) domain leading to the increased activity of aberrant STAT3 protein and the upregulation of its transcriptional targets. While germline STAT3activatingmutations represent a newly defined entity of immune dysregulations named infantile-onset multisystem autoimmune disease-1 (ADMIO1, #MIM 615952). Both the two diseases are rare and poorly understood. Here, we report a pedigree including a proband, a six-year-old girl, primarily manifesting as thrombocytopenia and lymphadenopathy and her father diagnosed as T-LGLL with pure red cell aplastic anemia without autoimmune disorders preceding or during his disease course. Morphology of the bone marrow smears of the proband indicated normal hyperplasia without evident dyspepsia or increased blast cells. However, the vacuoles in monocytes and the density and size of granules in neutrophils increased, and megaloblast transformation was observed in some neutrophils. (Fig. 1A, 1B) Biopsy of an enlarged lymph node showed the reactive follicular hyperplasia. (Fig. 1C) Whole exon sequencing and pedigree analysis of the family revealed the germline STAT3 c.833G&gt;A/p.R278Hmutation harbored by the proband which originated de novo from her father who additionally carried a germline TAL1G62Rmutation and somatically accumulated an FLT3-ITD mutation. (Fig. 2) Through single-cell RNA sequencing, we also found the increase of circulating CD8+ T cells and the decrease of NK cells of the proband. (Fig. 3) The STAT3 target genes were generally overactivated, and the expression of cytokines decreased in transcription level. In the genes participating in JAK/STATs pathways, the expression of JAK3, STAT1, and STAT3was up-regulated significantly. (data not shown) Immunophenotype of the proband by flow cytometry confirmed change in immunocyte compartments, (Fig. 4) but the serum cytokine concentrations measured by flow cytometry yielded controversial results, that most of cytokines were moderately elevated, and IL-1β, IL-5, TNF-α, and IFN-γ were of the most evident. (data not shown) During the treatment and follow-up, Cyclosporin A (CsA) was efficient in maintaining her circulating platelets in the range of 166×109/L to 302×109/L, but the enlarged lymph nodes and hepatosplenomegaly had no response. Eleven months later, CsA was replaced by tacrolimusfor the severe gingival hyperplasia, which has efficiently stabilized her platelets count and normalized the enlarged lymph nodes, liver, and spleen. On the contrary, in the three and a half years' span of illness, the father was refractory to CsA and methotrexate (MTX), moreover, lethal bone marrow suppression was induced by one course of fludarabine. For the high level of HLA-I and HLA-II antibodies in the circulation, plantlets transfusions were only efficient after plasmapheresis. The father eventually died from pulmonary and gastrointestinal infection due to the failure of maternal HLA-haploidentical hematopoietic stem cell transplantation (HSCT). We comprehensively elaborated the immunophenotype of the proband and thoroughly elucidated the genetic alternations of the father which led to the T cell leukemogenesis, which brought new insight on these two rare diseases and highlighted a more scrupulous therapeutic strategy in T-LGLL with congenital mutations. Figure 1 Disclosures No relevant conflicts of interest to declare.