Unrelated Hematopoietic Cell Transplantation Research Articles

Graft-versus-host-disease prophylaxis with ATG or PTCY in patients with lymphoproliferative disorders undergoing reduced intensity conditioning regimen HCT from one antigen mismatched unrelated donor

Post-transplant cyclophosphamide (PTCY) has been introduced as graft-versus-host disease (GvHD) prophylaxis in mismatched and matched unrelated hematopoietic cell transplant (HCT). However, data comparing outcomes of PTCY or ATG in patients undergoing a 1 antigen mismatched HCT for lymphoproliferative disease are limited. We compared PTCY versus ATG in adult patients with lymphoproliferative disease undergoing a first 9/10 MMUD HCT with a reduced intensity conditioning regimen from 2010 to 2021. Patients receiving PTCY were matched to patients receiving ATG according to: age, disease status at transplant, female to male matching, stem cell source and CMV serology. Grade II-IV acute GvHD at 100 day was 26% and 41% for the ATG and PTCY group, respectively (p = 0.08). Grade III–IV acute GvHD was not significantly different between the two groups. No differences were observed in relapse incidence, non-relapse mortality, progression-free survival, overall survival and GvHD-relapse-free survival at 1 year. The cumulative incidence of 1-year extensive chronic GvHD was 18% in the ATG and 5% in the PTCY group, respectively (p = 0.06). In patients with lymphoproliferative diseases undergoing 9/10 MMUD HCT, PTCY might be a safe option providing similar results to ATG prophylaxis. Due to the limited number of patients, prospective randomized trials are needed.

HLA Class I Mismatches Reduce Survival after HCT in the Ptcy Era: A Study By the EBMT Cellular Therapy and Immunobiology Working Party

Introduction: Human leukocyte antigen (HLA) compatibility between patient and donor is a mainstay in allogeneic hematopoietic cell transplantation (HCT) to reduce the risk of potentially fatal graft-versus-host disease (GvHD). Traditionally, mismatches at HLA class I (HLA-A, HLA-B, HLA-C) and class II (HLA-DRB1) have been associated with significantly reduced overall survival (OS) and increased risks of non-relapse mortality (NRM) and acute (a)GvHD compared to fully matched donors (Lee et al. Blood 2007). This has resulted in a preference for 8/8 (10/10 in Europe) HLA-matched donors in unrelated HCT (Dehn et al. Blood 2019). More recently, interest in expanding the donor pool to patients lacking a fully matched donor (Shaw et al. JCO 2021 & TCT 2023) and advances in the management and prevention of GvHD, in particular with post-transplant cyclophosphamide (PTCy) (Bolaños-Meade et al. NEJM 2023), are increasing the use of mismatched (i.e. <10/10) unrelated donors. However, the role of HLA mismatches in current HCT practice, including new strategies for GvHD prophylaxis, remains unclear. Here, we evaluated the effects of mismatching at the major HLA loci in a large contemporary cohort of patients transplanted for hematological malignancies. Methods: We studied outcomes in 17,276 adult patients transplanted from unrelated donors between 2005-2020 reported to the EBMT Registry. 67.5% of the patients were treated for acute myeloid or lymphoblastic leukemia, or myelodysplastic or myeloproliferative neoplasms. 23.5% of the transplants were performed across one (9/10; n=3,561) or two (8/10; n=499) high-resolution HLA mismatches. Reduced-intensity conditioning was used in 56% of the patients, with 76% having in vivo T-cell depletion, and 91% receiving peripheral blood stem cells. Standard GvHD prophylaxis based on calcineurin inhibitors alone or in combination with other drugs was used in all patients. PTCy was used in 7% of the 10/10 (n=924) vs 15% (n=599) of the <10/10 transplants. Univariable and multivariable models were constructed to analyze the effect of the number, class, and locus of HLA mismatches compared to 10/10 transplants in the presence or absence of PTCy. Results: In the whole cohort, the presence of one or two mismatches at the five main HLA loci significantly reduced OS (45% [95% CI 40-50%] and 47% [95% CI 45-49%] in 8/10 and 9/10, respectively, vs 52% [95% CI 51-53%] in 10/10 at 60 months; p<0.001; Figure 1A). In multivariable analysis adjusted for the most relevant clinical and transplant-related variables including the use of PTCy, the presence of one (HR 1.24 [99% CI 1.15-1.34]; p<0.001) or two (HR 1.29 [99% CI 1.09-1.54]; p<0.001) HLA mismatches was confirmed to be associated with a higher risk of mortality when compared to 10/10 transplants. When the type of mismatch was taken into account, results showed that only HLA class I (HR 1.31 [99% CI 1.20-1.42]; p<0.001) and not HLA class II (HR 1.07 [99% CI 0.93-1.22]; p=0.23) single mismatches were significantly associated with worse survival. For HLA class I, these associations were stronger for HLA-A (HR 1.37 [99% CI 1.21-1.54]; p<0.001) and HLA-B (HR 1.44 [99% CI 1.23-1.69]; p<0.001) than for HLA-C (HR 1.16 [99% CI 1.01-1.33]; p=0.005). Similar associations were observed for other endpoints, including GvHD-free, relapse-free (GRFS), and relapse-free (RFS) survival, NRM, and aGVHD grades II-IV and III-IV. In contrast, no significant differences were observed for the risks of relapse or chronic (c)GvHD. The use of PTCy significantly reduced the risks of aGvHD and mortality compared to transplants performed with standard prophylaxis. However, the effects of HLA mismatches were similar regardless of the administration of PTCy (non-significant interaction; p=0.22), with a single mismatch conferring significantly increased risks of mortality both in the presence (HR 1.38 [99% CI 1.14-1.68]; p<0.001) and in the absence (HR 1.23 [99% CI 1.13-1.33]; p<0.001) of PTCy ( Figure 1B). Conclusion: In contemporary HCT, HLA disparity is associated with increased risks of mortality, mainly driven by HLA class I mismatches. These associations are present even under GvHD prophylaxis with PTCy, challenging the notion that GvHD prophylaxis can completely overcome the effects of histocompatibility, and highlighting the need to continue defining better tolerated mismatches to provide the best possible outcome for all patients.

Hematopoietic Stem Cell Transplantation for Fanconi Anemia: Outcome and Prognostic Factors for Survival and Subsequent Neoplasms

Introduction Fanconi anemia (FA) is an inherited disorder of impaired DNA repair, associated with progressive bone marrow failure (BMF), leukemia, and cancer predisposition. Hematopoietic cell transplantation (HCT) may be curative for FA associated BMF, and changes in HCT practice over the past decades may have impacted outcomes in FA patients. Methods We used CIBMTR database to perform a retrospective cohort study of children and adults undergoing first allogeneic HCT for FA BMF (patients with MDS/AML excluded) from 2000-2018. We hypothesized that contemporary HCT approaches, including decreases in radiation and increase in use of serotherapy and ex-vivo graft manipulation, would associate with improved outcomes in FA patients receiving HCT. The primary endpoints were overall survival (OS) and early subsequent malignant neoplasm (SMN; by 5 yr post-HCT). Secondary endpoints included event free survival (EFS; death, SMN or graft failure), treatment related mortality (TRM), graft failure, and acute (grade II-IV) and cGVHD. Univariate and multivariate Cox regression models were created to evaluate the impact of conditioning, donor and graft source, treatment era, and patient characteristics on outcomes, adjusting for other significant covariates. Due to confounding factors, we were not able to create a single multivariate model that included radiation, ex-vivo graft manipulation, and donor and graft source; therefore, we performed subgroup univariate analysis for patients receiving unrelated donor bone marrow (BM) or peripheral blood stem cell (PBSC) HCT. Results We analyzed 652 HCTs from 2000-07 (n=353) and 2008-18 (n=293). 223 (35%) patients had a matched related donor (MRD) with any graft type, 244 (38%) had an unrelated donor BM or PBSC grafts, 123 (19%) had an unrelated cord blood graft, and 44 (7%) had a related haploidentical donor with any graft type. Between the two treatment eras, 5-yr OS has dramatically improved (78.8% 2008-18 v 62.5% 2000-07, p<0.01; figure 1) driven by lower 5-yr TRM (15.2% v 25.5%, p=0.004) and lower rates of primary (7.9% v 12.9% at 42 days, p=0.038) and secondary (4.1% v 8.9% at 1 year, p=0.014) graft failure. No statistically significant change was observed for aGVHD, cGVHD, or early SMN. Assessing the entire cohort, use of total body irradiation (TBI) >300cGy was associated with lower OS (HR=1.75, 95% CI 1.24-2.47) and increased TRM (HR=3.36, 95% CI 1.54-7.34; figure 2) on multivariable analysis. For patients that received unrelated BM or PBSC HCT, use of TBI was associated with inferior OS survival (HR=1.93, 95% CI 1.18-3.17), EFS (HR=1.78, 95% CI 1.13-2.80), and TRM (HR=2.31, 95% CI 1.20-4.46) on univariate analysis. Among all patients, CD34 selection or T-cell depletion ( ex vivo depletion) were not associated with better OS (95% HR=1.014, 95% CI 0.84-1.56), EFS (HR=1.163, 95% CI 0.86-1.58), or TRM (HR=0.79, 95% CI 0.52-1.19) but was associated with less aGVHD (HR=0.35 95% CI 0.22-0.57) and lower but not-statistically significant cGVHD (HR=0.54, 95% CI 0.29-1.01) on multivariable analysis. Within the unrelated donor setting, univariate analysis showed reduced aGVHD (HR=0.39 95% CI 0.23-0.68) and cGVHD (HR=0.47 95% CI 0.28-0.79) but did not have a significant effect on OS, EFS, or TRM. Early SMN occurred in 3.2% of participants by 5-years post-HCT and was associated with cGVHD occurrence (HR=2.14, 95% CI 1.06-4.33) and older age (>18 v <9 years, HR=6.35, 95% CI 2.66-15.14), but not ex-vivo depletion or use of ATG or alemtuzumab. Early SMN risk was not impacted by the use of TBI (HR=1.60, 95% CI 0.77-3.34), but secondary analysis demonstrated a trend towards a relationship with doses >300 cGy (HR=2.24, 95% CI 0.99-5.08). Conclusions Outcomes for patients with FA BMF have improved significantly in more recent HCT eras, driven by reductions in TRM and graft failure risk. Although radiation doses >300cGy were associated with greater toxicity, doses of 100-300cGy were not associated with inferior outcomes in our cohort. Use of CD34 selection or T-cell depletion may reduce the risk of GVHD in transplant FA patients, but does not appear to impact 5-yr OS. Risk for early SMN development in FA patients receiving HCT associates with older age and cGVHD.

Early Prognostic Biomarkers of Non-Relapse Mortality in Allogeneic Mismatched Unrelated Hematopoietic Cell Transplantation

Introduction A major challenge in allogeneic hematopoietic cell transplantation (HCT) has been advancing outcomes for individuals lacking a fully matched donor who require a mismatched unrelated donor (MMUD) HCT. Recently, the 15-MMUD study demonstrated encouraging results for post-transplant cyclophosphamide (PT-Cy)-based prophylaxis in MMUD recipients (Shaw, Jimenez, JCO 2021). Our retrospective analysis confirmed improvement in MMUD survival with PT-Cy compared to historical anti-thymocyte globulin (ATG)/calcineurin-based regimens (Jimenez, Blood Adv 2022). Elevations of plasma biomarkers such as Stimulation-2 (ST2) have demonstrated increased risk of non-relapse mortality (NRM) and GVHD, however these have not been validated in the MMUD setting. Here, we carried out a pilot study to determine if biomarker analysis of ST2, Chemokine ligand-9 (CXCL-9), and Regenerating islet-derived 3-α (REG3α) at Day 14 (D14) and 30 (D30) can identify patients at higher risk for NRM after MMUD HCT. Methods Patients with banked samples and underwent MMUD HCT with either ATG or PT-Cy as GVHD prophylaxis at the University of Miami between 2016 - 2020 were included. Enzyme-linked immunosorbent assays for ST2, CXCL-9, and REG3α were performed in batches on cryopreserved plasma. Descriptive statistics of demographic variables were compared using chi-squared, Fisher's exact, or Wilcoxon rank sum tests. ST2 values were treated as continuous variables, and CXCL-9 was dichotomized due to frequent values below the lower limit of detection. Cumulative incidences of NRM were analyzed with relapse as a competing risk. Time-dependent receiver operating curves (ROC) were constructed and Area Under the ROC Curve (AUC) calculated. Youden's index was used to select optimum thresholds for each biomarker. Results We included 47 patients (ATG: 23; PT-Cy: 24). The PT-Cy group had more bone marrow graft representation (50% vs 22%, p = 0.04) and more donors mismatched at >1 HLA-locus (29% vs 0%, p<0.01). Median follow up was 746 days (range 44-1968). Point estimate of overall survival at 2 years was 35% (95% CI 20-61) for ATG and 71% (95% CI 55-92) for PT-Cy (p=0.02). Median overall survival was estimated at 413 days among ATG patients and could not be estimated for PT-Cy patients. The cumulative incidence of NRM at 2-years was 30% (95% CI 13-51%) for ATG and 17% (95% CI 5-35%) for PT-Cy (p=0.03). Among all patients, ST2 was prognostic for NRM using time-varying covariates including combined D14 and D30 (D14+30) with a HR of 2.14 (95% CI 1.04-4.39, p = 0.04). The D14+30 ROC to predict NRM at 1-year using ST2 showed an AUC of 0.83 (95% CI 0.66-1). D+14 thresholded ST2 value maximizing Youden's index of ≥79.89 ng/mL was discriminative for 1-year NRM (p=0.002) (Fig. 1). Additionally, combination of CXCL-9 to ST2 could optimize the prognostic value when compared to ST2 alone: HR at D14+D30: 3.82 (95% CI 1.01-14.47, p=0.048) with an improved AUC of 0.9 (95% CI 0.79-1) (Fig. 2). REG3α did not significantly add to the AUC. Although limited by sample size, we explored the association by GVHD prophylaxis (ATG or PT-Cy). First, in the ATG group, the D14 ST2 value that maximized thresholded Youden's index of 61.39 ng/mL was predictive of 1-year NRM (p=0.04). Similarly, the D+30 ST2 values of 148.06 ng/mL was predictive of NRM (p<0.001). The AUC for prediction of 1-year NRM for Second, in the PT-Cy group, elevations of D30 ST2 were prognostic of 1-year NRM with HR 15.05 (95% CI 1.77-27.83, p=0.01). Consequently, the AUC for prediction of 1-year NRM for D30 ST2 was 0.92 (95% CI 0.77-1) and for ST2 + CXCL-9 was 0.96 (95% CI 0.86-1). Conclusions This pilot study suggests that after MMUD HCT, D14 and D30 biomarkers are prognostic for NRM across GVHD prophylaxis platforms. Importantly, we find that ST2 maintains its prognostic capacity in the increasingly popular PT-Cy group. This supplements what we previously reported in the haploidentical and matched unrelated donor PT-Cy setting (Kanakry, Haematologica 2017). Biomarker combination ST2 + CXCL-9 showed improved AUC over ST2 alone, and the composite D14+30 timepoint may have additive utility over a single timepoint. While the optimal time for biomarker collection is unknown, our data suggests D14 had value for ATG-treated patients, whereas D30 may be more important in the PT-Cy-treated group. A validation cohort is being assembled for PT-Cy based MMUD HCT.

HLA-OLI: A new MHC class I pseudogene and HLA-Y are located on a 60 kb indel in the human MHC between HLA-W and HLA-J.

Analysis of publicly available whole-genome sequence data from the Human Pangenome Project and the 1000 Genomes Project has identified a DNA segment of approximately 60 kb in the major histocompatibility complex (MHC) between HLA-W and HLA-J that is present in some MHC haplotypes but not others. This DNA segment is largely repeat element-rich but includes the pseudogene HLA-Y, thus pinpointing the location of this pseudogene, and a new HLA class I sequence we have called HLA-OLI. HLA-OLI clusters phylogenetically with the HLA class I pseudogenes, HLA-P and HLA-W, and appears to have a similar genetic structure. The availability of whole-genome sequence data from diverse populations enables a detailed characterization of the MHC at the population level and will have implications for understanding MHC disease associations and the non-HLA MHC factors that impact unrelated hematopoietic cell transplant outcomes.

Pretransplantation EASIX Score Predicts Nonrelapse and Overall Mortality of Adult Patients Undergoing Single-Unit Unrelated Cord Blood Transplantation

The Endothelial Activation and Stress Index (EASIX) is a laboratory-based score used to estimate endothelial damage occurring after hematopoietic cell transplantation (HCT). The EASIX score exhibits dynamic changes during the course of transplantation and has been identified as a predictor of nonrelapse mortality (NRM) and worse overall survival (OS) in studies focused mainly on patients who received matched related or unrelated donor allogeneic HCT. However, the role of EASIX score in the setting of cord blood transplantation (CBT) is unclear. This study examined the association between pretransplant EASIX score and post-transplantation outcomes in adult patients undergoing single-unit CBT. We retrospectively evaluated the impact of EASIX score at different time points on post-transplantation outcomes in adults following single-unit unrelated CBT between 1998 and 2022 at our institution. EASIX scores were calculated at the start of conditioning (EASIX-PRE), at day 30 post-CBT (EASIX-d30), at day 100 post-CBT (EASIX-d100), and at the onset of grade II-IV acute graft-versus-host disease (GVHD) (EASIX-GVHD II-IV). A total of 317 patients were included in this study. In the multivariate analysis, log2-EASIX-PRE (continuous variable) was significantly associated with lower risks of neutrophil engraftment (hazard ratio [HR], .87; 95% confidence interval [CI], .80 to .94; P < .001) and platelet engraftment (HR, .91; 95% CI, .83 to .99; P=.047), lower risk of grade II-IV acute GVHD (HR, .85; 95% CI, .76 to .94; P=.003), and higher risk of veno-occlusive disease/sinusoidal obstruction syndrome (VOD/SOS) (HR, 1.44; 95% CI, 1.03 to 2.02; P=.032). Log2-EASIX-PRE also was significantly associated with higher NRM (HR, 1.42; 95% CI, 1.08 to 1.86; P=.011) and worse OS (HR, 1.26; 95% CI, 1.08 to 1.46; P=.003), but not with relapse (HR, 1.02; 95% CI, .88 to 1.18; P=.780). Similarly, log2-EASIX-d30 (HR, 1.60; 95% CI, 1.26 to 2.05; P < .001), and log2-EASIX-d100 (HR, 2.01; 95% CI, 1.63 to 2.48; P < .001) were also significantly associated with higher NRM, but log2-EASIX-GVHD II-IV was not (HR, 1.15; 95% CI, .85 to 1.55; P=.360). Pretransplantation EASIX score is a powerful predictor of engraftment, VOS/SOS, NRM, and OS in adult patients undergoing single-unit unrelated CBT who mainly received intensified conditioning regimens. EASIX is an easily evaluable and dynamic prognostic score for accurately predicting post-transplantation outcomes in patients at any time during the course of allogeneic HCT, particularly for CBT.

Biologic indicators of donor socioeconomic disadvantage and recipient mortality following allogeneic hematopoietic cell transplantation.

6500 Background: Allogeneic hematopoietic cell transplantation (HCT) carries significant risks, with low socioeconomic status (SES) being predictive of increased mortality. Our team recently discovered that socioeconomic disadvantage among unrelated HCT donors results in decreased recipient overall survival (OS) and increased treatment-related mortality (TRM) within a cohort from the Center for International Blood and Marrow Transplant Research (CIBMTR). We also demonstrated that upregulation of the stress- and SES-related gene expression profile termed the ‘conserved transcriptional response to adversity’ (CTRA) is associated with low SES and worse outcomes among HCT recipients. Here, we hypothesize that donor immunologic characteristics associated with neighborhood socioeconomic disadvantage (CTRA) will confer prognostic risk to HCT recipients as indicated by inferior long-term recipient outcomes. Methods: Among a subset of the above cohort for which donor whole blood samples were available from the CIBMTR repository, we evaluated whether donor cell CTRA gene regulation was associated with inferior HCT outcomes at 3 years in recipients being treated for hematologic malignancy. Multivariable models adjusted for donor and recipient characteristics evaluated associations between donor CTRA and recipient OS, TRM, disease free survival (DFS), relapse, and acute and chronic graft versus host disease. Results were considered significant if P&lt;0.05. Results: We identified 263 donor-recipient pairs for study inclusion. Median recipient age at hematologic malignancy diagnosis was 53 years (range 19-77), 46% were female, and 54% had acute myeloid leukemia. Donors were 35% female and median age at donation was 31 years (range 18-60). In RNA sequencing data from HCT donors, greater CTRA expression was associated with reduced OS (covariate-adjusted HR=1.94/CTRA SD, 95% CI [1.01, 3.71], p=.046) which was driven predominately by increased TRM (adjusted HR=5.04, [2.20, 11.50], p=.0001). These clinical outcomes are consistent with those observed to be associated with donor SES in our prior work. Donor cell effects on transplant outcomes derived predominately from the pro-inflammatory component of the CTRA (OS: adjusted HR=1.67, [1.20, 2.33], p = .0026; TRM: adjusted HR=2.21, [1.21, 4.06], p=.010) and emerged above and beyond the effects of the recipients’ own SES, as well as multiple other recipient disease, treatment, and demographic factors. Donor CTRA was not associated with relapse, DFS, or other transplant outcomes. Conclusions: For the first time, we show that transcriptome patterning among HCT donors, consistent with neighborhood SES disadvantage, results in adverse recipient HCT outcomes. These findings suggest that SES has a biologic impact at either the stem or immune cell level that persists even when transplanted into a new host.

Graft-Versus-Host-Disease Prophylaxis with ATG or Ptcy in Patients with Lymphoproliferative Disorders Undergoing Reduced Intensity Conditioning Regimen 9/10 Mmud HCT

Introduction: Post-transplant cyclophosphamide (PTCY) has been introduced as a graft-versus-host disease (GvHD) prophylaxis in haploidentical setting with successful results. As a result, PTCY has been applied to other settings such as in mismatched and matched unrelated hematopoietic cell transplant (HCT). However, T-cell depletion with anti-thymocyte globulin (ATG) remains the main strategy in one antigen HLA-mismatched unrelated donor (9/10 MMUD). Data comparing the two GvHD prophylaxis strategies in patients undergoing MMUD 9/10 for lymphoproliferative disease are limited. Methods: We compared PTCY versus ATG as GvHD prophylaxis in patients with lymphoproliferative disease undergoing a first 9/10 MMUD HCT with a reduced intensity conditioning regimen from 2010 to 2021. Adult patients in all disease status for which high-resolution HLA-allele typing was available in the European Society for Blood and Marrow Transplantation (EBMT) data registry were included. Patients receiving PTCY were matched to patients receiving ATG according to the following variables: age, disease status at transplant, female to male donor status, stem cell source and CMV serology. Results: A total of 411 patients were identified (n=341 for ATG group and n=70 for PTCY group). According to the above mentioned variables, 106 patients receiving ATG were identified and matched with 58 patients receiving PTCY. Among the group of 164 patients paired up, diagnosis was Hodgkin Lymphoma in most of the cases (19% and 38% in the ATG and PTCY group, respectively). The median age was 54 (range 21-69) and 52 (range 22-69) years old in the ATG and PTCY group, respectively (p= NS). The majority of patients underwent a previous autologous HCT (72% in the ATG and 68% in the PTCY group, respectively). Disease state at HCT was complete remission in 71% of the patients in both ATG and PTCY group. The most frequent GvHD prophylaxis in the ATG group was cyclosporine A (CsA) and methotrexate (MTX) (n=51; 48%), followed by CsA and mycophenolate mofetil (MMF) (n=31; 29%). In the PTCY group, the majority of patients (n=30; 52%) received CsA and MMF, while tacrolimus and MMF (n=27; 46%) represented the second most used associated immunosuppressive agents. The median follow-up was 5.1 (CI: 3.8-6.7) years for the ATG group and 1.7 (CI 0.9-2.4) years in the PTCY group. The cumulative incidence of neutrophil engraftment was 97% (CI:90.5-99.1) and 100% in ATG and PTCY groups, respectively (p=0.08). Grade III-IV acute GVHD at 100 day was not significantly different between the two groups 11.3% (CI:6-18.6) versus 17.4% (CI: 8.1-29.7) in the ATG and PTCY group, respectively; p=0.60). No differences were observed in 1-y relapse incidence (22.3% (CI: 11.5-27.6) versus 17.3% (CI: 7.4-30.5), p=0.32) and non-relapse mortality (19% versus 32%, p=0.20). GvHD-free, relapse-free survival was not different across the two groups (43.5% (CI: 33.2-53.3) in ATG and 46.9% (CI: 31.2-61.2) in PTCY, p=0.88). The cumulative incidence of 1-year extensive chronic GvHD was 14.4% (CI: 7.8-22.9) in the ATG group and 5.3% (CI: 0.9-15.9) in the PTCY group, respectively (p=0.21). The 1 year-progression free survival was 58.9% (CI: 47.9-68.3) in patients receiving ATG and 50.7% (CI: 34.3-65) in those receiving PTCY (p=0.74) and 1-year overall survival was 65.9% (CI: 55.4-74.4) in the ATG group versus 55.2% (CI: 38.8-68.9) in the PTCY group (p=0.69). Forty-seven patients died in the ATG group, 20 died in the PTCY group. The main cause of death was transplant related complications (n=27 in ATG and n=14 in PTCY patients, respectively) followed by relapse of disease (n=13 in ATG and n=4 in PTCY group). Conclusions: In patients with lymphoproliferative diseases undergoing 9/10 MMUD HSCT, PTCY as GVHD prophylaxis might be a safe option providing similar results to ATG prophylaxis. Due to the limited number of patients, prospective randomized trials are needed to allow better understand the effectiveness of adding PTCY into different platforms, including MMUD 9/10 HSCT.

A Novel Multi-Analytic Clinical Diagnostic Assay to Detect HLA Loss of Heterozygosity in Post-Hematopoietic Cell Transplant Relapse Patients

Genomic loss of heterozygosity in the HLA region (HLA LOH) can be an underlying driver of disease relapse in haploidentical and HLA mismatched hematopoietic cell transplantation (HCT) in which relapsing cells evade donor T-cell allorecognition by deleting non-shared HLA alleles through an acquired somatic uniparental disomy event. The presence of HLA LOH may indicate a loss of graft vs. leukemia effect, render treatments such as donor leukocyte infusion ineffective, and impact donor selection for subsequent allogeneic HCT. A major challenge in developing a clinical diagnostic assay to detect HLA LOH post-HCT is sensitive detection of a loss of genomic material against a background of multiple genomes. Cell enrichment may address this issue by isolating relapsed cells for downstream molecular analysis. However, detection of HLA LOH is most clinically useful early in relapse when the relapsed cells are likely in low abundance, the relapsed cells may not be a single clonal population, and the immunophenotypic aberrancies may be variable and/or unknown. To address these issues, we have developed a comprehensive multi-analytic approach to detect HLA LOH that includes sensitive flow cytometric enrichment of leukemic cells followed by genomic analysis. First, a "difference from normal” flow cytometry approach (ΔN:™), the approach used for determination of residual disease in Children's Oncology Group AML clinical trials, is utilized to characterize the aberrant cells for each patient and relapse episode to ensure specific enrichment of relapsed cells to high purity. Next, two complementary molecular assays are used, including detection of short tandem repeat (STR) loci throughout the HLA region and next-generation sequencing (NGS) of HLA loci to identify deleted HLA alleles. In combination, the two assays provide a sensitive and spatially resolved assessment of LOH across the entire HLA genomic region, enabling molecular characterization of LOH events ranging from an entire HLA haplotype, partial HLA haplotype, or a single HLA locus. The ability to detect a locus-specific HLA LOH event could be useful in mismatched unrelated HCT donor/recipient pairs which may differ at only one or two HLA loci. Validation of the flow cytometric methods and genomic assays were performed separately. DNA isolated from the flow sorting process was shown to be suitable for both genomic assays. The sensitivity of the molecular assays to detect HLA LOH was defined using artificial mixes of DNA from two individuals with allelic mismatching at various HLA loci. Cell lines with known HLA LOH were also used to confirm the performance of the molecular assays. As of this writing, 16 samples from post-HCT relapse patients were tested with this assay and HLA LOH was detected in 3 cases (19%), consistent with published reports on the frequency of HLA LOH detected in allogeneic HCT patients. Samples with a range of relapsed leukemic cells from <1% to 85% and cell sorting output from 800 to 250,000 cells all yielded valid results. Results were reported within an average of 7 days, allowing adequate time for integration into therapeutic decision making. Challenging and unusual patient samples such as those with extremely low blast counts will be presented. Initial results indicate this clinical diagnostic assay provides reliable and accurate detection of HLA LOH during relapse in post-HCT patients. Detection of HLA LOH using our multi-analytic diagnostic approach may also aid in optimizing therapeutic decisions to improve outcomes in allogeneic HCT patients.

Alternative Transplantation With Post-Transplantation Cyclophosphamide in Aplastic Anemia: A Retrospective Report From the BMF-WG of Hunan Province, China

Although the possibility of first-line hematopoietic cell transplantation (HCT) from alternative donors in severe aplastic anemia (SAA) patients has been suggested recently, transplantation strategies are still being investigated. We established a novel post-transplantation cyclophosphamide-based HCT protocol for patients with SAA in prior studies. We explores the effectiveness and safety of this HCT approach either as first-line or as salvage treatment in SAA patients. Outcomes of 71 consecutive young patients, who received HCT from unrelated or haploidentical donors, were retrospectively analyzed. According to their treatment before transplantation, the patients were classified into treatment-naive (TN) and relapsed or refractory (R/R) patients. The R/R patients were designated as such when a patient did not respond to previous immunosuppressive therapy or relapsed. We administered an antithymocyte globulin (ATG)–free, total body irradiation (TBI)–free conditioning regimen comprising cyclophosphamide, busulfan, and fludarabine, all in an intravenous formula. We used a thorough post-transplantation prophylaxis regimen for GVHD, including post-transplantation cyclophosphamide (PTCy) and short-term methotrexate and long-term cyclosporine A. The median age of the cohort was 16 (95% confidence interval, 12-20) years at transplantation. Most patients (61 of 71) received HCT from haploidentical donors, and the others received HCT from unrelated donors. TN patients (n = 38) were younger and had a shorter time-to-transplant and lower HCT-specific comorbidity index than patients with R/R diseases (n = 33). The frequencies of graft failure, grade II-IV acute graft-versus-host disease (GVHD), and moderate-severe chronic GVHD were similar, at 5.3% versus 6.5% (P = .057), 8.3% versus 0% (P = .109), and 5.7% versus 0% (P = .199) between R/R and TN patients. With a median 42-month follow-up, the frequencies of overall survival (OS) and event-free survival (EFS) were higher in the TN group than in the R/R group (100% versus 84.8% [P = .013] and 86.8% versus 75.8% [P = .255], respectively). All patients who achieved successful engraftment showed full donor chimerism. Four patients, all in the R/R group, suffered from donor-type aplasia; of these, 2 died, 1 was salvaged with another transplantation, and the final one was still receiving transfusion at the last follow-up. Currently, 93.9% (62 of 66) of the patients are alive more than 12 months after transplantation; of these 93.5% (58 of 62) no longer receive immunosuppression, including 91.7% (33 of 34) of the TN group and 89.3% (25 of 28) in the R/R group. This novel TBI-free and ATG-free HCT protocol using a reduced-intensity conditioning regimen followed by modified PTCy achieved promising engraftment, minimal GVHD risk, and encouraging OS and EFS. Our study suggests that unrelated or haploidentical HCT with PTCy can be used as a first-line treatment for young patients with SAA. Nevertheless, further efforts are needed to explore possibilities for older patients and patients with a poor performance status.

IMPROVING OUTCOMES AFTER HEMATOPOIETIC CELL TRANSPLANTATION IN FA IN LOW-RESOURCES COUNTRIES: THE EXPERIENCE FROM CURITIBA

Fanconi Anemia (FA) is a rare and challenging disease to manage, and there is a substantial gap between treatments available in high- versus low- and middle-income countries. Although hematopoietic cell transplantation (HCT) is the only curative treatment for the hematological complications related to this disease, this procedure is highly complex, requiring sophisticated infrastructures and trained personnel. Describe the outcomes after matched related, unrelated and haploidentical HCT for 216 FA patients in aplastic phase in Curitiba, Brazil. The median age was 9-years (range: 3-32); all patients were in aplastic phase and received bone marrow as the stem cell source. 1st group: Matched Related Donors (MRD): 101 pts were transplanted between 1999-2021. Median follow-up: 9.6 years; 83 received HCT from matched siblings while 18 had other MRD. All patients received a simple preparatory regimen with Cyclophophamide (CY) 60 mg/kg with (n = 12) or without rabbit-ATG (n = 89) and GVHD-prophylaxis with cyclosporine and methotrexate (csa + MTX;96%) or mycophenolate (csa+MMF;4%). Six patients had primary or secondary graft failure (GF), all received a 2nd transplant, and 5 are alive and engrafted. Eight patients died at a median of 545 days after transplant (range: 3- 6271). Two-year transplant-related-mortality (TRM):4%. 10-year overall survival (OS) was 94%, and all patients transplanted in the past ten years are alive (n = 42). This regimen was well tolerated with a low TRM and acute and chronic GVHD incidence. 2nd group: Unrelated donors:75pts were transplanted between 2003-2021; median follow-up:6-years. HLA-compatibility: 10/10 (n = 68) and 9/10 (n = 7). 73% of donors were found in the Brazilian donor registry. All patients received a non-irradiation regimen including CY 60 mg/kg + Fludarabine + ATG, and the majority received csa + MTX as GVHD prophylaxis. GF was observed in two patients, and one is alive and well after a 2nd transplant.15pts died at a median of 117 days post-HCT (range: 3-4379), and infections were the major cause of death in 60% of patients. The day-100 CI of acute GVHD and 2-year CI of chronic GVHD was 17% and 25%, respectively. 5-year OS was 79%. 3rd group: Haploidentical donors:40pts were transplanted between 07/2013 to 01/2022, 31 patients received a preparatory regimen with Fludarabine + TBI (200) + rabbit-ATG, and 9 received Fludarabine + TBI(200) + Campath. GVHD prophylaxis with post-transplantation cyclophosphamide (PTCy) 50-60 mg/kg (total dose) + csa + MMF. Three patients in the ATG group had primary or secondary GF, received a 2nd haplo-PTCy transplant, and died. The CI of day-100 acute GVHD was 27%. The 2-year CI of chronic GVHD was 51% for the ATG group and 25% for the Campath group (p = 0.15). Six patients died at a median of 209 days due to rejection (n = 3) or GVHD (n = 3). 3-year OS was 85%. All patients in the Campath group are alive. These results show the feasibility of performing HCT for patients with FA in aplastic phase in Brazil. This experience also reflects more than 40 years of dedication to the treatment of FA and is based on strong national and international collaborations. These simple but effective preparatory regimens can lead to excellent outcomes, serve as a guideline, and be reproducible in other countries with similar resources.

Demand and usage of unrelated donor products for allogeneic haematopoietic cell transplantation during the COVID‐19 pandemic: A Canadian Blood Services Stem Cell Registry analysis

Background and ObjectivesUnderstanding changes in the demand and usage of unrelated allogeneic haematopoietic cell transplantation (HCT) donors during the COVID‐19 pandemic is needed to optimize pandemic preparedness of registry and donor collection services. The aim of this study was to understand the extent to which the pandemic has impacted the demand and usage of unrelated donors and cord blood units (CBUs) at Canadian Blood Services (CBS).Materials and MethodsData regarding stem cell donor interest and product usage for unrelated allogeneic HCT were retrieved from the database at CBS using de‐identified anonymous information.ResultsUnrelated donor searches for Canadian patients remained unchanged by the pandemic, reflecting stable demand. The number of unrelated allogeneic transplants performed within Canada also remained stable, while the number of cord blood transplants increased, chiefly for paediatric patients. Requests for donor verification typing, a first signal of potential interest, increased from domestic centres during the first 6 months of the pandemic and decreased from international centres, before returning to baseline levels. The proportion of transplants for Canadian patients who used stem cell products procured from Canadian donors increased between 3 and 6 months after the start of the pandemic before returning to baseline and appears to be increasing again more than 1 year after the start of the pandemic. Use of CBUs for Canadian paediatric patients increased and remains elevated.ConclusionDemand for unrelated adult HCT donors has remained stable despite the evolving pandemic with a transient and recurring increased interest and usage of domestic adult donors. Use of CBUs for paediatric patients has increased and remains elevated. Registries and donor collection centres should maintain the capacity to expand services for domestic donor collection during pandemics to offset threats to international donor usage.

Race and Survival in Unrelated Hematopoietic Cell Transplantation

Survival after hematopoietic cell transplantation depends on race/ethnicity and histocompatibility (HLA) between the patient and transplant donor. HLA sequence variation is a genetic construct of continental populations, but its role in accounting for racial disparities of transplant outcome is unknown. To determine disparities in transplant survivorship among patients of diverse race while accounting for patient and donor HLA variation. A total of 26,945 self-described Japanese, U.S. Asian, White, Hispanic, and Black patients received an unrelated donor transplant for the treatment of a life-threatening blood disorder. The risk of mortality with and without adjustment for known HLA risk factors (number and location of donor mismatches; patient HLA-B leader genotype and HLA-DRβ peptide-binding motif) was studied using multivariable models. Survival after HLA-matched transplantation for patients with optimal leader and peptide-binding features was estimated for each race, as was the improvement in survival over calendar-year time by considering year of transplantation as a continuous linear variable. The number, location, and nature of donor HLA mismatches and the frequency of patient HLA-B and HLA-DRB1 sequence motifs differed by race. Japanese patients had superior survival compared to other races without consideration of HLA. After HLA adjustment, three mortality risk strata were identified: Japanese and U.S. Asian (low-risk); White and Hispanic (intermediate-risk), and Black patients (high-risk). Survival for patients with optimal donor and HLA characteristics was superior for Japanese, intermediate for U.S. Asian, White, and Hispanic, and lowest for Black patients. Five-year increments of transplant year were associated with greater decreases in mortality hazards for Black and Hispanic patients than for Japanese, U.S. Asian and White patients. Transplant survivorship disparities are influenced by HLA as a genetic construct of race. A more complete understanding of the factors that influence transplant outcomes provides opportunities to narrow disparities for future patients.

30 - A refined model of HLA-DP permissiveness improves stratification of acute graft-versus-host disease risks after unrelated hematopoietic cell transplantation: a retrospective study from the CIBMTR

30 - A refined model of HLA-DP permissiveness improves stratification of acute graft-versus-host disease risks after unrelated hematopoietic cell transplantation: a retrospective study from the CIBMTR

Genetic associations with immune-mediated outcomes after allogeneic hematopoietic cell transplantation

AbstractPrevious studies have identified more than 200 genetic variants associated with acute or chronic graft-versus-host disease (aGVHD; cGVHD) or recurrent malignancy after allogeneic hematopoietic cell transplantation (HCT). We tested these candidate donor and recipient variants in a cohort of 4270 HCT recipients of European ancestry and in subcohorts of 1827 sibling and 1447 unrelated recipients who had 10/10 HLA-A, B, C, DRB1, and DQB1-matched donors. We also carried out a genome-wide association study (GWAS) for these same outcomes. The discovery and replication analysis of candidate variants identified a group of closely linked recipient HLA-DPB1 single-nucleotide polymorphisms (SNPs) associated with an increased risk of aGVHD and a corresponding decreased risk of recurrent malignancy after unrelated HCT. These results reflect a correlation with the level of HLA-DPB1 expression previously shown to affect the risks of aGVHD and relapse in unrelated recipients. Our GWAS identified an association of cGVHD with a locus of X-linked recipient intron variants in NHS, a gene that regulates actin remodeling and cell morphology. Evaluation of this association in a second replication cohort did not confirm the original replication results, and we did not reach any definitive conclusion regarding the validity of this discovery. The cohort used for our study is larger than those used in most previous HCT studies but is smaller than those typically used for other genotype-phenotype association studies. Genomic and disease data from our study are available for further analysis in combination with data from other cohorts.

A Refined Model of HLA-DP Permissiveness Improves Stratification of Acute Graft-Versus-Host Disease Risks after Unrelated Hematopoietic Cell Transplantation: A Retrospective Study from the CIBMTR

Introduction: Permissive HLA-DPB1 mismatches defined by the T-cell epitope (TCE) model are an established selection criterion for unrelated donors in allogeneic hematopoietic cell transplantation (alloHCT) (Dehn et al. Blood 2019). Based on biological evidence, the TCE model has classified HLA-DPB1 alleles into at least three functional groups, one of which (TCE group 3; TCE3) houses a large number of alleles with different structural and functional characteristics. We have recently shown that structurally close HLA-DP allotypes have similar peptide-binding motifs and share a significant proportion of their immunopeptidomes, the latter being fundamental for permissiveness (Meurer & Crivello et al. Blood 2021). Hence, we hypothesized that HLA-DPB1 mismatches involving alleles that encode structurally distant allotypes within TCE3 could be less permissive than those involving alleles that encode structurally closer allotypes, and thus have a differential impact on clinical outcomes.Methods: Multidimensional scaling techniques were used to compare 28 polymorphic positions (amino acids 8-215) among 51 alleles present in a cohort of 5,140 10/10 matched patient-donor pairs who received a first alloHCT for AML, ALL, or MDS between 2008-2017. Based on these analyses, TCE3-permissive mismatches (N=2,216) were further stratified into those involving structurally close or more distant combinations and compared with HLA-DPB1-matched (N=785) and non-permissively mismatched (N=2,023) pairs. These models were tested in parallel to the “classical” TCE model considering permissive mismatches (N=2,332) as a whole, to determine their association with overall survival (OS), disease-free survival (DFS), treatment-related mortality (TRM), primary disease relapse, and acute (a) and chronic (c)GVHD. Kaplan-Meier analysis and log-rank testing were used to compare the median OS and DFS. The incidences of GVHD, relapse and TRM were compared using competing risks and Gray's test. The effect of HLA-DPB1 mismatch on time-to-event outcomes was modelled by Cox regression after adjusting for confounders and testing for the proportional hazards assumption.Results: Within TCE3, we identified a subgroup of 4 frequent and structurally as well as functionally closely related alleles (i.e. DPB1*02:01, 04:01, 04:02, 23:01) that form a separate cluster (Figure 1A). These “core” alleles have similar bound-peptide motifs (van Balen et al. J Immunol 2020) and can be distinguished from other alleles in TCE3 in terms of the strength of in vitro alloreactive responses elicited from permissive responders (Meurer et al. Front Immunol 2018). Moreover, principal component analysis identified the HLA-DP 84-87 DEAV/GGMP motif as a major factor driving structural variability among TCE3 alleles (not shown). We used these observations to stratify TCE3 permissive mismatches in the allo-HCT cohort into “core” (N=930) and “non-core” (N=1,286) or into DEAV/GGPM-matched (N=1,209) and mismatched (N=1,007) pairs (Figure 1B).Multivariable analysis confirmed the association of aGVHD2-4 for the classical TCE model of non-permissive mismatching (p<.0001) and revealed a trend in DEAV/GGPM and “core”/“non-core” TCE3-permissive models. When compared to HLA-DPB1 allele matched pairs the risks of aGVHD2-4 increased progressively with “core” TCE3-permissive (HR 1.12 [0.98-1.28]; p=0.1012), “non-core” TCE3-permissive (HR 1.24 [1.06-1.46]; p= 0.0082), and non-permissive mismatches (HR 1.32 [1.16-1.50]; p<.0001) (Figure 1C, “core” vs. “non-core” HR 0.90 [0.80-1.01]; p=0.062). Similar albeit less significant results were obtained with the DEAV/GGPM model. The “core”/“non-core” TCE3 model was also associated with TRM with alloHCT from “core” TCE3-permissive donors showing lower risks of TRM than “non-core” TCE3-permissive (HR 0.82 [0.70-0.96]; p=0.0118) and non-permissive donors (HR 0.78 [0.68-0.88]; p=0.0002).Conclusion: Our results suggest that structural differences within TCE3 that reflect functional divergence and differential immunogenicity of alleles in this group associate with the risks of aGVHD and TRM after alloHCT. Hence, within the population of 10/10 matched donors, selection of “core” TCE3-permissive donors might reduce patient morbidity after transplantation. [Display omitted] DisclosuresPaczesny: Medical University of South Carolina: Patents & Royalties: inventor on the ST2 bispecific antibody patent application. Lee: AstraZeneca: Research Funding; Incyte: Research Funding; Janssen: Other; Kadmon: Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Research Funding; Syndax: Research Funding; Takeda: Research Funding; National Marrow Donor Program: Membership on an entity's Board of Directors or advisory committees; Amgen: Research Funding.

Donor Socioeconomic Status As a Predictor of Altered Immune Function and Treatment Response Following Hematopoietic Cell Transplantation for Hematologic Malignancy

Introduction: Hematopoietic cell transplantation (HCT) carries significant risks for mortality, which are not proportionally shared across individuals. Among HCT recipients, we have previously shown that low socioeconomic status (SES) is predictive of increased mortality following HCT, and the underlying mechanism for this outcome is not fully explained by race, insurance status or access to care. Furthermore, following HCT, the donor immune system replaces that of the recipient, leading to long-term engraftment with donor-derived immune cells. Previous work has not addressed the influence of donor socioeconomic factors on HCT recipient outcomes. Therefore, we hypothesized that SES would impact donor hematopoietic cells and this effect would be transferrable and associated with adverse recipient outcomes.Methods: Recipients of matched unrelated donor allogeneic peripheral blood stem cell HCT between 2000-2013 for hematologic malignancy, resided in the United States (US) with a documented ZIP code, and had a HCT donor with documented US ZIP code were identified from the Center for International Blood and Marrow Transplantation Research (CIBMTR). Using donor ZIP code, SES measures of household income, poverty, education, housing and employment were derived from the U.S. Census American Community Survey. A standardized donor SES composite score was computed as an equally weighted average of the 5 standardized SES variables (mean composite score = 0, standard deviation (SD) = 1). Multivariable models, adjusted for donor and recipient characteristics, were used to evaluate associations between donor SES composite score with HCT recipient disease free survival (DFS), overall survival (OS), treatment related mortality (TRM), relapse, and acute and chronic graft versus host disease (GVHD). Results were considered significant if P < 0.01.Results: Among 2,005 HCT recipients, median age at diagnosis was 51 years (range 1-77), 44% were female, and 55% had acute myeloid leukemia. Median post-HCT follow up was 120 months (range 4-219). Donors were 44% female and median age at hematopoietic cell donation was 34.7 years (range 18-62). The standardized donor composite scores ranged from -2.6 to 3.9, with a higher composite score indicative of greater socioeconomic disadvantage. Multivariable analyses identified significant associations between the standardized donor SES composite score and DFS (HR 1.07 per SD SES, 95% CI 1.02-1.13; p=0.0088), OS (HR 1.09 per SD SES, 95% CI 1.04-1.15; p=0.0007), and TRM (HR 1.10 per SD SES, 95% CI 1.03-1.17; p=0.0049). Significant associations were not identified between donor SES and relapse or GVHD. Quantitatively, recipients transplanted with cells from a donor of greater socioeconomic disadvantage (i.e. SES composite score 2 SD above the mean) experienced a 10% reduction in DFS and OS, and a 5% increase in TRM at 3 years compared with those transplanted with cells from a high-SES donor (SES composite score 2 SD below the mean) (Figure).Conclusions: For the first time, we have demonstrated that socioeconomic disadvantage among HCT donors results in adverse transplant outcomes in the HCT recipient. This novel finding suggests that SES has biologic impacts down to the stem cell level that persist even when transplanted into a new host during HCT. The implications of these findings are broad and suggest the need for public health interventions targeting socioeconomic support as a means for preventing social disparities in cancer treatment outcomes. [Display omitted] DisclosuresVerneris: Novartis: Other: advisory board; jazz: Other: advisory board; Fate Therapeutics: Consultancy.

Impact of HLA disparity on the risk of overall mortality in patients with grade II-IV acute GVHD on behalf of the HLA Working Group of Japan Society for Hematopoietic Cell Transplantation.

Acute graft-versus-host disease (aGVHD) is a major cause of morbidity and mortality after allogeneic hematopoietic cell transplantation (HCT). Stem cell source or HLA disparity may exert a significant impact on the overall survival (OS) after the development of aGVHD. In order to clarify this point, we performed a retrospective analysis using a database of the Japan Society for HCT. We analyzed the clinical outcomes of 10,035 patients who developed grade II-IV aGVHD. The median age of the patients was 48 years. The probability of 2-year OS after the onset of grade II-IV aGVHD in the study cohort was 54.1%. The multivariate analysis showed that the HLA ≥2-loci mismatched related donor and HLA 1-locus mismatched unrelated donor were significantly associated with an inferior OS after grade II-IV aGVHD. In a subgroup analysis, peripheral blood stem cells and HLA disparity were associated with an inferior OS in patients who received related or unrelated HCT. Thus, the clinical outcome after grade II-IV aGVHD significantly varied as per the combination of the presence of HLA disparity and stem cell source. Further research using other databases is necessary to confirm our findings.

One and a half million hematopoietic stem cell transplants: continuous and differential improvement in worldwide access with the use of non-identical family donors.

The Worldwide Network of Blood and Marrow Transplantation (WBMT) pursues the mission of promoting hematopoietic cell transplantation (HCT) for instance by evaluating activities through member societies, national registries and individual centers. In 2016, 82,718 first HCT were reported by 1,662 HCT teams in 86 of the 195 World Health Organization member states representing a global increase of 6.2% in autologous HCT and 7.0% in allogeneic HCT and bringing the total to 1,298,897 procedures. Assuming a frequency of 84,000/year, 1.5 million HCT were performed by 2019 since 1957. Slightly more autologous (53.5%) than allogeneic and more related (53.6%) than unrelated HCT were reported. A remarkable increase was noted in haploidentical related HCT for leukemias and lymphoproliferative diseases, but even more in non-malignant diseases. Transplant rates (TR; HCT/10 million population) varied according to region reaching 560.8 in North America, 438.5 in Europe, 76.7 in Latin America, 53.6 in South East Asia/Western Pacific (SEA/WPR) and 27.8 in African/East Mediterranean (AFR/EMR). Interestingly, haploidentical TR amounted to 32% in SEA/WPR and 26% in Latin America, but only 14% in Europe and EMR and 4.9% in North America of all allogeneic HCT. HCT team density (teams/10 million population) was highest in Europe (7.7) followed by North America (6.0), SEA/WPR (1.9), Latin America (1.6) and AFR/EMR (0.4). HCT are increasing steadily worldwide with narrowing gaps between regions and greater increase in allogeneic compared to autologous activity. While related HCT is rising, largely due to increase in haploidentical HCT, unrelated HCT is plateauing and cord blood HCT is in decline.

A Novel CD16xCD33 Bispecific Killer Cell Engager (BiKE) Mediates a Double Hit For Natural Killer (NK) Cells To Target CD33+ Myelodysplastic Syndrome (MDS) Cells and Myeloid Derived Suppressor Cells (MDSCs) At All Disease Stages

MDS is a clonal heterogeneous stem cell disorder identified by pancytopenia that frequently progresses to acute myeloid leukemia (AML). The only curative treatment is hematopoietic cell transplantation (HCT), but many patients are ineligible due to advanced age and comorbidities. New therapeutic strategies are urgently needed to reduce disease burden and improve overall survival. Studies of NK cell function from MDS patients have shown diminished natural cytotoxicity against K562 targets. These NK cell defects have been ascribed to abnormalities in expression and function of the NK cell activating receptors NKG2D, NKp30, NKp46 and DNAM-1. However, the properties of the potent activating receptor CD16 (FcgRIII) and its potential for mediating targeted immunotherapy remain unexplored in MDS. Frozen pre-transplant samples from 67 MDS patients (age 19-74 years, Median=47) receiving unrelated HCT were obtained from the research sample repository of the National Marrow Donor Program and were compared to normal volunteers. NK cell degranulation, cytotoxicity and cytokine production were evaluated using published methods. We focused on CD16-induced NK cell function using a bispecific killer cell engager generated to target CD16 along with the myeloid differentiation antigen CD33 (CD16xCD33 BiKE). CD16 expression on total CD56+ MDS-NK cells was significantly lower compared to normal donors (MDS vs. normal: 63 ± 3% (n=67) vs. 89 ± 2% (n=20); p < 0.0001). However, reverse-antibody dependent cell-mediated cytotoxicity (R-ADCC) assays revealed no significant differences in CD107a (46 ± 5% (n=16) vs. 46 ± 3% (n=12)), IFN-g (6 ± 1% vs. 10 ± 2%) or TNF-a (9 ± 2% vs. 6% ± 1%) production when resting MDS-NK cells were triggered with an agonistic CD16 mAb, indicating MDS-NK cell function triggered through CD16 is intact. To evaluate the therapeutic potential of targeting CD16 in MDS patients, resting MDS-mononuclear cells were coated with 10mg/mL of the CD16xCD33 BiKE and co-cultured for 4 hours with the CD33+ target cell line HL-60. MDS-NK cell CD107a (CD16xCD33 BiKE vs. no reagent: 42 ± 2% (n=62) vs. 22 ± 1% (n=20); p < 0.0001), IFN-g (15 ± 1% vs. 3 ± 1%; p < 0.0001) and TNF-a (13 ± 1% vs. 3 ± 1%; p < 0.0001) production was significantly increased compared to the no reagent and scFv CD16 controls. Moreover, in the absence of HL-60 targets, MDS-NK cells treated with the CD16xCD33 BiKE targeted endogenous CD33+ targets, significantly enhancing degranulation (37 ± 2% vs. 17 ± 1%; p < 0.0001), IFN-g (4 ± 1% vs. 2% ± 1%; p < 0.01) and TNF-a (5 ± 1% vs. 2 ± 1%; p < 0.01) production. Recent data have shown an increase in the frequency of MDSCs, phenotypically defined as CD33+/CD11b+/CD14-/HLA-DRlo/-, during oncogenesis and in the presence of inflammatory cytokines. Indeed, in our MDS patient cohort, the frequency of MDSCs of total viable mononuclear cells was significantly higher compared to normal donors (6 ± 1% (n=64) vs. 0.1 ± 0.02% (n=18), respectively; p < 0.0001) (figure). Furthermore, CD16xCD33 BiKE-treated resting NK cells from normal donors co-cultured with cytokine-induced MDSCs generated from normal PBMCs in a 51Cr-release cytotoxicity assay successfully targeted and lysed MDSCs (CD16xCD33 BiKE vs. no reagent (E:T = 20:1): 63 ± 5% vs. 7 ± 2% [p < 0.0001, n=4]; (E:T = 6.6:1): 35 ± 3% vs. 4 ± 1% [p < 0.0001]). CD107a (48 ± 2% (n=6) vs. 4 ± 1% (n=3); p < 0.0001), IFN-g (8 ± 1% vs. 1 ± 1%; p < 0.0001) and TNF-a (8 ± 1% vs. 1 ± 1%; p < 0.0001) production was also significantly increased against MDSC targets in the presence of the CD16xCD33 BiKE, demonstrating its ability to facilitate killing of both the CD33+ MDS clone and an immune suppressor cell population. Lastly, analysis of MDS patient karyotypes in correlation with CD16xCD33 BiKE-induced MDS-NK cell CD107a, IFN-g and TNF-a production did not reveal any significant differences between favorable, intermediate or poor international prognostic scoring system (IPSS) cytogenetic scores, further demonstrating the therapeutic potential of the CD16xCD33 BiKE to induce optimal MDS-NK cell function against CD33+ targets despite disease heterogeneity. In summary, our data suggest that the CD16xCD33 BiKE may function not only against CD33+ MDS targets themselves, but also against MDSCs. This double hit approach may protect against MDS progression/transformation to AML through immune targeting and may improve blood counts by targeting MDS-MDSCs that contribute to ineffective hematopoiesis. [Display omitted] Disclosures:No relesvant conflicts of interest to declare.