Signatures of GVHD and relapse after posttransplant cyclophosphamide revealed by immune profiling and machine learning

Post-transplant cyclophosphamide separates graft-versus host disease and graft versus leukemia effects after HLA-matched stem-cell transplantation for acute myeloid leukemia

The association of graft-versus-host disease (GVHD) and graft-versus-leukemia (GVL) effects after allogeneic stem-cell transplantation (SCT) is well-established but was not confirmed in the modern era and following post-transplant cyclophosphamide (PTCy). We assessed GVHD/ GVL association in AML patients following HLA-matched SCT with standard calcineurin-based (n = 12,653, 57% with additional in-vivo T-cell depletion) or PTCy-based (n = 508) GVHD prophylaxis. Following standard prophylaxis, acute GVHD grade II-IV and III-IV, chronic GVHD, and extensive chronic GVHD rates were 23.8%, 7.5%, 37.0%, and 16.3%, respectively. Acute GVHD grade II and III-IV were associated with lower relapse [hazard-ratio (HR) 0.85, P = 0.002; HR 0.76, P = 0.003, respectively)], higher non-relapse mortality (NRM) (HR 1.5, P < 0.001; HR 6.21, P < 0.001) and lower overall survival (OS) (HR 1.49, P < 0.001; HR 6.1, P < 0.001). Extensive chronic GVHD predicted lower relapse (HR 0.69, P < 0.001), higher NRM (HR 2.83, P < 0.001), and lower OS (HR 2.74, P < 0.001). Following PTCy, GVHD rates were 22.8%, 6.2%, 35.5%, and 17.7%, respectively. Acute GVHD was not associated with relapse (HR 1.37, P = 0.15) but predicted higher NRM (HR 3.34, P < 0.001) and lower OS (HR 1.92, P = 0.001). Chronic GVHD was not prognostic for these outcomes. In conclusion, GVHD and GVL are strongly associated with contemporary SCT. However, following PTCy, GVHD is not associated with reduced relapse.

Using T-lymphocyte subsets at engraftment to predict the risk of acute graft-versus-host disease in patients with thalassemia major: development of a new predictive nomogram

Background

Acute graft-versus-host disease (aGvHD) is the primary cause of mortality following allogeneic hematopoietic cell transplantation (HCT).

Objectives

This study aimed to predict the risk of aGvHD after HCT in patients with thalassemia major using a novel predictive nomogram.

Design

A retrospective study was used to develop the prediction model.

Methods

We performed retrospective analyses on 402 consecutive thalassemia patients who underwent HCT. Risk factors for aGvHD were analyzed using Cox proportional regression models. T-lymphocyte subsets were collected from 240 patients at the time of neutrophil engraftment. Least Absolute Shrinkage and Selection Operator regression was utilized to screen the indices, with cut-off values established through restricted cubic spline (RCS) regression. The predictive model was developed by integrating these T-lymphocyte subsets with clinical features, aiming to enhance the accuracy of aGvHD risk prediction.

Results

Among 402 thalassemia patients analyzed post-transplantation, significant independent risk factors for aGvHD included matched unrelated donors, haploid-related donors, peripheral blood stem cell infusions, and donor age older than 40 years. Our RCS analysis indicated a marked increase in aGvHD risk when CD4+ T-cell counts exceeded 36 cells/μL and CD8+ T-cell counts exceeded 43 cells/μL during neutrophil engraftment. The integration of T-lymphocyte subsets with clinical risk factors into a Cox regression model demonstrated good predictive performance for assessing aGvHD risk.

Conclusion

This study presents a novel model designed to predict aGvHD in thalassemia patients post-transplantation by utilizing T-lymphocyte data at the time of engraftment. The model facilitates the creation of personalized treatment plans, aiming to minimize the incidence of aGvHD and improve patient outcomes.

Haploidentical hematopoietic cell transplantation as a platform for natural killer cell immunotherapy

An innovative approach is crucially needed to manage relapse after allogeneic hematopoietic cell transplantation (HCT) in patients with advanced hematological malignancies. This review explores key aspects of haploidentical HCT with post-transplant cyclophosphamide, highlighting the potential and suitability of this platform for natural killer (NK) cell immunotherapy. NK cells, known for their unique abilities to eliminate cancer cells, can also exhibit memory-like features and enhanced cytotoxicity when activated by cytokines. By discussing promising results from clinical trials, the review delves into the recent major advances: donor-derived NK cells can be expanded ex vivo in large numbers, cytokine activation may enhance NK cell persistence and efficacy in vivo, and post-HCT NK cell infusion can improve outcomes in high-risk and/or relapsed myeloid malignancies without increasing the risk of graft-versus-host disease, severe cytokine release syndrome, or neurotoxicity. Looking ahead, cytokine-activated NK cells can be synergized with immunomodulatory agents and/or genetically engineered to enhance their tumor-targeting specificity, cytotoxicity, and persistence while preventing exhaustion. The ongoing exploration of these strategies holds promising preliminary results and could be rapidly translated into clinical applications for the benefit of the patients.

Higher survival following transplantation with a mismatched unrelated donor with posttransplant cyclophosphamide-based graft-versus-host disease prophylaxis than with double unit umbilical cord blood in patients with acute myeloid leukemia in first complete remission: A study from the Acute Leukemia Working Party of the European Society for Blood and Marrow Transplantation

The best donor option for acute myeloid leukemia (AML) patients lacking an HLA-matched donor has remained intensively debated. We herein report the results of a large retrospective registry study comparing hematopoietic cell transplantation (HCT) outcomes between double-unit umbilical cord blood transplantation (dCBT, n = 209) versus 9/10 HLA-matched unrelated donor (UD) with posttransplant cyclophosphamide (PTCy)-based graft-versus-host disease (GVHD) prophylaxis (UD 9/10, n = 270) in patients with AML in first complete remission (CR1). Inclusion criteria consisted of adult patient, AML in CR1 at transplantation, either peripheral blood stem cells (PBSC) from UD 9/10 with PTCy as GVHD prophylaxis or dCBT without PTCy, transplantation between 2013 and 2021, and no in vivo T-cell depletion. The 180-day cumulative incidence of grade II-IV acute GVHD was 29% in UD 9/10 versus 44% in dCBT recipients (p = .001). After adjustment for covariates, dCBT recipients had a higher non-relapse mortality (HR = 2.35, 95% CI: 1.23-4.48; p = .01), comparable relapse incidence (HR = 1.12, 95% CI: 0.67-1.86; p = .66), lower leukemia-free survival (HR = 1.5, 95% CI: 1.01-2.23; p = .047), and lower overall survival (HR = 1.66, 95% CI: 1.08-2.55; p = .02) compared with patients receiving UD 9/10 HCT. In summary, our results suggest that transplantation outcomes are better with UD 9/10 with PTCy-based GVHD prophylaxis than with dCBT for AML patients in CR1. These data might support the use of UD 9/10 with PTCy-based GVHD prophylaxis over dCBT in AML patients lacking an HLA-matched donor.

JAK2/mTOR inhibition fails to prevent acute GVHD despite reduced Th1/Th17 cells: final phase 2 trial results

ABSTRACT

Our phase 1 graft-versus-host disease (GVHD) prevention trial of JAK2 inhibitor, pacritinib (PAC; recommended phase 2 dose: 100 mg orally twice a day on day 0 to +70) plus sirolimus and tacrolimus (SIR/TAC) demonstrated the regimen was safe and free of pan-JAK myelosuppression after allogeneic hematopoietic cell transplantation (alloHCT). PAC inhibits interleukin 6 (IL-6) receptor activity and pathogenic T helper cell 1 (Th1)/Th17 differentiation in preclinical models and the phase 1 trial. Herein, we report on our completed phase 2 trial of PAC/SIR/TAC after 8/8 human leukocyte antigen matched alloHCT. This single-arm phase 2 trial (NCT02891603) was powered to determine if PAC/SIR/TAC suppressed percentage phosphorylated STAT3 (pSTAT3)+ CD4+ T cells at day +21 (primary end point: percentage pSTAT3+ CD4+ T cells ≤ 35%) and estimated grade II to IV acute GVHD by day +100. The impact of PAC/SIR/TAC on T-cell subsets, CD28 (pS6 and pH3ser10), and IL-2 receptor (pSTAT5) signal transduction was also evaluated. Eligible patients (n = 28) received alloHCT for hematologic malignancies or myeloproliferative neoplasms. Reduced or myeloablative intensity conditioning was permitted. PAC/SIR/TAC met the primary end point, reducing percentage pSTAT3+ CD4+ T cells to 9.62% at day +21. Th1/Th17 cells were decreased at day +21, increasing the ratio of regulatory T cells to Th1 and Th17 cells with PAC/SIR/TAC at recommended phase 2 dose PAC compared with dose level 1 PAC. The cumulative incidence of grade II to IV acute GVHD by day +100 with PAC/SIR/TAC was similar to historic SIR/TAC values (46% vs 43%). Although PAC/SIR/TAC suppressed pSTAT3 and Th1/Th17 cells, the regimen did not improve acute GVHD prevention.

High-dimensional Immune Profiles and Machine Learning May Predict Acute Myeloid Leukemia Relapse Early following Transplant

Identification of early immune signatures associated with acute myeloid leukemia (AML) relapse following hematopoietic stem cell transplant (HSCT) is critical for patient outcomes. We analyzed PBMCs from 58 patients with AML undergoing HSCT, focusing on T cell subsets and functional profiles. High-dimensional flow cytometry coupled with Uniform Manifold Approximation and Projection dimensionality reduction and PhenoGraph clustering revealed distinct changes in CD4+ and CD8+ T cell populations in 16 patients who relapsed within 1 y of HSCT. We observed increased IL-2, IL-10, and IL-17-producing CD4+ T cells, alongside decreased CD8+ T cell function early in relapsing patients. Notably, relapsing patients exhibited increased TCF-1intermediate cells, which lacked granzyme B or IFN-γ production in the CD4+ T cell compartment. We then developed a supervised machine learning algorithm that predicted AML relapse with 90% accuracy within 30 d after HSCT using high-throughput assays. The algorithm leverages condensed immune phenotypic data, alongside the ADASYN algorithm, for data balancing and 100 rounds of XGBoost supervised learning. This approach holds potential for detecting relapse-associated immune signatures months before clinical manifestation. Our findings demonstrate a distinct immunological signature potentially capable of predicting AML relapse as early as 30 d after HSCT.

Genetically modified and unmodified cellular approaches to enhance graft versus leukemia effect, without increasing graft versus host disease: the use of allogeneic cytokine-induced killer cells

Although allogeneic hematopoietic cell transplantation (HCT) represents a curative approach for many patients with hematological diseases, post-transplantation relapse occurs in 20-50% of cases, representing the primary cause of treatment failure and mortality. Alloreactive donor T cells are responsible for the graft versus leukemia (GvL) effect, which represents the key mechanism for the long-term curative effect of HCT. However, the downside is represented by graft versus host disease (GvHD), largely contributing to transplant-related mortality (TRM). Multiple factors play a role in regulating the delicate balance between GvL and GvHD, such as the optimization of the donor HLA and KIR match, the type of graft source, and the adaptive use of post-transplant cellular therapy. In addition to the standard donor lymphocyte infusion (DLI), several attempts were made to favor the GvL effect without increasing the GvHD risk. Selected DLI, NK DLI, activated DLI and more sophisticated genetically engineered cells can be employed. In this scenario, cytokine-induced killer (CIK) cells represent a suitable tool to boost GvL while minimizing GvHD. CIK cells are T lymphocytes activated in culture in the presence of monoclonal antibodies against CD3 (OKT3), interferon-gamma (IFN-g), and interleukin-2 (IL-2), characterized by the expression of markers typical of NK cells and T cells (CD3+, CD56+, with a prevalent CD8+ phenotype). CIK cells can mediate cytotoxicity through both MHC and non-MHC restricted recognition, which is the so-called "dual-functional capability" and display minimum alloreactivity. Allogeneic CIK cells showed a favorable rate of response, especially in the setting of minimal residual disease, with a rate of GvHD not exceeding 25%. Finally, the CIK cell platform can be adapted for chimeric antigen receptor (CAR) cell strategy, showing promising results in both preclinical and clinical settings. In this review, we describe the main immunological basis for the development of the GvL and the possible cellular therapy approaches used to boost it, with a particular focus on the use of CIK cells.

Human Leukocyte Antigen Mismatching and Survival in Contemporary Hematopoietic Cell Transplantation for Hematologic Malignancies

PURPOSEHuman leukocyte antigen (HLA) mismatching can reduce survival of patients with blood cancer after hematopoietic cell transplantation (HCT). How recent advances in HCT practice, in particular graft-versus-host disease (GVHD) prophylaxis by post-transplantation cyclophosphamide (PTCy), influence HLA risk associations is unknown.PATIENTS AND METHODSThe study included 17,292 unrelated HCTs with 6-locus high-resolution HLA typing, performed mainly for acute leukemia or related myeloid neoplasms between 2016 and 2020, including 1,523 transplants with PTCy. HLA risk associations were evaluated by multivariable Cox regression models, with overall survival (OS) as primary end point.RESULTSOS was lower in HLA mismatched compared with fully matched transplants (hazard ratio [HR], 1.23 [99% CI, 1.14 to 1.33]; P < .001). This was driven by class I HLA-A, HLA-B, HLA-C (HR, 1.29 [99% CI, 1.19 to 1.41]; P < .001) but not class II HLA-DRB1 and HLA-DQB1 (HR, 1.07 [99% CI, 0.93 to 1.23]; P = .19). Class I antigen-level mismatches were associated with worse OS than allele-level mismatches (HR, 1.36 [99% CI, 1.24 to 1.49]; P < .001), as were class I graft-versus-host peptide-binding motif (PBM) mismatches compared with matches (HR, 1.42 [99% CI, 1.28 to 1.59]; P < .001). The use of PTCy improved GVHD, relapse-free survival compared with conventional prophylaxis in HLA-matched transplants (HR, 0.77 [0.66 to 0.9]; P < .001). HLA mismatching increased mortality in PTCy transplants (HR, 1.32 [1.04 to 1.68]; P = .003) similarly as in non-PTCy transplants (interaction P = .43).CONCLUSIONClass I but not class II HLA mismatches, especially at the antigen and PBM level, are associated with inferior survival in contemporary unrelated HCT. These effects are not significantly different between non-PTCy compared with PTCy transplants. Optimized HLA matching should still be considered in modern HCT.

Comparable relapse incidence after unrelated allogeneic stem cell transplantation with post-transplant cyclophosphamide versus conventional anti-graft versus host disease prophylaxis in patients with acute myeloid leukemia: A study on behalf of the Acute Leukemia Working Party of the European Society for Blood and Marrow Transplantation

We compared relapse incidence (RI) post-unrelated transplantation with post-transplant cyclophosphamide (PTCy) versus no PTCy graft-versus-host disease (GVHD) prophylaxis, in 7049 acute myeloid leukemia (AML) patients in remission, 707 with PTCy, and 6342 without (No PTCy). The patients in the PTCy group were younger, 52.7 versus 56.6 years (p < .001). There were more 9/10 donors in the PTCy group, 33.8% versus 16.4% (p < .001), and more received myeloablative conditioning, 61.7% versus 50.2% (p < .001). In the No PTCy group, 87.7% of patients received in vivo T-cell depletion. Neutrophil and platelet engraftment were lower in the PTCy versus No PTCy group, 93.8% and 80.9% versus 97.6% and 92.6% (p < .001). RI was not significantly different in the PTCy versus the No PTCy group, hazard ratio (HR) of 1.11 (95% confidence interval [CI] 0.9-1.37) (p = .31). Acute GVHD grades II-IV and III-IV, were significantly lower in the PTCy versus the No PTCy group, HR of 0.74 (95% CI 0.59-0.92, p = .007) and HR = 0.56 (95% CI 0.38-0.83, p = .004), as were total and extensive chronic GVHD, HRs of 0.5 (95% CI 0.41-0.62, p < .001) and HR = 0.31 (95% CI 0.22-0.42, p < .001). Non-relapse mortality (NRM) was significantly lower with PTCy versus the No PTCy group, HR of 0.67 (95% CI 0.5-0.91, p = .007). GVHD-free, relapse-free survival (GRFS) was higher in the PTCy versus the No PTCy group, HR of 0.69 (95% CI 0.59-0.81, p = .001). Leukemia-free survival (LFS) and overall survival (OS) did not differ between the groups. In summary, we observed comparable RI, OS, and LFS, significantly lower incidences of GVHD and NRM, and significantly higher GRFS in AML patients undergoing unrelated donor-hematopoietic stem cell transplantation with PTCy versus No PTCy GVHD prophylaxis.

Novel MAGIC composite scores using both clinical symptoms and biomarkers best predict treatment outcomes of acute GVHD

ABSTRACT

Acute graft-versus-host disease (GVHD) grading systems that use only clinical symptoms at treatment initiation such as the Minnesota risk identify standard and high-risk categories but lack a low-risk category suitable to minimize immunosuppressive strategies. We developed a new grading system that includes a low-risk stratum based on clinical symptoms alone and determined whether the incorporation of biomarkers would improve the model's prognostic accuracy. We randomly divided 1863 patients in the Mount Sinai Acute GVHD International Consortium (MAGIC) who were treated for GVHD into training and validation cohorts. Patients in the training cohort were divided into 14 groups based on similarity of clinical symptoms and similar nonrelapse mortality (NRM); we used a classification and regression tree (CART) algorithm to create three Manhattan risk groups that produced a significantly higher area under the receiver operating characteristic curve (AUC) for 6-month NRM than the Minnesota risk classification (0.69 vs 0.64, P = .009) in the validation cohort. We integrated serum GVHD biomarker scores with Manhattan risk using patients with available serum samples and again used a CART algorithm to establish 3 MAGIC composite scores that significantly improved prediction of NRM compared to Manhattan risk (AUC, 0.76 vs 0.70, P = .010). Each increase in MAGIC composite score also corresponded to a significant decrease in day 28 treatment response (80% vs 63% vs 30%, P < .001). We conclude that the MAGIC composite score more accurately predicts response to therapy and long-term outcomes than systems based on clinical symptoms alone and may help guide clinical decisions and trial design.

Haploidentical transplantation in primary refractory/relapsed secondary vs de novo AML: from the ALWP/EBMT

ABSTRACT

We compared the outcomes of haploidentical stem cell transplantation (haplo-HSCT) with posttransplant cyclophosphamide (PTCy) in 719 patients with primary refractory (PR) or first relapse (Rel) secondary acute myeloid leukemia (sAML; n = 129) vs those with de novo AML (n = 590), who received HSCT between 2010 and 2022. A higher percentage of patients with sAML vs de novo AML had PR disease (73.6% vs 58.6%; P = .002). In 81.4% of patients with sAML , the antecedent hematological disorder was myelodysplastic syndrome. Engraftment was 83.5% vs 88.4% in sAML and de novo AML, respectively (P = .13). In multivariate analysis, haplo-HSCT outcomes did not differ significantly between the groups: nonrelapse mortality hazard ratio (HR), 1.38 (95% confidence interval [CI], 0.96-1.98; P = .083), relapse incidence HR, 0.68 (95% CI, 0.4.7.-1.00; P = .051). The HRs for leukemia-free survival, overall survival, and graft-versus-host disease (GVHD)-free, and GVHD and relapse-free survival were 0.99 (95% CI, 0.76-1.28; P = .94), 0.99 (95% CI, 0.77-1.29; P = .97), and 0.99 (95% CI, 0.77-1.27; P = .94), respectively. We conclude that outcomes of haplo-HSCT with PTCy are not different for PR/Rel sAML in comparison with PR/Rel de novo AML, a finding of major clinical importance.

Memory T-cell enriched haploidentical transplantation with NK cell addback results in promising long-term outcomes: a phase II trial

BACKGROUND

Relapse remains a challenge after transplantation in pediatric patients with hematological malignancies. Myeloablative regimens used for disease control are associated with acute and long-term adverse effects. We used a CD45RA-depleted haploidentical graft for adoptive transfer of memory T cells combined with NK-cell addback and hypothesized that maximizing the graft-versus-leukemia (GVL) effect might allow for reduction in intensity of conditioning regimen.

METHODS

In this phase II clinical trial (NCT01807611), 72 patients with hematological malignancies (complete remission (CR)1: 25, ≥ CR2: 28, refractory disease: 19) received haploidentical CD34 + enriched and CD45RA-depleted hematopoietic progenitor cell grafts followed by NK-cell infusion. Conditioning included fludarabine, thiotepa, melphalan, cyclophosphamide, total lymphoid irradiation, and graft-versus-host disease (GVHD) prophylaxis consisted of a short-course sirolimus or mycophenolate mofetil without serotherapy.

RESULTS

The 3-year overall survival (OS) and event-free-survival (EFS) for patients in CR1 were 92% (95% CI:72-98) and 88% (95% CI: 67-96); ≥ CR2 were 81% (95% CI: 61-92) and 68% (95% CI: 47-82) and refractory disease were 32% (95% CI: 11-54) and 20% (95% CI: 6-40). The 3-year EFS for all patients in morphological CR was 77% (95% CI: 64-87) with no difference amongst recipients with or without minimal residual disease (P = 0.2992). Immune reconstitution was rapid, with mean CD3 and CD4 T-cell counts of 410/μL and 140/μL at day + 30. Cumulative incidence of acute GVHD and chronic GVHD was 36% and 26% but most patients with acute GVHD recovered rapidly with therapy. Lower rates of grade III-IV acute GVHD were observed with NK-cell alloreactive donors (P = 0.004), and higher rates of moderate/severe chronic GVHD occurred with maternal donors (P = 0.035).

CONCLUSION

The combination of a CD45RA-depleted graft and NK-cell addback led to robust immune reconstitution maximizing the GVL effect and allowed for use of a submyeloablative, TBI-free conditioning regimen that was associated with excellent EFS resulting in promising long-term outcomes in this high-risk population. The trial is registered at ClinicalTrials.gov (NCT01807611).

The role and novel use of natural killer cells in graft-versus-leukemia reactions after allogeneic transplantation

Allogeneic hematopoietic cell transplantation (HCT) has transformed over the past several decades through enhanced supportive care, reduced intensity conditioning (RIC), improved human leukocyte antigen (HLA) typing, and novel graft-versus-host disease (GVHD)-prevention and treatment strategies. Most notably, the implementation of post-transplantation cyclophosphamide (PTCy) has dramatically increased the safety and availability of this life-saving therapy. Given reductions in nonrelapse mortality (NRM) with these advances, the HCT community has placed even greater emphasis on developing ways to reduce relapse - the leading cause of death after HCT. When using RIC HCT, protection from relapse relies predominantly on graft-versus-leukemia (GVL) reactions. Donor lymphocyte infusion (DLI), adoptive cellular therapy, checkpoint inhibition, and post-HCT maintenance strategies represent approaches under study that aim to augment or synergize with the GVL effects of HCT. Optimizing donor selection algorithms to leverage GVL represents another active area of research. Many of these strategies seek to harness the effects of T cells, which for decades were felt to be the primary mediators of GVL and the focus of investigation in relapse reduction. However, there is growing interest in capitalizing on the ability of natural killer (NK) cells to yield potent anti-tumor effects. A potential advantage of NK cell-based approaches over T cell-mediated is the potential to reduce NRM in addition to relapse. By decreasing infection, without increasing the risk of GVHD, NK cells may mitigate NRM, while still yielding relapse reduction through identification and clearance of cancer cells. Most T cell-focused relapse-prevention strategies must weigh the benefits of relapse reduction against the increased risk of NRM from GVHD. In contrast, NK cells have the potential to reduce both, potentially tipping the scales significantly in favor of survival. Here, we will review the role of NK cells in GVL, optimization of NK cell match or mismatch, and burgeoning areas of research in NK cell therapy such as adoptive transfer and chimeric antigen receptor (CAR) NK cells.

The role of immune reconstitution in relapse after allogeneic hematopoietic stem cell transplantation

INTRODUCTION

Leukemia relapse following stem cell transplantation remains a significant barrier to long-term remission. Timely and balanced immune recovery after transplantation is crucial for preventing leukemia relapse.

AREAS COVERED

After an extensive literature search of PubMed and Web of Science through October 2023, we provide an overview of the dynamics of immune reconstitution and its role in controlling leukemia relapse. We also discuss strategies to promote immune reconstitution and reduce disease recurrence following allogeneic hematopoietic stem cell transplantation.

EXPERT OPINION

Immune reconstitution after transplantation has substantial potential to prevent relapse and might predict disease recurrence and prognosis. High dimensional cytometry, multi-omics, and T cell repertoire analysis allow for a more comprehensive and detailed understanding of the immune system's dynamics post-transplantation, and contribute to the identification of rare immune cell subsets or potential biomarkers associated with successful immune reconstitution or increased risk of complications. Strategies to enhance the immune system, such as adoptive immunotherapy and cytokine-based therapy, have great potential for reducing leukemia relapse after transplantation. Future research directions should focus on refining patient selection for these therapies, implementing appropriate and timely treatment, investigating combination approaches to maximize therapeutic outcomes, and achieving a robust graft-versus-leukemia (GVL) effect while minimizing graft-versus-host disease (GVHD) for optimal results.

Outcomes with HLA-matched unrelated donor versus haploidentical hematopoietic cell transplantation

We investigated the outcomes after adult haploidentical (haplo) and matched unrelated donor (MUD) hematopoietic cell transplantation (HCT) in a single-center study (n = 452) including 276 MUD and 176 haplo transplants. Myeloablative (37%) and reduced-intensity conditioning (63%) were performed. Graft sources included peripheral blood (50%) and bone marrow (50%). GVHD prophylaxis included tacrolimus/methotrexate (53%) and post-transplant cyclophosphamide-based (47%). In MUD versus haplo HCT recipients, a similar incidence of neutrophil engraftment (18 vs 17 days, p = 0.895), grade II-IV acute GVHD (51% vs 50%, p = 0.773), relapse (26% vs 23%, p = 0.578), non-relapse mortality (22% vs 23%, p = 0.817), 1-year disease-free survival (62% vs 63%. p = 0.921), and 1-year overall survival (73% vs 74%, p = 0.744) were observed. Earlier platelet engraftment (22 vs 27 days, p < 0.001) and higher chronic GVHD (45% vs 35%, p = 0.040) were noted in MUD as compared to haplo HCT. Allogeneic transplantation should be done promptly whenever indicated, utilizing either matched unrelated or haploidentical donors.

Dual T cell depletion for graft versus host disease prevention in peripheral blood haploidentical hematopoietic cell transplantation for adults with hematological malignancies

The ideal immunosuppressive agents to complement post-transplant cyclophosphamide (PTCy) in PBSC-based haploidentical hematopoietic cell transplantation (haplo-HCT) remain debated. This study looks at our experience with ATG-PTCy-Cyclosporine (CsA) prophylaxis in PB haplo-HCT since 2015. Between October 2015 and December 2021, 157 adults underwent haploidentical hematopoietic cell transplantation (haplo-HCT) using a GVHD prophylaxis regimen comprising rabbit-ATG, PTCy, and CsA. Among these patients, 76.4% received a total ATG dose of 4.5 mg/kg, and 23.5% received 2 mg/kg. T-cell replete peripheral blood stem cell (PBSC) grafts were infused on day 0. The study reported a median follow-up of 32 months (range 0.3-61.64) for survivors. The cumulative incidence of grade II-IV and grade III-IV acute GVHD at day +100 was 26.3% and 9.5%, respectively. Moderate/severe chronic GVHD at 1 year was 19.9%. The 2-year overall survival (OS) was 49.4%, with a relapse-free survival (RFS) of 44.6%. In multivariate analysis, older patients, and those with high/very-high disease risk indices (DRI) were at higher risk for worse OS and higher non-relapse mortality (NRM). The study confirms that using PTCy and ATG (4.5 mg/kg), alongside CsA is safe and effective in preventing GVHD when using peripheral blood as the stem cell source in haploidentical hematopoietic cell transplantation (haplo-HCT).

Using Targeted Transcriptome and Machine Learning of Pre- and Post-Transplant Bone Marrow Samples to Predict Acute Graft-versus-Host Disease and Overall Survival after Allogeneic Stem Cell Transplantation

Acute graft-versus-host disease (aGvHD) remains a major cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation (HSCT). We performed RNA analysis of 1408 candidate genes in bone marrow samples obtained from 167 patients undergoing HSCT. RNA expression data were used in a machine learning algorithm to predict the presence or absence of aGvHD using either random forest or extreme gradient boosting algorithms. Patients were randomly divided into training (2/3 of patients) and validation (1/3 of patients) sets. Using post-HSCT RNA data, the machine learning algorithm selected 92 genes for predicting aGvHD that appear to play a role in PI3/AKT, MAPK, and FOXO signaling, as well as microRNA. The algorithm selected 20 genes for predicting survival included genes involved in MAPK and chemokine signaling. Using pre-HSCT RNA data, the machine learning algorithm selected 400 genes and 700 genes predicting aGvHD and overall survival, but candidate signaling pathways could not be specified in this analysis. These data show that NGS analyses of RNA expression using machine learning algorithms may be useful biomarkers of aGvHD and overall survival for patients undergoing HSCT, allowing for the identification of major signaling pathways associated with HSCT outcomes and helping to dissect the complex steps involved in the development of aGvHD. The analysis of pre-HSCT bone marrow samples may lead to pre-HSCT interventions including choice of remission induction regimens and modifications in patient health before HSCT.

Relapse after allogeneic transplantation with post-transplant cyclophosphamide: Shattering myths and evolving insight

Early studies in allogeneic blood or marrow transplantation (alloBMT) demonstrated that HLA-mismatching was protective again relapse. However, benefits in relapse reduction were outweighed by a high risk of graft-versus-host disease (GVHD) when using conventional pharmacological immunosuppression. Post-transplant cyclophosphamide(PTCy)-based platforms abated the risk of GVHD thereby overcoming the negative effects of HLA-mismatching on survival. However, since its inception, PTCy has been shadowed by a reputation for a greater risk of relapse when compared with traditional GVHD prophylaxis. Specifically, whether PTCy reduces the anti-tumor efficacy of HLA-mismatched alloBMT by killing alloreactive T cells has been the subject of debate since the early 2000's. Here we review the many studies demonstrating the potent graft-versus-malignancy (GVM) properties of alloBMT with PTCy. We discuss the laboratory data from PTCy platforms supporting that T regulatory cells may be a major mechanism of prevention of GVHD and that natural killer (NK) cells may be early effectors of GVM. Finally, we propose potential paths to optimize GVM through selecting for class II mismatching and augmenting NK cell activity.

Chronic GvHD NIH Consensus Project Biology Task Force: evolving path to personalized treatment of chronic GvHD

Chronic graft-versus-host disease (cGvHD) remains a prominent barrier to allogeneic hematopoietic stem cell transplantion as the leading cause of nonrelapse mortality and significant morbidity. Tremendous progress has been achieved in both the understanding of pathophysiology and the development of new therapies for cGvHD. Although our field has historically approached treatment from an empiric position, research performed at the bedside and bench has elucidated some of the complex pathophysiology of cGvHD. From the clinical perspective, there is significant variability of disease manifestations between individual patients, pointing to diverse biological underpinnings. Capitalizing on progress made to date, the field is now focused on establishing personalized approaches to treatment. The intent of this article is to concisely review recent knowledge gained and formulate a path toward patient-specific cGvHD therapy.

Phase II Study of Myeloablative 7-8/8-Matched Allotransplantation with Post-Transplantation Cyclophosphamide, Tacrolimus, and Mycophenolate Mofetil

Graft-versus-host disease (GVHD) is the major toxicity of allogeneic hematopoietic cell transplantation (HCT). We hypothesized that a GVHD prophylaxis regimen of post-transplantation cyclophosphamide (PTCy), tacrolimus (Tac), and mycophenolate mofetil (MMF) would be associated with incidences of acute and chronic GVHD in patients receiving a matched or single antigen mismatched HCT. This Phase II study was conducted at the University of Minnesota using a myeloablative regimen of either total body irradiation (TBI) at a total dose of 1320 cGy, administered in 165-cGy fractions, twice daily from day -4 to day -1, or busulfan (Bu) 3.2 mg/kg daily (cumulative area under the curve, 19,000 to 21,000 μmol/min/L) plus fludarabine (Flu) 40 mg/m2 once daily on days -5 to -2, followed by a GVHD prophylaxis regimen of PTCy 50 mg/kg on days +3 and +4, Tac, and MMF beginning on day +5. The primary endpoint was the cumulative incidence of chronic GVHD necessitating systemic immunosuppression (IST) at 1 year post-transplantation. Between March 2018 and May 2022, we enrolled 125 pediatric and adult patients, with a median follow-up of 813 days. The incidence of chronic GVHD necessitating systemic IST at 1 year was 5.5%. The rate of grade II-IV acute GVHD was 17.1%, and that of grade III-IV acute GVHD was 5.5%. Two-year overall survival was 73.7%, and 2-year graft-versus-host disease-free, relapse-free survival was 52.2%. The 2-year cumulative incidence of nonrelapse mortality was 10.2%, and the rate of relapse was 39.1%. There was no statistically significant difference in survival outcomes between recipients of matched donor transplants versus recipients of 7/8 matched donor transplants. Our data show that myeloablative HCT with PTCy/Tac/MMF results in an extremely low incidence of severe acute and chronic GVHD in well-matched allogeneic HCT.

Graft versus Leukemia in 2023

Allogeneic hematopoietic stem cell transplantation (HSCT) is commonly utilized in the management of leukemia across multiple subtypes. Graft versus leukemia (GVL) is a critical component of successful transplantation and involves donor cells eradicating residual leukemia within the recipient. Graft versus host disease (GVHD) by contrast is a common complication of the transplantation process in which donor cells identify the recipient's various organ systems as foreign, thereby leading to a multitude of organ toxicities that can be described as autoimmune in nature. As both GVL and GVHD are mediated by a similar mechanism, these processes are felt to occur in tandem with one another. Here, we review the allogeneic HCT process in the context of GVL.

Posttransplant cyclophosphamide vs tacrolimus-based GVHD prophylaxis: lower incidence of relapse and chronic GVHD

The ability of posttransplant cyclophosphamide (PTCY) to facilitate haploidentical transplantation has spurred interest in whether PTCY can improve clinical outcomes in patients with HLA-matched unrelated donors undergoing peripheral blood stem cell transplantation (PBSCT). We investigated our institutional experience using PTCY-based graft-versus-host disease (GVHD) prophylaxis compared with conventional tacrolimus-based regimens. We compared overall survival, progression-free survival (PFS), relapse, nonrelapse mortality, and acute and chronic GVHD in 107 adult patients receiving a PTCY-based regimen vs 463 patients receiving tacrolimus-based regimens for GVHD prophylaxis. The 2 cohorts were well balanced for baseline characteristics except that more patients in the PTCY cohort having received 7-of-8-matched PBSCT. There was no difference in acute GVHD. All-grade chronic GVHD and moderate-to-severe chronic GVHD were substantially reduced in patients receiving PTCY compared with in those receiving tacrolimus-based regimens (2-year moderate-to-severe chronic GVHD: 12% vs 36%; P < .0001). Recipients of PTCY-based regimens also had a lower incidence of relapse compared with recipients of tacrolimus-based regimens (25% vs 34% at 2-years; P = .027), primarily in patients who received reduced intensity conditioning. This led to improved PFS in the PTCY cohort (64% vs 54% at 2 years; P = .02). In multivariable analysis, the hazard ratio was 0.59 (P = .015) for PFS and the subdistribution hazard ratio was 0.27 (P < .0001) for moderate-to-severe chronic GVHD and 0.59 (P = .015) for relapse. Our results suggest that PTCY prophylaxis is associated with lower rates of relapse and chronic GVHD in patients who receive HLA-matched unrelated donor PBSCT.

Graft-versus-host disease: teaching old drugs new tricks at less cost

Graft-versus-host disease (GVHD) remains a major cause of morbidity and mortality after allogeneic stem cell transplantation (SCT). Currently, more patients can receive SCT. This is attributed to the use of reduced intensity regimens and the use of different GVHD prophylaxis that breaks the barrier of human leukocyte antigen, allowing an increase in the donor pool. Once an area with relatively few clinical trial options, there has been an increase in interest in GVHD prophylaxis and treatment, which has led to many US Food and Drug Administration (FDA) approvals. Although there is considerable excitement over novel therapies, many patients may not have access to them due to geographical or other resource constraints. In this review article, we summarize the latest evidence on how we can continue to repurpose drugs for GVHD prophylaxis and treatment. Drugs covered by our review include those that have been FDA approved for other uses for at least 15 years (since 2008); thus, they are likely to have generic equivalents available now or in the near future.

Joint models quantify associations between immune cell kinetics and allo-immunological events after allogeneic stem cell transplantation and subsequent donor lymphocyte infusion

Alloreactive donor-derived T-cells play a pivotal role in alloimmune responses after allogeneic hematopoietic stem cell transplantation (alloSCT); both in the relapse-preventing Graft-versus-Leukemia (GvL) effect and the potentially lethal complication Graft-versus-Host-Disease (GvHD). The balance between GvL and GvHD can be shifted by removing T-cells via T-cell depletion (TCD) to reduce the risk of GvHD, and by introducing additional donor T-cells (donor lymphocyte infusions [DLI]) to boost the GvL effect. However, the association between T-cell kinetics and the occurrence of allo-immunological events has not been clearly demonstrated yet. Therefore, we investigated the complex associations between the T-cell kinetics and alloimmune responses in a cohort of 166 acute leukemia patients receiving alemtuzumab-based TCD alloSCT. Of these patients, 62 with an anticipated high risk of relapse were scheduled to receive a prophylactic DLI at 3 months after transplant. In this setting, we applied joint modelling which allowed us to better capture the complex interplay between DLI, T-cell kinetics, GvHD and relapse than traditional statistical methods. We demonstrate that DLI can induce detectable T-cell expansion, leading to an increase in total, CD4+ and CD8+ T-cell counts starting at 3 months after alloSCT. CD4+ T-cells showed the strongest association with the development of alloimmune responses: higher CD4 counts increased the risk of GvHD (hazard ratio 2.44, 95% confidence interval 1.45-4.12) and decreased the risk of relapse (hazard ratio 0.65, 95% confidence interval 0.45-0.92). Similar models showed that natural killer cells recovered rapidly after alloSCT and were associated with a lower risk of relapse (HR 0.62, 95%-CI 0.41-0.93). The results of this study advocate the use of joint models to further study immune cell kinetics in different settings.

Validated graft-specific biomarkers identify patients at risk for chronic graft-versus-host disease and death

BACKGROUNDChronic graft-versus-host disease (cGVHD) is a serious complication of allogeneic hematopoietic cell transplantation (HCT). More accurate information regarding the risk of developing cGVHD is required. Bone marrow (BM) grafts contribute to lower cGVHD, which creates a dispute over whether risk biomarker scores should be used for peripheral blood (PB) and BM.METHODSDay 90 plasma proteomics from PB and BM recipients developing cGVHD revealed 5 risk markers that were added to 8 previous cGVHD markers to screen 982 HCT samples of 2 multicenter Blood and Marrow Transplant Clinical Trials Network (BMTCTN) cohorts. Each marker was tested for its association with cause-specific hazard ratios (HRs) of cGVHD using Cox-proportional-hazards models. We paired these clinical studies with biomarker measurements in a mouse model of cGVHD.RESULTSSpearman correlations between DKK3 and MMP3 were significant in both cohorts. In BMTCTN 0201 multivariate analyses, PB recipients with 1-log increase in CXCL9 and DKK3 were 1.3 times (95% CI: 1.1-1.4, P = 0.001) and 1.9 times (95%CI: 1.1-3.2, P = 0.019) and BM recipients with 1-log increase in CXCL10 and MMP3 were 1.3 times (95%CI: 1.0-1.6, P = 0.018 and P = 0.023) more likely to develop cGVHD. In BMTCTN 1202, PB patients with high CXCL9 and MMP3 were 1.1 times (95%CI: 1.0-1.2, P = 0.037) and 1.2 times (95%CI: 1.0-1.3, P = 0.009) more likely to develop cGVHD. PB patients with high biomarkers had increased likelihood to develop cGVHD in both cohorts (22%-32% versus 8%-12%, P = 0.002 and P < 0.001, respectively). Mice showed elevated circulating biomarkers before the signs of cGVHD.CONCLUSIONBiomarker levels at 3 months after HCT identify patients at risk for cGVHD occurrence.FUNDINGNIH grants R01CA168814, R21HL139934, P01CA158505, T32AI007313, and R01CA264921.

Complex interactions of cellular players in chronic Graft-versus-Host Disease

Chronic Graft-versus-Host Disease is a life-threatening inflammatory condition that affects many patients after allogeneic hematopoietic stem cell transplantation. Although we have made substantial progress in understanding disease pathogenesis and the role of specific immune cell subsets, treatment options are still limited. To date, we lack a global understanding of the interplay between the different cellular players involved, in the affected tissues and at different stages of disease development and progression. In this review we summarize our current knowledge on pathogenic and protective mechanisms elicited by the major involved immune subsets, being T cells, B cells, NK cells and antigen presenting cells, as well as the microbiome, with a special focus on intercellular communication of these cell types via extracellular vesicles as up-and-coming fields in chronic Graft-versus-Host Disease research. Lastly, we discuss the importance of understanding systemic and local aberrant cell communication during disease for defining better biomarkers and therapeutic targets, eventually enabling the design of personalized treatment schemes.

Tocilizumab increases regulatory T cells, reduces natural killer cells and delays graft-versus-host disease development in humanized mice treated with post-transplant cyclophosphamide

Graft-versus-host disease (GVHD) is a life-threatening complication following donor hematopoietic stem cell transplantation, where donor T cells damage host tissues. This study investigated the effect of tocilizumab (TOC) combined with post-transplant cyclophosphamide (PTCy) on immune cell engraftment and GVHD development in a humanized mouse model. NOD-scid-IL2Rγ^null (NSG) mice were injected intraperitoneally with 2 × 10⁷ human (h) peripheral blood mononuclear cells and cyclophosphamide (33 mg kg^-1 ) or saline on days 3 and 4, then TOC or control antibody (0.5 mg mouse^-1 ) twice weekly for 28 days. Mice were monitored for clinical signs of GVHD for either 28 or 70 days. Spleens and livers were assessed for human leukocyte subsets, and serum cytokines and tissue histology were analyzed. In the short-term model (day 28), liver and lung damage were reduced in PTCy + TOC compared with control mice. All groups showed similar splenic hCD45⁺ leukocyte engraftment (55-60%); however, PTCy + TOC mice demonstrated significantly increased (1.5-2-fold) splenic regulatory T cells. Serum human interferon gamma was significantly reduced in PTCy + TOC compared with control mice. Long-term (day 70), prolonged survival was similar in PTCy + TOC (median survival time, > 70 days) and PTCy mice (median survival time, 56 days). GVHD onset was significantly delayed in PTCy + TOC, compared with TOC or control mice. Notably, natural killer cells were reduced (77.5%) in TOC and PTCy + TOC mice. Overall, combining PTCy with TOC increases regulatory T cells and reduces clinical signs of early GVHD, but does not improve long-term survival compared with PTCy alone.

NK cell defects: implication in acute myeloid leukemia

Acute Myeloid Leukemia (AML) is a complex disease with rapid progression and poor/unsatisfactory outcomes. In the past few years, the focus has been on developing newer therapies for AML; however, relapse remains a significant problem. Natural Killer cells have strong anti-tumor potential against AML. This NK-mediated cytotoxicity is often restricted by cellular defects caused by disease-associated mechanisms, which can lead to disease progression. A stark feature of AML is the low/no expression of the cognate HLA ligands for the activating KIR receptors, due to which these tumor cells evade NK-mediated lysis. Recently, different Natural Killer cell therapies have been implicated in treating AML, such as the adoptive NK cell transfer, Chimeric antigen receptor-modified NK (CAR-NK) cell therapy, antibodies, cytokine, and drug treatment. However, the data available is scarce, and the outcomes vary between different transplant settings and different types of leukemia. Moreover, remission achieved by some of these therapies is only for a short time. In this mini-review, we will discuss the role of NK cell defects in AML progression, particularly the expression of different cell surface markers, the available NK cell therapies, and the results from various preclinical and clinical trials.

Phase II Study of Myeloablative 8/8- or 7/8-Matched Allotransplantation with Post-Transplant Cyclophosphamide, Tacrolimus, and Mycophenolate Mofetil: Marked Reduction in GVHD Risk Without Increased Relapse Risk Compared to Historical Cyclosporine/Methotrexate

Introduction

Graft-versus host disease (GVHD) is a major limitation to the success of allogeneic hematopoietic cell transplant (HCT). We hypothesized that the GVHD prophylaxis regimen of post-transplant cyclophosphamide (PTCy), tacrolimus (Tac) and mycophenolate mofetil (MMF) would reduce the incidence of GVHD in patients receiving a matched or single antigen mismatched HCT without an increase in risk of malignant relapse.

Methods

This is a phase II study conducted at the University of Minnesota using a myeloablative regimen of either: (A) total body irradiation (TBI, total dose 1320 cGy, administered in 165 cGy fractions, twice a day from days -4 to -1) or (B) Busulfan 3.2mg/kg daily (cumulative AUC 19,000 - 21,000 μmol/min/L) plus fludarabine 160mg/m2 days -5 to -2, followed by a GVHD prophylaxis regimen of PTCy (50mg/kg days +3 and +4), Tac and MMF (beginning day +5). The primary endpoint is cumulative incidence of chronic GVHD requiring systemic immunosuppression at 1-year post-transplant. We compared results to our previous myeloablative protocol for matched donors utilizing cyclosporine/methotrexate (CSA/MTX) GVHD prophylaxis.

Results

From March 2018 - June 2022, we enrolled and treated 125 pediatric and adult patients with a median follow up of 472 days. Grade II-IV acute GVHD occurred in 16% (95% confidence interval (CI): 9-23%); Grade III-IV acute GVHD was 4% (CI: 0-8%). No patients experienced grade IV GVHD, and there were no deaths due to GVHD before day 100. Only 3 developed chronic GVHD requiring immune suppression, (4%, CI: 0-8%). Two-year overall survival (OS) was 80% (CI: 69-87%), and (graft-versus-host disease-free, relapse-free survival) GRFS 57% (CI: 45-67%), both higher than historical CSA/MTX. The incidence of grade II-IV aGVHD, cGVHD, and NRM were all lower with PTCy/Tac/MMF compared to historical CSA/MTX. One-quarter (25%) experienced relapse (CI: 15-36%) similar to historical CSA/MTX. There was no statistically significant difference in survival outcomes between recipients of matched versus 7/8 donors.

Conclusion

Myeloablative HCT with PTCy/Tac/MMF results in extremely low incidence of severe acute or chronic GVHD, the primary endpoint of this clinical trial. Relapse risk is not increased compared to our historical CSA/MTX cohort.

Inflammatory CD4/CD8 double-positive human T cells arise from reactive CD8 T cells and are sufficient to mediate GVHD pathology

An important paradigm in allogeneic hematopoietic cell transplantations (allo-HCTs) is the prevention of graft-versus-host disease (GVHD) while preserving the graft-versus-leukemia (GVL) activity of donor T cells. From an observational clinical study of adult allo-HCT recipients, we identified a CD4+/CD8+ double-positive T cell (DPT) population, not present in starting grafts, whose presence was predictive of ≥ grade 2 GVHD. Using an established xenogeneic transplant model, we reveal that the DPT population develops from antigen-stimulated CD8 T cells, which become transcriptionally, metabolically, and phenotypically distinct from single-positive CD4 and CD8 T cells. Isolated DPTs were sufficient to mediate xeno-GVHD pathology when retransplanted into naïve mice but provided no survival benefit when mice were challenged with a human B-ALL cell line. Overall, this study reveals human DPTs as a T cell population directly involved with GVHD pathology.

Effect of graft-versus-host disease on posttransplant outcomes following single cord blood transplantation in comparison to haploidentical transplantation with posttransplant cyclophosphamide for adult acute myeloid leukemia

BACKGROUND

The possibility that human leukocyte antigen (HLA) mismatches could reduce relapse after alternative HLA-mismatched allogeneic hematopoietic cell transplantation (HCT) is an attractive concept for acute myeloid leukemia (AML). However, it remains unclear whether the prognostic effect of graft-versus-host disease (GVHD) on survival differs between single-unit cord blood transplantation (CBT) or haploidentical HCT using posttransplant cyclophosphamide (PTCy-haplo HCT) for AML.

OBJECTIVE

The objective of this retrospective study was to compare the effect of acute and chronic GVHD on posttransplant outcomes between CBT and PTCy-haplo HCT.

STUDY DESIGN

We retrospectively evaluated the effect of acute and chronic GVHD on posttransplant outcomes following CBT and PTCy-haplo HCT in adults with AML (n=1,981) between 2014 and 2020 using a Japanese registry database.

RESULTS

In the univariate analysis, the probability of overall survival was significantly greater in patients who developed grade I-II acute GVHD (P<0.001 by log-rank test) and limited chronic GVHD (P<0.001 by log-rank test) among CBT recipients, but these effects were not significant among PTCy-haplo HCT recipients. In the multivariate analysis, in which the development of GVHD was treated as a time-dependent covariate, the effect of grade I-II acute GVHD on reducing overall mortality was significant between CBT and PTCy-haplo HCT (adjusted hazard ratio [HR] for CBT: 0.73, 95% confidence interval [CI]: 0.60-0.87; adjusted HR for PTCy-haplo HCT: 1.07, 95% CI: 0.70-1.64; p for interaction=0.038).

CONCLUSION

Our data demonstrate that grade I-II acute GVHD was associated with a significant improvement in overall mortality in adults with AML receiving CBT but not PTCy-haplo HCT.

Three-Year Outcomes in Recipients of Mismatched Unrelated Bone Marrow Donor Transplants Using Post-Transplantation Cyclophosphamide: Follow-Up from a National Marrow Donor Program-Sponsored Prospective Clinical Trial

The use of post-transplantation cyclophosphamide (PTCy) as graft-versus-host disease (GVHD) prophylaxis has resulted in reductions in GVHD and improved outcomes in allogeneic hematopoietic cell transplantation (HCT) using HLA-mismatched related donors. We report the 3-year outcomes of the first multicenter prospective clinical trial using PTCy in the setting of mismatched unrelated donor (MMUD) bone marrow HCT. The study enrolled 80 patients, treated with either myeloablative conditioning (MAC; n = 40) or reduced-intensity conditioning (RIC; n = 40), with the primary endpoint of 1-year overall survival (OS). The median follow-up for this study was 34 months (range, 12 to 46 months) in the RIC group and 36 months (range, 18 to 49 months) in the MAC group. Three-year OS and nonrelapse mortality were 70% and 15%, respectively, in the RIC group and 62% and 10% in the MAC group. No GVHD was reported after 1 year. The incidence of relapse was 29% in the RIC group and 51% in the MAC group. OS did not differ based on HLA match grade (63% in the 7/8 strata and 71% in the 4 to 6/8 strata). These encouraging outcomes, which were sustained for 3 years post-HCT, support the continued exploration of MMUD HCT using a PTCy platform. Important future areas to address include relapse reduction and furthering our understanding of optimal donor selection based on HLA and non-HLA factors.

GVHD occurrence does not reduce AML relapse following PTCy-based haploidentical transplantation: a study from the ALWP of the EBMT

The association between graft-versus-host disease (GVHD) occurrence and acute myeloid leukemia (AML) relapse in patients treated with HLA-haploidentical allogeneic hematopoietic stem cell transplantation (Haplo-HCT) with post-transplant cyclophosphamide (PTCy)-based GVHD prophylaxis has remained debated. Here, we addressed this issue in patients with active AML at transplantation. 2-year cumulative incidences of relapse and leukemia-free survival (LFS) were 49% and 32.3%, respectively. There were no associations between acute nor chronic GVHD of any grade and lower relapse incidence. However, grade I acute GVHD was associated with better LFS (HR = 0.71, 95% CI 0.51-0.99, P = 0.04). In contrast, grade III-IV acute (HR = 3.09, 95% CI 1.87-5.12, P < 0.0001) as well as extensive chronic (HR = 3.3, 95% CI 1.81-6.04, P = 0.0001) GVHD correlated with higher nonrelapse mortality leading to lower LFS (HR = 1.36, 95% CI 0.99-1.86, P = 0.056 and HR = 1.97, 95% CI 1.35-2.89, P = 0.0004, respectively). In conclusion, these data suggest a dissociation of graft-versus-leukemia effects from GVHD in patients with active AML treated with PTCy-based Haplo-HCT.

Post-transplant cyclophosphamide prevents xenogeneic graft-versus-host disease while depleting proliferating regulatory T cells

Graft-versus-host disease (GVHD) remains a serious limitation of allogeneic hematopoietic cell transplantation (allo-HCT). While post-transplant administration of cyclophosphamide (PTCy) is increasingly used as GVHD prophylaxis, its precise mechanisms of action and its impact on graft-versus-leukemia effects have remained debated. Here, we studied the mechanisms of xenogeneic GVHD (xGVHD) prevention by PTCy in different humanized mouse models. We observed that PTCy attenuated xGVHD. Using flow cytometry and single-cell RNA-sequencing, we demonstrated that PTCy depleted proliferative CD8⁺ and conventional CD4⁺ T cells but also proliferative regulatory T cells (Treg). Further, T-cell receptor β variable region sequencing (TCRVB) analyses demonstrated that highly xenoreactive T-cell clones were depleted by PTCy. Although Treg frequencies were significantly higher in PTCy-treated than in control mice on day 21, xGVHD attenuation by PTCy was not abrogated by Treg depletion. Finally, we observed that PTCy did not abrogate graft-versus-leukemia effects.

Peripheral blood persistence and expansion of transferred non-genetically modified Natural Killer cells might not be necessary for clinical activity

Natural killer (NK) cells are innate lymphocytes that react without previous exposition to virus infected or malignant cells and stimulate adaptive immune response to build a long-lasting immunity against it. To that end, tissue resident NK cells are predominantly regulatory as opposed to cytotoxic. In the hematopoietic stem cell transplant (HSCT) setting, which curative potential relies on the graft versus leukemia effect, NK cells are known to play a significant role. This knowledge has paved the way to the active investigation on its anti-tumor effect outside the stem cell transplant scenario. Based on the relevant literature on the adoptive transfer of non-genetically modified NK cells for the treatment of relapsed/refractory acute leukemia and on our own experience, we discuss the role of donor cell peripheral blood persistence and expansion and its lack of correlation with anti-leukemia activity.

How I prevent GVHD in high-risk patients: posttransplant cyclophosphamide and beyond

Advances in conditioning, graft-versus-host disease (GVHD) prophylaxis and antimicrobial prophylaxis have improved the safety of allogeneic hematopoietic cell transplantation (HCT), leading to a substantial increase in the number of patients transplanted each year. This influx of patients along with progress in remission-inducing and posttransplant maintenance strategies for hematologic malignancies has led to new GVHD risk factors and high-risk groups: HLA-mismatched related (haplo) and unrelated (MMUD) donors; older recipient age; posttransplant maintenance; prior checkpoint inhibitor and autologous HCT exposure; and patients with benign hematologic disorders. Along with the changing transplant population, the field of HCT has dramatically shifted in the past decade because of the widespread adoption of posttransplantation cyclophosphamide (PTCy), which has increased the use of HLA-mismatched related donors to levels comparable to HLA-matched related donors. Its success has led investigators to explore PTCy's utility for HLA-matched HCT, where we predict it will be embraced as well. Additionally, combinations of promising new agents for GVHD prophylaxis such as abatacept and JAK inhibitors with PTCy inspire hope for an even safer transplant platform. Using 3 illustrative cases, we review our current approach to transplantation of patients at high risk of GVHD using our modern armamentarium.

Haploidentical Natural Killer Cell Therapy as an Adjunct to Stem Cell Transplantation for Treatment of Refractory Acute Myeloid Leukemia

Refractory acute myeloid leukemia (AML), defined as failure of two cycles of induction therapy at diagnosis or of one cycle at relapse, represents a subgroup with poor outcomes. Haploidentical natural killer cell (NK) therapy is a strategy that is being explored in refractory malignancies. Historically, at our center, patients with refractory AML have been treated with cytoreductive therapy (fludarabine + cytosine + granulocyte colony-stimulating factor ± idarubicin or mitoxantrone + etoposide) followed by 1-week rest and then reduced-intensity transplant with fludarabine + melphalan. We used the same backbone for this trial (CTRI/2019/02/017505) with the addition of CD56-positive cells from a family donor infused 1 day after the completion of chemotherapy. CD56-positive selection was done using a CliniMACS Prodigy system (Miltenyi Biotec, Bergisch Gladbach, Germany) followed by overnight incubation in autologous plasma with 2 micromolar arsenic trioxide and 500 U/mL of interleukin-2. From February 2019, 14 patients with a median age of 29 years (interquartile range [IQR]: 16.5-38.5) were enrolled in this trial. Six were females. Six had primary refractory AML while eight had relapsed refractory AML. The median CD56-cell dose infused was 46.16 × 106/kg (IQR: 25.06-70.36). One patient withdrew consent after NK cell infusion. Of the 13 patients who proceeded to transplant, five died of immediate post-transplant complications while two did not engraft but were in morphologic leukemia-free state (both subsequently died of infective complications after the second transplant). Of the remaining six patients who engrafted and survived beyond 1 month of the transplant, two developed disease relapse and died. The remaining four patients are alive and relapse free at the last follow-up (mean follow-up duration of surviving patients is 24 months). The 2-year estimated overall survival for the cohort was 28.6% ± 12.1% while the treatment-related mortality (TRM) with this approach was 38.5% ± 13.5%. Haploidentical NK cell therapy as an adjunct to transplant is safe and needs further exploration in patients with AML. For refractory AML, post-transplant NK infusion and strategies to reduce TRM while using pre-transplant NK infusion merit exploration.

Blasts in context: the impact of the immune environment on acute myeloid leukemia prognosis and treatment

Acute myeloid leukemia (AML) is a cancer that originates from the bone marrow (BM). Under physiological conditions, the bone marrow supports the homeostasis of immune cells and hosts memory lymphoid cells. In this review, we summarize our present understanding of the role of the immune microenvironment on healthy bone marrow and on the development of AML, with a focus on T cells and other lymphoid cells. The types and function of different immune cells involved in the AML microenvironment as well as their putative role in the onset of disease and response to treatment are presented. We also describe how the immune context predicts the response to immunotherapy in AML and how these therapies modulate the immune status of the bone marrow. Finally, we focus on allogeneic stem cell transplantation and summarize the current understanding of the immune environment in the post-transplant bone marrow, the factors associated with immune escape and relevant strategies to prevent and treat relapse.

Depletion of exhausted alloreactive T cells enables targeting of stem-like memory T cells to generate tumor-specific immunity

Some hematological malignancies such as multiple myeloma are inherently resistant to immune-mediated antitumor responses, the cause of which remains unknown. Allogeneic bone marrow transplantation (alloBMT) is the only curative immunotherapy for hematological malignancies due to profound graft-versus-tumor (GVT) effects, but relapse remains the major cause of death. We developed murine models of alloBMT where the hematological malignancy is either sensitive [acute myeloid leukemia (AML)] or resistant (myeloma) to GVT effects. We found that CD8+ T cell exhaustion in bone marrow was primarily alloantigen-driven, with expression of inhibitory ligands present on myeloma but not AML. Because of this tumor-independent exhaustion signature, immune checkpoint inhibition (ICI) in myeloma exacerbated graft-versus-host disease (GVHD) without promoting GVT effects. Administration of post-transplant cyclophosphamide (PT-Cy) depleted donor T cells with an exhausted phenotype and spared T cells displaying a stem-like memory phenotype with chromatin accessibility present in cytokine signaling genes, including the interleukin-18 (IL-18) receptor. Whereas ICI with anti-PD-1 or anti-TIM-3 remained ineffective after PT-Cy, administration of a decoy-resistant IL-18 (DR-18) strongly enhanced GVT effects in both myeloma and leukemia models, without exacerbation of GVHD. We thus defined mechanisms of resistance to T cell-mediated antitumor effects after alloBMT and described an immunotherapy approach targeting stem-like memory T cells to enhance antitumor immunity.

Impact of natural killer cells on outcomes after allogeneic hematopoietic stem cell transplantation: A systematic review and meta-analysis

Background

Natural killer (NK) cells play a vital role in early immune reconstitution following allogeneic hematopoietic stem cell transplantation (HSCT).

Methods

A literature search was performed on PubMed, Cochrane, and Clinical trials.gov through April 20, 2022. We included 21 studies reporting data on the impact of NK cells on outcomes after HSCT. Data was extracted following the PRISMA guidelines. Pooled analysis was done using the meta-package (Schwarzer et al.). Proportions with 95% confidence intervals (CI) were computed.

Results

We included 1785 patients from 21 studies investigating the impact of NK cell reconstitution post-HSCT (8 studies/1455 patients), stem cell graft NK cell content (4 studies/185 patients), therapeutic NK cell infusions post-HSCT (5 studies/74 patients), and pre-emptive/prophylactic NK cell infusions post-HSCT (4 studies/77 patients). Higher NK cell reconstitution was associated with a better 2-year overall survival (OS) (high: 77%, 95%CI 0.73-0.82 vs low: 55%, 95%CI 0.37-0.72; n=899), however, pooled analysis for relapse rate (RR) or graft versus host disease (GVHD) could not be performed due to insufficient data. Higher graft NK cell content demonstrated a trend towards a better pooled OS (high: 65.2%, 95%CI 0.47-0.81 vs low: 46.5%, 95%CI 0.24-0.70; n=157), lower RR (high: 16.9%, 95%CI 0.10-0.25 vs low: 33%, 95%CI 0.04-0.72; n=157), and lower acute GVHD incidence (high: 27.6%, 95%CI 0.20-0.36 vs low: 49.7%, 95%CI 0.26-0.74; n=157). Therapeutic NK or cytokine-induced killer (CIK) cell infusions for hematologic relapse post-HSCT reported an overall response rate (ORR) and complete response (CR) of 48.9% and 11% with CIK cell infusions and 82.8% and 44.8% with NK cell infusions, respectively. RR, acute GVHD, and chronic GVHD were observed in 55.6% and 51.7%, 34.5% and 20%, and 20.7% and 11.1% of patients with CIK and NK cell infusions, respectively. Pre-emptive donor-derived NK cell infusions to prevent relapse post-HSCT had promising outcomes with 1-year OS of 69%, CR rate of 42%, ORR of 77%, RR of 28%, and acute and chronic GVHD rates of 24.9% and 3.7%, respectively.

Conclusion

NK cells have a favorable impact on outcomes after HSCT. The optimal use of NK cell infusions post-HSCT may be in a pre-emptive fashion to prevent disease relapse.

Immune landscape after allo-HSCT: TIGIT- and CD161-expressing CD4 T cells are associated with subsequent leukemia relapse

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the most effective treatment for selected patients with acute myeloid leukemia (AML) and relies on a "graft-versus-leukemia" effect (GVL) where donor T lymphocytes mediate control of malignant cell growth. However, relapse remains the major cause of death after allo-HSCT. In various malignancies, several immunoregulatory mechanisms have been shown to restrain antitumor immunity, including ligand-mediated engagement of inhibitory receptors (IRs) on effector cells, and induction of immunosuppressive cell subsets, such as regulatory T cells (Tregs) or myeloid-derived suppressor cells (MDSCs). Relapse after HSCT remains a major therapeutic challenge, but immunoregulatory mechanisms involved in restraining the GVL effect must be better deciphered in humans. We used mass cytometry to comprehensively characterize circulating leukocytes in 2 cohorts of patients after allo-HSCT. We first longitudinally assessed various immunoregulatory parameters highlighting specific trends, such as opposite dynamics between MDSCs and Tregs. More generally, the immune landscape was stable from months 3 to 6, whereas many variations occurred from months 6 to 12 after HSCT. Comparison with healthy individuals revealed that profound alterations in the immune equilibrium persisted 1 year after HSCT. Importantly, we found that high levels of TIGIT and CD161 expression on CD4 T cells at month 3 after HSCT were distinct features significantly associated with subsequent AML relapse in a second cross-sectional cohort. Altogether, these data provide global insights into the reconstitution of the immunoregulatory landscape after HSCT and highlight non-canonical IRs associated with relapse, which could open the path to new prognostic tools or therapeutic targets to restore subverted anti-AML immunity.

Efflux Capacity and Aldehyde Dehydrogenase Both Contribute to CD8+ T-cell Resistance to Posttransplant Cyclophosphamide

CD8⁺ T cells increase drug effluxing and aldehyde dehydrogenase expression in allogeneic reactions, enhancing resistance to cyclophosphamide.

Common γ-chain cytokines and the proliferative state of the cell modulate these resistance pathways.

Mechanisms of T-cell survival after cytotoxic chemotherapy, including posttransplantation cyclophosphamide (PTCy), are not well understood. Here, we explored the impact of PTCy on human CD8⁺ T-cell survival and reconstitution, including what cellular pathways drive PTCy resistance. In major histocompatibility complex (MHC)-mismatched mixed lymphocyte culture (MLC), treatment with mafosfamide, an in vitro active cyclophosphamide analog, preserved a relatively normal distribution of naïve and memory CD8⁺ T cells, whereas the percentages of mucosal-associated invariant T (MAIT) cells and phenotypically stem cell memory (Tscm) T-cell subsets were increased. Activated (CD25⁺) and proliferating CD8⁺ T cells were derived from both naïve and memory subsets and were reduced but still present after mafosfamide. By contrast, cyclosporine-A (CsA) or rapamycin treatment preferentially maintained nonproliferating CD25⁻ naïve cells. Drug efflux capacity and aldehyde dehydrogenase-1A1 expression were increased in CD8⁺ T cells in allogeneic reactions in vitro and in patients, were modulated by common γ-chain cytokines and the proliferative state of the cell, and contributed to CD8⁺ T-cell survival after mafosfamide. The CD8⁺ T-cell composition early after hematopoietic cell transplantation (HCT) in PTCy-treated patients was dominated by CD25⁺ and phenotypically memory, including Tscm and MAIT, cells, consistent with MLC. Yet, MHC-mismatched murine HCT studies revealed that peripherally expanded, phenotypically memory T cells 1 to 3 months after transplant originated largely from naïve-derived rather than memory-derived T cells surviving PTCy, suggesting that initial resistance and subsequent immune reconstitution are distinct. These studies provide insight into the complex immune mechanisms active in CD8⁺ T-cell survival, differentiation, and reconstitution after cyclophosphamide, with relevance for post-HCT immune recovery, chemotherapy use in autologous settings, and adoptive cellular therapies.

Assessment of systemic and gastrointestinal tissue damage biomarkers for GVHD risk stratification

Two biomarker algorithms that include only systemic inflammation biomarkers predicted response to steroid treatment but not 6-month NRM.

Two biomarker algorithms that include ≥1 biomarker of GI tissue damage predicted both response to treatment and 6-month NRM.

We used a rigorous PRoBE (prospective-specimen collection, retrospective-blinded-evaluation) study design to compare the ability of biomarkers of systemic inflammation and biomarkers of gastrointestinal (GI) tissue damage to predict response to corticosteroid treatment, the incidence of clinically severe disease, 6-month nonrelapse mortality (NRM), and overall survival in patients with acute graft-versus-host disease (GVHD). We prospectively collected serum samples of newly diagnosed GVHD patients (n = 730) from 19 centers, divided them into training (n = 352) and validation (n = 378) cohorts, and measured TNFR1, TIM3, IL6, ST2, and REG3α via enzyme-linked immunosorbent assay. Performances of the 4 strongest algorithms from the training cohort (TNFR1 + TIM3, TNFR1 + ST2, TNFR1 + REG3α, and ST2 + REG3α) were evaluated in the validation cohort. The algorithm that included only biomarkers of systemic inflammation (TNFR1 + TIM3) had a significantly smaller area under the curve (AUC; 0.57) than the AUCs of algorithms that contained ≥1 GI damage biomarker (TNFR1 + ST2, 0.70; TNFR1 + REG3α, 0.73; ST2 + REG3α, 0.79; all P < .001). All 4 algorithms were able to predict short-term outcomes such as response to systemic corticosteroids and severe GVHD, but the inclusion of a GI damage biomarker was needed to predict long-term outcomes such as 6-month NRM and survival. The algorithm that included 2 GI damage biomarkers was the most accurate of the 4 algorithms for all endpoints.

HLA-haploidentical transplantation for relapsed/refractory AML: better LFS with BM than with PBSC in patients ≥ 55 years of age

The best stem cell source for T-cell replete HLA-haploidentical transplantation with post-transplant cyclophosphamide (PTCy) remains to be determined. In this EBMT retrospective study we analyzed the impact of stem cell source on leukemia-free survival (LFS) in adult patients with primary refractory or relapsed acute myeloid leukemia (AML) given grafts from HLA-haploidentical donors with PTCy as graft-versus-host disease (GVHD) prophylaxis. A total of 668 patients (249 bone marrow (BM) and 419 peripheral blood stem cells (PBSC) recipients) met the inclusion criteria. The use of PBSC was associated with a higher incidence of grade II-IV (HR = 1.59, P = 0.029) and grade III-IV (HR = 2.08, P = 0.013) acute GVHD. There was a statistical interaction between patient age and the impact of stem cell source for LFS (P < 0.01). In multivariate Cox models, among patients <55 years, the use of PBSC versus BM resulted in comparable LFS (HR = 0.82, P = 0.2). In contrast, in patients ≥55 years of age, the use of PBSC versus BM was associated with higher non-relapse mortality (NRM) (HR = 1.7, P = 0.01), lower LFS (HR = 1.37, P = 0.026) and lower overall survival (OS) (HR = 1.33, P = 0.044). In conclusions, our data suggest that in patients ≥55 years of age with active AML at HLA-haploidentical transplantation, the use of BM instead of PBSC as stem cell source results in lower NRM and better LFS. In contrast among younger patients, the use of PBSC results in at least a comparable LFS. This article is protected by copyright. All rights reserved.

Harnessing allogeneic NK cells: improving outcomes with tailored donor lymphocyte infusion

Since researchers first began to uncover the mechanisms underlying allogeneic transplantation, the focus has been on T cells. T cells are a major instigator of graft-versus-host disease (GVHD). The clear association between GVHD occurrence and subsequent reduction in relapse supported concentrating on T cells as the masterminds behind graft-versus-tumor (GVT) effects. Recently, an alternative mediator of GVT has taken center stage: natural killer (NK) cells. Part of the appeal of NK cells is their potential to provide antitumor immunity without GVHD. Donor lymphocyte infusion has been the predominant treatment of relapse after allogeneic transplant, but the mix of lymphocytes includes CD8+ T cells and, consequently, a substantial risk for GVHD. In this issue of the JCI, Shapiro and colleagues developed an adoptive NK cell transfer platform to treat relapse after haploidentical allogeneic transplant. The study demonstrated safety, sought to determine resistance mechanisms, and provided avenues for future research.

Post-transplant cyclophosphamide alters immune signatures and leads to impaired T cell reconstitution in allogeneic hematopoietic stem cell transplant

Despite the increased usage of post-transplant cyclophosphamide (PTCy) in allogeneic hematopoietic stem cell transplantation (allo-HSCT), our knowledge of immune reconstitution post-allo-HSCT in the setting of PTCy is limited. Adequate immune reconstitution is the key to a successful transplant. In this study, we aim to investigate the effect of PTCy on the reconstitution of each immune component; more focus was placed on the immunophenotype and functions of T cells. Using blood samples from patients who underwent allo-HSCT under regimens containing PTCy (n = 23) versus those who received no PTCy (n = 14), we examined the impact of PTCy on the post-transplant immune response. We demonstrated a distinct T cell immune signature between PTCy versus non-PTCy group. PTCy significantly delayed T cell reconstitution and affected the T cell subsets by increasing regulatory T cells (Treg) while reducing naïve T cells. In addition, we observed remarkable enhancement of multiple inhibitory receptors (TIGIT, PD-1, TIM-3, CD38, CD39) on both CD4⁺ and CD8⁺ T cells on day 30 post-transplantation in patients who received PTCy. Importantly, upregulation of PD-1 on CD8 T cells was persistent through day 180 and these T cells were less functional, manifested by reduced cytokine production upon anti-CD3/CD28 stimulation. Furthermore, we found a significant correlation of T cell immune phenotypes to clinical outcome (disease relapse and GVHD) in patients who received PTCy. Our novel findings provide critical information to understand the mechanism of how PTCy impacts immune reconstitution in allo-HSCT and may subsequently lead to optimization of our clinical practice using this treatment.

Haploidentical vs Matched Unrelated vs Matched Sibling Donor HCT with Post-Transplantation Cyclophosphamide

With the use of post-transplantation cyclophosphamide (PTCy), the outcomes of mismatched related donor hematopoietic cell transplantation (HCT) are now approaching those of matched donor HCT. Here we compared haploidentical donor HCT versus HLA-matched unrelated donor (MUD) HCT and HLA-identical sibling donor (MSD) HCT in a cohort in which all patients received PTCy for graft-versus-host disease (GVHD) prophylaxis. We included 661 patients (275 haploidentical, 246 MUD, and 140 MSD HCT). The most common diagnoses were acute myelogenous leukemia and myelodysplastic syndrome. In multivariate analysis, the haploidentical group was found to have significantly higher nonrelapse mortality (NRM) (hazard ratio [HR], 3.2; 95% confidence interval [CI], 2 to 4.9; P < .001) and inferior progression-free survival (HR, 1.8; 95% CI, 1.4 to 2.4; P < .001) and overall survival (OS; HR, 2.2; 95% CI, 1.6 to 3; P < .001) compared with the MUD group. Relapse was the most common cause of death in all groups. Among causes of NRM, the haploidentical group had more infection-related deaths and fewer GVHD-related deaths than the other groups. The haploidentical group also had a higher risk of viral and fungal infections, grade ≥3 hemorrhagic cystitis, and cardiovascular toxicities and slower reconstitution of CD4, CD8, and regulatory T cells but faster reconstitution of natural killer cells. In an exploratory analysis, older patients with older donors (>50 years for both) appeared to have particularly high NRM and lower OS in the haploidentical group compared with the other groups. Our data suggest that even with the use of PTCy, the outcomes of haploidentical HCT are inferior to those of HLA-matched donor HCT.