Nonmyeloablative bone marrow transplantation from partially HLA-mismatched related donors using posttransplantation cyclophosphamide

Debating the Future of Sickle Cell Disease Curative Therapy: Haploidentical Hematopoietic Stem Cell Transplantation vs. Gene Therapy

Hematopoietic stem cell transplantation (HSCT) is a well-established curative therapy for patients with sickle cell disease (SCD) when using a human leukocyte antigen (HLA)-matched sibling donor. Most patients with SCD do not have a matched sibling donor, thereby significantly limiting the accessibility of this curative option to most patients. HLA-haploidentical HSCT with post-transplant cyclophosphamide expands the donor pool, with current approaches now demonstrating high overall survival, reduced toxicity, and an effective reduction in acute and chronic graft-vs.-host disease (GvHD). Alternatively, autologous genetic therapies appear promising and have the potential to overcome significant barriers associated with allogeneic HSCT, such as donor availability and GvHD. Here the authors each take a viewpoint and discuss what will be the future of curative options for patients with SCD outside of a matched sibling transplantation, specifically haploidentical HSCT vs. gene therapy.

Mycophenolate Mofetil: A Friend or a Foe with PTCy and Tacrolimus Prophylaxis in HLA-Matched donors?

Adapted from the haploidentical literature, post-transplantation cyclophosphamide (PTCy) is increasingly being used with HLA-matched donors, generally with a calcineurin inhibitor, such as tacrolimus (Tac) with or without mycophenolate mofetil (MMF). Owing to its immunosuppressive, potentially antitumor, and antimicrobial properties, MMF is an attractive drug; however, it remains unclear how much benefit is gained when used with PTCy/Tac. To assess that, we compared PTCy/Tac (n=242) to PTCy/Tac/MMF (n= 144) in recipients of HLA-matched donors. In multivariate analysis, the PTCy/Tac/MMF group had a significantly higher risk of grade II-IV acute graft-versus-host disease (GVHD; hazard ratio (HR) 2.1, 95% confidence interval (CI) 1.6-2.8, p<0.001), and steroid-refractory/dependent acute GVHD (HR 4.8, 95% CI 2.4-9.6, p<0.001), yet a significantly lower risk of relapse (HR 0.5, 95% CI, 0.3-0.9, p=0.009) and better progression-free survival (PFS; HR 0.7, 95% CI 0.5-0.9, p=0.04). There was no difference in the risk of grade III-IV acute GVHD, chronic GVHD, non-relapse mortality, or overall survival. MMF was associated with prolonged neutrophil engraftment by 2 days, and a higher risk of bacterial infections. In an exploratory stool microbiome analysis (n=16), we noted a higher relative abundance of β-glucuronidase-producing bacteria in the MMF group, which may have a role in the pathogenesis of MMF-related GVHD. Our data suggest that the addition of MMF to PTCy/Tac for HLA-matched donor HCT does not provide any advantage for GVHD prevention. Further studies are needed to decipher this mechanism, and understand its role with PTCy-based prophylaxis.

PTCY and Tacrolimus for GVHD Prevention for Older Adults Undergoing HLA-Matched Sibling and Unrelated Donor AlloHCT

INTRODUCTION

The use of PTCY for graft-versus-host disease (GHVD) prevention is becoming prevalent in the transplant community when HLA-identical sibling (MSD) and 10/10 HLA-matched (MUD) and 9/10 mismatched (MMUD) unrelated donors are selected for alloHSCT. However, reported evidence on outcomes from elderly receiving PTCY-containing GVHD prophylaxis remains limited.

OBJECTIVES

This study aims to compare the outcomes of PTCY-TK prophylaxis and conventional GVHD prophylaxis in patients aged >50 years undergoing peripheral blood alloHSCT from a single institution.

STUDY DESIGN

A total of 161 consecutive patients aged >50 years undergoing alloHSCT between Jan-2014 and Feb-2021 were included. Data was collected retrospectively and updated in December 2021. Patients received grafts from HLA-identical sibling (MSD), and from 10/10 and 9/10 HLA matched and mismatched unrelated donors (UD).

RESULTS

Overall, median age was 60 years and 91 (54.8%) received PTCY-TK for GVHD prevention. Time to neutrophil and platelet engraftment was longer in the PTCY-TK group (20 vs. 16 days and 19 vs. 11 days, P< 0.001). The cumulative incidences of grade II-IV and III-IV aGVHD at day +100 and moderate/severe cGVHD at 2 years were 18.2%, 5.7% and 9.5% for patients receiving PTCY-TK, and 26.0%, 9.6% and 39.5% for those that did not. The multivariate analysis showed that PTCY-TK reduced the probability of grade II-IV aGVHD (HR 0.41, p=0.035), of cGVHD [any grade: HR 0.43 (p=0.014), and of moderate/severe cGVHD (HR 0.15 (p<0.001)]. At 2-years, the overall survival (65.4% vs. 65.6%, p=0.472), non-relapse mortality (17.4% vs. 13.7%, p=0.967), and cumulative incidence of relapse rates (24.2% vs. 27.5%, p=0.712) were comparable between both cohorts; GVHD-Free/Relapse-free survival (GRFS) was higher in the PTCY-TK group (2-years: 50.2% vs. 21.8%; HR 0.42, p=0.001). In patients aged ≥50 years, Conclusion: PTCY-TK was safe and a more effective drug combination than non-PTCY containing GVHD prophylaxis, even with the use of matched and mismatched UD, and resulted in comparable relapse rates and better GRFS.

Association between the pharmacokinetics of rabbit anti-thymocyte globulin and acute graft-versus-host disease in patients who received haploidentical hematopoietic stem cell transplantation

Anti-thymocyte globulin (ATG) is an important prophylactic drug against acute graft-versus-host disease (aGVHD) after haploidentical hematopoietic stem cell transplantation (haplo-HSCT). This study analyzed the pharmacokinetics of rabbit ATG 2.5 mg/kg and its effect against aGVHD in 24 patients undergoing unmanipulated haplo-HSCT. All patients had hematological malignancies not in remission. The median absolute lymphocyte count (ALC) before rabbit ATG administration was 9.5/µL (range 0-41/µL). The grade ≥ II aGVHD group had a significantly lower median rabbit ATG concentration on days 0 (C₀) and 7 (C₇) and areas under the curve on days 0-7 (AUC_0-7) and 0-32 (AUC_0-32) than the grade 0-I aGVHD group. Among the four parameters, C₀ was the most optimal for predicting aGVHD according to the receiver-operating characteristic (ROC) analysis (area under the ROC curve 0.893; 95% confidence interval 0.738-1.000). The high C₀ (≥ 27.8 µg/mL) group had significantly lower cumulative incidence of grade ≥ II aGVHD on day 100 than the low C₀ (< 27.8 µg/mL) group (13.8% vs. 88.9%, p < 0.001). In haplo-HSCT, the C₀ of rabbit ATG is a good predictor of grade ≥ II aGVHD, even though ALC before rabbit ATG administration is not a predictor of aGVHD.

Sub-myeloablative Second Transplantations with Haploidentical Donors and Post-Transplant Cyclophosphamide have limited Anti-Leukemic Effects in Pediatric Patients

Pediatric patients with high-risk hematologic malignancies who experience relapse after a prior allogeneic hematopoietic cell transplant (HCT) have an exceedingly poor prognosis. A second allogeneic HCT offers the potential for long-term cure but carries high risks of both subsequent relapse and HCT-related morbidity and mortality. Using haploidentical donors for HCT (haploHCT) can expand the donor pool and potentially enhance the graft-versus-leukemia effect but is accompanied by a risk of graft-versus-host disease (GVHD). The goal of this protocol was to intensify the antileukemia effect of haploHCT for pediatric patients with hematologic malignancies that relapsed after prior allogeneic HCT, while limiting regimen-associated toxicities. This phase II clinical trial evaluated a sub-myeloablative preparative regimen consisting of anti-thymocyte globulin, clofarabine, cytarabine, busulfan, and cyclophosphamide, in combination with plerixafor to sensitize leukemic blasts. Participants received a mobilized peripheral blood unmanipulated haploidentical donor graft with one dose of post-transplant cyclophosphamide as GVHD prophylaxis, followed by natural killer (NK) cell addback. Here we report the clinical outcomes and immune reconstitution of 17 participants treated on the study and 5 additional patients treated on similar single-patient treatment plans. Of the 22 participants analyzed, 12 (55%) had active disease at the time of HCT. The regimen provided robust immune reconstitution, with 21 participants (95%) experiencing neutrophil engraftment at a median of 14 days after HCT. In this high-risk population, the overall survival was 45% (95% confidence interval [CI], 24%-64%), with a 12-month event-free survival of 31% (95% CI, 14%-51%) and cumulative incidence of relapse at 12 months of 50% (95% CI, 27%-69%). Four participants (18%) remain in remission at >5 years follow-up. Expected HCT-related organ-specific toxicities were observed, and 13 participants (59%) experienced acute or chronic GVHD. This intensified but sub-myeloablative regimen, followed by a high-dose unmanipulated haploidentical graft, post-transplantation cyclophosphamide, and NK cell infusion, resulted in adequate immune reconstitution but failed to overcome the elevated risks of relapse and treatment-related morbidity in this high-risk population.

Are We Making PROGRESS in Preventing Graft-versus-Host Disease and Improving Clinical Outcomes? Impact of BMT CTN 1301 Study Results on Clinical Practice

The need for prospective randomized clinical trials investigating novel graft-versus-host disease (GVHD) prevention strategies that include other clinical outcomes impacted by GVHD has been highlighted as a priority for the field of hematopoietic cell transplantation. A recently completed study through the Blood and Marrow Transplant Clinical Trials Network (BMT CTN 1301) comparing CD34⁺ selection and post-transplantation cyclophosphamide with tacrolimus/methotrexate (Tac/MTX) for GVHD prevention demonstrated no significant differences in the primary endpoint of chronic GVHD relapse-free survival among the 3 approaches. The trial did not demonstrate a superior approach compared with Tac/MTX; however, it did highlight several challenges in determining the best and most relevant approaches to clinical trial design, particularly in the context of current and ongoing changes in real-world practices. Here we review the results of BMT CTN 1301 and their implications for clinical practice and future clinical trial design.

Establishment of Chimerism and Organ Transplant Tolerance in Laboratory Animals: Safety and Efficacy of Adaptation to Humans

The definition of immune tolerance to allogeneic tissue and organ transplants in laboratory animals and humans continues to be the acceptance of the donor graft, rejection of third-party grafts, and specific unresponsiveness of recipient immune cells to the donor alloantigens in the absence of immunosuppressive treatments. Actively acquired tolerance was achieved in mice more than 60 years ago by the establishment of mixed chimerism in neonatal mice. Once established, mixed chimerism was self-perpetuating and allowed for acceptance of tissue transplants in adults. Successful establishment of tolerance in humans has now been reported in several clinical trials based on the development of chimerism after combined transplantation of hematopoietic cells and an organ from the same donor. This review examines the mechanisms of organ graft acceptance after establishment of mixed chimerism (allo-tolerance) or complete chimerism (self-tolerance), and compares the development of graft versus host disease (GVHD) and graft versus tumor (GVT) activity in complete and mixed chimerism. GVHD, GVT activity, and complete chimerism are also discussed in the context of bone marrow transplantation to treat hematologic malignancies. The roles of transient versus persistent mixed chimerism in the induction and maintenance of tolerance and organ graft acceptance in animal models and clinical studies are compared. Key differences in the stability of mixed chimeras and tolerance induction in MHC matched and mismatched rodents, large laboratory animals, and humans are examined to provide insights into the safety and efficacy of translation of results of animal models to clinical trials.

Possible prognostic impact of WT1 mRNA expression at day + 30 after haploidentical peripheral blood stem cell transplantation with posttransplant cyclophosphamide for patients with myeloid neoplasm: a multicenter study from the Okayama Hematological Study Group

BACKGROUND

Previous studies have revealed that relapse of myeloid neoplasms after allogeneic hematopoietic stem cell transplantation (allo-HSCT) could be predicted by monitoring Wilms' tumor 1 (WT1) mRNA expression. However, only a few studies have investigated patients who received human leukocyte antigen-haploidentical stem cell transplantation with posttransplant cyclophosphamide (PTCY-haplo). In this study, we investigated the relationship between WT1 mRNA levels and clinical outcomes in the PTCY-haplo group, and compared them with those in the conventional graft-versus-host disease prophylaxis group (conventional group).

METHODS

We retrospectively analyzed 130 patients who received their first allo-HSCT between April 2017 and December 2020, including 26 who received PTCY-haplo.

RESULTS

The WT1 mRNA expression level at day + 30 after allo-HSCT associated with increased risk of 1-year cumulative incidence of relapse (CIR) was ≥ 78 copies/μg RNA in the conventional group (p < 0.01) and ≥ 50 copies/μg RNA in the PTCY-haplo group (p = 0.03).

CONCLUSIONS

The appropriate cutoff level of WT1 mRNA at day + 30 after allo-HSCT for predicting prognosis in patients treated with PTCY-haplo may be < 50 copies/μg RNA.

HLA-haploidentical peripheral blood stem cell transplantation following reduced-intensity conditioning with very low-dose antithymocyte globulin for relapsed/refractory acute leukemia in pediatric patients: a single-institution retrospective analysis

The prognosis of relapsed/refractory (R/R) pediatric acute leukemia is extremely poor. We retrospectively reviewed 20 consecutive pediatric patients with R/R acute leukemia who underwent a first HLA-haploidentical peripheral blood stem cell transplantation following reduced-intensity conditioning (haplo-RIC-PBSCT) with very low-dose antithymocyte globulin (ATG) between 2012 and 2019. Of these 20 patients, 7 patients had acute lymphoblastic leukemia, and 13 had acute myeloid leukemia. At the time of haplo-RIC-PBSCT, 15 patients had active disease. The median follow-up duration for survivors was 56 months (range 22-108 months). Graft-versus-host disease (GVHD) prophylaxis consisted of tacrolimus, short-term methotrexate, methylprednisolone, and ATG 1.25 mg/kg on day-2. The 2-year cumulative incidence of transplant-related mortality and relapse were 5.0% [95% confidence interval (CI) 0.7-30.5%)] and 57.8% (95% CI 37.4-79.6%), respectively. Among the 20 patients, 16 (80.0%) developed grade III-IV acute GVHD, and 2 developed severe chronic GVHD. The 2-year event-free survival and overall survival rates were 40.0% (95% CI 19.3-60.0%) and 50.0% (95% CI 27.1-69.2%), respectively. Although the sample size is small, the survival outcomes of the present study are encouraging.

Lower Absolute Lymphocyte Count Before Conditioning Predicts High Relapse Risk in Patients After Haploidentical Peripheral Blood Stem Cell Transplantation With Low Dose Anti-Thymocyte Globulin/Post-Transplant Cyclophosphamide for GvHD Prophylaxis

Standard anti-thymocyte globulin (ATG) weight-based dosing often resulted in highly variable ATG exposure, which had profound effects on relapse and survival, especially in recipients with relatively low absolute lymphocyte count (ALC) before conditioning. Data regarding rabbit ATG pharmacokinetics and pharmacodynamics in the setting of HLA-haploidentical peripheral blood stem cell transplantation (haplo-PBSCT) is lacking. We conducted a retrospective study on 90 consecutive patients who underwent haplo-PBSCT with low dose rabbit ATG (5 mg/kg) plus low dose post-transplant cyclophosphamide (50 mg/kg) based regimen for graft-versus-host disease (GvHD) prophylaxis. We compared serum concentration of ATG and post-transplant results between patients with ALC<500/μl and ALC≥500/μl before conditioning. Patients with ALC<500/μl had higher ATG concentrations, delayed immune reconstitution, lower incidence of grade II-IV acute GvHD (0 vs. 19.42%, P = 0.043), higher risk of Epstein-Barr virus infection within 100 days post-transplant (47.78% vs. 22.22%, P = 0.020) and 1-year relapse rate (33.33% vs.11.59%, P = 0.041), and lower 1-year overall survival (OS) (52.38% vs.79.71%, P = 0.004), 1-year relapse free survival (RFS) (47.62% vs. 75.36% for RFS, P = 0.014), and 1-year GvHD free relapse-free survival (GRFS) (42.89% vs. 65.22%, P = 0.043). ALC<500/μl before conditioning was a significant poor risk factor for relapse, OS, RFS, and GRFS.

Risk Factors for early CMV reactivation and Impact of early CMV reactivation on Clinical Outcomes after T Cell-replete Haploidentical Transplantation with Post-transplant Cyclophosphamide

BACKGROUND

Risk factors for cytomegalovirus (CMV) reactivation and the impact of CMV reactivation on patients' outcomes have been extensively investigated after matched related or unrelated donor transplants, but little is known in the setting of haploidentical stem cell transplant (Haplo-SCT) with post-transplant cyclophosphamide (PT-Cy), where recipients are supposed to be more severely immune-compromised.

METHODS

We retrospectively analyzed a cohort of 554 consecutive patients undergoing Haplo-SCT with PT-Cy at 3 different centers.

RESULTS

Early CMV reactivation, taking place within the first 120 days after transplant, occurred in 242 patients for an estimated cumulative incidence of 44%. Out of those patients, 74 (30%) had recurrent CMV and 20 (8%) CMV disease. By multivariable analysis, positive recipient CMV serostatus (Hazard ratio [HR] > 2.5, p<0.001), disease histology (lymphoid vs myeloid: HR 0.66, p=0.003) and increasing recipient age (HR 1.01, p=0.015) were independent predictors of CMV reactivation. At four months landmark analysis, CMV reactivation was associated with higher 1-year and 5-year cumulative incidence of non-relapse mortality (NRM) relative to patients without reactivation: 13% vs 5% and 22% vs 9%, respectively (p<0.001). By multivariable analysis, CMV reactivation was an independent negative predictor of non-relapse mortality (NRM) (HR 2.69, p<0.001) and was close to statistical significance for overall survival (OS) (HR: 1.38, p=0.062).

CONCLUSIONS

Our results suggest that CMV reactivation plays an important role at determining NRM. Because patient CMV serostatus is the main predictor of CMV reactivation, it should be considered when evaluating strategies for preventing CMV reactivation.

Total Body Irradiation in Haematopoietic Stem Cell Transplantation for Paediatric Acute Lymphoblastic Leukaemia: Review of the Literature and Future Directions

Total body irradiation (TBI) has been a pivotal component of the conditioning regimen for allogeneic myeloablative haematopoietic stem cell transplantation (HSCT) in very-high-risk acute lymphoblastic leukaemia (ALL) for decades, especially in children and young adults. The myeloablative conditioning regimen has two aims: (1) to eradicate leukaemic cells, and (2) to prevent rejection of the graft through suppression of the recipient's immune system. Radiotherapy has the advantage of achieving an adequate dose effect in sanctuary sites and in areas with poor blood supply. However, radiotherapy is subject to radiobiological trade-offs between ALL cell destruction, immune and haematopoietic stem cell survival, and various adverse effects in normal tissue. To diminish toxicity, a shift from single-fraction to fractionated TBI has taken place. However, HSCT and TBI are still associated with multiple late sequelae, leaving room for improvement. This review discusses the past developments of TBI and considerations for dose, fractionation and dose-rate, as well as issues regarding TBI setup performance, limitations and possibilities for improvement. TBI is typically delivered using conventional irradiation techniques and centres have locally developed heterogeneous treatment methods and ways to achieve reduced doses in several organs. There are, however, limitations in options to shield organs at risk without compromising the anti-leukaemic and immunosuppressive effects of conventional TBI. Technological improvements in radiotherapy planning and delivery with highly conformal TBI or total marrow irradiation (TMI), and total marrow and lymphoid irradiation (TMLI) have opened the way to investigate the potential reduction of radiotherapy-related toxicities without jeopardising efficacy. The demonstration of the superiority of TBI compared with chemotherapy-only conditioning regimens for event-free and overall survival in the randomised For Omitting Radiation Under Majority age (FORUM) trial in children with high-risk ALL makes exploration of the optimal use of TBI delivery mandatory. Standardisation and comprehensive reporting of conventional TBI techniques as well as cooperation between radiotherapy centres may help to increase the ratio between treatment outcomes and toxicity, and future studies must determine potential added benefit of innovative conformal techniques to ultimately improve quality of life for paediatric ALL patients receiving TBI-conditioned HSCT.

Is Haploidentical Hematopoietic Cell Transplantation Using Post-Transplantation Cyclophosphamide Feasible in Sub-Saharan Africa?

Identifying a suitable volunteer unrelated donor (UD) in South Africa is challenging due to the highly diverse ethnic groups and mixed-race populations in this region. Haploidentical hematopoietic cell transplantation (haploHCT) is thus an attractive procedure for patients with high-risk hematologic malignancies. This study was conducted to assess the safety and feasibility of haploHCT in South Africa. We retrospectively analyzed the outcome of 134 patients with hematologic malignancies who received unmanipulated haploHCT with post-transplantation cyclophosphamide at 2 high-volume HCT centers between 2014 and 2019. We assessed overall survival (OS), disease-free survival (DFS), nonrelapse mortality (NRM), relapse incidence (RI), and incidence of acute GVHD. The median recipient age was 44 years (range, 15 to 73 years) and the median donor age was 36 years (range, 9 to 68 years). Acute myelogenous leukemia or myelodysplastic syndrome (AML/MDS) and acute lymphoblastic leukemia (ALL) were the most common indications for haploHCT (61.2%). The European Society for Blood and Marrow Transplantation risk score was ≥5 in 44 patients (32.8%). Seventy-seven patients (57.4%) received a myeloablative conditioning regimen. The majority of patients received a sex-matched transplant (57.4%) and had peripheral blood stem cells (PBSCs) as the stem cell source (70.9%). Sixteen patients (11.9%) had an incongruent cytomegalovirus serostatus at transplantation. The median duration of follow-up was 10.8 months (range, 0.36 to 70.8 months). OS was 56% (95% confidence interval [CI], 47% to 64%) at 1 year and 37% (95% CI, 28% to 47%) at 3 years. DFS was 47% (95% CI, 38% to 55%) at 1 year and 32% (95% CI, 24% to 41%) at 3 years. The 100-day and 3-year cumulative incidence of NRM was 18% (95% CI, 11% to 25%) and 41% (95% CI, 32% to 50%), respectively, and the 1- and 3-year cumulative RI was 16% (95% CI, 11% to 24%) and 21% (95% CI, 14% to 29%), respectively. The 1-year OS was 55% (95% CI, 40% to 67%) for the patients with AML/MDS versus 41% (95% CI, 21% to 60%) for those with ALL. Forty-five patients (41.7%) developed acute GVHD by day +100; of these, 80% had grade I-II disease. Fifty patients (37.5%) developed cytomegalovirus infection that required therapy. On multivariable analysis, older donor age was an independent risk factor for lower DFS. RI was higher for diagnoses other than acute leukemia/MDS (relative risk [RR], 2.62; 95% CI, 1.12 to 6.15; P = .027), decreased for PBSC versus bone marrow (RR, 0.43; 95% CI, 0.19 to 0.95; P = .038) and decreased for offspring donors (RR, 0.25; 95% CI, 0.09 to 0.67; P = .006). These data support the feasibility of haploHCT and suggest that unmanipulated haploHCT using a younger parent or offspring donor is a viable option for adults in sub-Saharan Africa with acute leukemia and MDS who lack a suitable related or unrelated donor.

Graft-versus-Host Disease Prophylaxis with Post-Transplantation Cyclophosphamide versus Cyclosporine A and Methotrexate in Matched Sibling Donor Transplantation

Cyclosporine A (CSA) and methotrexate (MTX) is the standard graft-versus-host disease (GVHD) prophylaxis regimen for matched sibling donor (MSD) allogeneic hematopoietic cell transplantation (allo-HCT). Recently, post-transplantation cyclophosphamide (PTCy) has been shown to be effective in GVHD prevention. In this registry-based study, we compared outcomes of 118 patients treated with PTCy and 1202 patients with CSA/MTX who underwent MSD allo-HCT for acute myelogenous leukemia. In a matched-pair analysis, PTCy was associated with a higher incidence of relapse at 2 years compared with CSA/MTX (41.1% versus 21.3%; P = .039). The incidences of day +180 grade II-IV acute GVHD and 2-year chronic GVHD were comparable in the PTCy and CSA/MTX arms (25.2% versus 25.4% [P = .90] and 42.6% versus 42.6% [P = .84], respectively). Similarly, 2-year leukemia-free survival (LFS; 54.4% versus 74.32%; P = .052), overall survival (OS; 70.6% versus 79.7%; P = .15), and GVHD-free relapse-free survival (GRFS; 38.1% versus 52.5%; P = .49) were not statistically different in the 2 arms. Our data show that GVHD prophylaxis with PTCy is feasible, resulting in similar incidences of GVHD, GRFS, LFS, and OS as seen with conventional CSA/MTX in patients undergoing allo-HCT from an MSD. The higher rate of relapse observed with PTCy needs further evaluation in a prospective study. © 2021 American Society for Transplantation and Cellular Therapy. Published by Elsevier Inc.

Cytokine Release Syndrome Following Peripheral Blood Stem Cell Haploidentical Hematopoietic Cell Transplantation with Post-Transplantation Cyclophosphamide

Post-transplantation cyclophosphamide (PTCy) is a safe and efficacious graft-versus-host-disease (GVHD) prophylaxis following hematopoietic cell transplantation (HCT) from a haploidentical (haplo) donor. Cytokine release syndrome (CRS) is a common complication of this platform. Early fever post-haplo-HCT using bone marrow grafts is associated with higher CD3⁺ cell dose and CRS. However, the impact of CD3⁺ and CD34⁺ cell dose on CRS post-haplo-HCT using peripheral blood stem cell (PBSC) grafts is unknown. Our goals were to evaluate the incidence of CRS following PBSC transplantation (PBSCT) and to identify factors that can be modified to prevent the development of severe CRS in this setting. In 271 patients, we investigated factors associated with the development of CRS following haplo-PBSCT and examined the impact of CRS on clinical outcomes. Ninety-three percent of the patients developed CRS of any grade post-haplo-PBSCT. In multivariate analysis, severe CRS (grade 3-4 versus grade 0-1) was associated with higher nonrelapse mortality (hazard ratio [HR], 6.42; 95% confidence interval [CI], 2.68 to 15.39; P < .001), worse 1-year overall survival (HR, 3.40; 95% CI, 1.63 to 7.08; P = .005), and worse disease-free survival (HR, 4.02; 95% CI, 1.99 to 8.08; P < .001). Moderate to severe CRS (grade 2-4) did not impact 1-year relapse or acute GVHD (grade II-IV and III-IV) at 100 days (P = .71 and .19, respectively). Importantly, higher CD3⁺ cell dose, but not CD34⁺ cell dose, predicted a higher incidence of grade 2-4 CRS (HR, 1.20; 95% CI,1.07 to 1.36; P = .003) and grade 3-4 CRS (HR, 1.40; 95% CI, 1.05 to 1.86; P = .022). Both older age (HR, 8.57; 95% CI, 1.73 to 42.36; P < .001) and non-total body irradiation-based reduced-intensity conditioning with fludarabine/melphalan (HR, 15.38; 955 CI, 2.06 to 114.67; P < .001) were predictive of grade 3-4 CRS. Overall, we observed that severe CRS (grade 3-4) negatively affected transplantation outcome, and that higher CD3 cell dose was associated with the development of any grade CRS and severe CRS.

Sequential Transplantation of Haploidentical Stem Cell and Unrelated Cord Blood With Using ATG/PTCY Increases Survival of Relapsed/Refractory Hematologic Malignancies

Allogeneic haploidentical HSCT (haplo-HSCT) and unrelated umbilical cord blood transplantation(UCBT)are used in patients lacking HLA-identical sibling or unrelated donors. With myeloablative condition and GVHD prophylaxis of using low-dose ATG and post-transplantation cyclophosphamide (PTCY), we conducted a prospective clinical trial. Of eligible 122 patients from February 2015 to December 2019 in the study, 113 patients were involved. Forty-eight patients were in the group of sequential haplo-cord transplantation (haplo-cord HSCT), and 65 patients were in the group of single UCBT. The primary endpoint of 2-year disease-free survival (DFS) was no statistical difference between groups (64.1 vs. 56.5%), p>0.05. The analysis of subgroup patients with relapsed/refractory showed haplo-cord HSCT was associated with better OS (HR 0.348, 95% CI, 0.175–0.691; p=0.0025), DFS (HR 0.402, 95% CI, 0.208–0.779; p=0.0069), and GRFS (HR 0.235, 95% CI, 0.120–0.457, p<0.0001) compared to the single cord group. The 2-year’s probability in OS, DFS, and GRFS was 64.9 vs. 31.6%, 64.5 vs. 31.6%, and 60.8 vs. 15.0% in the haplo-cord group and single cord group, respectively. III-IV acute GVHD 8.3 vs. 6.2%, chronic GVHD 25.8 vs. 13.7%, and extensive chronic GVHD 5.3 vs. 1.8% were shown in corresponding group, p>0.05. The patients engrafted persistently with UCB showed better survival outcomes. Our sequential Haplo-cord HSCT with ATG/PTCY improved the survival of patients and might be an alternative transplantation approach for patients with relapsed/refractory hematologic malignancies.

Nonmyeloablative, HLA-Mismatched Unrelated Peripheral Blood Transplantation with High-Dose Post-Transplantation Cyclophosphamide

High-dose post-transplantation cyclophosphamide (PTCy) is an effective platform for prevention of severe graft-versus-host disease (GVHD) after allogeneic bone marrow (BM) transplantation with mismatched unrelated donors (mMUDs). Previous studies evaluating PTCy with mMUDs favored BM allografts over peripheral blood stem cell transplantation (PBSCT) due to concerns that PBSCT may be associated with an increased risk of acute and chronic GVHD. In addition, haploidentical PBSCT is associated with high rates of cytokine release syndrome (CRS), which is another concern with mMUD PBSCT. This study was conducted to determine the feasibility and safety of using mMUD PBSCT with PTCy as GVHD prophylaxis. Patients who received mMUD PBSCT using a PTCy-based GVHD prophylaxis at Johns Hopkins Hospital as part of a prospective clinical trial of mMUD and non-first-degree relative haploidentical transplantation with PTCy (ClinicalTrials.gov identifier NCT01203722) were included. All patients underwent T cell-replete PBSCT between November 2012 and August 2020. Statistical analyses were performed using the Kaplan-Meier method and proportional subdistribution hazard regression model for competing risks. The 29 patients in the study had a median age of 54 years, with 10 patients (34%) age ≥60 years. Nineteen grafts (66%) were matched for 9/10 HLA loci, 6 (21%) were match for 8/10, and 4 (14%) were matched for 7/10. No primary or secondary graft failure occurred. The median time to neutrophil recovery (≥500/µL) was 17 days, and that to platelet recovery (≥20,000/µL) was 28 days. Full donor chimerism was achieved in all patients by day +60. The cumulative incidence (CuI) of grade II-IV acute GVHD at 180 days was 15% (90% confidence interval [CI], 3% to 26%). There were no cases of severe chronic GVHD, 3 cases of mild chronic GVHD, and 1 case of moderate chronic GVHD. The CuI of nonrelapse mortality (NRM) was 7% (90% CI, NA to 18%) at 1 year. Eighteen patients (62%) experienced mild CRS (grade 1-2), and 1 patient (3%) experienced severe CRS (grade 3-5). At 1 year, the CuI of relapse was 29% (90% CI, 8% to 50%), overall survival was 93% (90% CI, 85% to 100%), progression-free survival was 64% (90% CI, 46% to 88%), GVHD-free relapse-free survival was 41% (90% CI, 23% to 73%), and chronic GVHD-free relapse-free survival was 64% (90% CI, 46% to 88%). Our data indicate that mMUD PBSCT using PTCy-based GVHD prophylaxis is safe and feasible. All patients engrafted, and rates of NRM (7%) and acute GVHD (15%) at 1 year were low. There was only 1 case (3%) of severe CRS. Compared with previously published outcomes, mMUD PBSCT using PTCy-based GVHD prophylaxis has a safety and efficacy profile that may not be different from that of PBSCT from matched donors. These results further solidify that all patients who require blood or BM transplantation should be able to find an acceptable donor.

A Review of Cyclophosphamide-Induced Transplantation Tolerance in Mice and Its Relationship With the HLA-Haploidentical Bone Marrow Transplantation/Post-Transplantation Cyclophosphamide Platform

The bone marrow transplantation (BMT) between haplo-identical combinations (haploBMT) could cause unacceptable bone marrow graft rejection and graft-versus-host disease (GVHD). To cross such barriers, Johns Hopkins platform consisting of haploBMT followed by post-transplantation (PT) cyclophosphamide (Cy) has been used. Although the central mechanism of the Johns Hopkins regimen is Cy-induced tolerance with bone marrow cells (BMC) followed by Cy on days 3 and 4, the mechanisms of Cy-induced tolerance may not be well understood. Here, I review our studies in pursuing skin-tolerance from minor histocompatibility (H) antigen disparity to xenogeneic antigen disparity through fully allogeneic antigen disparity. To overcome fully allogeneic antigen barriers or xenogeneic barriers for skin grafting, pretreatment of the recipients with monoclonal antibodies (mAb) against T cells before cell injection was required. In the cells-followed-by-Cy system providing successful skin tolerance, five mechanisms were identified using the correlation between super-antigens and T-cell receptor (TCR) Vβ segments mainly in the H-2-identical murine combinations. Those consist of: 1) clonal destruction of antigen-stimulated-thus-proliferating mature T cells with Cy; 2) peripheral clonal deletion associated with immediate peripheral chimerism; 3) intrathymic clonal deletion associated with intrathymic chimerism; 4) delayed generation of suppressor T (Ts) cells; and 5) delayed generation of clonal anergy. These five mechanisms are insufficient to induce tolerance when the donor-recipient combinations are disparate in MHC antigens plus minor H antigens as is seen in haploBMT. Clonal destruction is incomplete when the antigenic disparity is too strong to establish intrathymic mixed chimerism. Although this incomplete clonal destruction leaves the less-proliferative, antigen-stimulated T cells behind, these cells may confer graft-versus-leukemia (GVL) effects after haploBMT/PTCy.

Targeting the CD27-CD70 Pathway to Improve Outcomes in Both Checkpoint Immunotherapy and Allogeneic Hematopoietic Cell Transplantation

Immune checkpoint inhibitor therapies and allogeneic hematopoietic cell transplant (alloHCT) represent two distinct modalities that offer a chance for long-term cure in a diverse array of malignancies and have experienced many breakthroughs in recent years. Herein, we review the CD27-CD70 co-stimulatory pathway and its therapeutic potential in 1) combination with checkpoint inhibitor and other immune therapies and 2) its potential ability to serve as a novel approach in graft-versus-host disease (GVHD) prevention. We further review recent advances in the understanding of GVHD as a complex immune phenomenon between donor and host immune systems, particularly in the early stages with mixed chimerism, and potential novel therapeutic approaches to prevent the development of GVHD.

The Pathophysiology and Treatment of Graft-Versus-Host Disease: Lessons Learnt From Animal Models

Allogeneic hematopoietic cell transplantation (HCT) is a curative treatment for hematologic malignancies, bone marrow failure syndromes, and inherited immunodeficiencies and metabolic diseases. Graft-versus-host disease (GVHD) is the major life-threatening complication after allogeneic HCT. New insights into the pathophysiology of GVHD garnered from our understanding of the immunological pathways within animal models have been pivotal in driving new therapeutic paradigms in the clinic. Successful clinical translations include histocompatibility matching, GVHD prophylaxis using cyclosporine and methotrexate, posttransplant cyclophosphamide, and the use of broad kinase inhibitors that inhibit cytokine signaling (e.g. ruxolitinib). New approaches focus on naïve T cell depletion, targeted cytokine modulation and the inhibition of co-stimulation. This review highlights the use of animal transplantation models to guide new therapeutic principles.

New therapeutic targets and biomarkers for acute graft-versus-host disease (GVHD)

INTRODUCTION

Acute Graft-versus-Host Disease (GVHD) is the major toxicity of allogeneic hematopoietic cell transplantation (HCT). Systemic steroids are the standard primary treatment but only half of the patients will respond completely and the survival of steroid-refractory patients is poor. The gastrointestinal (GI) tract is a key target organ that usually determines a patient's response to therapy.

AREAS COVERED

This review summarizes the use of clinical grading systems and biomarkers in GVHD treatment and highlights pathophysiologic phases of acute GVHD as context for the mechanisms of action and therapeutic targets of various approaches. We reviewed >100 publications and performed a search of ongoing, current clinical trials on the emerging therapeutic targets for prophylaxis and treatment of acute GVHD. Search databases included clinicaltrials.gov and PUBMED. Search terms and keywords included 'acute graft-versus-host disease,' 'GVHD,' 'graft versus host,' 'treatment.'

EXPERT OPINION

Future strategies will employ a risk-adapted therapy using biomarkers, which more accurately predict 6-month NRM. Strategies for high-risk patients will inhibit GI tract damage by selective targeting of effectors (e.g. inhibition of JAK signaling in T cells), blockade of trafficking through mAbs against integrin receptors, or enhancement of target cell survival. Future strategieswill reduce immunosuppression to avoid risk of infections and relapse.

Is Post-Transplant Cyclophosphamide the New Methotrexate?

Introducing post-transplant, cyclophosphamide (PT-Cy) graft-versus-host disease (GVHD) prophylaxis in the setting of haploidentical donor transplantation has marked the most important advance in allogeneic hematopoietic cell transplantation (alloHCT) within the past 15 years. The efficacy of this procedure and its simple features have allowed for the significantly widespread application of alloHCT worldwide. Indeed, the procedure's effectiveness in reducing immunological complications in the haploidentical setting has even challenged the status quo use of calcineurin-inhibitor, methotrexate-based GVHD prophylaxis in the setting of HLA-identical donors. Currently, however, prospective clinical trials in support of PT-Cy-based GVHD prophylaxis in the HLA-matched setting are striving to resolve the matter of its potential role. This review will briefly report the overall outcomes of PT-Cy-based GVHD prophylaxis in the haploidentical setting and summarize results obtained in the HLA-identical field. We will present future perspectives at the end of the manuscript.

Engraftment of Double Cord Blood Transplantation after Nonmyeloablative Conditioning with Escalated Total Body Irradiation Dosing to Facilitate Engraftment in Immunocompetent Patients

To improve accrual to a randomized clinical trial of double unrelated cord blood (dUCB) versus HLA-haploidentical bone marrow (haplo-BM) transplantation, patients with less previous therapy and potentially greater immunocompetence were enrolled. To reduce the risk of graft rejection, patients randomized to receive dUCB received a higher dose of total body irradiation (TBI) (300 cGy versus 200 cGy). In this study, we investigated whether the inclusion of recipients of 300 cGy TBI influenced the trial outcomes. This was a secondary analysis of dUCB recipients, 161 who received TBI 200 cGy and 18 who received TBI 300 cGy. Fine and Gray regression was used to evaluate the effect of TBI dose on relapse and nonrelapse mortality (NRM). Cox regression was used for evaluation of neutrophil engraftment and overall survival. Patient characteristics were similar in the 2 TBI dose subgroups. The probability of neutrophil engraftment was 100% for patients who received TBI 300 cGy versus 91% (95% confidence interval, 86% to 95%) for those who received TBI 200 cGy (P = .64), which was similar after regression analysis adjusting for age, total infused nucleated cell dose, HLA matching to the patient, and comorbidity score. We also investigated whether the lower survival probability and higher cumulative incidence of NRM observed in the dUCB arm of BMT CTN 1101 could be influenced by the TBI 300 cGy patient subset. There was no significant difference in the 1-year incidences of NRM and relapse or in 1-year survival, even after adjustment in multivariate analysis. Patients in BMT CTN 1101 who received TBI 300 cGy and 200 cGy had similar engraftment and early mortality. We conclude that inclusion of a modified regimen for dUCB transplantation had no demonstrable influence on this large randomized trial.

Post-transplant cyclophosphamide versus anti-thymocyte globulin for graft-versus-host disease prevention in haploidentical transplantation for adult acute lymphoblastic leukemia

Graft-versus-host disease (GVHD) prophylaxis for unmanipulated haploidentical hematopoietic cell transplantation (haplo-HCT) include post-transplant cyclophosphamide (PTCy) and anti-thymocyte globulin (ATG). Utilizing EBMT registry, we compared ATG versus PTCy based GVHD prophylaxis in adult acute lymphoblastic leukemia (ALL) patients undergoing haplo-HCT. Included were 434 patients; ATG (n=98) and PTCy (n=336). Median follow-up was ~2 years. Baseline characteristics were similar between the groups except that the ATG-group was more likely to have relapsed/refractory ALL (P=0.008), non-TBI conditioning (P<0.001), peripheral blood graft source (P=<0.001) and transplanted at an earlier time-period (median year of HCT 2011 vs. 2015). The 100-day grade II-IV and III-IV acute-GVHD was similar between ATG and PTCy, as was 2-year chronic-GVHD. On multivariate analysis (MVA), leukemia-free survival (LFS) and overall survival (OS) was better with PTCy compared to ATG prophylaxis. Relapse incidence (RI) was lower in the PTCy group (P=0.03), while non-relapse mortality (NRM) was not different. Advanced disease and lower performance score were associated with poorer LFS and OS and advanced disease with inferior GVHD-free/relapse-free survival (GRFS). Peripheral grafts were associated with higher GVHD compared to bone marrow grafts. In ALL patients undergoing unmanipulated haplo-HCT, PTCy for GVHD prevention resulted in lower RI and improved LFS and OS compared to ATG.

Relationship of donor age and relationship to outcomes of haploidentical transplantation with posttransplant cyclophosphamide

Allogeneic blood or marrow transplantation (BMT) physicians seek to optimize all possible variables to improve outcomes. Selectable factors include conditioning, graft-versus-host disease (GVHD) prophylaxis, graft source, and donor. Many patients, especially those with eligible haploidentical (haplo) donors, will have multiple donor options. We seek to identify factors to optimize the choice of haplo donors when using posttransplantation cyclophosphamide (PTCy) GVHD prophylaxis. We evaluated the effect of modifiable donor characteristics (donor age and relationship) on outcomes following haplo BMT with a uniform nonmyeloablative conditioning and PTCy. From 2002 to 2017, 889 consecutive adult patients underwent nonmyeloablative haplo BMT with PTCy. Median follow-up among survivors was 2.5 years after BMT. Median recipient age was 59 (range: 18 to 76) years and median donor age was 40 (range: 13 to 79) years. Multivariable analyses demonstrated that increasing donor age by decade was associated with poorer overall survival (hazard ratio [HR], 1.13 [1.05, 1.22; P = .0015]), worse progression-free survival (HR, 1.09 [1.02, 1.16; P = .015]), and a higher risk for grade 2 to 4 and grade 3 to 4 GVHD (1.3 [1.06, 1.61; P = .013]), but not for chronic GVHD (HR, 1.06 [0.94, 1.2]; P = .37). These less-favorable results with older donors were attributable to worse nonrelapse mortality (HR, 1.19 [1.05, 1.34]; P = .006), not relapse. Parents were associated with inferior outcomes compared with sibling donors, whereas no significant differences were observed between parental donors. These data suggest that the youngest, adult-sized donors should be preferred when multiple haplo donors are available.

Post-transplant cyclophosphamide limits reactive donor T cells and delays the development of graft-versus-host disease in a humanized mouse model

Graft-versus-host disease (GVHD) is a major complication of allogeneic haematopoietic stem cell transplantation (allo-HSCT) that develops when donor T cells in the graft become reactive against the host. Post-transplant cyclophosphamide (PTCy) is increasingly used in mismatched allo-HSCT, but how PTCy impacts donor T cells and reduces GVHD is unclear. This study aimed to determine the effect of PTCy on reactive human donor T cells and GVHD development in a preclinical humanized mouse model. Immunodeficient NOD-scid-IL2Rγ^null mice were injected intraperitoneally (i.p.) with 20 × 10⁶ human peripheral blood mononuclear cells stained with carboxyfluorescein succinimidyl ester (CFSE) (day 0). Mice were subsequently injected (i.p.) with PTCy (33 mg kg^-1 ) (PTCy-mice) or saline (saline-mice) (days 3 and 4). Mice were assessed for T-cell depletion on day 6 and monitored for GVHD for up to 10 weeks. Flow cytometric analysis of livers at day 6 revealed lower proportions of reactive (CFSE^low ) human (h) CD3⁺ T cells in PTCy-mice compared with saline-mice. Over 10 weeks, PTCy-mice showed reduced weight loss and clinical GVHD, with prolonged survival and reduced histological liver GVHD compared with saline-mice. PTCy-mice also demonstrated increased splenic hCD4⁺ :hCD8⁺ T-cell ratios and reduced splenic Tregs (hCD4⁺  hCD25⁺  hCD127^lo ) compared with saline-mice. This study demonstrates that PTCy reduces GVHD in a preclinical humanized mouse model. This corresponded to depletion of reactive human donor T cells, but fewer human Tregs.

Comparing transplant outcomes in ALL patients after haploidentical with PTCy or matched unrelated donor transplantation

We compared outcomes of 1461 adult patients with acute lymphoblastic leukemia (ALL) receiving hematopoietic cell transplantation (HCT) from a haploidentical (n = 487) or matched unrelated donor (MUD; n = 974) between January 2005 and June 2018. Graft-versus-host disease (GVHD) prophylaxis was posttransplant cyclophosphamide (PTCy), calcineurin inhibitor (CNI), and mycophenolate mofetil (MMF) for haploidentical, and CNI with MMF or methotrexate with/without antithymoglobulin for MUDs. Haploidentical recipients were matched (1:2 ratio) with MUD controls for sex, conditioning intensity, disease stage, Philadelphia-chromosome status, and cytogenetic risk. In the myeloablative setting, day +28 neutrophil recovery was similar between haploidentical (87%) and MUD (88%) (P = .11). Corresponding rates after reduced-intensity conditioning (RIC) were 84% and 88% (P = .47). The 3-month incidence of grade II-IV acute GVHD (aGVHD) and 3-year chronic GVHD (cGVHD) was similar after haploidentical compared with MUD: myeloablative conditioning, 33% vs 34% (P = .46) for aGVHD and 29% vs 31% for cGVHD (P = .58); RIC, 31% vs 30% (P = .06) for aGVHD and 24% vs 29% for cGVHD (P = .86). Among patients receiving myeloablative regimens, 3-year probabilities of overall survival were 44% and 51% with haploidentical and MUD (P = .56). Corresponding rates after RIC were 43% and 42% (P = .6). In this large multicenter case-matched retrospective analysis, despite the limitations of a registry-based study (ie, unavailability of key elements such as minimal residual disease testing), our analysis indicated that outcomes of patients with ALL undergoing HCT from a haploidentical donor were comparable with 8 of 8 MUD transplantations.

Allogeneic hematopoietic cell transplantation with cord blood versus mismatched unrelated donor with post-transplant cyclophosphamide in acute myeloid leukemia

BACKGROUND

Allogeneic hematopoietic cell transplantation (allo-HCT) using a mismatched unrelated donor (MMUD) and cord blood transplantation (CBT) are valid alternatives for patients without a fully human leukocyte antigen (HLA)-matched donor. Here, we compared the allo-HCT outcomes of CBT versus single-allele-mismatched MMUD allo-HCT with post-transplant cyclophosphamide (PTCy) in acute myeloid leukemia.

METHODS

Patients who underwent a first CBT without PTCy (N = 902) or allo-HCT from a (HLA 9/10) MMUD with PTCy (N = 280) were included in the study. A multivariate regression analysis was performed for the whole population. A matched-pair analysis was carried out by propensity score-based 1:1 matching of patients (177 pairs) with known cytogenetic risk.

RESULTS

The incidence of grade II-IV and grade III-IV acute graft-versus-host disease (GVHD) at 6 months was 36% versus 32% (p = 0.07) and 15% versus 11% (p = 0.16) for CBT and MMUD cohorts, respectively. CBT was associated with a higher incidence of graft failure (11% vs. 4%, p < 0.01) and higher 2-year non-relapse mortality (NRM) (30% vs. 16%, p < 0.01) compared to MMUD. In the multivariate analysis, CBT was associated with a higher risk of, NRM (HR = 2.09, 95% CI 1.46-2.99, p < 0.0001), and relapse (HR = 1.35, 95% CI 1-1.83, p = 0.05), which resulted in worse leukemia-free survival (LFS) (HR = 1.68, 95% CI 1.34-2.12, p < 0.0001), overall survival (OS) (HR = 1.7, 95% CI 1.33-2.17, p < 0.0001), and GVHD-free, relapse-free survival (GRFS) (HR = 1.49, 95% CI 1.21-1.83, p < 0.0001) compared to MMUD. The risk of grade II-IV acute GVHD (p = 0.052) and chronic GVHD (p = 0.69) did not differ significantly between the cohorts. These results were confirmed in a matched-pair analysis.

CONCLUSIONS

CBT was associated with lower LFS, OS, and GRFS due to higher NRM, compared to MMUD allo-HCT with PTCy. In the absence of a fully matched donor, 9/10 MMUD with PTCy may be preferred over CBT.

Natural Killer Cells: The Linchpin for Successful Cancer Immunotherapy

Cancer immunotherapy is a highly successful and rapidly evolving treatment modality that works by augmenting the body’s own immune system. While various immune stimulation strategies such as PD-1/PD-L1 or CTLA-4 checkpoint blockade result in robust responses, even in patients with advanced cancers, the overall response rate is low. While immune checkpoint inhibitors are known to enhance cytotoxic T cells’ antitumor response, current evidence suggests that immune responses independent of cytotoxic T cells, such as Natural Killer (NK) cells, play crucial role in the efficacy of immunotherapeutic interventions. NK cells hold a distinct role in potentiating the innate immune response and activating the adaptive immune system. This review highlights the importance of the early actions of the NK cell response and the pivotal role NK cells hold in priming the immune system and setting the stage for successful response to cancer immunotherapy. Yet, in many patients the NK cell compartment is compromised thus lowering the chances of successful outcomes of many immunotherapies. An overview of mechanisms that can drive NK cell dysfunction and hinder immunotherapy success is provided. Rather than relying on the likely dysfunctional endogenous NK cells to work with immunotherapies, adoptive allogeneic NK cell therapies provide a viable solution to increase response to immunotherapies. This review highlights the advances made in development of NK cell therapeutics for clinical application with evidence supporting their combinatorial application with other immune-oncology approaches to improve outcomes of immunotherapies.

Combining Three Different Pretransplantation Scores Improves Predictive Value in Patients after Haploidentical Stem Cell Transplantation with Thiotepa, Busulfan, and Fludarabine Conditioning and Post-Transplantation Cyclophosphamide

One hundred and sixty-one patients underwent haploidentical stem cell transplantation (haploSCT) with thiotepa, busulfan, and fludarabine conditioning followed by post-transplantation cyclophosphamide (PTCy) (on days +3 and +4) and tacrolimus as graft-versus-host disease prophylaxis. Forty-two percent of patients had a high or very high revised Disease Risk Index (rDRI), 55% had an European Society for Blood and Marrow Transplantation risk score (EBMT-RS) ≥4, and 36% had an age-adjusted Hematopoietic Cell Transplant Comorbidity Index (HCT-CI-age) score ≥3. Each of these was considered an unfavorable score. Using the pretransplantation unfavorable scores that had an independent impact on each transplantation outcome studied in multivariate analysis allowed for better stratification of patient outcomes. Thus, the 3-year overall survival (OS) in patients with 0, 1, 2, and 3 unfavorable scores was 86%, 56%, 36%, and 24%, respectively. Nonrelapse mortality (NRM) was negatively impacted by the EBMT-RS and the HCT-CI-age score (3-year NRM in patients with 0, 1, and 2 unfavorable scores was 12%, 33%, and 43%, respectively), whereas the EBMT-RS and the rDRI had an impact on the 3-year relapse incidence (8%, 18%, and 41% in patients with 0, 1, and 2 unfavorable scores, respectively). In conclusion, our study shows that combining 2 or 3 of these well-defined pretransplantation scores improves the ability to predict transplantation outcomes in the setting of haploSCT with PTCy.

A Phase II Trial of Melphalan Based Reduced-Intensity Conditioning for Transplantation of T-Replete HLA-Haploidentical Peripheral Blood Stem Cells with Posttransplant Cyclophosphamide in Patients with Hematologic Malignancies

T-replete haploidentical donor transplants using posttransplant cyclophosphamide (haplo) have greatly expanded donor availability and are increasingly utilized. Haplo were originally performed using truly nonmyeloablative conditioning and a bone marrow graft. We have also developed myeloablative conditioning and peripheral blood stem cell (PBSC) grafts for use with haplo. However, some patients may not tolerate myeloablative conditioning but may still benefit from a more dose-intensified preparative regimen to control malignancy and diminish graft rejection. To this end, we enrolled 25 patients on a prospective phase II trial utilizing a regimen of fludarabine 30 mg/m²/day × 5 days and Melphalan 140 mg/m² on day -1 (flu/Mel) followed by infusion of unmanipulated PBSC graft from a haploidentical donor. GVHD prophylaxis included cyclophosphamide 50 mg/kg/day on days 3 and 4, mycophenolate mofetil on day 35, and tacrolimus on day 180. Median age was 57 years (range from 35 to 68). Transplantation diagnosis included AML (n = 11), ALL (n = 4), MDS/MPD (n = 6), NHL/CLL (n = 3), and MM (n = 1). Using the refined Disease Risk Index (DRI), patients were low (n = 1), intermediate (n = 13), and high/very high (n = 11). 22 out of 25 patients engrafted with a median time to neutrophil and platelet engraftment of 18 days and 36 days, respectively. All engrafting patients achieved full peripheral blood T-lymphocyte and myeloid donor chimerism at day 30. The 180-day cumulative incidence for acute GVHD grades II–IV and III-IV was seen in 20% (95% CI 8%–37%) and 8% (95% CI 2%–22%), respectively. The 2-year cumulative incidence of chronic GVHD was 16% (95% CI 5%–33%) (moderate-severe 12% (95% CI 3%–27%)). After a median follow-up of 28.3 months, the estimated 2-year OS, DFS, NRM, and relapse were 56% (95%CI 33–74%), 44% (95%CI 23%–64%), 20% (95% CI 8%–37%), and 36% (95% CI 17%–55%), respectively. Among patients with high/very high risk DRI, 2-year OS was 53% compared to 69% for low/intermediate DRI. When compared with a contemporaneous cohort of patients at our center receiving haploidentical transplant with nonablative fludarabine, Cytoxan, and total body irradiation flu/Cy/TBI regimen, the outcomes were statistically similar to the 2-year OS at 56% vs. 63% p=0.75 and DFS at 44% vs. 46% p=0.65.

Feasibility and Efficacy of CD45RA+ Depleted Donor Lymphocytes Infusion After Haploidentical Transplantation With Post-Transplantation Cyclophosphamide in Patients With Hematological Malignancies

Allogeneic stem cell transplantation from haploidentical donor using post-transplantation cyclophosphamide has been used to cure hematological diseases. Because of slow immunological reconstitution, there is an increased incidence of viral infection. The aim of our study was to prospectively evaluate the efficacy and the feasibility of a CD45RA+ depleted donor lymphocytes infusion (DLI) in terms of reduction of viral infection early after haploidentical transplantation. This a prospective single-center study. We enrolled 23 patients, of whom 19 were evaluable. Graft-versus-host disease (GVHD) prophylaxis was the same for all patients. The primary endpoint was 100-day cumulative incidence of viral infections. The primary endpoint was met, because the 100-day cumulative incidence of viral infection was 32%. The median time from transplantation to first CD45RA+ depleted DLI was 55 days (range, 46-63). 28% of patients had cytomegalovirus reactivation, no patients reactivated human herpesvirus-6; 1 patient developed BK virus related hemorrhagic cystitis. Most of the patients received the planned 3 infusions. Only 1 patient had development of grade 2 acute GVHD, and 2 patients had moderate chronic GVHD. All evaluable patients were off immunosuppressive therapy at last follow-up. The median follow-up was 12 months (range, 3-23), the 1-year overall survival and progression-free survival were 79% and 75%, respectively; the 100-day and 1-year non-relapse mortality were 5% and 12%, respectively. CD45RA+ depleted DLI are feasible in patients treated with haploidentical transplantation. The toxic profile is good with a low risk for development of both acute and chronic GVHD.

Contemporary haploidentical stem cell transplant strategies in children with hematological malignancies

The barriers to HLA-mismatched or haploidentical hematopoietic stem cell transplantation (HSCT), namely GvHD and graft failure, have been overcome with novel transplant platforms. Post-transplant Cyclophosphamide (PTCy) is widely available, feasible and easy to implement. TCRαβ T and B cell depletion comes with consistent GvHD preventive benefits irrespective of age and indication. Naive T-cell depletion helps prevention of severe viral reactivations. The Beijing protocol shows promising outcomes in patients with poor remission status at the time of transplantation. For children, the toxicities and late outcomes related to these transplants are truly relevant as they suffer the most in the long run from transplant-related toxicities, especially chronic GvHD. While comparing the outcomes of different Haplo-HSCT approaches, one must understand the transplant immunobiology and factors affecting the transplant outcomes. Leukemia remission status at the time of conditioning is a consistent factor affecting the transplant outcomes using any of these platforms. Prospective comparison of these platforms lacks in a homogenous population; however, the evidence is growing, and this review highlights the areas of research gaps.

Post-transplantation cyclophosphamide reduces the incidence of acute graft-versus-host disease in patients with acute myeloid leukemia/myelodysplastic syndromes who receive immune checkpoint inhibitors after allogeneic hematopoietic stem cell transplantation

Background

Immune checkpoint inhibitors (ICIs) are being used after allogeneic hematopoietic stem cell transplantation (alloHCT) to reverse immune dysfunction. However, a major concern for the use of ICIs after alloHCT is the increased risk of graft-versus-host disease (GVHD). We analyzed the association between GVHD prophylaxis and frequency of GVHD in patients who had received ICI therapy after alloHCT.

Methods

A retrospective study was performed in 21 patients with acute myeloid leukemia (n=16) or myelodysplastic syndromes (n=5) who were treated with antiprogrammed cell death protein 1 (16 patients) or anticytotoxic T lymphocyte-associated antigen 4 (5 patients) therapy for disease relapse after alloHCT. Associations between the type of GVHD prophylaxis and incidence of GVHD were analyzed.

Results

Four patients (19%) developed acute GVHD. The incidence of acute GVHD was associated only with the type of post-transplantation GVHD prophylaxis; none of the other variables included (stem cell source, donor type, age at alloHCT, conditioning regimen and prior history of GVHD) were associated with the frequency of acute GVHD. Twelve patients received post-transplantation cyclophosphamide (PTCy) for GVHD prophylaxis. Patients who received PTCy had a significantly shorter median time to initiation of ICI therapy after alloHCT compared with patients who did not receive PTCy (median 5.1 months compared with 26.6 months). Despite early ICI therapy initiation, patients who received PTCy had a lower observed cumulative incidence of grades 2–4 acute GVHD compared with patients who did not receive PTCy (16% compared with 22%; p=0.7). After controlling for comorbidities and time from alloHCT to ICI therapy initiation, the analysis showed that PTCy was associated with a 90% reduced risk of acute GVHD (HR 0.1, 95% CI 0.02 to 0.6, p=0.01).

Conclusions

ICI therapy for relapsed acute myeloid leukemia/myelodysplastic syndromes after alloHCT may be a safe and feasible option. PTCy appears to decrease the incidence of acute GVHD in this cohort of patients.

Haploidentical Peripheral Stem Cell Transplantation for Young Patients with Severe Aplastic Anemia Using Post-Transplantation Cyclophosphamide and Methotrexate

Severe aplastic anemia (SAA) is a serious bone marrow failure disorder that is often cured with hematopoietic stem cell transplantation (HSCT). The absence of a matched related donor is common, however, and thus novel approaches are needed to safely expand the donor pool to include alternative donors, especially haploidentical related donors, for patients with SAA. This study aimed to explore a novel approach to HSCT for patients with SAA without an available HLA-identical sibling or a matched unrelated donor, termed haploidentical peripheral blood stem cell transplantation (haplo-PBSCT), using a conditioning regimen comprising cyclophosphamide, busulfan, and fludarabine (CBF) and a graft-versus-host disease (GVHD) prophylaxis regimen with post-transplantation cyclophosphamide (PTCy), low-dose methotrexate (LD-MTX), and calcineurin inhibitors. This prospectively designed nonrandomized study included 29 patients with SAA who underwent haplo-PBSCT between November 2017 and May 2020. The median patient age was 17 years (range, 14 to 30 years), and the median time to neutrophil recovery was 13 days (range, 13 to 15 days). There was 1 primary graft failure (GF) in the group receiving PTCy at a dose of 50 mg/kg and no GFs in the group receiving PTCy at a dose of 100 mg/kg. The median duration of follow-up was 736 days (95% confidence interval, 512 to 879 days). The estimated 1-year overall survival and disease-free survival were 91.7 ± 5.7% and 89.7 ± 5.7%, respectively. Only 1 of the 27 patients developed grade II acute GVHD. Four patients developed limited and mild chronic GVHD, involving only the skin or/and oral mucosa. Haplo-PBSCT following CBF and followed by PTCy and LD-MTX represents a novel approach for safely expanding the donor pool to include alternative donors for young patients with SAA.

Multicenter Phase II Study on Haploidentical Bone Marrow Transplantation Using a Reduced-Intensity Conditioning Regimen and Posttransplantation Cyclophosphamide in Patients with Poor-Prognosis Lymphomas

Allogeneic stem cell transplantation from haploidentical donors using unmanipulated bone marrow and posttransplantation cyclophosphamide has been largely employed to cure high-risk lymphomas. However, the increased incidence of relapse associated with the use of a nonmyeloablative conditioning regimen is still considered a concerning issue. The aim of our study was to prospectively evaluate the efficacy and feasibility of a reduced-intensity conditioning regimen, including thiotepa, cyclophosphamide, and fludarabine, in high-risk lymphoma patients. This was a prospective multicenter study. We enrolled 49 patients, of whom 47 were evaluable. Graft source (bone marrow) and graft-versus-host disease (GVHD) prophylaxis were the same for all patients. The primary endpoint was the proportion of patients free of disease progression at 1 year. The primary endpoint was met, as 29 out of 47 patients were alive and free of disease at 1 year (1-year progression-free survival, 60%). Forty-five recipients engrafted and achieved full donor chimerism at day 100. The cumulative incidences (CIs) of ANC engraftment at 30 days and platelet engraftment at 60 days were 89% and 83%, respectively. Two patients experienced graft failure. The CIs of day 100 grades 2 to 4 acute GVHD and 2-year moderate-to-severe chronic GVHD were 26% and 16%, respectively. With a median follow-up of 47.5 months (range, 22 to 74), the 4-year progression-free survival and overall survival were 54% and 64%, respectively. The 4-year CI of relapse was 28%, and the 4-year nonrelapse mortality was 15%. Thiotepa-based reduced-intensity conditioning was well tolerated with encouraging survival in a cohort of patients with poor-prognosis lymphoma. Both the incidence of relapse and nonrelapse mortality were acceptable.

NK cell alloreactivity in acute myeloid leukemia in the post-transplant cyclophosphamide era

Allogeneic hematopoietic stem cell transplantation (alloSCT) for myeloid leukemia remains one of the most effective anti-tumor treatments available, capable of curing an increasingly higher proportion of patients. Alloreactivity generated by T cells has limited efficacy in the early post-transplant period while most patients will relapse within 6 months after transplantation. Prior studies in T cell depleted grafts showed that, with the elimination of T cells, natural killer (NK) cells provide most of the anti-tumor effect in the early post-transplant period. Administration of unmodified T cells to mitigate infections and relapse will expose the patient to a high risk of graft-vs-host disease (GvHD). Post-transplant cyclophosphamide (PTCy), initially used for haploidentical (haplo) donor transplants, is now also increasingly utilized in HLA matched donor transplants to prevent GvHD. In most patients, PTCy eliminates, at least in part, alloreactive T and NK cells early post-transplant. Administration of modified NK cells in the early post-transplant period makes intuitive sense to enhance the anti-tumor effect of the graft and thereby prevent relapse. Effective application of cellular therapy early after transplant has opened a new direction and could revolutionize the field of hematopoietic stem cell transplantation.

Comparison of Haploidentical Bone Marrow versus Matched Unrelated Donor Peripheral Blood Stem Cell Transplantation with Posttransplant Cyclophosphamide in Patients with Acute Leukemia

PURPOSE

Posttransplant cyclophosphamide (PTCy) is increasingly being utilized as a principle GvHD prophylaxis strategy in allogeneic hematopoietic cell transplantation (allo-HCT). A haploidentical (haplo) or matched unrelated donor (UD) is a valid option in the absence of a matched related donor.

EXPERIMENTAL DESIGN

We compared the outcomes of patients with acute leukemia who underwent haplo bone marrow (haplo-BM, N = 401) versus UD mobilized peripheral blood stem cells (UD-PB, N = 192) transplantation in the setting of PTCy.

RESULTS

The median follow-up duration was 36 months in the haplo-BM group and 16.6 months in the UD-PB group, respectively (P < 0.01). Myeloablative conditioning was used in 64.6% and 42.7% of haplo-BM and UD-PB patients, respectively (P < 0.01). Cumulative incidence of neutrophil engraftment at day 30 was 87% in haplo-BM versus 94% in UD-PB, respectively (P = 0.21). In the multivariate analysis, the risk of grade 2-4 acute GvHD (HR = 0.53, P = 0.01) and chronic GvHD (HR = 0.50, P = 0.02) was significantly lower in the haplo-BM group compared with the UD-PB group. There was no significant difference between the study groups with respect to relapse incidence, nonrelapse mortality, leukemia-fee survival, overall survival, or GvHD-free and relapse-free survival.

CONCLUSIONS

The use of a haplo donor with a BM graft resulted in a lower incidence of GvHD compared with a UD-PB stem cell graft in the setting of PTCy for patients with acute leukemia. However, differences in GvHD did not translate into a difference in survival outcomes. Based upon these data, UD-PB or haplo-BM should be considered equally acceptable sources for allo-HCT.

Haploidentical Hematopoietic Stem Cell Transplantation in Leukemia's: Experience from a Cancer Center in India

There has been a surge in haploidentical hematopoietic stem cell transplantation (HSCT) in India recently. However, there is a paucity of data on haploidentical HSCT from India. The report is an analysis of data of haploidentical HSCT performed at our center. Analysis of patients with acute leukemia or chronic myeloid leukemia who underwent haploidentical HSCT during 2014-2019 was performed. The graft versus host disease (GVHD) prophylaxis was post-transplant Cyclophosphamide with Mycophenolate-mofetil and Cyclosporine. All patients were transfused peripheral blood stem cells from donors. Overall survival (OS) was calculated using the Kaplan-Meier method. Twenty-one patients underwent haploidentical HSCT. Fourteen-patients were males. The median age of patients was 15 years. Fludarabine with total body irradiation was the most common conditioning regimen (n = 15, 71.4%). The median duration for neutrophil and platelet engraftment was 14 days. Cumulative incidence of acute and chronic GVHD was 19%, and 38% respectively. The median follow-up was 26 months and the two-year OS was 38%. Twelve (57%) patients died during the study period, 8 patients (38%) died from transplant-related mortality (TRM), and 4 from disease relapse. Sepsis was the cause of death in six of the eight TRM. Nine out of 21 patients (42.8%) are leukemia-free on follow-up. Haploidentical HSCT is a promising modality of treatment in patients who have no suitable matched donors. Though the TRM remains high, good disease control was achieved in 42.8% of patients. Multi-drug resistant bacterial infection remains a challenge in performing haploidentical HSCT in developing countries.

Total marrow and total lymphoid irradiation in bone marrow transplantation for acute leukaemia

The use of total body irradiation as part of conditioning regimens for acute leukaemia is progressively declining because of concerns of late toxic effects and the introduction of radiation-free regimens. Total marrow irradiation and total marrow and lymphoid irradiation represent more targeted forms of radiotherapy compared with total body irradiation that have the potential to decrease toxicity and escalate the dose to the bone marrow for high-risk patients. We review the technological basis and the clinical development of total marrow irradiation and total marrow and lymphoid irradiation, highlighting both the possible advantages as well as the current roadblocks for widespread implementation among transplantation units. The exact role of total marrow irradiation or total marrow and lymphoid irradiation in new conditioning regimens seems dependent on its technological implementation, aiming to make the whole procedure less time consuming, more streamlined, and easier to integrate into the clinical workflow. We also foresee a role for computer-assisted planning, as a way to improve planning and delivery and to incorporate total marrow irradiation and total marrow and lymphoid irradiation in multi-centric phase 2-3 trials.

Myeloablative vs reduced intensity T-cell-replete haploidentical transplantation for hematologic malignancy

In the absence of prospective studies that examine the effect of conditioning regimen intensity after T-cell-replete haploidentical transplant for acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL), and myelodysplastic syndrome (MDS), a retrospective cohort analysis was performed. Of the 1325 eligible patients (AML, n = 818; ALL, n = 286; and MDS, n = 221), 526 patients received a myeloablative regimen and 799 received a reduced-intensity regimen. Graft-versus-host disease prophylaxis was uniform with posttransplant cyclophosphamide, a calcineurin inhibitor, and mycophenolate mofetil. The primary end point was disease-free survival. Cox regression models were built to study the effect of conditioning regimen intensity on transplant outcomes. For patients aged 18 to 54 years, disease-free survival was lower (hazard ratio [HR], 1.34; 42% vs 51%; P = .007) and relapse was higher (HR, 1.51; 44% vs 33%; P = .001) with a reduced-intensity regimen compared with a myeloablative regimen. Nonrelapse mortality did not differ according to regimen intensity. For patients aged 55 to 70 years, disease-free survival (HR, 0.97; 37% vs 43%; P = .83) and relapse (HR, 1.32; 42% vs 31%; P = .11) did not differ according to regimen intensity. Nonrelapse mortality was lower with reduced-intensity regimens (HR, 0.64; 20% vs 31%; P = .02). Myeloablative regimens are preferred for AML, ALL, and MDS; reduced-intensity regimens should be reserved for those unable to tolerate myeloablation.

Prospective phase 2 trial of ixazomib after nonmyeloablative haploidentical peripheral blood stem cell transplant

Proteasome inhibition results in extensive immunomodulatory effects that augment natural killer cell cytotoxicity and inhibit aspects of T-cell, B-cell, and dendritic cell function. We performed a phase 2 study that examined the effects of ixazomib for graft-versus-host disease (GVHD) prophylaxis (up to 12 cycles) with posttransplant cyclophosphamide and tacrolimus after standard nonmyeloablative haploidentical donor transplantation (HIDT). Ixazomib was started on day +5 (4 mg on days 1, 8, and 15 of a 28-day cycle), with dose reductions allowed in future cycles for toxicity. All patients received peripheral blood stem cells. Twenty-five patients were enrolled with a median age of 62 years (range, 35-77 years) who had acute leukemia (4), myelodysplastic syndrome (7), non-Hodgkin lymphoma/Hodgkin lymphoma/chronic lymphocytic leukemia (8), and myeloma (6). The hematopoietic cell transplant comorbidity index was ≥3 in 68% of the patients. After a median follow-up of 33.5 months, the cumulative incidence of relapse/progression at 1 year was 24% and 44% at 3 years, which failed to meet the statistically predefined goal of decreasing 1-year risk of relapse. Engraftment occurred in all patients with no secondary graft failure, and 3-year nonrelapse mortality (NRM) was 12%. Cumulative incidence of grade 3 to 4 acute GVHD was 8%, whereas moderate-to-severe chronic GVHD occurred in 19%. Nineteen patients survive with an estimated 1-year overall survival (OS) of 84% and 3-year OS of 74%. Hematologic and cutaneous toxicities were common but manageable. The substitution of ixazomib for mycophenolate mofetil (MMF) post-HIDT results in reliable engraftment, comparable rates of clinically significant GVHD, relapse and NRM, and favorable OS. This trial was registered at www.clinicaltrials.gov as # NCT02169791.

Evolution of the role of haploidentical stem cell transplantation: past, present, and future

INTRODUCTION

The accessibility to haplo-donors has led to an increase in the number of haplo-HSCT worldwide. A systematic search of the PubMed database between 2000 to present was performed.

AREAS COVERED

In this review, the authors discussed the most used approaches to perform haplo-HSCT and its results: T-cell depletion (TCD, including Perugia platform and its modifications) and T-cell repleted haplo (TCR, including the high-dose post-transplant cyclophosphamide strategy (Baltimore protocol) and the Beijing protocol). The improvements and modifications made to the different strategies have increased the indications of haplo-HSCT, including both malignant and nonmalignant disorders. Focusing on the Baltimore protocol, the authors review the results of the retrospective studies that have compared it to other donor transplants. The limitations of this strategy in terms of toxicity, graft complications, and GVHD are also discussed in detail. Finally, possible approaches to improve the outcomes of TCR haplo-HSCT are presented.

EXPERT OPINION

The recent advances in the field of haplo-HSCT have allowed a large number of patients with incurable diseases to benefit from this procedure despite not having a matched donor. With all available strategies, virtually no patient who needs an allogeneic transplant should be excluded by the absence of a donor.

Non-Myeloablative Allogeneic Transplantation with Post-Transplant Cyclophosphamide after Immune Checkpoint Inhibition for Classic Hodgkin Lymphoma: A Retrospective Cohort Study

: Immune checkpoint inhibitors (ICIs) are approved in relapsed classic Hodgkin lymphoma (cHL). The safety and effectiveness of allogeneic blood or marrow transplantation (alloBMT) in ICI-pretreated patients with cHL remain unclear. The aim of this study is to assess outcomes of patients with cHL receiving ICIs before alloBMT using post-transplantation cyclophosphamide (PTCy) graft-versus-host-disease (GVHD) prophylaxis.  : We performed a retrospective study of relapsed/refractory patients with cHL undergoing alloBMT with PTCy at Johns Hopkins between November 2004 and September 2019. Engraftment, GVHD incidence, nonrelapse mortality, progression-free survival (PFS), and overall survival (OS) were compared between patients receiving pre-alloBMT ICI or standard salvage chemotherapy.  : We identified 105 consecutive relapsed/refractory patients with cHL, of whom 37 (35.2%) received ICIs and 68 (64.7%) received chemotherapy without ICIs (no-ICI) before alloBMT. ICI and no-ICI patients experienced a 3-year estimated OS of 94% versus 78% (hazard ratio [HR], 0.35; 95% confidence interval [CI], 0.08 to 1.56; P = .17) and a 3-year estimated PFS of 90% and 65% (HR, 0.3; 95% CI, 0.09 to 1; P = .05), respectively. We observed no statically significant difference in the 12-month cumulative incidence of acute grade II to IV GVHD or in the 24-month incidence of chronic GVHD.  : ICIs do not increase acute or chronic GVHD incidence compared with salvage chemotherapy. Patients with cHL receiving ICIs prior to alloBMT experienced outstanding PFS and OS. Thus, ICI therapy is safe in patients with cHL when undergoing alloBMT with PTCy and may improve post-alloBMT disease progression and survival.

Photodepletion with 2-Se-Cl prevents lethal graft-versus-host disease while preserving antitumor immunity

Acute graft-versus-host-disease (GVHD), limits the use of hematopoietic cell transplant (HCT) to treat a variety of malignancies. Any new therapeutic approach must satisfy three requirements: 1) Prevent GVHD, 2) Maintain anti-pathogen immunity, and 3) Maintain anti-tumor immunity. In prior studies we have shown that the selective photosensitizer 2-Se-Cl eliminates highly alloreactive lymphocytes from the graft prior to HCT preventing GVHD and that antiviral immune responses were preserved following incubation with 2-Se-Cl. In this report, we investigated whether 2-Se-Cl treatment preserves antitumor immunity, and then used high dimensional flow cytometry to identify the determinants of successful immune reconstitution. Donor C57BL/6 splenocytes were cocultured for 4 days with irradiated BALB/c splenocytes and then exposed to 2-Se-Cl. Photodepletion (PD)-treated splenocytes were then infused into lethally irradiated BALB/c mice inoculated with A20 leukemia/lymphoma cells. Recipient mice that received PD-treated splenocytes survived > 100 days without evidence of GVHD or leukemia. In contrast, mice that did not receive PD-treated cells at time of HCT died of leukemia progression. Multiparameter flow cytometry of cytokines and surface markers on peripheral blood samples 15 days after HCT demonstrated unique patterns of immune reconstitution. We found that before clinical disease onset GVHD was marked by functionally exhausted T cells, while tumor clearance and long-term survival were associated with an expansion of polyfunctional T cells, monocytes, and DCs early after transplantation. Taken together these results demonstrate that 2-Se-Cl photodepletion is a new treatment that can facilitate HCT by preventing GVHD while preserving antiviral and anti-tumor immunity.

Risk Factors for Graft-versus-Host Disease in Haploidentical Hematopoietic Cell Transplantation Using Post-Transplant Cyclophosphamide

Post-transplant cyclophosphamide (PTCy) has significantly increased the successful use of haploidentical donors with a relatively low incidence of graft-versus-host disease (GVHD). Given its increasing use, we sought to determine risk factors for GVHD after haploidentical hematopoietic cell transplantation (haplo-HCT) using PTCy. Data from the Center for International Blood and Marrow Transplant Research on adult patients with acute myeloid leukemia, acute lymphoblastic leukemia, myelodysplastic syndrome, or chronic myeloid leukemia who underwent PTCy-based haplo-HCT (2013 to 2016) were analyzed and categorized into 4 groups based on myeloablative (MA) or reduced-intensity conditioning (RIC) and bone marrow (BM) or peripheral blood (PB) graft source. In total, 646 patients were identified (MA-BM = 79, MA-PB = 183, RIC-BM = 192, RIC-PB = 192). The incidence of grade 2 to 4 acute GVHD at 6 months was highest in MA-PB (44%), followed by RIC-PB (36%), MA-BM (36%), and RIC-BM (30%) (P = .002). The incidence of chronic GVHD at 1 year was 40%, 34%, 24%, and 20%, respectively (P < .001). In multivariable analysis, there was no impact of stem cell source or conditioning regimen on grade 2 to 4 acute GVHD; however, older donor age (30 to 49 versus <29 years) was significantly associated with higher rates of grade 2 to 4 acute GVHD (hazard ratio [HR], 1.53; 95% confidence interval [CI], 1.11 to 2.12; P = .01). In contrast, PB compared to BM as a stem cell source was a significant risk factor for the development of chronic GVHD (HR, 1.70; 95% CI, 1.11 to 2.62; P = .01) in the RIC setting. There were no differences in relapse or overall survival between groups. Donor age and graft source are risk factors for acute and chronic GVHD, respectively, after PTCy-based haplo-HCT. Our results indicate that in RIC haplo-HCT, the risk of chronic GVHD is higher with PB stem cells, without any difference in relapse or overall survival.