Shortened-Duration Immunosuppressive Therapy after Nonmyeloablative, Related HLA-Haploidentical or Unrelated Peripheral Blood Grafts and Post-Transplantation Cyclophosphamide

The history of haploidentical stem cell transplantation: a trip from the bench to the bedside

Allogeneic bone marrow transplantation is a curative intervention for both neoplastic and non-malignant conditions. However, not all patients have an HLA-matched donor. Therefore, the development of an approach that expand the donor pool was of paramount relevance. The development of post-transplantation cyclophosphamide as graft versus host disease prophylaxis allows the safe use of haploidentical donors, solving the donor availability problem to the vast majority of patients in need. The present paper reviews the history of the development of haploidentical transplantation at Johns Hopkins University, from the bench to the bedside.

Recipient clonal hematopoiesis in allogeneic bone marrow transplantation for lymphoid malignancies

ABSTRACT

Allogeneic blood and marrow transplantation (alloBMT) is increasingly being used in older patients with blood cancer. Aging is associated with an increasing incidence of clonal hematopoiesis (CH). Although the effects of donor CH on alloBMT has been reported, the impact of recipient CH on alloBMT outcomes is unknown. In this retrospective study, alloBMT recipients age 60 and older with lymphoid malignancies were included. Among 97 consecutive patients who received alloBMT between 2017 and 2022, CH was detected in 60 (62%; 95% confidence interval [CI], 51-72). CH was found in 45% (95% CI, 28-64) of patients aged 60 to 64, 64% (95% CI, 44-81) of patients aged 65% to 69%, and 73% (95% CI, 59-87) in those above 70. Pretransplant CH was associated with worse survival after alloBMT: 3-year overall survival (OS) was 78% (95% CI, 65-94) for patients without CH vs 47% (95% CI, 35-63) for those with CH, (unadjusted HR, 3.1; [95% CI, 1.4-6.8; P < .001]). Nonrelapse mortality (NRM) was higher in patients with CH; cumulative incidence of NRM at 1-year was 11% (95% CI, 1-22) vs 35% (95% CI, 23-48), (HR, 3.4; [95% CI, 1.4-8.5], P = .009]). Among CH patients, worse OS and NRM was associated with CH burden and number of mutations. Recipient CH had no effect on relapse. In conclusion, older patients with CH experience worse outcomes after alloBMT, almost exclusively attributable to increased NRM. CH is a strong, independent predictor of outcomes. Novel strategies to ameliorate the adverse impacts of patient CH on transplant outcomes are being evaluated.

Engineering the best transplant outcome for high-risk acute myeloid leukemia: the donor, the graft and beyond

Allogeneic hemopoietic cell transplantation remains the goal of therapy for high-risk acute myeloid leukemia (AML). However, treatment failure in the form of leukemia relapse or severe graft-versus-host disease remains a critical area of unmet need. Recently, significant progress has been made in the cell therapy-based interventions both before and after transplant. In this review, the Stem Cell Engineering Committee of the International Society for Cell and Gene Therapy summarizes the literature regarding the identification of high risk in AML, treatment approaches before transplant, optimal transplant platforms and measures that may be taken after transplant to ideally prevent, or, if need be, treat AML relapse. Although some strategies remain in the early phases of clinical investigation, they are built on progress in pre-clinical research and cellular engineering techniques that are already improving outcomes for children and adults with high-risk malignancies.

Feasibility and safety of the discontinuation of systemic immunosuppressive treatment after single-unit cord blood transplantation in adults

We retrospectively evaluated the incidence, factors, and clinical outcomes of the discontinuation of immunosuppressive treatment (IST) after single-unit unrelated cord blood transplantation (CBT) in adults receiving cyclosporine-based graft-versus-host disease (GVHD) prophylaxis at our institute. Among the 309 patients who achieved engraftment, 247 were able to discontinue IST with a median follow-up of 121 months for survivors. The cumulative incidence of the discontinuation of IST was 46.2% at 180 days, 72.8% at 2 years, and 79.3% at 5 years post-CBT. In the multivariate analysis, discontinuation of IST after CBT was significantly associated with the requirement for steroid therapy (hazard ratio [HR]: 0.46; P < 0.001) and the recent calendar year of CBT (HR: 1.79; P < 0.001). In the conditional landmark analysis at 180 days, discontinuation of IST was not associated with the development of extensive chronic GVHD (HR: 1.00; P = 0.989), non-relapse mortality (HR: 0.49; P = 0.122), relapse (HR: 1.46; P = 0.388), or overall survival (HR: 1.91; P = 0.065). Our data showed that successful discontinuation of IST is common after single-unit CBT in adults. Discontinuation of IST did not affect subsequent outcomes, suggesting that discontinuation of IST is both feasible and safe in adults undergoing single-unit CBT.

Improved Outcome of Allogeneic Transplantation in Older Patients Treated for Myeloid Malignancies Using Post-Transplantation Cyclophosphamide and Reduced Duration of Immune Suppression

Allogeneic stem cell transplantation (alloSCT) offers curative potential for older patients with myeloid malignancies. We evaluated the efficacy and safety of alloSCT using post-transplantation cyclophosphamide (PTCy) in combination with a very short duration of immune suppression (IS) in this population. We retrospectively analyzed 92 consecutive patients aged 65 years and older who underwent an alloSCT for myeloid malignancies between February 2018 and December 2022 at our institution. Data on patient characteristics, treatment modalities, and outcomes were collected. Ninety-two patients received an alloSCT with PTCy-based graft versus host disease (GVHD) prophylaxis. The majority had minimal comorbidities and were diagnosed with acute myeloid leukemia. Patients mostly received conditioning regimens with low to intermediate transplant conditioning intensity scores. In 43% of patients, IS could be permanently stopped at day +90, resulting in a median time of IS of 2.93 months in high-risk patients. At a median follow-up of 21.3 months, the 1- and 2-year overall survival rates were 89% and 87%, respectively. Relapse-free survival rates were 88% and 84% at 1 and 2 years, respectively. The 1- and 2-year cumulative incidences of relapse were 8% and 13%, while treatment-related mortality (TRM) estimates were 9% at both time points. Acute GVHD grade 3 to 4 occurred in 7% within the first 180 days and severe chronic GVHD in 6% of patients. This all resulted in a 1- and 2-year graft versus host and relapse-free survival of 74% and 70%, respectively. AlloSCT using PTCy in combination with a short duration of IS in older patients with myeloid malignancies demonstrates favorable survival outcomes due to low relapse rates and a low TRM. The low incidence of relapse and acceptable rates of graft-versus-host disease suggest the efficacy and safety of this approach. Further studies are warranted to validate these findings and optimize transplant strategies for older patients with myeloid malignancies.

First complete remission favours haploidentical haematopoietic stem cell transplantation with post-transplant cyclophosphamide over cord blood transplantation in acute lymphoblastic leukaemia

To assess the benefits of HLA-haploidentical haematopoietic stem cell transplantation using post-transplant cyclophosphamide (PTCy-haplo) relative to those of umbilical cord blood (UCB) transplantation in acute lymphoblastic leukaemia (ALL), we analysed 1999 patients (PTCy-haplo, 330; UCB, 1669), using the nationwide Japanese registry. PTCy-haplo was associated with a significantly higher relapse rate, but lower non-relapse mortality, which results in overall survival and disease-free survival, comparable to those of UCB. Among patients in CR1, PTCy-haplo showed a significantly higher survival than UCB regardless of the CD34+ cell dose. Our findings provide valuable insights into the donor selection algorithm in allogeneic HSCT for adult patients with ALL.

Peripheral blood haploidentical hematopoietic cell transplantation for patients aged 70 years and over with acute myeloid leukemia or high-risk myelodysplastic syndrome

Haploidentical stem cell transplantation (Haplo-SCT) using non-myeloablative conditioning regimen (NMAC) has extended the feasibility of allogeneic transplantation, notably in older patients. However, there is few data specifically focusing on patients aged 70 years and over with AML and MDS. Thus the benefit of transplantation in this population is still debated. Here we report our single center experience of peripheral blood Haplo-SCT with NMAC and post-transplantation cyclophosphamide in AML and MDS patients aged 70 years and over. We analyzed 50 patients (27 AML, 23 MDS) with a median age of 72 years (70-77), 12/50 (24%) with active disease at Haplo-SCT. Cumulative incidence of grade 3-4 acute and moderate or severe chronic GVHD were 6% and 25%, respectively. Non-relapse mortality (NRM) at day +100 was 0%. NRM, relapse, PFS and OS at 3 years were 16%, 18%, 66%, and 69%, respectively. Among patients who were disease free at 2 years post Haplo-SCT, 88% are living without immunosuppressive treatment. Peripheral blood Haplo-SCT is feasible in selected AML/MDS patients over 70 years, without any early NRM. It produces long-term disease control and survival. Thus, age by itself should not be considered as a formal barrier to Haplo-SCT.

The development of post-transplant cyclophosphamide: Half a century of translational team science

Close HLA matching of donors and recipients has been the dogma for successful allogeneic blood or marrow transplantation (alloBMT), to limit the complications of graft-versus-host disease (GVHD). However, many patients in need, especially those within certain ethnic groups such as those of African-Americans and Hispanics, remain unable to find a match even with the increased availability of unrelated donors. Over half a century ago, investigators at Johns Hopkins found that cyclophosphamide's immunosuppressive properties made it the ideal replacement for total body irradiation in alloBMT conditioning regimens. They also found it to be the best chemotherapeutic for preventing GVHD in animal models, but its cytotoxic properties scared them from using it clinically in the high doses successful in animal models. Subsequent work showed that cyclophosphamide spared hematopoietic and other stem cells including memory lymphocytes, prompting re-examination at high doses for GVHD prophylaxis. Animal and extensive human studies demonstrated that high-dose post-transplantation cyclophosphamide (PTCy) effectively and safely limited GVHD such that mismatched transplants are now considered standard-of-care worldwide. The beneficial effects of PTCy on GVHD appears to be independent of donor type, graft source, or conditioning regimen intensity.

PTCy, abatacept, and a short course of tacrolimus for GVHD prevention after haploidentical transplantation

Reducing the incidence of graft-versus-host disease (GVHD) after haploidentical hematopoietic stem cell transplantation (HSCT) is warranted. Posttransplant cyclophosphamide (PTCy) is the main agent used for GVHD prevention in this setting. It remains unknown whether costimulation blockade can be safely combined with PTCy and enhance its efficacy. We performed a phase 1b-2 clinical trial to examine the combination of PTCy, abatacept, and a short course of tacrolimus (CAST) after peripheral blood haploidentical HSCT. The primary end point was the incidence of grades 2-4 acute GVHD by day +120. The study enrolled 46 patients with a median age of 60 years (range, 18-74 years). The cumulative incidences of grades 2-4 and 3 or 4 acute GVHD were 17.4% (95% confidence interval [CI], 9.2-32.9) and 4.4% (95% CI, 1.1-17.1), respectively. With a median follow-up of 15.3 months, the cumulative incidence of 1-year treatment-related mortality was 4.4% (95% CI, 1.1-17.1). The estimated 1-year moderate-to-severe chronic GVHD rate, relapse rate, progression-free survival, overall survival, and GVHD- and relapse-free survival were 15.9% (95% CI, 8-31.7), 11.7% (95% CI, 5-27.2), 84.1% (95% CI, 73.8-95.7), 85.9% (95% CI, 75.9-97.2), and 66.1% (95% CI, 53.4-81.8), respectively. Toxicities were similar to those expected in patients receiving haploidentical HSCT. This clinical trial showed that the CAST regimen is safe and effective in reducing the rate of grades 2-4 acute GVHD after haploidentical peripheral blood HSCT. This trial was registered at www.clinicaltrials.gov as #NCT04503616.

Allogeneic Blood or Marrow Transplantation with High-Dose Post-Transplantation Cyclophosphamide for Acute Lymphoblastic Leukemia in Patients Age ≥55 Years

Patients age ≥55 years with acute lymphoblastic leukemia (ALL) fare poorly with conventional chemotherapy, with a 5-year overall survival (OS) of ∼20%. Tyrosine kinase inhibitors and novel B cell-targeted therapies can improve outcomes, but rates of relapse and death in remission remain high. Allogeneic blood or marrow transplantation (alloBMT) provides an alternative consolidation strategy, and post-transplantation cyclophosphamide (PTCy) facilitates HLA-mismatched transplantations with low rates of nonrelapse mortality (NRM) and graft-versus-host disease (GVHD). The transplantation database at Johns Hopkins was queried for patients age ≥55 years who underwent alloBMT for ALL using PTCy. The database included 77 such patients. Most received reduced-intensity conditioning (RIC) (88.3%), were in first complete remission (CR1) (85.7%), and had B-lineage disease (90.9%). For the entire cohort, 5-year relapse-free survival (RFS) and overall survival (OS) were 46% (95% confidence interval [CI], 34% to 57%) and 49% (95% CI, 37% to 60%), respectively. Grade III-IV acute GVHD occurred in only 3% of patients, and chronic GVHD occurred in 13%. In multivariable analysis, myeloablative conditioning led to worse RFS (hazard ratio [HR], 4.65; P = .001), whereas transplantation in CR1 (HR, .30; P = .004) and transplantation for Philadelphia chromosome-positive (Ph+) ALL versus T-ALL (HR, .29; P = .03) were associated with improved RFS. Of the 54 patients who underwent RIC alloBMT in CR1 for B-ALL, the 5-year RFS and OS were 62% (95% CI, 47% to 74%) and 65% (95% CI, 51% to 77%), respectively, with a 5-year relapse incidence of 16% (95% CI, 7% to 27%) and an NRM of 24% (95% CI, 13% to 36%). RIC alloBMT with PTCy in CR1 represents a promising consolidation strategy for B-ALL patients age ≥55 years.

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.

Comparable survival outcomes with haploidentical stem cell transplantation and unrelated bone marrow transplantation

We retrospectively compared outcomes of unrelated donor bone marrow transplant (UBMT) and HLA-haploidentical peripheral blood stem cell transplantation using post-transplant cyclophosphamide (PTCy-haploPBSCT) using the Japanese registry data. Recipients of first HCT for acute leukemia and myelodysplastic syndromes between 2012 and 2015 were included. The analyzed subjects comprised UBMT recipients with 8/8 matched HLA alleles (n = 1470), 7/8 matched alleles (n = 859), 6/8 matched alleles (n = 186), and recipients of PTCy-haploPBSCT (n = 133). In multivariate analyses with 8/8 matched UBMT as the reference, PTCy-haploPBSCT showed similar overall mortality, decreased risk of non-relapse mortality (NRM), increased risk of relapse, and decreased risk of grade II-IV acute graft-versus-host disease (GVHD) and chronic GVHD. Adjusted probabilities for 8/8 matched UBMT, PTCy-haploPBSCT, and 7/8 and 6/8 matched UBMT groups at 2 years post-transplant were 61%, 60%, 58%, and 52% for overall survival, 23%, 28%, 21%, and 19% for relapse, and 20%, 7%, 24%, and 33% for NRM. PTCy-haploPBSCT was associated with remarkably low NRM, contributing to survival outcomes that were comparable to 8/8 matched UBMT. The higher relapse rate in the PTCy-haploPBSCT group might be associated with the higher proportion of high-risk patients. PTCy-haploPBSCT may be a viable alternative when HLA-matched related donors are not available.

Systematic overview of HLA-matched allogeneic hematopoietic cell transplantation with post-transplantation cyclophosphamide

The successful application of post-transplantation cyclophosphamide (PTCy) as graft-versus-host disease (GVHD) prophylaxis in HLA-haploidentical allogeneic hematopoietic cell transplantation (allo-HCT) led to the expansion of its application to HLA-matched related and unrelated allo-HCT. Notably, single-agent PTCy was found to be feasible for GVHD prevention in HLA-matched bone marrow transplantation. Single-agent PTCy prophylaxis was later attempted to control GVHD in HLA-matched peripheral blood stem cell transplantation (PBSCT), but this approach was inadequate to alleviate GVHD as evidenced by the high incidence of severe GVHD and/or non-relapse mortality. Therefore, various combinations of immunosuppressants with PTCy have been explored to identify the optimal drug combination that would efficiently prevent GVHD in HLA-matched PBSCT. A recent murine study helped clarify the putative mechanism underlying the activity of PTCy, demonstrating that PTCy impairs the proliferation and function of alloreactive T cells from the donor, but does not eliminate alloreactive T cells altogether. In addition, imbalanced reconstitution of NK cell as well as T cells has been observed in HLA-haploidentical allo-HCT. Therefore, it remains unclear whether or not PTCy-containing GVHD prophylaxis should replace the classical GVHD prophylaxis regimen in the HLA-matched setting, and convincing evidence supporting the benefits of PTCy is needed.

Impact of Center Experience with Donor Type on Outcomes: A Secondary Analysis, Blood and Marrow Transplant Clinical Trials Network 1101Open for Accrual June 2012Open for Accrual June 2012

We previously reported the results of Blood and Marrow Transplant Clinical Trials Network (BMT CTN) 1101, a randomized comparison of hematopoietic cell transplantation (HCT) performed with double umbilical cord blood units (dUCB) or with haploidentical bone marrow (haplo-BMT) with post-transplantation cyclophosphamide (PTCy) in the nonmyeloablative setting. Those results showed similar progression-free survival in the 2 treatment groups but lower nonrelapse mortality and better overall survival in the haplo-BM arm. In this secondary analysis, we sought to investigate whether transplantation center's previous experience with haplo-BM and/or dUCB HCT had an impact on outcomes. All patients randomized in BMT CTN 1101 were included. Center experience was assigned based on the number of transplantations with each platform performed in the year before initiation of the study according to the Center for International Blood and Marrow Transplant Research. Centers were then classified as a dUCB center (>10 dUCB HCTs; n = 117 patients, 10 centers), a haplo-BM center (>10 haplo-BM HCTs and ≤10 dUCB HCTs; n = 110 patients, 2 centers), or other center (≤10 haplo and ≤10 dUCB HCTs; n = 140 patients, 21 centers). After adjusting for age, Karnofsky Performance Status, and Disease Risk Index, we found that haplo-BM centers had lower overall mortality with this donor type compared with dUCB centers (hazard ratio [HR], 2.56; 95% confidence interval [CI], 1.44 to 4.56). In contrast, there were no differences in overall mortality between haplo-BM and dUCB in centers that were experienced with dUCB HCT (HR, 1.02; 95% CI, .59 to 1.79) or had limited to no experience with either dUCB or haplo-BM HCT (HR, 1.36; 95% CI, .83 to 2.21). The higher risk of treatment failure and overall mortality in dUCB HCT in haplo BM-experienced centers was driven by a significantly higher risk of relapse (HR, 1.78; 95% CI, 1.07 to 2.97). With the exception of worse outcomes among dUCB HCT recipients in haplo-BM centers, transplantation center experience in the year before initiation of BMT CTN 1101 had a limited impact on the outcomes of this randomized clinical trial.

Posttransplantation Cyclophosphamide-based Graft versus Host Disease Prophylaxis with Non-myeloablative Conditioning for Blood or Marrow Transplantation for Myelofibrosis

We describe outcomes with posttransplantation cyclophosphamide and non-myeloablative conditioning based allogeneic blood or marrow transplantation for myelofibrosis using matched or mismatched, family or unrelated donors. The conditioning regimen consisted of fludarabine, cyclophosphamide and total body irradiation. Forty-two patients, with a median age of 63 years, were included, of whom 19% had intermediate-1, 60% had intermediate-2, and 21% had high-risk DIPSS-plus disease, and 60% had atleast one high-risk somatic mutation. Over 90% patients engrafted neutrophils at a median of 19.5 days and 7% had graft failure. At 1 and 3-years, respectively, the overall survival was 65% and 60%, relapse-free survival was 65% and 31%, relapse was 5% and 40%, and non-relapse mortality was 30% and 30%. Acute graft versus host disease grade 3-4 was noted in 17% at 1 year and chronic graft versus host disease requiring systemic therapy in 12% patients. Spleen size ≥ 17 cm or prior splenectomy was associated with inferior relapse-free survival (HR 3.50, 95% CI 1.18-10.37, P=0.02) and higher relapse rate (SDHR not calculable, P=0.01). Age > 60 years (SDHR 0.26, 95% CI: 0.08-0.80, P=0.02) and peripheral blood graft (SDHR 0.34, 95% CI 0.11-0.99, P=0.05) was associated with lower risk of relapse. In our limited sample, the presence of a high-risk mutation was not statistically significantly associated with an inferior outcome although ASXL1 was suggestive of inferior survival (SDHR 2.36. 95% CI 0.85-6.6, P=0.09). Overall, this approach shows comparable outcomes as previously reported and underscores the importance of spleen size in evaluation of transplant candidates.

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.

Immune Reconstitution after Haploidentical Donor and Umbilical Cord Blood Allogeneic Hematopoietic Cell Transplantation

Allogeneic hematopoietic cell transplantation (HCT) is the only potentially curative therapy for a variety of hematologic diseases. However, this therapeutic platform is limited by an initial period when patients are profoundly immunocompromised. There is gradual immune recovery over time, that varies by transplant platform. Here, we review immune reconstitution after allogeneic HCT with a specific focus on two alternative donor platforms that have dramatically improved access to allogeneic HCT for patients who lack an HLA-matched related or unrelated donor: haploidentical and umbilical cord blood HCT. Despite challenges, interventions are available to mitigate the risks during the immunocompromised period including antimicrobial prophylaxis, modified immune suppression strategies, graft manipulation, and emerging adoptive cell therapies. Such interventions can improve the potential for long-term overall survival after allogeneic HCT.