Sirolimus and Mycophenolate Mofetil as Calcineurin Inhibitor-Free Graft-versus-Host Disease Prophylaxis for Reduced-Intensity Conditioning Umbilical Cord Blood Transplantation

Shared graft-versus-leukemia minor histocompatibility antigens in DISCOVeRY-BMT

T-cell responses to minor histocompatibility antigens (mHAs) mediate graft-versus-leukemia (GVL) effects and graft-versus-host disease (GVHD) in allogeneic hematopoietic cell transplantation. Therapies that boost T-cell responses improve allogeneic hematopoietic cell transplant (alloHCT) efficacy but are limited by concurrent increases in the incidence and severity of GVHD. mHAs with expression restricted to hematopoietic tissue (GVL mHAs) are attractive targets for driving GVL without causing GVHD. Prior work to identify mHAs has focused on a small set of mHAs or population-level single-nucleotide polymorphism-association studies. We report the discovery of a large set of novel GVL mHAs based on predicted immunogenicity, tissue expression, and degree of sharing among donor-recipient pairs (DRPs) in the DISCOVeRY-BMT data set of 3231 alloHCT DRPs. The total number of predicted mHAs varied by HLA allele, and the total number and number of each class of mHA significantly differed by recipient genomic ancestry group. From the pool of predicted mHAs, we identified the smallest sets of GVL mHAs needed to cover 100% of DRPs with a given HLA allele. We used mass spectrometry to search for high-population frequency mHAs for 3 common HLA alleles. We validated 24 predicted novel GVL mHAs that are found cumulatively within 98.8%, 60.7%, and 78.9% of DRPs within DISCOVeRY-BMT that express HLA-A∗02:01, HLA-B∗35:01, and HLA-C∗07:02, respectively. We confirmed the immunogenicity of an example novel mHA via T-cell coculture with peptide-pulsed dendritic cells. This work demonstrates that the identification of shared mHAs is a feasible and promising technique for expanding mHA-targeting immunotherapeutics.

Impact of posttransplant cyclophosphamide on the outcome of patients undergoing unrelated single-unit umbilical cord blood transplantation for pediatric acute leukemia

Background

Umbilical cord blood transplantation (UCBT) from unrelated donors is one of the successful treatments for acute leukemia in childhood. The most frequent side effect of UCBT is peri-engraftment syndrome (PES), which is directly associated with the greater prevalence of acute and chronic graft-versus-host-disease (aGvHD and cGvHD). In haploidentical stem cell transplantation, posttransplant cyclophosphamide (PTCY) has been demonstrated to be an effective method against GvHD. However, the effects of PTCY as a GvHD prophylactic in UCBT had not been investigated. This study aimed to evaluate the effects of PTCY on the outcomes of UCBT for pediatric acute leukemia.

Methods

This retrospective study included 52 children with acute leukemia who underwent unrelated single-unit UCBT after myeloablative conditioning regimens. The results from the PTCY and non-PTCY groups were compared.

Results

The incidence of transplantation-related mortality in non-PTCY and PTCY were 5% and 10% (p = 0.525), respectively. The incidence of relapse in non-PTCY and PTCY were 5% and 23% (p = 0.095), respectively. Second complete remission status (CR2) was an independent risk factor for relapse-free survival (hazard ratio = 9.782, p = 0.001). The odds ratio for sepsis or bacteremia incidence was significantly greater in the PTCY group (9.524, p = 0.017). PTCY group had increased rates of cytomegalovirus activity and fungal infection. The incidence of PES, aGvHD, cGvHD, and hemorrhagic cystitis in the PTCY group was lower than that in the non-PTCY group, although it was not significantly different. Additionally, higher doses of PTCY (29 mg/kg and 40 mg/kg) were associated with lower incidences of aGvHD and severe GvHD (65% and 29%, respectively) than lower doses (93% and 57%, respectively). Engraftment time and graft failure incidence were similar across groups.

Conclusion

The results support the safety and efficiency of PTCY as part of PES controlling and GvHD prophylaxis in single-unit UCBT for children with acute leukemia. A PTCY dosage of 29 mg/kg to 40 mg/kg appears to be more effective in GvHD prophylaxis for UCBT patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-10309-9.

Current Role of Prospective Monitoring, Pre-emptive and Prophylactic Therapy for Human Herpesvirus-6 after Allogeneic Stem Cell Transplantation

Human herpesvirus 6 (HHV-6) frequently reactivates after allogeneic stem cell transplantation (SCT). Most patients are asymptomatic and viremia often resolves without therapy; however, transplant-related complications may be associated with reactivation. Multiple presentations have been attributed to HHV-6 reactivation after SCT including encephalitis. Several strategies have been trialed to reduce such risks or complications. Challenges exist with prospective monitoring strategies, and established thresholds of high-level reactivation may be limited. Three published guidelines and extensive trials focusing on preemptive and prophylactic strategies are reviewed. Future areas of investigation and high-risk populations are described. Existing trials and testing platforms have significant limitations, and to date no clear benefit for a preemptive or prophylactic intervention has been demonstrated.

Immunometabolic Therapeutic Targets of Graft-versus-Host Disease (GvHD)

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a curative option in the treatment of aggressive malignant and non-malignant blood disorders. However, the benefits of allo-HSCT can be compromised by graft-versus-host disease (GvHD), a prevalent and morbid complication of allo-HSCT. GvHD occurs when donor immune cells mount an alloreactive response against host antigens due to histocompatibility differences between the donor and host, which may result in extensive tissue injury. The reprogramming of cellular metabolism is a feature of GvHD that is associated with the differentiation of donor CD4+ cells into the pathogenic Th1 and Th17 subsets along with the dysfunction of the immune-suppressive protective T regulatory cells (Tregs). The activation of glycolysis and glutaminolysis with concomitant changes in fatty acid oxidation metabolism fuel the anabolic activities of the proliferative alloreactive microenvironment characteristic of GvHD. Thus, metabolic therapies such as glycolytic enzyme inhibitors and fatty acid metabolism modulators are a promising therapeutic strategy for GvHD. We comprehensively review the role of cellular metabolism in GvHD pathogenesis, identify candidate therapeutic targets, and describe potential strategies for augmenting immunometabolism to ameliorate GvHD.

A case series of medication-related fibrovascular hyperplasia following hematopoietic stem cell transplantation for Fanconi anemia

Systemic medications categorized as diphenylhydantoin, calcineurin inhibitor and calcium channel blocker may have effects on the oral cavity by modifying the inflammatory and immune response and causing undesired tissue proliferative reactions. Calcineurin inhibitors are medications commonly used for long periods in patients undergoing allogeneic hematopoietic stem cell transplant (HSCT) and solid organ transplantation. Medication-related fibrovascular hyperplasia (MRFH) is an extra gingival hyperplastic nodular growth associated with medications use. This study reports five cases of pediatric patients (6 to 12-years-old) diagnosed with Fanconi anemia (FA) after HSCT who presented similar oral mucosal lesions associated with the use of cyclosporine, phenobarbital and amlodipine. After excision of the lesions, histopathological analysis described them as pyogenic granuloma (PG). As the aetiology of the lesions manifested by the patients was associated with the use of medications, the final diagnosis was MRFH. Despite the clinical and histopathological similarity between PG and MRFH, it is fundamental to know the aetiological agent for achieving definitive diagnosis and correct management. Considering the etiologic agent (medication) and histopathological findings, it is suggested that the most appropriate term for this manifestation should be "medication-related fibrovascular hyperplasia". The correct nomenclature related to extra gingival hyperplastic lesions identified in patients on medications with potential to induce hyperplastic reactions should be adopted to facilitate scientific communication and improve the treatment.

Guidelines for the Prevention and Management of Graft-versus-Host Disease after Cord Blood Transplantation

The incidence of graft-versus-host disease (GVHD) after cord blood (CB) transplantation (CBT) is lower than expected given the marked degree of human leukocyte antigen (HLA)-mismatch of CB grafts. While the exact mechanism that underlies this biology remains unclear, it is hypothesized to be due to the low number of mostly immature T-cells infused as part of the graft1,2, and increased tolerance of CB-derived lymphocytes induced by the state of pregnancy. Nevertheless, acute GVHD (aGVHD) is a significant complication of CBT. In contrast, the incidence of chronic GVHD (cGVHD) following CBT is lower than what is observed following matched related or unrelated donor HSC transplantation (HSCT)3-6. This review outlines the guidelines for the prevention and management of acute and chronic GVHD following CBT.

A phase 2 trial of GVHD prophylaxis with PTCy, sirolimus, and MMF after peripheral blood haploidentical transplantation

The introduction of posttransplant cyclophosphamide (PTCy) made performing allogeneic hematopoietic cell transplantation (HCT) from HLA haplotype-incompatible donors possible. In a setting of PTCy and tacrolimus/mycophenolate mofetil (MMF) as a graft-versus-host disease (GVHD) prophylaxis, a peripheral blood (PB) graft source as compared with bone marrow reduces the relapse rate but increases acute GVHD (aGVHD) and chronic GVHD (cGVHD). This phase 2 trial assessed sirolimus and MMF efficacy following PTCy as a GVHD prophylaxis after PB haploidentical HCT (haplo-HCT). With 32 evaluable patients (≥18 years) enrolled, this study had 90% power to demonstrate a reduction in 100-day grade II-IV aGVHD to 20% from the historical benchmark of 40% after haplo-HCT using PTCy/tacrolimus/MMF. At a median follow-up of 16.1 months, the primary end point of the trial was met with a day-100 grade II-IV aGVHD cumulative incidence of 18.8% (95% confidence interval [CI], 7.5% to 34.0%). There were no graft-failure events and the 1-year probability of National Institutes of Health (NIH) moderate/severe cGVHD was 18.8% (95% CI, 7.4% to 34.0%), nonrelapse mortality was 18.8% (95% CI, 7.4% to 34.0%), relapse was 22.2% (95% CI, 9.6% to 38.2%), disease-free survival was 59.0% (95% CI, 44.1% to 79.0%), GVHD-free relapse-free survival was 49.6% (95% CI, 34.9% to 70.5%), and overall survival was 71.7% (95% CI, 57.7% to 89.2%) for the entire cohort. These data demonstrate that GVHD prophylaxis with sirolimus/MMF following PTCy effectively prevents grade II-IV aGVHD after PB haplo-HCT, warranting prospective comparison of sirolimus vs tacrolimus in combination with MMF following PTCy as GVHD prophylaxis after PB HCT. This trial was registered at www.clinicaltrials.gov as #NCT03018223.

Cytomegalovirus-Specific Immunity Recovers More Slowly after Cord Blood Transplantation Compared with Matched Sibling Donor Allogeneic Transplantation

BACKGROUND

Rapid quantitative recovery of NK cells but slower recovery of T-cell subsets along with frequent viral infections are reported after umbilical cord blood (UCB) compared with matched sibling donor (MSD) hematopoietic cell transplantation (HCT). However, it remains unclear whether increased propensity for viral infections is also a result of slower recovery of virus-specific immunity after UCB as compared to MSD HCT.

OBJECTIVES

We examined the differences in the function of virus-specific peripheral blood mononuclear cells (PBMC) after UCB (N=17) vs. MSD (N=9) using previously collected patient blood samples at various time points after HCT.

METHODS

Interferon-gamma (IFN-γ) enzyme-linked immune absorbent spot (ELISpot) assay was used to quantify the PBMC frequencies that secrete IFN-γ in response to 11 immunopeptides from 5 common viruses. We included the patients who received the same reduced intensity conditioning regimen without ATG, no systemic glucocorticoids and had no relapse or acute/chronic graft-versus-host disease within 1 year after HCT.

RESULTS

The CMV-reactive PBMC frequencies were higher in CMV seropositive vs. seronegative patients after HCT. Among CMV seropositive patients, the frequency of CMV-reactive PBMC was lower after UCB compared to MSD throughout one year of HCT. We observed no differences in virus-specific PBMC responses towards HHV6, EBV, BK, and adenovirus antigens between UCB and MSD.

CONCLUSION

Our data demonstrate that the reconstitution of CMV-specific immunity is slower in CMV seropositive recipients of UCB vs. MSD HCT in contrast to other viruses which had similar recoveries. These study findings support implementation of more potent prophylactic strategies for preventing CMV reactivation in CMV seropositive patients receiving UCB HCT.

Allogeneic Stem Cell Transplantation in Mature T Cell and Natural Killer/T Neoplasias: A Registry Study from Spanish GETH/GELTAMO Centers

Despite advances in understanding the biology of mature T and natural killer (NK)/T cell neoplasia, current therapies, even the most innovative ones, are still far from ensuring its cure. The only treatment to date that has been shown to control aggressive T cell neoplasms in the long term is allogeneic stem cell transplantation (alloSCT). We aim to report the results of alloSCT for advanced mature T and NK/T neoplasias performed in centers from our national GELTAMO/GETH (Grupo Español de Linfoma y Trasplante de Médula Ósea/Grupo Español de Trasplante Hematopoyético y Terapia Celular) over the past 25 years. As a secondary objective, we analyzed the results of alloSCT from haploidentical donors. We performed a retrospective analysis of all patients who received an alloSCT in Spanish centers (n = 201) from September 1995 to August 2018. The 2-year overall survival (OS) and disease-free survival (DFS) were 65.5% and 58.2%, respectively. The univariate for OS and DFS showed statistically different hazard ratios for conditioning intensity, response pre-alloSCT, comorbidity index, donor/receptor cytomegalovirus status and Eastern Cooperative Oncology Group (ECOG) pre-alloSCT, but only a better ECOG pre-alloSCT remained significant in the multivariate analysis. There was an increased incidence of relapse in those patients who did not develop chronic graft-versus-host disease (GVHD) and an increased risk of death in those developing moderate to severe acute GVHD. The 1-year nonrelapse mortality was 21.9% and was mainly due to GVHD (30%) and bacterial infections (17%). When comparing unrelated donors with haploidentical donors, we found similar results in terms of OS and DFS. There was, however, a reduction of acute GVHD in the haploidentical group (P = .04) and trend to a reduction of chronic GVHD. In conclusion, alloSCT is the only curative option for most aggressive T cell neoplasias. Haploidentical donors offer similar results to related donors in terms of survival with a reduction of acute GVHD.

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.

Weight-based mycophenolate mofetil dosing predicts acute GVHD and relapse after allogeneic hematopoietic cell transplantation

OBJECTIVES

Higher MMF dose can reduce acute GVHD risk after allogeneic hematopoietic cell transplantation (HCT). We examined the effect of MMF dose, relative to patient actual body weight (mg/kg/day), on outcomes of 680 adults after HCT.

METHODS

MMF was combined with cyclosporine (n = 599) or sirolimus (n = 81). We divided MMF dose/kg/day in quartiles.

RESULTS

The median time to grade II-IV acute GVHD was 32 days. The incidence of grade II-IV acute GVHD at day 30 was 30% in 1st (<29), 20% in 2nd (29-34), 16% in 3rd (35-41), and 19% in 4th (≥42) quartile (P < .01). Corresponding relapse incidence at 1 year was 16%, 25%, 27%, and 31%, respectively (P = .01). In multivariate analysis, as compared to 1st quartile, higher dose of weight-based MMF reduced grade II-IV acute GVHD (HR = 0.64 for 2nd, HR = 0.48 for 3rd, and HR = 0.55 for 4th quartile), but increased the risk of relapse (HR = 1.63 for 2nd, HR = 1.75 for 3rd, and HR = 2.31 for 4th quartile).

CONCLUSIONS

Weight-based MMF dose had no significant impact on engraftment, chronic GVHD, or survival. These data suggest that higher weight-based MMF dose reduces the risk of acute GVHD at the expense of increased relapse and supports conducting prospective studies to optimize MMF dosing after HCT.

Prophylactic Foscarnet for Human Herpesvirus 6: Effect on Hematopoietic Engraftment after Reduced-Intensity Conditioning Umbilical Cord Blood Transplantation

The high incidence of human herpesvirus-6 (HHV-6) reactivation, potentially interfering with engraftment after umbilical cord blood (UCB) hematopoietic cell transplantation (HCT), remains a major challenge. To potentially address this problem, we evaluated the effect of prophylactic foscarnet administered twice daily beginning on day +7 and continuing through engraftment in 25 patients. To determine the impact of foscarnet on HHV-6, engraftment, and other transplantation outcomes, we compared results in 61 identically treated patients with hematologic malignancies. Treatment and control groups underwent reduced-intensity conditioning UCB HCT with a conditioning regimen of fludarabine, cyclophosphamide, and total body irradiation 200 cGy with or without antithymocyte globulin (ATG), using sirolimus plus mycophenolate mofetil immune suppression. The treatment and control groups were similar in terms of age, disease risk, use of ATG, Hematopoietic Cell Transplantation Comorbidity Index, and graft CD34 cell dose; however, foscarnet-treated patients were less likely to receive a double UCB graft and to be treated more recently (2016 to 2018). The cumulative incidence of HHV-6 reactivation by day +100 was 63% for all patients (95% confidence interval [CI], 51% to 75%) and was not significantly different between the 2 groups. HHV-6 reactivation occurred at a median of 34 days in the foscarnet group and 25.5 days in the control group. The incidence of neutrophil engraftment at day 42 was higher in the foscarnet group compared with the control group (96%; [95% CI, 83% to 100%] versus 75% [95% CI, 64% to 85%]; P< .01). The cumulative incidence of platelet engraftment by 6 months was 92% (95% CI, 69% to 100%) for the foscarnet group versus 75% (95% CI, 60% to 90%) for the control group (P= .08), and multivariate analysis identified the use of foscarnet as an independent predictor of better platelet engraftment. No patients died as a result of graft failure in recipients of foscarnet, whereas 5 patients died from graft failure in the control group. Six-month overall survival (OS) and nonrelapse mortality (NRM) were better in the foscarnet group (96% versus 72% [P= .02] and 4% versus 18% [P= .07], respectively). Even though foscarnet prophylaxis did not prevent HHV-6 viremia, we observed a delay in time to HHV-6 reactivation, a trend toward differences in engraftment, NRM, and OS compared with historical controls.

Medication-related fibrovascular hyperplasia lesion in tongue: Case report

OBJECTIVE

The objective of this study is to report the case of a patient who underwent hematopoietic stem cell transplantation for Hodgkin's lymphoma treatment and developed multiple tongue lesions during recovery.

METHODS AND RESULTS

This is the case report of a patient who developed ulcerated lesions with areas of depapillation on the border and dorsum of the tongue. The ulcer evolved to a reddish fibrous hyperplastic nodule, similar to adjacent mucosa. The patient was using a series of medications, such as antifungals, antibiotics, antivirals, corticosteroids, and analgesics in addition to immunosuppression with cyclosporine. Considering the medical history of the patient, a biopsy was performed. Histopathological analyses describe hyperplasia, granulation tissue, vascular proliferation, and intense inflammatory infiltrate, and the diagnosis was of medication-related fibrovascular hyperplasia (MRFH).

CONCLUSION

Patients in use of cyclosporine are at risk to develop oral lesions, such as MRFH. The correct diagnosis is important, so the adequate treatment and follow-up are instituted even considering the immunosuppression protocol.

Predictive value of disease risk comorbidity index for overall survival after allogeneic hematopoietic transplantation

Allogeneic hematologic cell transplantation (alloHCT) is the only curative therapy for many adults with hematological malignancies. However, it can be associated with substantial risks of morbidity and mortality that are dependent on patient comorbidity- or disease risk-related factors. Several pretransplantation prognostic scoring systems have been developed to estimate survival of patients undergoing alloHCT; however, there is significant interstudy variability in the predictive capacity of these assessment tools. We tested the prognostic capability of a composite scoring system including the disease risk index and HCT comorbidity index (DRCI). The DRCI scoring system was applied pretransplantation to determine whether it predicted clinical outcomes of 959 adult patients with hematological malignancies undergoing alloHCT from 2000 to 2013 at the University of Minnesota. The DRCI score categorized patients into 6 risk groups, with 2-year overall survival ranging between 74% for the very low-risk DRCI group and 34% for the very high-risk DRCI group. In multiple regression analyses adjusted for patient age and donor type, the risk of overall mortality independently increased as the DRCI score increased. Additionally, the DRCI score independently predicted risk of relapse, disease-free survival, and graft-versus-host disease-free/relapse-free survival. Our data demonstrate that the pretransplantation DRCI scoring system predicts outcomes after alloHCT and can be used to guide clinical decision making for patients considering alloHCT.

Current Status and Future Directions in Graft-Versus-Host Disease Prevention Following Allogeneic Blood and Marrow Transplantation in Adults

Graft-versus-host disease (GvHD) in its acute and chronic forms continues to represent a significant barrier to the success and wide-applicability of blood and marrow transplantation as a potentially curative treatment modality for a number of benign and malignant blood conditions. Presently, calcineurin inhibitor (CNI)-based regimens remain the most commonly used prevention strategy, although post-transplant cyclophosphamide is emerging as an alternative approach, and is providing a backbone for innovative CNI-free combinations. In this paper, we review the current strategies used for the prevention of GvHD, and highlight some of the developing and promising combinations.

Approaching treatment of transplant-associated thrombotic Microangiopathy from two directions with Eculizumab and transitioning from Tacrolimus to Sirolimus

BACKGROUND

In the past, conventional treatment strategies for transplant-associated thrombotic microangiopathy (TA-TMA) have not proven to be very effective. Recently, eculizumab which is a humanized monoclonal antibody that works as a terminal complement inhibitor has demonstrated promise in the treatment landscape of TA-TMA.

METHODS AND MATERIALS

This was a single-center retrospective analysis of 20 consecutive adult patients with TA-TMA: 10 patients who received conventional therapy and 10 patients who received eculizumab-based therapy. These patients had undergone allogeneic HSCT at MD Anderson Cancer Center between August 2011 and September 2016.

RESULTS

When comparing the treatment outcomes in the two cohorts, none of the patients in the conventional therapy group obtained a hematologic or complete response according to our response criteria whereas seven patients in the eculizumab group achieved a hematologic response with one patient achieving a complete response with organ recovery. In addition, overall survival at the end of assessment was 60% in the eculizumab cohort and 30% in the conventional cohort. One major difference in practice at our institution versus previously published studies is the management of immunosuppression. In a majority of patients, tacrolimus was continued or transitioned to sirolimus for GVHD prophylaxis.

CONCLUSION

Response rates and survival were improved for patients who were transitioned to sirolimus, so a two-pronged approach of inhibiting complement along with providing an alternative effective immunosuppressive agent may be beneficial in the treatment of early onset TA-TMA.

Delayed immune reconstitution after allogeneic transplantation increases the risks of mortality and chronic GVHD

Slow immune reconstitution is a major obstacle to the successful use of allogeneic hematopoietic cell transplantation (allo-HCT). As matched sibling donor (MSD) allo-HCT is regarded as the gold standard, we evaluated the pace of immune reconstitution in 157 adult recipients of reduced-intensity conditioning followed by MSD peripheral blood HCT (n = 68) and compared these to recipients of umbilical cord blood (UCB; n = 89). At day 28, UCB recipients had fewer natural killer (NK) cells than MSD recipients, but thereafter, NK cell numbers (and their subsets) were higher in UCB recipients. During the first 6 months to 1 year after transplant, UCB recipients had slower T-cell subset recovery, with lower numbers of CD3⁺, CD8⁺, CD8⁺ naive, CD4⁺ naive, CD4⁺ effector memory T, regulatory T, and CD3⁺CD56⁺ T cells than MSD recipients. Notably, B-cell numbers were higher in UCB recipients from day 60 to 1 year. Bacterial and viral infections were more frequent in UCB recipients, yet donor type had no influence on treatment-related mortality or survival. Considering all patients at day 28, lower numbers of total CD4⁺ T cells and naive CD4⁺ T cells were significantly associated with increased infection risk, treatment-related mortality, and chronic graft-versus-host disease (GVHD). Patients with these characteristics may benefit from enhanced or prolonged infection surveillance and prophylaxis as well as immune reconstitution-accelerating strategies.

Hematopoietic stem cell transplant with HLA-mismatched grafts: impact of donor, source, conditioning, and graft versus host disease prophylaxis

INTRODUCTION

Allogeneic hematopoietic cell transplantation is frequently used to treat malignant and non-malignant conditions, and many patients lack a human leukocyte antigen (HLA) matched related or unrelated donor. For those patients, available alternative graft sources include HLA mismatched unrelated donors, cord blood, or haplo-identical donors. These graft sources have unique characteristics and associated outcomes requiring graft-specific variations to conditioning regimens, graft-versus-host disease prophylaxis, and post-transplant care. Areas covered: This manuscript will cover approaches in selecting donors, conditioning regimens, graft versus host disease prophylaxis, post-transplant care, and ongoing clinical trials related to mismatched grafts. Expert commentary: In the setting, haplo-identical grafts are increasingly popular due to low graft versus host disease (GVHD) risk and control of cellular dose. We recommend young male donors, utilizing bone marrow with post-transplant cyclophosphamide for GVHD prophylaxis. Cord blood transplant is appropriate for young healthy patients, and we recommend 6/8 HLA matched grafts with at least 2.0 × 10⁷/kg total nucleated cell dose. For mismatched unrelated donors we recommend young male donors, utilizing bone marrow with in vivo T-cell conditioning with post-transplant cyclophosphamide, alemtuzumab, or ATG. With these transplants, significant post-transplant surveillance and infectious prophylaxis is key to reducing treatment-related mortality.

Combined OX40L and mTOR blockade controls effector T cell activation while preserving Treg reconstitution after transplant

A critical question facing the field of transplantation is how to control effector T cell (T_eff) activation while preserving regulatory T cell (T_reg) function. Standard calcineurin inhibitor-based strategies can partially control T_effs, but breakthrough activation still occurs, and these agents are antagonistic to T_reg function. Conversely, mechanistic target of rapamycin (mTOR) inhibition with sirolimus is more T_reg-compatible but is inadequate to fully control T_eff activation. In contrast, blockade of OX40L signaling has the capacity to partially control T_eff activation despite maintaining T_reg function. We used the nonhuman primate graft-versus-host disease (GVHD) model to probe the efficacy of combinatorial immunomodulation with sirolimus and the OX40L-blocking antibody KY1005. Our results demonstrate significant biologic activity of KY1005 alone (prolonging median GVHD-free survival from 8 to 19.5 days), as well as marked, synergistic control of GVHD with KY1005 + sirolimus (median survival time, >100 days; P < 0.01 compared to all other regimens), which was associated with potent control of both T_H/T_C1 (T helper cell 1/cytotoxic T cell 1) and T_H/T_C17 activation. Combined administration also maintained T_reg reconstitution [resulting in an enhanced T_reg/T_eff ratio (40% over baseline) in the KY1005/sirolimus cohort compared to a 2.9-fold decrease in the unprophylaxed GVHD cohort]. This unique immunologic signature resulted in transplant recipients that were able to control GVHD for the length of analysis and to down-regulate donor/recipient alloreactivity despite maintaining anti-third-party responses. These data indicate that combined OX40L blockade and sirolimus represents a promising strategy to induce immune balance after transplant and is an important candidate regimen for clinical translation.