Feasibility of HLA-haploidentical hematopoietic stem cell transplantation with post-transplantation cyclophosphamide for advanced pediatric malignancies

Human Leukocyte Antigen-Haploidentical Haematopoietic Stem Cell Transplantation Using Post-Transplant Cyclophosphamide for Paediatric Haematological Malignancies

The use of human leukocyte antigen (HLA)-haploidentical haematopoietic stem cell transplantation (HSCT) with post-transplant cyclophosphamide (PTCY), which markedly reduces the risk of graft-versus-host disease, has rapidly increased worldwide, even in children. It was initially developed for post-transplant relapse or non-remission at transplant for patients with high-risk haematologic malignancies. However, this strategy is currently used more frequently for standard-risk, transplant-eligible paediatric haematological malignancies. It has recently been recognised in adults that the transplant outcomes after PTCY-based HLA-haploidentical HSCT are comparable with those achieved after HLA-matched HSCT. Therefore, even in children, parental donors who are HLA-haploidentical donors and cord blood are currently considered the next donor candidates when an HLA-matched related or unrelated donor is unavailable. This review addresses the current status of the use of haplo-HSCT with PTCY for paediatric haematologic malignancies and future directions for donor selection (sex, age, ABO blood type, and HLA disparity), donor source, the dose of infused CD34+ cells, optimal conditioning, the concomitant graft-versus-host disease prophylaxis other than PTCY, and the pharmacokinetic study of CY and CY metabolites. These aspects present key solutions for further improvements in the outcomes of haplo-HSCT with PTCY for paediatric haematological malignancies.

Incidence, Risk Factors, Characteristics, and Outcome of Chronic Graft Versus Host Disease in Children Undergoing Haploidentical Peripheral Blood Stem Cell Transplant With Post-transplant Cyclophosphamide

AIM

Chronic graft versus host disease (cGVHD) is a major cause of morbidity postallogeneic peripheral blood stem cell transplant (PBSCT). There is paucity of literature describing incidence, risk factors, characteristics, and outcome of cGVHD in children undergoing haploidentical PBSCT with post-transplant cyclophosphamide (PTCy). Here, we describe our experience from our center regarding the same.

METHODS

All children who underwent haploidentical PBSCT with PTCy between January 2016 and December 2021 at our center and survived beyond day+100 post-transplant were included in this retrospective study. Conditioning regimens used were: Thiotepa-Fludarabine-Cyclophosphamide with 2 Gy single fraction total body irradiation, Thiotepa-Busulfan-Fludarabine, Fludarabine-total body irradiation and Fludarabine-Melphalan. Peripheral blood was used as stem cell source in all patients. GVHD prophylaxis was PTCy 50 mg/kg on day +3 and +4, Mycophenolate mofetil and Calcineurin inhibitors. Clinical and laboratory data was electronically retrieved and analyzed based on National Institute of Health Consensus Criteria-2014 at regular intervals. Impact of various patient, donor, and transplant-related factors on development of cGVHD were analyzed. Incidence of relapse, event free survival (EFS) and overall survival (OS) were calculated and compared between cGVHD and no cGVHD groups. Patients with rejection were excluded from risk factor analysis for cGVHD but were considered for survival analysis.

RESULTS

Fifty-one children included in this study. Median age of transplant of our cohort was 7.5 years with male:female=1.6:1. Eight patients had rejection with autologous recovery. History of acute GVHD (aGVHD) was present in 15/51 (Grade III to IV in 7/51). cGVHD developed in 19/51 patients (mild-9/51, moderate-6/51, and severe-4/51). Skin was the most common organ involved (100%) followed by gastrointestinal tract (47.4%), liver (36.8%), eyes (21%), lungs (21%), mouth (15.7%), and joints (5.2%). Advanced donor age (>30 y) and previous aGVHD were found to be significantly associated with increased risk of developing cGVHD. At last follow-up, complete response and partial response of cGVHD was seen in 6/19 and 4/19 patients, respectively. Overall mortality was 15/51 (cause of mortality was relapse of cancer 8/15, cGVHD-3/15, other 4/15). EFS and OS of full cohort was 55% and 70.6%, respectively. Compared with patients without cGVHD, patients with cGVHD demonstrated a lower relapse (18.2% vs. 40%, P =0.2333), higher EFS (68.4% vs. 53.1%, P =0.283), and higher OS (73.7% vs. 68.8%, P =0.708).

CONCLUSION

Incidence of cGVHD was high in children undergoing haploidentical PBSCT with PTCy. Other than PBSC graft source; donor age and previous aGVHD were the risks factors for development of cGVHD. Patients with cGVHD had lower incidence of relapse translating into better survival but this difference was not statistically significant.

Immunotherapy for neuroblastoma by hematopoietic cell transplantation and post-transplant immunomodulation

Neuroblastoma represents a relatively common childhood tumor that imposes therapeutic difficulties. High risk neuroblastoma patients have poor prognosis, display limited response to radiochemotherapy and may be treated by hematopoietic cell transplantation. Allogeneic and haploidentical transplants have the distinct advantage of reinstitution of immune surveillance, reinforced by antigenic barriers. The key factors favorable to ignition of potent anti-tumor reactions are transition to adaptive immunity, recovery from lymphopenia and removal of inhibitory signals that inactivate immune cells at the local and systemic levels. Post-transplant immunomodulation may further foster anti-tumor reactivity, with positive but transient impact of infusions of lymphocytes and natural killer cells both from the donor, the recipient or third party. The most promising approaches include introduction of antigen-presenting cells in early post-transplant stages and neutralization of inhibitory signals. Further studies will likely shed light on the nature and actions of suppressor factors within tumor stroma and at the systemic level.

Antithymocyte Globulin Plus Post-Transplant Cyclophosphamide Combination as an Effective Strategy for Graft-versus-Host Disease Prevention in Haploidentical Peripheral Blood Stem Cell Transplantation for Children with High-Risk Malignancies

Haploidentical hematopoietic stem cell transplantation using post-transplant cyclophosphamide (PTCy) for graft-versus-host disease (GVHD) prophylaxis has emerged as a valid alternative transplant strategy for patients lacking a suitable HLA-matched related donor. The high risk of severe GVHD remains the major clinical challenge in this setting. The addition of antithymocyte globulin (ATG) in PTCy-based regimens for GVHD reduction in haploidentical hematopoietic stem cell transplantation is rational and was reported in adult series. However, its feasibility is unknown in pediatric patients. Here, we firstly describe our experience of 15 consecutive children with high-risk malignancies receiving haploidentical peripheral blood stem cell transplantation using ATG plus PTCy for GVHD prophylaxis. Only three patients developed grade 1-2 acute GVHD, limited to skin. No grade 3-4 acute GVHD and chronic GVHD were observed. Viral reactivations were frequently seen but manageable. Six patients relapsed, as the main cause of death in our series. None died from events related to GVHD. Our data suggest that ATG plus PTCy is an effective strategy for GVHD prevention in haploidentical peripheral blood stem cell transplantation and is feasible in children with high-risk malignancies.

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.

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.

Single-Arm Non-Blinded Multicenter Clinical Trial on T-Cell-Replete Haploidentical Stem Cell Transplantation Using Low-Dose Antithymocyte Globulin for Relapsed and Refractory Pediatric Acute Leukemia

Although approximately 70% of pediatric hematological malignancies are curable, approximately 30% remain fatal. No standard treatment is available in patients showing relapse and those with refractory disease. Although different methods are adopted in different hospitals, its efficacy is extremely limited. In recent years, haploidentical stem cell transplantation, involving high-dose cyclophosphamide administration post-transplanta tion, has been used, mainly in adults; however, its application is limited to removal of alloreactive T cells. Multicenter single-arm clinical trials of T-cell replete haploidentical stem cell transplantation (TCR-haplo-SCT) will be conducted in children with relapsed and refractory acute leukemia. After myeloablative conditioning using total body irradiation or busulfan, intensive graft versus host disease prophylaxis is administered, consisting of low-dose rabbit anti-human thymocyte globulin, tacrolimus, methotrexate, and prednisolone. An external control group is set up for the study. The treatment period is around 3 months, and the follow-up period is 2 years from transplantation completion.The aim of this study is to verify the efficacy and safety of TCR-haplo-SCT and present it as a new immune cell therapy for improving survival rate in children with relapsed and refractory acute leukemia.

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.

Haploidentical Hematopoietic Stem Cell Transplantation with Post-Transplantation Cyclophosphamide in Children with High-Risk Leukemia Using a Reduced-Intensity Conditioning Regimen and Peripheral Blood as the Stem Cell Source

The use of haploidentical donor hematopoietic stem cell transplantation with post-transplantation cyclophosphamide (Haplo-PTCy) in children is increasing; however, it is still not clear which preparative regimen is best in this setting. We present the long-term results of 42 patients age <18 years with high-risk leukemia who underwent this procedure using a reduced-intensity conditioning regimen (RIC) and peripheral blood as the stem cell source. Twenty-six patients had acute lymphoblastic leukemia, 13 had acute myelogenous leukemia, 2 had juvenile myelomonocytic leukemia, and 1 had blast crisis of chronic myelogenous leukemia. One-third of the patients were in first remission, 50% were in second remission, 14% were in third remission, and 3% had refractory disease. Neutrophil recovery occurred in 100% of the 40 patients alive at day +30, and transplantation-related mortality at 1 year was 14%. The incidence of acute graft-versus-disease (GVHD) grade III-IV was 17%, and the cumulative incidence of moderate to severe chronic GVHD at 1 year was 29%. The median duration of follow-up for surviving patients was 45 months; overall survival and event-free survival at 36 months were 56% and 46%, respectively. Long-term results of this series show that the use of an RIC regimen with peripheral blood stem cells as the cell source, in children with high-risk leukemia who underwent haplo-PTCy has tolerable toxicity, universal engraftment, and good survival rates.

HLA-Haploidentical Family Donors: The New Promise for Childhood Acute Lymphoblastic Leukaemia?

Allogeneic haematopoietic stem cell transplantation (HSCT) is indicated in children with high-risk, relapsed or refractory acute lymphoblastic leukaemia (ALL). HLA-matched grafts from cord blood and stem cell repositories have allowed patients without suitable sibling donors to undergo HSCT. However, challenges in procuring matched unrelated donor (MUD) grafts due to high cost, ethnic disparity and time constraints have led to the exponential rise in the use of stem cells from human leukocyte antigen (HLA)-haploidentical family donors. Whilst HLA-haploidentical HSCT (hHSCT) performed in adult patients with acute leukaemia has produced outcomes similar to MUD transplants, experience in children is limited. Over the last 5 years, more data have emerged on hHSCT in the childhood ALL setting, allowing comparisons with matched donor transplants. The feasibility of hHSCT using adult family donors in childhood ALL may also address the ethical issues related to selection of minor siblings in matched sibling donor transplants. Here, we review hHSCT in paediatric recipients with ALL and highlight the emergence of hHSCT as a promising therapeutic option for patients lacking a suitable matched donor. Recent issues related to conditioning regimens, donor selection and graft-vs.-host disease prophylaxis are discussed. We also identify areas for future research to address transplant-related complications and improve post-transplant disease-free survival.

GRFS and CRFS in alternative donor hematopoietic cell transplantation for pediatric patients with acute leukemia

We report graft-versus-host disease (GVHD)-free relapse-free survival (GRFS) (a composite end point of survival without grade III-IV acute GVHD [aGVHD], systemic therapy-requiring chronic GVHD [cGVHD], or relapse) and cGVHD-free relapse-free survival (CRFS) among pediatric patients with acute leukemia (n = 1613) who underwent transplantation with 1 antigen-mismatched (7/8) bone marrow (BM; n = 172) or umbilical cord blood (UCB; n = 1441). Multivariate analysis was performed using Cox proportional hazards models. To account for multiple testing, P < .01 for the donor/graft variable was considered statistically significant. Clinical characteristics were similar between UCB and 7/8 BM recipients, because most had acute lymphoblastic leukemia (62%), 64% received total body irradiation-based conditioning, and 60% received anti-thymocyte globulin or alemtuzumab. Methotrexate-based GVHD prophylaxis was more common with 7/8 BM (79%) than with UCB (15%), in which mycophenolate mofetil was commonly used. The univariate estimates of GRFS and CRFS were 22% (95% confidence interval [CI], 16-29) and 27% (95% CI, 20-34), respectively, with 7/8 BM and 33% (95% CI, 31-36) and 38% (95% CI, 35-40), respectively, with UCB (P < .001). In multivariate analysis, 7/8 BM vs UCB had similar GRFS (hazard ratio [HR], 1.12; 95% CI, 0.87-1.45; P = .39), CRFS (HR, 1.06; 95% CI, 0.82-1.38; P = .66), overall survival (HR, 1.07; 95% CI, 0.80-1.44; P = .66), and relapse (HR, 1.44; 95% CI, 1.03-2.02; P = .03). However, the 7/8 BM group had a significantly higher risk for grade III-IV aGVHD (HR, 1.70; 95% CI, 1.16-2.48; P = .006) compared with the UCB group. UCB and 7/8 BM groups had similar outcomes, as measured by GRFS and CRFS. However, given the higher risk for grade III-IV aGVHD, UCB might be preferred for patients lacking matched donors.

Partially CD3+-Depleted Unrelated and Haploidentical Donor Peripheral Stem Cell Transplantation Has Favorable Graft-versus-Host Disease and Survival Rates in Pediatric Hematologic Malignancy

Most children who may benefit from stem cell transplantation lack a matched related donor. Alternative donor transplantations with an unrelated donor (URD) or a partially matched related donor (PMRD) carry an increased risk of graft-versus-host-disease (GVHD) and mortality compared with matched related donor transplantations. We hypothesized that a strategy of partial CD3⁺/CD19⁺ depletion for URD or PMRD peripheral stem cell transplantation (PSCT) would attenuate the risks of GVHD and mortality. We enrolled 84 pediatric patients with hematologic malignancies at the Children's Hospital of Philadelphia and the Children's Hospital of Wisconsin between April 2005 and February 2015. Two patients (2.4%) experienced primary graft failure. Relapse occurred in 23 patients (27.4%; cumulative incidence 26.3%), and 17 patients (20.2%) experienced nonrelapse mortality (NRM). Grade III-IV acute GVHD was observed in 18 patients (21.4%), and chronic GVHD was observed and graded as limited in 24 patients (35.3%) and extensive in 8 (11.7%). Three-year overall survival (OS) was 61.8% (95% confidence interval [CI], 50.2% to 71.4%) and event-free survival (EFS) was 52.0% (95% CI, 40.3% to 62.4%). Age ≥15 years was associated with decreased OS (P= .05) and EFS (P= .05). Relapse was more common in children in second complete remission (P = .03). Partially CD3⁺-depleted alternative donor PSCT NRM, OS, and EFS compare favorably with previously published studies of T cell-replete PSCT. Historically, T cell-replete PSCT has been associated with a higher incidence of extensive chronic GVHD compared with limited chronic GVHD, which may explain the comparatively low relapse and NRM rates in our study cohort despite similar overall rates of chronic GVHD. Partial T cell depletion may expand donor options for children with malignant transplantation indications lacking a matched related donor by mitigating, but not eliminating, chronic GVHD.

Haploidentical hematopoietic stem cell transplantation with post-transplant high-dose cyclophosphamide in high-risk children: A single-center study

BACKGROUND

Post-Cy administration for GVHD prophylaxis in unmanipulated haploidentical HSCT has resulted in improved outcomes in recent years. Studies in children are lacking and accordingly we present the outcomes of 62 haploidentical transplantation for high-risk children.

PROCEDURE

We retrospectively assessed 62 transplants in 60 patients who underwent haploidentical-related HSCT with unmanipulated stem cells and for whom Post-Cy was used for GVHD prophylaxis.

RESULTS

Myeloid reconstitution was achieved on day + 30 for 57 of the 62 patients. The median follow-up of the surviving 39 patients (63%) was 26 months, with a range of 6-57 months. The OS and EFS at 2 years were 64.6% (52.0%-77.2%, 95% CI) and 58.9% (46.1%-71.7%, 95% CI), respectively. The only factor in our multivariate analysis that contributed to an inferior EFS was a poor remission status prior to HSCT (HR, 8.30; 1.08-63.56; P = 0.041, 95% CI).

CONCLUSION

The results of T-cell replete haploidentical transplantation with Post-Cy GVHD prophylaxis in high-risk pediatric patients are promising. However, further research is needed to determine the factors that have affect HLA compatibility for predicting the success of haploidentical transplantations.

HLA-haploidentical stem cell transplantation using posttransplant cyclophosphamide

HLA-haploidentical stem cell transplantation using posttransplant cyclophosphamide has spread rapidly worldwide. This strategy was initially developed in the setting of bone marrow transplantation following nonmyeloablative conditioning. Recently, peripheral blood stem cell grafts and/or myeloablative conditioning regimen have been widely used. In Japan, prospective, multicenter, phase II studies have been conducted by the Japan Study Group for Cell Therapy and Transplantation to evaluate the safety and efficacy of HLA-haploidentical peripheral blood stem cell transplantation using posttransplant cyclophosphamide (PTCy-haploPBSCT). In the first such study (JSCT Haplo 13 study), we demonstrated that PTCy-haploPBSCT after busulfan-based reduced-intensity conditioning (RIC) enables stable donor engraftment and low incidences of both acute and chronic graft-versus-host disease (GVHD). In the second (JSCT Haplo 14 study), we showed that both myeloablative conditioning (MAC) and RIC are valid options for PTCy-haploPBSCT. Emerging evidence, including our findings, suggests that donor type (HLA-haploidentical donor versus HLA-matched related or unrelated donor) may no longer be a significant predictor of transplant outcome.

Selective T cell-depleted haploidentical hematopoietic stem cell transplantation for relapsed/refractory neuroblastoma

Relapsed/refractory NB carries a bleak outcome, warranting novel treatment options. HaploHSCT induces a graft-versus-NB effect via natural killer cell alloreactivity. Review of patients with relapsed/refractory NB who underwent haploHSCT with ex vivo T-cell depletion in our unit from 2013 through 2018. Ten patients were identified (male=5; median age at haploHSCT=6.45 y, range: 3.49-11.02 y). Indications were relapsed in 7 and refractoriness in 3; disease status at haploHSCT was CR in 2, PR in 6, and PD in 2. All patients received peripheral blood stem cell grafts after ex vivo T-cell depletion (CD3/CD19-depletion=1; TCR-αβ/CD19-depletion=4; CD3/CD45RA-depletion=4; and TCR-αβ/CD45RA-depletion=1). Conditioning regimens were fludarabine-based. Neutrophils engrafted on median D + 10 (range: D + 9 to +13), and platelets engrafted (≥20 × 109 /L) on median D + 8 (range: D + 5 to D + 14). Early T- and NK-cell recovery were evident. Of the 10 patients, acute rejection developed in 1 (who died of PD despite rescue HSCT), and 1 died of sepsis before engraftment; 8 experienced full donor-chimerism post-HSCT. Among the 8, 6 experienced CR, 1 died of PD, and 1 died of pulmonary hypertensive crisis before evaluation. At publication, 4 were in remission (2.8, 7.4, 28.5, and 58.9 months). No significant GvHD occurred. HaploHSCT with selective ex vivo T-cell depletion may be a safe and useful salvage strategy for relapsed/refractory NB.

Reduced-Intensity Haploidentical Bone Marrow Transplantation with Post-Transplant Cyclophosphamide for Solid Tumors in Pediatric and Young Adult Patients

High-risk, recurrent, or refractory solid tumors in pediatric, adolescent, and young adult (AYA) patients have an extremely poor prognosis despite current intensive treatment regimens. We piloted an allogeneic bone marrow transplant platform using reduced-intensity conditioning (RIC) and partially HLA-mismatched (haploidentical) related donors for this population of pediatric and AYA solid tumor patients. Sixteen patients received fludarabine, cyclophosphamide, melphalan, and low-dose total body irradiation RIC haploidentical BMT (haploBMT) followed by post-transplantation cyclophosphamide (PTCy), mycophenolate mofetil, and sirolimus. All assessable patients were full donor chimeras on day 30 with a median neutrophil recovery of 19 days and platelet recovery of 21 days. One patient (7%) exhibited secondary graft failure associated with concomitant infection. The median follow-up time was 15 months. Overall survival was 88%, 56%, and 21% at 6, 12, and 24 months, respectively. Median survival from transplant date was 14 months with a median progression-free survival 7 months. We observed limited graft-versus-host disease in 3 patients and nonrelapse mortality in 1 patient. We demonstrated that RIC haploBMT with PTCy is feasible and has acceptable toxicities in patients with incurable pediatric and AYA solid tumors; thus, this approach serves as a platform for post-transplant strategies to prevent relapse and optimize progression-free survival.

How we treat chronic active Epstein-Barr virus infection

Chronic active Epstein-Barr virus infection (CAEBV) is a prototype of the EBV-associated T- or NK-cell lymphoproliferative diseases, which also include hypersensitivity to mosquito bites and severe-type hydroavacciniforme. The manifestations of CAEBV are often self-limiting with minimum supportive care or only prednisolone and cyclosporine A with or without etoposide. However, allogeneic hematopoietic stem cell transplantation (HSCT) is the only cure, without which patients with CAEBV die within several years. A severe hypercytokinemia and hemophagocytic syndrome, which may occur suddenly, often results in a fatal clinical course. At out institute, we have established a 3-step strategy, including allogeneic HSCT, for the treatment of CAEBV. Seventy-nine patients with CAEBV and related diseases have been treated to date. The 3-year overall survival rate (3y-OS) is currently 87.3 ± 4.2% after planned allogeneic HSCT. However, 3y-OS in patients with uncontrolled active disease is only 16.7 ± 10.8%. To maximize survival rates with minimized late sequelae, we recommend earlier initiation and completion of the 3-step treatment without watchful waiting. We present six illustrative and difficult cases (including severe hypercytokinemia or emergent HSCT) and discuss them together with 73 residual cases.

Nonmyeloablative Haploidentical Bone Marrow Transplantation with Post-Transplantation Cyclophosphamide for Pediatric and Young Adult Patients with High-Risk Hematologic Malignancies

Lower-intensity conditioning regimens for haploidentical blood or marrow transplantation (BMT) are safe and efficacious for adult patients with hematologic malignancies. We report data for pediatric/young adult patients with high-risk hematologic malignancies (n = 40) treated with nonmyeloablative haploidentical BMT with post-transplantation cyclophosphamide from 2003 to 2015. Patients received a preparative regimen of fludarabine, cyclophosphamide, and total body irradiation. Post-transplantation immunosuppression consisted of cyclophosphamide, mycophenolate mofetil, and tacrolimus. Donor engraftment occurred in 29 of 32 (91%), with median time to engraftment of neutrophils >500/µL of 16 days (range, 13 to 22) and for platelets >20,000/µL without transfusion of 18 days (range, 12 to 62). Cumulative incidences of acute graft-versus-host disease (GVHD) grades II to IV and grades III and IV at day 100 were 33% and 5%, respectively. The cumulative incidence of chronic GVHD was 23%, with 7% moderate-to-severe chronic GVHD, according to National Institutes of Health consensus criteria. Transplantation-related mortality (TRM) at 1 year was 13%. The cumulative incidence of relapse at 2 years was 52%. With a median follow-up of 20 months (range, 3 to 148), 1-year actuarial overall and event-free survival were 56% and 43%, respectively. Thus, we demonstrate excellent rates of engraftment, GVHD, and TRM in pediatric/young adult patients treated with this regimen. This approach is a widely available, safe, and feasible option for pediatric and young adult patients with high-risk hematologic malignancies, including those with a prior history of myeloablative BMT and/or those with comorbidities or organ dysfunction that preclude eligibility for myeloablative BMT.

Haploidentical peripheral blood stem cell transplantation with posttransplant cyclophosphamide in children and adolescents with hematological malignancies

BACKGROUND

Haploidentical hematopoietic stem cell transplantation (haplo-HSCT) using posttransplant cyclophosphamide (Cy) for graft versus host disease (GVHD) prophylaxis has emerged as an alternative transplant strategy for patients without related donors, especially in the setting of limited resources in which T-cell ex vivo depletion is not affordable. Experience with this transplant modality in children and adolescents is limited.

PROCEDURE

We report a retrospective analysis of 25 consecutive outpatients under 21 years of age with high-risk hematological malignancies, who received a haplo-HSCT using posttransplant Cy as GVHD prophylaxis.

RESULTS

Twenty-three (92%) of the 25 patients engrafted, and 20 (95%) of 21 evaluable subjects achieved full donor chimerism by day +30. One-year estimated overall survival and event-free survival were 50% and 33%, respectively. The cumulative incidence rate of severe acute GVHD was 19%, and 15% of patients developed chronic GVHD.

CONCLUSIONS

Haplo-HSCT with posttransplant Cy is a feasible therapeutic option for children and adolescents with high-risk hematological malignancies in a limited resource setting.

Haploidentical transplantation in children with unmanipulated peripheral blood stem cell graft: The need to look beyond post-transplantation cyclophosphamide in younger children

Haploidentical transplantation with PTCY following marrow or PBSC graft has been associated with low incidence of GVHD in adults with similar data lacking in children. We report on the outcome of 25 patients <20 yr of age (median age 12 yr), undergoing a haploidentical PBSC transplantation for both malignant and non-malignant disorders. Engraftment was prompt and sustained. Cumulative incidences of acute GVHD and chronic GVHD were 40.3% and 16.7%, respectively. On subgroup analysis, it was evident that acute GVHD developed in 80% of patients <10 yr compared to only 13.3% in those between 10 and 20 yr [log-rank p = 0.001], despite similar graft composition with significantly higher NRM (60% vs. 0%; p = 0.001). The FFS was 63.5%; (79% in >10 yr and 40% in <10 yr, p = 0.01). Our data suggest that PTCY-based haploidentical PBSC transplantation is feasible in older children, but results in early and severe alloreactivity in younger children. These findings, despite being counterintuitive, could be explained by the variable metabolism of CY and oral mycophenolate in younger children indicating that PTCY-based approach as used in adults might not be adequate for younger children.

Haploidentical hematopoietic stem cell transplantation with post-transplant high-dose cyclophosphamide in high-risk children: A single-center study

Recently, haploidentical transplantations have been performed with unmanipulated BM or PBSC. This approach is becoming more widely adopted with the use of PTCY. However, there is limited evidence about this approach in children. We present 15 children who received 16 haploidentical HSCT with unmanipulated BM or PBSC using PTCY for GVHD prophylaxis. Post-transplant CY(50 mg/kg IV) was given on the third and fifth day, and CsA or tacrolimus with MMF or MP was also used for GVHD prophylaxis. All patients engrafted at a median of 16 and 18 days for neutrophil and thrombocyte recovery, respectively. Grades II-III acute GVHD developed in seven patients, and mild chronic GVHD was found in two patients. Two patients died within the first 100 days due to sepsis (TRM 12.5%). Eleven patients are currently alive, with a median follow-up of 12 months (range 6-22 months). The 12-month OS and DFS were 75 ± 10.8% and 68.8 ± 11.6%, respectively. Our results with these high-risk patients are encouraging for haploidentical HSCT in pediatric patients. Future studies should continue to assess haploidentical HSCT, including comparison of other modalities, in a primary pediatric population.

Haploidentical Transplantation in Children with Acute Leukemia: The Unresolved Issues

Allogeneic hematopoietic stem cell transplantation (HSCT) remains a curative option for children with high risk and advanced acute leukemia. Yet availability of matched family donor limits its use and although matched unrelated donor or mismatched umbilical cord blood (UCB) are viable options, they fail to meet the global need. Haploidentical family donor is almost universally available and is emerging as the alternate donor of choice in adult patients. However, the same is not true in the case of children. The studies of haploidentical HSCT in children are largely limited to T cell depleted grafts with not so encouraging results in advanced leukemia. At the same time, emerging data from UCBT are challenging the existing paradigm of less stringent HLA match requirements as perceived in the past. The use of posttransplantation cyclophosphamide (PTCY) has yielded encouraging results in adults, but data in children is sorely lacking. Our experience of using PTCY based haploidentical HSCT in children shows inadequacy of this approach in younger children compared to excellent outcome in older children. In this context, we discuss the current status of haploidentical HSCT in children with acute leukemia in a global perspective and dwell on its future prospects.

Maternal T-Cell Engraftment Interferes With Human Leukocyte Antigen Typing in Severe Combined Immunodeficiency

OBJECTIVES

To report the laboratory investigation of a case of severe combined immunodeficiency (SCID) with maternal T-cell engraftment, focusing on the interference of human leukocyte antigen (HLA) typing by blood chimerism.

METHODS

HLA typing was performed with three different methods, including sequence-specific primer (SSP), sequence-specific oligonucleotide, and Sanger sequencing on peripheral blood leukocytes and buccal cells, from a 3-month-old boy and peripheral blood leukocytes from his parents. Short tandem repeat (STR) testing was performed in parallel.

RESULTS

HLA typing of the patient's peripheral blood leukocytes using the SSP method demonstrated three different alleles for each of the HLA-B and HLA-C loci, with both maternal alleles present at each locus. Typing results from the patient's buccal cells showed a normal pattern of inheritance for paternal and maternal haplotypes. STR enrichment testing of the patient's CD3+ T lymphocytes and CD15+ myeloid cells confirmed maternal T-cell engraftment, while the myeloid cell profile matched the patient's buccal cells.

CONCLUSIONS

Maternal T-cell engraftment may interfere with HLA typing in patients with SCID. Selection of the appropriate typing methods and specimens is critical for accurate HLA typing and immunologic assessment before allogeneic hematopoietic stem cell transplantation.

Inducible caspase-9 suicide gene controls adverse effects from alloreplete T cells after haploidentical stem cell transplantation

To test the feasibility of a single T-cell manipulation to eliminate alloreactivity while sparing antiviral and antitumor T cells, we infused 12 haploidentical hematopoietic stem cell transplant patients with increasing numbers of alloreplete haploidentical T cells expressing the inducible caspase 9 suicide gene (iC9-T cells). We determined whether the iC9-T cells produced immune reconstitution and if any resultant graft-versus-host disease (GVHD) could be controlled by administration of a chemical inducer of dimerization (CID; AP1903/Rimiducid). All patients receiving >10(4) alloreplete iC9-T lymphocytes per kilogram achieved rapid reconstitution of immune responses toward 5 major pathogenic viruses and concomitant control of active infections. Four patients received a single AP1903 dose. CID infusion eliminated 85% to 95% of circulating CD3(+)CD19(+) T cells within 30 minutes, with no recurrence of GVHD within 90 days. In one patient, symptoms and signs of GVHD-associated cytokine release syndrome (CRS-hyperpyrexia, high levels of proinflammatory cytokines, and rash) resolved within 2 hours of AP1903 infusion. One patient with varicella zoster virus meningitis and acute GVHD had iC9-T cells present in the cerebrospinal fluid, which were reduced by >90% after CID. Notably, virus-specific T cells recovered even after AP1903 administration and continued to protect against infection. Hence, alloreplete iC9-T cells can reconstitute immunity posttransplant and administration of CID can eliminate them from both peripheral blood and the central nervous system (CNS), leading to rapid resolution of GVHD and CRS. The approach may therefore be useful for the rapid and effective treatment of toxicities associated with infusion of engineered T lymphocytes. This trial was registered at www.clinicaltrials.gov as #NCT01494103.