Haploidentical Transplantation in Children with Acute Leukemia: The Unresolved Issues

Anti-thymocyte globulin combined with post-transplantation cyclophosphamide reduce graft-versus-host disease in hematopoietic stem cell transplantation for pediatric leukemia

This retrospective analysis evaluated the use of anti-thymocyte globulin (ATG) with or without post-transplantation cyclophosphamide (PTCy) for graft-versus-host disease (GvHD) prophylaxis in children with acute leukemia undergoing hematopoietic stem cell transplantation (HSCT). The study included 57 children, with 35 in the ATG-PTCy group and 22 in the ATG group. While overall incidence of acute and chronic GvHD did not differ significantly between groups, the ATG-PTCy group had lower rates of grade II-IV acute GvHD (p = 0.013) and moderate-to-severe chronic GvHD (p = 0.001) compared to the ATG group. Importantly, ATG-PTCy significantly improved GvHD/relapse-free survival (GRFS) compared to ATG (65.71% vs. 36.63%; p = 0.003). There were no differences in engraftment, infection rates, immune reconstitution, overall survival, leukemia-free survival, relapse rate, or non-relapse mortality between the two groups. Combining ATG with PTCy may reduce moderate-to-severe GvHD and improve GRFS in children undergoing HSCT for acute leukemia.

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.

Haploidentical transplantation in high-risk pediatric leukemia: A retrospective comparative analysis on behalf of the Spanish working Group for bone marrow transplantation in children (GETMON) and the Spanish Grupo for hematopoietic transplantation (GETH)

A total of 192 pediatric patients, median age 8.6 years, with high-risk hematological malignancies, underwent haploidentical stem cell transplantation (haplo-HSCT) using post-transplantation cyclophosphamide (PT-Cy), or ex vivo T cell-depleted (TCD) graft platforms, from January 1999 to December 2016 in 10 centers in Spain. Some 41 patients received an unmanipulated graft followed by PT-Cy for graft-vs-host disease (GvHD) prophylaxis. A total of 151 patients were transplanted with CD3-depleted peripheral blood stem cells (PBSCs) by either CD34⁺ selection, CD3⁺ CD19⁺ depletion, TCRαβ⁺ CD19⁺ depletion or CD45RA⁺ depletion, added to CD34⁺ selection for GvHD prophylaxis. The PBSCs were the only source in patients following ex vivo TCD haplo-HSCT; bone marrow was the source in 9 of 41 patients following PT-CY haplo-HSCT. Engraftment was achieved in 91.3% of cases. A donor younger than 30 years, and the development of chronic GvHD were positive factors influencing survival, whereas positive minimal residual disease (MRD) before transplant and lymphoid disease were negative factors. The probability of relapse increased with lymphoid malignancies, a donor killer-cell immunoglobulin-like receptor (KIR) haplotype A and positive MRD pretransplant. No difference was found in overall survival, disease-free survival or relapse incidence between the two platforms. Relapse is still of concern in both platforms, and it should be the focus of future efforts. In conclusion, both platforms for haplo-HSCT were effective and could be utilized depending on the comfort level of the center.

Favorable Outcome of Post-Transplantation Cyclophosphamide Haploidentical Peripheral Blood Stem Cell Transplantation with Targeted Busulfan-Based Myeloablative Conditioning Using Intensive Pharmacokinetic Monitoring in Pediatric Patients

Haploidentical hematopoietic stem cell transplantation (haplo-HSCT) with post-transplantation cyclophosphamide (PTCy) was performed previously in adults using a nonmyeloablative conditioning regimen and bone marrow as a graft source. In an effort to reduce relapse rates, myeloablative conditioning regimens with higher intensities are now used. We used an intensive daily pharmacokinetic monitoring method for busulfan dosing in children for effective myeloablation and to reduce toxicity. Here, we report the retrospective results of 34 patients (median age 11.1 years) who underwent haplo-HSCT with PTCy using a targeted busulfan-based myeloablative conditioning regimen and peripheral blood as a stem cell source. The donor-type neutrophil engraftment rate was 97.1%, and the cumulative incidence rates of grade II to IV and grade III to IV acute and extensive chronic graft-versus-host disease were 38.2%, 5.9%, and 9.1%, respectively. The overall survival and event-free survival rates, and treatment-related mortality were 85.0%, 79.4%, and 2.9%, respectively. Based on the subgroup analysis of patients with malignancies (n = 23), the relapse incidence rate was 21.7%. Haplo-HSCT using PTCy with targeted busulfan-based myeloablative conditioning and peripheral blood as a stem cell source was a safe and promising therapeutic option for children.