T Cell-Replete HLA Haploidentical Donor Transplantation with Post-Transplant Cyclophosphamide Is an Effective Salvage for Patients Relapsing after an HLA-Matched Related or Matched Unrelated Donor Transplantation

- Relapse after a matched related (MRD) or unrelated (MUD) transplantation carries a very bad prognosis.
- A second allogeneic transplantation using the same or different donor for patients relapsing after an MRD or MUD transplantation is an acceptable therapeutic modality for patients eligible for such a procedure.
- Haploidentical transplant using post-transplant cyclophosphamide has low treatment-related mortality as a second transplant for patients relapsing after MRD or MUD transplantation.
- Haploidentical transplant using post-transplant cyclophosphamide results in acceptable long-term disease-free and overall survival for patients relapsing after MRD or MUD transplantation.

A second allogeneic hematopoietic stem cell transplantation (HSCT) using the same donor or another fully matched donor is an effective treatment approach for a subset of patients relapsing after a matched related (MRDT) or matched unrelated donor transplant (MUDT). There are limited data on the use of haploidentical transplantation (HIDT) with post-transplant cyclophosphamide in the setting of a second HSCT after an MRDT or MUDT. We analyzed the outcomes of 20 patients who received HIDT with post-transplant cyclophosphamide as a second HSCT after an MRDT (n = 10) or MUDT (n = 10). The median time from the first to the second HSCT was 20.7 months (range, 2.7 to 65.8). Ten patients had acute myelogenous leukemia/myelodysplastic syndrome, 6 had acute lymphoblastic leukemia, 2 had chronic lymphoblastic leukemia, and 2 had myeloproliferative neoplasms. All patients received cytoreductive therapy before HIDT, with 12 (60%) achieving complete remission and 8 (40%) with active disease at the time of transplant. All patients achieved sustained engraftment with median times to neutrophil and platelet engraftment of 17.5 days (range, 14 to 44) and 32 days (range, 15 to 99), respectively. Nineteen patients (95%) achieved full donor chimerism in both the T cell and myeloid lineages at day 30 post-HSCT. The cumulative incidences of grades II to IV and grades III to IV acute graft-versus-host disease at 180 days were 36% and 10%, respectively. The cumulative incidence of moderate to severe chronic graft-versus-host disease was 13% at 1 year post-HIDT. At a median follow-up of 38 months, the probability of overall survival, disease-free survival, nonrelapse mortality, and relapse post-HIDT were 52%, 39%, 29%, and 33% at 1 year and 34%, 31%, 29%, and 40% at 3 years, respectively. These data suggest that HIDT is an effective strategy to treat relapsed hematologic malignancies after MRDT or MUDT. Further studies to confirm these observations are warranted.