Recovery of immunity is delayed in recipients of T-depleted grafts. Adoptive transfer of memory T-cells may improve immune response to common pathogens. A cohort of 53 patients with malignant (n = 36) and non-malignant conditions (n = 17) received TCR alpha/beta depleted grafts from haploidentical (n = 25) or MUD (n = 28) donors. Donor lymphocytes were depleted of CD45RA-positive cells. At a median of 48 days after transplantation, patients received DLI at 25 × 10/kg CD3 cells from haploidentical or 100 × 10/kg CD3 from MUD donors. Up to 3 doses of donor lymphocytes were administered at monthly intervals, escalating to 100 × 10/kg in haploidentical transplants and 300 × 10/kg in MUD transplants. At a median follow-up of 23 months, the cumulative incidence of de novo acute GVHD after DLI is 2% (1 of 43), while the rate of reactivation of preexisting aGVHD was 50% (5 of 10). The transplant-related mortality is 6%. The overall survival rates are 80% and 88% in malignant and non-malignant conditions, respectively. Among patients with absent CMV-specific immune reactivity at baseline (n = 31) expansion of CMV-specific T-cells was demonstrated in 20 (64.5%) within 100 days. Infusions of low dose donor memory T-lymphocytes are safe and constitute a simple measure to prevent infections in the setting of alpha/beta T cell-depleted transplantation.

We evaluated the outcome of ab T cell-depleted haploidentical hematopoietic stem cell transplantation (HSCT) in a cohort of children with chemorefractory acute myelogenous leukemia (AML). Twenty-two patients with either primary refractory (n = 10) or relapsed refractory (n = 12) AML in active disease status received a transplant from haploidentical donors. The preparative regimen included cytoreduction with fludarabine and cytarabine and subsequent myeloablative conditioning with treosulfan and thiotepa. Antithymocyte globulin was substituted with tocilizumab in all patients and also with abatacept in 10 patients. Grafts were peripheral blood stem cells engineered by ab T cell and CD19 depletion. Post-transplantation prophylactic therapy included infusion of donor lymphocytes, composed of a CD45RA-depleted fraction with or without a hypomethylating agent. Complete remission was achieved in 21 patients (95%). The cumulative incidence of grade II-IV acute graft-versus-host disease (GVHD) was 18%, and the cumulative incidence of chronic GVHD was 23%. At 2 years, transplantation-related mortality was 9%, relapse rate was 42%, event-free survival was 49%, and overall survival was 53%. Our data suggest that ab T cell-depleted haploidentical HSCT provides a reasonable chance of long-term survival in a cohort of children with chemorefractory AML and creates a solid basis for further improvement.

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