Dose escalation prophylactic donor lymphocyte infusion after T-cell depleted matched related donor allogeneic hematopoietic cell transplantation is feasible and results in higher donor chimerism, faster immune re-constitution, and prolonged progression-free survival.

Prophylactic donor lymphocyte infusion (pDLI) is a potential intervention to prolong remission for patients receiving allogeneic hematopoietic stem cell transplantation (allo-SCT), however, the optimal timing and dose are unknown. We conducted a prospective trial exploring the feasibility of early withdrawal of immunosuppression (WOI) at day 60 followed by dose escalation of pDLI after alemtuzumab-based, T-cell depleted conditioning for patients with high-risk hematologic malignancies. pDLI were administered at day 75 to day 90 and again in 4-8 week intervals with receipt of up to 5 pDLI infusions. Fourty-six patients with matched-related donors (MRD) and 29 patients with matched-unrelated donors (MUD) were considered. Twenty-eight MRD patients were able to undergo WOI, 26 patients (93%) received at least 1 DLI, 16 patients (57%) received 3+, and 7 patients (25%) received 5 pDLI. Only 7 MUD patients were able to undergo WOI, 4 (57%) received at least 1 pDLI, 1 patient (14%) received 3 DLI, and no patients received all 5. Median PFS for patients on the study was 366 days. The estimated 2-year PFS and OS rates for all patients were 41% (95% CI, 32-54%) and 51% (95% CI, 41-63%) compared with 57% (95% CI, 41-77%) and 67% (95% CI, 52-86%) for patients who received at least one pDLI. In addition, MRD patients receiving pDLI had faster immune re-constitution and improved donor chimerism. Our trial proposes a novel dosage and treatment schedule for pDLI that is tolerable for patients who have received MRD allo-SCT and leads to improved outcomes.