Allogeneic Hematopoietic Cell Transplants as Dynamical Systems: Effect of Early-Term Immune Suppression Intensity on Long-Term T Cell Recovery

Reduced intensity conditioning (RIC) is fraught with risk for disease relapse. This may be overcome by donor T cell alloreactivity. Reducing the duration of intense immune suppression in the early term following transplantation may create an immunologic environment favoring rapid T cell reconstitution to influence longer term transplant outcomes. Twenty-six patients were adaptively randomized based on donor-derived T cell recovery, between 2 different dosing schedules of mycophenolate mofetil (MMF): MMF for 30 days post-transplant, with filgrastim for cytokine support (MMF30 arm, 11 patients), or MMF for 15 days post-transplant, with sargramostim (MMF15 arm, 15 patients). All patients were treated with anti-thymocyte globulin at a dose of 1.7 mg/kg/day from day - 9 through day -7 and total body irradiation, 450 cGy given in 3 fractions. Patients were well matched between the study arms and underwent HLA matched related and unrelated donor hematopoietic cell transplantation (HCT). The MMF15 arm demonstrated superior T cell recovery in the first month. This difference persisted through the first year for total T cells, T cell subsets and NK cells. T cell repertoire tended to be more diverse in the MMF15 arm. The long term superior immune recovery in the MMF15 arm is consistent with a disproportionate impact of early interventions in HCT. Clinically, shorter course MMF post-transplant was not associated with increased risk of acute or chronic graft vs. host disease (GVHD), and relapse and there was a trend toward improved overall survival in the MMF15 arm. Reducing the duration of intense immunosuppression in the early term and the use of sargramostim following allogeneic HCT is feasible and leads to superior long-term T cell recovery. This regimen should be studied to improve immune recovery in large cohorts of patients undergoing HCT with RIC.