BENDAMUSTINE CONDITIONING REDUCES GVHD WHILE MAINTAINING GVL IN MURINE MHC-MISMATCHED HEMATOPOIETIC CELL TRANSPLANTATION

Abstract

Graft-versus-host disease (GvHD) remains a significant obstacle to the success of hematopoietic stem cell transplantation due to challenges in uncoupling GvHD from the highly beneficial graft-versus-leukemia (GvL), both of which are mediated by donor T-cells. Our laboratory has previously shown that pre-transplant conditioning with bendamustine (BEN) and total body irradiation (TBI) significantly reduces GvHD when compared to cyclophosphamide (CY)+TBI in a major histocompatibility complex (MHC) mismatched murine bone marrow transplant model. Despite reduced GvHD, conditioning with BEN+TBI retains GvL effects in mice with A20-luciferase. To determine which cells are responsible for this GvL effect, CD4+ and CD8+ T-cells and NK cells were depleted. We see the greatest deficit in anti-tumor effect when CD8+ T-cells are depleted, followed by CD4+ T-cells, with depletion of NK cells showing little change to GvL effects. This indicates that CD8+ T-cells primarily contribute to the GvL effect seen in this model. As GvHD and GvL are mediated by donor T-cells, whose effector functions are informed by dendritic cells (DCs), we characterized DCs that were conditioned with BEN+TBI compared to CY+TBI to understand the mechanism of BEN. We hypothesized that BEN inhibits STAT3 signaling causing a compensatory increase in Flt3 and Akt1 expression to increase signaling through this alternative pathway. Contrary to our hypothesis, the qRT-PCR results showed a significant decrease in Akt1 transcripts in both mice and humans as the concentration of BEN increased.