Sequential Cyclophosphamide and Trametinib Improve Clinical Graft Versus Host Disease and Survival in Murine Hematopoietic Stem Cell Transplant

Abstract

Background Ongoing acute graft versus host disease (aGVHD) after allogeneic stem cell transplantation (alloSCT) causes significant morbidity and mortality with no standard therapy except corticosteroids, which are broadly immunosuppressive and toxic. Cyclophosphamide (Cy) given day 3 and day 4 is effective for prophylaxis of aGVHD but has proven ineffective when given later as in ongoing aGVHD in both murine and human studies. We previously demonstrated that the MEK inhibitor trametinib (Tram) is effective for aGVHD prophylaxis in murine models of aGVHD through the novel mechanism of inhibition of naive T cells (CD44−CD62L+). Our hypothesis is that ongoing aGVHD could be better inhibited by sequential Cy and post-Cy Tram inhibition (to prevent naive T cells from re-initiating alloreactivity) without compromising graft-versus-malignancy (GVM) responses. Methods Mice were administered sequential Cy and Tram post SCT starting day 12. Efficacy of treatment was assessed in a murine model of MHC-mismatched alloSCT. Overall survival was assessed and clinical GVHD was scored three times weekly. Peripheral blood, spleen, and lymph node cells phenotypes were determined by flow cytometry. GVM was also assessed with A20 luciferase/YFP (A20luc/YFP) lymphoma cells imaged with in vivo imaging system (IVIS). Results Overall survival following sequential Cy and Tram was identical to that seen with T cell depleted bone marrow alone and significantly superior to treatment using either single-agent Cy or Tram (p Conclusions Combination cyclophosphamide and trametinib demonstrates superior overall survival and limits GVHD severity without affecting regulatory T cells or GVM in murine allogeneic stem cell models. Utilizing Cy and Tram are readily translatable and support the notion that clinical approaches can be developed in the future.