Graft versus Host Disease (GVHD) remains a critical morbidity and mortality factor following allogeneic hematopoietic stem cell transplant (HSCT) for hematologic malignancy.Prophylactic drug regimens using immunosuppressive drugs can manage disease, but bring additional complications with increased infection and rates of malignant relapse.When acute GVHD does arise, high dose steroid treatment is second line treatment, but many patients progress to steroid refractory disease with associated high mortality (>70%).Over the last decade, adjunctive cell therapies have been developed to prevent or treat acute GVHD and balance immunomodulation against the benefit of Graft vs Leukemia (GVL) effect conferred by the allogeneic HSCT.Mesenchymal stem cells (MSC) were first shown in 2004 by Katarina Le Blanc to be effective in rescuing a steroid refractory acute GVHD patient, and from that time clinical proof of concept studies have been run by both corporate and academic stem cell centers globally.These studies have yield mixed results, with support for the potency of MSC being mixed with questions about dose and dose regimen decisions.An interpretive review of the state of the art for MSC GVHD treatment will be made.Additional studies have been performed using similar stem cells for prophylaxis of acute GVHD with dose regimens spanning the first 30 days post HSCT.Clinical results from such studies will also be presented, with a recommendation for clinical design in later stage trials.The problem of dealing with tumor relapse during immunomodulatory therapy still exists.Recently,very exciting results have been published in a small group of patients receiving autologous T cells primed and engineered to react against tumor using chimeric antigen receptors (CAR).These CAR T cells exploit anti-B cell receptor binding combined with T cell signaling domains to greatly reduce or eliminate tumor burden.These two adjunctive cell therapies reflect new therapeutic paradigms in managing allogeneic HSCT and signal a new horizon for combination therapy for allogeneic transplant.