IL15 and graft versus host disease: It has prolonged survival in a model of GVHD and blocked the spontaneous proliferation of smoldering adult T cell leukemia T cells.338 In another effort, Dean Pettit and colleagues demonstrated that mutations D8S and Q108S on IL-15 could individually block the binding of the beta and gamma receptor subunits.409 Expanding on this knowledge, a variant of IL-15 (Q101D/Q108D) was identified as an IL-15 antagonist, proving effective in countering CD8+ T cell-driven rejection that was resistant to costimulation blockade.410