Since the co-blockade of CTLA-4:B7 and PD-1:PD-1L interactions was additive in GVHD acceleration [28], suggesting the two pathways are not redundant, the engagement of the Lag-3 pathway may prove to be another mechanism of down-regulating proliferative T cell responses in vivo. The gene discussed is CTLA4; the disease is graft versus host disease.