CTLA4 and graft versus host disease: Given the importance of co-stimulatory pathways and attempts to use CTLA-4-Ig to prevent GvHD in animal models (Blazar et al. 1996;Ichiki et al. 2006), several published reports evaluated the association between donor CTLA-4 gene polymorphisms and outcome after hematopoietic stem cell transplantation (Bosch-Vizcaya et al. 2012;Iravani-Saadi et al. 2014;Mossallam and Samra 2013;Perez-Garcia et al. 2009;Piccioli et al. 2010).