ICOS and graft versus host disease: Additionally, TCF1+ CD8+ T cells showed higher expression of costimulatory molecules including CD28 and ICOS, as well as activation marker CXCR3, and lower expression of effector marker granzyme B. Both TCF1+ and TCF1- subsets of PD-1+ alloreactive CD8+ T cells in the acute GvHD mouse model expressed CD44 and Eomes similarly, but TCF1+ cells presented higher TOX and lower T-bet expression than TCF1- cells.