CD8A and B-cell chronic lymphocytic leukemia: PD-1 expression was enhanced in lymph node CD8+ cells purified from wild-type mice cultured in Eμ-TCL1 cell-conditioned media (Fig. 3F) (same experimental workflow as for human CD8+ cells, Fig. 1A), indicating that, similar to human CLL, leukemic cells promote bystander CD8+ cell exhaustion in Eμ-TCL1 mice through a contact-independent mechanism.