PDCD1 and neoplasm: Similarly, infection of non-tumour-bearing animals with VSV expressing ovalbumin (OVA) (VSV-OVA) was associated with greater expression of suppressive Ctla4 and Pdcd1 on OVA-specific effector and memory CD8+ T cell populations compared to the same cells responding to infection with Listeria monocytogenes expressing OVA (Lm-OVA) [41].