PDCD1 and neoplasm: Splenocytes 7- and 14-days post VSV-OVA administration showed no significant difference of expression between OVA-specific subtypes in activation markers CD44 and Programmed Cell Death Protein 1 (PD-1), and we observed similar expression levels of CD39, an ATP hydrolase often associated with T cell experience in the tumor microenvironment (TME)38 (Fig. 2C).