PDCD1 and neoplasm: By flow cytometric analysis, it was found that the tumor-infiltrating CD8+ T cells from both PDX expressed higher levels of cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), PD-1, lymphocyte-associated gene 3 (LAG3) and T-cell immunoglobulin and mucin domain 3 (TIM3) when compared to those in the circulation and spleen (Figure 4A–D; Figure S4L–O), revealing that the T cells exhibited exhausted phenotype in the immunosuppressive tumor milieu [30].