PDCD1 and neoplasm: The UN-KC-6141 model used in this study, similar to the CT26 tumor model [26], could be considered as an “uninflamed” or “cold” tumor with relatively low numbers of CD4+ (~1%) and CD8+ (~2%) T cells and no response to anti-PD-L1 therapy because only 12.5% CD8+ T cells express PD-1.