PDCD1 and cancer: Other negative (pro-tumor) regulators in cancers, including ovarian cancer, are M-2 macrophages [94], N-2 tumor-associated neutrophils (TANS) [95], immature dendritic cells (DCs) [96,97], plasmacytoid DCs [98], T regulatory cells (T regs), T cells expressing chemokine receptor CCR4, exhausted T cells expressing immune checkpoint molecules PD-1, CTLA-4, or lymphocyte activation gene-3 (LAG-3; CD223) [99,100,101], and natural killer (NK) cells with impaired functions [102].