PDCD1 and neoplasm: Following treatment with anti-PD-1 in the early-stage model, the tumor microenvironment changed to favor an antitumor profile, with potent T-cell infiltration into tumor beds, greater proportions of CD-8+ to CD-4+ cells, increased CD-3+ T cells in tumor-burdened lungs, and an increase in polymorphonuclear myeloid-derived suppressor cells.