PDCD1 and lung carcinoma: Moreover, an anti-PD-1-resistant murine lung cancer model established through sequential in vivo passage of nonresponsive tumors to ongoing anti-PD-1 therapy was characterized by significant downregulation of MHC class I and II genes including β2-microglobulin and reduction in CD4+/CD8+ TILs and IFN-γ production in resistant tumors compared to parental tumors [91].