CD8A and neoplasm: However, in a melanoma model, in spite of upregulation of the PD-1/PD-L1 immunosuppressive pathway in the tumor microenvironment, STAT5ca-expressing CD8 T effector cells were found to be resistant to inhibition by PD-1/PD-L1 engagement as measured by their efficient IFNγ production, in contrast to their control counterpart [132].