PDCD1 and neoplasm: To investigate the effect of PD1 checkpoint blockade on the global immune composition of two established syngeneic tumors (αPD1 responsive (MC38) and αPD1 non-responsive (B16)), we devised an experimental setup by tailoring injected cell numbers to equalize tumor size at 9 days after tumor cell injection and before starting αPD1 treatment or isotype control (intraperitoneally 3×250 μg/week; figure 1A, online supplementary figure 1A).