PDCD1 and neoplasm: In contrast, anti-PD-L1 alone had minimal effect on the growth of tumor 1 or tumor 2 consistent with the known resistance of this cell line to PD-1 based therapy.27,28 Combination RT and anti-PD-L1, however, dramatically slowed the growth of both the irradiated tumor 1 and the unirradiated tumor 2 to a greater extent than either monotherapy (Figure 1B, S1B-S1C).