The investigators will collect 50 milliliter blood samples from each patient before and after the first cycle of Pembrolizumab therapy. White blood cells will be separated according to cluster of differentiation (CD) markers into CD4+, CD8+, CD14+ populations using magnetic beads. A portion of each cellular fraction will be stimulated in the lab with a lineage-specific agonist cocktail. Ribonucleic acid (RNA) will be purified from both unstimulated and stimulated cell populations from both pre- and post-therapy timepoints for each patient. Lineage-specific transcriptomes will be quantitated and used to derive gene expression profiles for comparisons to clinical phenotypes.