Immunotherapy, especially blockade of the PD-1/PD-L1 and CTLA-4 axes, has resulted in durable responses in a range of cancers. However, responses remain heterogeneous among patients. Treatment outcome results from changes in the tumor microenvironment imposed by such blockade. Here, we use immuno-PET and single-cell RNA sequencing to increase our understanding of the dynamics of immune cells and their functional status in the tumor microenvironment in response to PD-1 blockade. Our data provide insights into the dynamics of CD8+ T cells and the functional status of the myeloid compartment in response to PD-1 blockade.