Immune checkpoint inhibitors, such as anti-PD-1 and anti-PD-L1, have been approved as first or second-line therapies in melanoma, lung cancer, renal cancer, and urothelial cancer. More recently, these therapies have been approved in MSI-high colorectal cancer. In the Discovery Life Sciences clinical network, we observe high percentages of patients on PD-1 and PD-L1 immunotherapies across the relevant indications. However, despite these successes, there are still some patients that have no or partial remission in response to these therapies. Understanding the expression of checkpoint inhibitors within the complex cellular components of the tumor microenvironment provides not only crucial information on the potential functionality of these therapies, but also allows for the identification of potential companion diagnostic markers to stratify patients prior to treatment. We present below our initial exploration of these markers in our dissociated tumor and normal tissues via multiparametric flow cytometry to evaluate their expression on cellular subsets in both cancerous and non-cancerous tissues.