Merkel cell carcinoma (MCC) is a rare and lethal cancer of the skin that can arise through Merkel cell polyomavirus (MCPyV) integration. Through clonal integration, MCPyV can incorporate itself into the tumor genome and initiate tumorigenesis. One way the virus begins this tumorigenesis is via the expression of the small T and large T antigens, but there is evidence of an immune response to these viral antigens. The presence of T cells, which responds to large T, has been linked to higher survival rates in prior studies. However, T cells alone are not responsible for the total antitumor immune response, as there is evidence to suggest B cells may be an overlooked factor. In MCC, tumor-infiltrating B cells and their antigen specificity should be further studied to determine their contribution to antitumor immunity. The antibodies produced by these tumor-infiltrating B cells are of key importance in understanding MCC as they may interact with disease-relevant antigens such as small T and large T. Single-cell RNA and 5’ VDJ sequencing was conducted on a MCC612 tumor biopsy to identify these antibodies. In order to characterize these antibodies, I will clone their variable regions into vectors with heavy chain and light chain constant regions, express them in HEK293 cells, purify them, and test their reactivity.  Initially, I will assess the reactivity of these antibodies to the large-T antigen, and next I will explore their interaction with other antigens through ELISA and immunofluorescence. The overall goal of this experiment is to understand what B cells recognize in the tumor microenvironment (TME). In the future, this research will be beneficial in understanding the nuances of MCC immunology and developing new therapeutics using tumor-infiltrating B cells to enhance the care of MCC patients.