The infrequency of known T cell targets in high grade serous ovarian carcinoma (HSGC) is a substantial barrier to the development of targeted immunotherapies. Due to their infrequency, antigen discovery is a crucial component of immunotherapeutic design. In our cohort of HGSC cases, the cancer testis (CT) antigen lactate dehydrogenase C (LDHC) is expressed in 76% of tumours (22/29). As LDHC presents with tumour specificity in women, I hypothesize that LDHC is an immunogenic target in HGSC patients, and that LDHC-specific T cells can be activated and expanded for therapeutic purposes. As such, I sought to examine whether endogenous LDHC-specific T cells were present in the ascites of HGSC patients. A standard Rapid Expansion Protocol was used to expand CD8 T cell cultures from patient ascites. These cultures were screened for reactivity to a peptide library encompassing all possible epitopes of the LDHC protein by interferon-γ ELISpot. With this approach, T cell clones from one of five patients were identified that were reactive to minimal peptides contained within LDHC. In this patient, the antigenic LDHC peptide differentiated from LDHA by a single amino acid at its C-terminus (YTSWAIGLSVM versus YTSWAIGLSVA). In recognition assays, tumour cell lines expressing endogenous LDHC, autologous ascites, or autologous B cells transfected with LDHC were unable to elicit T cell responses. Although this study suggests that LDHC is not immunogenic, continued screening of LDHC and other CT proteins will likely provide additional immunotherapeutic targets. / Graduate