Our immune system is capable of attacking cancer. However, sometimes proteins present in cancer, called checkpoint proteins, stop the immune system from attacking the cancer cells. Checkpoint inhibitors are drugs that treat cancer and called immunotherapy. These drugs block different checkpoint proteins, so that they turn the immune system back on and enable immune cells to detect the cancer cells once more. Checkpoint inhibitors are a major breakthrough for cancer therapy, some patients originally given just weeks or months to live now survive for many years following treatment. Unfortunately, currently only 15-20% of patients with cancer treated with checkpoint inhibitors have improvement in their survival. This is because our library of checkpoint inhibitors is incomplete. To increase the percentage of patients who response to checkpoint inhibitors, researchers are developing ways to block other checkpoint proteins. LAG3 proteins is one of the candidates. Each year, ovarian cancer kills 4200 women in the UK. When we examined ovarian tumours, we found LAG3 protein in important cells of the immune system, T cells, and another protein called CD74 in cancer cells. The CD74 protein associates with another protein called MHC class II, and the MHC class II protein interacts with LAG3 protein. We speculate that CD74 protein contributes to the action of LAG3 protein in the immune resistance of ovarian cancer. In this project, we aim to investigate the characteristics and functions of CD74 protein in Page 5 ovarian cancer. Our work has the potential of identifying new checkpoint inhibitors for ovarian cancer patients.