Eisen was a pioneering immunologist and founding member of the MIT Center for Cancer Research. Much of his work focused on studying myeloma tumors in mice and screening their associated proteins. He also studied how CD8 T cells develop into cytotoxic “killer” T cells and long-lived memory T cells. In doing so, he was working to overcome the barriers to creating effective CD8 vaccines, and his research on the subject made important contributions that helped to advance the field of cancer immunology.