Abstract: The disclosure provides methods of improving the effectiveness of an immunomodulatory cancer therapy by selecting a patient population amenable to immunomodulatory cancer therapy and methods of selecting cancer patient populations amenable to immunomodulatory therapy by measuring T cell repertoire clonality as well as methods of selecting cancer patients at reduced risk of developing an adverse event in response to such therapy. Also provided are methods of screening for adjuvants for immunomodulatory cancer therapy by measuring the frequency or severity of at least one adverse event that develops in response to the therapy.