CTLA4 and metastatic malignant neoplasm: While improved IL-2 formulations may be used as monotherapies, their combination with other anticancer immunotherapies, such as adoptive cell transfer regimens, antigen-specific vaccination, and blockade of immune checkpoint inhibitory molecules, e.g. cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) and programmed death 1 (PD-1) mono-antibodies, have the potential to treat metastatic cancer [90].