An immune response is modulated by selectively inhibiting ERAAP (an acronym for ER aminopeptidase associated with antigen processing) and confirming a resultant immune response modulation. More particularly, the method comprises contacting a patient determined to be in need of immune response modulation with a physiologically acceptable dosage composition comprising an effective amount of an inhibitor of ERAAP activity; confirming a resultant inhibition of said ERAAP activity and confirming a resultant immune response modulation in the patient. A variety of selective inhibitors are shown to be effective, including amino thiols, such as leucine thiol, ERAAP-specific antibody complementarity-determining region, and an ERAAP-specific siRNA.