Compositions including at least one PNP inhibitor or at least one PNP inhibitor in combination with one or more agents identified as endogenous adjuvants useful for enhancing the potency of vaccine and cancer immunotherapies being administered for the prevention or treatment of infectious diseases or cancer. The compositions may be formulated as pharmaceutical dosage forms and components may be assembled as kits. Methods for increasing the levels of endogenous adjuvants to enhance the immunogenicity of an antigen as well as to augment the potency of vaccine and cancer immunotherapies are also disclosed.
