Compositions and methods including at least one PNP inhibitor or at least one PNP inhibitor in combination with guanosine identified as endogenous adjuvant useful to enhance Graft versus Malignancy effects in patients, with relapse of malignancy after hematopoietic stem cell transplantation, to reverse or prevent relapse or progression of malignancy. The compositions may be formulated as pharmaceutical dosage forms and components may be assembled as kits.
