Impairment of cellular immunity upon hematopoietic stem cell transplantation (HSCT) may lead to serious clinical manifestations induced by human cytomegalovirus (HCMV) and varicella-zoster virus (VZV) infections. Although the clinical presentations, preferential organ involvement and clinical courses are different, infections with both herpesviruses are similar with respect to many pathophysiological aspects and the therapeutic strategies that are employed to combat them. Antiviral drug prophylaxis and therapy are successfully used to limit the risk of reactivated HCMV and VZV infections, but are unable to absolutely prevent episodes of virus disease in long-term follow-up after HSCT. Control of infection requires the re-establishment of protective antiviral cellular immunity in the host. Here we review the most recent developments in the field of HCMV and VZV immunotherapy with specific emphasis on the question of how vaccines against HCMV and VZV may aid in enhancing the reconstitution of antiviral immunity after HSCT, and thereby support the control of these two agents by transplant recipients.