Peptide Vaccination Against Cytomegalovirus (CMV) Elicits Immunological and Clinical Responses after Allogeneic Stem Cell Transplantation Even from a CMV Seronegative Donor

Introduction: Patients receiving an allogeneic stem cell graft from a cytomegalovirus (CMV) seronegative donor are prone to CMV reactivation with high risk of disease and mortality. Therefore we initiated a clinical phase I trial with a novel vaccine designed by our group: a CMV phosphoprotein 65 (CMVpp65)-derived peptide in water-in-oil emulsion (Montanide™) plus administration of granulocyte-macrophage colony stimulating factor.

Material and Methods: 10 patients after allogeneic stem cell transplantation received four vaccines s.c. at a biweekly interval. Patients were monitored for clinical course and CMVpp65 antigenemia. CMV-specific CD8⁺ and gamma/delta T cells were analyzed by multi-color flow cytometry. Neutralizing anti-CMV antibody assays were established and correlated to clinical parameters.

Results: Peptide vaccination was well tolerated, no drug-related serious adverse events were detected. 7 of 9 patients with CMVpp65 antigenemia cleared the CMV with enduring response > 1.5 years after 4 vaccinations and are still free from antigenemia until present. 2 patients with CMV reactivation showed persisting CMV antigenemia. One patient received prophylactic vaccination and did not develop antigenemia. An up to 6-fold increase in frequency of both CMV-specific CD8⁺ T cells or Vdelta2^- gamma/delta T cells with a maximum of 1.32% CMV-specific CD8⁺ T cells ex vivo without priming and 13.7% Vdelta2^- gamma/delta T cells of all CD8⁺ T cells was detected in five patients. Also titers of neutralizing antibodies increased in four patients up to 10-fold over the time of vaccination. Humoral and cellular immune responses correlated with clearance of the CMV load.

Conclusion: Administration of CMVpp65 peptide vaccination for patients after allogeneic stem cell transplantation at high risk for CMV reactivation was safe, well tolerated and clinically encouraging. A study in solid-organ transplant patients is ongoing.