Dendritic Cell Vaccination Induces HCMV Specific T-Cell Responses in Allogeneic Stem Cell Recipients.

Human cytomegalovirus (HCMV) infection remains a major and life threatening infectious complication after allogeneic stem cells transplantation (SCT). We performed a Dendritic cell (DC) vaccination trial by utilizing HCMV peptide loaded mature DC to boost HCMV specific T-cell responses which have been demonstrated to be protective against the development of HCMV disease. DCs were pulsed with nonamer peptides from the HCMV proteins pp65 and pp150, restricted by the HLA-class I elements A1,A2,A3,A11,A68 and B7. We enrolled 24 allogeneic SCT recipients, 6 patients received prophylactic vaccination in view of high risk for HCMV disease. 18 patients were vaccinated therapeutically after HCMV reactivation failed to respond to 4 weeks course of antiviral chemotherapy. Our primary objectives were safety and feasibility of DC vaccination after allogeneic SCT. As all patients with active HCMV infections already received antiviral chemotherapy at the time of DC vaccination, viral load was not a suitable efficacy parameter. Thus, evaluation of efficacy as a secondary objective was based on reconstitution of HCMV-specific CTL responses and long term control of HCMV infection. The study protocol was approved by the local ethical committee and all patients gave written informed consent. DC were generated under GMP conditions and displayed typical surface markers of mature DC (CD1a⁺/CD14⁻/CD83⁺). No local or systemic acute side effects occurred during the first week post vaccination. An observation period of 3 months was determined to evaluate long term side effects and control of HCMV infection. Six patients died during this observation period from other causes and one had no follow-up blood samples, so, 17 patients (5 received prophylactic and 12 received therapeutic vaccination) were evaluable. Only one patient developed Graft-Versus-Host-Disease (GVHD) grade III of the skin and gut. Due to a time lag of 2 months between vaccination and the onset of GVHD, a causative relationship seems to be unlikely. Four of the five patients receiving prophylactic vaccination never showed HCMV reactivation. 10 patients from the therapeutic group cleared their HCMV infection after a mean of 50 days post vaccination. Therefore, 15 of the 17 evaluable patients demonstrated control of HCMV infection after DC vaccination. Among these 15 patients, 10 had detectable specific T-cell response against the vaccine peptides after a mean of 23 days post vaccination. Only 2 from these 10 patients developed a further HCMV reactivation after high dose steroid therapy. Our results show that no relevant side effect was observed in this first DC vaccination trial among allogeneic SCT patients. Additionally, DC are able to induce an efficient peptide specific immune response among allogeneic SCT patients which is capable to protect against HCMV reactivation. In the future, further investigations should be performed to evaluate the feasibility of DC vaccination not only against other infectious complications but also against tumour associated antigens to induce specific T-cell response effectively targeting the particular tumour cell.