Ex vivo generation of human cytomegalovirus-specific cytotoxic T cells by peptide-pulsed dendritic cells

Adoptive transfer of donor-derived human cytomegalovirus (HCMV)-specific T-cell clones can restore protective immunity after stem cell transplantation. Ex vivo induction of HCMV-specific T cells using HCMV-infected fibroblasts as stimulator cells confines this approach to HCMV-seropositive donors and requires the presence of infectious virus during the stimulation procedure. In this study, we describe a potential alternative strategy to generate HCMV-specific T cells ex: vivo for adoptive immunotherapy. Generation of HCMV-specific cytotoxic T lymphocytes (CTLs) ex vivo was investigated using peptide-pulsed dendritic cells as antigen-presenting cells. HCMV-specific T cells were generated and sufficiently expanded for adoptive immunotherapy in 6 out of 14 HCMV-seropositive and 2 out of 11 HCMV-seronegative donors. The CTLs recognized HCMV-infected autologous fibroblasts. No lysis was observed with either non-infected autologous or HLA-mismatched infected fibroblasts, Staining with tetrameric HLA/peptide complexes revealed significant enrichment for peptide-specific T cells of up to 28% and >90% of CD8(+) T cells after three and five specific stimulations respectively. In addition, the expansion rates indicated that ex: vivo generation of >1 x 10(9) HCMV-specific T cells was possible after 6-7 weeks when cultures were initiated with 1-5 x 10(6) responder cells. Thus, the approach with peptide-pulsed DCs to generate HCMV-specific CTLs is feasible for clinical application after allogeneic stem cell transplantation.