[Controlled live dendritic cell vaccine mediates potent antitumor immune responses]

To investigate the efficiency of antitumor immune responses induced by a controlled live dendritic cell (DC) vaccine.

DC precursors were isolated from Fischer 344 rat bone marrow and cultured with granulocyte-macrophage colony-stimulating factor and interleukin-4. The rat ovarian tumor cell line NuTu-19 was genetically modified by retroviral-mediated suicide gene (HSV(1)-TK), and the positive clones were selected using G418. Live DC vaccine was then fused with DC and NuTu-19/TK cell by polyethylene glycol. The characteristics of live DC vaccine were assayed with flow cytometry and confocal laser scanning microscopy. The specific expression of HSV(1)-TK gene in live DC vaccine was evaluated by RT-PCR and western blot. The sensitivity of live DC vaccine to ganciclovir (GCV) was evaluated by methylthiazoletetrazolium assay. In vivo, rats vaccinated twice with live DC vaccine were compared to those vaccinated with killed DC vaccine, unfused DC and NuTu-19/TK cell or phosphate buffered saline. Seven days following the last immunization, the rats were sacrificed to test the specific cytotoxic T lymphocyte (CTL) activity by lactate dehydrogenase release assay, or challenged with NuTu-19 and tumor incidence was observed.

The fusion efficiency was approximately (23 +/- 14). Live DC vaccine displayed an up-regulated expression of major histocompatibility complex (MHC)-IIOX6 (87.6 +/- 3.4)%, costimulatory molecule B(1 - 2) (71.1 +/- 9.3)%, integrin OX 62 (68.0 +/- 7.4)%, and adhesion ICAM-1 (77.1 +/- 2.0)%, and specifically expressed HSV(1)-TK gene. Our data showed that spleen T lymphocytes from rats vaccinated with live vaccine displayed enhanced CTL activity (61.8 +/- 8.3)% contrast to that of rats vaccinated with killed vaccines (26.0 +/- 3.8)% (P < 0.05). Compared to the control groups, rats immunized with live DC vaccine demonstrated a significant delay in tumor development [(39 +/- 8) d vs (70 +/- 16) d], reduced tumor incidence (100% vs 80%) and decreased tumor volume [(806 +/- 553) mm(3) vs (89 +/- 53) mm(3), P < 0.05]. Seventy-three percent of TK-transduced live DC vaccine was killed after 7 of GCV treatment by a functional assay.

The results demonstrate that DC live vaccine modified by HSV(1)-TK gene can induce efficient protective immunity and be killed by GCV.