Targeting apoptotic tumor cells to Fcgamma receptors provides efficient and versatile vaccination against tumors by dendritic cells

K Akiyama MD PhD^a,b, S Ebihara^a, A Yada^a, K Matsumura^a, S Aiba MD PhD^c, T Nukiwa MD PhD^b, T Takai PhD^a

^aDepartment of Experimental Immunology and the CREST Program of JST, ^bDepartment of Respiratory Oncology and Molecular Medicine; Institute of Development, Aging and Cancer, Tohoku University, Sendai, Japan, ^cDepartment of Dermatology, Tohoku University School of Medicine, Sendai, Japan

Aim. The aim of this study was to enhance anti-tumor immune response by taking advantage of apoptotic tumor cells (ATCs) that have been opsonized with IgG (ATC-immune complexes: ATC-ICs) so as to target them to Fc receptors for IgG (FcgRs) on dendritic cells (DCs). Methods. All the experiments were performed on 6- to 10- week-old C57BL/6 mice. OVA-ICs were prepared by incubating OVA with rabbit anti-OVA IgG. The murine EL4 thymoma cell line genetically modified to express OVA gene (E.G7 cells) was used to induce apoptotic tumor cell death. After apoptotic cell induction, the surface of cells was bound with TNP. For the preparation of ATC-ICs, the cells were further opsonized with mouse anti-TNP IgG1. For the detection of cytotoxic T cells (CTLs), standard cytotoxicity assay was performed. Groups of three mice were injected i.v. through the tail vein with DCs loaded with OVA/OVA-ICs or ATCs/ATC-ICs. One to two weeks post-vaccination, mice were sacrificed and splenocytes were re-stimulated in vitro for 5 days with irradiated E.G7 cells. After re-stimulation, the target E.G7 cells were labeled with Na251CrO4 for 1 h and incubated with the stimulated splenocytes . CTL activity was measured using an auto well gamma system. Results. First by using soluble antigen (OVA), we were able to demonstrate that DCs can take up OVA-ICs and enhance both MHC class I and class II-restricted antigen presentation in vivo, in terms of OVA-specific antibody production and CTL induction. By applying this in vivo augmenting function of FcgR-mediated antigen presentation to tumor immunotherapy, we also found that when compared to ATCs, ATC-ICs were efficiently internalized by DCs via FcgRs, and this process induced an efficient maturation of DCs without any additional stimulation. Importantly, ATC-IC loading was shown to be more efficient than ATCs alone in its capacity in inducing anti-tumor immunity in vivo, in terms of CTL induction and tumor rejection. Conclusion. The present study showed that ICs targeted to FcgRs on DCs can enhance antigen presentation to T cells in vivo. It also demonstrated that by using this positive role of FcgR-mediated antigen presentation, DCs pulsed with ATC-ICs can significantly enhance in vivo generation of tumor-specific CTLs and induce effective tumor rejection compared to DCs pulsed with ATCs alone. ATC-ICs may overcome the limitations and enhance the immune response of current ATC-based DC vaccination therapy.

Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Nice, France; February 7 - 10, 2004; in poster session 1091 (Vaccine trials).