CpG Oligodeoxynucleotide1826 combined with radioresistant cancer cell vaccine confers significant antitumor effects

Immunotherapy is a hot issue in cancer research over the years and tumor cell vaccine is one of the increasing number of studies. Although the whole tumor cell vaccine can provide the best source of immunizing antigens, there is still a limitation that most tumors are not naturally immunogenic. CpG Oligodeoxynucleotides (CpG ODNs), synthetic oligonucleotides containing a cytosine-phosphate-guanine(CpG) motif, was shown to enhance immune responses to a wide variety of antigens. In this study, we generated the radioresistant Lewis lung cancer cell by repeated X-ray radiation and inactivated it as a whole tumor cell vaccine to enhance the immunogenicity of tumor cell vaccine. Mice were subcutaneously immunized with this inactivated vaccine combined with CpG ODN1826 and then inoculated with autologous Lewis lung cancer (LLC) to estimate the antitumor efficacy. The results showed that the radioresistant tumor cell vaccine combined with CpG ODN1826 could significantly inhibit tumor growth, increased survival of the mice and with 20% of the mice surviving tumor free in vivo compared with the unimmunized mice bearing LLC tumor. A significant increase of apoptosis was also observed in the tumor prophylactically immunized with vaccine of inactivated radioresistant tumor cell plus CpG ODN1826. The potent antitumor effect correlated with higher secretion levels of tumor necrosis factor-alpha(TNF-α) and lower levels of interleukin-10(IL-10) concentration in serum. Furthermore, the results suggested that the antitumor mechanism was probably depended on the decreased level of programmed death ligand-1(PD-L1) which plays an important role in the negative regulation of immune response by the inhibition of tumor antigen-specific T cell activation. These findings clearly demonstrated that the radioresistant tumor cell vaccine combined with CpG ODN1826 as an appropriate adjuvant could induce effective antitumor immunity in vivo.

Dose-effect relationship of CpG oligodeoxyribonucleotide 1826 in murine Lewis lung cancer treated with irradiation

Background

Cytosine-phosphate-guanine (CpG) oligodeoxyribonucleotides (ODNs), which induce signaling via Toll-like receptor 9, have recently been suggested to enhance sensitivity to traditional therapies, including chemotherapy, in certain cancer cell lines. This study aimed to define the dose-effect relationship for CpG ODN 1826 in increasing radiosensitivity and its impact on immune function in a mouse model of Lewis lung cancer.

Methods

The tumor-bearing mouse model was induced by injecting Lewis lung cancer cells into the right anterior leg subcutaneously. Sixty-four C57BL/6 J mice were evenly randomized into eight groups, comprising: a control group; an irradiation group; a CpG ODN 0.15 group; a CpG ODN 0.3 group; a CpG ODN 0.45 group; a CpG 0.15 + irradiation group; a CpG 0.3 + irradiation group; and a CpG 0.45 + irradiation group. Tumor growth, serum tumor necrosis factor-alpha and interleukin-12 concentrations, spleen and thymus exponents, and effect of CpG on the secondary immune response were measured, and apoptosis of tumor cells was investigated using TdT-mediated dUTP nick end labeling (TUNEL) after treatment.

Results

Tumor volumes in the treated groups were smaller than in the control group, with those of the CpG 0.45 + irradiation group being the smallest. TUNEL showed that the apoptosis rate in all the active treatment groups was higher than in the control group. CpG ODN apoptosis rate, serum tumor necrosis factor-alpha and interleukin-12 levels, and the spleen and thymus exponent showed greater improvement in the groups receiving combination therapy of CpG ODN and irradiation than the control group or the group receiving irradiation alone. With the increasing concentration of CpG ODN 1826, its effect became more and more significant, meanwhile, inoculation of Lewis lung cancer cells failed in those CpG ODN-cured mice.

Conclusion

CpG ODNs dramatically increased the radiosensitivity of Lewis lung cancer and enhanced immune function in mice in a dose-related manner.