An In Situ Autologous Tumor Vaccination with Combined Radiation Therapy and TLR9 Agonist Therapy

Purpose: Recent studies have shown that a new generation of synthetic agonist of Toll-like receptor (TLR) 9 consisting a 3'-3'-attached structure and a dCp7-deaza-dG dinucultodie shows more potent immunostimulatory effects in both mouse and human than conventional CpG oligonucleotides. Radiation therapy (RT) provides a source of tumor antigens that are released from dying, irradiated, tumor cells without causing systemic immunosuppression. We, therefore, examined effect of combining RT with a designer synthetic agonist of TLR9 on anti-tumoral immunity, primary tumor growth retardation and metastases in a murine model of lung cancer. Methods: Grouped C57BL/6 and congenic B cell deficient mice (B-/-) bearing footpad 3LL tumors were treated with PBS, TLR9 agonist, control oligonucelotide, RT or the combination of RT and TLR9 agonist. Immune phenotype of splenocytes and serum IFN-gamma and IL-10 levels were analyzed by FACS and ELISA, 24 h after treatment. Tumor growth, lung metastases and survival rate were monitored and tumor specific antibodies in serum and deposition in tumor tissue were measured by ELISA and immunofluorescence. Results: TLR9 agonist expanded and activated B cells and plasmacytoid dendritic cells in wild-type mice and natural killer DCs (NKDCs) in B cell-deficient (B-/-) mice bearing ectopic Lewis lung adenocarcinoma (3LL). Combined RT with TLR9 agonist treatment inhibited 3LL tumor growth in both wild type and B-/- mice. A strong tumor-specific humoral immune response (titer: 1/3200) with deposition of mouse IgG auto-antibodies in tumor tissue were found in wildtype mice, whereas the number of tumor infiltrating NKDCs increased in B-/- mice following RT+ TLR9 agonist therapy. Furthermore, mice receiving combination therapy had fewer lung metastases and a higher survival than single treatment cohorts. Conclusions: Combination therapy with TLR9 agonist and RT induces systemic anti-tumoral humoral response, augments tumoral infiltration of NKDCs, reduces pulmonary metastases and improves survival in a murine model of 3LL cancer.