Adjuvant combination and antigen targeting as a strategy to induce polyfunctional and high-avidity T-cell responses against poorly immunogenic tumors.

Low antigen expression and an absence of coimmunostimulatory signals may be partly responsible for the low immunogenicity of many tumors. It may be possible to overcome this situation by defining a combination of adjuvants and antigens that can activate a high-avidity antitumor response. Using the poorly immunogenic B16-OVA melanoma cells as tumor model, we tested different combinations of adjuvants and antigens to treat established tumors. In the absence of exogenous antigens, repeated administration of the TLR7 ligand Imiquimod together with anti-CD40 agonistic antibodies activated only innate immunity, which was insufficient to reject intradermal tumors. Administering this adjuvant combination together with OVA as a tumor antigen induced T-cell responses that delayed tumor growth. However, administering a combination of anti-CD40 plus TLR3 and TLR7 ligands, together with antigen targeting to dendritic cells through TLR4, was sufficient to induce tumor rejection in 50% of mice. This response was associated with a greater activation of innate immunity and induction of high-avidity polyfunctional CD8(+) T-cell responses, which each contributed to tumor rejection. This therapy activated T-cell responses not only against OVA, which conferred protection against a rechallenge with B16-OVA cells, but also activated T-cell responses against other melanoma-associated antigens. Our findings support the concept that multiple adjuvant combination and antigen targeting may be a useful immunotherapeutic strategy against poorly immunogenic tumors.