Endoplasmic reticulum-targeting sequence enhanced the cellular immunity of a tumor-associated antigen L6-based DNA vaccine.

Cancer vaccine design to effectively eliminate tumors requires triggering strong immune reactions to elicit long-lasting humoral and cellular immunity and DNA vaccines have been demonstrated to be an attractive immunotherapeutic approach. The tumor-associated antigen L6 (TAL6) is overexpressed on the surface of different cancer cells and promotes cancer progression; therefore, it could be a potential target for cancer treatment. We have revealed that a synthetic peptide containing HLA-A2-restricted cytotoxic T lymphocyte (CTL) and B cell epitope can induce cellular and humoral immunity against TAL6-expressing cancer. To enhance the efficacy of immunotherapy, in this report, we designed an endoplasmic reticulum (ER)-targeting sequence (adenovirus E3/19K protein) at the N-terminus of TAL6 to facilitate MHC class I antigen presentation to CD8 T cells. Transfection of mammalian cells with the plasmid containing TAL6 fused with the ER-targeting sequence (pEKL6) resulted in higher levels of TAL6 antigens in the ER than transfection with the full-length TAL6 (pL6). The plasmid pEKL6 induced both TAL6-specific CTL responses and antibody titers after intramuscular (IM) immunization with electroporation and it elicited higher levels of antigen-specific CTLs in HLA-A2 transgenic mice. Immunization with pEKL6 induced higher levels of protective antitumor immunity against tumor growth than pL6 immunization in thymoma and melanoma tumor animal models. Notably, pEKL6 elicited long-term anti-tumor immunity against the recurrence of cancers. We found that CD4 T, CD8 T, and NK cells are all important for the effector mechanisms of pEKL6 immunization. Thus, cancer therapy using an ER-targeting sequence linked to a tumor antigen holds promise for treating tumors by triggering strong immune reactions.