Antitumor Response by Endoplasmic Reticulum-Targeting DNA Vaccine Is Improved by Adding a KDEL Retention Signal

Directing an antigen to the endoplasmic reticulum (ER) improves the antigen-specific immune response, revealing a potentially useful strategy in cancer immunotherapy using tumor-associated antigens (TAAs). This can be achieved by fusing the antigen to an ER chaperone protein, such as calreticulin (CRT). We previously reported the antitumor response by fusing the CRT signal peptide (SP) and its ER retention sequence (KDEL) to full-length human papillomavirus type 16 (HPV-16) E6 and E7 antigens, obtaining a potent antitumoral effect. In this article, we compare the antitumor response due to the use of each signal (SP and/or KDEL) fused to HPV16 E6 and E7 antigens in a DNA vaccination model. Using both SP and KDEL signals promotes higher interferon (IFN)-γ production and a faster antitumor response than using only the SP, resulting in better tumor growth restraint and higher survival, indicating that the KDEL addition to an ER-directed antigen helps by shortening the time to response. Meanwhile, antigens without signals or only the KDEL signal showed no induction of antigen-specific IFN-γ or antitumor response. Our results indicate that directing the E6E7m antigen to the ER by the SP signal is sufficient to promote an efficient antitumor response. Importantly, this effect is stronger and faster when the antigen also has an ER retention sequence, such as the KDEL signal.