Potent therapeutic efficacy of an alphavirus replicon DNA vaccine expressing human papilloma virus E6 and E7 antigens

Abstract

Cervical cancer develops as a result of infection with high-risk human papillomavirus (HPV) through persistent expression of early proteins E6 and E7. Our group pioneered a recombinant viral vector system based on Semliki Forest virus (SFV) for vaccination against cervical cancer. The most striking benefit of this alphavirus vector-based vaccine platform is its high potency. DNA vaccines on the other hand, have a major advantage with respect to ease of production. In this study, the benefits associated with both SFV-based vaccines and DNA vaccines were combined with the development of a DNA-launched RNA replicon (DREP) vaccine targeting cervical cancer. Using intradermal delivery followed by electroporation, we demonstrated that DREP encoding for E6,7 (DREP-E6,7) induced effective, therapeutic antitumor immunity. While immunizations with a conventional DNA vaccine did not prevent tumor outgrowth, immunization with a 200-fold lower equimolar dose of DREP (0.05 µg of DREP) resulted in approximately 85% of tumor-free mice. To overcome the safety concern of potential malignant transformation at the vaccination site, we evaluated the anti-tumor effect of a DREP vaccine encoding a shuffled version of E7 (DREP-E7sh). DREP-E7sh delayed tumor growth yet not to the same extent as DREP-E6,7. In addition, inclusion of a helper cassette and an ER targeting signal (sigHelp) did not significantly further enhance the suppression of tumor outgrowth in the long term, albeit exhibiting better tumor control early after immunization. Collectively, this study points towards the clinical evaluation of DREP encoding HPV antigens as a potent immunotherapy for patients with HPV16 (pre)-malignancies.

Self-Amplifying RNA Viruses as RNA Vaccines

“…Similarly, 100- to 1000-fold lower doses of DNA replicon SIN-HSV-1-gB compared to conventional DNA plasmids were required to obtain antibody responses and protection against lethal challenges with virus in mice [ 163 ]. In the context of cervical cancer, where conventional DNA-based immunization failed to prevent tumor outgrowth, already a 200-fold lower equimolar dose of 0.05 µg of SFV-HPV E6/7 DNA provided complete tumor regression in 85% of immunized mice [ 93 ].…”

“…In another approach, immunization of mice with an SFV vector engineered with the translation enhancer signal from the SFV capsid gene and an HPV E6-E7 fusion protein resulted in tumor regression and complete elimination of established tumors [ 92 ]. Therapeutic antitumor immunity was established in mice after the combination of intradermal administration of an SFV DNA replicon expressing HPV E6/7 [ 93 ] and electroporation. In comparison to conventional DNA plasmid vectors, a 200-fold lower equimolar dose of 0.05 µg resulted in 85% of immunized mice becoming tumor-free.…”

Therapeutic Vaccines Against Human Papilloma Viruses: Achievements and Prospects

“…Combined DNA/RNA replicon vaccines have been developed further and currently show high efficacy in pre venting deaths associated with viral infection and implan tation of cancer cells [56], in particular, in preclinical treatments of HPV 16 associated CC in mice [59]. A recent study evaluated antitumor effect of the DNA/RNA replicon constructs encoding E6 and E7 proteins (DREP 6,7), as well as a variant encoding the reshuffled version of E7 (DREP E7sh).…”

“…Interestingly, DREP E7sh delayed tumor growth to a lesser extent than the non reshuffled version of DREP E6,7. Incorporation into the recombi nant vaccine vector of an auxiliary cassette containing a set of epitopes of T helper cells, the signal peptide, and the KDEL motif for the import and retention of the encoded proteins in the endoplasmic reticulum (DREP sHelpE6,7; DREP sHelpE7sh) did not promote the anti tumor effect, although accelerated its manifestations [59]. Indirectly, this result indicates the absence of direct need for extensive modification of the viral proteins encoded by the genetic vaccine, except for the removal or modifica tion of the protein domains causing direct adverse effects.…”

Self-amplifying RNA virus vectors: clinical applications in cancer drug delivery

“…For instance, comparison to synthetic mRNA, self-amplifying VEE RNA replicons expressing the influenza hemagglutinin (HA) required 1.25 µg (64fold less material) to achieve protection of mice against influenza virus challenges [21]. Similarly, a 200-fold lower equimolar dose of 0.05 µg SFV DNA replicon-based cervical cancer vaccine was sufficient to generate complete tumor regression in 85% of immunized mice [22]. These findings make self-amplifying RNA viruses attractive as an alternative approach for future development of cancer drugs.…”