Codon optimized expression of HPV 16 E6 renders target cells susceptible to E6-specific CTL recognition

Area of Science:

• Immunology
• Virology
• Oncology

Background:

• Human papillomavirus type 16 (HPV 16) E6 and E7 oncoproteins are key drivers of cervical cancer.
• While E7 immunogenicity is well-studied, the immune response to E6 remains less understood.
• E6 and E7 are targets for immune therapeutic strategies against HPV-induced cancers.

Purpose of the Study:

• To evaluate E6-specific DNA immunization strategies in a preclinical mouse model.
• To assess the induction of E6-specific cytotoxic T lymphocytes (CTLs).
• To investigate factors influencing CTL recognition of E6-expressing cells.

Main Methods:

• C57BL/6 mice were immunized with plasmid pTHampE6.
• E6-specific CTL induction was analyzed.
• Target cells expressing natural or codon-optimized E6 (E6opt) were used.
• Monoclonal antibodies and proteasome inhibitor lactacystin were employed.

Main Results:

• E6-specific CTLs were detected post-immunization.
• Cells with natural E6 gene expression showed low protein levels and poor CTL recognition.
• Codon optimization (E6opt) significantly increased E6 protein expression and CTL susceptibility.
• TC-1 cells, recognized by CTLs, lacked detectable E6 protein, suggesting rapid degradation and epitope presentation.
• Lactacystin treatment affected CTL recognition and E6 protein accumulation.

Conclusions:

• Codon optimization of the E6 gene enhances target cell susceptibility to E6-specific CTL recognition.
• Absence of detectable E6 protein does not preclude epitope presentation for MHC class I restricted antigen presentation.
• Findings are relevant for designing HPV tumor vaccines targeting E6.