Human CLDN6 Virus-Like Particles

Virus-like particles (VLPs) displaying foreign antigens have become an important tool for vaccination, including inducing immune responses against self-antigens. Claudin 6 (CLDN6) has been identified as a tumor-associated antigen and is therefore a potential target for tumor vaccination strategies. However, as a tetraspanin, its incorporation into VLPs while retaining its native folded structure is a challenge. Here, researchers attempted to incorporate a panel of engineered CLDN6 variants into retrovirus-derived VLP membranes. Interestingly, wild-type CLDN6 was displayed with the highest efficiency. VLPs displaying murine CLDN6 were used to immunize mice. In vaccinated animals, antibodies were able to recognize native CLDN6 displayed on the cell surface and mediated complement-dependent cytotoxicity. These data suggest that CLDN6-displaying VLPs could be used for cancer immunotherapy.

Here, the researchers evaluated the immunogenicity of VLPs produced by 293T cells displaying wild-type CLDN6 or the variants ∆loop1+2, ∆loop1, and ∆loop2. Controls were empty particles produced in the absence of a CLDN6 encoding plasmid (MLV-gag). BALB/c mice were immunized using a prime-boost regimen consisting of subcutaneous injections of particles adjuvanted with Gerbu P (Figure 1A). To test for the presence of antibodies recognizing native CLDN6 expression on the cell surface, mouse sera were used for flow cytometric analysis of mouse CT26 cells expressing CLDN6 at native endogenous levels (CT26-WT) or CT26 cells overexpressing CLDN6 (CT26-mmCLDN6). The ratio of serum obtained after the first or last bleeding of each mouse to the mean fluorescence intensity (MFI) was then determined and normalized to the ratio observed after immunization with control particles without CLDN6. Control particles did not result in any increase in the MFI ratio after immunization, whether with CT26 or CT26-mmCLDN6 cells. The same was true for three VLPs displaying deletion variants of CLDN6 (Figure 1B). In stark contrast, four of five injected mice immunized with wt-CLDN6 VLPs generated a strong antibody response against native CLDN6 (Figure 1B). This ratio was higher when CT26-mmCLDN6 cells were used.

Figure 1. Immunization of BALB/c mice with CLDN6-VLPs. (Schneider I C, et al., 2018)