Enabling the evaluation of COVID-19 vaccines with correlates of protection.

In February 2023, a meeting about correlates of protection (CoPs) against COVID-19 was organized by the International Alliance for Biological Standardization, the European Plotkin Institute for Vaccinology, and Vaccinopolis. The meeting aimed at reviewing the evidence, drawing conclusions, and identifying knowledge gaps. Collection of evidence is not straightforward. Neutralizing antibodies correlate with protection and are used for immunobridging studies within and between vaccine platforms for approval of new COVID-19 vaccines. In preparation for the next pandemic, it is vital that rapidly authorized initial vaccines are available to perform immunobridging studies very early. Additional components of the immune response likely contribute to protection against symptomatic infection. Current evidence is strongest for T lymphocytes and binding antibodies. Further studies are needed to consolidate this evidence and define their potential role in the evaluation of vaccines. For evaluation of mucosal vaccines, identifying CoPs against infection and transmission is key; further research is needed to identify and standardize methods suitable for clinical studies. CoPs for broadly protective beta-coronavirus vaccines remain a critical area of research. The knowledge, expertise, and capacity exist to conduct clinical studies using different designs in different populations to discover and validate CoPs, facilitating and accelerating evaluation of novel vaccines/vaccination platforms.

Establishment of an HLA-A*0201 human papillomavirus type 16 tumor model to determine the efficacy of vaccination strategies in HLA-A*0201 transgenic mice.

With the increasing generation of new cancer vaccine strategies, there is also an increasing demand for preclinical models that can carefully predict the efficacy of these vaccines in humans. However, the only tumor models available to study vaccines against human papillomavirus (HPV) 16 have been developed in C57BL/6 mice. To test the HLA-restricted capabilities of vaccination strategies, it is important to establish a tumor model in HLA-A*0201 transgenic mice. By transfecting heart lung fibroblasts from HLA-A*0201 mice with HPV16 E6 and E7 oncogenes and H-Ras V12, we have generated a transgenic cell line that is tumorigenic in HLA-A*0201 mice. The dominant H-2D(b) HPV16 E7 epitope was removed from the E7 construct to ensure that all antitumor responses were mediated through the HLA-A*0201-restricted epitopes. We used this tumor model to test the efficacy of two genetic vaccines: a plasmid DNA multi-epitope vaccine encoding human epitopes of HPV16, and a Venezuelan equine encephalitis (VEE) virus-based vector to deliver HPV16 E6 and E7 RNA. We show that both our multi-epitope DNA- and VEE-based vaccines protect 100% of HLA-A*0201 transgenic mice from tumor challenge and elicit a specific T-cell response against multiple HLA-A*0201-restricted HPV16 epitopes. Furthermore, both vaccines significantly decreased tumor burden when tested therapeutically. In conclusion, this is the first tumor model that allows for the assessment of the potential of a vaccine to induce HPV-directed, HLA-A*0201-restricted, antitumor responses in mice. These results pave the way for the clinical evaluation of these vaccines.