Nanobody-Antigen Conjugates Elicit HPV-Specific Antitumor Immune Responses.

High-risk human papillomavirus-associated cancers express viral oncoproteins (e.g., E6 and E7) that induce and maintain the malignant phenotype. The viral origin of these proteins makes them attractive targets for development of a therapeutic vaccine. Camelid-derived single-domain antibody fragments (nanobodies or VHHs) that recognize cell surface proteins on antigen-presenting cells (APC) can serve as targeted delivery vehicles for antigens attached to them. Such VHHs were shown to induce CD4 and CD8 T-cell responses against model antigens conjugated to them via sortase, but antitumor responses had not yet been investigated. Here, we tested the ability of an anti-CD11b VHH (VHH) to target APCs and serve as the basis for a therapeutic vaccine to induce CD8 T-cell responses against HPV tumors. Mice immunized with VHH conjugated to an H-2D-restricted immunodominant E7 epitope (E7) had more E7-specific CD8 T cells compared with those immunized with E7 peptide alone. These CD8 T cells acted prophylactically and conferred protection against a subsequent challenge with HPV E7-expressing tumor cells. In a therapeutic setting, VHH-E7 vaccination resulted in greater numbers of CD8 tumor-infiltrating lymphocytes compared with mice receiving E7 peptide alone in HPV tumor-bearing mice, as measured by noninvasive VHH-based immune-positron emission tomography (immunoPET), which correlated with tumor regression and survival outcome. Together, these results demonstrate that VHHs can serve as a therapeutic cancer vaccine platform for HPV-induced cancers. .