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 antiiumor responses had not yet been investigated. Here, we tested the ability of an anti-CD11b VHH (VHHCD11b) to target APCs and serve as the basis for a therapeutic vaccine to induce CD8(+) T-cell responses against HPV+ tumors. Mice immunized with VHHCD11b conjugated to an H-2D(b)-restricted immunodominant E7 epitope (E7(49-57)) had more E7-specific CD8(+) Tcells compared with those immunized with E7(49-57) 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, VHHCD11b-E7(49-57) vaccination resulted in greater numbers of CD8(+) tumor-infiltrating lymphocytes compared with mice receiving E7(49-57) peptide alone in HPV+ tumor-hearing mice, as measured by in vivo 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. (C) 2018 AACR.