Immune responses triggered by nanobody-targeted photodynamic therapy

Nanobodies are single domain antibodies derived from heavy chain antibodies that exist in Camelids1. The relatively small dimensions of nanobodies combined with high binding affinities to their targets, lead to rapid tumor accumulation, homogenous distribution, and rapid clearance of unbound fractions. We took advantage of these properties and have developed an alternative approach for targeted photodynamic therapy (PDT) by conjugating photosensitizers to nanobodies2. Several of our studies are targeting the epidermal growth factor receptor (EGFR) for head and neck cancer. As photosensitizer, we employ the IRDye700DX, that is a silicon phthalocyanine derivative, currently being tested in clinical trials conjugated to the monoclonal antibody cetuximab, and already approved for clinical use in Japan. Notably, with nanobody-targeted PDT, cytotoxicity is selectively induced in cells which have high target expression level. Preclinical studies have shown selective tumor necrosis3 and significant tumor regression after a single treatment session4.Similar to conventional PDT, we have shown that nanobody-targeted PDT can stimulate the immune system5. This was documented by the release of damage-associated molecular patterns (DAMPs), such as HSP70 and ATP, as well as the pro-inflammatory cytokines IL- 1β and IL-6. Conditioned medium from EGFR-expressing tumor cells treated with nanobody-targeted PDT led to the maturation of human monocyte-derived dendritic cells, and subsequently, these dendritic cells induced CD4+ T cell proliferation. After our initial studies exploring the immunomodulatory potential of nanobody-targeted PDT in vitro, we are currently conducting studies in vivo to further investigate the systemic reach of this selective and localized treatment. This presentation will summarize these studies and discuss preliminary data obtained from testing this treatment in cats that are diagnosed with oral squamous cell carcinoma.Acknowledgements: This work was supported by the European Research Council (ERC, Starting Grant 677582) and is supported by the Dutch Cancer Foundation (KWF, High Risk Grant 12736) and the Morris Animal Foundation (MAF, Established Investigator Grant D21FE-021).