Engineered cross‐reacting nanobodies simplify comparative oncology between humans and dogs

Antibodies cross‐reacting with homologue antigens in different species would be essential reagents for the development of comparative oncology studies. In comparison with conventional immunoglobulin Gs, recombinant nanobodies (single‐domain variable regions of heavy‐chain only antibodies of Camelidae origin) can be easily isolated in vitro and engineered into a variety of reagents with optimized characteristics for different research and clinical applications. We recovered an anti‐human epidermal growth factor receptor 2 (anti‐HER2) nanobody from a naïve llama library by direct panning on whole cells and expressed it fused to Fc and green fluorescent protein. These immunoreagents were assessed by flow cytometry and immunofluorescence with both human and canine cells overexpressing HER2 and its canine homologue dog epidermal growth factor receptor 2. The reported data illustrate the potential of using this class of antibodies in comparative oncology and suggest some development perspectives enabled by in vitro panning of pre‐immune nanobody libraries.