Davis, T. W.; Holmes, J. C.; He, A.; Hess, P. R.; Mariani, C. L.; Brudno, Y.

Dogs are becoming an important model for human cancers, and successfully troubleshooting issues with genetically modified T cell immunotherapy for round cell and solid neoplasms in dogs provides a unique opportunity to improve efficacy, safety, and affordability for humans as well. Unfortunately, T cell activation in dogs for optimal viral transduction has not been determined, restricting advancements in canine T cell immunotherapy. Two CD3 and two CD28 antibody clones for canine T cell stimulation have been described in the literature, but no studies have been undertaken to evaluate which CD3/CD28 combination is most effective, nor has anyone directly compared the efficacy of the two most popular antibody presentation strategies: antibody-coated plates and antibody-conjugated beads. In evaluating the effects of plate- or bead-bound CD3 stimulation alone versus CD3/CD28 in combination, we tested 12 possible antibody stimulation strategies in addition to evaluating two largely unexplored mitogens in canine T cell transduction, phorbol myristate acetate (PMA) with ionomycin and concanavalin A (ConA). We investigated the impact of these stimulation strategies on canine T cell activation, expansion, and transduction. For stimulation strategies producing the best results, we also examined how each strategy affected the proportions of CD4/CD8 T cell subsets and regulatory T cell (Treg) prevalence. We determined that, in general, plate-bound antibodies were far superior to bead-bound antibodies for canine T cell stimulation, and that plate-bound CD3 clone CA17.6F9 in combination with CD28 clone 5B8 or the mitogen PMA with ionomycin produced better activation and expansion profiles, better transduction, and more desirable T cell subsets that are more likely to improve patient outcomes in dogs suffering from round cell and solid tumors.