Project Summary This is a new MPI R01 proposal bringing together protein engineering for immunotherapy (Wittrup, MIT) with comparative oncology/veterinary medicine (Fan, UIUC) to test clinical strategies for combining radiotherapy with intratumoral cytokine administration/retention in pet dogs with melanoma, at the UIUC veterinary clinic. We have developed a strategy for retaining injected cytokines (IL-2 and IL-12 in particular) in situ by expressing them as fusions to natural collagen-binding domains. This approach has been found to be safely curative in challenging murine transplant and GEM tumor models, and will now be advanced into a more faithful model for human cancer: spontaneous canine melanoma. These tumors arise spontaneously in outbred populations, and undergo a natural progression of immunoediting prior to clinical presentation. Canine melanoma exhibits pathophysiology similar to human melanoma, including the presence of immune infiltrated, excluded, and desert subtypes. In Aim 1, we will exploit the more-realistic anatomy of these tumors to optimize the micropharmacokinetics of intratumoral administration, establishing foundational principles with respect to injectable volume fractions, needle types, and numbers of sites. In Aim 2, we will test the therapeutic hypothesis that precisely temporally programmed intense localized cytokine stimulation can be optimally combined with radiation therapy so as to prime a strong T cell vaccinal response with consequent systemic impact on efficacy. In Aim 3, we will perform a clinical trial in canine melanoma to rigorously compare alternative dose scheduling for intratumoral cytokine therapy following irradiation. We hypothesize that the time delay prior to cytokine injection will have a critical, all-or-nothing effect on outcomes. This intradisciplinary collaboration has commenced, and exciting preliminary treatment data is presented herein. The overarching objective of this project is to develop improved human cancer immunotherapy protocols that combine intratumoral immunotherapy with local radiation. Multiple previous clinical trials in this area have yet to realize the full promise of this approach, but by performing rapid design-build-test-learn cycles in spontaneous canine melanoma, we hope to converge more efficiently to efficacious strategies.