LAUSR

Abstract Human and canine sarcomas are difficult to treat soft tissue malignancies with an urgent need for new improved therapeutic options. Local recurrence rates for humans are between 10%–30%, and 30%–40% develop metastases. Outcomes for dogs with sarcoma vary with grade but can be similar. Pet dogs share the human environment and represent human cancer with genetic variation in hosts and tumours. We asked if our murine studies using genetically identical mice and cloned tumour cells were translatable to larger, genetically diverse domestic dogs with naturally occurring tumours, to (i) develop a canine cancer therapeutic, and (ii) to use as a translational pathway to humans. Our murine studies showed that intra‐tumoral delivery of interleukin‐2 (IL‐2) plus an agonist anti‐CD40 antibody (Ab) induces long‐term curative responses ranging from 30% to 100%, depending on tumour type. We developed an agonist anti‐canine‐CD40 Ab and conducted a phase I dose finding/toxicology 3 + 3 clinical trial in dogs (n = 27) with soft tissue sarcomas on account of suitability for intratumoral injection and straightforward monitoring. Dogs were treated with IL‐2 plus anti‐CD40 antibody for 2 weeks. Three dose levels induced tumour regression with minimal side effects, measured by monitoring, haematological and biochemical assays. Importantly, our mouse and canine studies provide encouraging fundamental proof‐of‐concept data upon which we can develop veterinary and human immunotherapeutic strategies.