Evaluation of lymphocyte-specific PD-1 receptor expression and cytokines in blood and urine in canine urothelial carcinoma patients.

Urothelial carcinoma (UC) is the most common urinary tumour in dogs. Despite a range of treatment options, prognosis remains poor in dogs. In people, breakthroughs with checkpoint inhibitors have established new standards of care for muscle-invasive bladder cancer patients and elevated levels of PD-1 suggest immune checkpoint blockade may be a novel target for therapy. The goal of this study was to determine if canine UC patients express elevated levels of lymphocyte-specific PD-1 and/or urinary cytokine biomarkers compared to healthy dogs. Paired blood and urine were evaluated in ten canine UC patients, five cystitis patients and ten control dogs for lymphocyte-specific PD-1 expression via flow cytometry and relative cytokine expression. In UC patients, PD-1 expression was significantly elevated on CD8+ lymphocytes in urine samples. UC patients had a higher CD4:CD8 ratio in their urine compared to healthy dogs, however there was no variation in the CD8:Treg ratio between any group. Cystitis patients had significantly elevated levels of CD4+ T cells, CD8+ T cells, and Tregs in their blood samples compared to UC patients and healthy dogs. Cytokine analysis demonstrated significant elevations in urinary cytokines (GM-CSF, IFN-γ, IL-2, IL-6 IL-7, IL-8, and IL-15, IP-10, KC-like, IL-18, MCP-1, and TNFα). Several of these cytokines have been previously correlated with both lymphocyte-specific PD-1 expression (IFN-γ, IL-2, IL-7, and IL-15) in muscle-invasive urothelial carcinoma in humans. Our results provides evidence of urinary lymphocyte PD-1 expression and future studies could elucidate whether veterinary UC patients will respond favorably to anti-PD-1 immune checkpoint inhibitor therapy. This article is protected by copyright. All rights reserved.