Immunological assessment and dose optimization of recombinant canine interleukin-15 following subcutaneous administration in Beagle dogs

Abstract Interleukin-15 (IL-15) is a cytokine critical to the activation and maintenance of natural killer (NK) cells and cytotoxic T lymphocytes. In veterinary medicine, recombinant canine IL-15 (rcIL-15) has emerged as a potential immunotherapeutic agent; however, limited information is available on its safety and efficacy when administered subcutaneously (SC) compared to the intravenous (IV) route. This study aimed to determine whether SC administration of rcIL-15 provides comparable safety and immunological effects to IV administration in Beagle dogs, and to identify an optimal SC dosing regimen. Three male Beagle dogs were sequentially administered rcIL-15 at 20 µg/kg/day via IV and SC routes for four consecutive days. Subsequently, SC doses of 40 and 60 µg/kg/day were tested in the same dogs. Clinical assessments were conducted throughout the study. Peripheral blood mononuclear cells were collected before treatment and on day 7 post-treatment for flow cytometric analysis of lymphocyte subsets. All dogs tolerated rcIL-15 well, with no adverse effects or injection site reactions observed, even at the highest SC dose (60 µg/kg/day), which was threefold higher than the standard IV dose. Flow cytometric analysis showed increased frequencies of CD3⁺CD5⁺low, Nkp46⁺CD5⁺low, and non-B non-T cells, indicating NK cell activation. CD8⁺CD5⁺low NK-like T cells were consistently increased, whereas CD4⁺CD5⁺ T cell responses were variable. SC administration at 40 and 60 µg/kg/day elicited immunological responses comparable to those observed with IV administration. These findings suggest that SC delivery of rcIL-15 is well tolerated and induces immune activation similar to IV administration, suggesting the need for further investigation for its clinical applicability in canine immunotherapy.