EXPRESS: Clinical and virological effects of the integrase inhibitor raltegravir in cats with naturally progressive feline leukaemia virus infection.

Abstract

ObjectivesFeline leukaemia virus (FeLV) infection-particularly the progressive course-continues to cause substantial morbidity and reduced survival in cats. Therapeutic options with proven antiviral effectiveness remain limited. This study aimed to evaluate the clinical and virological effects of the integrase inhibitor raltegravir in naturally infected, FeLV-progressive cats with FeLV-related conditions, clinical outcome, viraemia, proviral burden and survival.MethodsFourteen client-owned cats with confirmed progressive FeLV infection and at least one FeLV-related condition was enrolled. Raltegravir was administered for 90 days, followed by a 90-day treatment-free observation period. Clinical evaluation and quantification of viral RNA and proviral DNA loads were performed at treatment initiation (t0), day 45 (t45), day 90 (t90) and day 180 (t180). Cats continued to receive standard-of-care as clinically indicated. Survival data were recorded until study closure.ResultsAfter 45 days of treatment, plasma viral RNA load showed a non-significant mean reduction of 1.34 log₁₀ (P = 0.204). At day 90, mean viral load continued to decrease, with reductions of 1.10 log₁₀ at 40 mg (P = 0.208) and 1.39 log₁₀ at 80 mg (P = 0.195), none of which reached statistical significance. Raltegravir did not exert a consistent effect on proviral DNA load. Most FeLV-related conditions remained clinically stable or improved during the 180-day monitoring period. Leukaemia and lymphoma were the main causes of death. Median survival time was 48 months from FeLV diagnosis and 10.8 months from treatment initiation.Conclusions and relevanceTo the authors' knowledge, this is the first prospective longitudinal study in naturally infected, FeLV-progressive cats with FeLV-related conditions assessing the effects of raltegravir on viraemia, proviral load and clinical outcomes. These real-world data suggest that raltegravir may be associated with numerical reductions in viraemia and clinical stabilisation in some cats. A definitive virological or survival benefit, however, could not be demonstrated. Longer-term, controlled studies-potentially within multimodal antiviral strategies-are warranted to further define its therapeutic role.