Cytotoxic T cells (CTLs) are one of the major early defenses against viral infections. A positive correlation between FeLV recovery and the level of FeLV-specific circulating CTLs has been shown. This study evaluated the response to transdermal administration of a recombinant FeLV (r-FeLV) or a killed whole virus vaccine (KV-FeLV). Controls were sham vaccinated with a recombinant rabies vaccine or saline. The cats were injected twice at 3-week intervals. Two weeks after the last vaccination, they were given a challenge dose of FeLV-A. Blood was collected, and the T cell response was quantified by using either an IFNγ-ELISpot assay or by flow cytometry.

Cats vaccinated with the r-FeLV vaccine developed a FeLV-specific IFNγ + T-cell response 14 days after the last vaccination and 21 and 111 days after the challenge. The KV-FeLV vaccinated cats mounted only a weak response 111 days after challenge. IFNγ is a key component of type 1 cell-mediated immunity, which has been recognized as a critical component in antiviral immunity. The cats vaccinated with r-FeLV tended to have higher CD8+ TNFα + FeLV-specific T cell responses. The r-FeLV vaccine given transdermally induced a broad FeLV-specific T cell response of both IFNγ- and TNFα-secreting cells. Study by Merial

Transdermal vaccine technology has been used successfully in both veterinary and human medicine for several years. Our increased understanding of how the different immune responses contribute to control and prevention of infectious diseases allows for new
vaccine types and delivery mechanisms. Cell-mediated immunity is important for the control of FeLV, and this recombinant vaccine performed well in inducing a cell-mediated response.

Feline leukemia virus (FeLV)-Specific IFNγ+ T-cell responses are induced in cats following transdermal vaccination with a recombinant FeLV vaccine. Garch HE, Richard S, Piras F, et al. IntL J Appl Res Vet Med 4:100-108, 2006.