Anti-SU Antibody Responses in Client-Owned Cats Following Vaccination against Feline Leukaemia Virus with Two Inactivated Whole-Virus Vaccines (Fel-O-Vax® Lv-K and Fel-O-Vax® 5).

Mark Westman,Mike Mcdonald,Evelyn Hall,Jacqueline Norris,Emma Armstrong,Richard Malik,Yasmin A Parr,Paul Sheehy,Margaret J Hosie,Regina Hofmann-Lehmann

doi:10.3390/v13020240

Abstract

A field study undertaken in Australia compared the antibody responses induced in client-owned cats that had been vaccinated using two inactivated whole feline leukaemia virus (FeLV) vaccines, the monovalent vaccine Fel-O-Vax® Lv-K and the polyvalent vaccine Fel-O-Vax® 5. Serum samples from 428 FeLV-uninfected cats (118 FeLV-vaccinated and 310 FeLV-unvaccinated) were tested for anti-FeLV neutralising antibodies (NAb) using a live virus neutralisation assay to identify 378 FeLV-unexposed (NAb-negative) and 50 FeLV-exposed (NAb-positive; abortive infections) cats, following by anti-surface unit (SU) FeLV-A and FeLV-B antibody ELISA testing. An additional 42 FeLV-infected cats (28 presumptively regressively infected, 14 presumptively progressively infected) were also tested for anti-SU antibodies. NAb-positive cats displayed significantly higher anti-SU antibody ELISA responses compared to NAb-negative cats (p < 0.001). FeLV-unexposed cats (NAb-negative) that had been vaccinated less than 18 months after a previous FeLV vaccination using the monovalent vaccine (Fel-O-Vax® Lv-K) displayed higher anti-SU antibody ELISA responses than a comparable group vaccinated with the polyvalent vaccine (Fel-O-Vax® 5) (p < 0.001 for both anti-FeLV-A and FeLV-B SU antibody responses). This difference in anti-SU antibody responses between cats vaccinated with the monovalent or polyvalent vaccine, however, was not observed in cats that had been naturally exposed to FeLV (NAb-positive) (p = 0.33). It was postulated that vaccination with Fel-O-Vax® 5 primed the humoral response prior to FeLV exposure, such that antibody production increased when the animal was challenged, while vaccination with Fel-O-Vax® Lv-K induced an immediate preparatory antibody response that did not quantitatively increase after FeLV exposure. These results raise questions about the comparable vaccine efficacy of the different FeLV vaccine formulations and correlates of protection.

Highlights

Feline leukaemia virus (FeLV), a member of the Retroviridae family, was first reported in 1964 following its discovery by Bill Jarrett and colleagues during the investigation of a time–space cluster of cats with T-cell lymphoma [1]
The age, sex and breed of Fel-O-Vax® Lv-K vaccinated on-time/FeLV-unexposed cats (n = 10) and Fel-O-Vax® 5 vaccinated on-time/FeLV-unexposed cats (n = 40) were similar (p = 0.94, 0.51 and 1.00, respectively), as were the age, sex and breed of Fel-O-Vax® Lv-K vaccinated on-time/FeLV-exposed cats (n = 13) and Fel-O-Vax® 5 vaccinated on-time/FeLV-exposed cats (n = 26) (p = 0.56, 0.51 and 1.00, respectively; 2-sample t-testing for age, Ordinal logistic regression (OLR) testing for sex and breed for both comparisons)
While vaccination with the polyvalent Fel-O-Vax® 5 reproduced the response reported from experimental studies, in which FeLV vaccination led to minimal antibody production but primed the cat’s humoral immune system in case of FeLV exposure [19], vaccination with the monovalent Fel-O-Vax® Lv-K resulted in a robust humoral response irrespective of FeLV exposure

Summary

Introduction

Feline leukaemia virus (FeLV), a member of the Retroviridae family, was first reported in 1964 following its discovery by Bill Jarrett and colleagues during the investigation of a time–space cluster of cats with T-cell lymphoma [1]. Subsequent research reported persistently viraemic cats with progressive FeLV infections to be 62 times more likely to develop lymphoma or leukaemia than FeLV-uninfected cats [2,3]. A potential link between transiently viraemic cats with regressive FeLV infections and lymphoma has been suggested [4,5,6]. The analysis of immune responses facilitating complete recovery in FeLV-exposed cats with abortive infections, and those protecting cats following FeLV vaccination, are important to assist with current efforts to develop effective vaccines against other retroviruses, such as HIV-1 [17,18]

Objectives

Methods

Results

Discussion

Conclusion