Dual-subtype feline immunodeficiency virus vaccine provides 12 months of protective immunity against heterologous challenge

Abstract

The duration of immunity of the dual-subtype feline immunodeficiency virus (FIV) vaccine, Fel-O-Vax FIV, for protection against subtype-B FIV was assessed in this study. Vaccinated cats along with controls were challenged with FIV(FC1), a subtype-B FIV strain, 54 weeks after the final vaccination, and monitored for 46-48 weeks for provirus and viral RNA in peripheral blood, provirus in lymphoid organs, and CD4:CD8 ratios. Results of provirus detection in peripheral blood and lymphoid organs and plasma viral RNA loads showed that 10/14 vaccinated cats were fully protected for 48 weeks against infection with FIV(FC1) whereas 5/5 controls were persistently infected with FIV(FC1). CD4:CD8 inversions were noted in association with FIV infection and viral loads were not significantly different between FIV infected controls and the unprotected vaccinated animals.

Fig 1

Kinetics of the humoral immune responses in vaccinate and control groups. ELISA was performed at a serum dilution of 1:200, and results are expressed as mean normalized Vmax values for various groups. The protected vaccinates (n=10) were FIV provirus negative whereas the unprotected vaccinates (n=4) and controls (n=5) were FIV provirus positive following challenge with FIV_FC1. Panel A represents the kinetics of anti-FIV p24 antibody responses. Panel B represent the kinetics of anti-FIV TM antibody responses.

Fig 2

Measurement of plasma viral load (copies of viral RNA/ml) by TaqMan RT-PCR in unprotected vaccinate and control groups. Plasma samples taken at indicated times following challenge with FIV_FC1 were examined for viral RNA load using real-time RT-PCR. Panel A: unprotected vaccinates. Panel B: viremic controls. Cat identification numbers are shown on the right.

Fig 3

Measurement of FIV proviral load in lymphoid tissues by TaqMan PCR in unprotected vaccinate and control groups. Various lymphoid tissues were taken at 46–48 wpc and the proviral load measured using real-time PCR. The mean and standard deviation are shown for each lymphoid tissue.

Fig 4

Measurement of CD4:CD8 ratios following challenge with FIV_FC1. The CD4:CD8 lymphocyte ratios were determined for all cats at 0 dpc, 31 wpc and 40 wpc. The mean and standard deviation are shown for each group.