Possible immunoenhancement of persistent viremia by feline leukemia virus envelope glycoprotein vaccines in challenge-exposure situations where whole inactivated virus vaccines were protective

Abstract

Kittens immunized with purified native FeLV-gp70 or -gp85 envelope proteins developed ELISA, but not virus neutralizing, antibodies in their serum to both whole FeLV and FeLV-gp70. Kittens vaccinated with envelope proteins and infected with feline sarcoma virus (FeSV) developed smaller tumors than nonvaccinates, but a greater incidence of persistent retroviremia. Similarly, FeLV-gp70 and -gp85 vaccinated kittens were more apt to become persistently retroviremic following virulent FeLV challenge exposure than nonvaccinates. Kittens vaccinated with inactivated whole FeLV developed smaller tumors after FeSV inoculation and had a lower incidence of persistent retroviremia than nonvaccinates. The protective effect of inactivated whole FeLV vaccine against persistent retroviremia was also seen with FeLV challenge-exposed cats. Protection afforded by inactivated whole FeLV vaccine was not associated with virus neutralizing antibodies, although ELISA antibodies to both whole FeLV and FeLV-gp70 were induced by vaccination.

Induction of Protective Immunity againstChlamydia trachomatisGenital Infection by a Vaccine Based on Major Outer Membrane Protein–Lipophilic Immune Response-Stimulating Complexes

“…In a growing list of accomplishments in these new approaches to vaccinology, human subunit vaccines are currently available against pneumococci, meningococci, Haemophilus influenzae, and hepatitis B and influenza viruses. While the era of the epitope or subunit vaccines have obviated the concerns inherent in inactivated or live attenuated whole pathogen vaccines (35)(36)(37), including infectious, noxious, or integrating nucleic acid contents, induction of nonprotective blocking antibodies (41), epitope destruction during inactivation (16), and the presence of pathogenic antigenic (18,37), it has also encountered a major setback associated with the relatively poor immunogenicity of such preparations. Thus, the preference for epitopic or subunit vaccines has necessitated the search for more-efficient delivery vehicles, such as adjuvants, to boost immune responses against less-complex antigens.…”

Equine Infectious Anemia Virus (EIAV): what has HIV?s country cousin got to tell us?

“…A subunit vaccine enriched in EIAV envelope glycoproteins not only failed to protect the vaccinated ponies against homologous or heterologous strains but had a high potential to enhance viral replication and to exacerbate clinical disease in challenged animals [66]. Disease enhancement has been described in FIV [67,131,144] or CAEV [73,109] vaccine trials. In a similar manner, a recombinant subunit vaccine, containing a baculovirus-expressed EIAVenvelope surface glycoprotein, enhanced the disease in challenged ponies [138,183].…”

Feline Leukemia Virus DNA Vaccine Efficacy Is Enhanced by Coadministration with Interleukin-12 (IL-12) and IL-18 Expression Vectors

“…In practice, however, although the efficacy of these FeLV vaccines has been demonstrated (24,41,45,(55)(56)(57)77), the level of protection has not always been complete (31,38,39,58). Attempts have been made to produce more effective vaccines, using novel adjuvants such as immune-stimulating complexes (51,52) or live virus vectors, including vaccinia virus, canarypox virus, and feline herpesvirus, that contain one or more FeLV genes.…”