Vaccination with experimental feline immunodeficiency virus vaccines, based on autologous infected cells, elicits enhancement of homologous challenge infection.

Cats were vaccinated with fixed autologous feline immunodeficiency virus (FIV)-infected cells in order to present viral proteins to the immune system of individual cats in an MHC-matched fashion. Upon vaccination, a humoral response against Gag was induced. Furthermore, virus-neutralizing antibodies were detected in a Crandell feline kidney cell-based neutralization assay, but not in a neutralization assay based on primary peripheral blood mononuclear cells.

Accelerated viraemia in cats vaccinated with fixed autologous FIV-infected cells.

We have vaccinated cats with fixed autologous FIV infected PBMC to determine whether autologous presentation of antigen is capable of inducing a protective immune response against homologous challenge. To this end autologous PBMC were infected with a FIV molecular clone (19k1). When infection was established, cells were inactivated by dialysis against paraformaldehyde.

Feline immunodeficiency virus subunit vaccines that induce virus neutralising antibodies but no protection against challenge infection.

Three experimental vaccines against feline immunodeficiency virus (FIV), all based on viral antigens presented via immune stimulating complexes (iscoms), were tested for their capacity to induce protection in cats from FIV infection. The respective vaccines consisted of FIV propagated in Crandell feline kidney (CrFK) cells (FIV-iscoms); FIV-iscoms spiked with recombinant vaccinia virus expressed FIV envelope glycoprotein incorporated into iscoms (FIV-iscoms + vGR657x15-iscoms) and vGR657x15-iscoms spiked with recombinant FIV Gag protein incorporated into iscoms (vGR657x15-iscoms + FIV-Gag-iscoms). Simian immunodeficiency virus envelope glycoprotein incorporated into iscoms, iscoms prepared with uninfected CrFK cells, and PBS served as controls.

Salmonella typhimurium aroA recombinants and immune-stimulating complexes as vaccine candidates for feline immunodeficiency virus.

Two experimental feline immunodeficiency virus (FIV) vaccines were tested, either alone or in combination, in four groups of cats (A-D). One vaccine (SL3261-FIV) was composed of live attenuated Salmonella typhimurium aroA (SL3261) strains expressing the capsid (Gag) and part of the envelope (Env) proteins of FIV. The other was composed of FIV Gag and Env proteins incorporated into immune-stimulating complexes (iscom-FIV).

Induction of feline immunodeficiency virus specific antibodies in cats with an attenuated Salmonella strain expressing the Gag protein.

Salmonella typhimurium aroA strains (SL3261), expressing high levels of the Gag protein of feline immunodeficiency virus (FIV) fused with maltose binding protein (SL3261-MFG), were constructed using an invertible promoter system that allows the stable expression of heterologous antigens at levels toxic for bacteria. A SL3261 strain expressing the B subunit of cholera toxin by a similar system (SL3261-CtxB) served as a control in FIV-immunization experiments. Cats immunized once orally or intraperitoneally with SL3261-MFG or SL3261-CtxB all developed serum antibodies to SL3261 lipopolysaccharide and against maltose binding protein or the B subunit of cholera toxin, respectively.

Canine distemper virus from diseased large felids: biological properties and phylogenetic relationships.

Specific pathogen free (SPF) domestic cats were inoculated with tissue homogenate obtained from a Chinese leopard (Panthera pardus japonensis) that had died in a North American zoo from a natural infection with canine distemper virus (CDV). The cats developed a transient cell-associated CDV viraemia along with pronounced lymphopenia but did not show any clinical symptoms. Plasma neutralizing-antibody titres against the homologous CDV (A92-27/4, isolated from the Chinese leopard) were consistently higher than against the CDV vaccine strain 'Bussell'.

Vaccine-induced virus-neutralizing antibodies and cytotoxic T cells do not protect macaques from experimental infection with simian immunodeficiency virus SIVmac32H (J5).

To gain further insight into the ability of subunit vaccines to protect monkeys from experimental infection with simian immunodeficiency virus (SIV), two groups of cynomolgus macaques were immunized with either recombinant SIVmac32H-derived envelope glycoproteins (Env) incorporated into immune-stimulating complexes (iscoms) (group A) or with these SIV Env iscoms in combination with p27gag iscoms and three Nef lipopeptides (group B). Four monkeys immunized with recombinant feline immunodeficiency virus Env iscoms served as controls (group C). Animals were immunized intramuscularly at weeks 0, 4, 10, and 16.

Neutralization of feline immunodeficiency virus by polyclonal feline antibody: simultaneous involvement of hypervariable regions 4 and 5 of the surface glycoprotein.

Sites involved in antibody-mediated neutralization of feline immunodeficiency virus were mapped by reciprocal exchange of envelope fragments or amino acids between molecular clones of feline immunodeficiency virus with different susceptibilities to neutralization by a polyclonal cat serum. Combinations of mutations within HV-4 or within HV-4 and HV-5 changed the susceptibility of the viruses to neutralizing antibody.

Enhancement of feline immunodeficiency virus infection after immunization with envelope glycoprotein subunit vaccines.

Cats were immunized three times with different recombinant feline immunodeficiency virus (FIV) candidate vaccines. Recombinant vaccinia virus (rVV)-expressed envelope glycoprotein with (vGR657) or without (vGR657 x 15) the cleavage site and an FIV envelope bacterial fusion protein (beta-Galactosidase-Env) were incorporated into immune-stimulating complexes or adjuvanted with Quil A. Although all immunized cats developed antibodies against the envelope protein, only the cats vaccinated with the rVV-expressed envelope glycoproteins developed antibodies which neutralized FIV infection of Crandell feline kidney cells.

A determinant of feline immunodeficiency virus involved in Crandell feline kidney cell tropism.

Viral progeny of the molecular clone 19k1 of feline immunodeficiency virus (FIV) can infect feline T-cells but not Crandell feline kidney (CrFK) cells. In contrast, the biological isolate FIV-AM6c, which was CrFK adapted by co-cultivation of FIV-AM6 infected thymocytes with CrFK cells, can infect both thymocytes and CrFK cells. The envelope gene of FIV-AM6c was amplified by polymerase chain reaction using DNA from infected CrFK cells, and subsequently cloned and sequenced.

Two different mutations in the envelope protein of feline immunodeficiency virus allow the virus to escape from neutralization by feline serum antibodies.

Viral progeny of two molecular clones of feline immunodeficiency virus (FIV), 19k1 and 19k32, were tested in a virus neutralization assay. In this assay the infection of thymocytes with FIV19k1 was neutralized by serum S1422, derived from an SPF cat 22 weeks after infection with FIV19k1. We previously reported that a point mutation at position 560 in hypervariable region-5 (HV-5) of 19k1 confers resistance to virus neutralization (Siebelink et al.

Virus neutralization reveals antigenic variation among feline immunodeficiency virus isolates.

By using a focus reduction assay in CrFK feline fibroblast cells, virus neutralizing antibodies (VNA) to feline immunodeficiency virus (FIV) were demonstrated in cats that had been naturally or experimentally infected with FIV. The antigenic relatedness of four strains of FIV, divergent in nucleotide sequence within the env gene, was investigated by neutralization following adaptation of each virus for growth in CrFK cells. Two of the viruses were from The Netherlands (FIV/AM-4 and AM-6), one was from the U.

Removal of the cleavage site of recombinant feline immunodeficiency virus envelope protein facilitates incorporation of the surface glycoprotein in immune-stimulating complexes.

Recombinant vaccinia viruses were constructed that expressed the complete env gene of feline immunodeficiency virus with or without the nucleotide sequence encoding the cleavage site between the surface (SU) protein and the transmembrane (TM) protein. The removal of this cleavage site resulted in the expression of a 150K protein that was processed into a 130K protein and was not cleaved into the SU and the TM proteins. Removal of the cleavage site also facilitated incorporation of the SU protein in immune-stimulating complexes (iscoms).

gag- and env-specific serum antibodies in cats after natural and experimental infection with feline immunodeficiency virus.

In order to monitor the antibody response to feline immunodeficiency virus (FIV) in cats, following experimental and natural infection, enzyme-linked immunosorbent assays (ELISAs) were developed using recombinant env and gag proteins and p24-specific monoclonal antibodies. It was shown that in experimentally infected cats an env protein-specific antibody response was directly followed by a gag protein-specific response. Furthermore, an ELISA for the detection of env protein-specific serum antibodies proved more sensitive in identifying experimentally and naturally infected cats than ELISAs demonstrating gag protein-specific antibodies.

Neutralizing antibodies in cats infected with feline immunodeficiency virus.

Sera from cats experimentally infected with five isolates of feline immunodeficiency virus (FIV) from various geographical regions and from FIV enzyme-linked immunosorbent assay-seropositive field cats from four European countries neutralized the Petaluma strain of FIV (FIV-P), originally isolated in California, at high titers. In addition, FIV-P and a European isolate proved equally susceptible to neutralization by all sera tested. Coupled with observations by Fevereiro et al.

A single amino acid substitution in hypervariable region 5 of the envelope protein of feline immunodeficiency virus allows escape from virus neutralization.

We infected a specific-pathogen-free cat (cat 14) with molecularly cloned feline immunodeficiency virus clone 19k1 (FIV19k1 [K. H. J.

Simple in vitro methods for titrating feline immunodeficiency virus (FIV) and FIV neutralizing antibodies.

The feline immunodeficiency virus (FIV) readily produced syncytia in Crandell feline kidney (CrFK) cells adapted to a medium containing 0.5% fetal calf serum, a variety of growth factors and other supplements. This finding has been exploited to develop simple and sensitive virus titration and neutralization assays.

Isolation and partial characterization of infectious molecular clones of feline immunodeficiency virus obtained directly from bone marrow DNA of a naturally infected cat.

Replication-competent molecular clones of feline immunodeficiency virus (FIV) were isolated directly from the DNA of bone marrow cells of a naturally FIV-infected cat. After transfection in a feline kidney cell line (CrFK) and subsequent cocultivation with peripheral blood mononuclear cells (PBMC), the viral progeny of the clones was infectious for PBMC but not for CrFK cells. PBMC infected with these clones showed syncytium formation, a decrease in cell viability, and gradual loss of CD4+ cells.

Feline immunodeficiency virus (FIV) infection in the cat as a model for HIV infection in man: FIV-induced impairment of immune function.

To assess the value of feline immunodeficiency virus (FIV) infection as a model for human immunodeficiency virus (HIV) infection in man, we studied the impairment of certain immunological functions following natural or experimental FIV infection. Proliferative responses of peripheral blood mononuclear cells (PBMC) from symptomatic and asymptomatic cats after naturally or experimentally acquired FIV infection, induced by activation with the mitogens concanavalin A, pokeweed mitogen, or lipopolysaccharide or by stimulation with human interleukin-2 (IL-2), were significantly lower than the proliferative responses found with PBMC from noninfected control cats. Also IL-2 production levels of mitogen-activated PBMC from naturally infected symptomatic cats were significantly reduced.

Production and characterization of a human monoclonal antibody, reactive with a conserved epitope on gp41 of human immunodeficiency virus type I.

A human Epstein-Barr virus-transformed lymphoblastoid B-cell line was generated from peripheral blood mononuclear cells (PBMC) of an asymptomatic human immunodeficiency virus type I (HIV-1) seropositive donor, which produces a human monoclonal antibody K14 (IgG1), reactive with an epitope on the transmembrane part (gp41) of the envelope glycoprotein of HIV-1. This monoclonal antibody reacts with a lysate of HIV-1-infected H9 cells, gradient purified HIV-1, and a vaccinia recombinant HIV-1 gp160 protein, but not with HIV-2 antigens in an enzyme-linked immunosorbent assay (ELISA). When used as an immobilized ligand in an immune affinity column, K14 selectively purifies gp41 from a HIV-1-infected H9 cell lysate.

Impairment of in vitro immune responses occurs within 3 months after HIV-1 seroconversion.

In a previous study we have shown that peripheral blood mononuclear cells (PBMC) from asymptomatic HIV-seropositive male homosexuals, who had seroconverted more than 2 years before, were unable to mount a secondary immune response in vitro to certain viral and bacterial antigens. We have extended this study by investigating the secondary immune responses of five male homosexuals, who, by regular screening, were found to have seroconverted for HIV-1 during the preceding 3 months and were subsequently vaccinated with tetanus toxoid and poliovirus vaccine. Six weeks after the booster vaccination, PBMC of the five recently seroconverted individuals were assayed for in vitro mitogen or recall antigen-induced antibody synthesis and lymphocyte proliferation.

[Prevalence of FTLV (feline T-lymphotropic lentivirus) infections in cats in The Netherlands and in West Germany].

The prevalence in the Netherlands and the Free Republic of Germany (FRG) of the newly discovered retrovirus of cats, which causes an immunodeficiency syndrome in this species and is termed feline T-lymphotropic lentivirus (FTLV), was estimated by conducting a serological survey among cats with different histories of disease. In an enzyme-linked immunosorbent assay (Petcheck, Agritech Trademark, Portland, USA) 265 samples of cats with chronic disease symptoms, and 78 samples of clinically healthy cats in the Netherlands, and 138 samples of cats with chronic disease symptoms in the FRG, were tested for the presence of FTLV-specific antibodies. All these samples had been taken from cats which were negative for FeLV antigen in the immunofluorescence test.

Analysis of the antigen- and mitogen-induced differentiation of B lymphocytes from asymptomatic human immunodeficiency virus-seropositive male homosexuals. Discrepancy between T cell-dependent and T cell-independent activation.

Five asymptomatic human immunodeficiency virus (HIV)-seropositive male homosexuals were immunized with the recall antigens tetanus toxoid (TT) and the three types of poliovirus present in diphtheria, tetanus, and polio vaccine. Four weeks after immunization, the in vivo response to booster immunization, the in vitro pokeweed mitogen (PWM)-induced IgG secretion, and the in vitro T cell-dependent and T cell-independent antigen-induced antibody response were assayed. Increase in serum antibody titer to TT and poliovirus was low and normal, respectively.