[Show abstract][Hide abstract] ABSTRACT: Although most viral infections cause minor, if any, symptoms, a certain number result in serious illness. Viral disease symptoms result both from direct viral replication within host cells and from indirect immunopathological consequences. Dendritic cells (DCs) are key determinants of viral disease outcome; they activate immune responses during viral infection and direct T cells toward distinct T helper type responses. Certain viruses are able to skew cytokine secretion by DCs inducing and/or downregulating the immune system with the aim of facilitating and prolonging release of progeny. Thus, the interaction of DCs with viruses most often results in the absence of disease or complete recovery when natural functions of DCs prevail, but may lead to chronic illness or death when these functions are outmanoeuvred by viruses in the exploitation of DCs.
[Show abstract][Hide abstract] ABSTRACT: T lymphocyte helper (Th) responses start from the activation of naive Th0 cells that get polarized towards Th1, Th2, Treg and Th17. Such polarization is achieved by delivering activation stimuli to naive T cells in the presence of given cytokines and by triggering certain receptors rather than others; indeed, the cytokine conditioning environment where cells get their activation signal is considered pivotal in determining the quality of the T cell response, and viruses seem to exert at least part of their influence on the antiviral response through cytokines. Indeed, the direction of polarization, and immune reactivity in general, have long been known to be influenced by viral infections. Because dendritic cells (DCs) not only start a response by Th0 but are also in charge of polarizing the Th immune response, they are also key determinants of the pathogenetic outcome of viral infection.
No preview · Article · Jul 2009 · Current Immunology Reviews
[Show abstract][Hide abstract] ABSTRACT: Dendritic cells are the only antigen-presenting cells that can present exogenous antigens to both helper and cytolytic T cells and prime Th1-type or Th2-type cellular immune responses. Given their unique immune functions, dendritic cells are considered attractive "live adjuvants" for vaccination and immunotherapy against cancer and infectious diseases. The present study was carried out to assess whether the reinjection of autologous monocyte-derived dendritic cells loaded with an aldithriol-2-inactivated primary isolate of feline immune deficiency virus (FIV) was able to elicit protective immune responses against the homologous virus in naive cats. Vaccine efficacy was assessed by monitoring immune responses and, finally, by challenge with the homologous virus of vaccinated, mock-vaccinated, and healthy cats. The outcome of challenge was followed by measuring cellular and antibody responses and viral and proviral loads and quantitating FIV by isolation and a count of CD4(+)/CD8(+) T cells in blood. Vaccinated animals exhibited clearly evident FIV-specific peripheral blood mononuclear cell proliferation and antibody titers in response to immunization; however, they became infected with the challenge virus at rates comparable to those of control animals.
[Show abstract][Hide abstract] ABSTRACT: Immunotherapy of feline immunodeficiency virus (FIV)-infected cats with monocyte-derived dendritic cells (MDCs) loaded with aldrithiol-2 (AT2)-inactivated homologous FIV was performed. Although FIV-specific lymphoproliferative responses were markedly increased, viral loads and CD4+ T cell depletion were unaffected, thus indicating that boosting antiviral cell-mediated immunity may not suffice to modify infection course appreciably.
[Show abstract][Hide abstract] ABSTRACT: A more or less pronounced resistance to superinfection by a second strain of the infecting virus has been observed in many
lentivirus-infected hosts. We used a chimeric feline immunodeficiency virus (FIV), designated FIVχ, containing a large part of the env gene of a clade B virus (strain M2) and all the rest of the genome of a clade A virus (a p34TF10 molecular clone of the Petaluma
strain modified to grow in lymphoid cells), to gain insights into such resistance. FIVχ was infectious and moderately pathogenic for cats and in vitro exhibited the neutralization specificity of the env donor. The experiments performed were bidirectional, in that cats preinfected with either parental virus were challenged
with FIVχ and vice versa. The preinfected animals were partially or completely protected relative to what was observed in naïve control
animals, most likely due, at least in part, to the circumstance that in all the preinfecting/challenge virus combinations
examined, the first and the second virus shared significant viral components. Based on the proportions of complete protection
observed, the role of a strongly matched viral envelope appeared to be modest and possibly dependent on the time interval
between the first and the second infection. Furthermore, complete protection and the presence of measurable neutralizing antibodies
capable of blocking the second virus in vitro were not associated.
Full-text · Article · Nov 2007 · Journal of Virology
[Show abstract][Hide abstract] ABSTRACT: During type 1 human immunodeficiency virus infection, not only can dendritic cells (DCs) prime T cells against the virus, but they can also infect them in trans. Feline AIDS is caused by feline immunodeficiency virus (FIV) and is considered a model for the human illness because the two diseases have many features in common. Little is known about the interaction of feline DCs with FIV; therefore, this study attempts to tackle such an issue. Infection of feline monocyte-derived DCs (MDDCs) was attempted by spinoculation with FIV strains Petaluma (FIV-Pet) and M2. FIV-Pet was released rapidly in the supernatants of both infected MDDCs and activated T cells after spinoculation. It is shown that FIV-Pet was produced by MDDCs by monitoring viral content in the supernatants of infected MDDCs, by intracellular staining for p25 and by showing its cytopathic effect. Although activated T cells were better substrates for FIV replication, leading to prolonged viral shedding, both immature MDDCs and MDDCs matured with lipopolysaccharide supported virus production, mostly during the first 2 days after infection. At later times, FIV induced syncytium formation by MDDCs. Concerning the FIV receptors, MDDCs were shown to be CD134-negative and CXCR4-positive, a phenotype compatible with permissiveness to FIV-Pet. These results also suggest that maturation is not hampered by FIV infection and that virus exposure itself does not induce MDDC maturation. It is also shown that infected MDDCs can infect activated PBMCs efficiently in trans. It is concluded that MDDCs can be infected by FIV, although infection does not appear to influence their functionality.
Full-text · Article · Oct 2007 · Journal of General Virology
[Show abstract][Hide abstract] ABSTRACT: Treatment of feline immunodeficiency virus (FIV) infection has been hampered by the absence of a specific combination antiretroviral treatment (ART). Integrase strand transfer inhibitors (INSTIs) are emerging as a promising new drug class for HIV-1 treatment, and we evaluated the possibility of inhibiting FIV replication using INSTIs.
Phylogenetic analysis of lentiviral integrase (IN) sequences was carried out using the PAUP* software. A theoretical three-dimensional structure of the FIV IN catalytic core domain (CCD) was obtained by homology modeling based on a crystal structure of HIV-1 IN CCD. The interaction of the transferred strand of viral DNA with the catalytic cavity of FIV IN was deduced from a crystal structure of a structurally similar transposase complexed with transposable DNA. Molecular docking simulations were conducted using a genetic algorithm (GOLD). Antiviral activity was tested in feline lymphoblastoid MBM cells acutely infected with the FIV Petaluma strain. Circular and total proviral DNA was quantified by real-time PCR.
The calculated INSTI-binding sites were found to be nearly identical in FIV and HIV-1 IN CCDs. The close similarity of primate and feline lentivirus IN CCDs was also supported by phylogenetic analysis. In line with these bioinformatic analyses, FIV replication was efficiently inhibited in acutely infected cell cultures by three investigational INSTIs, designed for HIV-1 and belonging to different classes. Of note, the naphthyridine carboxamide INSTI, L-870,810 displayed an EC50 in the low nanomolar range. Inhibition of FIV integration in situ was shown by real-time PCR experiments that revealed accumulation of circular forms of FIV DNA within cells treated with L-870,810.
We report a drug class (other than nucleosidic reverse transcriptase inhibitors) that is capable of inhibiting FIV replication in vitro. The present study helped establish L-870,810, a compound successfully tested in human clinical trials, as one of the most potent anti-FIV agents ever tested in vitro. This finding may provide new avenues for treating FIV infection and contribute to the development of a small animal model mimicking the effects of ART in humans.
[Show abstract][Hide abstract] ABSTRACT: Determining which antigen must be included in AIDS vaccines to confer maximum protection is of utmost importance. In primate models, vaccines consisting of or including accessory viral proteins have yielded conflicting results. We investigated the protective potential of the accessory protein ORF-A of feline immunodeficiency virus (FIV) in cats. All three immunization strategies used (protein alone in alum adjuvant, DNA alone, or DNA prime-protein boost) clearly generated detectable immune responses. Upon challenge with ex vivo homologous FIV, ORF-A-immunized cats showed distinct enhancement of acute-phase infection relative to mock-immunized animals given alum or empty vector DNA. This effect was tentatively attributed to increased expression of the FIV receptor CD134 that was observed in the immunized cats. However, at subsequent sampling points that were continued for up to 10 months postchallenge, the average plasma viral loads of the ORF-A-immunized animals were slightly but consistently reduced relative to those of the control animals. In addition, CD4(+) T lymphocytes in the circulation system declined more slowly in immunized animals than in control animals. These findings support the contention that immunization with lentiviral accessory proteins can improve the host's ability to control virus replication and slow down disease progression but also draw attention to the fact that even simple immunogens that eventually contribute to protective activity can transiently exacerbate subsequent lentiviral infections.
Full-text · Article · Oct 2006 · Journal of Virology
[Show abstract][Hide abstract] ABSTRACT: Dendritic cells (DCs) are professional antigen-presenting cells that can prime T cells and polarize the cellular immune response. Because Th1-type immune responses have been connected to success in combating viral infection, a promising therapeutic application of DCs would be their differentiation in vitro and injection back into the host to boost an immune response in infected animals. This study was aimed both at developing a protocol to cultivate feline DCs in the absence of exogenous proteins for their use in vivo and at investigating what might be the most appropriate stimulus to induce their maturation in vitro and finding correlates of maturation. We generated DCs from peripheral blood monocytes in the presence of feline interleukin-4 and granulocyte-macrophage colony stimulating factor, and after 5 days their maturation was induced with either lipopolysaccharide, human recombinant tumor necrosis factor alpha, poly(I:C), or activated feline platelets. After 48 h, their CD14, CD1a, major histocompatibility complex class II, and B7.1 surface expression was analyzed in parallel with their ability to uptake antigen or prime a mixed leukocyte reaction. The results presented show that feline DCs cultured in autologous plasma differentiate and are able to mature in the presence of stimuli similar to the ones currently used for other species. The present work sets the grounds for future use of DCs obtained by the protocol described for in vivo vaccination and immunotherapy of feline immunodeficiency virus-infected cats.
Full-text · Article · Nov 2005 · Clinical and Diagnostic Laboratory Immunology
[Show abstract][Hide abstract] ABSTRACT: The potential of immunotherapy with autologous virus-specific T cells to affect the course of feline immunodeficiency virus
(FIV) infection was explored in a group of specific-pathogen-free cats infected with FIV a minimum of 10 months earlier. Popliteal
lymph node cells were stimulated by cocultivation with UV-inactivated autologous fibroblasts infected with recombinant vaccinia
viruses expressing either FIV gag or env gene products, followed by expansion in interleukin-2. One or two infusions of both Gag- and Env-stimulated cells resulted
in a slow increase in FIV-specific gamma interferon-secreting T cells in the circulation of cats. In the same animals, viral
set points fluctuated widely during the first 2 to 3 weeks after adoptive transfer and then returned to pretreatment levels.
The preexisting viral quasispecies was also found to be modulated, whereas no novel viral variants were detected. Circulating
CD4+ counts underwent a dramatic decline early after treatment. CD4/CD8 ratios remained instead essentially unchanged and eventually
improved in some animals. In contrast, a single infusion of Gag-stimulated cells alone produced no apparent modulations of
[Show abstract][Hide abstract] ABSTRACT: Feline immunodeficiency virus (FIV) made defective in the accessory gene ORF-A were previously shown to be greatly attenuated in its ability to replicate in lymphocytes but to grow normally or near normally in other cell types. Here, we examined whether FIV thus mutated could protect specific pathogen-free cats against challenge with ex vivo fully virulent homologous virus. No reversion of the vaccinating infections to wild type ORF-A was noted over 22 months of in vivo infection. Following challenge, 6/6 unvaccinated control cats became readily and heavily infected. In contrast, 3/9 vaccinees showed no evidence of the challenge virus over a 15-month observation period. In the other vaccinees, the challenge virus was predominant for various periods of time, but pre-existing viral loads and CD4 lymphocyte counts were either unaffected or altered only marginally and transiently. These findings show that ORF-A-defective FIV should be further examined as a candidate live attenuated vaccine.
[Show abstract][Hide abstract] ABSTRACT: An inactivated virus vaccine was prepared from a pathogenic isolate of feline immunodeficiency virus containing a mutation
that eliminated an endocytic sorting signal in the envelope glycoprotein, increasing its expression on virions. Cats immunized
with inactivated preparations of this modified virus exhibited strong titers of antibody to Env by enzyme-linked immunosorbent
assay. Evidence of protection following challenge demonstrated the potential of this approach to lentiviral vaccination.
Full-text · Article · Mar 2005 · Journal of Virology
[Show abstract][Hide abstract] ABSTRACT: The mechanisms whereby feline immunodeficiency virus (FIV) adsorbs and enters into susceptible cells are poorly understood. Here, we investigated the role exerted in such functions by the tryptophan (Trp)-rich motif present membrane-proximally in the ectodomain of the FIV transmembrane glycoprotein. Starting from p34TF10, which encodes the entire genome of FIV Petaluma, we produced 11 mutated clones having the Trp-rich motif scrambled or variously deleted or substituted. All mutated progenies adsorbed normally to cells, but the ones with severe disruptions of the motif failed to generate proviral DNA. In the latter mutants, proviral DNA formation was restored by providing an independent source of intact FIV envelope glycoproteins or by addition of the fusing agent polyethylene glycol, thus clearly indicating that their defect resided primarily at the level of cell entry. In addition, the replication-competent mutants exhibited a generally enhanced susceptibility to selected entry inhibitory synthetic peptides, suggestive of a reduced efficiency of the entry step.
[Show abstract][Hide abstract] ABSTRACT: Fresh isolates of lentiviruses are characterized by an outstanding resistance to antibody-mediated neutralization. By investigating
the changes that occurred in a neutralization-sensitive tissue culture-adapted strain of feline immunodeficiency virus after
it was reinoculated into cats, a previous study had identified two amino acid positions of the surface glycoprotein (residues
481 and 557) which govern broad neutralization resistance (BNR) in this virus. By extending the follow-up of six independently
evolving in vivo variants of such virus for up to 92 months, we now show that the changes at the two BNR-governing positions
not only were remarkably stereotyped but also became fixed in an ordered sequential fashion with the duration of in vivo infection.
In one variant, the two positions were also seen to slowly alternate at determining BNR. Evidence that evolution at the BNR-governing
positions was accompanied, and possibly driven, by changes in the antigenic makeup of the viral surface brought about by the
mutations at such positions is also presented.
Full-text · Article · Dec 2003 · Clinical and Diagnostic Laboratory Immunology
[Show abstract][Hide abstract] ABSTRACT: Feline immunodeficiency virus (FIV) infection of domestic cats represents a valuable system through which to investigate criteria
for antilentiviral vaccines in a natural host species. Here, we examined whether vaccination with a strain of FIV attenuated
as a result of prolonged growth in vitro could protect against a fully virulent, highly heterologous intraclade challenge.
The results indicated that the vaccine virus produced a low-grade infection with no detectable pathological effects and afforded
a long-lasting sterilizing immunity if the challenge was delivered intraperitoneally as cell-free virus but not against a
cell-associated intravaginal challenge. In the latter case, however, the replication and pathological consequences of the
challenge virus were markedly suppressed. Together with similar results obtained in rhesus monkey models, these findings should
give impulse to the development of attenuated FIV vaccines to be tested in controlled studies in field cats. Field studies
may provide answers to some of the existing safety concerns surrounding attenuated AIDS vaccines in humans.
Full-text · Article · Nov 2003 · Journal of Virology
[Show abstract][Hide abstract] ABSTRACT: Feline immunodeficiency virus (FIV) provides a valuable animal model by which criteria for lentivirus control strategies can
be tested. Previous studies have shown that a 20-mer synthetic peptide of the membrane-proximal ectodomain of FIV transmembrane
glycoprotein, designated peptide 59, potently inhibited the growth of tissue culture-adapted FIV in feline fibroblastoid CrFK
cells. In the present report we describe the potential of this peptide to inhibit the replication of primary FIV isolates
in lymphoid cells. Because antiviral activity of peptide 59 was found to map to a short segment containing three conserved
Trp residues, further analyses focused on a derivative of eight amino acids (770W-I777), designated C8. Peptide C8 activity was found to be dependent on conservation of the Trp motif, to be removed from solution
by FIV absorbed onto substrate cells, and to be blocked by a peptide derived from the N-terminal portion of FIV transmembrane
glycoprotein. Structural studies showed that peptide C8 possesses a conformational propensity highly uncommon for peptides
of its size, which may account for its considerable antiviral potency in spite of small size.
Full-text · Article · Apr 2003 · Journal of Virology
[Show abstract][Hide abstract] ABSTRACT: Immunogenicity and protective activity of four cell-based feline immunodeficiency virus (FIV) vaccines prepared with autologous lymphoblasts were investigated. One vaccine was composed of FIV-infected cells that were paraformaldehyde fixed at the peak of viral expression. The other vaccines were attempts to maximize the expression of protective epitopes that might become exposed as a result of virion binding to cells and essentially consisted of cells mildly fixed after saturation of their surface with adsorbed, internally inactivated FIV particles. The levels of FIV-specific lymphoproliferation exhibited by the vaccinees were comparable to the ones previously observed in vaccine-protected cats, but antibodies were largely directed to cell-derived constituents rather than to truly viral epitopes and had very poor FIV-neutralizing activity. Moreover, under one condition of testing, some vaccine sera enhanced FIV replication in vitro. As a further limit, the vaccines proved inefficient at priming animals for anamnestic immune responses. Two months after completion of primary immunization, the animals were challenged with a low dose of homologous ex vivo FIV. Collectively, 8 of 20 vaccinees developed infection versus one of nine animals mock immunized with fixed uninfected autologous lymphoblasts. After a boosting and rechallenge with a higher virus dose, all remaining animals became infected, thus confirming their lack of protection.
Full-text · Article · Aug 2002 · Journal of Virology
[Show abstract][Hide abstract] ABSTRACT: A functional ORF-A is essential for efficient feline immunodeficiency virus replication in lymphocytes. We have characterized a series of mutants of the Petaluma strain, derived from p34TF10 and having different combinations of stop codons and increasingly long deletions in ORF-A. Six clones proved fully replicative in fibroblastoid Crandell feline kidney cells and monocyte-derived macrophage cultures but failed to replicate in T cell lines and primary lymphoblasts. Cats inoculated with three selected mutants had considerably milder infections than controls given intact ORF-A virus. In vivo, the mutants maintained growth properties similar to those in vitro for at least 7 months, except that replication in lymphoid cells was strongly reduced but not ablated. One mutant underwent extensive ORF-A changes without, however, reverting to wild-type. Antiviral immune responses were feeble in all cats, suggesting that viral loads were too low to represent a sufficiently powerful antigenic stimulus.
[Show abstract][Hide abstract] ABSTRACT: We previously reported that, upon reinoculation into cats, a neutralization-sensitive, tissue culture-adapted strain of feline immunodeficiency virus constantly reverted to the broad neutralization resistance typical of primary virus isolates and identified residue 481 in the V4 region of the surface glycoprotein as a key determinant of the reversion. Here, we found that well-characterized immune sera, obtained from cats in which such reversion had occurred, selected in tissue culture in favor of virus variants that also had a neutralization-resistant phenotype and had amino acid 481 changed, thus indicating that the host's humoral immune response is capable of driving the reversion in the absence of other intervening factors. In contrast, a second group of immune sera, elicited by a virus variant that had already reverted to neutralization resistance in independent cats, induced the emergence of escape mutants lacking broad neutralization resistance and neutralized fewer virus variants. It is proposed that the viral variants used to produce the two sets of sera may have generated different antibody repertoires.
Full-text · Article · Oct 2001 · Journal of Virology