Degenerate recognition of MHC class I molecules with Bw4 and Bw6 motifs by a killer cell Ig-like receptor 3DL expressed by macaque NK cells

The killer cell immunoglobulin-like receptors (KIRs) expressed on the surface of natural killer (NK) cells recognize specific major histocompatibility complex class I (MHC-I) molecules and regulate NK cell activities against pathogen-infected cells and neoplasia. In human immunodeficiency virus (HIV) infection, survival is linked to host KIR and MHC-I genotypes. In the simian immunodeficiency virus (SIV) macaque model, however, the role of NK cells is unclear due to the lack of information on KIR-MHC interactions. Here, we describe the first characterization of a KIR-MHC interaction in pig-tailed macaques (Macaca nemestrina). Initially, we identified three distinct subsets of macaque NK cells that stained ex vivo with macaque MHC-I tetramers loaded with SIV peptides. We then cloned cDNAs corresponding to 15 distinct KIR3D alleles. One of these, KIR049-4, was an inhibitory KIR3DL that bound MHC-I tetramers and prevented activation, degranulation and cytokine production by macaque NK cells after engagement with specific MHC-I molecules on the surface of target cells. Furthermore, KIR049-4 recognized a broad range of MHC-I molecules carrying not only the Bw4 motif but also Bw6 and non-Bw4/Bw6 motifs. This degenerate, yet peptide-dependent, MHC reactivity differs markedly from the fine specificity of human KIRs

Induction of Disease by a Molecularly Cloned Highly Pathogenic Simian Immunodeficiency Virus/Human Immunodeficiency Virus Chimera Is Multigenic

One of three full-length infectious molecular clones of SHIV(DH12R), designated SHIV(DH12R-CL-7) and obtained from productively infected rhesus monkey peripheral blood mononuclear cells, directed rapid and irreversible loss of CD4(+) T cells within 3 weeks of its inoculation into Indian rhesus monkeys. Induction of complete CD4(+) T-cell depletion by SHIV(DH12R-CL-7) was found to be dependent on inoculum size. The acquisition of this pathogenic phenotype was accompanied by the introduction of 42 amino acid substitutions into multiple genes of parental nonpathogenic SHIV(DH12). Transfer of the entire SHIV(DH12R-CL-7) env gene into the genetic background of nonpathogenic SHIV(DH12) failed to confer the rapid CD4(+) T-lymphocyte-depleting syndrome; similarly, the substitution of gag plus pol sequences from SIV(smE543) for analogous SIV(mac239) genes in SHIV(DH12R-CL-7) attenuated the pathogenic phenotype. Amino acid changes affecting multiple viral genes are necessary, but insufficient by themselves, to confer the prototypically rapid and irreversible CD4(+) T-cell-depleting phenotype exhibited by molecularly cloned SHIV(DH12R-CL-7)

Early Control of Highly Pathogenic Simian Immunodeficiency Virus/Human Immunodeficiency Virus Chimeric Virus Infections in Rhesus Monkeys Usually Results in Long-Lasting Asymptomatic Clinical Outcomes

In contrast to simian immunodeficiency viruses (SIVs), which induce immunodeficiency over a 1- to 2-year period, highly pathogenic simian-human immunodeficiency viruses (SHIVs) cause an irreversible and systemic depletion of CD4(+) T lymphocytes in macaque monkeys within weeks of inoculation. Nonetheless, the seemingly more aggressive SHIVs have proven to be easier to control by the same vaccine regimens which fail to contain SIV. Because early events during in vivo infections may determine both the pathogenic consequences of the challenge virus and its sensitivity to interventions that prevent disease, we have evaluated the effects of inoculum size and a potent antiretroviral drug on the development of disease in monkeys infected with SHIV(DH12R). The results obtained show that in a majority of inoculated animals, suppression of SHIV replication during the first 2 weeks of infection, which prevents complete loss of CD4(+) T cells, leads to very low to undetectable postpeak viremia and an asymptomatic clinical course for periods up to 4 years

Rapid and Irreversible CD4(+) T-Cell Depletion Induced by the Highly Pathogenic Simian/Human Immunodeficiency Virus SHIV(DH12R) Is Systemic and Synchronous

Highly pathogenic simian/human immunodeficiency virus chimeric viruses are known to induce a rapid, irreversible depletion of CD4(+) T lymphocytes in the peripheral blood of acutely infected macaque monkeys. To more fully assess the systemic effects of this primary virus infection, specimens were collected serially between days 3 and 21 postinfection from variety of lymphoid tissues (lymph nodes, thymus, and spleen) and gastrointestinal tract and examined by DNA and RNA PCR, in situ hybridization, and immunohistochemical assays. In addition, the lymphoid tissues were evaluated by fluorescence-activated cell sorting. Virus infection was initially detected by DNA PCR on day 3 postinfection in lymph node samples and peaked on day 10 in the T-lymphocyte-rich areas of this tissue. CD4(+) T-cell levels remained stable through day 10 in several lymphoid tissue specimens examined but fell precipitously between days 10 and 21. In situ terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling (TUNEL) assays revealed the accumulation of apoptotic cells during the second week of infection in both lymph nodes and thymus, which colocalized, to a large extent, to sites of both virus replication and CD4(+) T-lymphocyte loss

Preexposure passive transfer predicts plasma antibody levels prevent HIV-I aquisition

Background: It is widely appreciated that effective human vaccines directed against viral pathogens elicit neutralizing antibodies (NAbs). During the past four years, a new generation of potent broadly reacting neutralizing monoclonal antibodies (mAbs) have been isolated from HIV-I infected individuals. These mAbs typically exhibit great breadth and potency against heterologous HIV isolates when assayed for neutralization in vitro. The passive transfer of anti-HIV l neutralizing antibodies conferring sterilizing immunity to macaques has been used to determine the plasma neutralization titers, which must be present at the time of exposure to prevent acquisition of SIV/HIV chimeric virus (SHIV) infections. Methods: In this study, five recently isolated potent and broadly acting anti-HIV neutralizing mAbs, interacting with the HIV l gp 120 CD4 binding site (VRCO I, 45-46 m^2 and 3BNC 117) or dependent on the gp120 N332 glycan, (10-1074 and PGTl2l) were individually administered to 60 rhesus monkeys, which were challenged intrarectally 24 hours later with either of two different R5-tropic SHIVs. Results: Of the 5 neutralizing mAbs evaluated, PGT121 was clearly the most effective against both viruses. In addition to measuring the plasma concentrations of the different mAbs at the time of challenge and their respective in vivo half lives, the corresponding protective neutralization titers were also determined. By combining the results obtained from 60 challenged animals, we determined that the protective neutralization titer in plasma preventing virus acquisition in 50% of the exposed monkeys was approximately 1:100. Conclusion: These results are informative for establishing a threshold level of protective neutralizing activity to be induced by a prophylactic HIV I vaccine

The Expression of Functional Vpx during Pathogenic SIVmac Infections of Rhesus Macaques Suppresses SAMHD1 in CD4⁺ Memory T Cells

<div><p>For nearly 20 years, the principal biological function of the HIV-2/SIV Vpx gene has been thought to be required for optimal virus replication in myeloid cells. Mechanistically, this Vpx activity was recently reported to involve the degradation of Sterile Alpha Motif and HD domain-containing protein 1 (SAMHD1) in this cell lineage. Here we show that when macaques were inoculated with either the T cell tropic SIVmac239 or the macrophage tropic SIVmac316 carrying a Vpx point mutation that abrogates the recruitment of DCAF1 and the ensuing degradation of endogenous SAMHD1 in cultured CD4⁺ T cells, virus acquisition, progeny virion production in memory CD4⁺ T cells during acute infection, and the maintenance of set-point viremia were greatly attenuated. Revertant viruses emerging in two animals exhibited an augmented replication phenotype in memory CD4⁺ T lymphocytes both <i>in vitro</i> and <i>in vivo</i>, which was associated with reduced levels of endogenous SAMHD1. These results indicate that a critical role of Vpx <i>in vivo</i> is to promote the degradation of SAMHD1 in memory CD4⁺ T lymphocytes, thereby generating high levels of plasma viremia and the induction of immunodeficiency.</p></div

SIVs deficient in degrading SAMHD1 in memory CD4⁺ T cells exhibit an attenuated replication phenotype in inoculated rhesus macaques.

<p>Rhesus macaques were inoculated intrarectally with 1 x 10⁴ TCID₅₀ of SIVmac239 WT or SIVmac239 X-Q76A derivatives (A and C) or 1 x 10³ TCID₅₀ of SIVmac316 WT or the SIVmac316X-Q76A derivatives (B and D). The infectious virus titers in the inocula were determined by end-point dilution using SAMHD1 negative SupT1-R5 cells to avoid suppressive effects of SAMHD1 restriction. Plasma viral copies/ml are shown in panel A and C. Memory CD4+ T cell counts/μl are shown in panel C and D. Black curves: WT virus; blue curves: putative revertant Vpx mutants; red curves: non-revertant Vpx mutants. (E) Amino acid substitutions present in the starting Q76A Vpx mutant virus or in the putative revertant virus populations present in the plasmas of macaques K42 and JAX4 at week 35 PI, based on SGA (see <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1004928#ppat.1004928.g006" target="_blank">Fig 6</a>) are shown. The locations of the three helical domains of SIVmac Vpx are indicated.</p

Infection of rhesus macaques with WT SIVmac and Q76A Vpx SIVmac mutants.

<p>Infection of rhesus macaques with WT SIVmac and Q76A Vpx SIVmac mutants.</p