We previously reported the derivation of a CCR5 (R5)-tropic pathogenic strain SHIVSF162P3. Here, we show that a simian-HIV (SHIV) molecular clone expressing the entire env gp160 of SHIVSF162P3, termed SHIV P3gp160, could fully recapitulate the in vivo replicative characteristics of the parental isolate. SHIV P3gp160 is mucosally transmissible, preferentially depletes memory CD4 T cells, and induced simian AIDS in 2 of 6 infected macaques. The availability of an infectious R5 SHIV molecular clone that can be transmitted mucosally and causes disease provides an important reagent for studies of lentiviral pathogenesis and AIDS vaccine research.
[Show abstract][Hide abstract] ABSTRACT: Passive transfer of antibodies can be protective in the simian human immunodeficiency virus (SHIV) - rhesus macaque challenge model. The human monoclonal antibody IgG1 b12 neutralizes human immunodeficiency type 1 (HIV-1) in vitro and protects against challenge by SHIV. Our hypothesis is that neutralizing antibodies can only completely inactivate a relatively small number of infectious virus.
We have used GHOST cell assays to quantify individual infectious events with HIV-1SF162 and its SHIV derivatives: the relatively neutralization sensitive SHIVSF162P4 isolate and the more resistant SHIVSF162P3. A plot of the number of fluorescent GHOST cells with increasing HIV-1SF162 dose is not linear. It is likely that with high-dose inocula, infection with multiple virus produces additive fluorescence in individual cells. In studies of the neutralization kinetics of IgG1 b12 against these isolates, events during the absorption phase of the assay, as well as the incubation phase, determine the level of neutralization. It is possible that complete inactivation of a virus is limited to the time it is exposed on the cell surface. Assays can be modified so that neutralization of these very low doses of virus can be quantified. A higher concentration of antibody is required to neutralize the same dose of resistant SHIVSF162P3 than the sensitive SHIVSF162P4. In the absence of selection during passage, the density of the CCR5 co-receptor on the GHOST cell surface is reduced. Changes in the CD4 : CCR5 density ratio influence neutralization.
Low concentrations of IgG1 b12 completely inactivate small doses of the neutralization resistant SHIV SF162P3. Assays need to be modified to quantify this effect. Results from modified assays may predict protection following repeated low-dose shiv challenges in rhesus macaques. It should be possible to induce this level of antibody by vaccination so that modified assays could predict the outcome of human trials.
PLoS ONE 08/2013; 8(8):e72702. DOI:10.1371/journal.pone.0072702 · 3.23 Impact Factor
"Molecular clones of subtype B  and subtype C [60,61] R5 SHIVs that are mucosally transmissible, highly replication competent and capable of inducing AIDS in rhesus macaques have been described, but expansion or conversion to CXCR4 usage has not been observed. In this regard, we show that both R5 SHIVSF162P3N molecular clones exhibited coreceptor switching that followed the 11/25 rule derived from subtype B HIV-1 . "
[Show abstract][Hide abstract] ABSTRACT: Background
Mucosally transmissible and pathogenic CCR5 (R5)-tropic simian-human immunodeficiency virus (SHIV) molecular clones are useful reagents to identity neutralization escape in HIV-1 vaccine experiments and to study the envelope evolutionary process and mechanistic basis for coreceptor switch during the course of natural infection.
We observed progression to AIDS in rhesus macaques infected intrarectally with molecular clones of the pathogenic R5 SHIVSF162P3N isolate. Expansion to CXCR4 usage was documented in one diseased macaque that mounted a neutralizing antibody response and in another that failed to do so, with the latter displaying a rapid progressor phenotype. V3 loop envelop glycoprotein gp120 sequence changes that are predictive of a CXCR4 (X4)-using phenotype in HIV-1 subtype B primary isolates, specifically basic amino acid substations at positions 11 (S11R), 24 (G24R) and 25 (D25K) of the loop were detected in the two infected macaques. Functional assays showed that envelopes with V3 S11R or D25K mutation were dual-tropic, infecting CD4+ target cells that expressed either the CCR5 or CXCR4 coreceptor. And, consistent with findings of coreceptor switching in macaques infected with the pathogenic isolate, CXCR4-using variant was first detected in the lymph node of the chronically infected rhesus monkey several weeks prior to its presence in peripheral blood. Moreover, X4 emergence in this macaque coincided with persistent peripheral CD4+ T cell loss and a decline in neutralizing antibody titer that are suggestive of immune deterioration, with macrophages as the major virus-producing cells at the end-stage of disease.
The data showed that molecular clones derived from the R5 SHIVSF162P3N isolate are mucosally transmissible and induced disease in a manner similar to that observed in HIV-1 infected individuals, providing a relevant and useful animal infection model for in-depth analyses of host selection pressures and the env evolutionary changes that influence disease outcome, coreceptor switching and vaccine escape.
"Sequence analysis of SIV RT (551 bp; amino acids 52–234) was done using an RT-nested PCR method previously described (Subbarao et al., 2006). Env sequences (1570 bp; nucleotides 230–2030 of HIV −1 env) were also generated by RT-nested PCR as described (Hsu et al., 2005). PCR products were sequenced using an ABI 3130 × Genetic Analyzer. "
[Show abstract][Hide abstract] ABSTRACT: Transmission of drug-resistant HIV has been widely documented. We generated tenofovir (TFV)- and emtricitabine (FTC)-resistant SHIV162P3 mutants that can be used to investigate the transmission efficiency of drug-resistant viruses and their impact on the efficacy of pre-exposure prophylaxis. Both SHIV162p3(M184V) and SHIV162p3(K65R) replicated in vitro at high titers. Drug resistance profiles were similar to those seen in HIV. Virus infectivity to virion particle ratios were 4- and 10-fold lower in SHIV162p3(M184V) and SHIV162p3(K65R), compared to a concurrently generated WT SHIV162p3, respectively. Mucosal transmissibility studies using a repeat low-dose macaque model of rectal and vaginal transmission showed that both mutants were able to efficiently infect macaques only after the dose was increased to adjust for fitness reductions due to K65R and M184V. Our results in limited number of macaques suggest that the reduction in fitness due to M184V and K65R decreases virus transmissibility, and identify in vitro infectivity parameters that associate with mucosal transmissibility.
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