Coreceptor use in nonhuman primate models of HIV infection

SIV or SHIV infection of nonhuman primates (NHP) has been used to investigate the impact of coreceptor usage on the composition and dynamics of the CD4+ T cell compartment, mechanisms of disease induction and development of clinical syndrome. As the entire course of infection can be followed, with frequent access to tissue compartments, infection of rhesus macaques with CCR5-tropic SHIVs further allows for study of HIV-1 coreceptor switch after intravenous and mucosal inoculation, with longitudinal and systemic analysis to determine the timing, anatomical sites and cause for the change in envelope glycoprotein and coreceptor preference. Here, we review our current understanding of coreceptor use in NHPs and their impact on the pathobiological characteristics of the infection, and discuss recent advances in NHP studies to uncover the underlying selective pressures for the change in coreceptor preference in vivo

Mucosal transmissibility, disease induction and coreceptor switching of R5 SHIVSF162P3N molecular clones in rhesus macaques

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. Results: 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. Conclusions: 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

Full-length genome sequences of two SARS-like coronaviruses in horseshoe bats and genetic variation analysis

Bats were recently identified as natural reservoirs of SARS-like coronavirus (SL-CoV) or SARS coronavirus-like virus. These viruses, together with SARS coronaviruses (SARS-CoV) isolated from human and palm civet, form a distinctive cluster within the group 2 coronaviruses of the genus Coronavirus, tentatively named group 2b (G2b). In this study, complete genome sequences of two additional group 2b coronaviruses (G2b-CoVs) were determined from horseshoe bat Rhinolophus ferrumequinum (G2b-CoV Rf1) and Rhinolophus macrotis (G2b-CoV Rm1). The bat G2b-CoV isolates have an identical genome organization and share an overall genome sequence identity of 88–92 % among themselves and between them and the human/civet isolates. The most variable regions are located in the genes encoding nsp3, ORF3a, spike protein and ORF8 when bat and human/civet G2b-CoV isolates are compared. Genetic analysis demonstrated that a diverse G2b-CoV population exists in the bat habitat and has evolved from a common ancestor of SARS-CoV

Fitness Disadvantage of Transitional Intermediates Contributes to Dynamic Change in the Infecting-Virus Population during Coreceptor Switch in R5 Simian/Human Immunodeficiency Virus-Infected Macaques▿

Fitness disadvantage of the transitional intermediates compared to the initial R5 viruses has been suggested to constitute one of the blockades to coreceptor switching, explaining the late appearance of X4 viruses. Using a simian model for human immunodeficiency virus type 1 (HIV-1) coreceptor switching, we demonstrate in this study that similar molecular evolutionary pathways to coreceptor switch occur in more than one R5 simian/human immunodeficiency virus (SHIV)SF162P3N-infected macaque. In infected animals where multiple pathways for expansion or switch to CXCR4 coexist, fitness of the transitional intermediates in coreceptor usage efficiency influences their outgrowth and representation in the infecting virus population. Dualtropic and X4 viruses appear at different disease stages, but they have lower entry efficiency than the coexisting R5 strains, which may explain why they do not outcompete the R5 viruses. Similar observations were made in two infected macaques with coreceptor switch, providing in vivo evidence that fitness disadvantage is an obstacle to X4 emergence and expansion

Different Tempo and Anatomic Location of Dual-Tropic and X4 Virus Emergence in a Model of R5 Simian-Human Immunodeficiency Virus Infection▿

We previously reported coreceptor switch in rhesus macaques inoculated intravenously with R5 simian-human immunodeficiency virus SF162P3N (SHIVSF162P3N). Whether R5-to-X4 virus evolution occurs in mucosally infected animals and in which anatomic site the switch occurs, however, were not addressed. We herein report a change in coreceptor preference in macaques infected intrarectally with SHIVSF162P3N. The switch occurred in infected animals with high levels of virus replication and undetectable antiviral antibody response and required sequence changes in the V3 loop of the gp120 envelope protein. X4 virus emergence was associated with an accelerated drop in peripheral CD4+ T-cell count but followed rather than preceded the onset of CD4+ T-cell loss. The conditions, genotypic requirements, and patterns of coreceptor switch in intrarectally infected animals were thus remarkably consistent with those found in macaques infected intravenously. They also overlapped with those reported for humans, suggestive of a common mechanism for coreceptor switch in the two hosts. Furthermore, two independent R5-to-X4 evolutionary pathways were identified in one infected animal, giving rise to dual-tropic and X4 viruses which differed in switch kinetics and tissue localization. The dual-tropic switch event predominated early, and the virus established infection in multiple tissues sites. In contrast, the switch to X4 virus occurred later, initiating and expanding mainly in peripheral lymph nodes. These findings help define R5 SHIVSF162P3N infection of rhesus macaques as a model to study the mechanistic basis, dynamics, and sites of HIV-1 coreceptor switch

Difference in Receptor Usage between Severe Acute Respiratory Syndrome (SARS) Coronavirus and SARS-Like Coronavirus of Bat Origin▿

Severe acute respiratory syndrome (SARS) is caused by the SARS-associated coronavirus (SARS-CoV), which uses angiotensin-converting enzyme 2 (ACE2) as its receptor for cell entry. A group of SARS-like CoVs (SL-CoVs) has been identified in horseshoe bats. SL-CoVs and SARS-CoVs share identical genome organizations and high sequence identities, with the main exception of the N terminus of the spike protein (S), known to be responsible for receptor binding in CoVs. In this study, we investigated the receptor usage of the SL-CoV S by combining a human immunodeficiency virus-based pseudovirus system with cell lines expressing the ACE2 molecules of human, civet, or horseshoe bat. In addition to full-length S of SL-CoV and SARS-CoV, a series of S chimeras was constructed by inserting different sequences of the SARS-CoV S into the SL-CoV S backbone. Several important observations were made from this study. First, the SL-CoV S was unable to use any of the three ACE2 molecules as its receptor. Second, the SARS-CoV S failed to enter cells expressing the bat ACE2. Third, the chimeric S covering the previously defined receptor-binding domain gained its ability to enter cells via human ACE2, albeit with different efficiencies for different constructs. Fourth, a minimal insert region (amino acids 310 to 518) was found to be sufficient to convert the SL-CoV S from non-ACE2 binding to human ACE2 binding, indicating that the SL-CoV S is largely compatible with SARS-CoV S protein both in structure and in function. The significance of these findings in relation to virus origin, virus recombination, and host switching is discussed