Conserved CXCR4 usage and enhanced replicative capacity of HIV-2/287, an isolate highly pathogenic in Macaca nemestrina

Population genetics of the Washington National Primate Research Center's (WaNPRC) captive pigtailed macaque (Macaca nemestrina) population

Pigtailed macaques (Macaca nemestrina) provide an important model for biomedical research on human disease and for studying the evolution of primate behavior. The genetic structure of captive populations of pigtailed macaques is not as well described as that of captive rhesus (M. mulatta) or cynomolgus (M. fascicularis) macaques. The Washington National Primate Research Center houses the largest captive colony of pigtailed macaques located in several different housing facilities. Based on genotypes of 18 microsatellite (short tandem repeat [STR]) loci, these pigtailed macaques are more genetically diverse than captive rhesus macaques and exhibit relatively low levels of inbreeding. Colony genetic management facilitates the maintenance of genetic variability without compromising production goals of a breeding facility. The periodic introduction of new founders from specific sources to separate housing facilities at different times influenced the colony's genetic structure over time and space markedly but did not alter its genetic diversity significantly. Changes in genetic structure over time were predominantly due to the inclusion of animals from the Yerkes National Primate Research Center in the original colony and after 2005. Strategies to equalize founder representation in the colony have maximized the representation of the founders' genomes in the extant population. Were exchange of animals among the facilities increased, further differentiation could be avoided. The use of highly differentiated animals may confound interpretations of phenotypic differences due to the inflation of the genetic contribution to phenotypic variance of heritable traits.

Novel TRIM5 isoforms expressed by Macaca nemestrina

The TRIM5 family of proteins contains a RING domain, one or two B boxes, and a coiled-coil domain. The TRIM5alpha isoform also encodes a C-terminal B30.2(SPRY) domain, differences within which define the breadth and potency of TRIM5alpha-mediated retroviral restriction. Because Macaca nemestrina animals are susceptible to some human immunodeficiency virus (HIV) isolates, we sought to determine if differences exist in the TRIM5 gene and transcripts of these animals. We identified a two-nucleotide deletion (Delta2) in the transcript at the 5' terminus of exon 7 in all M. nemestrina TRIM5 cDNA clones examined. This frameshift results in a truncated protein of 300 amino acids lacking the B30.2(SPRY) domain, which we have named TRIM5theta. This deletion is likely due to a single nucleotide polymorphism that alters the 3' splice site between intron 6 and exon 7. In some clones, a deletion of the entire 27-nucleotide exon 7 (Deltaexon7) resulted in the restoration of the TRIM5 open reading frame and the generation of another novel isoform, TRIM5eta. There are 18 amino acid differences between M. nemestrina TRIM5eta and Macaca mulatta TRIM5alpha, some of which are at or near locations previously shown to affect the breadth and potency of TRIM5alpha-mediated restriction. Infectivity assays performed on permissive CrFK cells stably transduced with TRIM5eta or TRIM5theta show that these isoforms are incapable of restricting either HIV type 1 (HIV-1) or simian immunodeficiency virus infection. The expression of TRIM5 alleles incapable of restricting HIV-1 infection may contribute to the previously reported increased susceptibility of M. nemestrina to HIV-1 infection in vivo.

Non-human primate models for AIDS vaccine research

Since the discovery of simian immunodeficiency viruses (SIV) causing AIDS-like diseases in Asian macaques, non-human primates (NHP) have played an important role in AIDS vaccine research. A multitude of vaccines and immunization approaches have been evaluated, including live attenuated viruses, DNA vaccines, viral and bacterial vectors, subunit proteins, and combinations thereof. Depending on the particular vaccine and model used, varying degrees of protection have been achieved, including prevention of infection, reduction of viral load, and amelioration of disease. In a few instances, potential safety concerns and vaccine-enhanced pathogenicity have also been noted. In the past decade, sophisticated methodologies have been developed to define the mechanisms of protective immunity. However, a clear road map for HIV vaccine development has yet to emerge. This is in part because of the intrinsic nature of the surrogate model and in part because of the improbability of any single model to fully capture the complex interactions of natural HIV infection in humans. The lack of standardization, the limited models available, and the incomplete understanding of the immunobiology of NHP contribute to the difficulty to extrapolate findings from such models to HIV vaccine development. Until efficacy data become available from studies of parallel vaccine concepts in humans and macaques, the predictive value of any NHP model remains unknown. Towards this end, greater appreciation of the utility and limitations of the NHP model and further developments to better mimic HIV infection in humans will likely help inform future AIDS vaccine efforts.

The CCR5 and CXCR4 coreceptors--central to understanding the transmission and pathogenesis of human immunodeficiency virus type 1 infection

In this review, we will discuss what is known, what is suspected, and what still remains obscure about the central role played by coreceptor expression and usage in the transmission and pathogenic consequences of human immunodeficiency virus type 1 (HIV-1) infection. An emphasis will be on the HIV-1 phenotypic variants that are defined by their usage of the CCR5 or CXCR4 coreceptors, and how the different cellular tropism of these variants influences how and where HIV-1 replicates in vivo. We will also review what might happen when coreceptor antagonists are used clinically to treat HIV-1 infection.

Blockade of HIV-1 infection of New World monkey cells occurs primarily at the stage of virus entry

HIV-1 naturally infects chimpanzees and humans, but does not infect Old World monkeys because of replication blocks that occur after virus entry into the cell. To understand the species-specific restrictions operating on HIV-1 infection, the ability of HIV-1 to infect the cells of New World monkeys was examined. Primary cells derived from common marmosets and squirrel monkeys support every phase of HIV-1 replication with the exception of virus entry. Efficient HIV-1 entry typically requires binding of the viral envelope glycoproteins and host cell receptors, CD4 and either CCR5 or CXCR4 chemokine receptors. HIV-1 did not detectably bind or utilize squirrel monkey CD4 for entry, and marmoset CD4 was also very inefficient compared with human CD4. A marmoset CD4 variant, in which residues 48 and 59 were altered to the amino acids found in human CD4, supported HIV-1 entry efficiently. The CXCR4 molecules of both marmosets and squirrel monkeys supported HIV-1 infection, but the CCR5 proteins of both species were only marginally functional. These results demonstrate that the CD4 and CCR5 proteins of New World monkeys represent the major restriction against HIV-1 replication in these primates. Directed adaptation of the HIV-1 envelope glycoproteins to common marmoset receptors might allow the development of New World monkey models of HIV-1 infection.