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Many pathogens evade cytotoxic T lymphocytes (CTLs) by downregulating HLA molecules on infected cells, but the loss of HLA can trigger NK cell-mediated lysis. HIV-1 is thought to subvert CTLs while preserving NK cell inhibition by Nef-mediated downregulation of HLA-A and -B but not HLA-C molecules. We find that HLA-C is downregulated by most primary HIV-1 clones, including transmitted founder viruses, in contrast to the laboratory-adapted NL4-3 virus. HLA-C reduction is mediated by viral Vpu and reduces the ability of HLA-C restricted CTLs to suppress viral replication in CD4+ cells in vitro. HLA-A/B are unaffected by Vpu, and primary HIV-1 clones vary in their ability to downregulate HLA-C, possibly in response to whether CTLs or NK cells dominate immune pressure through HLA-C. HIV-2 also suppresses HLA-C expression through distinct mechanisms, underscoring the immune pressure HLA-C exerts on HIV. This viral immune evasion casts new light on the roles of CTLs and NK cells in immune responses against HIV.

HIV-1 can downregulate HLA-C on infected cells, using the viral protein Vpu, and the magnitude of this downregulation varies widely between primary HIV-1 variants. The selection pressures that result in viral downregulation of HLA-C in some individuals, but preservation of surface HLA-C in others are not clear. To better understand viral immune evasion targeting HLA-C, we have characterized HLA-C downregulation by a range of primary HIV-1 viruses. 128 replication competent viral isolates from 19 individuals with effective anti-retroviral therapy, show that a substantial minority of individuals harbor latent reservoir virus which strongly downregulates HLA-C. Untreated infections display no change in HLA-C downregulation during the first 6 months of infection, but variation between viral quasispecies can be detected in chronic infection. Vpu molecules cloned from plasma of 195 treatment naive individuals in chronic infection demonstrate that downregulation of HLA-C adapts to host HLA genotype. HLA-C alleles differ in the pressure they exert for downregulation, and individuals with higher levels of HLA-C expression favor greater viral downregulation of HLA-C. Studies of primary and mutant molecules identify 5 residues in the transmembrane region of Vpu, and 4 residues in the transmembrane domain of HLA-C, which determine interactions between Vpu and HLA. The observed adaptation of Vpu-mediated downregulation to host genotype indicates that HLA-C alleles differ in likelihood of mediating a CTL response that is subverted by viral downregulation, and that preservation of HLA-C expression is favored in the absence of these responses. Finding that latent reservoir viruses can downregulate HLA-C could have implications for HIV-1 cure therapy approaches in some individuals.

Aim It was recently found that HIV can downregulate HLA-C on infected cells. This is mediated by the viral protein Vpu, and is in addition to the downregulation of HLA-A/B by Nef. The magnitude of HLA-C downregulation varies widely between primary HIV viruses, but the selection pressures resulting in either HLA-C downregulation or preservation are not clear. Methods To better understand viral immune evasion targeting HLA-C, we have characterized HLA-C downregulation by a range of primary HIV-1 viruses. Results 100 replication competent viral isolates, from limiting dilution outgrowth assays of 20 individuals with effective anti-retroviral therapy, show a substantial minority of individuals harbor reservoir virus which strongly downregulates HLA-C. 20 longitudinal samples from 4 untreated individuals demonstrate no changes in HLA-C downregulation during acute infection, but show variation between viral quasispecies that can persist in chronic infection. 200 Vpu molecules cloned from plasma of treatment naive individuals in chronic infection, show that downregulation of HLA-C adapts to host HLA genotype. HLA-C alleles differ in the pressure they exert for viral downregulation of HLA-C, and individuals with higher levels of HLA-C expression favour greater viral downregulation of HLA-C. Studies of primary and mutant molecules show the transmembrane regions of both Vpu and HLA are responsible for their interaction when removing HLA-C from the cell surface. Conclusions Finding that reservoir virus can downregulate HLA-C could have implications for HIV cure therapy approaches in some individuals. The adaptation of HLA-C downregulation to host HLA genotype which is observed, indicates a subset of HLA-C alleles restrict HIV-specific CTL responses which are subverted by viral downregulation of HLA-C. Differential viral modulation of HLA-C, compared to HLA-A/B, can be used to understand differences in the biological roles of these HLA molecules in HIV infection.

Human T-cell leukemia virus type I (HTLV-I) is the etiologic agent for adult T-cell leukemia and the neurological disorder tropical spastic paraparesis/HTLV-I-associated myelopathy. CD4+ T lymphocytes, the primary hosts for HTLV-I, undergo a series of changes that lead to T-cell activation, immortalization, and transformation. To gain insight into the genetic differences between activated and HTLV-I-infected lymphocytes, we performed Affymetrix GeneChip analysis of activated and HTLV-I-infected cells. Using the Hu6800 GeneChip, we identified approximately 763 genes that had differentially regulated expression in at least three of five HTLV-I cell lines. Classification of these genes into functional groups including cellular receptors, kinases, phosphatases, cytokines, signal proteins, and transcription factors provides insight into genes and pathways that are differentially regulated during HTLV-I transformation.

It has been demonstrated previously that molecular decoys of the acetylcholine receptor have therapeutic efficacy as antitoxins [Gershoni, J. and Aronheim, A. (1988) Proc. Natl Acad. Sci. USA, 85, 4087-4089], but surely a most challenging goal is to apply this approach towards the development of antiviral drugs. As viruses present multiple copies of their envelope proteins, it was proposed that polyvalent decoys could be advantageous. Here we report the design and expression of recombinant linear polymers of the HIV gp120-binding domains which are situated within the T-cell membrane protein CD4. Whereas the production of linear concatemers of CD4 variable domains is feasible, a number of conformational constraints must be considered when designing a polymeric molecule which retains biological function. Most significant is the contribution of domains flanking the binding site that apparently enable correct folding of the latter.

Viral transcripts, particularly those of the regulatory genes (e.g., rev) in lymphocytic cells chronically infected with human immunodeficiency virus type 2, consist of two types, differing in the structure of the leader sequence derived from the 5' long terminal repeat (LTR). Some transcripts undergo a specific splicing event within the 5' LTR, removing an intron consisting of a part of the R region whereas others do not. Because this spliced-out R region is a part of the trans-activation response element (TAR), it could influence trans-activator (Tat)-mediated trans-activation of viral gene expression. Moreover, this part of the R region is predicted to contain a stable secondary structure that could affect the efficiency of translation of the transcripts without this splicing. Thus, the 5' LTR splicing could have important consequences for virus replication, latency, and pathogenicity.