does this mean you have hiv when u have this hla

Epitope-Enhanced Conserved HIV-1 Peptide Protects HLA-A2-Transgenic Mice Against Virus Expressing HIV-1 Antigen
Takahiro Okazaki1,*, C. David Pendleton*, François Lemonnier and Jay A. Berzofsky2,*
* Molecular Immunogenetics and Vaccine Research Section, Metabolism Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892; and Unité d’Immunité Cellulaire Antivirale, Institut Pasteur, Paris, France

Abstract
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Abstract
Introduction
Materials and Methods
Results
Discussion
References

HIV epitopes may have developed to be poor immunogens. As a counterapproach HIV vaccine strategy, we used epitope enhancement of a conserved HIV reverse transcriptase (RT) epitope for induction of antiviral protection in HLA-A2-transgenic mice mediated by human HLA-A2-restricted CTLs. We designed two epitope-enhanced peptides based on affinity for HLA-A2, one substituted in anchor residues (RT-2L9V) and the other also with tyrosine at position 1 (RT-1Y2L9V), and examined the balance between HLA binding and T cell recognition. CTL lines and bulk cultures in two HLA-A2-transgenic mouse strains showed that RT-2L9V was more effective in inducing CTL reactive with wild-type Ag than RT-1Y2L9V, despite the higher affinity of the latter, because the 1Y substitution unexpectedly altered T cell recognition. Accordingly, RT-2L9V afforded the greatest protection in vivo against a surrogate virus expressing HIV-1 RT mediated by HLA-A2-restricted CTL in a mouse in which all CTL are restricted to only the human HLA molecule. Such antiviral protection has not been previously achieved with an HLA epitope-enhanced vaccine. These findings define a critical balance between MHC affinity and receptor cross-reactivity required for effective epitope enhancement and also demonstrate construction and efficacy of such a component of a new generation vaccine.

Introduction
Top
Abstract
Introduction
Materials and Methods
Results
Discussion
References

In protection against HIV or SIV virus (1, 2, 3), CD8 CTL play a major role. Nevertheless, the natural immune response to HIV is often unable to clear the infection. Although a number of Ags that induce CTL responses and can help to eliminate or reduce virus production by killing viral producer cells have been reported thus far, these do not seem to be sufficient to eliminate infection in most cases. There is no reason to expect that the HIV sequence would have evolved to have optimal CTL epitopes to allow eradication of the virus. Thus, in principle it should be possible to improve the immunogenicity of epitopes, a process called "epitope enhancement," to develop a more highly effective HIV vaccine (4, 5).

A first approach to enhance peptide immunogenicity is to improve the affinity of CTL epitopes for HLA class I molecules. For this reason, we decided to focus on a peptide from a conserved region of the HIV reverse transcriptase (RT) 3 designated RT179–187, VIYQYMDDL. This epitope is endogenously processed and presented and recognized by HLA-A2.1-restricted CTL in HIV-infected patients (6) and has been described as a binder with weak affinity to HLA-A2.1 molecule (7). This weak binding affinity allowed us to introduce modifications aimed at improving binding, compared with other HIV epitopes described as high affinity binders and less in need of improvement. The advantage of this epitope is that it is also strongly conserved because its amino acid sequence, YMDD, is part of an active site of HIV RT. Such a conserved epitope may be more valuable in a vaccine than a higher affinity but more mutable one subject to viral escape. The VIYQYMDDL epitope is found in the vast majority of HIV strains and may be harder for the virus to mutate without loss of fitness.

We have previously succeeded in improving the affinity of a hepatitis C core epitope for HLA-A2.1 (8) and of a helper epitope for murine class II MHC (9, 10), and an epitope-enhanced melanoma peptide has shown efficacy in human clinical trials (11). Other complementary approaches to improve affinity for TCRs have been devised (12, 13, 14). Although one substitution resulting in higher affinity HLA binding of another HIV peptide has been reported (15), no rational strategy to improve epitopes of HIV has been conducted. In particular, no systematic analysis of the competing effects of substitutions on HIV peptide binding to the HLA class I molecule vs peptide-HLA complex binding to the TCR has been reported.

Further, to our knowledge, protection against viral infection in vivo by an epitope-enhanced vaccine mediated by CTL restricted by a human HLA molecule has not previously been demonstrated. To study such protection, we have taken advantage of a novel strain of mice, HHD-2, that is transgenic for human HLA-A2.1 with a covalent human 2-microglobulin and lacks any murine class I molecules because it is deficient in murine 2-microglobulin and murine H-2Db. Thus, in this strain, all CTL are restricted only to the human class I HLA molecule, and any protection cannot be mediated by CTL restricted to murine class I MHC molecules (7, 16). Because of the importance of HIV and AIDS and the critical need for an effective vaccine that is more effective than the natural virus for inducing protective responses, we have now undertaken a systematic program to enhance conserved epitopes of HIV. Here, we show not only such HLA-restricted CTL-mediated antiviral protection but also the design and construction of an enhanced conserved HIV epitope based on balancing effects of binding to an HLA molecule and binding to the TCR that may be a useful component of a second-generation human HIV vaccine.

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