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    ABSTRACT: The observed association between HLA-B*13 and control of human immunodeficiency virus type 1 (HIV-1) infection has been linked to the number of Gag-specific HLA-B*13-restricted cytotoxic T-cell (CTL) responses identified. To date, the Gag escape mutations described that result in an in vitro fitness cost to the virus have been located within structural protein p24 only. Here we investigated the hypothesis that CTL escape mutations within other regions of HIV Gag may also reduce viral fitness and contribute to immune control. We analyzed an HLA-B*13-restricted CTL response toward an epitope in p1 Gag, RQANFLGKI(429-437) (RI9), where amino acid variation at Gag residues 436 and 437 is associated with HLA-B*13 expression. In this work, we assessed the impact of amino acid substitutions at these positions on CTL recognition and on HIV-1 fitness. We demonstrated that substitutions I437L and I437M largely abrogate CTL recognition and reduce viral fitness while variants K436R and I437V have only a marginal effect on recognition and fitness. Examination of the patterns of protein synthesis indicated that the loss of fitness in the I437L and I437M mutants is associated with the accumulation of unprocessed Gag precursors. A significant reduction in ribosomal frameshifting efficiency was observed with I437M, suggesting that this mechanism contributes to the observed reduced fitness of this virus. These studies illustrate the apparent trade-off available to the virus between evasion of CTL recognition in p1 Gag and the functional consequences for viral fitness.
    Journal of Virology 11/2008; 83(2):1018-25. · 5.08 Impact Factor
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    ABSTRACT: Cytotoxic-T-lymphocyte (CTL) escape mutations in human immunodeficiency viruses encode amino acid substitutions in positions that disrupt CTL targeting, thereby increasing virus survival and conferring a relative fitness benefit. However, it is now clear that CTL escape mutations can also confer a fitness cost, and there is increasing evidence to suggest that in some cases, e.g., escape from HLA-B*57/B*5801-restricted responses, the costs to the escape virus may affect the clinical course of infection. To quantify the magnitude of the costs of HLA-B*57/B*5801 escape, a highly sensitive dual-infection assay that uses synonymous nucleotide sequence tags to quantify viral relative replication capacity (RRC) was developed. We then asked whether such CTL escape mutations had an impact equivalent to that seen for a benchmark mutation, the M184V antiretroviral drug resistance mutation of reverse transcriptase (RRC(V184) = 0.86). To answer the question, the RRCs were quantified for escape mutations in three immunodominant HLA-B*57/B*5801 epitopes in capsid: A146P in IW9 (RRC(P146) = 0.91), A163G in KF11 (RRC(G163) = 0.89), and T242N in TW10 (RRC(N242) = 0.86). Individually, the impact of the escape mutations on RRC was comparable to that of M184V, while coexpression of the mutations resulted in substantial further reductions, with the maximum impact observed for the triple mutant (RRC(P146-G163-N242) = 0.62). By comparison to M184V, the magnitude of the reductions in RRC caused by the escape mutations, particularly when coexpressed, suggests that the costs of escape are sufficient to affect in vivo viral dynamics and may thus play a role in the protective effect associated with HLA-B*57/B*5801.
    Journal of Virology 01/2009; 83(6):2460-8. · 5.08 Impact Factor
  • Studies in Surface Science and Catalysis - STUD SURF SCI CATAL. 01/1997; 105:1867-1874.

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