CD8 Epitope Escape and Reversion in Acute HCV Infection

In the setting of acute hepatitis C virus (HCV) infection, robust HCV-specific CD8+ cytotoxic T lymphocyte (CTL) responses are associated with initial control of viremia. Despite these responses, 70–80% of individuals develop persistent infection. Although viral escape from CD8 responses has been illustrated in the chimpanzee model of HCV infection, the effect of CD8 selection pressure on viral evolution and containment in acute HCV infection in humans remains unclear. Here, we examined viral evolution in an immunodominant human histocompatibility leukocyte antigen (HLA)-B8–restricted NS3 epitope in subjects with acute HCV infection. Development of mutations within the epitope coincided with loss of strong ex vivo tetramer and interferon γ enzyme-linked immunospot responses, and endogenous expression of variant NS3 sequences suggested that the selected mutations altered processing and presentation of the variant epitope. Analysis of NS3 sequences from 30 additional chronic HCV-infected subjects revealed a strong association between sequence variation within this region and expression of HLA-B8, supporting reproducible allele-specific selection pressures at the population level. Interestingly, transmission of an HLA-B8–associated escape mutation to an HLA-B8 negative subject resulted in rapid reversion of the mutation. Together, these data indicate that viral escape from CD8+ T cell responses occurs during human HCV infection and that acute immune selection pressure is of sufficient magnitude to influence HCV evolution

Broadly directed virus-specific CD4+ T cell responses are primed during acute hepatitis C infection, but rapidly disappear from human blood with viral persistence

Vigorous proliferative CD4+ T cell responses are the hallmark of spontaneous clearance of acute hepatitis C virus (HCV) infection, whereas comparable responses are absent in chronically evolving infection. Here, we comprehensively characterized the breadth, specificity, and quality of the HCV-specific CD4+ T cell response in 31 patients with acute HCV infection and varying clinical outcomes. We analyzed in vitro T cell expansion in the presence of interleukin-2, and ex vivo staining with HCV peptide-loaded MHC class II tetramers. Surprisingly, broadly directed HCV-specific CD4+ T cell responses were universally detectable at early stages of infection, regardless of the clinical outcome. However, persistent viremia was associated with early proliferative defects of the HCV-specific CD4+ T cells, followed by rapid deletion of the HCV-specific response. Only early initiation of antiviral therapy was able to preserve CD4+ T cell responses in acute, chronically evolving infection. Our results challenge the paradigm that HCV persistence is the result of a failure to prime HCV-specific CD4+ T cells. Instead, broadly directed HCV-specific CD4+ T cell responses are usually generated, but rapid exhaustion and deletion of these cells occurs in the majority of patients. The data further suggest a short window of opportunity to prevent the loss of CD4+ T cell responses through antiviral therapy

Invariant points of low dimensional curve families

From noisy observations of a finite family of functions an approximation in a lower dimensional space can be constructed using the method of principal components. If certain restrictions are to be satisfied by the approximation, e.g. being densities, this leads to a modified estimation procedure. It is shown that in certain dimensions this will produce a family of curves which all intersect in the same points. This property may be interpreted in some cases as a characteristic feature of regularity of the data or as an artificial creation by the device in others. (orig.)SIGLEAvailable from TIB Hannover: RO 2708(516) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Stereotypic escape from CD8+ T-cell responses represents a major driving force of HIV-1 sequence diversity and reveals constraints on HIV-1 evolution

Background: Understanding the factors driving global HIV-1 sequence diversity is critical for vaccine development. While viral escape from CD8+ T-cell responses is well documented, it remains unclear the extent to which intra-host and global HIV-1 evolution is specifically driven by these selective pressures. Similarly, little is known regarding the extent to which sequence constraints upon protein structure affect the accumulation of mutations arising from immune selection pressures. Methods: We assessed the relationship between genome-wide viral evolution (excluding Env) and HIV-1-specific cellular immune responses in 4 patients followed longitudinally for as long as 5 years after acute infection. Ten additional chronically infected subjects expressing HLA-B57 were examined to assess reproducibility of escape mutations. Full genome population sequencing of HIV-1 was employed, and measurement of HIV-1-specific CD8+ T-cell responses using consensus, and in some cases autologous peptides, was conducted using an IFN-γ ELISpot assay. Results: A total of 98 mutations evolved in the 4 study subjects, 52 of which were associated with detectable virus-specific CD8+ T-cell responses, accounting for 48 to 60% of the mutations in each subject. In addition, 18 mutations reverted to common consensus residues, 9 of which were associated with HLA class I alleles not expressed by the respective subject, consistent with adaptations due to previous CD8+ T-cell selective pressures. Therefore, nearly two-thirds of all mutations were attributable to CD8+ T-cell selective pressures. Although the majority of CD8+ T-cell responses did not result in detectable viral evolution, targeted residues in epitopes that did mutate correlated with the most polymorphic sites in both clade B and C viruses, and selection pressure frequently resulted in identical amino acid substitutions arising in a given CD8 epitope across multiple subjects. Conclusions: These data indicate a dominant role of cellular immune responses in driving both individual and global HIV-1 evolution, and the stereotypic nature of acquired mutations provides evidence for constraints on evolution of highly variable RNA viruses

De Novo Generation of Escape Variant-Specific CD8(+) T-Cell Responses following Cytotoxic T-Lymphocyte Escape in Chronic Human Immunodeficiency Virus Type 1 Infection

Human immunodeficiency virus type 1 (HIV-1) evades CD8(+) T-cell responses through mutations within targeted epitopes, but little is known regarding its ability to generate de novo CD8(+) T-cell responses to such mutants. Here we examined gamma interferon-positive, HIV-1-specific CD8(+) T-cell responses and autologous viral sequences in an HIV-1-infected individual for more than 6 years following acute infection. Fourteen optimal HIV-1 T-cell epitopes were targeted by CD8(+) T cells, four of which underwent mutation associated with dramatic loss of the original CD8(+) response. However, following the G(357)S escape in the HLA-A11-restricted Gag(349-359) epitope and the decline of wild-type-specific CD8(+) T-cell responses, a novel CD8(+) T-cell response equal in magnitude to the original response was generated against the variant epitope. CD8(+) T cells targeting the variant epitope did not exhibit cross-reactivity against the wild-type epitope but rather utilized a distinct T-cell receptor Vβ repertoire. Additional studies of chronically HIV-1-infected individuals expressing HLA-A11 demonstrated that the majority of the subjects targeted the G(357)S escape variant of the Gag(349-359) epitope, while the wild-type consensus sequence was significantly less frequently recognized. These data demonstrate that de novo responses against escape variants of CD8(+) T-cell epitopes can be generated in chronic HIV-1 infection and provide the rationale for developing vaccines to induce CD8(+) T-cell responses directed against both the wild-type and variant forms of CD8 epitopes to prevent the emergence of cytotoxic T-lymphocyte escape variants

Transmission and Long-Term Stability of Compensated CD8 Escape Mutations▿

Human immunodeficiency virus effectively evades CD8+ T-cell responses through the development of CD8 escape mutations. Recent reports documenting reversion of transmitted mutations and the impact of specific escape mutations upon viral replication suggest that complex forces limit the accumulation of CD8 escape mutations at the population level. However, the presence of compensatory mutations capable of alleviating the impact of CD8 escape mutations on replication capacity may enable their persistence in an HLA-mismatched host. Herein, we illustrate the long-term stability of stereotypic escape mutations in the immunodominant HLA-B27-restricted epitope KK10 in p24/Gag following transmission when accompanied by a specific compensatory mutation