Dirk Meyer-Olson

Limited T Cell Receptor Diversity of HCV-specific T Cell Responses Is Associated with CTL Escape

Escape mutations are believed to be important contributors to immune evasion by rapidly evolving viruses such as hepatitis C virus (HCV). We show that the majority of HCV-specific cytotoxic T lymphocyte (CTL) responses directed against viral epitopes that escaped immune recognition in HCV-infected chimpanzees displayed a reduced CDR3 amino acid diversity when compared with responses in which no CTL epitope variation was detected during chronic infection or with those associated with protective immunity. Decreased T cell receptor (TCR) CDR3 amino acid diversity in chronic infection could be detected long before the appearance of viral escape mutations in the plasma. In both chronic and resolved infection, identical T cell receptor clonotypes were present in liver and peripheral blood. These findings provide a deeper understanding of the evolution of CTL epitope variations in chronic viral infections and highlight the importance of the generation and maintenance of a diverse TCR repertoire directed against individual epitopes.

Expansion of pre-existing, lymph node-localized CD8+ T cells during supervised treatment interruptions in chronic HIV-1 infection

To date, most studies have focused on the characterization of HIV-1-specific cellular immune responses in the peripheral blood (PB) of infected individuals. Much less is known about the comparative magnitude and breadth of responses in the lymphoid tissue. This study analyzed HIV-1-specific CD8+ T cell responses simultaneously in PB and lymph nodes (LNs) of persons with chronic HIV-1 infection and assessed the dynamics of these responses during antiretroviral treatment and supervised treatment interruption (STI). In untreated chronic infection, the magnitude of epitope-specific CD8+ T cell activity was significantly higher in LNs than in PB. Responses decreased in both compartments during highly active antiretroviral therapy, but this decline was more pronounced in PB. During STI, HIV-1-specific CD8+ T cell responses in PB increased significantly. Enhancement in breadth and magnitude was largely due to the expansion of pre-existing responses in the LNs, with new epitopes infrequently targeted. Taken together, these data demonstrate that HIV-1-specific CD8+ T cells are preferentially located in the LNs, with a subset of responses exclusively detectable in this compartment. Furthermore, the enhanced CD8+ T cell responses observed during STI in chronically infected individuals is largely due to expansion of pre-existing virus-specific CD8+ T cells, rather than the induction of novel responses.

Short-Term Monotherapy in HIV-Infected Patients with a Virus Entry Inhibitor Against the gp41 Fusion Peptide

An optimized derivative of a natural HIV-1 entry inhibitor targeting the gp41 fusion peptide shows antiviral potency and minimal side effects in a Phase I/II clinical trial. Anchors Away: Blocking HIV Entry Combination antiretroviral therapy has been very successful for treating infection with the human immunodeficiency virus (HIV-1), which causes AIDS. However, drug resistance is emerging and there is a need to develop new antiretroviral drugs that work earlier in the virus life cycle, for example, by preventing HIV-1 from entering host cells. Two such virus entry inhibitors, maraviroc and T-20, are in clinical use, but both have drawbacks. Forssmann, Kirchhoff and their colleagues have now developed a new virus entry inhibitor called VIRIP (VIRus-Inhibitory Peptide), a 20-peptide fragment of α1-antitrypsin, an abundant circulating serine protease inhibitor. VIRIP and its optimized derivative VIR-576 are so-called anchoring inhibitors because they prevent the gp41 fusion peptide of HIV-1 from inserting itself into the host cell membrane. This then blocks the next step in the virus life cycle, which is fusion of the virion envelope with the host cell membrane. Forssmann and co-workers now report on a Phase I/II clinical trial in which 18 HIV-1–infected patients who were not on any other antiretroviral therapy were treated for 10 days with three different doses of VIR-576 (0.5, 1.5, 5.0 g/day). They show that VIR-576 reduced the viral load in the plasma of patients on the highest dose by an order of magnitude and that the drug was well tolerated. Previous studies have shown that the gp41 fusion peptide is essential for HIV-1 entry into host cells, and suggest that it may be difficult for HIV-1 to develop resistance to VIR-576 because the fusion peptide is highly conserved and hardly tolerates changes without loss of function. This anchoring inhibitor, unlike other HIV entry inhibitors, is also active against many different HIV strains and has a different target (the gp41 fusion peptide). Thus, VIR-576 represents a potential new class of HIV entry inhibitor. However, VIR-576 does have some drawbacks too. Because VIR-576 is a peptide, it will be costly and time-consuming to produce and it must be administered intravenously. This has prompted Kirchhoff and colleagues to start searching for a small molecule that would block the gp41 fusion peptide in the same way as VIR-576 but would have the advantage that it could be made cheaper and given orally. To infect host cells, most enveloped viruses must insert a hydrophobic fusion peptide into the host cell membrane. Thus, fusion peptides may be valuable targets for developing drugs that block virus entry. We have shown previously that a natural 20-residue fragment of α1-antitrypsin, designated VIRus-Inhibitory Peptide (VIRIP), that binds to the gp41 fusion peptide of HIV-1 prevents the virus from entering target cells in vitro. Here, we examine the efficacy of 10-day monotherapy with the optimized VIR-576 derivative of VIRIP in treatment-naïve, HIV-1–infected individuals with viral RNA loads of ≥10,000 copies per ml. We report that at the highest dose (5.0 grams per day), intravenous infusion of VIR-576 reduced the mean plasma viral load by 1.23 log10 copies per ml without causing severe adverse effects. Our results are proof of concept that fusion peptide inhibitors suppress viral replication in human patients, and offer prospects for the development of a new class of drugs that prevent virus particles from anchoring to and infecting host cells.

Clinical impact of Hiv-related lipodystrophy and metabolic abnormalities on cardiovascular disease

Metabolic complications and altered fat distribution associated with HIV infection and antiretroviral therapy may lead to accelerated coronary artery disease (CAD). The high prevalence of multiple cardiovascular risk factors in a significant number of HIV patients is a cause for concern in both patients and physicians. Non-invasive strategies to measure subclinical CAD have been inconclusive. Long-term studies are underway to determine cardiac event rates, intervention strategies and consequences for the clinical management of HIV disease. In the present paper, we summarize the most prevalent risk factors in individuals with HIV infection receiving highly active antiretroviral therapy by focusing on the clinical implications of metabolic abnormalities and HIV-related lipodystrophy on CAD.

CD26 expression determines lung metastasis in mutant F344 rats: involvement of NK cell function and soluble CD26

The association between CD26 expression, tumor cell adhesion, metastasis, and natural killer (NK) cell function was investigated in a CD26 mutant Fischer 344 (F344/DuCrj) substrain from Japanese breeders (F344JAP) in comparison with wild-type F344 substrains from US (F344/Crl) and Hannover (HAN; F344/Ztm) breeders. F344JAP rats lack the dipeptidyl peptidase IV activity of CD26 and show a reduced cell surface expression of the mutated CD26 glycoprotein. In vivo adhesion of vital dye-labeled MADB106 tumor cells, tumor colonization, CD26 enzymatic activity, and CD26 immunoreactivity in lungs and soluble CD26-like protein expression in serum were markedly reduced in F344JAP rats. These findings demonstrate that CD26 protein expression exerts a key role in lung metastasis. In addition, NK cell cytotoxicity against MADB106 cells was diminished in the mutant F344 substrain, suggesting that CD26 enzymatic activity sustains NK cytotoxicity. Interestingly, tumor cells lacked CD26 immunoreactivity in vitro, but displayed CD26 immunoreactivity in situ after in vivo inoculation as well as after incubation with rat serum, indicating that soluble CD26-like protein assembles in tumor cells during in vivo passage, which may interact with the process of tumor adhesion and metastasis. Overall, these findings indicate that altered expression and function of a single enzyme—the CD26 protein—can drastically change the outcome of metastatic disease.

Phenotypically and functionally distinct subsets contribute to the expansion of CD56-/CD16+ natural killer cells in HIV infection.

Objective:Chronic HIV infection has been associated with activation and increased turnover of natural killer (NK) cells as well as with disturbed homeostasis of the NK cell compartment, including loss of CD56+ NK cells and accumulation of dysfunctional CD56−/CD16+ NK cells. We performed a comprehensive phenotypical and functional characterization of this population. Design:A cross-sectional study was performed to analyze CD56−/CD16+ NK cells from 34 untreated HIV-infected and 15 seronegative individuals. Methods:NK cells were analyzed by flow cytometry. Degranulation was assessed by measuring their expression of CD107a after stimulation with K562 cells, interleukin-12 and interleukin-15. Results:CD56−/CD16+ NK cells are heterogeneous and composed of two populations, namely CD122−/CCR7+ cells and CD122+/CCR7− cells. We show that expanded CD122+ but not CCR7+ cells in HIV-seropositive individuals are characterized by expression of senescence marker CD57 similarly to CD56dim/CD16+ NK cells along with expression of KIRs, CD8, perforin and granzyme B. Despite expression of perforin and granzyme B, CD57 expressing cells exhibited less numbers of degranulating cells as measured by CD107a, indicating their functional impairment. However, there was no correlation between expansion of total CD56−/CD16+ NK cells or the distinct subpopulations and viral load or CD4 cell count. Conclusion:These data indicate that expansion of CD56−/CD16+ cells in HIV infection is driven by a distinct subset within this population with high expression of terminal differentiation marker with a phenotype resembling CD56dim/CD16+ NK cells.

Despite Biased TRBV Gene Usage against a Dominant HLA B57-Restricted Epitope, TCR Diversity Can Provide Recognition of Circulating Epitope Variants

The role of epitope-specific TCR repertoire diversity in the control of HIV-1 viremia is unknown. Further analysis at the clonotype level is important for understanding the structural aspects of the HIV-1 specific repertoire that directly relate to CTL function and ability to suppress viral replication. In this study, we performed in-depth analysis of T cell clonotypes directed against a dominantly recognized HLA B57-restricted epitope (KAFSPEVIPMF; KF11) and identified common usage of the TCR β-chain TRBV7 in eight of nine HLA B57 subjects examined, regardless of HLA B57 subtype. Despite this convergent TCR gene usage, structural and functional assays demonstrated no substantial difference in functional or structural avidity between TRBV7 and non-TRBV7 clonotypes and this epitopic peptide. In a subject where TRBV7-usage did not confer cross-reactivity against the dominant autologous sequence variant, another circulating TCR clonotype was able to preferentially recognize the variant peptide. These data demonstrate that despite selective recruitment of TCR for a conserved epitope over the course of chronic HIV-1 infection, TCR repertoire diversity may benefit the host through the ability to recognize circulating epitope variants.

Exogenous HIV-1 Vpr disrupts IFN-α response by plasmacytoid dendritic cells (pDCs) and subsequent pDC/NK interplay

HIV Vpr is known for its immunomodulatory capacities including its impairment of NK cell functions. However, the role of pDCs in this context remains elusive. We show that synthetic Vpr substantially inhibits type I IFN production by pDCs without inducing apoptosis in pDCs. Furthermore, we found that exogenous Vpr compromises subsequent pDC/NK interplay as shown by diminished IFN-gamma production by NK cells. Thus, Vpr-mediated dysregulation of IFN-alpha and IFN-gamma production affects key components of the innate immune response supporting an essential role of Vpr in HIV pathogenesis.

Dominant Clonotypes within HIV-Specific T Cell Responses Are Programmed Death-1high and CD127low and Display Reduced Variant Cross-Reactivity

HIV epitope-specific T cell responses are often comprised of clonotypic expansions with distinct functional properties. In HIV+ individuals, we measured programmed death-1 (PD-1) and IL-7Rα expression, MHC class I tetramer binding, cytokine production, and proliferation profiles of dominant and subdominant TCR clonotypes to evaluate the relationship between the composition of the HIV-specific T cell repertoire and clonotypic phenotype and function. Dominant clonotypes are characterized by higher PD-1 expression and lower C127 expression compared with subdominant clonotypes, and TCR avidity positively correlates with PD-1 expression. At low peptide concentrations, dominant clonotypes fail to survive in culture. In response to stimulation with peptides representing variant epitopes, subdominant clonotypes produce higher relative levels of cytokines and display greater capacity for cross-recognition compared with dominant clonotypes. These data indicate that dominant clonotypes within HIV-specific T cell responses display a phenotype consistent with ongoing exposure to cognate viral epitopes and suggest that cross-reactive, subdominant clonotypes may retain greater capacity to suppress replication of viral variants as well as to survive in the absence of strong antigenic signaling.

Clonal expansion and TCR-independent differentiation shape the HIV-specific CD8+ effector-memory T-cell repertoire in vivo.

Flexibility of the HIV-specific T-cell receptor repertoire is a hallmark of HIV-1 infection. Altered differentiation of HIV-specific CD45RO(+)/CCR7(-) (TemRO) CD8(+) effector-memory T cells into CD45RA(+)/CCR7(-) (TemRA) CD8(+) effector-memory T cells as well as increased expression of the senescence marker CD57 has been frequently observed HIV-1 infection, but the structural relationship between clonal expansion and T-cell differentiation has not been defined. In this study, we demonstrate that HIV-specific clonotypes have differing degrees of TemRA differentiation but always maintain a significant proportion of TemRO-phenotype cells. These data indicate that structural constraints of the TCR/peptide major histocompatibility complex interaction play a central role in the TemRA differentiation of HIV-specific CD8(+) T cells in chronic HIV-1 infection. Clonotypes with a predominantly TemRA phenotype had a substantial fraction of cells without expression of CD57; and in contrast to the high clonotypic variability of TemRA differentiation, expression of CD57 was highly correlated among T-cell clonotypes within epitope-specific responses, indicating TCR-independent expression of CD57 in vivo. Our data highlight the importance of the structural composition of the TCR repertoire for the effector-memory differentiation of the immune response in chronic viral infections and suggest that TCR-dependent and -independent homeostasis shapes the pathogen-specific effector-memory repertoire in vivo.