Debbie van Baarle

HIV-specific CD8+ T cell proliferation is coupled to perforin expression and is maintained in nonprogressors

It is unclear why immunological control of HIV replication is incomplete in most infected individuals. We examined here the CD8+ T cell response to HIV-infected CD4+ T cells in rare patients with immunological control of HIV. Although high frequencies of HIV-specific CD8+ T cells were present in nonprogressors and progressors, only those of nonprogressors maintained a high proliferative capacity. This proliferation was coupled to increases in perforin expression. These results indicated that nonprogressors were differentiated by increased proliferative capacity of HIV-specific CD8+ T cells linked to enhanced effector function. In addition, the relative absence of these functions in progressors may represent a mechanism by which HIV avoids immunological control.

High viral burden in the presence of major HIV-specific CD8(+) T cell expansions: evidence for impaired CTL effector function.

To investigate the effect of HIV‐specific CD8+ T cells on viral plasma load and disease progression, we enumerated HLA‐A2‐, B8‐ and B57‐restricted CD8+ T cells directed against several HIV epitopes in a total of 54 patients by the use of tetrameric HLA‐peptide complexes. In patients with high CD4+ T cell numbers, HIV‐specific tetramer+ cells inversely correlated with viral load. Patients with CD4+ T cell numbers below 400/μ l blood, however, carried high viral load despite frequently having high tetramer+ T cell numbers. This lack of correlation between viral load and tetramer+ cells did not result from viral escape variants, as in only 4 of 13 patients, low frequencies of viruses with mutated epitopes were observed. In 15 patients we measured CD8+ T cell antigen responsiveness to HIV peptide stimulation in vitro. FACS analyses showed differential IFN‐γ production of the tetramer+ cells, and this proportion of IFN‐γ‐producing tetramer+ cells correlated with AIDS‐free survival and with T cell maturation to the CD27– effector stage. These data show that most HIV‐infected patients have sustained HIV‐specific T cell expansions but many of these cells seem not to be functional, leaving the patient with high numbers of non‐functional virus‐specific CD8+ T cells in the face of high viral burden.

Failing immune control as a result of impaired CD8+ T-cell maturation: CD27 might provide a clue

Despite readily detectable virus-specific CD8(+) T cells in most HIV-infected patients, immune surveillance is eventually lost, leading to progression to AIDS. Recently developed insights into human T-cell differentiation have been used to study the phenotype of virus-specific T cells in HIV-infected individuals. Based on these results, we propose that failing immune control in human viral infection could be a result of impaired cytotoxic T-lymphocyte (CTL) maturation into fully differentiated effector T cells. Impaired maturation is not confined to HIV-specific CD8(+) T cells but could also be involved in failing immunity to Epstein-Barr virus and other viral infections. We postulate that CD27(-) effector CD8(+) T cells might be required for adequate control of chronic viral infection and prevention of disease development.

Changes in the Composition of Circulating CD8+ T Cell Subsets during Acute Epstein-Barr and Human Immunodeficiency Virus Infections in Humans

In response to viral infection, unprimed naive CD8(+), major histocompatibility complex class I-restricted, virus-specific T cells clonally expand and differentiate into memory- and effector-type cells. Changes in CD8(+) subset distribution were studied in 17 subjects with acute human immunodeficiency virus type 1 infection and in 14 subjects with acute Epstein-Barr virus (EBV) infection, with combined CD45RO, CD27, and CD28 monoclonal antibodies. A vast expansion of memory-type CD45RO(+)CD27(+)CD8(+) T cells, with high expression of the cell-cycle marker Ki-67, was observed in both infections. Strikingly, CD45RO(+)CD27(+)CD28(-) cells increased >10-fold in acute viral infection and had high Ki-67 expression. In acute EBV infection, a substantial portion of the expanded T cells were EBV-peptide specific. These cells resided mainly in the CD45RO(+)CD27(+) subpopulation, with most in the CD27(+)CD28(-) subpopulation. Content of perforin expression, as a measure of cytotoxic capacity, was relatively low in the CD27(+)CD28(+) T cells and highest in the CD27(-)CD28(-) subpopulation.

Recognition of Homo- and Heterosubtypic Variants of Influenza A Viruses by Human CD8+ T Lymphocytes

In the present study, the recognition of epitope variants of influenza A viruses by human CTL was investigated. To this end, human CD8+ CTL clones, specific for natural variants of the HLA-B*3501-restricted epitope in the nucleoprotein (NP418–426), were generated. As determined in 51Cr release assays and by flow cytometry with HLA-B*3501-peptide tetrameric complexes, CTL clones were found to be specific for epitopes within one subtype or cross-reactive with heterosubtypic variants of the epitope. Using eight natural variants of the epitope, positions in the 9-mer important for T cell recognition and involved in escape from CTL immunity were identified and visualized using multidimensional scaling. It was shown that positions 4 and 5 in the 9-mer epitope were important determinants of T cell specificity. The in vivo existence of CD8+ cells cross-reactive with homo- and heterosubtypic variants of the epitope was further confirmed using polyclonal T cell populations obtained after stimulation of PBMC with different influenza A viruses. Based on the observed recognition patterns of the clonal and polyclonal T cell populations and serology, it is hypothesized that consecutive infections with influenza viruses containing different variants of the epitope select for cross-reactive T cells in vivo.

Viral Replication Capacity as a Correlate of HLA B57/B5801-Associated Nonprogressive HIV-1 Infection

HLA B57 and the closely related HLA B5801 are over-represented among HIV-1 infected long-term nonprogressors (LTNPs). It has been suggested that this association between HLA B57/5801 and asymptomatic survival is a consequence of strong CTL responses against epitopes in the viral Gag protein. Moreover, CTL escape mutations in Gag would coincide with viral attenuation, resulting in low viral load despite evasion from immune control. In this study we compared HLA B57/5801 HIV-1 infected progressors and LTNPs for sequence variation in four dominant epitopes in Gag and their ability to generate CTL responses against these epitopes and the autologous escape variants. Prevalence and appearance of escape mutations in Gag epitopes and potential compensatory mutations were similar in HLA B57/5801 LTNPs and progressors. Both groups were also indistinguishable in the magnitude of CD8+ IFN-γ responses directed against the wild-type or autologous escape mutant Gag epitopes in IFN-γ ELISPOT analysis. Interestingly, HIV-1 variants from HLA B57/5801 LTNPs had much lower replication capacity than the viruses from HLA B57/5801 progressors, which did not correlate with specific mutations in Gag. In conclusion, the different clinical course of HLA B57/5801 LTNPs and progressors was not associated with differences in CTL escape mutations or CTL activity against epitopes in Gag but rather with differences in HIV-1 replication capacity.

Human herpes virus 6 plasma DNA positivity after hematopoietic stem cell transplantation in children: an important risk factor for clinical outcome.

Human herpes virus 6 (HHV6) is known to reactivate after hematopoietic stem cell transplantation (HSCT), and has been suggested to be associated with severe clinical manifestations in adults. The clinical significance in children remains unclear. We investigated the incidence of HHV6 reactivation in relation to HSCT-associated morbidity and mortality in children. Between January 2004 and May 2006, 58 pediatric patients, median age 7.6 years (range: 0.1-18.1 years), received their first allogeneic HSCT. After HSCT, HHV6, Epstein Barr Virus (EBV), cytomegalovirus (CMV), and adenovirus (AdV)-plasma loads were weekly measured by quantitative PCR. Clinical features, engraftment, graft-versus-host disease (GVHD), and HSCT-associated mortality and morbidity were monitored. HHV6 reactivations were classified in group I (no reactivation), group II (loads <1000 cp/mL) and group III (loads >1000 cp/mL). CMV, EBV, Herpes Simpex Virus, Varicella Zoster Virus, and AdV-reactivations were treated according to local guidelines. HHV6 was treated only when there was clinical suspicion of disease. Thirty-six HLA-identical and 22 HLA nonidentical grafts were transplanted of which 43 were bone marrow or peripheral blood stem cells grafts and 15 were cord blood (CB) grafts. Median follow-up of the patients was 15.5 (1-35) months. HHV6 reactivation occurred in 39 of 58 (67%) patients with 31 of 39 (80%) occurring within the first 30 days post-HSCT. In 26 of 58 (45%) patients (group III), HHV 6 reactivation was significantly associated with higher nonrelapse mortality (P = .02), using multivariate Cox proportional hazard models and grade 2-4 acute GVHD (P = .03) and chronic GVHD (P = .05) in a multivariate logistic regression analysis. HHV6 reactivation is very common after HSCT in children and is associated with serious transplantation-related morbidity and mortality. Although the exact role of HHV6 reactivation after HSCT has to be elucidated, early detection and initiation of therapy might be of benefit.

Naive CD8+ T-cell precursors display structured TCR repertoires and composite antigen-driven selection dynamics

Basic parameters of the naive antigen (Ag)‐specific T‐cell repertoire in humans remain poorly defined. Systematic characterization of this ‘ground state’ immunity in comparison with memory will allow a better understanding of clonal selection during immune challenge. Here, we used high‐definition cell isolation from umbilical cord blood samples to establish the baseline frequency, phenotype and T‐cell antigen receptor (TCR) repertoire of CD8+ T‐cell precursor populations specific for a range of viral and self‐derived Ags. Across the board, these precursor populations were phenotypically naive and occurred with hierarchical frequencies clustered by Ag specificity. The corresponding patterns of TCR architecture were highly ordered and displayed partial overlap with adult memory, indicating biased structuring of the T‐cell repertoire during Ag‐driven selection. Collectively, these results provide new insights into the complex nature and dynamics of the naive T‐cell compartment.

Absolute Level of Epstein-Barr Virus DNA in Human Immunodeficiency Virus Type 1 Infection Is Not Predictive of AIDS-Related Non-Hodgkin Lymphoma

To study whether Epstein-Barr virus (EBV) load can be used to predict the occurrence of acquired immunodeficiency syndrome-related non-Hodgkin lymphoma (AIDS-NHL), we determined EBV load longitudinally for individuals infected with human immunodeficiency virus type 1. EBV load in peripheral blood mononuclear cells (PBMC) was high and displayed considerable fluctuations over time, indicating that absolute EBV load in PBMC is not predictive of the development of AIDS-NHL. EBV DNA was also detectable in serum at some time points but at a lower level.

Female sex and IL28B, a synergism for spontaneous viral clearance in hepatitis C virus (HCV) seroconverters from a community-based cohort.

Background & Aims Since acute hepatitis C virus (HCV) infection is often asymptomatic, it is difficult to examine the rate and determinants of spontaneous clearance. Consequently, these studies are subject to bias, which can potentially lead to biased rates of viral clearance and risk estimates. We evaluated determinants of spontaneous HCV clearance among HCV seroconverters identified in a unique community-based cohort. Methods Subjects were 106 drug users with documented dates of HCV seroconversion from the Amsterdam Cohort Study. Logistic regression was used to examine sociodemographic, behavioral, clinical, viral and host determinants, measured around acute infection, of HCV clearance. Results The spontaneous viral clearance rate was 33.0% (95% confidence interval (CI) 24.2–42.8). In univariate analyses female sex and fever were significantly associated with spontaneous clearance. The favorable genotypes for rs12979860 (CC) and rs8099917 (TT) were associated with spontaneous clearance, although borderline significant. In multivariate analysis, females with the favorable genotype for rs12979860 (CC) had an increased odds to spontaneously clear HCV infection (adjustedOR 6.62, 95% 2.69–26.13), whereas females with the unfavorable genotype were as likely as men with the favorable and unfavorable genotype to clear HCV. Chronic Hepatitis B infection and absence of HIV coinfection around HCV seroconversion also favor HCV clearance. Conclusions This study shows that co-infection with HIV and HBV and genetic variation in the IL28B region play an important role in spontaneous clearance of HCV. Our findings suggest a possible synergistic interaction between female sex and IL28B in spontaneous clearance of HCV.