Human leukocyte antigen (HLA) B*27 and B*57 are associated with protection against HIV-1 disease progression, yet most persons expressing these alleles are unable to control HIV-1. Here we show that HLA-B*27-restricted CD8+ T cells in controllers and progressors differ in their ability to inhibit virus replication through targeting of the immunodominant Gag epitope. This is associated with distinct TCR clonotypes, characterized by superior control of HIV-1 replication in vitro, greater cross-reactivity against epitope variants, and enhanced perforin delivery. Clonotype-specific differences in antiviral efficacy were also observed for an immunodominant HLA-B*57 restricted response in controllers and progressors. Thus, the efficacy of protective alleles is modulated by specific TCR clonotypes selected in natural infection, providing a functional explanation for divergent HIV-1 outcomes.

Control of human immunodeficiency virus type 1 (HIV-1) by HLA-B27-positive subjects has been linked to an immunodominant CD8؉ cytotoxic T-lymphocyte (CTL) response targeting the conserved KK10 epitope (KRWIILGLNK 263-272 ) in p24/Gag. Viral escape in KK10 typically occurs through development of an R 264 K substitution in conjunction with the upstream compensatory mutation S 173 A, and the difficulty of the virus to escape from the immune response against the KK10 epitope until late in infection has been associated with slower clinical progression. Rare alternative escape mutations at R 264 have been observed, but factors dictating the preferential selection of R 264 K remain unclear. Here we illustrate that while all observed R 264 mutations (K, G, Q, and T) reduced peptide binding to HLA-B27 and impaired viral replication, the replicative defects of the alternative mutants were actually less pronounced than those for R 264 K. Importantly, however, none of these mutants replicated as well as an R 264 K variant containing the compensatory mutation S 173 A. In assessing the combined effects of viral replication and CTL escape using an in vitro coculture assay, we further observed that the compensated R 264 K mutant also displayed the highest replication capacity in the presence of KK10-specific CTLs. Comparisons of codon usage for the respective variants indicated that generation of the R 264 K mutation may also be favored due to a G-to-A bias in nucleotide substitutions during HIV-1 replication. Together, these data suggest that the preference for R 264 K is due primarily to the ability of the S 173 Acompensated virus to replicate better than alternative variants in the presence of CTLs, suggesting that viral fitness is a key contributor for the selection of immune escape variants.

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CD8 + T cells are a key component of the adaptive immune response to viral infection. An inadequate CD8 +T cell response is thought to be partly responsible for the persistent chronic infection that arises following infection with HIV. It is therefore critical to identify ways to define what constitutes an adequate or inadequate response. IFN-γ production has been used as a measure of T cell function, but the relationship between cytokine production and the ability of a cell to lyse virus-infected cells is not clear. Moreover, the ability to assess multiple CD8 + T cell functions with single-cell resolution using freshly isolated blood samples, and subsequently to recover these cells for further functional analyses, has not been achieved. As described here, to address this need, we have developed a high-throughput, automated assay in 125-pl microwells to simultaneously evaluate the ability of thousands of individual CD8 + T cells from HIV-infected patients to mediate lysis and to produce cytokines. This concurrent, direct analysis enabled us to investigate the correlation between immediate cytotoxic activity and short-term cytokine secretion. The majority of in vivo primed, circulating HIV-specific CD8 + T cells were discordant for cytolysis and cytokine secretion, notably IFN-γ, when encountering cognate antigen presented on defined numbers of cells. Our approach should facilitate determination of signatures of functional variance among individual effector CD8 + T cells, including those from mucosal samples and those induced by vaccines.

IntroductionThe first recorded outbreak of severe acute respiratory syndrome (SARS) in late February 2003 has led to thousands of infected patients and hundreds of deaths. The etiologic agent of the syndrome, a novel coronavirus termed SARS-associated coronavirus (SARS-CoV), has since been identified and isolated, 1-4 and its genome sequenced. 5,6 SARS is characterized by high fever, rigor, headache, nonproductive cough, or dyspnea and may progress to generalized, interstitial infiltrates in the lung, requiring intubation and mechanical ventilation. 1,2,7-9 A common observation in patients with SARS is pronounced lymphopenia. 1,10,11 A notable drop in CD4 ϩ and CD8 ϩ T lymphocyte counts occurs early in the course of the disease and is associated with adverse outcomes. 12 To date, studies on SARS have generally been retrospective or limited to the description of initial clinical, hematologic, radiologic, and microbiologic findings. Further studies to evaluate the mechanisms of these manifestations may help us to better understand this disease.Evidence suggests that CD8 ϩ cytotoxic T lymphocytes (CTLs) play a pivotal role in both virus elimination and induction of immunopathology in respiratory syncytial virus (RSV) infection, following recognition of epitopes presented on target cells in the context of major histocompatibility complex (MHC) class I. [13][14][15][16][17] Similarly, CTLs may participate in the clearance of virus in recovered SARS patients but also contribute to immunopathology in early stages of the disease; the molecular mechanisms underlying these CD8 ϩ CTL-mediated effects remain poorly defined. HLA-A2 is the most common HLA-A allele in Asian populations, particularly in the Chinese, with an estimated frequency of more than 50%. 18 As SARS affected many parts of Asia, and a reservoir of infection may persist in these regions, the identification of HLA-A*0201-restricted CTL epitopes of SARS-CoV is an important contribution to future studies concerning the role of CTLs in SARS-CoV pathogenesis and protection in at-risk populations.Here we have studied a panel of SARS-CoV spike protein (SARS/S)-derived peptides to identify those with binding motifs for HLA-A*0201 molecules. We evaluated the ability of HLA-A*0201 binding peptides to provoke in vivo-and in vitro-specific CTL responses in HLA-A2.1/K b transgenic (Tg) mice and peripheral blood lymphocyte (PBL) preparations from MHC-matched healthy donors, using dendritic cells (DCs) prepulsed with the peptides. Our findings show that anti-SARS-CoV CTLs generated from Tg mice and PBLs of healthy donors can elicit an antigenspecific, HLA-A2.1-restricted response, effectively killing peptidepulsed T2 cells or HLA-A2.1 ϩ tumor cell lines endogenously For personal use only. on May 10, 2018. by guest www.bloodjournal.org From expressing S protein. To the best of our knowledge, our study is the first successful prospective identification of a novel HLA-A*0201-restricted CD8 ϩ T-cell epitope from the SARS-CoV spike protein. Materials and methods PeptidesTo ide...

Defining the antiviral efficacy of CD8 T cells is important for immunogen design

To date, the pathogenesis of severe acute respiratory syndrome (SARS) in humans is still not well understood. SARS coronavirus (SARS-CoV)-specific CTL responses, in particular their magnitude and duration of postinfection immunity, have not been extensively studied. In this study, we found that heat-inactivated SARS-CoV elicited recall CTL responses to newly identified spike protein-derived epitopes (SSp-1, S978, and S1202) in peripheral blood of all HLA-A*0201+ recovered SARS patients over 1 year postinfection. Intriguingly, heat-inactivated SARS-CoV elicited recall-like CTL responses to SSp-1 but not to S978, S1202, or dominant epitopes from several other human viruses in 5 of 36 (13.8%) HLA-A*0201+ healthy donors without any contact history with SARS-CoV. SSp-1-specific CTLs expanded from memory T cells of both recovered SARS patients, and the five exceptional healthy donors shared a differentiated effector CTL phenotype, CD45RA+CCR7−CD62L−, and expressed CCR5 and CD44. However, compared with the high avidity of SSp-1-specific CTLs derived from memory T cells of recovered SARS patients, SSp-1-specific CTLs from the five exceptional healthy donors were of low avidity, as determined by their rapid tetramer dissociation kinetics and reduced cytotoxic reactivity, IFN-γ secretion, and intracellular production of IFN-γ, TNF-α, perforin, and granzyme A. These results indicate that SARS-CoV infection induces strong and long-lasting CTL-mediated immunity in surviving SARS patients, and that cross-reactive memory T cells to SARS-CoV may exist in the T cell repertoire of a small subset of healthy individuals and can be reactivated by SARS-CoV infection.

Oral tongue squamous cell carcinoma (OTSCC) is the most common oral cavity tumor. In this study, we examined the basis for the activity of PD-1-based immune checkpoint therapy that is being explored widely in head and neck cancers. Using multispectral imaging, we systematically investigated the OTSCC tumor microenvironment (TME) by evaluating the frequency of PD-1 expression in CD8+, CD4+ and FoxP3+ tumor-infiltrating lymphocytes (TIL). We also defined the cellular sources of PD-L1 to evaluate the utility of PD-1:PD-L1 blocking antibody therapy in this patient population. PD-L1 was expressed in 79% of the OTSCC specimens examined within the TME. Expression of PD-L1 was associated with moderate to high levels of CD4+ and CD8+ TIL. We found that CD4+ TIL were present in equal or greater frequencies than CD8+ TIL in 94% of OTSCC, and that CD4+ FOXP3neg TIL were co-localized with PD-1/PD-L1/CD68 more frequently than CD8+ TIL. However, both CD4+PD1+ and CD8+PD1+ TIL were anergic in the setting of PD-L1 expression. Overall, our results highlight the importance of CD4+ TIL as pivotal regulators of PD-L1 levels and in determining the responsiveness of OTSCC to PD1-based immune checkpoint therapy.