Antigen Load and Viral Sequence Diversification Determine the Functional Profile of HIV-1–Specific CD8+ T Cells

Abstract

BackgroundVirus-specific CD8+ T lymphocytes play a key role in the initial reduction of peak viremia during acute viral infections, but display signs of increasing dysfunction and exhaustion under conditions of chronic antigen persistence. It has been suggested that virus-specific CD8+ T cells with a “polyfunctional” profile, defined by the capacity to secrete multiple cytokines or chemokines, are most competent in controlling viral replication in chronic HIV-1 infection. We used HIV-1 infection as a model of chronic persistent viral infection to investigate the process of exhaustion and dysfunction of virus-specific CD8+ T cell responses on the single-epitope level over time, starting in primary HIV-1 infection.Methods and FindingsWe longitudinally analyzed the polyfunctional epitope-specific CD8+ T cell responses of 18 patients during primary HIV-1 infection before and after therapy initiation or sequence variation in the targeted epitope. Epitope-specific CD8+ T cells responded with multiple effector functions to antigenic stimulation during primary HIV-1 infection, but lost their polyfunctional capacity in response to antigen and up-regulated programmed death 1 (PD-1) expression with persistent viremic infection. This exhausted phenotype significantly decreased upon removal of stimulation by antigen, either in response to antiretroviral therapy or by reduction of epitope-specific antigen load in the presence of ongoing viral replication, as a consequence of in vivo selection of cytotoxic T lymphocyte escape mutations in the respective epitopes. Monofunctionality increased in CD8+ T cell responses directed against conserved epitopes from 49% (95% confidence interval 27%–72%) to 76% (56%–95%) (standard deviation [SD] of the effect size 0.71), while monofunctionality remained stable or slightly decreased for responses directed against escaped epitopes from 61% (47%–75%) to 56% (42%–70%) (SD of the effect size 0.18) (p < 0.05).ConclusionThese data suggest that persistence of antigen can be the cause, rather than the consequence, of the functional impairment of virus-specific T cell responses observed during chronic HIV-1 infection, and underscore the importance of evaluating autologous viral sequences in studies aimed at investigating the relationship between virus-specific immunity and associated pathogenesis.

Antigen amount dictates CD8+T‐cell exhaustion during chronic viral infection irrespective of the type of antigen presenting cell

“…As a correlation of the degree of CD8 + T-cell exhaustion with the viral load was observed in M. tuberculosis [27] and HIV [24,26] infected humans, our findings likely have a strong relevance for treatment of chronically infected patients. It is currently widely discussed to treat chronically infected patients with regimes aimed at boosting the antiviral CD8 + T-cell response, for example, with antibodies blocking the interaction of PD-1 and PD-L1 [50] (in combination with antibodies directed against other inhibitory receptors [51,52]).…”

“…Finally, it is conceivable that extensive killing of antigen-presenting DCs might be involved in the observed pathology in chronically infected DC-MHCI mice, potentially leading to severe immunosuppression and inability of chronically infected mice to cope with other viral or bacterial infections. However, this hypothesis is rather unlikely as the number of DCs was not severely compromised in chronically infected DC-MHCI mice and since development of pathology was very acute which is unlikely to be caused by heterologous infections in the setting of a clean specific pathogen free facility.As a correlation of the degree of CD8 + T-cell exhaustion with the viral load was observed in M. tuberculosis [27] and HIV [24,26] infected humans, our findings likely have a strong relevance for treatment of chronically infected patients. It is currently widely discussed to treat chronically infected patients with regimes aimed at boosting the antiviral CD8 + T-cell response, for example, with antibodies blocking the interaction of PD-1 and PD-L1 [50] …”

“…Recent work has highlighted a negative correlation between viral load and CTL function in chronically infected humans and mice [24][25][26][27]. Even though these studies indicate that high overall antigen levels correlate with T-cell exhaustion, it was never directly shown whether alterations of antigen levels can substantially influence T-cell function independently of the cell type presenting the antigen in vivo.…”

“…This is likely due to a high number of infected nonhematopoietic cells (with hepatocytes [36], fibroblastic reticular cells [33], lamina propria cells [37], glial cells and microglia being infected [38], and high expression of the LCMV receptor α-dystroglycan being present on stromal and epithelial cells [39] in many tissues, suggesting that these cells might also be infected) compared with hematopoietic cells (with mainly DCs [40,41] and macrophages [42] being infected by LCMV). However, by selective provision of antigen presentation in hematopoietic cells, CD8 + T-cell exhaustion can also be promoted, indicating that the overall amount of antigen, independent of the cell type (hematopoietic versus nonhematopoietic), can drive CD8 + T-cell exhaustion.The necessity of high antigen levels for the induction of CD8 + T-cell exhaustion was suggested in several settings of chronic infection such as LCMV infection of mice [25,43], repeated injection of antigen into mice [44], but also in humans a correlation between high antigen levels and T-cell exhaustion was observed after Mycobacterium tuberculosis [27] and HIV [24,26] infection. However, these studies were not able to distinguish whether increased exhaustion in the presence of more antigen is only due to the amount of antigen that is recognized by CD8 + T cells, or if certain cell types induce exhaustion more potently than others.…”

Premature Terminal Exhaustion of Friend Virus-Specific Effector CD8+ T Cells by Rapid Induction of Multiple Inhibitory Receptors

“…There has been considerable evidence that the initial viral load inversely correlates with the functionality of Ag-specific CD8 + T cells (10,54,55). Recently, a combined in situ tetramer staining and in situ hybridization approach showed that relative rates of increase in Agspecific effector CD8 + T cells and virally infected targets during the early stage predict the outcome of viral infection (56).…”