Simona Urbani

PD-1 Expression in Acute Hepatitis C Virus (HCV) Infection Is Associated with HCV-Specific CD8 Exhaustion

ABSTRACT Hepatitis C virus (HCV)-specific CD8 cell exhaustion may represent a mechanism of HCV persistence. The inhibitory receptor PD-1 has been reported to be up-regulated in exhausted CD8 cells. Therefore, we studied PD-1 expression longitudinally during acute HCV infection. Most HCV-specific CD8 cells expressed PD-1 at the time of acute illness, irrespective of the final outcome. PD-1 expression declined with the acquisition of a memory phenotype and recovery of an efficient CD8 cell function in resolving HCV infections, whereas high levels were maintained when HCV persisted and HCV-specific CD8 cells remained dysfunctional. Blocking PD-1/PDL-1 interaction with an anti-PDL-1 antibody improved the capacity of expansion of virus-specific CD8 cells.

Lamivudine treatment can restore T cell responsiveness in chronic hepatitis B.

High viral and/or antigen load may be an important cause of the T cell hyporesponsiveness to hepatitis B virus (HBV) antigens that is often observed in patients with chronic HBV infection. Reduction of viral and antigen load by lamivudine treatment represents an ideal model for investigating this hypothesis. HLA class II restricted T cell responses and serum levels of HBV-DNA, HBsAg, and HBeAg were studied before and during lamivudine treatment in 12 patients with hepatitis B e antigen positive chronic active hepatitis B to assess possible correlations between viral and/or antigen load and vigor of the T cell response. Cell proliferation to HBV nucleocapsid antigens and peptides and frequency of circulating HBV nucleocapsid-specific T cells were assessed to characterize CD4-mediated responses. A highly significant enhancement of the CD4-mediated response to HBV nucleocapsid antigens was already detectable in most patients 7-14 d after the start of lamivudine treatment. This effect was dramatic and persistent in 10 patients but undetectable in 2. It occurred concomitant with a rapid and marked reduction of viremia. Interestingly, lamivudine also enhanced the responses to mitogens and recall antigens, showing that its effect was not limited to HBV-specific T cells. In conclusion, an efficient antiviral T cell response can be restored by lamivudine treatment in patients with chronic hepatitis B concurrently with reduction of viremia, indicating the importance of viral load in the pathogenesis of T cell hyporesponsiveness in these patients. Since lamivudine treatment can overcome T cell hyporeactivity, combining lamivudine with treatments directed to stimulate the T cell response may represent an effective strategy to induce eradication of chronic HBV infection.

CD8 + T lymphocyte responses are induced during acute hepatitis C virus infection but are not sustained

Cellular immune responses are likely to play a key role in determining the clinical outcome in acute infection with hepatitis C virus (HCV), but the dynamics of such responses and their relationship to viral clearance are poorly understood. In a previous study we have shown highly activated, multispecific cytotoxic T lymphocyte responses arising early and persisting in an individual who subsequently cleared the virus. In this study the HCV‐specific CD8+ lymphocytes response has been similarly analyzed, using peptide‐HLA class I tetramers, in a further nine individuals with documented acute HCV infection, six of whom failed to clear the virus. Significant populations of virus‐specific CD8+ lymphocytes were detected at the peak of acute hepatic illness (maximally 3.5 % of CD8+ lymphocytes). Frequencies were commonly lower than those seen previously and were generally not sustained. Early HCV‐specific CD8+ lymphocytes showed an activated phenotype in all patients (CD38+ and HLA class II+), but this activation was short‐lived. Failure to sustain sufficient numbers of activated virus‐specific CD8+ lymphocytes may contribute to persistence of HCV.

Transient restoration of anti-viral T cell responses induced by lamivudine therapy in chronic hepatitis B

BACKGROUND/AIMS Lamivudine therapy in patients with chronic hepatitis B can induce the recovery of antiviral T cell responses. It is unknown whether the recovery of T cell responsiveness is long-lasting and persists throughout the treatment and whether the elevation of viremia which follows therapy withdrawal can restore a condition of T cell unresponsiveness. METHODS Frequency and function of circulating hepatitis B virus (HBV)-specific CD4 and CD8 cells from 12 hepatitis e surface antigen + patients with chronic hepatitis B were studied longitudinally before, during and after lamivudine therapy by intracellular cytokine staining, proliferation and cytotoxicity assays against HBV proteins and peptides. CD4-mediated responses were analyzed in all patients, whereas CD8 cells were studied in 6 HLA-A2+ patients. RESULTS HBV-specific CD4 and CD8 reactivity showed a bi-phasic behavior under lamivudine therapy with an early enhancement of T cell frequency and intensity of responses followed by a persistent decline starting from the 5th to 6th month of treatment. CONCLUSIONS Since restoration of HBV-specific T cell reactivity is only transient, our study indicates that therapeutic stimulation of HBV-specific T cell responses to complement lamivudine treatment should be done early after the initiation of lamivudine. Moreover, the transient nature of the immune reconstitution may represent a favorable condition for virus reactivation once lamivudine therapy is withdrawn.

Virus-Specific CD8+ Lymphocytes Share the Same Effector-Memory Phenotype but Exhibit Functional Differences in Acute Hepatitis B and C

ABSTRACT Hepatitis B and hepatitis C viruses (HBV and HCV) are both noncytopathic and can cause acute and chronic infections of the liver. Although they share tropism for the same organ, development of chronic hepatitis is much more frequent following HCV infection, suggesting different mechanisms of viral persistence. In this study, we show that circulating HBV- and HCV-specific tetramer-positive CD8 cells during the acute phase of hepatitis B and C belong almost entirely to an effector-memory subset (CCR7− CD45RA−). Despite this phenotypic similarity, HBV- and HCV-specific CD8 cells show striking functional differences. HBV-specific tetramer-positive CD8 cells express high perforin content ex vivo, expand vigorously, and display efficient cytotoxic activity and gamma interferon (IFN-γ) production upon peptide stimulation. A comparable degree of functional efficiency is maintained after the resolution of hepatitis B. In contrast, HCV-specific CD8 cells in the acute phase of hepatitis C express significantly lower levels of perforin molecules ex vivo and show depressed CD8 function in terms of proliferation, lytic activity, and IFN-γ production, irrespective of the final outcome of the disease. This defect is transient, because HCV-specific CD8 cells can progressively improve their function in patients with self-limited hepatitis C, while the CD8 function remains persistently depressed in subjects with a chronic evolution.

Outcome of acute hepatitis C is related to virus-specific CD4 function and maturation of antiviral memory CD8 responses†

A timely, efficient, and coordinated activation of both CD4 and CD8 T cell subsets following HCV infection is believed to be essential for HCV control. However, to what extent a failure of the individual T cell subsets can contribute to the high propensity of HCV to persist is still largely undefined. To address this issue, we analyzed the breadth, vigor, and quality of CD4 and CD8 responses simultaneously with panels of peptides covering the entire HCV sequence or containing the HLA‐A2–binding motif, and with recombinant HCV proteins in 16 patients with acute HCV infection by tetramer staining, ELISPOT, and intracellular cytokine staining for interferon γ, interleukin (IL)‐2, IL‐4, and IL‐10. Our results indicate that at clinical onset, CD8 responses are similarly weak and narrowly focused in both self‐limited and chronically evolving infections. At this stage, CD4 responses are deeply impaired in patients with a chronic outcome as they are weak and of narrow specificity, unlike the strong, broad and T helper 1–oriented CD4 responses associated with resolving infections. Only patients able to finally control infection show maturation of CD8 memory sustained by progressive expansion of CD127+ CD8 cells. Thus, a poor CD8 response in the acute stage of infection may enhance the overall probability of chronic viral persistence. In conclusion, the presence of functional CD4 responses represents one of the factors dictating the fate of infection by directly contributing to control of the virus and by promoting maturation of protective memory CD8 responses. (HEPATOLOGY 2006;44:126–139.)

Activation of Natural Killer Cells During Acute Infection With Hepatitis C Virus

BACKGROUND & AIMS Natural killer (NK) cells are essential early after infection, not only for viral containment but also for timely and efficient induction of adaptive responses. An inhibitory effect of hepatitis C virus (HCV)-E2 proteins on NK cells has been reported, but the features of NK cell responses in the acute phase of hepatitis C are still largely undefined. Therefore, the aim of this study was to characterize the function and phenotype of NK cells in the acute phase of infection and compare individuals with chronic and self-limited outcomes. METHODS Twenty-two individuals with acute HCV infection, 14 with chronic evolution, and 8 with self-limited infection, were studied using NK phenotypic and functional assays. RESULTS An increased expression of NKG2D on both CD56(bright) and CD56(dim) NK cells was detected in patients with acute HCV, irrespective of the outcome, as compared with healthy controls. Also, interferon gamma production and cytotoxicity by NK cells were higher in individuals with acute HCV infection than in healthy controls. Subset analysis showed increased interferon gamma production in both NK cell subsets carrying group 1 and group 2 HLA-C-specific killer cell immunoglobulin-like receptors. However, increased CD107a was noted only on NK cells expressing the group 1 HLA-C-specific killer cell immunoglobulin-like receptor and was maximal in self-limited infection. CONCLUSIONS Our data show that in the acute phase of HCV infection, NK cells are activated regardless of outcome, with no evidence of a suppressive effect of HCV on NK cell function.

Heterologous T cell immunity in severe hepatitis C virus infection

Hepatitis C virus (HCV) can cause liver disease of variable severity. Expansion of preexisting memory CD8 T cells by cross-reactivity with a new heterologous virus infection has been shown in mice to shape the repertoire of the primary response and to influence virus-related immunopathology (Selin, L.K. 2004. Immunity. 20:5–16). To determine whether this mechanism can influence the course of HCV infection, we analyzed the features of the HCV-specific CD8 T cell response in eight patients with acute HCV infection, two of whom had a particularly severe illness. Patients with severe hepatitis, but not those with mild disease, showed an extremely vigorous CD8 T cell response narrowly focused on a single epitope (NS3 1073–1081), which cross-reacted with an influenza neuraminidase sequence. Our results suggest that CD8 T cell cross-reactivity influences the severity of the HCV-associated liver pathology and depicts a model of disease induction that may apply to different viral infections.

Restoration of HCV-specific T cell functions by PD-1/PD-L1 blockade in HCV infection: Effect of viremia levels and antiviral treatment

BACKGROUND/AIMS HCV-specific T cells in acute hepatitis C with subsequent chronic evolution are dysfunctional and most of them express PD-1. The aim of the study was to investigate to what extent the antiviral T cell function can be restored by reversing T cell exhaustion by PD-1/PD-L1 blockade and to assess whether this restoration is favored by IFN-alpha treatment. METHODS PD-1 and PD-L1 expression was studied on T cells and dendritic cells, respectively, of 14 patients with acute hepatitis C and different evolutions of infection. The effect of anti-PD-L1 was analyzed on proliferation, cytokine production and cytolytic activity of CD4 and CD8 T cells. RESULTS While PD-1 expression dropped concurrently with spontaneous or IFN-alpha induced HCV-RNA decline, PD-L1 levels on dendritic cells increased during IFN-alpha treatment. Anti-PD-L1 antibodies improved expansion and cytokine production but not the cytolytic activity of HCV-specific T cells. This restoration tended to be greater at lower levels of viremia and PD-1 expression and during PEG-IFNalpha treatment. CONCLUSIONS PD-1/PD-L1 blockade has an immunoregulatory activity which may synergize with the antiviral effect of IFN-alpha therapy and should be thus explored further in long-lasting chronic HCV infections in the perspective of improving the efficacy of available antiviral treatments.

Immunopathogenesis of hepatitis B

The type of cell-mediated responses expressed at the early stages of HBV infection can influence the subsequent outcome of hepatitis B. Indeed, recovery is associated with efficient activation of mechanisms of the innate immunity, which seem to be responsible for the early inhibition of viral replication. A subsequent activation of HBV-specific T cells is probably crucial to complement the effect of the innate immunity and to allow complete control of virus replication. Moreover, control of infection cannot be achieved without rapid and efficient development of anti-envelope neutralizing antibody responses that are needed for elimination of free viral particles and inhibition of cell to cell spread of the virus.