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

The Impairment of CD8 Responses Limits the Selection of Escape Mutations in Acute Hepatitis C Virus Infection

Abstract Evasion from protective CD8 responses by mutations within immunodominant epitopes represents a potential strategy of HCV persistence. To investigate the pathogenetic relevance of this mechanism, a careful search for immunodominant CD8 epitopes was conducted in six patients with chronic evolution of HCV infection by analyzing their global CD8 response with a panel of overlapping synthetic peptides covering the overall HCV sequence and by studying the CD8 frequency by tetramer staining. Immunodominant responses were followed longitudinally from the time of acute onset in relation to the evolution of the epitopic sequences. Although intensity of CD8 responses and frequency of HCV-specific CD8 cells declined over time in all patients, mutations emerged in only three of the six acute patients studied. Variant sequences were less efficiently recognized by CD8 cells than parental epitopes and were poorly efficient in inducing a CD8 response in vitro. CD8 epitopes undergoing mutations were targeted by high avidity CD8 cells more efficient in effector function. Our data support the view that immunodominant CD8 responses are affected by inhibitory mechanisms operating early after infection and that the emergence of escape mutations represents an additional mechanism of virus evasion from those CD8 responses that are functionally preserved

Activation of natural killer cells during acute infection with hepatitis C virus

Il virus dell’epatite C (HCV) è l’agente eziologico di epatiti virali che durante la fase acuta sono spesso asintomatiche, e quindi difficili da diagnosticare. Questo virus è in grado di stabilire un’infezione cronica persistente nella maggioranza degli individui esposti e la risposta immunitaria contro HCV gioca un ruolo importante sia nel controllo virale che nella patogenesi della malattia. Molti lavori hanno studiato il ruolo della risposta dell’immunità adattativa durante la fase acuta dell’infezione in relazione all’evolvere di malattia. La risoluzione spontanea dell’infezione da HCV è stata associata a risposte CD4 e CD8 vigorose e multispecifiche, mentre l’indebolimento dell’immunità adattativa è stato osservato nell’infezione cronica. Il sistema dell’immunità innata è stato studiato poco nell’infezione acuta da virus C, ed il proprio ruolo nel determinare l’evoluzione di malattia è ancora da chiarire. Comunque, è stata dimostrata l’attivazione delle cellule T durante la fase acuta dell’infezione e sono state descritte anomalie di queste cellule e delle loro sub-popolazioni in pazienti con infezione cronica da virus C. Le cellule Natural Killer (NK) sono uno dei principali attori dell’immunità innata, vale a dire l’insieme di quelle componenti delle nostre difese comparse precocemente nell’evoluzione e che costituiscono vere e proprie fondamenta del sistema immunitario. Le cellule NK sono essenziali nelle prime fasi dopo un’infezione, non solo per controllare il virus, ma anche per un’efficiente induzione della risposta adattativa. E’ stato riportato un effetto inibitorio da parte delle cellule NK, sulla proteina (HCV)-E2 del virus dell’epatite C, ma sono ancora da definire le caratteristiche delle risposte delle cellule NK nella fase acuta dell’epatite C. Il controllo delle cellule NK è determinato dalla combinazione di espressione di recettori di inibizione e di attivazione. E’ probabile che, l’integrazione delle cellule NK e dei segnali derivati da questi recettori, determini se le cellule si attiveranno. Per questo motivo lo scopo dello studio è stato quello di caratterizzare la funzione ed il fenotipo delle cellule NK durante la fase acuta dell’infezione, confrontando pazienti che cronicizzano e pazienti che guariscono spontaneamente. Sono stati reclutati 22 pazienti, di cui 14 con evoluzione cronica di malattia e 8 che sono guariti spontaneamente. E’ stato osservato un aumento di espressione del recettore NKG2D sia sulle cellule NK CD56Dim e CD56Bright nei pazienti con epatite acuta, indipendentemente dall’esito di malattia, rispetto ai controlli sani. Anche la produzione di IFN-gamma e la capacità litica delle cellule NK è più alta negli individui con infezione acuta C rispetto ai controlli sani. L’analisi dei subset mostra un aumento di produzione di IFN- sia nel gruppo 1 che nel gruppo 2 HLA-C-KIR-specifico. L’aumento del CD107 è espresso solo sulle cellule NK del gruppo 1 HLA-C KIR-specifico ed è massimo in coloro che guariscono spontaneamente. In conclusione i risultati mostrano che durante la fase acuta dell’infezione da virus C, le cellule NK sono attivate indipendentemente dall’esito di malattia, e non mostrano un effetto soppressivo nei confronti di HCV da parte delle cellule NK

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

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

The impairment of CD8 responses limits the selection of escape mutations in acute hepatitis C virus infection

Evasion from protective CD8 responses by mutations within immunodominant epitopes represents a potential strategy of HCV persistence. To investigate the pathogenetic relevance of this mechanism, a careful search for immunodominant CD8 epitopes was conducted in six patients with chronic evolution of HCV infection by analyzing their global CD8 response with a panel of overlapping synthetic peptides covering the overall HCV sequence and by studying the CD8 frequency by tetramer staining. Immunodominant responses were followed longitudinally from the time of acute onset in relation to the evolution of the epitopic sequences. Although intensity of CD8 responses and frequency of HCV-specific CD8 cells declined over time in all patients, mutations emerged in only three of the six acute patients studied. Variant sequences were less efficiently recognized by CD8 cells than parental epitopes and were poorly efficient in inducing a CD8 response in vitro. CD8 epitopes undergoing mutations were targeted by high avidity CD8 cells more efficient in effector function. Our data support the view that immunodominant CD8 responses are affected by inhibitory mechanisms operating early after infection and that the emergence of escape mutations represents an additional mechanism of virus evasion from those CD8 responses that are functionally preserved

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, CDS 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. Copyright © 2006 by the American Association for the Study of Liver Diseases

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-a 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-a induced HCV–RNA decline, PD-L1 levels on dendritic cells increased during IFN-a 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-IFNa treatment. Conclusions:PD-1/PD-L1 blockade has an immunoregulatory activity which may synergize with the antiviral effect of IFN-a therapy and should be thus explored further in long-lasting chronic HCV infections in the perspective of improving the efficacy of available antiviral treatments