Virus-specific effector CD4+T-cell responses in hemodialysis patients with hepatitis C virus infection

New perspectives in occult hepatitis C virus infection

Occult hepatitis C virus (HCV) infection, defined as the presence of HCV RNA in liver and in peripheral blood mononuclear cells (PBMCs) in the absence of detectable viral RNA in serum by standard assays, can be found in anti-HCV positive patients with normal serum levels of liver enzymes and in anti-HCV negative patients with persistently elevated liver enzymes of unknown etiology. Occult HCV infection is distributed worldwide and all HCV genotypes seem to be involved in this infection. Occult hepatitis C has been found not only in anti-HCV positive subjects with normal values of liver enzymes or in chronic hepatitis of unknown origin but also in several groups at risk for HCV infection such as hemodialysis patients or family members of patients with occult HCV. This occult infection has been reported also in healthy populations without evidence of liver disease. Occult HCV infection seems to be less aggressive than chronic hepatitis C although patients affected by occult HCV may develop liver cirrhosis and even hepatocellular carcinoma. Thus, anti-HCV negative patients with occult HCV may benefit from antiviral therapy with pegylated-interferon plus ribavirin. The persistence of very low levels of HCV RNA in serum and in PBMCs, along with the maintenance of specific T-cell responses against HCV-antigens observed during a long-term follow-up of patients with occult hepatitis C, indicate that occult HCV is a persistent infection that is not spontaneously eradicated. This is an updated report on diagnosis, epidemiology and clinical implications of occult HCV with special emphasis on anti-HCV negative cases.

Long-term virological follow up of patients with occult hepatitis C virus infection

BACKGROUND

Patients with occult hepatitis C virus (HCV) infection (HCV-RNA in liver without detectable anti-HCV and serum HCV-RNA) may have viral RNA in peripheral blood mononuclear cells (PBMCs) and in serum after ultracentrifugation, and may present HCV-specific T-cell responses, but it is unknown whether these markers persist to be detectable over time.

AIM

To perform a prospective virological long-term follow up of patients with occult HCV.

METHODS

Viral markers were tested every 3-4 months during 55.7 ± 20.3 months in 37 patients with occult HCV who were under ursodeoxycholic acid treatment.

RESULTS

Viral RNA was detectable in PBMCs of 31 patients during the follow up. In 23 of them, viral RNA in PBMCs was detected intermittently and in the other eight patients HCV-RNA was positive in a single sample. After ultracentrifugation, serum HCV-RNA was detected in 33 patients, being the viraemia intermittently detectable in 28, whereas in the remaining five patients, serum HCV-RNA was positive only once. Only one patient tested always HCV-RNA negative in PBMCs and in ultracentrifuged serum during follow up. Specific Core, NS3, and/or NS4 T-cell responses were found in 31 of the patients. The patient who was always HCV-RNA negative in PBMCs and in ultracentrifuged serum had specific HCV-T-cell responses.

CONCLUSIONS

Occult HCV infection persists over time with fluctuating viraemia levels that induce and maintain specific T-cell responses against viral proteins.

Hepatitis C in hemodialysis patients: current global magnitude, natural history, diagnostic difficulties, and preventive measures

Hepatitis C virus (HCV) infection is a significant cause of morbidity and mortality in hemodialysis (HD) patients. The reported prevalence of HCV among the HD population has varied greatly from 1.9 to 84.6% in different countries in recent years. The length of time on HD is generally believed to be associated with HCV acquisition in HD subjects. Nevertheless, several recent reports failed to recognize any significant role of blood transfusion. Although there are some considerations about the accuracy of serologic testing in detecting HCV in HD patients, the accumulated data in this review suggest the false-negativity rate to be not more than 1.66% (153/9,220). Therefore, substituting virologic for serologic testing in the routine diagnosis of HCV infection in HD patients seems unreasonable. Several phylogenetic analyzes of viral isolates suggested nosocomial patient-to-patient transmission of HCV among HD patients for which the main potential source is believed to be contaminated hands and articles. However, isolation of HCV-infected HD patients and use of dedicated machines are currently unjustified while strict adherence to universal precautions seems to be enough to control disease spread in HD units. The present article is an update on epidemiological and clinical features of HCV in HD population.

Cellular immune responses associated with occult hepatitis C virus infection of the liver

Occult hepatitis C virus (HCV) infection is a type of recently identified chronic infection that is evidenced only by detection of HCV RNA in liver; patients consistently test negative for antibodies to HCV and HCV RNA in serum. Using ex vivo and in vitro measures of T-cell responses, we have identified functional virus-specific memory CD4(+) and CD8(+) T cells in the peripheral blood of patients with occult HCV infection. The features of the virus-specific T cells were consistent with immune surveillance functions, supporting previous exposure to HCV. In addition, the magnitudes of CD4(+) and CD8(+) T-cell responses were in parallel and correlated inversely with the extent of liver HCV infection. The detection of HCV-specific T cells in individuals in whom HCV RNA can persist in the liver despite the absence of viremia and antibodies indicates that HCV replication is prolonged in the face of virus-specific CD4(+) and CD8(+) T-cell responses. These findings demonstrate that HCV-specific cellular immune responses are markers not only of previous exposure to and recovery from HCV but also of ongoing occult HCV infection.

Virus-specific T-cell responses associated with hepatitis C virus (HCV) persistence in the liver after apparent recovery from HCV infection

Hepatitis C virus (HCV) RNA persistence in the liver has been described even after apparent resolution of HCV infection. Because T-cell reactivity plays a role in recovery from HCV infection, virus-specific T-cell responses were investigated in apparently recovered individuals in whom hepatic HCV RNA persistence was documented: 15 sustained virological responders to interferon (IFN)-treatment and 9 asymptomatic aviremic anti-HCV carriers. HCV-specific CD4(+) T-cell proliferative responses were detected significantly more often in apparently recovered individuals (sustained virological responders: 60%; asymptomatic anti-HCV carriers: 66%) compared with 50 chronic hepatitis C patients (28%; P < 0.05). However, T-cell frequencies and numbers tended to decline over time and the number of HCV proteins targeted by CD4(+) T-cell proliferative responses was limited. Interestingly, liver viral load correlated inversely with virus-specific immune responses. Thus, CD4(+) T-cell responders showed significantly lower hepatic HCV RNA levels (P < 0.05). HCV-specific IFN-gamma-secreting CD4(+) T-cells were not detected in all the apparently recovered patients although they were found significantly more often compared with chronic hepatitis C patients (P < 0.05). Also, HCV NS3-specific CD8(+) T-cells were detected in 11 HLA-A2-positive apparently recovered individuals (8 sustained virological responders and 3 asymptomatic anti-HCV carriers); T-cell frequencies tended to be greater in those patients who had lower hepatic viral levels. In conclusion, HCV-specific T-cells are detectable in apparently recovered individuals in whom HCV RNA can persist in the liver indicating that HCV replication may be prolonged in the face of an insufficient or inadequate virus-specific CD4(+) and CD8(+) T-cell response.

Induction of Primary Human T Cell Responses against Hepatitis C Virus-Derived Antigens NS3 or Core by Autologous Dendritic Cells Expressing Hepatitis C Virus Antigens: Potential for Vaccine and Immunotherapy

Hepatitis C virus (HCV)-specific T cell responses have been suggested to play significant role in viral clearance. Dendritic cells (DCs) are professional APCs that play a major role in priming, initiating, and sustaining strong T cell responses against pathogen-derived Ags. DCs also have inherent capabilities of priming naive T cells against given Ags. Recombinant adenoviral vectors containing HCV-derived Core and NS3 genes were used to endogenously express HCV Core and NS3 proteins in human DCs. These HCV Ags expressing DCs were used to prime and stimulate autologous T cells obtained from uninfected healthy donors. The DCs expressing HCV Core or NS3 Ags were able to stimulate T cells to produce various cytokines and proliferate in HCV Ag-dependent manner. Evidence of both CD4(+) and CD8(+) T cell responses against HCV Core and NS3 generated in vitro were obtained by flow cytometry and Ab blocking experiments. Further, in secondary assays, the T cells primed in vitro exhibited HCV Ag-specific proliferative responses against recombinant protein Ags and also against immunodominant permissive peptide epitopes from HCV Ags. In summary, we demonstrate that the dendritic cells expressing HCV Ags are able to prime the Ag-specific T cells from uninfected healthy individuals in vitro. These studies have implications in designing cellular vaccines, T cell adoptive transfer therapy or vaccine candidates for HCV infection in both prophylactic and therapeutic settings.