Prospective analysis of effector and regulatory CD4⁺ T cells in chronic HCV patients undergoing combination antiviral therapy

Background/Aims

The role of HCV-specific CD4⁺ T cells and regulatory T cells in influencing the outcome of antiviral therapy is incompletely defined.

Methods

CD4⁺ IFN-γ ELISPOT assays (n = 58) and flow cytometric analysis of FoxP3-expressing T regulatory cells (n = 62) were performed on patients from the Virahep-C study at baseline, during and after cessation of antiviral therapy.

Results

Total HCV-specific IFN-γ CD4⁺ T cell ELISPOT responses did not increase with therapy, but rather decreased by 8 weeks and remained below baseline 24 weeks after cessation of therapy. There were no statistically significant differences with respect to viral kinetics, race and virologic outcome. In contrast, viral relapse after treatment was associated with a three-fold increase in HCV-specific responses. The frequency and phenotype of regulatory T cells during therapy were not significantly different in terms of race, viral kinetic groups or virologic outcome.

Conclusions

A contraction of HCV-specific CD4⁺ T cell responses was found during treatment with recovery of responses in patients experiencing virologic relapse after treatment. The levels of FoxP3-expressing regulatory T cells did not vary by race and were not predictive of virologic outcome. Work is ongoing to explore the contribution of mechanisms independent of CD4⁺ T cells in therapy-induced viral clearance.

Introduction

Hepatitis C virus (HCV) infection is a major cause of chronic hepatitis in the world affecting approximately 175 million people [1]. The prevalence of cirrhosis from chronic HCV infection and the incidence of its complications are expected to increase in the United States over the next 10 to 20 years [1], [2]. Despite significant advances in treatment, approximately one-half of HCV genotype 1-infected patients fail to eradicate infection with standard combination therapy using pegylated interferon (peginterferon) and ribavirin [3]. Elucidation of the factors that determine the differential response rates to therapy is important to understanding the causes of antiviral resistance and to identify potential therapeutic targets in the future. Because strong and multispecific cellular immune responses are indispensable for spontaneous recovery from HCV infection [4], [5], it has been suggested that CD4⁺ T cell responses also mediate therapy-induced recovery. Theoretically, antiviral therapy might reverse the functional exhaustion of HCV-specific T cells by a number of mechanisms, e.g., rapid reduction of viral titer [6], upregulation of soluble factors involved in T cell activation, maturation of dendritic cells [7], [8], or elimination of viral proteins known to inhibit innate immune responses [9], [10], [11], [12].

To date, studies examining the effect of antiviral therapy on HCV-specific immunity have provided conflicting results [13], [14], [15], [16], [17]. Studies have shown that patients with chronic HCV have elevated circulating frequencies of regulatory T cells (Tregs) that impair HCV-specific responses [18], [19], [20], [21]; however, to date, no study has examined their potential role during antiviral therapy. As a part of a prospective, multi-centered NIH-funded study of viral resistance to antiviral therapy of hepatitis C (Virahep-C), immune responses to HCV were assessed for their association with outcome of therapy [22]. In an effort to better understand the role of immunity in determining response to antiviral therapy, particularly with regards to race and early viral kinetics, patients from the Virahep-C cohort were studied longitudinally. For this analysis we examined changes in HCV-specific and non HCV-specific Th1 immune responses during combination therapy and whether the proportional frequency and phenotype of Tregs are associated with race and ultimate virologic response.