Successful Interferon-Free Therapy of Chronic Hepatitis C Virus Infection Normalizes Natural Killer Cell Function
Serti E,  Chepa-Lotrea X,  Kim Y J, Keane M, Fryzek N,  Liang TJ, Ghany G,  and  Rehermann B.
Gastroenterology 2015;149:190-200 .

Fibrosis Progression and cirrhosis in Chronic hepatitis C Infection is related to the presence of Viral replication and a  low-level inflammatory response. An interferon driven innate immune activation with the  up-regulation of interferon-stimulated genes (ISGs)  are detectable in liver biopsy specimens of chronically infected patients. Serti et al analyze Natural Killer (NK) cells from the liver and blood of 13 HCV-infected patients who have failed to treatment with pegylated interferon  (IFN) and ribavirin (RBV) and were retreated with an IFN free regimen, including Daclatasvir  (DCV) and asunaprevir(ASV) .The results obtained  were compared  with those obtained   from  the blood samples of 13 healthy individuals (controls).

Before treatment, all patients had increased levels of CXCL10 orCXCL11, the products of ISGs , and a different NK cell phenotype from controls, characterized by increased expression of HLA-DR, NKp46, NKG2A, CD85j, signal transducer and activator of transcription 1 (STAT1), phosphorylated STAT1, and tumor necrosis factor related apoptosis-inducing ligand (TRAIL). NK cells from patients also had increased degranulation and decreased productionof IFNg and tumor necrosis factor a compared with NK cells from controls. Nine patients had an end-of-treatment response and 4 had virologic breakthrough between weeks 4 and 12 of therapy. A rapid decrease in viremia and level of inflammatory cytokines in all patients was associated with decreased activation of intrahepatic and blood NK cells; it was followed by restoration of a normal NK cell phenotype and function by week 8 in patients with undetectable viremia. This normalized NK cell phenotype was maintained until week 24 (end of treatment). In summary, Direct-acting antiviral–mediated clearance of HCV is associated with loss of intrahepatic immune activation by IFNa, which is indicated by decreased levels of CXCL10 and CXCL11 and normalization of NK cell phenotype and function.

Commentary

Interferon based therapies did not allow studies examining  the role of HCV itself on innate and adaptative immunity to HCV due to the immunological proprieties of IFN. The approval of IFN free regimens provides a unique opportunity  to assess whether a combination of two Direct Antiviral Agents (DAAs) could normalizes innate immune activation and NK cell function which have been previously described to be dysfunctional in these setting.

HCV infection is characterized by a high rate of chronicity and disease progression. The high rate of persistence has been related  to its capacity to evade the host´s innate and adaptive immune response. In the IFN and RBV era, different studies  did not  show HCV specific T cell changes  among patient who did or did not achieve an early virologic response suggesting that T cells did not play a key role in viral eradication. On the other hand,  IFN is a potent activator of NK cells, and  early activation of NK cell has been associated with SVR. The problem is that NK cells are already activated in Chronic Hepatitis C before and interferon exogenous  but are not able to produce adequate amounts of IFNγ and tumor necrosis factor-α with consequent inability to eradicate HCV. The administration of exogenous IFN enhances this "functional dichotomy". The development of highly effective IFN-free regimens against HCV infection provides a unique opportunity to analyze whether and how fast NK cell activation and liver inflammation resolve when HCV replication is blocked. A normalization of NK cell effector functions also would be of interest in the context of adaptive immune responses because HCV-specific T cells are dysfunctional as a result of chronic antigen stimulation in HCV infection.  Although a recovery of T-cell proliferation recently was reported during treatment of HCV-infected patients with  DAAs, it remains unknown whether this translates into a full recovery of effector functions. Past IFN-based treatment regimens were not suitable to answer these questions because IFN not only has an antiviral, but also an immunomodulatory function.

All 13 HCV-infected nonresponders to PegIFN/RBV experienced a rapid decrease inserum HCV-RNA levels within the first 2 weeks of DCV/ASVtherapy . Nine patients developed an end of treatment (EOT) response, whereas 4 patients had a virologic breakthrough).Seven of 9 EOT responders achieved a sustained virologic response at 24 weeks after treatment; CXCL10, and CXCL11 levels decreased significantly within the first 8 weeks of DCV/ASV therapy.

Serti et al. analyzing frozen peripheral blood mononuclear cells of  small number of patients who a achieved SVR with two direct antiviral  agents in an IFN free regimen show that the expression of several NK cell-activating receptors decreased to normal levels within few days after starting therapy.  Suppression of viral replication is associated with a decrease in the products of IFN stimulating  genes such as the  concentrations of  CXCL10 and CXCL11  and normalization of NK function by  decreasing  STAT1 expression and STAT1 phosphorylation.  The levels normalization of NK cell cytotoxic effector functions were similar to those observed in uninfected subjects. This normalization in NK function was maintained through the treatment and follows up in cases of SVR indicating that that viral cure is equivalent to and immunologic cure.

Very interesting are the NK cells response in the few patients who had virologic breakthrough or did not achieve a sustained virologic response. These patients usually have resistant associated variants to the DAAs. Failure to therapy is related to selection of these variants but innate immunity also can play a role particularly in patients who relapse. In the study , viremic patients exhibited a less decrease or no changes in NK cell activation that need to be address in more patients with detail.

All the patients included in the study were genotype 1b, currently these are the patients who achieved the highest SVR rates with DAAs and less relapse. Other genotype such as 1a and particularly genotype 3 and patients with cirrhosis should be tested.

In summary this is the first study that shows successful IFN free treatment with DAAs of Chronic Hepatitis C infection normalizes natural killer cell function and can "cure" innate immunity.