Two distinct functional patterns of hepatitis C Virus (HCV)-specific T cell responses in seronegative, aviremic patients

Direct Ex Vivo Functional Analysis of HCV-Specific T Cells

CD8⁺ and CD4⁺ T cells play a critical role in viral clearance during self-limited HCV infection. Moreover, induction of robust and polyfunctional memory T cells is a primary goal in the development of T-cell-based HCV prophylactic vaccines. Direct ex vivo function of HCV-specific T cells without in vitro expansion can be assessed by measuring cytokine secretion or cell proliferation upon in vitro stimulation with HCV antigens using enzyme-linked immunospot (ELISpot) assays, intracellular cytokine staining (ICS) assays, and flow cytometry-based T-cell proliferation assays. In particular, polyfunctionality of T cells can be assessed by ICS assays using multicolor flow cytometry. Here, we provide protocols to measure direct ex vivo functions of HCV-specific T cells.

The Significance of Discordant Serology in Chagas Disease: Enhanced T-Cell Immunity to Trypanosoma cruzi in Serodiscordant Subjects

Background

Subjects are considered infected with Trypanosoma cruzi when tested positive by at least two out of three serological tests, whereas a positive result in only one of up to three tests is termed “serodiscordant” (SD). Assessment of parasite-specific T-cell responses may help discriminate the uninfected from infected individuals among SD subjects.

Methods

Peripheral blood mononuclear cells from SD and seropositive (SP) subjects, who were born in areas endemic for T. cruzi infection but living in Buenos Aires city, Argentina, at the time of the study, and seronegative unexposed subjects were included for analysis. The function and phenotype of T cells were assessed by interferon-γ (IFN-γ) and interleukin (IL)-2 enzyme-linked immunospot assay and multiparameter flow cytometry. T. cruzi-specific antibodies were quantified by conventional serology and a multiplex assay format.

Results

SD subjects exhibited immunity cell responses to T. cruzi but in contrast to SP subjects, T cells in SD subjects more often display the simultaneous production of IFN-γ and IL-2 in response to T. cruzi antigens and have a resting phenotype. SD individuals also have higher IFN-γ spot counts, polyfunctional CD4⁺ T-cells enriched in IL-2 secreting cells and low levels of antibodies specific for a set of T. cruzi-derived recombinant proteins compared with the SP group. Long-term follow-up of SD individuals confirmed that humoral and T-cell responses fluctuate but are sustained over time in these subjects. T cells in SD subjects for T. cruzi infection did not recognize Leishmania antigens.

Conclusion

Both T-cell and humoral responses in most subjects assessed by conventional tests as SD for T. cruzi infection indicate prior exposure to infection and the establishment of immunological memory suggestive of a resolved infection.

Hepatitis C virus: A time for decisions. Who should be treated and when?

Cirrhosis is the most important risk factor for hepatocellular carcinoma (HCC) regardless of the etiology of cirrhosis. Compared to individuals who are anti-hepatitis C virus (HCV) seronegative, anti-HCV seropositive individuals have a greater mortality from both hepatic as well as nonhepatic disease processes. The aim of this paper is do describe the burden of HCV infection and consider treatment strategies to reduce HCV-related morbidity and mortality. The newly developed direct acting antiviral (DAA) therapies are associated with greater rates of drug compliance, fewer adverse effects, and appear not to be limited by the presence of a variety of factors that adversely affect the outcome of interferon-based therapies. Because of the cost of the current DAA, their use has been severely rationed by insurers as well as state and federal agencies to those with advanced fibrotic liver disease (Metavir fibrosis stage F3-F4). The rationale for such rationing is that many of those recognized as having the disease progress slowly over many years and will not develop advanced liver disease manifested as chronic hepatitis C, cirrhosis, and experience any of the multiple complications of liver disease to include HCC. This mitigation has a short sided view of the cost of treatment of hepatitis C related disease processes and ignores the long-term expenses of hepatitis C treatment consisting of the cost of treatment of hepatitis C, the management of cirrhosis with or without decompensation as well as the cost of treatment of HCC and liver transplantation. We believe that treatment should include all HCV infected patients including those with stage F0-F2 fibrosis with or without evidence of coexisting liver disease. Specifically, interferon (IFN)-free regimens with the current effective DAAs without liver staging requirements and including those without evidence of hepatic diseases but having recognized extrahepatic manifestations of HCV infection is projected to be the most cost-effective approach for treating HCV in all of its varied presentations. Early rather than later therapy of HCV infected individuals would be even more efficacious than waiting particularly if it includes all cases from F0-F4 hepatic disease. Timely therapy will reduce the number of individuals developing advanced liver disease, reduce the cost of treating these cases and more importantly, reduce the lifetime cost of treatment of those with any form of HCV related disease as well as HCV associated all - cause mortality. Importantly, HCV treatment regimens without any restrictions would result in a substantial reduction in health care expenditure and simultaneously reduce the number of infected individuals who are infecting others.

Cellular immune response to hepatitis-C-virus in subjects without viremia or seroconversion: is it important?

Hepatitis C Virus (HCV) causes chronic infection and represents a global health burden. To date, there is no licensed vaccine for HCV. The high viral replication rate and the existence of several HCV genotypes and quasispecies hamper the development of an effective universal vaccine. In this regard, the current HCV vaccine candidates show genotype-specific protection or narrow cross reactivity against other genotypes. Importantly, HCV spontaneous clearance occurs in 15-50 % of infected subjects, indicating that natural resistance to chronic infection exists. This phenomenon was demonstrated among humans and chimpanzees and continues to motivate researchers attempting to develop an effective HCV vaccine. However, what constitutes a protective immune response or correlate of protection against HCV infection is still vague. Additionally, the mechanisms behind successful HCV clearance suggest the coordination of several arms of the immune system, with cell-mediated immunity (CMI) playing a crucial role in this process. By contrast, although neutralizing antibodies have been identified, they are isolate-specific and poorly correlate with viral clearance. Antigen-specific CD4 T cells, instead, correlate with transient decline in HCV viremia and long-lasting control of the infection. Unfortunately, HCV has been very successful in evading host immune mechanisms, leading to complications such as liver fibrosis, cirrhosis and hepatocellular carcinoma. Interestingly, CMI to HCV antigens were shown among exposed individuals without viremia or seroconversion, suggesting the clearance of prior HCV infection(s). These individuals include family members living with HCV-infected subjects, healthcare workers, IV drug users, and sexual contacts. The correlates of protection could be closely monitored among these individuals. This review provides a summary of HCV-specific immune responses in general and of CMI in particular in these cohorts. The importance of these CMI responses are discussed.

A New Twist to a Chronic HCV Infection: Occult Hepatitis C

Background. The prevalence of occult hepatitis C infection (OCI) in the population of HCV-RNA negative but anti-HCV positive individuals is presently unknown. OCI may be responsible for clinically overt recurrent disease following an apparent sustained viral response (SVR) weeks to years later. Purpose. To review the available current literature regarding OCI, prevalence, pathogenic mechanisms, clinical characteristics, and future directions. Data Sources. Searching MEDLINE, article references, and national and international meeting abstracts for the diagnosis of OCI (1990-2014). Data Synthesis. The long-term followup of individuals with an OCI suggests that the infection can be transient with the loss of detectable HCV-RNA in PPBMCs after 12-18 months or alternatively exist intermittently and potentially long term. The ultimate outcome of HCV infection is decided by interplay between host immune responses, antiviral therapies, and the various well-identified viral evasion mechanisms as well as the presence of HCV infection within extrahepatic tissues. Conclusion. The currently widely held assumption of a HCV-cure in individuals having had "SVR" after 8-12 weeks of a course of DAA therapy as recently defined may not be entirely valid. Careful longitudinal followup utilizing highly sensitive assays and unique approaches to viral isolation are needed.

DNA immunization of Mycobacterium tuberculosis resuscitation-promoting factor B elicits polyfunctional CD8(+) T cell responses

Purpose

T cell-mediated immune responses, and particularly activation of polyfunctional T cells that simultaneously produce multiple cytokines, are necessary for the control of Mycobacterium tuberculosis. In the present study, we examined if DNA immunization of Mycobacterium tuberculosis resuscitation-promoting factor B (RpfB) elicits polyfunctional T cell responses in mice.

Materials and Methods

C57BL/6 mice were immunized intramuscularly three times, at 3-week intervals, with RpfB-expressing plasmid DNA. For comparison, protein immunization was performed with recombinant RpfB in control mice. After immunization, RpfB-specific T cell responses were assessed by interferon-γ (IFN-γ) enzyme-linked immunosorbent spot assay and intracellular cytokine staining (ICS), and T cell polyfunctionality was assessed from the ICS data.

Results

RpfB DNA immunization induced not only humoral immune responses, but also CD8⁺ and CD4⁺ T cell responses. Immunodominant T-cell epitopes were identified within RpfB by assays with overlapping peptides. RpfB DNA immunization elicited a polyfunctional CD8⁺ T cell response that was dominated by a functional phenotype of IFN-γ⁺/TNF-α⁺/IL-2^-/CD107a⁺.

Conclusion

RpfB DNA immunization elicits polyfunctional CD8⁺ T cell responses, suggesting that RpfB DNA immunization might induce protective immunity against tuberculosis.

Detection of HCV-Specific IFN-γ Responses in HCV Antibody and HCV RNA Negative Injecting Drug Users

BACKGROUND

Detectable HCV-specific cellular immune responses in HCV antibody and RNA negative people who inject drugs (PWID) raise the question of whether some are resistant to HCV infection. Immune responses from people who have been exposed to hepatitis C virus (HCV) and remain anti-HCV negative are of interest for HCV vaccine development; however, limited research addresses this area.

OBJECTIVES

In a cohort of HCV antibody and RNA negative PWID, we assessed whether the presence of HCV-specific IFN-γ responses or genetic associations provide any evidence of protection from HCV infection.

PATIENTS AND METHODS

One hundred and ninety-eight participants were examined longitudinally for clinical, behavioral, social, environmental and genetic characteristics (IFNL3 genotype [formally IL-28B] and HLA type). Sixty-one of the 198 participants were HCV antibody and RNA negative, with 53 able to be examined longitudinally for HCV-specific IFN-γ ELISpot T cell responses.

RESULTS

Ten of the 53 HCV antibody and RNA negative participants had detectable HCV-specific IFN-γ responses at baseline (18%). The magnitude of IFN-γ responses averaged 131 +/- 96 SFC/106 PBMC and the breadth was mean 1 +/- 1 pool positive. The specificity of responses were mainly directed to E2, NS4b and NS5b. Participants with (10) and without (43) HCV-specific IFN-γ responses did not differ in behavioral, clinical or genetic characteristics (P > 0.05). There was a larger proportion sharing needles (with 70%, without 49%, P = 0.320) and a higher incidence of HCV (with 35.1 per 100 py, 95% CI 14.6, 84.4, without 16.0 per 100 py, 95% CI 7.2, 35.6, P = 0.212) in those with IFN-γ responses, although not statistically significant. Half the participants with baseline IFN-γ responses became HCV RNA positive (5/10), with one of these participants spontaneously clearing HCV. The spontaneous clearer had high magnitude and broad Th1 responses, favorable IFNL3 genotype and favorable HLA types.

CONCLUSIONS

This study demonstrated the detection of HCV-specific IFN-γ responses in HCV antibody and RNA negative individuals, with a tendency for HCV-specific IFN-γ responses to be associated with HCV exposure. The potential role of HCV-specific IFN-γ responses in those who remained HCV RNA negative is of value for the development of novel HCV therapeutics.