Phenotype and fate of liver-resident CD8 T cells during acute and chronic hepacivirus infection

Hyperfunctional T cell responses unchecked by regulatory T cells are unable to resolve hepaciviral infection without humoral contribution

BACKGROUND & AIMS

The most recent T cell-based vaccine against HCV tested in humans failed to swing the pendulum from chronicity to resolution, despite eliciting cellular responses in most individuals. These results naturally evoke the question of whether hyperactivated responses of a single adaptive immune arm are capable of inducing HCV clearance or if coordinated efforts between antibodies and T cells are indeed necessary. Here, we sought to address this point in determining whether the suppression of antiviral T cell and IgG responses by regulatory T cells (Tregs) is a critical prerequisite of delayed viral clearance or overt chronicity.

METHODS

Using a surrogate model of HCV infection, rodent hepacivirus (RHV) infection in mice, we utilized Foxp3-DTR mice to assess how Tregs modulate the generation of acute antiviral adaptive immune responses and indirectly dictate infection fate via intracellular flow cytometry staining, ELISA, RNA sequencing, and qPCR.

RESULTS

Transient depletion of Tregs prior to infection decreased viral-specific CD4+ T cell function, IgG production, and delayed viral clearance. In contrast, transient Treg depletion after infection increased both T cell functionality and IgG production, thereby facilitating accelerated viral clearance. Hyperactivated T cells, achieved via transient Treg depletion, were unable to clear the virus as an isolated effector arm without the help of viral-specific IgG production.

CONCLUSIONS

Tregs control the outcome of RHV infection via direct modulation of CD4+ T cells and IgG production. Hyperactivated T cell responses are incapable of compensating for experimentally induced lack of antibodies, further reinforcing the notion of cooperative interplay between adaptive immune arms in facilitating hepaciviral clearance.

IMPACT AND IMPLICATIONS

Herein, we demonstrate how timing of regulatory T cell depletion determines the fate of effector T cells, humoral responses, and the kinetics of viral clearance. Our observations provide direct evidence that functional T cell responses are incapable of compensating for suboptimal humoral responses to facilitate viral resolution. Our results imply that future HCV vaccine regimens should not solely rely on eliciting focused responses of a single effector arm, but rather incorporate immunogens capable of inducing durable features of both humoral and cellular memory.

Norway rat hepacivirus resembles hepatitis C virus in terms of intra-host evolution and escape from neutralizing antibodies

BACKGROUND AND AIMS

Norway rat hepacivirus 1 (NrHV) is an attractive surrogate model for evaluating vaccine strategies against hepatitis C virus (HCV). Yet the immune response in NrHV infections remains poorly understood, particularly the role of neutralizing antibodies (nAbs). Here, we explore nAb development and viral evolution during chronic NrHV infection of inbred rats to understand neutralization and viral escape dynamics.

METHODS

Lewis rats inoculated with the NrHV RHV-rn1 strain were monitored for >52 weeks. Viremia was quantified by RT-qPCR, and NrHV nAbs were characterized by infectious cell culture-based neutralization assays and challenge experiments. Viral evolution was followed over time by whole open reading frame deep sequencing.

RESULTS

In most animals, high levels of nAbs appeared after 20 to 45 weeks of infection, coinciding with the emergence of numerous mutations in the envelope proteins. Incorporation of these E1/E2 mutations into cell-culture-adapted RHV-rn1 reduced sensitivity to neutralization by autologous contemporary serum. Five key recurrent E1/E2 substitutions (E209K, R224Q, V275I, T500K, and L569P) were identified, collectively impairing serum neutralization, with E209K in E1 alone proving sufficient to confer neutralization escape. In contrast, NrHV-infected rats devoid of nAbs displayed fewer envelope mutations. Finally, pretreatment of cells with rat serum with high-titer nAbs led to partial control of NrHV-infection, and passive immunization with such sera protected SCID mice from subsequent challenge.

CONCLUSIONS

This study demonstrates the correlation between nAbs and viral evolution during long-term NrHV infection. The observed humoral immunity for NrHV infection closely resembles that of chronic HCV infection, where late-emerging high-level nAbs fail to clear evolving viral populations, thereby contributing to the evasion of the adaptive immune response. Preexisting antibodies do, however, protect from infection.

CD4+ T cell help during early acute hepacivirus infection is critical for viral clearance and the generation of a liver-homing CD103+CD49a+ effector CD8+ T cell subset

In hepatitis C virus (HCV) infection, CD4+ and CD8+ T cells are crucial for viral control. However, a detailed understanding of the kinetic of CD4+ T cell help and its role in the generation of different CD8+ T cell subsets during acute infection is lacking. The absence of a small HCV animal model has impeded mechanistic studies of hepatic antiviral T cell immunity and HCV vaccine development. In this study, we used a recently developed HCV-related rodent hepacivirus infection mouse model to investigate the impact of CD4+ T cell help on the hepatic CD8+ T cell response and viral clearance during hepacivirus infection in vivo. Our results revealed a specific kinetic of CD4+ T cell dependency during acute infection. Early CD4+ T cell help was essential for CD8+ T cell priming and viral clearance, while CD4+ T cells became dispensable during later stages of acute infection. Effector CD8+ T cells directly mediated timely hepacivirus clearance. An analysis of hepatic CD8+ T cells specific for two different viral epitopes revealed the induction of subsets of liver-homing CD103+CD49a+ and CD103-CD49a+ effector CD8+ T cells with elevated IFN-γ and TNF-α production. CD103+CD49a+ T cells further persisted as tissue-resident memory subsets. A lack of CD4+ T cell help and CD40L-CD40 interactions resulted in reduced effector functions and phenotypical changes in effector CD8+ T cells and a specific loss of the CD103+CD49a+ subset. In summary, our study shows that early CD4+ T cell help through CD40L signaling is essential for priming functional effector CD8+ T cell subsets, including unique liver-homing subsets, and hepacivirus clearance.

Concerted synergy between viral-specific IgG and CD8 + T cells is critical for clearance of an HCV-related rodent hepacivirus

BACKGROUND AND AIMS

Evidence assessing the role of B cells and their antibodies, or lack thereof, in the spontaneous resolution of acute HCV infection is conflicting. Utilization of a strictly hepatotropic, HCV-related rodent hepacivirus (RHV) model circumvents many of the challenges facing the field in characterizing the immunological correlates of dichotomous infection outcomes. This study seeks to elucidate the importance of B cells in the clearance of acute RHV infection.

APPROACH AND RESULTS

µMT mice were infected i.v. with RHV and found to develop chronic infection for over a year. Wild-type (WT) mice depleted of B cells also exhibited persistent viremia that resolved only upon B cell resurgence. The persistent infection developed by B1-8i and AID cre/cre mice revealed that antigen-specific, class-switched B cells or their antibodies were crucial for viral resolution. Virus-specific CD8 + and CD4 + T cells were characterized in these mice using newly developed major histocompatibility complex class I and II tetramers and ex vivo peptide stimulation. Immunoglobulin G (IgG) was purified from the serum of RHV- or lymphocytic choriomeningitis virus Armstrong-infected mice after viral clearance and passively transferred to AID cre/cre recipients, revealing viral clearance only in αRHV IgG recipients. Further, the transfer of αRHV IgG into B cell-depleted recipients also induced viral resolution. This ability of RHV-specific IgG to induce viral clearance was found to require the concomitant presence of CD8 + T cells.

CONCLUSIONS

Our findings demonstrate a cooperative interdependence between immunoglobulins and the T cell compartment that is required for RHV resolution. Thus, HCV vaccine regimens should aim to simultaneously elicit robust HCV-specific antibody and T cell responses for optimal protective efficacy.