Functional attributes of responding T cells in HCV infection: the recent advances in engineering functional antiviral T cells

Telomerase Expression Related with Poor Immune Response to HCV Core Antigen in Egyptian HCV Patients' PBMCs

Background

Hepatocellular carcinoma (HCC) is the most common primary malignant tumor of the liver.

Aim

This study aimed to assess serum human telomerase enzyme (hTERT) levels and their relation to the progression of liver disease. Also, it aimed to assess the effect of hepatitis C virus (HCV) core protein on memory T-cells in HCV patients with or without HCC and the correlation between memory cell phenotype and the progression of the disease in the same patients.

Methods

HTERT level in serum was assessed through relative quantitative RT-PCR. Flow cytometric analysis was used to assess T-cell responsiveness (as IFN- γ secretion) before and after stimulation with HCV core protein and the memory CD8+ cell phenotype using several differentiation markers.

Results

HTERT was found to be increased in a stepwise manner upon comparing its level in controls, chronic hepatitis patients, cirrhotic patients, and HCC patients. T-cells showed a similar manner of stepwise decrease in response (decreased IFN- γ secretion) in HCC patients compared to HCV patients without HCC and controls. Also, late differentiated memory cells (CD8+, CD27-, CD28-, CD45RA+, and CCR7-) were depleted in HCC patients compared to HCV patients without HCC.

Conclusion

These results suggest a negative correlation between hTERT and IFN- γ secretion by T-cells in HCV patients and that this relationship, along with the depletion of late differentiated memory cells, could help the progression of liver disease to HCC.

Hepatitis C Virus-Specific T Cell Receptor mRNA-Engineered Human T Cells: Impact of Antigen Specificity on Functional Properties

Therapy with genetically modified autologous T cells has shown great promise in cancer therapy. For an efficient control of hepatitis C virus (HCV) infection, cytotoxic T cells (CTL) are pivotal, but persistence of activated T cells may lead to liver toxicity. Here, anti-HCV T cell receptors (TCRs) recognizing the HCV nonstructural (NS) NS3 or NS5 viral peptide target were examined by mRNA transfection of human peripheral blood lymphocytes (PBLs) derived from healthy donors as well as chronically infected HCV patients. Immunological analysis shows that while the CTLs expressing the NS5-specific TCR reduced HCV RNA replication by a noncytotoxic mechanism, the NS3-specific TCR-redirected CTLs were polyfunctional and inhibited HCV RNA replication through antigen-specific cytotoxicity. Transcriptome signatures from these two types of CTL responses revealed uniquely expressed gene clusters upon encountering hepatoma target cells presenting endogenously expressed HCV proteins. The NS3 TCR induced a rapid expression of apoptotic signaling pathways and formation of embryonic gene clusters, whereas the NS5A TCR activation induced extended proliferative and metabolic pathways as the HCV target cells survived. Our results provide detailed insights into basic HCV T cell immunology and have clinical relevance for redirecting T cells to target virally infected hepatoma cells.IMPORTANCE Due to the protective ability of HCV-specific T cells and the hepatotoxic potential that they possess, there is a great need for the understanding of the functional aspects of HCV-specific T cells. To circumvent the low level of precursor frequency in patients, we engineered primary CD8⁺ T cells by mRNA TCR vectors to confer HCV specificity to new T cells. HCV TCRs that differ in antigen specificity and polyfunctionality were examined. mRNA TCR engineering of peripheral blood lymphocytes from healthy donors or chronically infected HCV patients resulted in strikingly high levels of HCV TCR expression and HCV-specific responses. While a cytotoxicity response from a polyfunctional T cell activation caused hepatotoxicity and the rapid induction of apoptotic signaling pathways, the noncytotoxic T cell activation showed extended proliferative, metabolic pathways and persistence of HCV target cells. Our results provide detailed insights into basic HCV T cell immunology and have clinical relevance for immune protection of HCV-associated diseases.

Targeting naturally occurring epitope variants of hepatitis C virus with high-affinity T-cell receptors

Hepatitis C virus (HCV) readily establishes chronic infection, which is characterized by failure of virus-specific CD8⁺ T cells. HCV uses epitope mutation and T-cell exhaustion to escape from the host immune response. Previously, we engineered high-affinity T-cell receptors (HATs) targeting human immunodeficiency virus escape mutants. In this study, the affinity of a T-cell receptor specific for the HLA-A2-restricted HCV immunodominant epitope NS3 1406–1415 (KLVALGINAV) was improved from a K_D of 6.6 µM to 40 pM. These HATs could also target HCV NS3 naturally occurring variants, including an escape variant vrt1 (KLVVLGINAV), with high affinities. The HATs can be used as high-affinity targeting molecules at the centre of the immune synapse for the HLA-restricted NS3 antigen. By fusing the HAT with a T-cell activation molecule, an anti-CD3 single-chain variable fragment, we constructed a molecule called high-affinity T-cell activation core (HATac), which can redirect functional CTLs possessing any specificity to recognize and kill cells presenting HCV NS3 antigens. This capability was verified with T2 cells loaded with prototype or variant peptides and HepG2 cells expressing the truncated NS3 prototype or variant proteins. The results indicate that HATac targeting the HLA-restricted NS3 antigen may provide a useful tool for circumventing immune escape mutants and T-cell exhaustion caused by HCV infection.