Detection and Characterization of Virus-Specific CD8+ T Cells Using the Tetramer Approach

Hepatitis B virus (HBV)-specific CD8⁺ T cells, or cytotoxic T lymphocytes (CTLs), are believed to play an important role in the control of infection and development of liver injury (1 ). Therefore the quantitative and qualitative analyses of such cells is important for understanding the mechanisms underlying the pathogenesis associated with the infection as well as the clearance or persistence of the infecting virus. Traditionally, HBV-specific CD8⁺ T cells were detected by cytotoxicity assay, while the frequency of such cells was estimated by limiting dilution assay (LDA). Both assays are based on the killing activity of CTLs. The number of virus-specific CTLs in clinical specimens (blood or liver samples) is usually very small. Therefore these assays require extensive in vitro expansion of virus-specific CD8+ T cells to generate CTL lines or clones, which is time consuming and labor intensive. As such assays can detect only CD8⁺ T cells that expand in vitro and kill specific target cells, they may not represent the characteristics of the overall CD8⁺ T cell responses against the virus.