HLA-restricted and Antigen-specific CD8+ T Cell Responses by K562 Cells Expressing HLA-A*0201

BACKGROUND: Identification of antigen-specific T cells has yielded valuable information on pathologic process and the disease state. Assays for quantification of inflammatory cytokines or lytic-granule molecules have been generally used to evaluate antigen specific T cell response, however their applicability have been hampered due to the limited source of autologous antigen-presenting target cells (APC). METHODS: K562, a leukemic cell line deficient of human leukocyte antigen (HLA), was transfected with a gene encoding HLA-A*02 (K562/A*02) and its function as stimulator cells in inducing activation of HLA-matched T cells was evaluated by IFN-gamma enzyme linked immunospot (ELISPOT) assay. RESULTS: The stable transfectant K562/A*02 pulsed with HLA- A*02 restricted peptide could specifically induce IFN-gamma secretion by CD8+ T cells compared to no detectable secretion by CD4+ T cells. However, CD56+ NK cells secreted IFN-gamma in both K562/A*02 with peptide and without peptide. The number of IFN-gamma secreted CD8+ T cells was increased according to the ratio of T cells to K562 and peptide concentration. Formalin-fixed K562/A*02 showed similar antigen presenting function to live K562/A*02. Moreover, K562/A*02 could present antigenic- peptide to not only A*0201 restricted CD8+ T cells but also CD8+ T cells from A*0206 donor. CONCLUSION: These results suggest that K562/A*02 could be generally used as target having specificity and negligible background for measuring CD8+ T cell responses and selective use of K562 with responsder matched HLA molecules on its surface as APC may circumvent the limitation of providing HLA-matched autologous target cells.

The Study of MHC class I Restricted CD8+ T Cell Mediated Immune Responses against Mycobacterium tuberculosis Infection: Evidence of M. tuberculosis Specific CD8+ T Cells in TB Patients and PPD+ Healthy Individuals

BACKGROUND: The protective immunity against tuberculosis (TB) involves both CD4+ T cells and CD8+ T cells. In our previous study, we defined four Mycobacterium tuberculosis derived peptide epitopes specific for HLA-A*0201 restricted CD8+ T cells (ThyA30-38, RpoB127-135, 85B15-23, PstA175-83). In this study, we investigated the immune responses induced by these peptide specific CD8+ T cells in latently and chronically infected people with TB. METHODS: We characterized these peptide specific CD8+ T cell population present in PBMC of both TB patients and PPD healthy people using IFN-gammaelispot assay, intracellular staining and HLA-A2 dimer staining. RESULTS: The frequency of peptide specific CD8+ T cell was in the range of 1 to 25 in 1.7x10(5) PBMC based on ex vivo IFN-gamma elispot assay, demonstrating that these peptide specific CD8+ T cell responses are induced in both TB patients and PPD people. Short term cell lines (STCL) specific for these peptides proliferated in vitro and secreted IFN-gamma upon antigenic stimulation in PPD+ donors. Lastly, HLA-A*0201 dimer assays indicated that PstA175-83 specific CD8+ T cell population in PPD+ healthy donors is heterogeneous since approximately 25~33% of PstA175-83 specific CD8+ T cell population in PPD+ healthy donors produced IFN-gamma upon peptide stimulation. CONCLUSION: Our results suggest that MHC class I restricted CD8+ T cell mediated immune responses to M. tuberculosis infection are induced in both TB patients and PPD+ people; however, the CD8+ T cell population is functionally heterogeneous.