High Frequency CD4+CD25+ Treg Cells in Nasopharyngeal Carcinoma Is Associated with Suppression of CD8 T Cell Mediated Response to Latency II EBV Antigens.

Nasopharyngeal Carcinoma (NPC) is associated with latent Epstein Barr Virus (EBV) infection and expression of EBV latent antigen LMP2. Because of the possibility of targeting viral antigens, there is interest in developing EBV-LMP2-specific Cytotoxic T lymphocyte (CTL) immunotherapy for NPC. However, evidence suggests that CD8+ T cell responses to EBV latency II antigens are rarely detectable in these patients. Regulatory T cells have been shown to inhibit stimulation of CD8+ T cells by Antigen Presenting Cells (APC) in vitro, and may play an important role in immune tolerance to tumours. Thirteen newly diagnosed untreated HLA A2 NPC patients were investigated for CTL responses to EBV latency II antigens by flow cytometry using HLA A2 restricted tetramers specific for LMP2a derived peptides (CLG, LTA). No LMP2-specific CD8+ T cells were detected amongst peripheral blood CD8+ T cells either ex vivo or in vitro following short stimulation in ELIspot assays, although strong responses to CMV and flu peptides and PHA were elicited. To investigate the antigen presenting capability of professional APC in NPC, dendritic cells (DC) were generated from ex vivo peripheral blood monocytes and shown to express a stimulatory mature phenotype with expression of CD83 and markers of costimulation CD80 and CD86. Despite this, mature DC pulsed with LMP2 derived peptides failed to stimulate and expand autologous LMP2-specific CTL, suggesting either absence or tolerance of LMP2-specific CTL. CD4+CD25+ regulatory cells have been implicated in peripheral tolerance and inhibition of antigen-specific T cell responses, and analysis of ex vivo peripheral blood T cells from NPC patients showed increased CD25 expression constituting a mean of 22.23 % of total CD4+ T cells compared to normal control mean of 5.35% (student t-test p<0.001). CD25 was not expressed by non-CD4+ T cells including CD8+ and NK cells, indicating that CD25 expression was unlikely to have represented activation. The findings suggest that CD4+CD25+ regulatory cells may play an important role in inhibiting antigen-specific anti-tumour responses in patients with established disease.