EBV-specific memory CD8⁺ T cell phenotype and function in stable solid organ transplant patients

Immune responses to EBV in immunosuppressed (IS) solid organ transplant (SOTx) recipients have not been well characterized. Here we evaluate the phenotype and function of EBV-specific CD8⁺ T cells in peripheral blood isolated from "stable" IS SOTx recipients. The EBV-specific CD8⁺ T cell memory subset distribution in the peripheral blood of patients was examined by flow cytometric analysis using HLA-A2 tetramers incorporating BMLF1 (lytic), and LMP2 and EBNA3A (latent)-derived peptides, in conjunction with mAbs against the CD45RO, CD45RA, and CD62L markers. The ability of CD8⁺ T cells to produce IFN-γ in response to the same EBV-derived peptides was measured by ELISPOT assay. Patients and healthy normal donors exhibited similar anti-EBV CD8⁺ T cell frequencies and specificities against the EBV epitopes evaluated. When compared to healthy normal donors, an overall significant expansion of the CD8⁺ T cell "effector memory" (CD45RO⁺/CD62L^-) pool, including that of EBV "latent" (LMP2 and EBNA3A)-specific CD8 ⁺ T cells was detected in IS SOTx patients. However, the patients' EBV-specific CD8⁺ T cells showed decreased IFN-γ production to the EBV-peptide stimulation. These results indicate that the impairment of EBV-specific CD8⁺ T cell activity is not due to clonal depletion, but is mainly due to impaired functional activation.