Successful In Vitro Priming of EBV-Specific CD8+ T Cells Endowed with Strong Cytotoxic Function for Prophylaxis or Treatment of PTLD in EBV Seronegative Hosts.

EBV-seronegative solid organ transplant recipients, or recipients of T-cell depleted hematopoietic stem cell from a EBV-seronegative donor, are cohorts at high risk for the development of EBV-associated posttransplant lymphoproliferative disease (PTLD), and would maximally benefit from an EBV-directed T-cell therapy for prevention or treatment of PTLD. Reported experiences have shown that CTL obtained from EBV-seronegative individuals are almost exclusively HLA-class II-restricted CD4+ cytotoxic T cells, and efficiency of this CTL subset in the control of PTLD has not yet been demonstrated in vivo. Conversely, the central role of CD8+ CTL in the cell-mediated containment of EBV infection is well established. Therefore, we endeavoured to develop a protocol of EBV-CTL priming that would allow optimal expansion and high specific cytotoxic activity of CD8+ CTL. We employed naïve lymphocytes obtained from 5 EBV seronegative patients with end-stage renal failure receiving dialysis while listed for a kidney transplantation (4 children, 1 adult). In particular, we compared the CD8+ CTL priming efficiency of three different modified activation protocols, based on LCL stimulation potentially enhanced by either LCL presentation through DC, or selection of IFNg+ cultured cells, or culture in the presence of rhIL-12 and rhIL-7, to the standard protocol for reactivation of EBV-specific CTL from EBV-seropositive individuals. We found that while all protocols employed, with the exception of IFN-g+ T cell selection, allowed for the amplification of CD8+ and CD4+ mediated EBV-specific cytotoxic T cell responses in the EBV-seronegative adult, only specific EBV-transformed lymphoblastoid cell lines (LCL) stimulation in the presence of rhIL-12 and rhIL-7 was able to reproducibly generate and expand EBV-specific CD8+ CTL endowed with strong cytotoxic activity from truly EBV-seronegative children (mean lysis at a E:T ratio of 10:1: 14±10% with the standard protocol vs. 66±30% with the addition of rhIL-7 and rhIL-12). The lines thus activated showed a higher percentage CD8+ T cells, with less than 10% naïve CD8+/CCR7+/CD45RA+ cells. Overall, the total number of CD8+ central memory cells, and of CCR7- T cell effectors was comparable to that observed in healthy EBV-seropositive controls. In conclusion, stimulation with LCL in the presence of IL-12 and IL-7 activates EBV-specific, highly cytotoxic CD8+ CTL from EBV-seronegative subjects, this opening new perspectives for prevention/treatment of PTLD.