The T cell repertoire selected in vitro against EBV:: Diversity, specificity, and improved purification through early IL-2 receptor α-chain (CD25)-positive selection

Polyclonal T cell lines specific for EBV proteins have proved efficient in preventing EBV-related immunoblastic lymphoma after allogeneic bone marrow transplantation. To gain insight into the composition of the EBV-specific T cell repertoire that ensured patient protection, we performed for the first time an extensive characterization of eight cytotoxic T cell lines selected in vitro against EBV-transformed autologous lymphoblastoid cell lines (BLCL). These T cell lines consist of 50-100 distinct T cell clones, of which 32-96% are specific for autologous BLCL. Moreover, we demonstrate that reactivities against only five EBV proteins (BZLF1, BMLF1, EBNA-3A, EBNA-3C, and LMP2) cover 86% (32/37) of the specificities detected. In addition, we describe an improved method of T cell harvesting using a CD25 selection procedure which reduces the time required to obtain specific T cells and improves the purity of EBV-specific T cells, thus showing promise for use in adoptive transfer protocols.