Large‐scale expansion of cytomegalovirus‐specific cytotoxic T cells in suspension culture

Clinical trials in recent years involving the adoptive transfer of antigen‐specific cytotoxic T lymphocytes (CTL) have shown promise in restoring immunity against viral infection and reducing tumor burden in patients with solid and hematological malignancies. However, the large cell number required to achieve efficacy, 109 to 1011, makes routine application of adoptive immunotherapy impractical. Investigation into new methods of CTL expansion may be useful in addressing this problem. Use of stirred suspension bioreactors are one such method that may allow large‐scale T‐cell expansion. Suspension cultures offer advantages over conventional static culture methods, including providing a homogeneous culture environment, and the potential for optimization and control of culture conditions. We generated cytomegalovirus (CMV)‐specific CTL and investigated the potential of stirred bioreactor systems for expansion of large cell numbers. We found that CTL can be readily expanded ( > 200‐fold) from cryopreserved stocks by nonspecific stimulation in the presence of allogeneic feeder cells and interleukin‐2 (IL‐2). Activated CTL inoculated into either suspension or static cultures could be subsequently expanded tenfold, and showed similar growth kinetics and metabolism independent of the culture vessel used. Furthermore, CTL remained specific for CMVpp65 peptide through the expansion phases, as demonstrated by pp65–tetramer staining ( > 95% tetramer+) and cytotoxicity assays. This study indicates that suspension reactor systems may be useful in large‐scale expansion of antigen‐specific CTL lines or clones, and may facilitate the advancement of routine adoptive immunotherapy. © 2003 Wiley Periodicals, Inc.