Myeloma-reactive allospecific cytotoxic T lymphocytes lyse target cells via the granule exocytosis pathway

Accumulating evidence indicates that a graft-vs.-myeloma effect (GVM) and i ts associated clinical remission of the disease can be induced by donor lym phocyte infusion in myeloma patients who have relapsed after allogeneic bon e marrow transplantation. Although it is believed that GVM is induced by al lospecific T cells, T-cell subsets and the mechanisms involved in the killi ng of myeloma cells by donor T cells have not been studied. In this study, we generated allospecific cytotoxic T lymphocyte (CTL) lines against three different myeloma cell lines, ARK, ARP-1 and U266, from unmatched healthy d onors and examined their cytotoxicity against the target cells. Our results demonstrate that the allospecific CTLs efficiently lysed myeloma cells. Th e observed cytotoxicity was mediated mainly by CD8(+) T cells and inhibited by MHC class I-blocking antibody. Furthermore, the CTLs lysed the target c ells via the perforin-mediated pathway, as concanamycin A, but not brefeldi n A (the selective inhibitors for perforin- or Fas-mediated pathways respec tively) or tumour necrosis factor-alpha (TNF-alpha)-blocking antibody, abro gated the cytolytic activity of the cells. These CTLs expressed and produce d predominantly TNF-alpha and interferon-gamma (IFN-gamma), indicating that they belong to the type 1 T-cell subsets. Taken together, these results in dicate that CD8(+) allospecific T cells may be responsible for mediating GV M and that the granule-mediated lysis of target cells is the major pathway in the CD8(+) T-cell response against myeloma cells.