Fas-independent and nonapoptotic cytotoxicity mediated by a human CD4(+) T-cell clone directed against an acute myelogenous leukemia-associated DEK-CAN fusion peptide

The mechanism underlying the cytotoxicity mediated by a human CD4(+) cytoto xic T-lymphocyte (CTL) clone directed against a peptide derived from the ac ute myelogenous leukemia-associated fusion protein, DEK-CAN, was investigat ed. A DEK-CAN fusion peptide-specific CD4(+) Th0 CTL clone, designated HO-1 , was established from the peripheral blood lymphocytes of a healthy indivi dual. HO-1 exerted direct but not "innocent bystander" cytotoxicity within 2 hours. The cytotoxicity mediated by HO-1 was completely Ca2+-dependent. B ecause HO-1 lysed peptide-loaded Fas-deficient target cells derived from a patient with a homozygous Fas gene mutation, its cytotoxicity appeared to b e mediated by a Fas-independent pathway. in addition, its cytotoxicity was only partially inhibited by treatment with concanamycin A and strontium ion s, which are inhibitors of the perforin-based cytotoxic pathway. Although m embrane-bound type of tumor necrosis factor-alpha (TNF-alpha) was expressed on HO-1. an anti-TNF-alpha antibody had no effect on HO-1-mediated cytotox icity. HO-1 expressed mRNA for apoptosis-inducing mediators, including perf orin, granzyme B, Fas ligand, TNF-alpha, and lymphotoxin; however, no DNA f ragmentation was detected in target cells incubated with HO-1 by 5-[I-125]I odo-2'-deoxyuridine release assay and agarose gel electrophoresis of DNA. A lthough it has been suggested that the Fas/Fas ligand system is the main pa thway by which CD4(+) CTL-mediated cytotoxicity is exerted in murine system s, HO-1 produced peptide-specific and HLA-restricted cytotoxicity via a Fas -independent and nonapoptotic pathway. The present study thus describes a n ever mechanism of cytotoxicity mediated by CD4(+) CTL. (C) 1999 by The Amer ican Society of Hematology.