Inhibition of tumor-specific cytotoxic T-lymphocyte responses by transforming growth factor beta 1.
Transforming growth factor beta (TGF-beta) is a potent immunosuppressive cytokine that is produced by neoplastic and normal cells. It has not been demonstrated directly, however, that TGF-beta can inhibit antigen-specific T-cell responses to tumor cells in vitro. We show here that generation of antitumor cytotoxic T-lymphocyte (CTL) activity in mixed-lymphocyte tumor cultures of splenocytes from DBA/2 mice immunized with the syngeneic P815 mastocytoma + Corynebacterium parvum was consistently and profoundly inhibited when 0.675 to 10 ng/ml of TGF-beta were added on Day 0 of culture. TGF-beta added on Day 1 or later had little or no effect. In contrast to the results with P815 immune mice, mixed-lymphocyte tumor cultures established with splenocytes from P815 tumor-bearing hosts showed variable degrees of inhibition by TGF-beta, depending on the stage of the ongoing in vivo immune response. Addition of recombinant murine tumor necrosis factor alpha (1,000 or 10,000 units/ml) partially reversed inhibition of CTL responses by TGF-beta, while recombinant interleukin 2 nearly completely reversed the suppression. These data indicate that one level at which TGF-beta may act to inhibit mixed-lymphocyte tumor cultures is that of cytokine production. To determine whether TGF-beta also has any direct effect on CTL, P815-specific CTL clones derived from tumor-bearing host mice were utilized. We found that proliferation of rested CTL clones in response to tumor cells + interleukin 2 was inhibited by 5 ng/ml of TGF-beta, while the interleukin 2-dependent reactivation of cytolytic activity was not affected by TGF-beta. In contrast to rested CTL, when TGF-beta was added to cultures of previously activated CTL, proliferation was not inhibited. These data demonstrate that TGF-beta has profound inhibitory effects on the in vitro generation of effector CTL from tumor-specific murine splenocytes, and this inhibition may be an indirect result of suppressed cytokine production as well as a direct antiproliferative effect on CTL.
Inge
T H
TH
Department of Microbiology and Immunology, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298.
Hoover
S K
SK
Susskind
B M
BM
Barrett
S K
SK
Bear
H D
HD
D000818:Animals; D007156:Immunologic Memory; D007376:Interleukin-2 / Q000494:pharmacology; D008213:Lymphocyte Activation / Q000187:drug effects*; D007959:Lymphocyte Culture Test, Mixed; D012515:Mast-Cell Sarcoma / Q000276:immunology; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D013601:T-Lymphocytes / Q000276:immunology*; D016211:Transforming Growth Factor alpha / Q000494:pharmacology; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D007376:Interleukin-2; D016211:Transforming Growth Factor alpha; D016212:Transforming Growth Factor beta