Superantigen-induced cytokines suppress growth of human colon-carcinoma cells.
We have recently demonstrated that the superantigen staphylococcal enterotoxin A (SEA) conjugated to colon-carcinoma-reactive monoclonal antibodies (MAbs) directs T cells to lyse human colon-carcinoma cells, representing a potential novel tumor therapy. To further analyze the mechanism of antitumor effects of superantigen-activated T cells, we compared the activity of free and MAb-conjugated SEA in a long term in vitro co-culture assay of human peripheral-blood mononuclear cells (PBMC) and colon-carcinoma cell lines. Activation of resting T lymphocytes with SEA conjugated to the colon-carcinoma-reactive MAb C215 or free SEA resulted in strong inhibition of the growth of all studied colon-carcinoma cell lines. The growth of WiDr colon-carcinoma cells was unaffected by the presence of unactivated mononuclear cells, whereas addition of pM concentrations of SEA or C215-SEA conjugate completely suppressed tumor-cell growth. The suppressive effect was mediated by both CD4+ and CD8+ T cells and required the presence of MHC-Class II+ monocytes. The inhibition of tumor-cell growth was to a large extent mediated by soluble factors present in supernatants from SEA- or C215-SEA-activated mononuclear cells. Quantitation of cytokine mRNA in SEA-activated mononuclear cells by the reverse transcriptase-polymerase chain reaction (RT-PCR) revealed strong induction of mRNA encoding the cytokines IL-1 alpha, IL-1 beta, IL-2, IL-6, TNF-alpha, TNF-beta and IFN-gamma. The use of cytokine-specific MAb demonstrated that IFN-gamma was of major importance for the tumor-growth-inhibitory activity in supernatants of SEA-activated lymphocytes. Addition of recombinant cytokines to WiDr colon-carcinoma cells showed that TNF-alpha was able to act synergistically with IFN-gamma to suppress tumor-cell growth. The local production of tumor-suppressive cytokines induced by MAb-targeted superantigens is likely to be of particular relevance for inhibition of the growth of tumor cells not expressing the targeted tumor-associated antigen.
Kabi Pharmacia Therapeutics, Lund, Sweden.
M
M
Dohlsten
A
A
Sundstedt
M
M
Björklund
G
G
Hedlund
T
T
Kalland
D000911:Antibodies, Monoclonal; D000942:Antigens, Bacterial / Q000494:pharmacology*; D000951:Antigens, Neoplasm / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D003110:Colonic Neoplasms / Q000276:immunology* / Q000378:metabolism / Q000628:therapy*; D016207:Cytokines / Q000096:biosynthesis* / Q000276:immunology; D004768:Enterotoxins / Q000494:pharmacology*; D006801:Humans; D000922:Immunotoxins / Q000494:pharmacology*; D008213:Lymphocyte Activation / Q000187:drug effects / Q000276:immunology; D009504:Neutrophils / Q000187:drug effects / Q000276:immunology; D013601:T-Lymphocytes / Q000187:drug effects / Q000276:immunology; D014407:Tumor Cells, Cultured
D000911:Antibodies, Monoclonal; D000942:Antigens, Bacterial; D000951:Antigens, Neoplasm; D016207:Cytokines; D004768:Enterotoxins; D000922:Immunotoxins; C026066:enterotoxin A, Staphylococcal