FLT3 ligand gene expression and protein production in human colorectal cancer cell lines and clinical tumor specimens

Dendritic cells (DC) are professional antigen presenting cells (APC) whose proliferation and functional differentiation can be induced by hematopoieti c growth factors including GM-CSF and FLT3 ligand (FL), Colorectal cancers are known to be infiltrated by dendritic cells (DC) and neoplastic cells ha ve been shown to produce GM-CSF. In this work we investigated FLT3 ligand ( FL) gene expression and protein production in human colorectal cancer cell lines and clinical tumor specimens. Using reverse transcription polymerase chain reaction (RT-PCR), 6 out of 6 established tumor lines were found to e xpress to variable extents FL gene. In I of them, SW480, FL immunoreactivit y could be observed by taking advantage of specific antibodies. In contrast , soluble FL could not be detected in any culture supernatant. FLT3 recepto r (FR) gene was not expressed and exogenous addition to the cultures of rec ombinant FL (rFL) did not affect the proliferation of the tumor lines. FL g ene expression was investigated using a densitometry-assisted, semiquantita tive RT-PCR in clinical tumor specimens. Specific FL gene transcripts were amplified from 12 of 12 surgical samples. In these cases, FL gene expressio n of significantly lower intensity was also detected in healthy mucosa samp led in the vicinity (2 cm) or at a distance (10 cm) from neoplastic outgrow th. Immunohistochemical studies identified FL-positive cancer cells in 5 of 5 cases tested. No positivity was detected in healthy mucosa epithelia at a distance from the tumor or in stromal cells. FL content in preoperative s era from colorectal cancer patients (n = 13) did not exceed the levels dete cted in healthy donors (less than or equal to 100 pg/ml), Int J. Cancer 86: 238-243, 2000. (C) 2000 Wiley-Liss, Inc.