Expression of regeneration and tolerance factor on B cell chronic lymphocytic leukemias: A possible mechanism for escaping immune surveillance

Regeneration and tolerance factor (RTF) is a protein expressed on developin g tissue such as the thymus and the placenta. RTF has been reported to down -regulate cell-mediated immune responses. To examine the potential role of tumor-derived RTF to suppressing antitumor responses, we analyzed a panel o f seven B cell tumor lines for the membrane RTF using a fluorescein isothio cyanate (FITC) conjugated monoclonal antibody, which reacts with membrane R TF. All the B cell tumor lines we examined express RTF on the cell surface. We also tested conditioned media from these B cell lines for their ability to suppress IL-2R expression on activated cells. Conditioned media from ea ch a cell line suppressed IL-2R expression on activated Jurkat T cells and activated peripheral blood mononuclear cells. A monoclonal antibody to the biologically active portion of RTF reversed this suppressive activity. Fina lly, the tumor cell population from patients with chronic lymphocytic leuke mia was found to express cell surface RTF. Thus, RTF expression could be a new mechanism used by tumor cells to escape immune surveillance. (C) 1999 W iley-Liss, Inc.