ACTIVATED ALPHA(2)-MACROGLOBULIN REVERSES THE IMMUNOSUPPRESSIVE ACTIVITY IN HUMAN BREAST-CANCER CELL-CONDITIONED MEDIUM BY SELECTIVELY NEUTRALIZING TRANSFORMING-GROWTH-FACTOR-BETA IN THE PRESENCE OF INTERLEUKIN-2

The immunosuppressive activity of tumor cells may be mediated by tumor -derived cytokines such as transforming growth factor-beta (TGF-beta) and interleukin-10 (IL-10). A human breast cancer cell line derived fr om malignant ascites (BRC 173) secreted TGF-beta, but not IL-10, into tissue culture supernatant (TCS). BRC 173 TCS suppressed natural kille r (NK) and lymphokine-activated killer (LAK) cell activity and also bl ocked the generation of HLA-A0201-restricted tumor-reactive cytotoxic T-lymphocyte (CTL) lines in vitro. Human alpha(2)-macroglobulin (alph a(2)M), a plasma protein and cytokine carrier that binds isoforms in t he TGF-beta family, was tested for its ability to neutralize the immun osuppressive activity in BRC 173 TCS. alpha(2)M was converted to its a ctivated conformation by reaction with methylamine (alpha(2)M-MA) and then incubated with normal human peripheral blood lymphocytes (PBL) in the presence of IL-2 and BRC 173 TCS. Lysis of NK targets (K562) and LAK cell targets (DM6 melanoma) by the PBL was examined after 6 days o f culture. PBL cultured in IL-2, without TCS or alpha(2)M-MA, were lyt ic for both target cells. BRC 173 TCS substantially suppressed the lyt ic activity of the PBL in the presence of IL-2. When TGF-beta-neutrali zing antibody was added to the PBL culture medium with IL-2 and TCS, a majority of the lytic activity was restored. alpha(2)M-MA (280 nM) ne utralized almost all of the immunosuppressive activity in the TCS, res toring 80-100% of the lytic activity without any apparent effect on th e activity of IL-2. The ability of alpha(2)M-MA to counteract immunosu ppressive cytokines in breast cancer TCS was evident in serum-containi ng and serum-free medium. These studies demonstrate that activated alp ha(2)M can function as a selective cytokine neutralizer to thereby pro mote the activation of NK, LAK, and tumor-specific CTL responses.