Tumor-derived suppressor factors (TDSFs) in normal and neoplastic colon and rectum

Immunosuppressive Factors: Role in Cancer Development and Progression

The concept of the immunological surveillance against neoplastic cells was initially proposed by Erlich in 1909 and later elaborated by Burnet. This hypothesis states that the normal function of the immune system, in particular the cell-mediated immunity, is to recognize and destroy the transformed and proliferating tumor cells. The role of cell-mediated immunity during the first steps of tumorigenesis remains controversial. However, there is certain evidence about its importance in the progression and dissemination of cancer. The frequent immunosuppressed condition of cancer patients at tumor relapse or recurrence of secondary tumors is a clinical sign supporting this hypothesis, and many studies have demonstrated a defective immune response in patients diagnosed with advanced cancer. Several mechanisms of escape from the immune surveillance have been described, including the immunoselection of tumor antigen-negative variants, the downregulation of MHC class I expression, suppressive T cells, and the elaboration of immunosuppressive cytokines and other factors. Because of the technical difficulty of isolating the very small amounts from culture supernatants or body fluids, only a few of these substances have been characterized and studied with respect to their biological activity: transforming growth factor-β (TGF-β), the protein p15E, interleukin 10 (IL-10), prostaglandin E2 (PGE2), mucins, suppressive E-receptor (SER), immunosuppressive acidic protein (IAP), and adhesion molecules. The possibility of monitoring cancer patients by testing biochemical factors related to cancer growth led to a proposal to measure a number of these factors as tumor markers. Some of them, e.g mucins, enjoy the consensus of the oncologic community, as for some indications they can help the clinician in the management of cancer patients. Except for the class of mucins, the other above-mentioned immunosuppressive factors have not found any clinical application in the laboratory routine because the information deriving from their measurement, although of speculative and scientific interest, has limited clinical value at present. Nevertheless, even if they have no impact on patient management, these substances do have a potential role to play in the study of cancer patients, and should be taken into account when developing new therapeutic strategies.

Inhibitors of lymphocyte activation secreted by human melanoma cell lines

The concentrated supernatants of nine human melanoma cell line cultures were analyzed for the presence of factors that inhibit in vitro immunological reactions. All cell lines secreted a factor that inhibited LPS-induced proliferation of murine B cells; eight cell lines released a factor that inhibited PHA-induced proliferation of murine T cells; all of the three cell lines investigated secreted a factor that inhibited the allogeneic stimulation of BALB/c spleen cells by mitomycin-C-treated C57BL spleen cells. Further analysis of the M21 cell supernatant indicated that its continuous presence was required for the inhibition of the PHA but not of the LPS response suggesting a different mechanism of action. High levels of PHA, but not of LPS, could overcome the inhibitory effect of M21 supernatants. Fractionation of M21 supernatants by sucrose gradient centrifugation, DEAE chromatography and gel filtration suggested that the anti-PHA and the anti-LPS activities were due to different factors. These factors differed from a serine proteinase inhibitor that is also released by M21 cells. Since these inhibitory factors may have a role in protecting a melanoma tumor from attack by the immune system of the host, their consideration may be helpful in designing protocols for therapy which include methods to boost the antitumor responses of the host.

Immunohistochemical analysis of mesocolic lymph node cells in human colorectal cancer

Localization of lymphocyte subsets and macrophages in the mesocolic lymph node of the colorectal cancer and their distribution among the paracolic, intermediate, and main nodes were studied quantitatively by means of immunohistochemical staining with monoclonal antibodies. In all of the three lymph node groups, in the paracortex, helper/inducer T cells were more numerous than suppressor/cytotoxic T cells. The number of whole T cells in the paracortex diminished with increasing proximity to the primary tumor. In the three lymph node groups, no significant difference was found regarding the ratio of the cell number among suppressor/cytotoxic T cells, natural killer cells, and macrophages. Lymphocytes in the paracortex of lymph node had a positive correlation to lymphocytes in the peritumoral stroma and intratumoral fields. These data neither suggest the presence of a powerful immunological reaction in the mesocolic lymph node nor support the concept of conservation of uninvolved regional lymph nodes in the surgery of the colorectal cancer.