The dark side of stem cells: triggering cancer progression by cell fusion.

The phenomenon of cell fusion plays a crucial role in a plethora of physiological processes, including fertilization, wound healing, and tissue regeneration. In addition to this, cell fusion also takes place during pathophysiological processes such as virus entry into host cells and cancer. Particularly in cancer, cell fusion has been linked to a number of properties being associated with the progression of the disease including an increased proliferation rate, an enhanced metastatogenic behavior, an increased drug resistance and an increased resistance towards apoptosis. Although the process of cell fusion including the molecules to be involved-in is not completely understood in higher organisms, recent data revealed that chronic inflammation seems to be strong mediator. Since tumor tissue resembles chronically inflamed tissue, it can be concluded that cell fusion between recruited macrophages, bone marrow-derived cells (BMDCs), and tumor (stem) cells should be a common phenomenon in cancer. In the present review, we will summarize how a chronic inflamed microenvironment could originate in cancerous tissues, the role of M2-polarized tumor associated macrophages (M2-TAMs) within this process and how fusion between macrophages and BMDCs will trigger cancer progression. A particular emphasis will be drawn on recurrence cancer stem cells (rCSCs), which will play a pivotal role in "oncogenic resistance" and which might originate from fusion events between tumor (stem) cells and BMDCs.

Antibodies to chromosome 21 coded cell surface components block binding of human alpha interferon but not gamma interferon to human cells.

Antisera raised against a human X mouse hybrid cell line containing human chromosome 21 as its only human chromosome, block induction of an antiviral state by human alpha interferon (IFN-alpha), block induction of (2'-5')oligoisoadenylate synthetase [2'-5')A synthetase), and block binding of 125I-labeled and 35S-labeled recombinant, human IFN-alpha A, but not 125I-labeled IFN-gamma, to cell surface receptors. The data presented clearly demonstrate that the cell surface receptors for IFN-alpha and IFN-gamma are different, and provide independent evidence of the role of a chromosome 21 coded cell surface molecule in the pathway to the generation of the antiviral state.

Photoaffinity labeling of an interferon-gamma receptor on the surface of cultured fibroblasts.

Highly purified native and recombinant 125I-interferon-gamma was acylated with the photoreactive cross-linking reagent, N-succinimidyl-6(4'-azido-2'-nitrophenylamino) hexanoate. Derivatized interferon covalently labeled a cell surface component with an aggregate Mr = 230,000 +/- 7,000 (n = 7). Photoaffinity labeling was judged to be specific for the IFN-gamma receptor as it did not occur in the absence of light or in the presence of excess unlabeled interferon-gamma.

Three molecular weight forms of natural human interferon-gamma revealed by immunoprecipitation with monoclonal antibody.

Immune interferon (IFN-gamma), endogenously labeled with [35S]methionine, was produced in human peripheral blood lymphocyte cultures stimulated with 12-O-tetradecanoylphorbol-13-acetate and phytohemagglutinin. 35S-IFN-gamma, immunoprecipitated from the crude culture fluid with a monoclonal antibody, was resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis into three monomeric forms with molecular weights of 25,000, 20,000, and 15,500, which we designate IFN-gamma I, II, and III, respectively. IFN-gamma I was the most, and IFN-gamma III the least, abundant in both immunoprecipitated 35S-IFN-gamma and chromatographically purified IFN-gamma preparations. Changes in the molecular size of the monomeric forms after glycosidase treatment suggested that IFN-gamma I contains more carbohydrate than IFN-gamma II, and that IFN-gamma III may not be glycosylated at all. Hence, the differences in the carbohydrate contents are likely to be the major cause of the molecular size heterogeneity of IFN-gamma I, II, and III.

Natural and recombinant Escherichia coli-derived interferon-gamma differ in their reactivity with monoclonal antibody.

Monoclonal antibody GIF-1 was found to neutralize human natural immune interferon (IFN-gamma), but not Escherichia coli-derived recombinant IFN-gamma. In addition, GIF-1 antibody failed to immunoprecipitate 125I-labeled recombinant IFN-gamma, whereas it precipitated natural IFN-gamma in a concentration-dependent manner. The lack of recognition of recombinant IFN-gamma by antibody GIF-1 may not be due to the absence of the oligosaccharide moiety in the molecules of recombinant IFN-gamma alone, because removal of carbohydrate from natural IFN-gamma by treatment with a mixture of glycosidases did not alter the selective binding of antibody, i.e., deglycosylated and untreated natural IFN-gamma were equally neutralized and immunoprecipitated by GIF-1 antibody. In addition, a minor monomeric component of natural IFN-gamma with the m.w. of 15,500, which apparently lacks carbohydrate, was also recognized by antibody GIF-1. These results suggest that the discriminative recognition of natural and recombinant IFN-gamma by monoclonal antibody GIF-1 may be due to a conformational difference at or near the active regions of natural and recombinant human IFN-gamma molecules.

Ia-restricted interaction of normal lymphoid cells and SJL lymphoma (reticulum cell sarcoma) leading to lymphokine production. II. Rapid production of antibody-enhancing factor, interleukin 2, and immune interferon.

Mixed cell cultures of syngeneic lymph node (LN), spleen, or thymus and gamma-irradiated, syngeneic lymphoma cells of transplantable reticulum cell sarcomas (gamma-RCS) produced within 24 hours high titers of interleukin 2 (IL-2) and immune interferon in their supernatant (SN). These lymphokine titers were much higher than those seen after stimulation with allogeneic cells. SN also had marked enhancing activity for antibody production by anti-T-cell serum plus complement-treated spleen cells to trinitrophenylated polyacrylamide in vitro. This activity could be removed by absorption with cells of an IL-2-dependent cytotoxic cell line. Mixtures of gamma-RCS and LN cells from SJL/J F1 hybrid mice produced these lymphokines only when the non-SJL parent contributed H-2s or H-2b, but not H-2k or H-2d, in the I-region. These I-region restrictions were similar to those observed previously with respect to the ability of T-cells from SJL F1 hybrids to give proliferative responses to gamma-RCS in vitro and of these mice to support tumor growth in vivo. gamma-RCS also induced rapid interferon production in vivo, but serum titers 24 hours after injection consisted primarily of interferon resistant to pH 2 and neutralized by antibody to virally induced interferon (IFN-alpha/beta), and the production of IFN-alpha/beta was not subject to the same genetic restrictions. Although reticulum cell sarcoma cell extracts had no detectable effect in vitro, they were capable of inducing transient IFN production in vivo.

Ia-restricted interaction of normal lymphoid cells and SJL lymphoma (reticulum cell sarcoma) leading to lymphokine production. III. Relative roles of reticulum cell sarcoma and normal lymphoid cells in lymphokine production.

Production of interleukin 2 (IL-2) in mixed lymphocyte cultures of SJL/J lymph node (LN) and gamma-irradiated, syngeneic lymphoma cells of transplantable reticulum cell sarcoma (gamma-RCS) was abolished by pactamycin pretreatment of gamma-RCS. LN cells needed for this interaction were Lyt-2 T-cells, not adherent to Sephadex G-10. The effect of separation of T-cells and gamma-RCS after the first 24 hours of culture suggested that both components contributed to the IL-2 production. Exogenous IL-2, but not interleukin 1 (IL-1), restored the ability of pactamycin-treated gamma-RCS to induce syngeneic T-cell proliferation. The inability of T-cells from "nonresponder" F1 hybrids of SJL to proliferate to gamma-RCS was not corrected by addition of IL-1 or IL-2. Interferon (IFN) production also required the presence of untreated gamma-RCS and LN cells, but it was dependent on a Sephadex G-10 and plastic adherent cell in LN. IFN-free supernatant of LN cells plus gamma-RCS induced IFN production in fresh normal lymphoid cells, suggesting a possible indirect induction of this lymphokine. In addition, unirradiated RCS cells (la+ cells) produced immune IFN over a period of 3 weeks in vitro, after which the cells lost their viability. Prolonged IL-2 production was not observed in these cultures. The possible biological importance of the lymphokine production during the exaggerated syngeneic mixed lymphocyte reactions induced by RCS cells is discussed.

Ia-restricted interaction between normal lymphoid cells and SJL lymphoma (RCS) leading to lymphokine production. I. Enhancement and suppression of antibody formation to TI antigens by supernatants and cells from cocultures of RCS and lymphoid cells.

Addition of gamma-irradiated reticulum cell sarcoma (RCS) cells causes suppression of the antibody response to trinitrophenyl (TNP)-keyhole limpet hemocyanin (KLH)-primed syngeneic SJL spleen cells to TNP-polyacrylamide (PAA) in vitro. The response of anti-brain antigen (BAT) + C-treated spleen cells is not suppressed by gamma-RCS, but is suppressed by cells from 48-hr SJL lymph node or thymus + gamma-RCS cultures. Addition of as few as 2.5 x 10(5) cultured (anti-I-A + C treated to remove gamma-RCS) cells causes significant inhibition of the responses of both syngeneic and allogeneic spleen cells. Treatment of gamma-RCS-induced suppressor cells with anti-BAT + C reduces their suppressive activity. In contrast to the cells, supernatants (SN) from (lymph node (LN) + gamma-RCS) cultures greatly enhance, in an antigen-dependent fashion, the responses of untreated or anti-BAT + C-treated Sephadex G10-passed spleen cells to TNP-PAA. TNP-SIII polysaccharide, or TNP-Ficoll, but not as much to TNP-KLH. Addition of SN as late as Day 3 of culture still causes about half as much enhancement as leaving SN in throughout the culture period, but it has no effect if left with the spleen cells for only the first day of culture. SN contains high levels of IL-2 and IFN-gamma; absorption with cells from an IL-2-dependent cytotoxic T-cell line removes the enhancing activity, while treatment with pH 2 to remove the IFN-gamma has no effect. SN from an IL-2-producing T-cell line (LBRM-33) has a similar effect on antibody production to TI antigens as does SN of (LN + gamma-RCS). The results suggest a marked dependency of PFC responses to TI antigen on IL-2 in all strains examined, including SJL, LAF1, DBA/2Ha, and CBA/N, probably through a direct activation of B cells. The findings also suggest that suppressor T cells, induced by gamma-RCS in syngeneic lymphoid cells, absorb the IL-2 needed for responses to TI antigens in vitro.