Downregulation of transcription factor SOX2 in cancer stem cells suppresses growth and metastasis of lung cancer.

BACKGROUND: The cancer stem cell hypothesis suggests that neoplastic clones are maintained exclusively by a small subpopulation of cells, which have indefinite proliferation and differentiation potentials and give rise to phenotypically diverse cancer cells. Cancer stem cells have been isolated by their ability to efflux Hoechst 33342 dye and are referred to as the 'side population' (SP). METHODS AND RESULTS: The Hoechst efflux assay was used to isolate and characterize the SP from murine D121 lung carcinoma cells. Here, we demonstrated that D121-SP cells contain cancer stem cell characteristics, that is, upregulation of the transcription factors SOX2 and Oct 4 in D121-SP cells. In addition, the migration of D121-SP was decreased, and apoptosis of D121-SP was upregulated following knocking down of SOX2 in D121 cells. Importantly, downregulation of SOX2 in D121 cells markedly suppressed their metastatic potential in syngeneic mice. CONCLUSIONS: These results suggest that the SP is an enriched source of lung tumour cells with stem cell properties and that SOX2 has an important role in maintaining stem cell properties and functions that may be a potential target for effective lung cancer therapy.

C3-mediated cytoadherence. Formation of C3 receptor aggregates as prerequisite for cell attachment.

Inhibition of free movement of C3 receptors by either applying low temperature (3 degrees C) or fixing the cell surfce of lymphocytes with glutaraldehyde (2 times 10(-5) to 2 times 10(-1)%) results in loss of firm attachment of EAC142 3b cells to the lympocytes as demonstrated here by loss of rosette formation of Raji lymphoid cells. Under the same conditions soluble C3 can still bind but is unable to induce aggregation of C3 receptors into small patches. It is suggested that the local increase of C3 receptor density by aggregation is a prerequisite for C3-dependent cytoadherence. Microaggregation of corresponding receptor sites may be essential also in other recognition systems.

A recurrent idiotype on monoclonal anti-human Ia antibodies.

We report a recurrent idiotype on a remarkably high fraction (4/19) of murine monoclonal antibodies specific for human Ia monomorphic determinants and elicited by separate immunizations. For three of them, the shared idiotype is associated with the antigen-combining site. These results indicate that the spectrum of mouse antibody responses to human Ia antigens may be based on recurrent idiotypes, suggesting a limited potential repertoire of murine monoclonal antibodies to human Ia antigens. Anti-idiotypic reagents might be helpful in dissecting this repertoire and to generate a mirror image of a human Ia antigenic map. Furthermore, antisera to the idiotype of antibodies specific for human Ia monomorphic determinants might help in elucidating the interactions between Ia molecules and receptors on immune cells.

Serologic evidence for antigens controlled by the Ir region in mice.

Antibodies produced in B10.D2 mice against soluble lymphocyte membrane antigens of B10.A (H-2(a)) mice reacted only with lymphocytes of the strains carrying the Ir(k) region, i.e., B10.A(2R), B10.K, B10.BR, B10.HTT, AQR, A.TE, C3H, and CBA; they did not react with cells of strains carrying different Ir regions, i.e., B10.A(4R), B10, B10.M, A.SW, DBA/1. It is therefore concluded that the antigen detected with these antibodies is apparently controlled by the Ir region of the H-2 complex. The antigen is present on some T lymphocytes and absent on B lymphocytes. Its presence or absence seems to correlate with MLC and GVH reactivity.

Eradication of established human melanoma tumors in nude mice by antibody-directed effector cells.

The simultaneous injection of monoclonal antibody 9.2.27, directed against a chondroitin sulfate proteoglycan preferentially expressed on human melanoma cells, and 2 X 10(7) mononuclear splenocytes, eradicated established, progressively growing human melanoma tumors in nude mice. Neither splenocytes nor antibody alone achieved significant tumor regression. The cells responsible for tumor elimination are most likely natural killer (NK) cells: they are present in splenocytes of T cell-deficient nude mice, and cloned cells with NK activity are able to suppress tumor growth. Moreover, splenocytes treated with anti-asialo GM1 and complement or harvested from NK-deficient C57BL/6 beige mice did not cause tumor rejection. Furthermore, treatment of BALB/c nude mice just before injection with anti-asialo GM1 antiserum, which is known to eliminate NK activity in vivo, resulted in better tumor growth. In addition, evidence is presented that cells with NK activity are probably the effectors responsible for melanoma target cell lysis in vitro: Antibody-dependent and -independent cell-mediated lysis of M21 melanoma cells was suppressed when splenocytes were preincubated with complement and antibodies specific for cell surface antigens of NK cells, i.e., anti-asialo GM1, anti-Qa5, and anti-NK1.1. Moreover, splenocytes of C57BL/6 beige mice were not able to lyse M21 cells in vitro. These results strongly support the conclusion that cells with NK activity are indeed responsible for the antibody-dependent destruction of M21 melanoma cells in vivo and in vitro.

Interaction of histocompatibility (HL-A) antibodies and complement with synchronized human lymphoid cells in continuous culture.

The interaction of histocompatibility (HL-A) antibodies and complement with synchronized human lymphoid cells in continuous culture has been investigated. The sensitivity of cultured lymphoid cells to HL-A antibody-mediated lysis in the cytotoxic test, the extent of activation of the complement system, the degree to which labeled complement components are bound, and the ability of these cells to absorb HL-A alloantibodies do not vary significantly during the cell growth cycle. The constancy of histocompatibility antigen expression throughout the growth cycle of cultured cells suggests that these cell surface markers are an essential part of membrane cytoarchitecture and could well play a critical role in determining the normal function of the cell membrane.

Variation in susceptibility of a human lymphoid cell line to immune lysis during the cell cycle. Lack of correlation with antigen density and complement binding.

Cultured human lymphoid cells RPMI 8866 at different stages of their growth cycle vary in their susceptibility to lysis by rabbit, human, and guinea pig complement activated by HL-A antibodies or heterologous antibodies directed to membrane antigens; cells in G(1) phase are the least sensitive to lysis. To investigate the cause of differential susceptibility of cells RPMI 8866 to lysis, the expression of HL-A determinants and the ability of cells to react with complement were investigated. No change was detected in the density of HL-A antigens on RPMI 8866 cells in synchronous growth as determined by quantitative microabsorption assays, isotopic antiglobulin tests and yields of soluble HL-A antigens. Cells did not vary during the growth cycle in their ability to interact with complement components and in their capacity to activate the complement system through the classical or alternate pathway. These data suggest that variability in lytic susceptibility is due to changes in the structure of the cell membrane or in its ability to repair complement induced damage at certain intervals during the cell cycle. Therefore, this cell line constitutes a useful model to investigate the final steps of the cytolytic reaction.

T cell-mediated eradication of murine metastatic melanoma induced by targeted interleukin 2 therapy.

Induction of a T-cell mediated antitumor response is the ultimate goal for tumor immunotherapy. We demonstrate here that antibody-targeted IL2 therapy is effective against established pulmonary and hepatic melanoma metastases in a syngeneic murine tumor model. The effector mechanisms involved in this tumor eradication are not dependent on NK cells, since the therapeutic effect of antibody-IL2 fusion protein was not altered in NK cell-deficient mice. In contrast, T cells are essential for the observed antitumor effect, since therapy with antibody IL2 fusion proteins is unable to induce tumor eradication in T cell-deficient SCID mice. In vivo depletion studies characterized the essential effector cell population further as CD8 + T cells. Such CD8 + T cells, isolated from tumor bearing mice after antibody-directed IL2 therapy, exerted a MHC class I-restricted cytotoxicity against the same tumor in vitro. These data demonstrate the ability of antibody-targeted IL2 delivery to induce a T cell-dependent host immune response that is capable of eradicating established melanoma metastases in clinically relevant organs.

The anamnestic antibody response to type 3 specific pneumococcal polysaccharide.

Rabbits immunized with killed type III pneumococci respond to anamnestic challenge by type specific polysaccharide (S III) with the synthesis of anti-S III antibody if a long interval is allowed to elapse between primary and secondary immunization. A study of the anti-S III antibody produced early and late in the immune response revealed no change in molecular class, banding pattern of dissociated light chains, or S III binding characteristics as measured under equilibrium conditions or by study of dissociation kinetics utilizing radioiodinated p-OH-benzyl-S III. Sequential booster injections of S III into rabbits primarily immunized with whole organisms 8 or 9 months earlier led to a progressive decrease in the number of animals showing successful anamnestic responses and in the magnitude of those responses. It is concluded that S III depletes the antigen sensitive cell population in the secondary response largely because of its limited ability to stimulate sustained proliferation by such cells.

An Arg-Gly-Asp-directed receptor on the surface of human melanoma cells exists in an divalent cation-dependent functional complex with the disialoganglioside GD2.

The disialogangliosides GD2 and GD3 play a major role in the ability of human melanoma cells to attach to Arg-Gly-Asp-containing substrates such as fibronectin and vitronectin, since pretreatment of these cells with monoclonal antibodies to the oligosaccharide of GD2 and GD3 can inhibit their attachment and spreading on such adhesive proteins. This report demonstrates that human melanoma cells (M21) synthesize and express a glycoprotein receptor that shares antigenic epitopes with the vitronectin receptor on human fibroblasts and is capable of specifically recognizing the Gly-Arg-Gly-Asp-Ser-Pro sequence. In the presence of calcium, GD2, the major ganglioside of M21 cells, colocalized with this receptor on the surface of human melanoma cells and their focal adhesion plaques as demonstrated by double-label transmission immunoelectron microscopy and indirect immunofluorescence. Biochemical evidence is presented indicating that the vitronectin receptor on M21 human melanoma cells contains associated calcium and GD2. This ganglioside copurified with the glycoprotein receptor for vitronectin on affinity columns containing either an Arg-Gly-Asp-containing peptide, concanavalin A, or lentil lectin. This major Arg-Gly-Asp-directed receptor on M21 cells could be metabolically labeled with 45Ca2+. Chelation of this ion with EDTA caused the dissociation of GD2 from the receptor and rendered the remaining glycoprotein incapable of binding to an Arg-Gly-Asp-containing peptide. Reconstitution experiments demonstrated a requirement for calcium, and not magnesium, for receptor binding to Arg-Gly-Asp and indicated that addition of ganglioside can enhance this interaction.

Human neural cell adhesion molecule L1 and rat homologue NILE are ligands for integrin alpha v beta 3.

Integrin alpha v beta 3 is distinct in its capacity to recognize the sequence Arg-Gly-Asp (RGD) in many extra-cellular matrix (ECM) components. Here, we demonstrate that in addition to the recognition of ECM components, alpha v beta 3 can interact with the neural cell adhesion molecule L1-CAM; a member of the immunoglobulin superfamily (IgSF). M21 melanoma cells displayed significant Ca(++)-dependent adhesion and spreading on immunopurified rat L1 (NILE). This adhesion was found to be dependent on the expression of the alpha v-integrin subunit and could be significantly inhibited by an antibody to the alpha v beta 3 heterodimer. M21 cells also displayed some alpha v beta 3-dependent adhesion and spreading on immunopurified human L1. Ligation between this ligand and alpha v beta 3 was also observed to promote significant haptotactic cell migration. To map the site of alpha v beta 3 ligation we used recombinant L1 fragments comprising the entire extracellular domain of human L1. Significant alpha v beta 3-dependent adhesion and spreading was evident on a L1 fragment containing Ig-like domains 4, 5, and 6. Importantly, mutation of an RGD sequence present in the sixth Ig-like domain of L1 abrogated M21 cell adhesion. We conclude that alpha v beta 3-dependent recognition of human L1 is dependent on ligation of this RGD site. Despite high levels of L1 expression the M21 melanoma cells did not display significant adhesion via a homophilic L1-L1 interaction. These data suggest that M21 melanoma cells recognize and adhere to L1 through a mechanism that is primarily heterophilic and integrin dependent. Finally, we present evidence that melanoma cells can shed and deposit L1 in occluding ECM. In this regard, alpha v beta 3 may recognize L1 in a cell-cell or cell-substrate interaction.

KSA antigen Ep-CAM mediates cell-cell adhesion of pancreatic epithelial cells: morphoregulatory roles in pancreatic islet development.

Cell adhesion molecules (CAMs) are important mediators of cell-cell interactions and regulate cell fate determination by influencing growth, differentiation, and organization within tissues. The human pancarcinoma antigen KSA is a glycoprotein of 40 kD originally identified as a marker of rapidly proliferating tumors of epithelial origin. Interestingly, most normal epithelia also express this antigen, although at lower levels, suggesting that a dynamic regulation of KSA may occur during cell growth and differentiation. Recently, evidence has been provided that this glycoprotein may function as an epithelial cell adhesion molecule (Ep-CAM). Here, we report that Ep-CAM exhibits the features of a morphoregulatory molecule involved in the development of human pancreatic islets. We demonstrate that Ep-CAM expression is targeted to the lateral domain of epithelial cells of the human fetal pancreas, and that it mediates calcium-independent cell-cell adhesion. Quantitative confocal immunofluorescence in fetal pancreata identified the highest levels of Ep-CAM expression in developing islet-like cell clusters budding from the ductal epithelium, a cell compartment thought to comprise endocrine progenitors. A surprisingly reversed pattern was observed in the human adult pancreas, displaying low levels of Ep-CAM in islet cells and high levels in ducts. We further demonstrate that culture conditions promoting epithelial cell growth induce upregulation of Ep-CAM, whereas endocrine differentiation of fetal pancreatic epithelial cells, transplanted in nude mice, is associated with a downregulation of Ep-CAM expression. In addition, a blockade of Ep-CAM function by KS1/4 mAb induced insulin and glucagon gene transcription and translation in fetal pancreatic cell clusters. These results indicate that developmentally regulated expression and function of Ep-CAM play a morphoregulatory role in pancreatic islet ontogeny.

Electrophoretic heterogeneity of polypeptide chains of specific antibodies.

Heavy and light polypeptide chains isolated from different specific antibodies to haptens and from (gamma)G-immunoglobulin of normal rabbits have been resolved into distinct, multiple components by disc electrophoresis in polyacrylamide gels in the presence of urea. In spite of the resolution of these chains into multiple bands, different specific antibodies and normal rabbit (gamma)G-immunoglobulin were indistinguishable from each other by this method.

O-acetylation of disialoganglioside GD3 by human melanoma cells creates a unique antigenic determinant.

Monoclonal antibody Mab D1.1 recognizes on human melanoma cells a ganglioside antigen characterized by an alkali-labile O-acetylated sialic acid residue. Immunochemical analysis showed that this molecule is an O-acetylated product of the neuroectoderm-associated disialoganglioside GD3. Controlled chemical O-acetylation of purified GD3 resulted in the generation of this same epitope. Lysates of human melanoma cells were found to contain O-acetyltransferase activity capable of generating the antigenic epitope recognized by Mab D1.1. Thus, the addition of a single O-acetyl group to a common cell surface-associated ganglioside can create a potentially tumor-specific antigen.

Salt extraction of soluble HL-A antigens.

Extraction of cultured human lymphoid cells with hypertonic salt solutions (3 molar potassium chloride) resulted in high recoveries of membrane-associated histocompatibility (HL-A) antigens in soluble form with potent activity and marked immunologic specificity. The active principle was purified by preparative acrylamide-gel electrophoresis. Application of the hypertonic salt extraction method is now yielding sufficient HL-A antigen to begin the elucidation of the molecular basis of transplantation individuality.

Electrophoretic heterogeneity of the polypeptide chains of human G-myeloma proteins.

The light and heavy polypeptide chains derived from human Gmyeloma proteins are electrophoretically heterogeneous as judged by disc electrophoresis of the polypeptide chains in urea-acrylamide gels. Individual myeloma proteins contained as many as eight light-chain and nine heavy-chain components.

Utilization of cultured human lymphoid cells for detection of humoral sensitization in prospective recipients of kidney transplants.

Prospective recipients of kidney transplants were tested for lymphocytotoxicity; from these we selected 102 sera that lacked cytotoxic antibodies against peripheral lymphocytes from at least 80 unrelated subjects. To detect humoral sensitization, we then reacted these with 17 cultured human lymphoid cell lines having different HL-A phenotypes. Cytotoxic antibodies reacting with these cultured cells were now detected in some of the sera. These antibodies were not directed against HL-A antigens, yet mediated lysis of target cells in the presence of rabbit but not of human or guinea pig complement. Furthermore, they activated the classical pathway of the rabbit complement system. Later, a significant association was found between occurrence of cytotoxic antibodies and rejection of the transplant. Thus, cultured human lymphoid cells, because of their great susceptibility to complement-mediated lysis, appear to be useful in detecting humoral sensitization in candidates for kidney grafts.

Long-lived and transferable tumor immunity in mice after targeted interleukin-2 therapy.

A major goal of tumor immunotherapy is the induction of tumor-specific T cell responses that are effective in eradicating disseminated tumor, as well as mounting a persistent tumor-protective immunity. We demonstrate here that a genetically engineered fusion protein consisting of human/mouse chimeric anti-ganglioside GD2 antibody and human interleukin-2 is able to induce eradication of established B78-D14 melanoma metastases in immunocompetent syngeneic C57BL/6J mice. This therapeutic effect is mediated by host immune cells, particularly CD8+ T cells and is associated with the induction of a long-lived immunity preventing tumor growth in the majority of animals when challenged up to four months later with B78-D14 cells. This effect was tumor-specific, since no cross-protection against syngeneic, ganglioside GD2+ EL-4 thymoma cells was observed. Furthermore, this tumor-specific protection can be transmitted horizontally to naive, syngeneic SCID mice by passive transfer of CD8+ T lymphocytes derived from immune animals. These results suggest that antibody-targeted delivery of cytokines provides a means to elicit effective immune responses against established tumors in the immunotherapy of neoplastic disease.

Melanoma immunotherapy by targeted IL-2 depends on CD4(+) T-cell help mediated by CD40/CD40L interaction.

The induction of tumor-protective immunity against malignancies remains a major challenge in cancer immunotherapy. A novel, humanized anti-ganglioside-GD(2)-IL-2 immunocytokine (hu14.18-IL-2) induced CD8(+) T cells to eradicate established pulmonary metastases of B78-D14 murine melanoma, in a process that required help by CD4(+) T cells and was mediated by the CD40/CD40 ligand (CD40L) interaction. The anti-tumor effect was diminished in mice deficient in CD4(+) T-cells. Three lines of evidence show that CD4(+) T-cell help was mediated by CD40/CD40L interaction but not by endogenous IL-2 production. First, the hu14.18-IL-2-induced anti-tumor response is partially abrogated in C57BL/6J CD40L knockout (KO) mice in contrast to C57BL/6J IL-2 KO animals, in which the immunocytokine was completely effective. Second, partial abrogation of the anti-tumor effect is induced with anti-CD40L antibodies to the same extent as with CD4(+) T-cell depletion. Third, a complete anti-tumor response induced by hu14.18-IL-2 can be reconstituted in C57BL/6J CD40L KO mice by simultaneous stimulation with an anti-CD40 mAb. These results suggest that help provided by CD4(+) T cells via CD40/CD40L interactions in our tumor model is crucial for effective immunotherapy with an IL-2 immunocytokine.

Pharmacokinetics and mechanism of action of a doxorubicin-monoclonal antibody 9.2.27 conjugate directed to a human melanoma proteoglycan.

Doxorubicin (DXR) conjugated to a monoclonal antibody (MAb), 9.2.27, which recognizes a human melanoma-associated proteoglycan, effectively suppresses the growth of human melanoma xenografts and prolongs the life span of tumor-bearing athymic nude (nu/nu) mice. We have investigated further the mechanism(s) of this in vivo antitumor activity. Our results indicate that following iv injection, the DXR-MAb 9.2.27 conjugate is cleared from the circulation with typical biphasic kinetics, similar to the clearance process of the unconjugated MAb 9.2.27. In contrast, less than 10% of injected dose per milliliter of blood is found in the circulation at any given time after ip injection. Toxicity studies further indicate that DXR-MAb 9.2.27 conjugate is less toxic in vivo than the freely administered DXR, which is known to cause considerable cardiotoxic effects. Direct autoradiography demonstrates that the DXR-MAb 9.2.27 conjugate binds specifically to the tissue sections derived from a human melanoma xenograft of a nude mouse. A critical evaluation is given of the relevance of these findings and their impact on the design of future strategies for the immunochemotherapy of malignant melanoma.