Mechanisms of in vivo anti-neuroblastoma activity of human natural IgM

Structural elucidation of a polysaccharide from Flammulina velutipes and its immunomodulation activities on mouse B lymphocytes

A novel polysaccharide FVPB2 was purified from fruiting bodies of Flammulina velutipes. Its structure was elucidated by monosaccharide composition and methylation analyses, UV-Visible and FTIR spectroscopy as well as NMR. FVPB2 was a homogeneous heteropolysaccharide (molecular weight ~ 1.50 × 104 Da) containing D-galactose, D-mannose, L-fucose, and D-glucose at molar ratio of 1.9:1.2:1:2.5. In vitro immunomodulatory studies showed FVPB2 induced proliferation of mouse spleen lymphocytes in a dose-dependent manner. The levels of IgM and IgG, secreted by B cells, increased after FVPB2 treatment. So FVPB2 has potential to be a new important immunomodulatory nutraceutical.

Anti-ganglioside anti-idiotypic vaccination: more than molecular mimicry

Surgery, chemotherapy, and radiation therapy are standard modalities for cancer treatment, but the effectiveness of these treatments has reached a plateau. Thus, other strategies are being explored to combine with the current treatment paradigms in order to reach better clinical results. One of these approaches is the active immunotherapy based on the induction of anti-tumor responses by anti-idiotypic vaccination. This approach arose from Jerne’s idiotypic network theory, which postulates that B lymphocytes forms a functional network, with a role in the establishment of the immune repertoires, in the regulation of natural antibody production and even in the establishment of natural tolerance. Due to the large potential diversity of the immunoglobulin variable regions, the idiotypes repertoire can mimic the universe of self and foreign epitopes, even those of non-protein nature, like gangliosides. Gangliosides are sialic acid-containing glycolipids that have been considered attractive targets for cancer immunotherapy, based on the qualitative and quantitative changes they suffer during malignant transformation and due to their importance for tumor biology. Although any idiotype could be able to mimic any antigen, only those related to antigens involved in functions relevant for organism homeostasis, and that in consequence has been fixed by evolution, would be able not only to mimic, but also to activate the idiotypic cascades related with the nominal antigen. The present review updates the results, failures and hopes, obtained with ganglioside mimicking anti-idiotypic antibodies and presents evidences of the existence of a natural response against gangliosides, suggesting that these glycolipids could be idiotypically relevant antigens.

Naturally occurring antibodies directed against carbohydrate tumor antigens

Healthy persons carry within their pool of circulating antibodies immunoglobulins preferentially of IgM isotype, which are directed against a variety of tumor-associated antigens. In closer scrutiny of their nature, some of these antibodies could be defined as naturally occurring antibodies due to the germline configuration of the variable immunoglobulin region. The majority of these immunoglobulins recognize carbohydrate antigens which can be classified as oncofetal antigens. Many of these IgM antibodies present in the peripheral blood circulation can bind to tumor cells and of these a minor portion are also able to destroy tumor cells by several mechanisms, as for instance complement-mediated cytolysis or apoptosis. It was postulated that anti-carbohydrate antibodies are part of an anti-tumor immune response, while their presence in the peripheral blood of healthy donors is still waiting for a plausible explanation. It may be that recognition of defined epitopes, including carbohydrate sequences, by naturally occurring antibodies constitutes the humoral arm of an anti-tumor immune response as part of the often postulated tumor surveillance. The cytotoxic capacity of these antibodies inspired several research groups and pharmaceutical companies to design novel strategies of immunoglobulin-based anti-tumor immunotherapy.

Cytotoxic natural antibodies against human tumours: an option for anti-cancer immunotherapy?

Healthy individuals may contain in their peripheral blood antibodies which are able to destroy human tumour cells mediated either by complement-dependent cytotoxicity or by apoptosis. The largest proportion of these antibodies is of IgM isotype and directed against distinct tumour associated carbohydrate epitopes. Although the origin of these antibodies is not clear they seem to belong to the class of natural antibodies because they are not affinity matured and are encoded by distinct germ-line restricted gene families. It is most likely that this class of natural antibodies has in vivo an anti-tumour protective effect which may contribute to so-called tumour surveillance. On the other hand malignant tumour cells exert mechanisms to counteract such an antibody attack. These comprise soluble factors as well as cell surface expressed membrane complement regulatory proteins (mCRP). Further studies are needed to elucidate molecular mechanisms leading to either tumour destruction induced by natural antibodies or to overcome the protective strategies of the tumour against antibody attack.

Actin-binding protein filamin A is displayed on the surface of human neuroblastoma cells

We previously reported the identification of natural human IgM antibodies, which recognize a M(r) 260 000 surface protein (NB-p260) and induce both complement-mediated cytotoxicity and apoptosis of human neuroblastoma cells. NB-p260 was shown to belong to the family of filamin proteins. Filamin A is a high molecular weight actin-binding protein, previously thought to be only located intracellularly. Here we show that NB cells as well as three NB-unrelated human cell lines express filamin A also on the cell surface. Our findings suggest new biological functions for filamins, including a role as mediators in anti-NB IgM-induced apoptosis, and they add to the growing body of evidence of the interaction of cytoskeletal proteins with the extracellular matrix.

The effect of dexamethasone on human mucin 1 expression and antibody-dependent complement sensitivity in a prostate cancer cell line in vitro and in vivo

Dexamethasone has been shown to up-regulate human mucin 1 (MUC1) expression in certain types of cancer cell lines in vitro, suggesting that this gluocorticoid may enhance MUC1-based immunotherapies. Here we investigated the effect of dexamethasone on MUC1 expression in the DU145 human prostate cancer cell line in terms of antibody-mediated complement-dependent cell lysis. Cells treated with 1 x 10-8 m dexamethasone in vitro expressed maximal levels of MUC1 after 6 days, with an approximately 3-fold increase over MUC1 levels on untreated cells. DU145 cells were highly resistant to lysis by anti-MUC1 antibody and complement, and their susceptibility to antibody and complement was unaffected by dexamethasone treatment. However, dexamethasone also induced expression of the complement inhibitor decay accelerating factor (DAF) on DU145 cells. Blocking or overcoming the function of DAF resulted in enhanced complement-dependent lysis of dexamethasone-treated cells with anti-MUC1 antibodies, indicating that the failure of dexamethasone to enhance the complement susceptibility of DU145 cells was caused by the up-regulated expression of DAF. We also investigated MUC1 expression in vivo and found that MUC1 expression was significantly up-regulated on tumour cells isolated from immune-deficient mice that had been injected with dexamethasone. However, in contrast to in vitro data, there was no difference between the levels of DAF expressed on tumour-derived DU145 cells isolated from either phosphate buffered saline (PBS)-treated or dexamethasone-treated mice, and tumour cells isolated from dexamethasone-treated mice were more sensitive to complement-mediated lysis. In the broad context of immunotherapy, the in vivo data support the use of dexamethasone as an adjunct treatment. Up-regulated DAF expression would not be a favourable outcome of dexamethasone treatment in terms of complement-dependent antibody therapy, but the in vivo data caution against extrapolation of in vitro data with regard to the modulation of complement inhibitors reported here and elsewhere.

Novel products of the HUD, HUC, NNP-1 and alpha-internexin genes identified by autologous antibody screening of a pediatric neuroblastoma library

Autologous serological screening of a cDNA expression library (SEREX) derived from childhood neuroblastoma led to the identification of 10 different antigens, including 6 novel gene products. The novel antigen 018INX was derived from a small open reading frame in a region of alpha-internexin mRNA that was previously described as 3' untranslated region. 018INX thus represents a novel type of tumor antigen. Five novel gene products were derived from NNP-1 (NNP3) and Hu genes (HuC-L, HuD3, HuDY, HuD1pro(c)). As indicated by sequence analysis, these antigens were generated by alternative splicing and/or alternative promoter usage or allelic polymorphism. mRNA expression analyses revealed different tissue restrictions of novel compared to known HuD and NNP-1 transcripts in normal and malignant tissues. The expressions patterns of distinct transcripts indicated potential clinical meanings as diagnostic and/or prognostic tissue markers. When kinetics of serum antibody titres against SEREX-defined antigens were compared to tumor load over time in our patient with neuroblastoma, we found 100-fold increases of anti-Hu and anti-018INX antibody titres preceding the clinical diagnosis of recurrent tumor growth after 2 years. When sera of pediatric patients with cancer (30) and healthy controls (30) were tested for humoral responses to SEREX-defined neuroblastoma antigens, we detected antibodies against all known antigens and NNP3 with low frequencies and titres in control sera, while anti-018INX and anti-Hu antibodies were found in cancer patients only. Our findings indicate that SEREX-defined tumor antigens might provide novel tools for understanding and treatment of this aggressive childhood malignancy.

Initial characterization of the apoptosis-inducing receptor for natural human anti-neuroblastoma IgM

BACKGROUND

Human neuroblastoma (NB) cells contain a 260 kDa surface antigen (NB-p260), which serves as receptor for natural human IgM antibodies (anti-NB IgM). Upon binding to NB-p260, these antibodies induce apoptosis in human NB cells.

PROCEDURE AND RESULTS

In this study, we purified NB-p260 to homogeneity from human LA-N-1 NB cells by sequential ion exchange chromatography followed by preparative SDS gel electrophoresis. Purified NB-p260 exhibited rapid autodegradation despite the presence of various protease inhibitors. The autodegradation process precluded extensive N-terminal sequencing. However, from repeat N-terminal sequence analysis, a consensus sequence of seven amino acid residues emerged that exhibited significant homology to the subunit c of the human mitochondrial ATP synthase, a hydrophobic membrane protein of 7.6 kDa. Western blot analyses demonstrated that purified NB-p260 was recognized by polyclonal antibodies raised against both subunit c-containing storage bodies and a synthetic peptide consisting of amino acid residues 32-45 of subunit c. In addition to peptide sequences related to subunit c, NB-p260 also contained epitopes related to the human heat shock protein HSP90. In Western blots, a monoclonal anti-HSP90 antibody reacted with purified NB-p260 as well as with a predominant protein fragment of approximately 90 kDa that appeared during the process of NB-p260 autodegradation. The anti-HSP90 antibody was also capable of binding to the surface of LA-N-1 cells and inhibiting the binding of human anti-NB IgM in a dose-dependent manner.

CONCLUSIONS

Collectively, our data suggest that NB-p260, the apoptosis-mediating receptor for natural human anti-NB IgM, represents a novel surface protein of human NB cells containing polypeptide sequences related to the subunit c of the mitochondrial ATP synthase and the heat shock protein HSP90.

Differential mechanisms of neutrophil and monocyte adhesion on neuroblastoma cells: CD18 and VLA-4 integrins mediate adhesion to SK-N-SH, but not to SK-N-MC cell line

We examined the adhesion of monocytes and polymorphonuclear leukocytes (PMNLs) to the neuroblastoma (NB) cell lines SK-N-SH and SK-N-MC, which have some distinct differentiation characteristics. Monocytes adhered to SK-N-SH and SK-N-MC to the same extent (20 +/- 1.4% and 24 +/- 0.8% of monocytes added). Monocyte adhesion to SK-N-SH but not SK-N-MC was partially inhibited by treating monocytes with a mAb to the CD18 (beta2) integrin chain. The adhesion was further inhibited when monocytes were treated with a combination of mAb to CD18 and VLA-4. Treatment of both NB cell lines with interleukin-1alpha (0.5 ng/ml), tumor necrosis factor alpha (100 U/ml), interferon gamma (200 U/ml), or their combinations increased monocyte adhesion to SK-N-SH and SK-N-MC. With each condition, monocyte adhesion to SK-N-SH was partially blocked by mAb to CD18. The inhibition of adhesion to IL-1alpha- or TNFalpha-treated SK-N-SH cells was greater when the monocytes were treated with mAb to both CD18 and VLA-4. In contrast, monocyte adhesion to IL-1alpha or IFNgamma treated SK-N-MC was only slightly inhibited with a combination of mAb to CD18 + VLA-4 and there was no inhibition at all to TNFalpha-treated SK-N-MC. Spontaneous PMNL adhesion to SK-N-SH was almost negligible but increased by treating the cell line with IL-1alpha, TNFalpha, IFNgamma or their combinations. A mAb to CD18 blocked this increase in each case. The pattern of adhesion of PMNLs to SK-N-MC was totally different. PMNL adhesion to unstimulated SK-N-MC was very high (24 +/- 1.3%), was not inhibited by mAb to CD18, and did not increase by stimulating the cell line with IL-1alpha, TNFalpha, IFNgamma or their combinations. Overall, these results suggest two distinct patterns of monocyte and PMNL interaction with neural cells, such as the SK-N-SH and MC cell lines. While monocyte and PMNL adhesion to SK-N-SH is mainly via CD18/VLA-4 or the CD18 mechanisms, respectively, leukocyte adhesion to SK-N-MC is CD18- and VLA-4-independent. Thus, leukocyte-neural cell interactions share some mechanisms common also to leukocyte-endothelium interaction, but there are also unique mechanisms which may be neural cell and differentiation specific.

Immune evasion of tumor cells using membrane-bound complement regulatory proteins

Membrane-bound complement regulatory proteins (mCRPs) play an important role in the protection of cells from complement-mediated injury. It is now apparent that malignant tumor cells also express these proteins to escape complement attack. Here, Arko Gorter and Seppo Meri discuss the implications of complement resistance for the immunotherapeutic treatment of solid tumors with monoclonal antibodies.

How pre-existing, germline-derived antibodies and complement may help induce a primary immune response to nonself

In the hypothesis that pre-existing, germline-encoded antibodies (naturally occurring antibodies, NAb) bind to conserved epitopes on invading nonself antigens, bound NAbs may initiate complement deposition and become targets of nascent C3b, which generates C3b-C3b-NAb complexes that remain associated with the nonself antigen (C3b-C3b-NAb...antigen). The inactivated form of these complexes (C3dg-C3dg-NAb...nonself antigen) may bind bivalently and thus firmly to B cells via CR2, a process stimulating antigen presentation. In some cases, CR2-bound 'C3dg-C3dg-NAb...antigen complexes' may further be recognized by immunoglobulin (Ig) determinants on B cells, whereby an immune response is elicited. As conserved epitopes on the nonself antigen are already complexed to NAbs, only B cells carrying Ig determinants specific for nonself epitopes may be stimulated. This hypothesis can explain directed affinity maturation towards nonself, protection from a strong immune response to conserved epitopes, down-regulation of antibody formation and unresponsiveness to high-dose antigen.