Naturally occurring antibodies directed against carbohydrate tumor antigens

B cell clonality in cancer

Carcinogenesis in the process of long-term co-evolution of tumor cells and immune environment essentially becomes possible due to incorrect decisions made, remembered, and reproduced by the immune system at the level of clonal populations of antigen-specific T- and B-lymphocytes. Tumor-immunity interaction determines the nature of such errors and, consequently, delineates the possible ways of successful immunotherapeutic intervention. It is generally recognized that tumor-infiltrating B cells (TIL-B) can play both pro-tumor and anti-tumor roles. However, the exact mechanisms that determine the contribution of clonal B cell lineages with different specificities and functions remain largely unclear. This is due to the variability of cancer types, the molecular heterogeneity of tumor cells, and, to a large extent, the individual pattern of each immune response. Further progress requires detailed investigation of the functional properties and phenotypes of clonally heterogeneous B cells in relation to their antigenic specificities, which determine the functionality of both effector B lymphocytes and immunoglobulins produced in the tumor environment. Based on a real understanding of the role of clonal antigen-specific populations of B lymphocytes in the tumor microenvironment, we need to learn how to develop new methods of targeted immunotherapy, as well as adapt existing treatment options to the specific needs of different patients and patient subgroups. In this review, we will cover B cells functional diversity and their multifaceted roles in the tumor environment.

Prevalence of high affinity naturally occurring IgG2 antibodies against human chorionic gonadotropin and its subunits in patients with ovarian cyst

Naturally occurring antibodies to tumour antigens are gaining interest as clinically important cancer biomarkers for early diagnosis, prognosis and for the development of anti-cancer therapeutics. The glycoprotein αβ heterodimer hormone human chorionic gonadotropin (hCG) and its β subunit (hCGβ) are produced by various cancers, and their increased serum levels correlate with poor prognosis. We have previously reported that patients with benign ovarian cysts, but not the malignant tumours, were characterized by augmented serum levels of naturally-occurring IgG antibodies to hCG and hCGβ. Here we further characterise these antibodies in patients with ovarian cysts. IgG and IgM antibody binding to whole hCG, hCGβ, hCGα, hCGβ C-terminal peptide (hCGβCTP), and the hCGβ core fragment (hCGβCF) were measured in the sera from 36 patients with ovarian cysts and 12 healthy non-pregnant women using a standard ELISA. IgG subclass usage and affinity was also determined together with cross-binding to whole hCG and its subunits of four selected commercial monoclonal antibodies generated against ovarian cyst mucins. Our results showed that 91.7% of the sera tested contained elevated IgG, but not IgM antibodies to one or several antigens, with an overwhelming prevalence of high affinity IgG2 indicating their binding to carbohydrate epitopes and possibly ovarian cyst mucins. Anti-mucin commercial antibody ab212418 (Abcam) produced against Gal1-3GalNAc, exhibited strong cross-binding to hCGαβ, hCGβ, hCGα and hCGβCTP. The protective anti-cancer potential of these antibodies will be further investigated and could lead to the development of novel treatment strategies for ovarian cancer.

The Potential Action of Thomsen-Friedenreich Monoclonal Antibody (A78-G/A7) in Thyroid Cancer

Background

Thomsen–Friedenreich antibody (TF-Ab) is a specific antibody against the Thomsen–Friedenreich antigen (TF-Ag). At present, studies on a number of other tumors have shown that TF-Ab can effectively inhibit metastasis and induce apoptosis in tumor cells. However, the role of TF-Ab in thyroid cancer (TC) remains unclear.

Materials and Methods

Normal subjects and patients with primary papillary TC with or without lymph node metastasis were tested for TF-Ab expression by enzyme-linked immunosorbent assays (ELISAs). Immunofluorescence was used to assess the expression of TF-Ag in thyroid papillary carcinoma with or without lymph node metastasis and undifferentiated cancer tissues. To evaluate the role of TF-Ab in TC, the effects of TF monoclonal antibody (mAb A78-G/A7) on cell biological function were investigated by MTT assays, flow cytometry, adhesion assays and transwell experiments.

Results

Compared with normal individuals, TF-Ab levels in patients with TC were decreased, but no changes were observed with respect to lymph node metastasis. The expression of TF-Ag in TC tissues was relatively higher than that detected in adjacent tissues, but it was not affected by the presence or absence of lymph node metastasis. Upon treatment mAb A78-G/A7 treating, TC cell cycles were affected, meanwhile the abilities to adhere, invade and migrate were also significantly reduced.

Conclusion

The results of the present study showed that mAb A78-G/A7 could affect the invasion and migration of all assayed TC cell lines. The effects of mAb A78-G/A7 on the cell cycle, adhesion, invasion and migration of TC cells were more significant than those observed for proliferation and apoptosis.

Profiling of Naturally Occurring Antibodies to the Thomsen-Friedenreich Antigen in Health and Cancer: The Diversity and Clinical Potential

The Thomsen-Friedenreich (TF) antigen is expressed in a majority of human tumors due to aberrant glycosylation in cancer cells. There is strong evidence that humoral immune response to TF represents an effective mechanism for the elimination of cancer cells that express TF-positive glycoconjugates. The presence of naturally occurring antibodies to tumor-associated TF and cancer-specific changes in their levels, isotype distribution and interrelation, avidity, and glycosylation profile make these Abs a convenient and ubiquitous marker for cancer diagnostics and prognostics. In this review, we attempt to summarize the latest data on the potential of TF-specific Abs for cancer diagnostics and prognostics.

Autoantibody-targeted TAAs in pancreatic cancer: A comprehensive analysis

BACKGROUND

Pancreatic cancer is one of the leading causes of cancer mortality and lacks efficient biomarkers for early diagnosis. In the early stages of pancreatic cancer, humoral immunity can respond to a certain amount of tumor-associated antigens (TAAs) with the production of corresponding autoantibodies. Such autoantibody-targeted TAAs (autoTAAs) are highly likely to indicate early events during pancreatic carcinogenesis. Herein, we performed a comprehensive analysis of these autoTAAs to explore their physiological function and their involvement and prognostic value in pancreatic cancer.

METHODS

We first searched the literature to identify the autoTAAs. A PPI network of these autoTAAs was constructed, and core network modules were extracted by Cytoscape software. GO annotation and KEGG pathway analysis were performed to analyze the main physiological functions of these autoTAAs. The prognostic value of autoTAAs in pancreatic cancer was analyzed by using RNA-seq data generated by TCGA.

RESULTS

The PPI network including 98 autoTAAs was constructed, and 2 subgroups were extracted as core modules. GO and KEGG analysis revealed that key functions and pathways of these autoTAAs were significantly enriched in nucleotide repair, protein synthesis, and cancer-associated events. MSH2, EZR, PGK1, VCL and ANXA2 have prognostic value in pancreatic cancer, and high mRNA expression of these 5 proteins is associated with unfavorable prognosis in pancreatic cancer.

CONCLUSIONS

AutoTAAs may be associated with early events in the carcinogenesis of pancreatic cancer. MSH2, EZR, PGK1, VCL and ANXA2 predict poor prognosis in pancreatic cancer. Some autoTAAs also have prognostic value in other cancers.

IgM Natural Autoantibodies in Physiology and the Treatment of Disease

Antibodies are vital components of the adaptive immune system for the recognition and response to foreign antigens. However, some antibodies recognize self-antigens in healthy individuals. These autoreactive antibodies may modulate innate immune functions. IgM natural autoantibodies (IgM-NAAs) are a class of primarily polyreactive immunoglobulins encoded by germline V-gene segments which exhibit low affinity but broad specificity to both foreign and self-antigens. Historically, these autoantibodies were closely associated with autoimmune disease. Nevertheless, not all human autoantibodies are pathogenic and compelling evidence indicates that IgM-NAAs may exert a spectrum of effects from injurious to protective depending upon cellular and molecular context. In this chapter, we review the current state of knowledge regarding the potential physiological and therapeutic roles of IgM-NAAs in different disease conditions such as atherosclerosis, cancer, and autoimmune disease. We also describe the discovery of two reparative IgM-NAAs by our laboratory and delineate their proposed mechanisms of action in central nervous system (CNS) disease.

The Thomsen-Friedenreich Antigen-Specific Antibody Signatures in Patients with Breast Cancer

Alterations in the glycosylation of serum total immunoglobulins show these antibodies to have a diagnostic potential for cancer but the disease-related Abs to the tumor-associated antigens, including glycans, have still poorly been investigated in this respect. We analysed serum samples from patients with breast carcinoma (n = 196) and controls (n = 64) for the level of Thomsen-Friedenreich (TF) antigen-specific antibody isotypes, their sialylation, interrelationships, and the avidity by using ELISA with the synthetic TF-polyacrylamide conjugate as an antigen and the sialic acid-specific Sambucus nigra agglutinin (SNA) and ammonium thiocyanate as a chaotrope. An increased sialylation of IgG and IgM, but a lower SNA reactivity of IgA TF antibodies, and a higher level and avidity of the TF-specific IgA were found in cancer patients. Other cancer-related signatures were the highly significant increase of the IgG/IgA ratio and the very low SNA/IgA index in cancer, including patients with an early stage of the disease. These changes showed a good diagnostic potential with about 80% accuracy. Thus, the level of naturally occurring anti-TF antigen antibodies, their sialylation profile, isotype distribution, and avidity displayed cancer-specific changes that could serve as novel noninvasive Ab-based biomarkers for early breast cancer.

Assessment of Anti-Tumor Cytotoxic Activity of Naturally Occurring Antibodies in Human Serum or Plasma

A small percentage of the Western population carries antibodies in the peripheral blood, which are able to kill human tumors such as neuroblastoma or melanoma. Several observations indicate that these antibodies, preferentially of IgM isotype, belong to the class of naturally occurring antibodies. Here, we describe two screening methods for the detection and quantification of such antibodies in human blood samples: a cellular ELISA technique and a flow cytometric assay, based on intercalation of fluorescent propidium iodide into the DNA of dying or dead cells.

Downregulation of miR-199a/b-5p is associated with GCNT2 induction upon epithelial-mesenchymal transition in colon cancer

β-1,6-N-acetylglucosaminyltransferase 2 (GCNT2), which encodes a key glycosyltransferase for blood group I antigen synthesis, is induced upon epithelial-mesenchymal transition (EMT). Our results indicate that GCNT2 is upregulated upon EMT induced with epidermal growth factor and basic FGF in cultured human colon cancer cells. GCNT2 knockdown or overexpression decreases or increases, respectively, malignancy-related characteristics of colon cancer cells and I antigen levels. MiR-199a/b-5p is markedly downregulated upon EMT in colon cancer cells. Here, we find that miR-199a/b-5p consistently regulates GCNT2 expression in reporter assays and that it binds directly to the GCNT2 3' untranslated region intracellularly in RNA-induced silencing complex-trap assays. Overexpression of miR-199a/b-5p decreases GCNT2 expression and suppresses I antigen production. Based on these findings, we propose that miR-199a/b-5p regulates GCNT2 and I antigen expression in colon cancer cells undergoing EMT.

Blood Plasma-Derived Anti-Glycan Antibodies to Sialylated and Sulfated Glycans Identify Ovarian Cancer Patients

Altered levels of naturally occurring anti-glycan antibodies (AGA) circulating in human blood plasma are found in different pathologies including cancer. Here the levels of AGA directed against 22 negatively charged (sialylated and sulfated) glycans were assessed in high-grade serous ovarian cancer (HGSOC, n = 22) patients and benign controls (n = 31) using our previously developed suspension glycan array (SGA). Specifically, the ability of AGA to differentiate between controls and HGSOC, the most common and aggressive type of ovarian cancer with a poor outcome was determined. Results were compared to CA125, the commonly used ovarian cancer biomarker. AGA to seven glycans that significantly (P<0.05) differentiated between HGSOC and control were identified: AGA to top candidates SiaTn and 6-OSulfo-TF (both IgM) differentiated comparably to CA125. The area under the curve (AUC) of a panel of AGA to 5 glycans (SiaTn, 6-OSulfo-TF, 6-OSulfo-LN, SiaLea, and GM2) (0.878) was comparable to CA125 (0.864), but it markedly increased (0.985) when combined with CA125. AGA to SiaTn and 6-OSulfo-TF were also valuable predictors for HGSOC when CA125 values appeared inconclusive, i.e. were below a certain threshold. AGA-glycan binding was in some cases isotype-dependent and sensitive to glycosidic linkage switch (α2-6 vs. α2-3), to sialylation, and to sulfation of the glycans. In conclusion, plasma-derived AGA to sialylated and sulfated glycans including SiaTn and 6-OSulfo-TF detected by SGA present a valuable alternative to CA125 for differentiating controls from HGSOC patients and for predicting the likelihood of HGSOC, and may be potential HGSOC tumor markers.

The Potential Role of Solvation in Antibody Recognition of the Lewis Y Antigen

Solvents play an important role in protein folding, protein-protein associations, stability, and specificity of recognition as in the case of antibody-antigen interactions through hydrogen bonds. One of the underappreciated features of protein-associated waters is that it weakens inter- and intra-molecular interactions by modulating electrostatic interactions and influencing conformational changes. Such observations demonstrate the direct relationship between macroscopic solvent effects on protein-protein interactions and atom-scale solvent-protein interactions. Although crystallographic solvents do explain some aspects of solvent-mediated interactions, molecular simulation allows the study of the dynamic role of solvents. Thus, analysis of conformations from molecular simulations are employed to understand the role of solvent on the inherent polyspecificity of a Lewis Y reactive germline gene relative to its expanded hybridomas and a humanized anti-Lewis Y antibody. Our analysis reveals that solvent mediates critical contacts through charged residues to facilitate cross-reactivity to carbohydrate antigens, but also increases the flexibility of some anti-Lewis Y antibodies concomitant with mutations (amino acid substitutions) to the germline antibody. Such flexibility might better allow for recognition and binding of internal structures of extended carbohydrate structures on tumor cells.

Metabolic Glycoengineering with N-Acyl Side Chain Modified Mannosamines

In metabolic glycoengineering (MGE), cells or animals are treated with unnatural derivatives of monosaccharides. After entering the cytosol, these sugar analogues are metabolized and subsequently expressed on newly synthesized glycoconjugates. The feasibility of MGE was first discovered for sialylated glycans, by using N-acyl-modified mannosamines as precursor molecules for unnatural sialic acids. Prerequisite is the promiscuity of the enzymes of the Roseman-Warren biosynthetic pathway. These enzymes were shown to tolerate specific modifications of the N-acyl side chain of mannosamine analogues, for example, elongation by one or more methylene groups (aliphatic modifications) or by insertion of reactive groups (bioorthogonal modifications). Unnatural sialic acids are incorporated into glycoconjugates of cells and organs. MGE has intriguing biological consequences for treated cells (aliphatic MGE) and offers the opportunity to visualize the topography and dynamics of sialylated glycans in vitro, ex vivo, and in vivo (bioorthogonal MGE).

Cytotoxic activity against human neuroblastoma and melanoma cells mediated by IgM antibodies derived from peripheral blood of healthy donors

A small percentage of healthy donors identified in the Western population carry antibodies in their peripheral blood which convey cytotoxic activity against certain human melanoma and neuroblastoma cell lines. We measured the cytotoxic activity of sera and plasmas from healthy donors on the human neuroblastoma cell line Kelly and various melanoma cell lines. Antibodies of IgM isotype, presumably belonging to the class of naturally occurring antibodies, exerted cytotoxic activity in a complement-dependent fashion. Apart from complement-dependent tumor cell lysis, we observed C3 opsonization in all tumor cell lines upon treatment with cytotoxic plasmas. Cell lines tested primarily expressed membrane complement regulatory proteins (mCRP) CD46, CD55 and CD59 to various extents. Blocking of mCRPs by monoclonal antibodies enhanced cell lysis and opsonization, though some melanoma cells remained resistant to complement attack. Epitopes recognized by cytotoxic antibodies were represented by gangliosides such as GD2 and GD3, as evidenced by cellular sialidase pretreatment and enhanced expression of distinct gangliosides. It remains to be clarified why only a small fraction of healthy persons carry these antitumor cytotoxic antibodies.

Factors Affecting Anti-Glycan IgG and IgM Repertoires in Human Serum

Serum anti-glycan antibodies play important roles in many immune processes and are of particular interest as biomarkers for many diseases. Changes in anti-glycan antibodies can occur with the onset of disease or in response to stimuli such as pathogens and vaccination. Understanding relationships between anti-glycan antibody repertoires and genetic and environment factors is critical for basic research and clinical applications, but little information is available. In this study we evaluated the effects of age, race, gender, and blood type on anti-glycan antibody profiles in the serum of 135 healthy subjects. As expected, IgG and IgM antibody signals to blood group antigens correlated strongly with blood type. Interestingly, antibodies to other non-ABH glycans, such as the alpha-Gal antigen, also correlated with blood type. A statistically significant decline in IgM signals with age was observed for many antibody subpopulations, but not for IgG. Moreover, statistically significant correlations between race and IgG levels to certain LacNAc-containing glycans were observed. The results have important implications for designing studies and interpreting results in the area of biomarker discovery and for the development of vaccines. The study also highlights the importance of collecting and reporting patient information that could affect serum anti-glycan antibody levels.

IgE-based immunotherapy of cancer: challenges and chances

Passive immunotherapy with monoclonal antibodies is an indispensable cornerstone of clinical oncology. Notably, all FDA-approved antibodies comprise the IgG class, although numerous research articles proposed monoclonal antibodies of the IgM, IgG, IgA and IgE classes directed specifically against tumor-associated antigens. In particular, for the IgE isotype class, several recent studies could demonstrate high tumoricidic efficacy. Therefore, this review specifically highlights the latest developments toward IgE-based immunotherapy of cancer. Possible mechanisms and safety aspects of IgE-mediated tumor cell death are discussed with special focus on the attracted immune cells. An outlook is given on how especially comparative oncology could contribute to further developments. Humans and dogs have a highly comparable IgE biology, suggesting that translational AllergoOncology studies in patients with canine cancer could have predictive value for the potential of IgE-based anticancer immunotherapy in human clinical oncology.

The (1->6)-β-glucan moiety represents a cross-reactive epitope of infection-induced malignancy surveillance

Exposure to pathogen-associated molecular patterns (PAMPs) by vaccination or infection is known to have beneficial effects on neoplastic diseases, although the underlying molecular mechanisms are so far unclear. In this article, we report that Abs against (1→6)-β-d-glucan, a typical microbial PAMP and a major target for high titer circulating natural Abs in healthy human subjects, cross-recognize a novel tumor-associated carbohydrate Ag on cancer cells. The (1→6)-β-glucan cross-reactive moiety is immunologically dominant in tumor cells, as C57BL/6 mice harboring EL-4 solid tumors produced anti-(1→6)-β-glucan Abs and the titer of which significantly correlated with enhanced survival and smaller tumor burden. Moreover, the (1→6)-β-glucan-specific Abs exhibited potent tumoricidal activities in vitro. C57BL/6 mice immunized with Candida albicans produced protective immunity against inoculated EL-4 tumors, which was attributed to the formation of (1→6)-β-glucan-specific Abs. Importantly, (1→6)-β-glucan-specific Abs significantly prolonged the survival and reduced the tumor size in mice inoculated with EL-4 tumors. Our results demonstrate that the (1→6)-β-glucan cross-reactive moiety represents a focal point between infection immunity and cancer surveillance, and natural Abs against this epitope may contribute to the first-line antitumor surveillance in humans. Our data also provide important explanation for the long-observed relationship between feverish infection and concurrent remission from cancer.

Tumor-Associated Glycans and Immune Surveillance

Changes in cell surface glycosylation are a hallmark of the transition from normal to inflamed and neoplastic tissue. Tumor-associated carbohydrate antigens (TACAs) challenge our understanding of immune tolerance, while functioning as immune targets that bridge innate immune surveillance and adaptive antitumor immunity in clinical applications. T-cells, being a part of the adaptive immune response, are the most popular component of the immune system considered for targeting tumor cells. However, for TACAs, T-cells take a back seat to antibodies and natural killer cells as first-line innate defense mechanisms. Here, we briefly highlight the rationale associated with the relative importance of the immune surveillance machinery that might be applicable for developing therapeutics.