Immunohistochemical detection of heterophile Hanganutziu-Deicher antigen in human malignant melanoma

From "Serum Sickness" to "Xenosialitis": Past, Present, and Future Significance of the Non-human Sialic Acid Neu5Gc

The description of "serum sickness" more than a century ago in humans transfused with animal sera eventually led to identification of a class of human antibodies directed against glycans terminating in the common mammalian sialic acid N-Glycolylneuraminic acid (Neu5Gc), hereafter called "Neu5Gc-glycans." The detection of such glycans in malignant and fetal human tissues initially raised the possibility that it was an oncofetal antigen. However, "serum sickness" antibodies were also noted in various human disease states. These findings spurred further research on Neu5Gc, and the discovery that it is not synthesized in the human body due to a human-lineage specific genetic mutation in the enzyme CMAH. However, with more sensitive techniques Neu5Gc-glycans were detected in smaller quantities on certain human cell types, particularly epithelia and endothelia. The likely explanation is metabolic incorporation of Neu5Gc from dietary sources, especially red meat of mammalian origin. This incorporated Neu5Gc on glycans appears to be the first example of a "xeno-autoantigen," against which varying levels of "xeno-autoantibodies" are present in all humans. The resulting chronic inflammation or "xenosialitis" may have important implications in human health and disease, especially in conditions known to be aggravated by consumption of red meat. In this review, we will cover the early history of the discovery of "serum sickness" antibodies, the subsequent recognition that they were partly directed against Neu5Gc-glycans, the discovery of the genetic defect eliminating Neu5Gc production in humans, and the later recognition that this was not an oncofetal antigen but the first example of a "xeno-autoantigen." Further, we will present comments about implications for disease risks associated with red meat consumption such as cancer and atherosclerosis. We will also mention the potential utility of these anti-Neu5Gc-glycan antibodies in cancer immunotherapy and provide some suggestions and perspectives for the future. Other reviews in this special issue cover many other aspects of this unusual pathological process, for which there appears to be no other described precedent.

Recent approaches for directly profiling cell surface sialoform

Sialic acids (SAs) are nine-carbon monosaccharides existing at the terminal location of glycan structures on the cell surface and secreted glycoconjugates. The expression levels and linkages of SAs on cells and tissues, collectively known as sialoform, present the hallmark of the cells and tissues of different systems and conditions. Accordingly, detecting or profiling cell surface sialoforms is very critical for understanding the function of cell surface glycans and glycoconjugates and even the molecular mechanisms of their underlying biological processes. Further, it may provide therapeutic and diagnostic applications for different diseases. In the past decades, several kinds of SA-specific binding molecules have been developed for detecting and profiling specific sialoforms of cells and tissues; the experimental materials have expanded from frozen tissue to living cells; and the analytical technologies have advanced from histochemistry to fluorescent imaging, flow cytometry and microarrays. This review summarizes the recent bioaffinity approaches for directly detecting and profiling specific SAs or sialylglycans, and their modifications of different cells and tissues.

Involvement of a non-human sialic Acid in human cancer

Sialic acids are common monosaccharides that are widely expressed as outer terminal units on all vertebrate cell surfaces, and play fundamental roles in cell–cell and cell–microenvironment interactions. The predominant sialic acids on most mammalian cells are N-glycolylneuraminic acid (Neu5Gc) and N-acetylneuraminic acid (Neu5Ac). Neu5Gc is notable for its deficiency in humans due to a species-specific and species-universal inactivating deletion in the CMAH gene encoding the hydroxylase that converts CMP-Neu5Ac to CMP-Neu5Gc. However, Neu5Gc is metabolically incorporated into human tissues from dietary sources (particularly red meat), and detected at even higher levels in some human cancers. Early life exposure to Neu5Gc-containing foods in the presence of certain commensal bacteria that incorporate dietary Neu5Gc into lipooligosaccharides can lead to generation of antibodies that are also cross-reactive against Neu5Gc-containing glycans in human tissues (“xeno-autoantigens”). Such anti-Neu5Gc “xeno-autoantibodies” are found in all humans, although ranging widely in levels among individuals, and displaying diverse and variable specificities for the underlying glycan. Experimental evidence in a human-like Neu5Gc-deficient Cmah^−/−mouse model shows that inflammation due to “xenosialitis” caused by this antigen–antibody interaction can promote tumor progression, suggesting a likely mechanism for the well-known epidemiological link between red meat consumption and carcinoma risk. In this review, we discuss the history of this field, mechanisms of Neu5Gc incorporation into tissues, the origin and specificities of human anti-Neu5Gc antibodies, their use as possible cancer biomarkers, implications of xenosialitis in cancer initiation and progression, and current and future approaches toward immunotherapy that could take advantage of this unusual human-specific phenomenon.

Glycans in immune recognition and response

Glycans at the forefront of cells facilitate immune recognition processes. Cancer cells commonly present altered cell surface glycosylation, especially manifested in the expression of sialic acid at the termini of glycolipids and glycoproteins. Although tumor-associated carbohydrate antigens (TACAs) result in expression of altered-self, most such carbohydrates do not elicit strong humoral responses. Various strategies had been devised to elicit increased immunogenicity of such TACA aiming for potent immunotherapeutic antibodies or cancer vaccines. However some carbohydrates are immunogenic in humans and hold potential for novel glycotherapies. N-Glycolylneuraminic acid (Neu5Gc) is a foreign immunogenic sugar in humans originating from the diet (e.g., red meat) and subsequently expressed on the cell surface, especially accumulating on carcinoma. Consequently, the human immune system detects this non-self carbohydrate generating a broad anti-Neu5Gc antibody response. The co-existence of Neu5Gc/anti-Neu5Gc within humans spurs chronic inflammation mediated disease, including cancer. Concurrently, anti-Neu5Gc antibodies hold potential for novel targeted therapy. αGal is another foreign immunogenic carbohydrate antigen in humans and all humans have circulating anti-Gal antibodies. This review aims to describe the immunogenicity of Neu5Gc and its implications for human diseases, highlighting differences and similarities with αGal and its potential for novel targeted theranostics.

L1CAM from human melanoma carries a novel type of N-glycan with Galβ1-4Galβ1- motif. Involvement of N-linked glycans in migratory and invasive behaviour of melanoma cells

Dramatic changes in glycan biosynthesis during oncogenic transformation result in the emergence of marker glycans on the cell surface. We analysed the N-linked glycans of L1CAM from different stages of melanoma progression, using high-performance liquid chromatography combined with exoglycosidase sequencing, matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry, and lectin probes. L1CAM oligosaccharides are heavily sialylated, mainly digalactosylated, biantennary complex-type structures with galactose β1-4/3-linked to GlcNAc and with or without fucose α1-3/6-linked to GlcNAc. Hybrid, bisected hybrid, bisected triantennary and tetraantennary complex oligosaccharides, and β1-6-branched complex-type glycans with or without lactosamine extensions are expresses at lower abundance. We found that metastatic L1CAM possesses only α2-6-linked sialic acid and the loss of α2-3-linked sialic acid in L1CAM is a phenomenon observed during the transition of melanoma cells from VGP to a metastatic stage. Unexpectedly, we found a novel monoantennary complex-type oligosaccharide with a Galβ1-4Galβ1- epitope capped with sialic acid residues A1[3]G(4)2S2-3. To our knowledge this is the first report documenting the presence of this oligosaccharide in human cancer. The novel and unique N-glycan should be recognised as a new class of human melanoma marker. In functional tests we demonstrated that the presence of cell surface α2-3-linked sialic acid facilitates the migratory behaviour and increases the invasiveness of primary melanoma cells, and it enhances the motility of metastatic cells. The presence of cell surface α2-6-linked sialic acid enhances the invasive potential of both primary and metastatic melanoma cells. Complex-type oligosaccharides in L1CAM enhance the invasiveness of metastatic melanoma cells.

Immunorecognition of the 14F7 Mab Raised against N-Glycolyl GM3 Ganglioside in Some Normal and Malignant Tissues from Genitourinary System

N-glycolyl neuraminic acid has been considered as a tumour-associated antigen forming both glycolipid and glycoprotein, expressed in some human malignant cells. In this work, we evaluate the 14F7 Mab (an IgG1 murine highly specific to N-glycolyl GM3 ganglioside) reactivity in a variety of genitourinary-system-derived tumors as well as in their normal counterparts. Immunohistochemical assays with 14F7 followed by anti-mouse biotinylated antibody and ABC/HRP system using formalin-fixed and paraffin-embedded tissues were carried out. In normal tissues, 14F7 was reactive only in renal tubules of kidney (2/6) and in the stromal component and blood vessels of ovary (3/5). Tumors of kidney (12/38), urinary bladder (8/9), breast (41/42), ovary (21/34), testis (4/5), prostate (17/20), and uterus (5/14) as well as prostatic nodular hyperplasia (5/8) were stained with 14F7. N-glycolyl GM3 recognized by 14F7 could be considered as one attractive target for both active and passive immunotherapy of genitourinary malignancies expressing this molecule.

Immunohistochemical Reactivity of the 14F7 Monoclonal Antibody Raised against N-Glycolyl GM3 Ganglioside in Some Benign and Malignant Skin Neoplasms

The evaluation of 14F7 Mab (anti-N-glycolyl GM3 ganglioside) immunorecognition in normal skin, cutaneous malignant melanoma (CMM), and in lymph node metastases (LNM) has been previously reported. In this work we extended the study to benign (BMN) and dysplastic (DMN) melanocytic nevi, basal (BCC), and squamous cell carcinoma (SCC). Immunohistochemical assays with 14F7 followed by a biotinylated link universal and streptavidin-AP in normal and pathological tissues were made. No reaction of 14F7 in normal skin (0/10) as well as a low reactivity in BMN (2/11) and DMN (1/7) was detected. A limited staining in BCC (2/13) and in SCC (4/8) was also evidenced, while 14F7 Mab were mostly reactive in CMM (28/28) and in LNM (6/7). These results suggest that 14F7 reactivity could be closely related with the more aggressive biological behavior of CMM and also support the use of NeuGcGM3 as target for both passive and active melanoma immunotherapy.

Sensitive and specific detection of the non-human sialic Acid N-glycolylneuraminic acid in human tissues and biotherapeutic products

BACKGROUND

Humans are genetically defective in synthesizing the common mammalian sialic acid N-glycolylneuraminic acid (Neu5Gc), but can metabolically incorporate it from dietary sources (particularly red meat and milk) into glycoproteins and glycolipids of human tumors, fetuses and some normal tissues. Metabolic incorporation of Neu5Gc from animal-derived cells and medium components also results in variable contamination of molecules and cells intended for human therapies. These Neu5Gc-incorporation phenomena are practically significant, because normal humans can have high levels of circulating anti-Neu5Gc antibodies. Thus, there is need for the sensitive and specific detection of Neu5Gc in human tissues and biotherapeutic products. Unlike monoclonal antibodies that recognize Neu5Gc only in the context of underlying structures, chicken immunoglobulin Y (IgY) polyclonal antibodies can recognize Neu5Gc in broader contexts. However, prior preparations of such antibodies (including our own) suffered from some non-specificity, as well as some cross-reactivity with the human sialic acid N-acetylneuraminic acid (Neu5Ac).

METHODOLOGY/PRINCIPAL FINDINGS

We have developed a novel affinity method utilizing sequential columns of immobilized human and chimpanzee serum sialoglycoproteins, followed by specific elution from the latter column by free Neu5Gc. The resulting mono-specific antibody shows no staining in tissues or cells from mice with a human-like defect in Neu5Gc production. It allows sensitive and specific detection of Neu5Gc in all underlying glycan structural contexts studied, and is applicable to immunohistochemical, enzyme-linked immunosorbent assay (ELISA), Western blot and flow cytometry analyses. Non-immune chicken IgY is used as a reliable negative control. We show that these approaches allow sensitive detection of Neu5Gc in human tissue samples and in some biotherapeutic products, and finally show an example of how Neu5Gc might be eliminated from such products, by using a human cell line grown under defined conditions.

CONCLUSIONS

We report a reliable antibody-based method for highly sensitive and specific detection of the non-human sialic acid Neu5Gc in human tissues and biotherapeutic products that has not been previously described.

Loss of N-glycolylneuraminic acid in humans: Mechanisms, consequences, and implications for hominid evolution

The surface of all mammalian cells is covered with a dense and complex array of sugar chains, which are frequently terminated by members of a family of molecules called sialic acids. One particular sialic acid called N‐glycolylneuraminic acid (Neu5Gc) is widely expressed on most mammalian tissues, but is not easily detectable on human cells. In fact, it provokes an immune response in adult humans. The human deficiency of Neu5Gc is explained by an inactivating mutation in the gene encoding CMP‐N‐acetylneuraminic acid hydroxylase, the rate‐limiting enzyme in generating Neu5Gc in cells of other mammals. This deficiency also results in an excess of the precursor sialic acid N‐acetylneuraminic acid (Neu5Ac) in humans. This mutation appears universal to modern humans, occurred sometime after our last common ancestor with the great apes, and happens to be one of the first known human‐great ape genetic differences with an obvious biochemical readout. While the original selection mechanisms and major biological consequences of this human‐specific mutation remain uncertain, several interesting clues are currently being pursued. First, there is evidence that the human condition can explain differences in susceptibility or resistance to certain microbial pathogens. Second, the functions of some endogenous receptors for sialic acids in the immune system may be altered by this difference. Third, despite the lack of any obvious alternate pathway for synthesis, Neu5Gc has been reported in human tumors and possibly in human fetal tissues, and traces have even been detected in normal human tissues. One possible explanation is that this represents accumulation of Neu5Gc from dietary sources of animal origin. Finally, a markedly reduced expression of hydroxylase in the brains of other mammals raises the possibility that the human‐specific mutation of this enzyme could have played a role in human brain evolution. Yrbk Phys Anthropol 44:54–69, 2001. © 2001 Wiley‐Liss, Inc.

N-Glycolylneuraminic acid in human tumours

N-Glycolylneuraminic acid (Neu5Gc) is an abundant sialic acid, occurring in the glycoconjugates of most deuterostome animals. Homo sapiens is a notable exception, since Neu5Gc is effectively absent from normal human tissues. This is due to a deletion in the human gene coding for CMP-Neu5Ac hydroxylase, the enzyme usually responsible for Neu5Gc biosynthesis. Despite this mutation, persistent reports in the literature suggest that Neu5Gc occurs in the glycoconjugates of many human tumours, where it might be responsible for the formation of so-called Hanganutziu-Deicher antibodies. However, the variety of systems studied and the various experimental approaches adopted have yielded a complex picture of Neu5Gc occurrence in human neoplasias. The aim of this paper is therefore to provide a critical review of the evidence for Neu5Gc in human tumours, paying particular attention to the analytical methods employed. The possible clinical applications of Neu5Gc-containing glycoconjugates and Hanganutziu-Deicher antibodies in the diagnosis and treatment of breast cancer and melanoma are also discussed. In view of the lack of CMP-Neu5Ac hydroxylase in human cells, alternative metabolic pathways for the biosynthesis of glycoconjugate-bound Neu5Gc are considered.

Detection of sialic acids and gangliosides with special reference to 9-O-acetylated species in basaliomas and normal human skin

Basal cell carcinomas and normal skin were examined in relation to the abnormal expression of gangliosides. The content of gangliosides with 9-O-acetylated sialic acids of 26 sample pairs was analyzed by a microtiter assay using influenza C virus as well as by fluorimetric high-performance liquid chromatography of the sialic acids released. The 9-O-acetylation levels were significantly (up to 56-fold) higher in basal cell carcinoma tissues than in the skin surrounding basal cell carcinomas. Slightly elevated amounts of O-acetylated gangliosides were also seen in the skin marginal to the basaliomas. The ganglioside composition of four sets of pooled samples of basal cell carcinoma and one pool of normal skin were studied by high-performance thin-layer chromatography and immune high-performance thin-layer chromatography using monoclonal antibodies against 9-O-acetyl GD3. The lipid-bound sialic acid content of normal skin was 0.029 microg dry weight, whereas in nodular basal cell carcinomas it was approximately twice as much. Several O-acetylated sialic acids were seen by high-performance liquid chromatography analysis, but N-acetyl-9-O-acetylneuraminic acid prevailed. Only in the tumor ganglioside fraction, a small amount of N-glycolylneuraminic acid was found. The 9-O-acetylated gangliosides with mainly 9-O-acetyl-GD3 can be considered as tumor-associated antigens or markers for basal cell carcinomas. This finding about tumor-associated carbohydrates may contribute to new strategies in current tumor diagnosis and therapy.

Loss of N-glycolylneuraminic acid in humans: Mechanisms, consequences, and implications for hominid evolution

The surface of all mammalian cells is covered with a dense and complex array of sugar chains, which are frequently terminated by members of a family of molecules called sialic acids. One particular sialic acid called N-glycolylneuraminic acid (Neu5Gc) is widely expressed on most mammalian tissues, but is not easily detectable on human cells. In fact, it provokes an immune response in adult humans. The human deficiency of Neu5Gc is explained by an inactivating mutation in the gene encoding CMP-N-acetylneuraminic acid hydroxylase, the rate-limiting enzyme in generating Neu5Gc in cells of other mammals. This deficiency also results in an excess of the precursor sialic acid N-acetylneuraminic acid (Neu5Ac) in humans. This mutation appears universal to modern humans, occurred sometime after our last common ancestor with the great apes, and happens to be one of the first known human-great ape genetic differences with an obvious biochemical readout. While the original selection mechanisms and major biological consequences of this human-specific mutation remain uncertain, several interesting clues are currently being pursued. First, there is evidence that the human condition can explain differences in susceptibility or resistance to certain microbial pathogens. Second, the functions of some endogenous receptors for sialic acids in the immune system may be altered by this difference. Third, despite the lack of any obvious alternate pathway for synthesis, Neu5Gc has been reported in human tumors and possibly in human fetal tissues, and traces have even been detected in normal human tissues. One possible explanation is that this represents accumulation of Neu5Gc from dietary sources of animal origin. Finally, a markedly reduced expression of hydroxylase in the brains of other mammals raises the possibility that the human-specific mutation of this enzyme could have played a role in human brain evolution.

A mouse IgG1 monoclonal antibody specific for N-glycolyl GM3 ganglioside recognized breast and melanoma tumors

14F7 murine monoclonal antibody (MAb) is an IgG1 immunoglobulin that is generated by immunizing Balb/c mice with GM3(NeuGc) ganglioside hydrophobically conjugated with human very-low-density lipoproteins and in the presence of Freund's adjuvants. 14F7 MAb binds specifically to GM3(NeuGc), whereas neither N-glycolyl or N-acetyl gangliosides, nor a sulfated glycolipid, are recognized as assessed by enzyme-linked immunosorbent assay or immunostaining on thin layer chromatograms. Immunohistochemical studies in fresh tumor tissues showed that 14F7 MAb strongly recognized in antigen expressed in human breast and melanoma tumors.

Heterophile antigens in serous cystadenocarcinoma of the human ovary

As the aberrance of carbohydrate moieties, the appearance of heterophile antigens in human ovarian cancer tissue was studied using various heterophile antigens and antibodies together with antisera raised in rabbits by immunization with extracts of human ovarian cancer tissues. In the immunodiffusion test, rabbit antisera reacted with a heat-stable, perchloric-acid extractable antigen that was different from CEA and CA125 and possessed Hanganutziu-Deicher (HD)-type specificity in all 4 specimens of serous cystadenocarcinoma of the ovary. Furthermore, a pathologic serum with strong HD-antibody complex formed a precipitin line with one of them. In the cancer tissue, we also immunochemically demonstrated the presence of rat-erythrocyte antigens. However, other types of heterophile antigens, such as Paul-Bunnell and Forssman, were not detected. These results suggest that HD-type antigens appear in serous cystadenocarcinoma of the human ovary, one in broad distribution and some in specific cases.

Analysis of the expression of Hanganutziu-Deicher (HD) antigen in human malignant melanoma

Hanganutziu-Deicher (HD) antigen is classified as a heterophile antigen and chemically defined as a ganglioside and/or glycoprotein containing N-glycolylneuraminic acid (NeuGc). HD antigen is absent from normal tissues in humans and chickens but can be expressed in human malignant neoplasms including melanoma. We analysed HD antigen expression in ganglioside and glycoprotein fractions of human melanoma tissues by means of TLC enzyme-immunostaining and Western blotting with biotinylated affinity-purified chicken anti-NeuGc-lactosylceramide (anti-HD3) antibody. No HD-antigenic gangliosides were detected in 11 specimens of human melanoma. In the glycoprotein fractions, however, a strong HD-positive band of 58 kD was detected in 3 of 10 specimens and several minor bands (37 kD, 13.5 kD, etc.) were also found in 5 specimens. The positive bands completely disappeared after treatment with neuraminidase. These results suggest that HD antigen is expressed on the carbohydrate chains of glycoproteins but not on those of gangliosides in human melanoma.