Human antibodies against the polymorphic epithelial mucin in ovarian cancer patients recognise a novel sequence in the tandem repeat region

Human MUC1 Mucin: A Multifaceted Glycoprotein

Human MUC1 mucin, a membrane-bound glycoprotein, is a major component of the ductal cell surface of normal glandular cells. MUC1 is overexpressed and aberrantly glycosylated in carcinoma cells. The role MUC1 plays in cancer progression represents two sides of one coin: on the one hand, loss of polarity and overexpression of MUC1 in cancer cells interferes with cell adhesion and shields the tumor cell from immune recognition by the cellular arm of the immune system, thus favoring metastases; on the other hand, MUC1, in essence a self-antigen, is displaced and altered in malignancy and induces immune responses. Tumor-associated MUC1 has short carbohydrate sidechains and exposed epitopes on its peptide core; it gains access to the circulation and comes into contact with the immune system provoking humoral and cellular immune responses. Natural antibodies to MUC1 present in the circulation of cancer patients may be beneficial to the patient by restricting tumor growth and dissemination: early stage breast cancer patients with a humoral response to MUC1 have a better disease-specific survival. Several MUC1 peptide vaccines, differing in vectors, carrier proteins and adjuvants, have been tested in phase I clinical trials. They are capable of inducing predominantly humoral responses to the antigen, but evidence that these immune responses may be effective against the tumor in humans is still scarce.

Vaccine draining lymph nodes are a source of antigen-specific B cells

PURPOSE

Our research is focused on using vaccine draining lymph nodes as a source of immune cells to better understand the immune response and to attempt to generate new anti-cancer reagents. Following a vaccine, harvesting the lymph node can only be done once. We endeavored to determine the range of times that B cells secreting anti-KLH antibodies were present in the node of KLH-vaccinated mice.

RESULTS

Following vaccination the total number of mononuclear cells (MNCs) increased in the vaccine-draining lymph node (VDN). The percentage of MNCs that were B cells nearly doubled. B cells recovered from the node that secreted anti-KLH antibodies were evident by day 7. The number continued to increase and then slowly decreased over the observed time range to 28days after vaccination. The VDN, compared to the spleen, the bone marrow and the nonVDN, contained a higher percentage of B cells that secreted anti-KLH antibodies.

CONCLUSIONS

After a vaccine, there is a multi-week window of time when an increasing number of B cells are present in a VDN that secrete anti-KLH antibodies. These results support using the VDN as a source for B cells that secrete anti-vaccine antibodies.

Natural and Induced Humoral Responses to MUC1

MUC1 is a membrane-tethered mucin expressed on the ductal cell surface of glandular epithelial cells. Loss of polarization, overexpression and aberrant glycosylation of MUC1 in mucosal inflammation and in adenocarcinomas induces humoral immune responses to the mucin. MUC1 IgG responses have been associated with a benefit in survival in patients with breast, lung, pancreatic, ovarian and gastric carcinomas. Antibodies bound to the mucin may curb tumor progression by restoring cell-cell interactions altered by tumor-associated MUC1, thus preventing metastatic dissemination, as well as counteracting the immune suppression exerted by the molecule. Furthermore, anti-MUC1 antibodies are capable of effecting tumor cell killing by antibody-dependent cell-mediated cytotoxicity. Although cytotoxic T cells are indispensable to achieve anti-tumor responses in advanced disease, abs to tumor-associated antigens are ideally suited to address minimal residual disease and may be sufficient to exert adequate immune surveillance in an adjuvant setting, destroying tumor cells as they arise or maintaining occult disease in an equilibrium state. Initial evaluation of MUC1 peptide/glycopeptide mono and polyvalent vaccines has shown them to be immunogenic and safe; anti-tumor responses are scarce. Progress in carbohydrate synthesis has yielded a number of sophisticated substrates that include MUC1 glycopeptide epitopes that are at present in preclinical testing. Adjuvant vaccination with MUC1 glycopeptide polyvalent vaccines that induce strong humoral responses may prevent recurrence of disease in patients with early stage carcinomas. Furthermore, prophylactic immunotherapy targeting MUC1 may be a strategy to strengthen immune surveillance and prevent disease in subjects at hereditary high risk of breast, ovarian and colon cancer.

MUC1 expression and anti-MUC1 serum immune response in head and neck squamous cell carcinoma (HNSCC): a multivariate analysis

Background

HNSCC progression to adjacent tissue and nodes may be mediated by altered glycoproteins and glycolipids such as MUC1 mucin. This report constitutes a detailed statistical study about MUC1 expression and anti-MUC1 immune responses in relation to different clinical and pathological parameters which may be useful to develop new anti HNSCC therapeutic strategies.

Patients and methods

Fifty three pre treatment HNSCC patients were included: 26 (49.1%) bearing oral cavity tumors, 17 (32.1%) localized in the larynx and 10 (18.8%) in the pharynx. Three patients (5.7%) were at stage I, 5 (9.4%) stage II, 15 (28.3%) stage III and 30 (56.6%) at stage IV. MUC1 tumor expression was studied by immunohistochemistry employing two anti-MUC1 antibodies: CT33, anti cytoplasmic tail MUC1 polyclonal antibody (Ab) and C595 anti-peptidic core MUC1 monoclonal antibody. Serum levels of MUC1 and free anti-MUC1 antibodies were detected by ELISA and circulating immune complexes (CIC) by precipitation in polyethylene glycol (PEG) 3.5%; MUC1 isolation from circulating immune complexes was performed by protein A-sepharose CL-4B affinity chromatography followed by SDS-PAGE and Western blot. Statistical analysis consisted in Multivariate Principal Component Analysis (PCA); ANOVA test (Tukey's test) was employed to find differences among groups; nonparametrical correlations (Kendall's Tau) were applied when necessary. Statistical significance was set to p < 0.05 in all cases.

Results

MUC1 cytoplasmic tail was detected in 40/50 (80%) and MUC1 protein core in 9/50 (18%) samples while serum MUC1 levels were elevated in 8/53 (15%) patients. A significant statistical correlation was found between MUC1 serum levels and anti-MUC1 IgG free antibodies, while a negative correlation between MUC1 serum levels and anti-MUC1 IgM free antibodies was found. Circulating immune complexes were elevated in 16/53 (30%) samples and were also statistically associated with advanced tumor stage. MUC1 was identified as an antigenic component of IgG circulating immune complexes. Moreover, poorly differentiated tumors were inversely correlated with tumor and serum MUC1 detection and positively correlated with node involvement and tumor mass.

Conclusion

Possibly, tumor cells produce MUC1 mucin which is liberated to the circulation and captured by IgG antibodies forming MUC1-IgG-CIC. Another interesting conclusion is that poorly differentiated tumors are inversely correlated with tumor and serum MUC1 detection.

Identification of a novel cancer-specific immunodominant glycopeptide epitope in the MUC1 tandem repeat

The cell membrane mucin MUC1 is over-expressed and aberrantly glycosylated in many cancers, and cancer-associated MUC1 glycoforms represent potential targets for immunodiagnostic and therapeutic measures. We have recently shown that MUC1 with GalNAcalpha1-O-Ser/Thr (Tn) and NeuAcalpha2-6GalNAcalpha1-O-Ser/Thr (STn) O-glycosylation is a cancer-specific glycoform, and that Tn/STn-MUC1 glycopeptide-based vaccines can override tolerance in human MUC1 transgenic mice and induce humoral immunity with high specificity for MUC1 cancer-specific glycoforms (Sorensen AL, Reis CA, Tarp MA, Mandel U, Ramachandran K, Sankaranarayanan V, Schwientek T, Graham R, Taylor-Papadimitriou J, Hollingsworth MA, et al. 2006. Chemoenzymatically synthesized multimeric Tn/STn MUC1 glycopeptides elicit cancer-specific anti-MUC1 antibody responses and override tolerance. Glycobiology. 16:96-107). In order to further characterize the immune response to Tn/STn-MUC1 glycoforms, we generated monoclonal antibodies with specificity similar to the polyclonal antibody response found in transgenic mice. In the present study, we define the immunodominant epitope on Tn/STn-MUC1 glycopeptides to the region including the amino acids GSTA of the MUC1 20-amino acid tandem repeat (HGVTSAPDTRPAPGSTAPPA). Most other MUC1 antibodies are directed to the PDTR region, although patients with antibodies to the GSTA region have been identified. A panel of other MUC1 glycoform-specific monoclonal antibodies was included for comparison. The study demonstrates that the GSTA region of the MUC1 tandem repeat contains a highly immunodominant epitope when presented with immature short O-glycans. The cancer-specific expression of this glycopeptide epitope makes it a prime candidate for immunodiagnostic and therapeutic measures.

Malignancy-induced autoimmunity to MUC1: initial antibody characterization

Numerous reports document the existence of autoantibodies to MUC1 in the circulation of individuals with breast and other solid malignancies, with the majority of researchers utilizing MUC1 peptides in their detection. This report documents the purification, using peptide and whole molecule, and characterization of such autoantibodies from an individual with an unusual, highly MUC1-positive, myosarcoma. Purification of autoantibodies from serum was performed using affinity chromatography against either MUC1 peptide or whole molecule MUC1 [derived both from the patient (Pt-MUC1) and from a pool of sera from patients with advanced breast cancer (ABC-MUC1)]. Enzyme-linked immunosorbent assays (ELISAs) were used to compare specificity of purified autoantibodies. Peptide epitopes were determined by Ptifcan system against 7-mer peptides covering the 20 amino acid repeat of the MUC1 extracellular domain. Substantially higher amounts of autoantibodies were isolated when purifying against Pt-MUC1 rather than either ABC-MUC1 or peptide. Whole molecule purified autoantibodies demonstrated an increased specificity for tumour-derived MUC1. Pt-MUC1 autoantibodies were of both the immunoglobulin (Ig)G and IgM class, whilst autoantibodies purified against ABC-MUC1 and MUC1 peptide were IgG only. A greater range of peptide epitopes was defined by those autoantibodies purified against whole molecule. This report presents data indicating the presence of autoantibodies to MUC1 in an individual diagnosed with a MUC1 over-expressing myosarcoma. Confirmation of these autoantibodies as being specific for tumour-associated MUC1 is given. Further, it suggests that, although autoantibodies are present that recognize core protein determinants, the initial, and dominant, immunizing epitope is not purely pretentious in nature.

Reactivity of natural and induced human antibodies to MUC1 mucin with MUC1 peptides and n-acetylgalactosamine (GalNAc) peptides

Antibodies (Abs) to MUC1 occur naturally in both healthy subjects and cancer patients and can be induced by MUC1 peptide vaccination. We compared the specificity of natural and induced MUC1 Abs with the objective of defining an effective MUC1 vaccine for active immunotherapy of adenocarcinoma patients. Serum samples, selected out of a screened population of 492 subjects for their high levels of IgG and/or IgM MUC1 Abs, were obtained from 55 control subjects and from 26 breast cancer patients before primary treatment, as well as from 19 breast cancer patients immunized with MUC1 peptides coupled to keyhole limpet hemocyanin (KLH) and mixed with QS-21. The samples were tested with enzyme-linked immunoassays for reactivity with (1) overlapping hepta- and 20-mer peptides spanning the MUC1 tandem repeat sequence; (2) two modified 60-mer peptides with substitutions in the PDTR (PDTA) or in the STAPPA (STAAAA) sequence of each tandem repeat; and (3) four 60-mer glycopeptides with each 1, 2, 3 and 5 mol N-acetylgalactosamine (GalNAc) per repeat. More than one minimal epitopic sequence could be defined, indicating that Abs directed to more than one region of the MUC1 peptide core can coexist in one and the same subject. The most frequent minimal epitopic sequence of natural MUC1 IgG and IgM Abs was RPAPGS, followed by PPAHGVT and PDTRP. MUC1 peptide vaccination induced high titers of IgM and IgG Abs predominantly directed, respectively, to the PDTRPAP and the STAPPAHGV sequences of the tandem repeat. Natural MUC1 Abs from breast cancer patients reacted more strongly with the N-acetylgalactosamine (GalNAc) peptides than with the naked 60-mer peptide, while reactivity with the GalNAc-peptides was significantly reduced (2-tailed p < 0.0001) in the MUC1 IgG and IgM Abs induced by MUC1 peptide vaccination. Whereas in cancer patients glycans appear to participate in epitope conformation, the epitope(s) recognized by MUC1 Abs induced by peptide vaccination are already masked by minimal glycosylation. Therefore, our results indicate that a MUC1 glycopeptide would be a better vaccine than a naked peptide.

Survival in early breast cancer patients is favorably influenced by a natural humoral immune response to polymorphic epithelial mucin

PURPOSE

Polymorphic epithelial mucin (PEM or MUC1) is being studied as a vaccine substrate for the immunotherapy of patients with adenocarcinoma. The present study analyzes the incidence of naturally occurring MUC1 antibodies in early breast cancer patients and relates the presence of these antibodies in pretreatment serum to outcome of disease.

MATERIALS AND METHODS

We measured immunoglobulin G (IgG) and immunoglobulin M (IgM) antibodies to MUC1 with an enzyme-linked immunoassay (PEM.CIg), which uses a MUC1 triple-tandem repeat peptide conjugated to bovine serum albumin, in pretreatment serum samples obtained from 154 breast cancer patients (52 with stage I disease and 102 with stage II) and 302 controls. The median disease-specific survival time of breast cancer patients was 74 months (range, 15 to 118 months). A positive test result was defined as MUC1 IgG or IgM antibody levels equal to or greater than the corresponding rounded-up median results obtained in the total breast cancer population.

RESULTS

A positive test result for both MUC1 IgG and IgM antibodies in pretreatment serum was associated with a significant benefit in disease-specific survival in stage I and II (P =.0116) breast cancer patients. Positive IgG and IgM MUC1 antibody levels had significant additional prognostic value to stage (P =.0437) in multivariate analysis. Disease-free survival probability did not differ significantly. However, stage II patients who tested positive for MUC1 IgG and IgM antibody and who relapsed had predominantly local recurrences or contralateral disease, as opposed to recurrences at distant sites in the patients with a negative humoral response (P =.026).

CONCLUSION

Early breast cancer patients with a natural humoral response to MUC1 have a higher probability of freedom from distant failure and a better disease-specific survival. MUC1 antibodies may control hematogenic tumor dissemination and outgrowth by aiding the destruction of circulating or seeded MUC1-expressing tumor cells. Vaccination of breast cancer patients with MUC1-derived (glyco)peptides in an adjuvant setting may favorably influence the outcome of disease.

High density O-glycosylation on tandem repeat peptide from secretory MUC1 of T47D breast cancer cells

The site-specific O-glycosylation of MUC1 tandem repeat peptides from secretory mucin of T47D breast cancer cells was analyzed. After affinity isolation on immobilized BC3 antibody, MUC1 was partially deglycosylated by enzymatic treatment with alpha-sialidase/beta-galactosidase and fragmented by proteolytic cleavage with the Arg-C-specific endopeptidase clostripain. The PAP20 glycopeptides were isolated by reversed phase high pressure liquid chromatography and subjected to the structural analyses by quadrupole time-of-flight electrospray ionization mass spectrometry and to the sequencing by Edman degradation. All five positions of the repeat peptide were revealed as O-glycosylation targets in the tumor cell, including the Thr within the DTR motif. The degree of substitution was estimated to average 4.8 glycans per repeat, which compares to 2.6 glycosylated sites per repeat for the mucin from milk (Müller, S., Goletz, S., Packer, N., Gooley, A. A., Lawson, A. M., and Hanisch, F.-G. (1997) J. Biol. Chem. 272, 24780-24793). In addition to a modification by glycosylation, the immunodominant DTR motif on T47D-MUC1 is altered by amino acid replacements (PAPGSTAPAAHGVTSAPESR), which were revealed in about 50% of PAP20 peptides. The high incidence of these replacements and their detection also in other cancer cell lines imply that the conserved tandem repeat domain of MUC1 is polymorphic with respect to the peptide sequence.

Antibody and T cell responses of patients with adenocarcinoma immunized with mannan-MUC1 fusion protein

Mucin 1 (MUC1) is a large complex glycoprotein that is highly expressed in breast cancer, and as such could be a target for immunotherapy. In mice, human MUC1 is highly immunogenic, particularly when conjugated to mannan, where a high frequency of CD8(+) MHC-restricted cytotoxic T lymphocytes is induced, accompanied by tumor protection. On this basis, a clinical trial was performed in which 25 patients with advanced metastatic carcinoma of breast, colon, stomach, or rectum received mannan-MUC1 in increasing doses. After 4 to 8 injections, large amounts of IgG1 anti-MUC1 antibodies were produced in 13 out of 25 patients (with antibody titers by ELISA of 1/320-1/20,480). Most of the antibodies reacted to the epitopes STAPPAHG and PAPGSTAP. In addition, T cell proliferation was found in 4 out of 15 patients, and CTL responses were seen in 2 out of 10 patients. Mannan-MUC1 can immunize patients, particularly for antibody formation, and to a lesser extent, cellular responses. It remains to be seen whether such responses have antitumor activity.

Comparison of O-linked carbohydrate chains in MUC-1 mucin from normal breast epithelial cell lines and breast carcinoma cell lines. Demonstration of simpler and fewer glycan chains in tumor cells

MUC-1 mucin is considered to be aberrantly glycosylated in breast, ovary, and other carcinomas in comparison with mucin from corresponding normal tissues. In order to clarify these differences in glycosylation, we have compared the O-linked carbohydrate chains from MUC-1 immunoprecipitated from [3H]GlcN-labeled breast epithelial cell lines (MMSV1-1, MTSV1-7, and HB-2) derived from cells cultured from human milk, with three breast cancer cell lines (MCF-7, BT-20, and T47D). Analysis by high pH anion chromatography showed that the normal cell lines had a higher ratio of GlcN/GalN and more complex oligosaccharide profiles than the cancer cell lines. Structural analyses were carried out on the oligosaccharides from MTSV1-7 and T47D MUC-1, and the following structures were proposed. MUC-1 from T47D had rather a simple glycosylation pattern, with NeuAcalpha2-3Galbeta1-3GalNAc-ol, Galbeta1-3GalNAc-ol, and GalNAc-ol predominating; in contrast, MUC-1 from MTSV1-7 had more complex structures, including a number of disialo, core 2 species, i.e. NeuAcalpha2-3Galbeta1-4GlcNAcbeta1-6[NeuAcalpha2 -3Galbeta1-3]GalNAc- ol and NeuAcalpha2-3Galbeta1-4GlcNAcbeta1-6[NeuAcalpha2 -3Galbeta1-4GlcNAcbet a1-3Galbeta1-3]GalNAc-ol. Double-labeling experiments with [3H]GlcN and 14C-aminoacids and analysis of GalNAc or GalNAc-ol:protein ratios in MUC-1 showed that there was also a significant difference in the degree of glycosylation of the mucin between the two cell types. We conclude that MUC-1 from breast cancer cell lines has simpler, and fewer, carbohydrate chains than MUC-1 from normal breast epithelial cells, and that these differences, combined or separately, explain the differential tumor specificity of some MUC-1 antibodies and T cells.