S. von Mensdorff-Pouilly

Summary Report on the ISOBM TD-4 Workshop: Analysis of 56 Monoclonal Antibodies against the MUC1 Mucin

Sixteen research groups participated in the ISOBM TD-4 Workshop in which the reactivity and specificity of 56 monoclonal antibodies against the MUC1 mucin was investigated using a diverse panel of target antigens and MUC1 mucin- related synthetic peptides and glycopeptides. The majority of antibodies (34/56) defined epitopes located within the 20-amino acid tandem repeat sequence of the MUC1 mucin protein core. Of the remaining 22 antibodies, there was evidence for the involvement of carbohydrate residues in the epitopes for 16 antibodies. There was no obvious relationship between the type of immunogen and the specificity of each antibody. Synthetic peptides and glycopeptides were analyzed for their reactivity with each antibody either by assay of direct binding (e.g. by ELISA or BiaCore) or by determining the capacity of synthetic ligands to inhibit antibody binding interactions. There was good concordance between the research groups in identifying antibodies reactive with peptide epitopes within the MUC1 protein core. Epitope mapping tests were performed using the Pepscan analysis for antibody reactivity against overlapping synthetic peptides, and results were largely consistent between research groups. The dominant feature of epitopes within the MUC1 protein core was the presence, in full or part, of the hydrophilic sequence of PDTRPAP. Carbohydrate epitopes were less easily characterized and the most useful reagents in this respect were defined oligosaccharides, rather than purified mucin preparations enriched in particular carbohydrate moieties. It was evident that carbohydrate residues were involved in many epitopes, by regulating epitope accessibility or masking determinants, or by stabilizing preferred conformations of peptide epitopes within the MUC1 protein core. Overall, the studies highlight concordance between groups rather than exposing inconsistencies which gives added confidence to the results of analyses of the specificity of anti-mucin monoclonal antibodies.

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.

Humoral immune response to polymorphic epithelial mucin (MUC-1) in patients with benign and malignant breast tumours

To investigate the clinical significance of an immune response to the MUC-1 encoded polymorphic epithelial mucin (PEM) breast cancer, circulating immune complexes containing PEM (PEM.CIC) were measured in sera from 96 healthy women, in pretreatment serum samples from 40 patients with benign breast tumours and from 140 patients with breast cancer and in serum samples from 61 breast cancer patients with recurrent or progressive disease. PEM.CIC were measured using a sandwich enzyme-linked immunoassay, and PEM serum levels were measured with CA 15.3 IRMA (Centocor Inc., Malvern, Pennsylvania, U.S.A.). Cut-off levels used for PEM.CIC and CA 15.3 were 120 Optical Density Units (O.D.) x 10(3) and 30 U/ml, respectively. In benign tumours, positivity for PEM.CIC was 37.5% (15/40). 36 of the 140 patients (25.7%) in the breast cancer pretreatment group had elevated PEM.CIC values. In patients with advanced metastatic disease, positivity for PEM.CIC was 18% (11/61). PEM.CIC was elevated in 32% (24/74) of node-negative patients, but only in 20% (12/59) of node-positive patients and absolute values were higher in node-negative patients (Mann-Whitney U test, two-tailed P = 0.0168). There was an inverse correlation between positivity for PEM.CIC and extent of disease: while 3 of the 6 patients with a carcinoma in situ were positive, only 1 of the 15 patients with more than five nodes involved had elevated levels of PEM.CIC. All 7 patients with distant metastases at first diagnosis were PEM.CIC negative. 28 out of 133 patients had a recurrence during the observation period (median 55 months, range 27-84 months). 23 of these 28 patients (82%) were PEM.CIC negative at the moment of first diagnosis. None of the patients with pretreatment elevation of both PEM.CIC and CA 15.3 (n = 13) relapsed. Our preliminary clinical results suggest that a humoral immune response to PEM protects against disease progression, and further support the idea of using synthetic peptides or glycopeptides containing the immunogenic core of the mucin as cancer vaccines.

Polymorphic epithelial mucin (MUC-1)-containing circulating immune complexes in carcinoma patients

Circulating immune complexes (CICs) containing polymorphic epithelial mucin (PEM/MUC-1) were found in sera of 24.5% of 151 primary breast carcinoma patients and 18-21.4% of patients with advanced ovarian (n = 56) and breast carcinomas (n = 61), 37% of patients with benign breast tumours, but in only 2.1% of 96 healthy individuals. The incorporation of PEM into CICs affects the detection of circulating PEM in commercial immunoassays such as the CA 15-3 assay, as suggested by a negative correlation between levels of PEM-containing immune complexes (PEM-CICs) and CA 15-3 values, and confirmed by isolation of PEM from CA 15-3-negative sera containing high levels of PEM-CICs. The amounts of PEM masked by human antibodies correspond to significant values of the CA 15-3 assay when monitoring patients for carcinoma. Most antibodies in PEM-CICs were of IgG class, suggesting their specific nature to the PEM epitopes.

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.

Cellular and humoral immune responses to MUC1 mucin and tandem-repeat peptides in ovarian cancer patients and controls.

Abstract The objective of this study was to demonstrate the presence of proliferative T cell responses to human polymorphic epithelial mucin (MUC1) and its tandem-repeat peptides in peripheral blood mononuclear cells (PBMC) from ovarian cancer patients and from controls and to correlate these cellular responses to a humoral response to MUC1. PBMC were obtained from 6 healthy women, from 13 women in the third trimester of pregnancy and from 21 ovarian cancer patients. Only 1 of the 6 healthy women showed a weak primary proliferative response (stimulation index, SI<2) to a 20-mer MUC1 tandem-repeat peptide in the presence of interleukin-2 (IL-2). In PBMC from 5/13 pregnant women (38%) a weak response could be induced by the 20-mer and/or 60-mer tandem-repeat peptides (SI ≤ 3.0) and in PBMC from 8/15 ovarian cancer patients (53%) 20-mer and/or 60-mer MUC1 tandem-repeat peptides induced primary responses (SI ≤ 5.4). MUC1 mucin purified from a breast tumor cell line and/or from urine of a healthy donor had a relatively strong stimulating effect (SI ≤ 19) on PBMC from 4 of 16 ovarian cancer patients (25%). In contrast, in PBMC of 9 ovarian cancer patients stimulated by the addition of a Candida albicans extract, MUC1 mucin strongly inhibited proliferation. This inhibition could partially be abrogated by the addition of IL-2. MUC1 (CA 15.3 assay) and free circulating MUC1 IgG and IgM antibodies (PEM.CIg assay) were determined in the plasma of all subjects. The MUC1 and the free circulating MUC1 IgG antibody plasma levels were significantly higher in the ovarian cancer patients than in the healthy women. Although no significant correlations were found between MUC1 mucin, MUC1 Ab plasma levels and the individual proliferative responses to the MUC1 antigens, an association may exist between them, since all three are significantly higher in the ovarian cancer patients than in the healthy women.

Characterization of a new MUC1 monoclonal antibody (VU-2-G7) directed to the glycosylated PDTR sequence of MUC1

A monoclonal antibody (MAb), VU-2-G7, was generated against a synthetic 60-mer MUC1 triple tandem repeat peptide with N-acetyl-galactosamine (GalNAc) O-linked to the threonine in the PDTR region of each repeat (3M GalNAc). VU-2-G7 and 8 MUC1 MAbs (VU-3-C6, VU-4-H5, 139H2, A76-A/C7, VU-12-E1, BCP9, MF11 and BW835) were tested against various glycosylated and nonglycosylated MUC1 tandem repeat peptides. VU-2-G7 showed strong reactivity with its immunogen, 3M GalNAc, and much lower reactivity with the nonglycosylated 60-mer MUC1 triple tandem repeat peptide. VU-2-G7 showed no reactivity with a 60-mer MUC1 triple tandem repeat peptide modified at the PDTR region or with a 60-mer MUC1 triple tandem repeat peptide with 3 GalNAc per repeat outside the PDTR region (9M GalNAc). In ELISA and flow cytometry, VU-2-G7 ubiquitously reacted with 4 MUC1-expressing breast cancer and 2 ovarian cancer cell lines and with a MUC1-gene-transfected Chinese hamster ovary cell line. The reactivity of VU-2-G7 was always higher than that of VU-4-H5, raised against a nonglycosylated 60-mer MUC1 triple tandem repeat peptide. Immunohistochemical staining of paraffin sections of breast and ovarian tumor tissues showed strong binding of VU-2-G7 predominantly at the cell membrane. The dominant epitope of VU-2-G7 is in the glycosylated PDTR motif of the MUC1 tandem repeat, and this epitope is abundantly present on the surface of tumor cell lines and breast and ovarian tumor tissues. Given the ubiquitously aberrant glycosylation of MUC1 in malignant cells, the production of MAbs against highly purified glycosylated MUC1 tandem repeat peptides may yield MAbs better suited for the immunotherapy of carcinomas than those available at the moment.

Impact of Helicobacter pylori Infection on the Humoral Immune Response to MUC1 Peptide in Patients with Chronic Gastric Diseases and Gastric Cancer

Many investigators have demonstrated alteration of gastric mucins in H. pylori infected individuals. The inflammatory environment induced by H. pylori leading to aberrant glycosylation of MUC1 and demasking of core peptide MUC1 epitope could enhance immune responses to MUC1. IgG and IgM immune response to MUC1 in patients with gastric cancer (n = 214) chronic gastroduodenal diseases (n = 160) and healthy blood donors (n = 91) was studied with ELISA using bovine serum albumin-MUC1 60-mer peptide as antigen. H. pylori serologic status was evaluated with ELISA and CagA status by immunoblotting. Gastric mucosa histology was scored according to the Sydney system. Compared to H. pylori seronegative individuals, higher levels of IgG antibody to MUC1 were found in H. pylori seropositive patients with benign gastric diseases (p < 0.01) and blood donors (p < 0.03). Higher MUC1 IgG antibody levels were associated with a higher degree of gastric corpus mucosa inflammation in patients with chronic gastroduodenal diseases (p < 0.0025). There was a positive correlation between the levels of anti-H. pylori IgG and MUC1 IgG antibody levels in blood donors (p = 0.03), and in patients with benign diseases (p < 0.0001). In patients with gastric cancer (n = 214) a significantly higher level of anti-MUC1 IgG than in blood donors was observed (p < 0.001) irrespective of H. pylori status or stage of cancer. MUC1 IgM antibody levels were not related to the H. pylori serology. IgG immune response to tumor-associated MUC1 is up regulated in H. pylori infected individuals. This increase is associated with a higher IgG immune response to H. pylori and with a higher degree of gastric mucosa inflammation. High levels of MUC1 IgG antibody irrespective of H. pylori serologic status characterized patients with gastric cancer. The findings suggest that, in some individuals, the H. pylori infection may stimulate immune response to tumor-associated MUC1 peptide antigen thus modulating tumor immunity.

Prognostic value of soluble MUC1 and anti-MUC1 antibody levels in patients with diffuse large B-cell lymphoma.

6586 Background: A soluble form of mucin MUC1 (sMUC1) as well as antibodies anti-MUC1 can be found in peripheral blood (PB) of patients with MUC1+ carcinoma or myeloma. MUC1 is expressed in 80% of diffuse large cell lymphoma (DLCL). METHODS sMUC1 level was evaluated in 80 VBD (Volunteer Blood Donor) and 95 DLCL pts using an immunoassay that detects the MUC1 CA27.29 epitope. All DLCL pts were treated on study with the same anthracyclins-containing regimen at MD Anderson between 1993 and 1996. IgM and IgG antibodies against MUC1 were quantified using an immunoassay with a 60aa peptide part of MUC1 tandem repeat. The median level of sMUC1, anti-MUC1-IgG and anti-MUC1-IgM found in VBD was used as a cutoff to separate the patients in two groups. RESULTS The sMUC1 level was significantly higher in DLCL (mean 25.4 ± 11.3 U/ml) than in VBD (mean value 15.6 ± 9.1 U/ml) (p < .0001, Mann-Whitney). The level of circulating anti-MUC1-IgG was also significantly higher in DLCL (1.211 ± 0.959 Arb, U/ml) than in VBD (1.015 ± 0.667 Arb, U/ml) (p=. 0041, Mann-Whitney), but not for anti-MUC1-IgM. There was no statistical correlation between the levels of sMUC1 and the presence of anti-MUC1 antibodies. The 10-year failure-free survival (FFS) was 87.1% for pts with low sMUC1 vs. 56.7% for pts with high sMUC1 (p = .026; log-rank test.). The same correlation was seen with overall survival (P < .05). In addition sMUC1 remained an independent prognostic variable for FFS. The level of circulating anti-MUC1-IgG or anti-MUC1-IgM did not correlate with either FFS or OS. CONCLUSIONS A high level of circulating of sMUC1 is associated with a poor outcome in patients with DLCL. The level of circulating anti-MUC1 antibody was not found predictive of survival in DLCL patients in our study. No significant financial relationships to disclose.