Cell Surface-Associated Anti-MUC1-Derived Signal Peptide Antibodies: Implications for Cancer Diagnostics and Therapy

Abstract

The MUC1 tumor associated antigen is highly expressed on a range of tumors. Its broad distribution on primary tumors and metastases renders it an attractive target for immunotherapy. After synthesis MUC1 is cleaved, yielding a large soluble extracellular alpha subunit containing the tandem repeats array (TRA) domain specifically bound, via non-covalent interaction, to a smaller beta subunit containing the transmembrane and cytoplasmic domains. Thus far, inconclusive efficacy has been reported for anti-MUC1 antibodies directed against the soluble alpha subunit. Targeting the cell bound beta subunit, may bypass limitations posed by circulating TRA domains. MUC1’s signal peptide (SP) domain promiscuously binds multiple MHC class II and Class I alleles, which upon vaccination, generated robust T-cell immunity against MUC1-positive tumors. This is a first demonstration of non-MHC associated, MUC1 specific, cell surfaces presence for MUC1 SP domain. Polyclonal and monoclonal antibodies generated against MUC1 SP domain specifically bind a large variety of MUC1-positive human solid and haematological tumor cell lines; MUC1-positive bone marrow derived plasma cells obtained from multiple myeloma (MM)-patients, but not MUC1 negative tumors cells, and normal naive primary blood and epithelial cells. Membranal MUC1 SP appears mainly as an independent entity but also co-localized with the full MUC1 molecule. MUC1-SP specific binding in BM-derived plasma cells can assist in selecting patients to be treated with anti-MUC1 SP therapeutic vaccine, ImMucin. A therapeutic potential of the anti-MUC1 SP antibodies was suggested by their ability to support of complement-mediated lysis of MUC1-positive tumor cells but not MUC1 negative tumor cells and normal naive primary epithelial cells. These findings suggest a novel cell surface presence of MUC1 SP domain, a potential therapeutic benefit for anti-MUC1 SP antibodies in MUC1-positive tumors and a selection tool for MM patients to be treated with the anti-MUC1 SP vaccine, ImMucin.

The use of signal peptide domains as vaccine candidates

“…Since soluble MUC1 SP was not detected in the sera of these patients, it was speculated that the naturally generated autoantibodies were primed by non-MHC-restricted, tumor MUC1-associated cell-bound SP. This hypothesis was confirmed using the MUC1 SP-specific polyclonal (R23IgG) and monoclonal (SPmAb-2.1 and SPmAb-6) antibodies, 51 which showed high specificity to MUC1 SP, without binding unrelated SPs. Cell-surface expression of MUC1 SP was detected on various MUC1-positive tumor cell-lines and primary tumors, but not on primary na€ ıve blood and epithelial cells.…”

“…3). 51 In parallel, loading experiments with ImMucin's 9-mer epitopes MUC1-SP-S2 and MUC1-SP-S4 (which are SPmAb-2.1 and SPmAb-6 epitopes) on MUC1 negative, HLA-A2.1-transfected TAP-deficient RMA-S cells, revealed strong HLA-A2.1 stabilization but no MUC1 SP binding, thereby confirming that MUC1 SP surface expression most likely exists without MHC class I association (unpublished data). In the context of active vaccination, 10/15 MUC1 SP ImMucin-vaccinated MM cancer patients demonstrated a significant increase in anti-ImMucin IgG concentrations, with a mean 6.86-fold (range: 1.4-40) increase at the response peak, which was observed after receiving 6 or 7 immunizations.…”

Nonviral Oncogenic Antigens and the Inflammatory Signals Driving Early Cancer Development as Targets for Cancer Immunoprevention

“…MUC1 is a mucin-like, glycosylated TAA that is overexpressed in several epithelial carcinomas including breast, colon, lung, prostate, and ovarian carcinomas (3, 27, 28). The posttranslational modifications of MUC1 define its tumorigenicity (3, 27).…”

Phase I/II study exploring ImMucin, a pan‐major histocompatibility complex, anti‐MUC1 signal peptide vaccine, in multiple myeloma patients

“…MUC1 (mucin 1, cell surface associated) is a glycoprotein that is highly expressed by carcinomas and haematological tumours, including MM (Kovjazin et al , ). Its broad tumour distribution, including on cancer stem cells (Engelmann et al , ), has established it as a promising target for active vaccination (Cheever et al , ).…”

“…Additionally, active suppression of T‐cell function by sMUC1 may interfere with the desired response (van de Wiel‐van Kemenade et al , ; Agrawal et al , ). Induction of a stronger and broader B‐ and T‐cell response against MUC1 epitopes exclusively expressed on tumour cells (Kovjazin et al , , ), may lead to improved clinical outcomes.…”