Immunization of breast cancer patients using a synthetic sialyl-Tn glycoconjugate plus Detox adjuvant

Abstract

We have synthesized various formulations that have potential for active specific immunotherapy (ASI) of human cancers. Sialyl-Tn (STn) is a potentially important target structure for ASI because its expression on mucins is a strong, independent predictor of poor prognosis, suggesting that it may have functional significance in the metastatic process. In this first pilot study of synthetic sialyl-Tn hapten conjugated to keyhole limpet hemocyanin (STn-KLH), with Detox adjuvant, toxicity and humoral immunogenicity were assessed in 12 patients with metastatic breast cancer. Toxicity was minimal, restricted to local cutaneous reactions (apart from transient nausea and vomiting following single low-dose cyclophosphamide treatment). Using STn-conjugated human serum albumin in a solid-phase enzyme-linked immunosorbent assay, it was shown that all patients developed IgM and IgG specific for the synthetic STn hapten. Following immunization, most patients were shown to develop increased titres of complement-mediated cytotoxic antibodies, partially inhibited by synthetic STn hapten, but not by the related TF hapten. We also detected IgM and IgG antibodies reactive with natural STn determinants expressed on ovine submaxillary mucin, the STn specificity of this reactivity being confirmed by hapten inhibition. Evaluation of clinical efficacy in a small pilot study is difficult. Five patients are alive 12 or more months after entry, and another 4 patients are alive 6 or more months after entry into the study. All 3 patients with known widespread bulky disease progressed despite ASI, 2 having died from widespread cancer. Two patients had partial responses, each lasting 6 months. While several patients had disease stability for 3-10 months, 1 patient with pulmonary metastases remains stable 15 months after entry into the program.

Antibodies against Tumor Cell Glycolipids and Proteins, but Not Mucins, Mediate Complement-Dependent Cytotoxicity

“…The first demonstrated CDC against a breast cancer cell line with sera from breast cancer patients immunized with a MUC1 vaccine. Although the chromium release assay was similar to ours, there were two differences: rabbit, not human, complement and round-, not flat-, bottom plates were used (62). We have reported previously that Abs induced against polysialic acid (another Ag that extends a great distance from the cell surface) were not able to induce CDC against tumor cells (65).…”

Improving the Antigenicity of sTn Antigen by Modification of Its Sialic Acid Residue for Development of Glycoconjugate Cancer Vaccines

“…The protein conjugates of sTn antigen could indeed elicit humoral immune response that showed remarkable specificity for cancer cells (21). The keyhole limpet hemocyanin (KLH) conjugate of sTn antigen (19,20) has been developed and tested as a therapeutic vaccine (Theratope ® ) for treatment of metastatic breast cancer (22,23). Unfortunately, at the Phase III clinical trial Theratope ® failed to meet the endpoints of time-to-disease progression and overall survival rate (23), which was largely because it cannot induce strong T-cell-mediated immune response in patients.…”

The ST6GalNAc-I Sialyltransferase Localizes throughout the Golgi and Is Responsible for the Synthesis of the Tumor-associated Sialyl-Tn O-Glycan in Human Breast Cancer

“…Expression of STn in breast cancer correlates with poor prognosis (20) and predicts a poor response to chemotherapy (19), whereas expression of STn on normal tissues is highly restricted. Thus the STn O-glycan has been seen as a possible target for therapeutic intervention (21)(22)(23)(24). In human cells, the enzyme ST6GalNAc-I has been identified as a glycosyltransferase able to add sialic acid in ␣2,6 linkage to GalNAc linked to serine or threonine, thus creating the STn epitope (25).…”