Challenges in Antibody Development against Tn and Sialyl-Tn Antigens

Abstract

The carbohydrate antigens Tn and sialyl-Tn (STn) are expressed in most carcinomas and usually absent in healthy tissues. These antigens have been correlated with cancer progression and poor prognosis, and associated with immunosuppressive microenvironment. Presently they are used in clinical trials as therapeutic vaccination, but with limited success due to their low immunogenicity. Alternatively, anti-Tn and/or STn antibodies may be used to harness the immune system against tumor cells. Whilst the development of antibodies against these antigens had a boost two decades ago for diagnostic use, so far no such antibody entered into clinical trials. Possible limitations are the low specificity and efficiency of existing antibodies and that novel antibodies are still necessary. The vast array of methodologies available today will allow rapid antibody development and novel formats. Following the advent of hybridoma technology, the immortalization of human B cells became a methodology to obtain human monoclonal antibodies with better specificity. Advances in molecular biology including phage display technology for high throughput screening, transgenic mice and more recently molecularly engineered antibodies enhanced the field of antibody production. The development of novel antibodies against Tn and STn taking advantage of innovative technologies and engineering techniques may result in innovative therapeutic antibodies for cancer treatment.

Novel anti-Sialyl-Tn monoclonal antibodies and antibody-drug conjugates demonstrate tumor specificity and anti-tumor activity

“…Historically, glycans have been difficult targets to raise a robust immune response against 14,33 . We have completed multiple rounds of mouse STn immunization to optimize the immunogen and adjuvant selected.…”

“…TACAs are poorly immunogenic, and thus making effective vaccines or antibodies against these targets has proven difficult 14 . Previous antibody development efforts used purified glycoproteins from cancer samples and Freund's adjuvant, or mucin-coated heat-inactivated bacteria, for mouse immunization.…”

“…Previous antibody development efforts used purified glycoproteins from cancer samples and Freund's adjuvant, or mucin-coated heat-inactivated bacteria, for mouse immunization. These approaches have resulted in the development of several murine anti-STn monoclonal antibodies (mAbs), including B72.3 19 (and its successor antibody CC49 20 ), TKH2, 21 and HB-STn1(clone 3F1 21,22 ), and others 14 . The target specificity of these mAbs have come into question as these mAbs bind additional glycan targets and may have glycoprotein preferences for antigen recognition 23 .…”

Targeting cancer-specific glycans by cyclic peptide lectinomimics

“…Significant efforts have been undertaken to produce glycan-specific antibodies (Dalziel et al 2014; Fuster and Esko 2005) However, these have been difficult, as glycans are poor immunogens often resulting in weak affinity IgM antibodies with limited clinical value and low specificity of existing antibodies (Pinho and Reis 2015; Sterner et al 2016) One of the most promising and the most widely explored tumor-associated glycan structures in many diagnostic and (immuno)therapeutic approaches are truncated mucin-type O -glycans such as Tn (αGalNAc-Thr/Ser), sTn (αNeu5Ac-(2,6)-αGalNAc-Thr/Ser), and T (Galβ1-3GalNAcα1- O -Ser/Thr) (Cazet et al 2010) The major protein carrier of these tumor-associated glycans is the MUC1 glycoprotein, highly expressed in a variety of epithelial cancers, but absent from normal tissues (Nath and Mukherjee 2014) Despite the great potential, the generation of clinically relevant human antibodies with good affinity and specificity for tumor-associated glycans of MUC1 proves to be a challenging task (Loureiro et al 2015; Feng et al 2016) Identification of MUC1 glycan/peptide epitopes within a MUC1 tandem repeat, which are able to overcome immunological self-tolerance and yet induce stronger and long-lasting immune response is the current focus of immunotherapy approaches (McDonald et al 2015; Hossain and Wall 2016) An excellent example of such approaches is the PankoMab-GEX, a humanized monoclonal antibody that binds to a novel carbohydrate-induced conformational epitope on MUC1 (glycopeptide epitope) with a high affinity, which is currently undergoing clinical trials for ovarian cancer (Fiedler et al 2016)…”

C1GALT1 Seems to Promote In Vitro Disease Progression in Ovarian Cancer

“…9Y11 Despite the diversity of glycans at the cell surface, only a few distinct structures are associated with malignant transformation and tumor progression, such as Tn, sialyl-Tn (sTn), T, sialyl Lewis X , and sialyl Lewis A antigens. 12,13 The sTn antigen is the GalNAc residue on Tn antigen bound with a sialic acid. The sialyl-T (sT) antigen is the Gal residue on T antigen bound with a sialic acid.…”