Protective Epitope Discovery and Design of MUC1-based Vaccine for Effective Tumor Protections in Immunotolerant Mice

Abstract

Human mucin-1 (MUC1) is a highly attractive antigen for the development of anticancer vaccines. However, in human clinical trials of multiple MUC1 based vaccines, despite the generation of anti-MUCl antibodies, the antibodies often failed to exhibit much binding to tumor presumably due to the challenges in inducing protective immune responses in the immunotolerant environment. To design effective MUC1 based vaccines functioning in immunotolerant hosts, vaccine constructs were first synthesized by covalently linking the powerful bacteriophage Qβ carrier with MUC1 glycopeptides containing 20–22 amino acid residues covering one full length of the tandem repeat region of MUC1. However, IgG antibodies elicited by these first generation constructs in tolerant human MUC1 transgenic (Tg) mice did not bind tumor cells strongly. To overcome this, a peptide array has been synthesized. By profiling binding selectivities of antibodies, the long MUC1 glycopeptide was found to contain immunodominant but nonprotective epitopes. Critical insights were obtained into the identity of the key protective epitope. Redesign of the vaccine focusing on the protective epitope led to a new Qβ-MUC1 construct, which was capable of inducing higher levels of anti-MUC1 IgG antibodies in MUC1.Tg mice to react strongly with and kill a wide range of tumor cells compared to the construct containing the gold standard protein carrier, i.e., keyhole limpet hemocyanin. Vaccination with this new Qβ-MUC1 conjugate led to significant protection of MUC1.Tg mice in both metastatic and solid tumor models. The antibodies exhibited remarkable selectivities toward human breast cancer tissues, suggesting its high translational potential.

Viral nanoparticles for drug delivery, imaging, immunotherapy, and theranostic applications

“…For example, Qβ has been engineered to present TACAs such as the poorly immunogenic monomeric Tn antigen and the ganglioside antigen GM2 [156,157]. Furthermore, tumor associated MUC1 glycopeptide antigens were conjugated to Qβ, and the obtained Qβ-MUC1 vaccine induced high titers of anti-MUC1 IgG antibodies in both MUC1 transgenic and WT mice, conferring protection against primary and metastatic breast cancers [158][159][160]. Likewise, Huang et al developed CPMV-TACA conjugates, specifically targeting the Tn antigen (GalNAc-α-O-Ser/Thr) [161].…”

Carbohydrate Conjugates in Vaccine Developments

“…Like most types of carbohydrate antigens, TACAs induce only weak IgM responses when administered alone. For successful TACA vaccines, TACAs are commonly conjugated with strong immunogenic proteins, such as bovine serum albumin (BSA), tetanus toxoid (TT), keyhole limpet hemocyanin (KLH), and virus like particles, in order to generate high levels of IgG responses (Kaltgrad et al, 2007;Heimburg-Molinaro et al, 2011;Wu et al, 2018Wu et al, , 2019. However, these carrier proteins can result in carrier induced suppression of antibody responses to the desired TACA due to high antibody responses to the carrier itself (Leclerc et al, 1990).…”

Going Native: Synthesis of Glycoproteins and Glycopeptides via Native Linkages To Study Glycan-Specific Roles in the Immune System

“…However, the recent emergence of patient-specific vaccine strategies may in future also be applied here. 61 We therefore strongly encourage the immunology and carbohydrate communities to join forces to an extent that is much larger than what is being done today. Such collaborations will almost certainly lead to many exciting discoveries which will greatly advance our fundamental as well as translational scientific view of the immune system in action.…”