Development of a new vaccine formulation that enhances the immunogenicity of tumor-associated antigen CaMBr1.

Aberrant glycosylation is one of the most constant traits of malignant cells. The CaMBr1 hexasaccharide antigen, originally defined on the human breast carcinoma cell line MCF7, is expressed on some normal tissues but overexpressed in a high percentage of human breast, ovary, prostate and lung carcinomas. CaMBr1 overexpression is associated with poor prognosis. The epitope consists of the tetrasaccharide Fuc(alpha1-2)Ga1(beta1-3)GalNAc(beta1-3)Ga1alpha-O-spacer, which has recently become available as a synthetic oligosaccharide. Here we report the CaMBr1 tetrasaccharide conjugation to two different carrier proteins (CRM197 and KLH) and the evaluation of conjugate immunogenicity in mice following their administration in various vaccine formulations with two adjuvants (MPL-SE and Detox-PC). Radioimmunoassay to determine the level and isotype of anti-tetrasaccharide antibodies in mouse sera, and cytofluorimetric analysis and 51Cr-release assay on human tumor cells, to evaluate specificity of binding and complement-dependent lysis respectively, identified CaMBr1-CRM197, in association with the MPL-SE adjuvant, as the best vaccine formulation. This combination induced (1) production of tetrasaccharide-specific antibodies, with negligible side-effects; (2) antibodies with complement-mediated cytotoxic activity on human CaMBr1-positive cells and (3) a high titer of IgG1 detected in sera obtained 3 months after the first injection, indicating that the anti-tetrasaccharide antibody response was mediated by T cell activation. The availability of CaMBr1-glycoconjugate in the minimal and functional antigenic structure and the identification of an efficacious vaccine formulation opens the way to exploring the activity of this glycoconjugate in a clinical setting.