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 cell s. The CaMBr1 hexasaccharide antigen, originally defined on the human breas t carcinoma cell line MCF7, is expressed on some normal tissues but overexp ressed in a high percentage of human breast, ovary, prostate and lung carci nomas. CaMBr1 overexpression is associated with poor prognosis. The epitope consists of the tetrasaccharide Fuc(alpha 1-2)Gal(beta 1 -3)GalNAc(beta 1 -3)Gal alpha-O-spacer, which has recently become available as a synthetic o ligosaccharide. Here we report the CaMBr1 tetrasaccharide conjugation to tw o different carrier proteins (CRM197 and KLH) and the evaluation of conjuga te immunogenicity in mice following their administration in various vaccine formulations with two adjuvants (MPL-SE and Deter-PC). Radioimmunoassay to determine the level and isotype of anti-tetrasaccharide antibodies in mous e sera, and cytofluorimetric analysis and Cr-51-release assay on human tumo r cells, to evaluate specificity of binding and complement-dependent lysis respectively, identified CaMBr1-CRM197, in association with the MPL-SE adju vant, as the best vaccine formulation. This combination induced (1) product ion of tetrasaccharide-specific antibodies, with negligible side-effects; ( 2) antibodies with complement-mediated cytotoxic activity on human CaMBr1-p ositive cells and (3) a high titer of IgG1 detected in sera obtained 3 mont hs after the first injection, indicating that the anti-tetrasaccharide anti body response was mediated by T cell activation. The availability of CaMBr1 -glycoconjugate in the minimal and functional antigenic structure and the i dentification of an efficacious vaccine formulation opens the way to explor ing the activity of this glycoconjugate in a clinical setting.