Here, we report on the in vivo efficacy of a fully synthetic saccharide-glycolipid conjugate vaccine platform that allows for the multivalent display of glycan antigens with minimal synthetic effort. The weakly immunogenic cancer-associated Tn (α-N-acetylgalactosamine linked to serine or threonine)24,25 served as a model antigen that was efficiently coupled to the glycosphingolipid α-GalCer. This internal immune stimulatory moiety has recently been shown to promote strong antibody responses when coformulated26 or covalently coupled with polysaccharides23 or peptides.27,28 The liposome-formulated self-adjuvanting Tn-α-GalCer conjugate consistently induced strong anti-Tn antibody responses characterized by an immunoglobulin switch to IgG and affinity maturation in all immunized mice. Control liposomes prepared with stearoylated Tn lacking the α-GalCer moiety were also immunogenic but elicited lower antibody levels. In contrast, a semisynthetic glycoconjugate composed of the Tn antigen and the carrier protein CRM197 induced antiglycan IgG only in a subset of immunized mice. Larger liposomes (∼400 nm diameter) promoted Th1-type IgG2a antibodies, while smaller ones(∼120 nm) favored the production of IgG1 associated with Th2-mediated immunity. Thus, modulating the size of liposomes allows for directing antiglycan antibody responses toward either cellular (Th1) or humoral (Th2) immunity. Overall, this study establishes a vaccine platform based on fully synthetic saccharide-α-GalCer conjugates for the robust generation of high-affinity IgG even against the weakly immunogenic carbohydrate antigen Tn.