The present invention provides immunogenic compounds which stimulate immune responses in a subject. The present invention provides compositions comprising an isolated glycoprotein antigen covalently bound at pre-existing carbohydrate residues present on the glycoprotein to a carbohydrate epitope. The present invention also provides a method to induce an immune response in a subject comprising administering the compounds of the invention. The present invention further provides methods of making the compounds of the invention and methods of using the compounds of the invention to stimulate immune responses to infectious disease agents and tumors.