The development of an effective immunotherapy is an attractive strategy towards cancer treatment. Tumor associated carbohydrate antigens (TACAs) are overexpressed on a variety of cancer cell surfaces, which present tempting targets for anti-cancer vaccine development. However, such carbohydrates are often poorly immunogenic. To overcome this challenge, we show here that the display of a very weak TACA, the monomeric Tn antigen, on bacteriophage Qβ virus-like particles elicits powerful humoral responses to the carbohydrate. The effects of adjuvants, antigen display pattern and vaccine dose on the strength and subclasses of antibody responses were established. The local density of antigen rather than the total amount of antigen administered was found to be crucial for induction of high Tn-specific IgG titers. The ability to display antigens in an organized and high density manner is a key advantage of virus like particles such as Qβ as vaccine carriers. Glycan microarray analysis showed that the antibodies generated were highly selective towards Tn antigens. Furthermore, Qβ elicited much higher levels of IgG antibodies than other types of virus like particles and the IgG antibodies produced reacted strongly with the native Tn antigens on human leukemia cells. Thus, Qβ presents a highly attractive platform for the development of carbohydrate based anti-cancer vaccines.

Tumor associated carbohydrate antigens (TACAs) are being actively studied as targets for anti-tumor vaccine development. One serious challenge was the low immunogenecity of these antigens. Herein, we report the results on using the tobacco mosaic virus (TMV) capsid as a promising carrier of a weakly immunogenic TACA, the monomeric Tn antigen. The copper(I) catalyzed azide-alkyne cycloaddition reaction was highly efficient in covalently linking Tn onto the TMV capsid without resorting to a large excess of the Tn antigen. The location of Tn attachment turned out to be important. Tn introduced at the N terminus of TMV was immunosilent, while that attached to tyrosine 139 elicited strong immune responses. Both Tn specific IgG and IgM antibodies were generated as determined by enzyme linked immunosorbent assay and a glycan microarray screening study. The production of high titers of IgG antibodies suggested that the TMV platform contained the requisite epitopes for helper T cells and was able to induce antibody isotype switching. The antibodies exhibited strong reactivities towards Tn antigen displayed in its native environment, i.e., cancer cell surface, thus highlighting the potential of TMV as a promising TACA carrier.