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Self-assembly of polystyrene sulfonate and modified cowpea chlorotic mottle virus protein yields monodisperse icosahedral nanoparticles of 16 nm size.

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.

In this paper, we describe the controlled incorporation of two synthetic polymers with different structures in the cowpea chlorotic mottle virus (CCMV) capsid. Poly(ethylene glycol) (PEG) chains have been attached to the amine groups of lysine residues on the outer surface of the viral capsid. The functionalization of CCMV with PEG chains provoked a slow but irreversible dissociation of the virus into PEG-coat protein (CP) subunits, likely due to steric interference between the protein-protein subunits as a result of the presence of the PEG chains. This thermodynamic instability, however, can be overcome if a second polymer, such as polystyrene sulfonate (PSS), is present within the capsid. After complete disassembly of the PEG-CCMV conjugates and removal of the viral RNA, incubation of the PEG-functionalized coat proteins with PSS resulted in the formation of much more robust PSS-CCMV-PEG capsids with a diameter of 18 nm (T = 1 capsids). These are the first virus-like particles bearing synthetic organic polymers both inside and outside the viral capsid, opening a new route to the synthesis of biohybrid nanostructured materials based on viruses.

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