Boosting Immunity to Small Tumor-Associated Carbohydrates with Bacteriophage Qβ Capsids

Abstract

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.

Significant Impact of Immunogen Design on the Diversity of Antibodies Generated by Carbohydrate-Based Anticancer Vaccine

“…Next, the density of Tn on Q β was increased from 340 to 540 (Q β –Tn 5 , Figure 1D), since higher local antigen density was previously shown to enhance anti-Tn antibody titers. 32 of 49 100), while the average triazole titer increased to 175 000 (Figure 1F). The postimmune sera from mice immunized with Q β –Tn 4 or Q β –Tn 5 again failed to bind with TA3Ha cells.…”

“…We became interested in investigating the utility of VLPs such as bacteriophage Q β as a carrier for Tn. Our first generation construct Q β –Tn 1 was synthesized using the copper-catalyzed alkyne–azide cyclo-addition (CuAAC) click reaction, 32 which attached an average of 340 copies of Tn per Q β capsid through a triazole linker (termed internal triazole), as well as 200 copies of triazole without Tn (external triazole) (Figure 1A). Mice were immunized with Q β –Tn 1 with two booster injections on days 14 and 28.…”

The True Story and Advantages of RNA Phage Capsids as Nanotools

“…The display of small antigens, such as nicotine [231,232,233,234] or carbohydrate moieties [235,236], on RNA phage VLP surfaces is a novel approach that enabled the generation of strong immunological responses against nonpeptide antigens and paved the way for the development of experimental vaccines against nicotine addiction and cancer, respectively. We recommend a recent review on novel vaccines constructed on RNA phage VLPs [237] as well as special reviews on vaccines against allergies [238,239,240], Alzheimer disease [241], hypertension [242,243,244], influenza [245,246], malaria [247], and nicotine addiction [248,249,250,251,252].…”

Strategies to guide the antibody affinity maturation process

“…The goal of extended antigen presence may be achieved with replication-competent vectors such as adenovirus-4, or non-replicating systems that have slow release or long residency in secondary lymphoid tissue [93]. Nanoparticles [94] such as ferritin displaying viral proteins [95] are preferentially taken up by dendritic cells [96], with the added benefit of improved B cell receptor clustering and activation and increased immunogenicity [97–99]. …”