Structure Guided Design of Bacteriophage Qβ Mutants as Next Generation Carriers for Conjugate Vaccines

Abstract

Vaccines are critical tools to treat and prevent diseases. For an effective conjugate vaccine, the carrier is crucial, but few carriers are available for clinical applications. In addition, a drawback of current protein carriers is that high levels of antibodies against the carrier are induced by the conjugate vaccine, which are known to interfere with the immune responses against the target antigen. To overcome these challenges, we obtained the near atomic resolution crystal structure of an emerging protein carrier, i.e., the bacteriophage Qβ virus like particle. On the basis of the detailed structural information, novel mutants of bacteriophage Qβ (mQβ) have been designed, which upon conjugation with tumor associated carbohydrate antigens (TACAs), a class of important tumor antigens, elicited powerful anti-TACA IgG responses and yet produced lower levels of anticarrier antibodies as compared to those from the wild type Qβ-TACA conjugates. In a therapeutic model against an aggressive breast cancer in mice, 100% unimmunized mice succumbed to tumors in just 12 days even with chemotherapy. In contrast, 80% of mice immunized with the mQβ-TACA conjugate were completely free from tumors. Besides TACAs, to aid in the development of vaccines to protect against COVID-19, the mQβ based conjugate vaccine has been shown to induce high levels of IgG antibodies against peptide antigens from the SARS-CoV-2 virus, demonstrating its generality. Thus, mQβ is a promising next-generation carrier platform for conjugate vaccines, and structure-based rational design is a powerful strategy to develop new vaccine carriers.

Virus-like Particle Display of Vibrio cholerae O-Specific Polysaccharide as a Potential Vaccine against Cholera

“…Lactoside 3 was prepared by derivatizing lactose 4 24 with dimethyl squarate 2 in 76% yield (Scheme S1). In parallel, the coat protein of Qβ triple mutant A38K/A40C/D102C was expressed in E. coli, 25 which selfassembled into nanoparticles with average diameters of 28 nm consisting of 180 copies of the monomer. The Qβ triple mutant A38K/A40C/D102C was selected as the carrier as it has been shown to induce lower levels of antibodies against the carrier itself as compared to the wild type Qβ, thus leading to stronger IgG antibody responses against the target antigen.…”

“…The Qβ triple mutant A38K/A40C/D102C was selected as the carrier as it has been shown to induce lower levels of antibodies against the carrier itself as compared to the wild type Qβ, thus leading to stronger IgG antibody responses against the target antigen. 25 The lactoside 3 (14 equiv per monomer) was then incubated with Qβ at 22 °C for 20 h leading to the Qβ-lactose conjugate 5 (Scheme S1). In order to quantify the degree of modification, surface-enhanced laser desorption/ionization time-of-flight (SELDI-TOF) mass spectrometry analysis was performed (Figure S1).…”

“…coli, which self-assembled into nanoparticles with average diameters of 28 nm consisting of 180 copies of the monomer. The Qβ triple mutant A38K/A40C/D102C was selected as the carrier as it has been shown to induce lower levels of antibodies against the carrier itself as compared to the wild type Qβ, thus leading to stronger IgG antibody responses against the target antigen . The lactoside 3 (14 equiv per monomer) was then incubated with Qβ at 22 °C for 20 h leading to the Qβ-lactose conjugate 5 (Scheme S1).…”

“…22 Qβ capsid was expressed recombinantly following the reported procedure. 25,45 Qβ Conjugation to Lactoside 3 and Purification. A stock solution of 4.8 mg/mL Qβ in 0.1 M (pH 7.0) KPB buffer (208 μL) was placed in a Millipore Amicon Ultra-0.5 (10k Da cutoff) ultrafiltration device and the content was ultrafiltered against 0.5 M pH 9.0 borate buffer for three times (at 10 °C, 7500 rcf, 10 min/run) to exchange the buffer to 0.5 M pH 9.0 borate buffer.…”

“…OSP and BSA-OSP was produced as previously described . Qβ capsid was expressed recombinantly following the reported procedure. , …”