Non-glycosylated G protein with CpG ODN provides robust protection against respiratory syncytial virus without inducing eosinophilia

Abstract

IntroductionRespiratory syncytial virus (RSV) vaccines targeting the fusion glycoprotein (F protein) are highly effective clinically in preventing RSV challenges. The attachment glycoprotein (G protein) is a potentially effective vaccine antigen candidate, as it is important for cell adhesion during infection. However, vaccine-associated enhanced diseases in mice, such as eosinophilic lung inflammation following RSV challenge, are a concern with G protein vaccines. This study aimed to design an effective G protein vaccine with enhanced safety and efficacy by evaluating the efficacy and adverse reactions of vaccines composed of different recombinant G proteins and adjuvants in mice.MethodsMice were subcutaneously immunized with glycosylated G protein expressed in mammalian cells (mG), non-glycosylated G protein expressed in Escherichia coli (eG), or F protein with or without aluminum salts (alum), CpG oligodeoxynucleotide (CpG ODN), or AddaVax. After vaccination, the levels of G-specific antibody and T-cell responses were measured. The immunized mice were challenged with RSV and examined for the viral load in the lungs and nasal turbinates, lung-infiltrating cells, and lung pathology.ResultsmG with any adjuvant was ineffective at inducing G-specific antibodies and had difficulty achieving both protection against RSV challenge and eosinophilia suppression. In particular, mG+CpG ODN induced G-specific T helper 1 (Th1) cells but only a few G-specific antibodies and did not protect against RSV challenge. However, eG+CpG ODN induced high levels of G-specific antibodies and Th1 cells and protected against RSV challenge without inducing pulmonary inflammation. Moreover, the combination vaccine of eG+F+CpG ODN showed greater protection against upper respiratory tract RSV challenge than using each single antigen vaccine alone.DiscussionThese results indicate that the efficacy of recombinant G protein vaccines can be enhanced without inducing adverse reactions by using appropriate antigens and adjuvants, and their efficacy is further enhanced in the combination vaccine with F protein. These data provide valuable information for the clinical application of G protein vaccines.

Development and Validation of an Enzyme-Linked Immunosorbent Assay-Based Protocol for Evaluation of Respiratory Syncytial Virus Vaccines

“…Finally, the G protein produced in this study was not glycosylated due to the use of the E. coli expression system, making it difficult to compare what would actually happen in vivo. Nevertheless, Kawahara et al reported that non-glycosylated G protein provided robust protection against RSV, as shown by the modest correlation with neutralizing activities in this study, particularly in children and adolescents ( Figure 4 ) [ 19 ].…”

Design and Preclinical Evaluation of a Nanoparticle Vaccine against Respiratory Syncytial Virus Based on the Attachment Protein G

“…The realization that the efficacy of viral vaccines does not necessarily depend on a strong response against the fusion protein was recognized for both influenza, where vaccine efficacy declined when the neuraminidase content was low [ 15 ], and for the paramyxovirus Hendra virus, for which an efficacious vaccine is approved based solely on the attachment protein H [ 16 , 17 ]. Although the G protein has been undervalued compared to F, the recent demonstration of strong neutralization in hAEC cultures of antibodies against G show the potential as a vaccine component [ 5 , 18 , 19 , 20 ], and protection from RSV challenge was demonstrated in mice after immunization with G [ 21 , 22 , 23 , 24 , 25 ]. Therefore, if durability and breadth of immunity elicited by current F-based RSV vaccines may turn out to be insufficient, inclusion of an additional RSV vaccine component based on the attachment protein G might increase the chance of durable and broad protection.…”