A study of a virus-like particle vaccine against Aspergillus fumigatus

Abstract

Aspergillus fumigatusis one of the ubiquitous fungi with airborne conidia, which accounts for most cases of aspergillosis. In immunocompetent hosts, the inhaled conidia are rapidly eliminated. However, immunocompromised or immunodeficient hosts are particularly vulnerable to most Aspergillus infections and invasive aspergillosis (IA), with the mortality from above 50%to 95%.Despite the improvement of antifungal drugs over the last few decades, the therapeutic effect for IA patients is still limited and do not provide significant survival benefits. The antifungal drugs are usually associated with side effects, drug resistance as well as high costs. These drawbacks highlight the importance of finding novel therapeutic and preventive approaches to fight against IA. The development of antifungal vaccines is therefore proposed as an attractive strategy. In this study, a virus-like particle (VLP) vaccine was developed in order to obtain a potent vaccine against Aspergillus fumigatus. As a virus-like particle carrier model, Hepatitis B virus core (HBc) particle not only can be easily and rapidly produced in various known expression systems, but also elicits strong B cell, T helper and cytotoxic T cell immune responses. Moreover, the capability of HBc particle to preferentially induce Th1 cells response makes it attractive as an antigen carrier in the development of novel antifungal vaccines. Therefore, in this investigation, a cell wall mannoprotein of A. fumigatus–AFMP4, as a promising antigen, was inserted into the HBc VLP to develop a candidate antifungal vaccine against A. fumigatus. The efficacy of this VLP vaccine was evaluated in a murine model. Briefly, HBc149-AFMP4 VLPs were firstly expressed in Escherichia coli system and purified by the ÄKTA™ FPLC system. However, this HBc149-AFMP4 VLP vaccine failed to protect mice from lethal challenge of IA. Therefore, some modifications for vaccine optimization were made. Firstly, Pichnia pastoris was used instead of the E. coli expression system. Secondly, full-length HBc (1-183aa)particles were employed instead of C-terminal truncated HBc (1-149aa) particles. Then, HBc183-AFMP4 VLPs were expressed using the P. pastoris system and purified by FPLC. To assess the efficacy of this HBc183-AFMP4 VLP vaccine, BALB/c mice were immunized for three times and then lethally challenged with A. fumigatus conidia. ELISA results showed that higher levels of AFMP4-specific antibodies were induced by this VLP vaccinations. This VLP vaccine protected 30%of the infected mice from lethal A. fumigatus challenge. The ELISPOT results revealed that this HBc183-AFMP4 VLP vaccinations stimulated great Th1 cell response, and implied that the protection might originate from the cell-mediated immune response. In summary, the experimental results of this study showed that the HBc183-AFMP4 VLP vaccination could induce strong AFMP4-specific B cell and Th1 cell immune responses, as well as partial protection against the lethal challenge, whereas AFMP4protein alone did not provide effective protection against the same challenge. The difference in the effects of protection may probably be related to the involvement of HBc particles. These results provided significant instructions for the development of VLP-based antifungal vaccines.