Boosting Respiratory Immunity with Nasal Commensals and Advancing a Novel Recombinant Vaccine Against Bordetella Pertussis Infection

Abstract

Whooping cough caused by Bordetella pertussis (B. pertussis) is a contagious respiratory tract disease. Acellular pertussis (aP) vaccines were developed as a replacement for whole-cell pertussis (wP) vaccines, which contain inactivated pertussis toxin (PTX) and other bacterial components, filamentous hemagglutinin (FHA) and pertactin (PRN). However, whooping cough outbreaks occurred in aP-vaccinated populations because of the limited and transient T helper 1 (Th1) / T helper 17 (Th17)-mediated immunogenicity of aP vaccines as well as their propensity to generate T helper 2 (Th2)-biased immune responses. To overcome the limitations of these aP vaccines, we developed two promising strategies: (1) administering nasal commensals to protect the host against respiratory pathogens through mucosal immune boosting and (2) developing novel recombinant aP (NRaP) vaccines based on recombinant pertussis proteins. Nasal commensals reside in the upper respiratory mucus layer, which is the first line of defense and acts as a gatekeeper of the respiratory tract. The respiratory microbiome protects the host through direct competition with pathogens and indirectly modulates innate and adaptive immune responses. Bacteria that are frequently found in nasal mucosal niches are Staphylococcus species. Staphylococcus epidermidis (S. epidermidis) is a representative microbiota that restricts opportunistic pathogen invasion by secreting serine proteases or inducing proinflammatory cytokine production by stimulating the nasal epithelium. To investigate the immunological properties of this bacterium, we inoculated S. epidermidis and identified its antimicrobial effects using a B. pertussis infection mouse model. We revealed that S. epidermidis enhances the IL-17a+ mediated immune responses and suppresses B. pertussis colonization in acute infection. We have engineered a novel subunit pertussis vaccine by introducing pertussis antigens into competent cells, aiming to boost the immunogenicity of current aP vaccines. Mice immunized with this new vaccine, ChaH2-Prn, exhibited higher titers of Prn-specific IgG antibodies compared to those immunized with the conventional aP vaccines. Moreover, mice vaccinated with our NRaP vaccine demonstrated a reduced bacterial load in the lungs following B. pertussis infection, indicating an enhanced protective response. Furthermore, our research has shed light on the antibacterial properties of nasal commensals that activate mucosal immunity and offer immediate defense against bacterial pathogens. By improving upon the NRaP vaccines, we have addressed the shortcomings of current aP vaccines and introduced a promising approach for bolstering immunogenicity to prevent B. pertussis infections. 백일해 균은 호흡기 질환을 유발하는 전염성이 강한 기회 감염균으로 폐의 상피에 결합하여 독소를 분비 하며 주변 면역 세포들을 자극한다. 1940년대에는 백일해 균 전 세포 사백신이 개발되었지만, 독성이 강하다는 단점이 있어 이를 개선하고자 백일해 주요 항원인 Pertussis toxin, Filamentous hemagglutinin, Pertactin을 표적화한 백신이 개발되었다. 하지만 이는 백일해 균의 주요 T 도움 1/17 세포 (Th1/Th17)의 분화 보다는 T 도움 2 세포 (Th2)의 면역 반응이 증진되어 접종 후에도 백일해 균이 폐에 높게 검출된다는 한계가 있다. 또한, 백신 접종 후에도 방어 면역이 2년 이상 지속되지 못한다는 점에서 높은 백신 접종률에도 백일해가 반복하여 발생한다. 따라서, 백일해 감염이 지속하는 현 시점에서 본 연구에서는 두 가지 전략을 통해 호흡기 감염으로 부터 예방하고자 한다. 비강 내 공생 미생물이 호흡기 면역을 증진 시키며 백일해 균의 감염이 급성 감염 시기에 억제되는 것을 확인하였다. 또한 대장균에서 유래한 새로운 재조합 단백질 백일해 백신 개발을 통해 상용화되는 백신의 낮은 면역원성의 한계를 극복하고자 했고, 증진된 백신 면역원성을 백일해 감염 마우스 모델을 통해 검증하였다. 이를 통해 백일해 감염 뿐만 아니라 호흡기 감염을 억제할 수 있는 적절한 모델로 활용될 수 있을 것이다.