Transregional Collaborative Research Center SFB-TR 84 - “Innate Immunity of the Lung: Mechanisms of Pathogen Attack and Host Defence in Pneumonia“

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C8-Subproject

Tuning innate immune responses to augment anti-carbohydrate vaccines against bacterial pneumonia (Seeberger / Sander)

 

Persistently high mortality-rates of bacterial pneumonia combined with an unparalleled increase of antibiotic resistance in recent years, especially in the gram-negative spectrum, urgently call for the development for new, efficacious vaccines against respiratory pathogens.

Opsonizing and bactericidal antibodies are often directed against capsular polysaccharide (PS) epitopes (=glycotopes). Thus, major efforts have been focused on capsular PSs as antigens for vaccines. However, the current approach has major limitations, since PS isolation is a complex, expensive and poorly controlled step, often forming a bottleneck in the entire vaccine manufacturing process. To date, bacterial PSs are purified from industry-scaled bacterial cultures through a series of fermentation and filtration steps, yielding PSs with varying amounts of impurities including bacterial cell wall and broth constituents. Moreover, not all pathogens can be cultured, especially on large scale; and not all carbohydrates can be isolated.

The Seeberger group has previously established a unique, fully automated system for solid-phase carbohydrate synthesis. Using this system, the Seeberger lab has generated a fully synthetic tetrasaccharide from the capsule of S. pneumoniae (SP) serotype 3 (SP3tetra) conjugated to CRM197 carrier protein. In collaboration between the Sander and the Seeberger groups we showed that immunization with the SP3-tetra conjugate induces the production of antibodies with opsonophagocytic activity that confers protection against pneumococcal pneumonia in mice.

Given that adaptive immunity is critically shaped by the innate immune system, it is not surprising that the efficacy of SP3tetra conjugate is strongly dependent on the adjuvant. Alum, the most widely used adjuvant in human vaccines, elicited only moderate antibody production as compared to complete Freund’s adjuvant (CFA), which is not suitable for clinical applications. Moreover, alum failed to induce sustained protection, indicating a deficiency to generate sufficient immune memory and long-lived antibody responses. Ideally, adjuvants should be designed to selectively elicit specific innate immune responses that instruct the desired mode of adaptive immunity. T helper 1 (TH1) directing adjuvants potently augment humoral responses to glycoconjugate vaccines. The Sander group has previously discovered that live bacteria contain a specialized class of pathogen associated molecular patterns (PAMPs), called viability-associated PAMPs (vita-PAMPs), which are powerful inducers of innate and subsequent adaptive anti-bacterial immune responses, when recognized in the context of phagocytosed bacteria. Therefore, we will identify combinations of (vita-)PAMPs and/or synthetic ligands capable of recapitulating the innate and adaptive immune responses induced by live bacteria. To this end, we will encapsulate ligand combinations into biodegradable microparticles and assess their capacity to stimulate innate and subsequent adaptive immune responses. With this approach we aim to combine the often-observed superiority of live vaccines with the safety and stability of dead ones. We intend to further broaden and enhance the immunoprotective effects of SP3tetra by replacing CRM197 with conserved pneumococcal proteins (PdB and PspA) as carriers. Moreover, we will deliver this novel particulate, fully synthetic carbohydrate-conjugate vaccine intranasally, thereby enhancing local immunity, as well as vaccine compliance and applicability in regions with limited medical infrastructure and personnel. Finally, we will use this system as a blueprint to develop a synthetic carbohydrate conjugate vaccine against K. pneumonia, a leading cause of hospital acquired pneumonia, often associated with multidrug resistance and high mortality.

In summary, we will combine our unique sets of expertise in the fields of synthetic glycochemistry and innate immunity to jointly develop a new generation of fully synthetic, highly efficacious vaccines against respiratory bacterial pathogens.