Expression of PspA fragments in the CyaA vector for the development of a broad-coverage vaccine against Streptococcus pneumoniae

• Grant number: 22/06501-0
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate (Direct)
• Start date: November 20, 2022
• End date: April 19, 2023
• Field of knowledge: Biological Sciences - Microbiology - Applied Microbiology
• Principal Investigator: Maria Leonor Sarno de Oliveira
• Grantee: Giovanna de Brito Carneiro
• Supervisor: Daniel Ladant
• Host Institution: Instituto Butantan. Secretaria da Saúde (São Paulo - Estado). São Paulo , SP, Brazil
• Institution abroad: Institut Pasteur, France
• Associated to the scholarship: 21/05671-7 - Development of vaccines against Streptococcus pneumoniae using bacterial components as adjuvants for the PspA antigen, BP.DD

Abstract

Streptococcus pneumoniae (pneumococcus) is an important human pathogen that causes diseases such as pneumonia, sepsis and meningitis, being responsible for several hospitalizations and deaths. Vaccines currently available on the market are composed of polysaccharides derived from the capsule of prevalent serotypes; however, an important concern is related to their efficacy limited to the serotypes included the formulations. Aiming at the development of broad-coverage pneumococcal vaccines, several protein antigens have been evaluated as vaccine candidates. Pneumococcal Surface Protein A (PspA) is a well-characterized antigen that has proven to be effective against pneumococcal disease in animal models. Based on antigenic variability, PspAs were classified into clades and grouped into families: clades 1 and 2 belong to family 1; clades 3, 4 and 5 belong to family 2; clade 6, rarely isolated, belongs to family 3. Cross-reactivity among clades from the same family has been reported, indicating that the development of a broad protective vaccine may be achieved with the use of few PspA molecules. An antigen delivery system based on the adenylate cyclase toxin (CyaA) from Bordetella pertussis has been tested for the presentation of PspA fragments to immune cells and has proven to elicit specific immune responses in mice. CyaA-PspA proteins were constructed with fragments derived from the N-terminal region (F5) of PspAs from clades 2 and 4, thus contemplating the two major PspA families. A formulation containing CyaA-PspA2-F5 and CyaA-PspA4-F5 induced high levels of anti-PspA antibodies that reacted in vitro with pneumococcal strains expressing PspAs from clades 2, 3, 4 and 5. This formulation was also able to protect mice against invasive pneumococcal challenges with isolates that express PspA2, PspA4 or PspA5. Moreover, a CyaA protein containing the fragments in fusion, CyaA-PspA2-F5-PspA4-F5, induced antibodies at similar levels and with similar reactivity as the formulation containing both proteins, and protected mice against the invasive challenge. Nevertheless, no cross-reactivity and lack of protection was observed with strains expressing PspA1. In order to improve the coverage of isolates, we propose the inclusion of PspA1-F5 in the CyaA-PspA formulations. Anti-PspA1-F5 hyperimmune sera presented high levels of reactivity with isolates expressing PspA1, which indicates the potential of this fragment to improve the coverage of the formulations being tested. For this project, we propose the production of CyaA-PspA1-F5, which may be used in combination with CyaA-PspA2-F5-PspA4-F5, and the construction of a single antigen candidate containing all three PspA fragments, CyaA-PspA1-F5-PspA2-F5-PspA4-F5. (AU)