THE INCREASING prevalence of invasive beta-haemolytic streptococcal (iBHS) infections has raised concerns and highlighted the need for preventive strategies, particularly for high-risk populations. One promising avenue under investigation is the development of a vaccine targeting Streptococcus pyogenes (Strep A), the primary agent in iBHS infections. If cross-species immunity could be established against other related streptococcal species – specifically Streptococcus dysgalactiae subspecies equisimilis (SDSE) and Streptococcus agalactiae (GBS) – the potential impact of such a vaccine could be significantly enhanced.
In a recent study, researchers conducted a prospective, observational analysis of adult patients with iBHS infections caused by Strep A, SDSE, or GBS. This study aimed to assess whether patients infected with these different strains produce antibodies against specific Strep A antigens and whether these responses could suggest cross-protection among species. The study involved testing acute and convalescent sera from participants for antibody responses to six candidate Strep A vaccine antigens. A serological response was considered positive if antibody levels increased by more than 0.2 log10 arbitrary units/mL (AU/mL).
Out of 67 participants, 33 were included in the final analysis: 12 with Strep A, 11 with SDSE, and 10 with GBS. For Strep A-infected participants, the antibody responses to all six tested antigens were significantly elevated, indicating a strong immune response. Participants with SDSE also demonstrated significant antibody responses to three specific antigens: streptolysin-O, the S. pyogenes adhesion and division protein, and C5a peptidase (ScpA). Responses in GBS-infected participants were more limited, showing a significant increase only to ScpA.
These findings suggest that a Strep A vaccine targeting non-M protein antigens could potentially provide cross-species immunity against SDSE and, to a lesser extent, GBS. In particular, the C5a peptidase antigen appears to play a role in cross-species immune responses, warranting further investigation. This research underscores the importance of continued exploration into the cross-protective potential of Strep A vaccines, which could lead to broader immunological protection against multiple types of invasive streptococcal infections.
Katie Wright, EMJ
Reference
Langworthy K et al. Serological responses to target Streptococcus pyogenes vaccine antigens in patients with proven invasive beta-haemolytic streptococcal infections. J Infect Dis. 2024;DOI:10.1093/infdis/jiae496.
