Predicted Coverage and Immuno-Safety of a Recombinant C-Repeat Region Based Streptococcus pyogenes Vaccine Candidate.

Celia Mcneilly,Anna Henningham,Louise M Hafner,Anne Fane,David J Mcmillan,Therese Vu,Catherine M Rush,Pierre R Smeesters,Andreas Hofmann,Kadaba S Sriprakash,Samantha Cosh,Natkuman Ketheesan,Jemma Nichols

doi:10.1371/journal.pone.0156639

Abstract

The C-terminal region of the M-protein of Streptococcus pyogenes is a major target for vaccine development. The major feature is the C-repeat region, consisting of 35–42 amino acid repeat units that display high but not perfect identity. SV1 is a S. pyogenes vaccine candidate that incorporates five 14mer amino acid sequences (called J14i variants) from differing C-repeat units in a single recombinant construct. Here we show that the J14i variants chosen for inclusion in SV1 are the most common variants in a dataset of 176 unique M-proteins. Murine antibodies raised against SV1 were shown to bind to each of the J14i variants present in SV1, as well as variants not present in the vaccine. Antibodies raised to the individual J14i variants were also shown to bind to multiple but different combinations of J14i variants, supporting the underlying rationale for the design of SV1. A Lewis Rat Model of valvulitis was then used to assess the capacity of SV1 to induce deleterious immune response associated with rheumatic heart disease. In this model, both SV1 and the M5 positive control protein were immunogenic. Neither of these antibodies were cross-reactive with cardiac myosin or collagen. Splenic T cells from SV1/CFA and SV1/alum immunized rats did not proliferate in response to cardiac myosin or collagen. Subsequent histological examination of heart tissue showed that 4 of 5 mice from the M5/CFA group had valvulitis and inflammatory cell infiltration into valvular tissue, whereas mice immunised with SV1/CFA, SV1/alum showed no sign of valvulitis. These results suggest that SV1 is a safe vaccine candidate that will elicit antibodies that recognise the vast majority of circulating GAS M-types.

Highlights

Streptococcus pyogenes is Gram-positive bacterium responsible for a wide range of diseases in humans
Subsequent histological examination of heart tissue showed that 4 of 5 mice from the M5/Complete Freund's Adjuvant (CFA) group had valvulitis and inflammatory cell infiltration into valvular tissue, whereas mice immunised with SV1/CFA, SV1/alum showed no sign of valvulitis
The selection of the J14i variants present in SV1 was originally made after the examination of genes representing 77 different emm-types that were present in the Genbank database [19]

Summary

Introduction

Streptococcus pyogenes (group A streptococcus, GAS) is Gram-positive bacterium responsible for a wide range of diseases in humans These include self-limiting pharyngitis, skin infections, invasive diseases and the autoimmune sequelae post-streptococcal glomerulonephritis, rheumatic fever (RF) and Rheumatic Heart Disease (RHD). The majority of these cases occur in developing nations and Indigenous communities within developed nations, where both streptococcal carriage and infection are considered to be endemic [1,2,3,4]. It has been estimated that up to half a million people die of GAS related diseases each year [5]; hundreds of millions more suffer from the less severe diseases This burden of GAS disease positions the causative organism as one of the major human pathogens for which no vaccine is available. The presence of epitopes in the B-repeat region of the protein associated with autoimmune sequelae [14] preclude its use in any vaccine candidate

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