Evaluation of synthetic, M type-specific peptides as antigens in a multivalent group A streptococcal vaccine

Recent Advances in the Development of Peptide Vaccines and Their Delivery Systems Against Group A Streptococcus

Group A Streptococcus (GAS) infection can cause a variety of diseases in humans, ranging from common sore throats and skin infections, to more invasive diseases and life-threatening post-infectious diseases, such as rheumatic fever and rheumatic heart disease. Although research has been ongoing since 1923, vaccines against GAS are still not available to the public. Traditional approaches taken to develop vaccines for GAS failed due to poor efficacy and safety. Fortunately, headway has been made and modern subunit vaccines that administer minimal bacterial components provide an opportunity to finally overcome previous hurdles in GAS vaccine development. This review details the major antigens and strategies used for GAS vaccine development. The combination of antigen selection, peptide epitope modification and delivery systems have resulted in the discovery of promising peptide vaccines against GAS; these are currently in preclinical and clinical studies.

Augmented Passive Immunotherapy with P4 Peptide Improves Phagocyte Activity in Severe Sepsis

INTRODUCTION

Antimicrobial resistance threatens to undermine treatment of severe infection; new therapeutic strategies are urgently needed. Preclinical work shows that augmented passive immunotherapy with P4 peptide increases phagocytic activity and shows promise as a novel therapeutic strategy. Our aim was to determine ex vivo P4 activity in a target population of patients admitted to critical care with severe infection.

METHODS

We prospectively recruited UK critical care unit patients with severe sepsis and observed clinical course (≥3 months postdischarge). Blood samples were taken in early (≤48 h postdiagnosis, n = 54), latent (7 days postdiagnosis, n = 39), and convalescent (3-6 months postdiagnosis, n = 18) phases of disease. The primary outcome measure was killing of opsonized Streptococcus pneumoniae by neutrophils with and without P4 peptide stimulation. We also used a flow cytometric whole blood phagocytosis assay to determine phagocyte association and oxidation of intraphagosomal reporter beads.

RESULTS

P4 peptide increased neutrophil killing of opsonized pneumococci by 8.6% (confidence interval 6.35-10.76, P < 0.001) in all phases of sepsis, independent of infection source and microbiological status. This represented a 54.9% increase in bacterial killing compared with unstimulated neutrophils (15.6%) in early phase samples. Similarly, P4 peptide treatment significantly increased neutrophil and monocyte intraphagosomal reporter bead association and oxidation, independent of infection source.

CONCLUSIONS

We have extended preclinical work to demonstrate that P4 peptide significantly increases phagocytosis and bacterial killing in samples from a target patient population with severe sepsis. This study supports the rationale for augmented passive immunotherapy as a therapeutic strategy in severe sepsis.

Induction of a mucosal immune response to the streptococcal M protein by intramuscular administration of a PADRE-ASREAK peptide

In a previous study, it was shown that an intramuscular administration of amino acid PADRE-ELDKWA sequence induced a mucosal immune response to a conserved epitope of human immunodeficiency virus in mice. In the same model, here it is shown that this method can be used with a selected peptide from the M protein of group A streptococci. The PADRE-ASREAK sequence was injected in mice by the intramuscular route. Antibodies against M protein were detected in extracts of mucosal tissues and in serum. The repertoire isotypes of serum immunoglobulin G (IgG) and mucosal IgA and IgG antibodies varied, according to the dose of injected peptide. The highest mucosal IgA antibody response was obtained with 0.01 micro g of antigen per injection, whereas the systemic IgG antibody response increased with 10 micro g of antigen. Mucosal antibody production against streptococci was confirmed by immunofluorescence analysis. These results provide evidence that this novel approach of mucosal vaccination may be of advantage for bacterial systems and suggest a new field of investigation based on synthetic peptide analogues.