Background: Previous studies in mice show P*17 and K4S2 are protective against GAS infection and toxicology studies in healthy rats found no evidence of toxicity. We have now utilised a rodent model that displays both the cardiac and neurobehavioural pathology associated with post-streptococcal sequelae, to assess the potential of the vaccine candidates to induce autoimmune complications.
Methods: Lewis rats were administered GAS rM5 (pos. cont.), PBS (neg. cont.), P*17-DT or K4S2-DT on day 0. Days 1 and 3, rats were administered Bordetella pertussis toxin as adjuvant. All rats received booster injections of antigen on days 7, 14 and 21. Behavioural assessments and ECG were performed prior to primary antigen injection and two weeks post final booster. Day 35 all rats were euthanised. Sera was screened for antibody titres and cross-reactivity to cardiac, connective tissue and neuronal proteins. Histological examination was performed on heart tissue.
Results: P*17-DT and K4S2-DT treated rats induced a robust antigen-specific immune response and P*17-DT antibodies were cross-reactive with rM5 antigen. The vaccine candidates did not induce antibodies that were cross-reactive with host cardiac or neurological tissues and there was no evidence in the vaccine treated groups of functional or histological abnormalities in cardiac tissues. In addition, neurobehavioural changes associated with post-streptococcal sequelae observed in control group, did not develop in the vaccine treated groups.
Conclusions: In a rodent model of rheumatic heart disease, investigational Strep A vaccines P*17-DT and K4S2-DT protected from the development of autoimmune valvulitis and myocardititis and against development of associated neurobehavioural pathology.