The invention provides mutants of GAS57 which are unable to cleave IL-8 and similar substrates but which still maintain the ability to induce protection against S. pyogenes. The invention also provides antibodies which specifically bind to GAS57 and which inhibit its ability to cleave IL-8 and similar substrates. The mutants are useful, inter alia, in vaccine compositions to induce protection against S. pyogenes. The antibodies are useful, e.g., as therapeutics for treating S. pyogenes infections.
