Over time programming languages develop, paradigms evolve, development teams change. The effect of this is that test suites wear out, therefore these also need to evolve. Mutation testing is an effective fault-based testing approach, but it is computationally expensive. Any evolutionary based approach to this process needs to simultaneously manage execution costs. In this conceptual paper we adopt immune systems as a metaphor for the basis of an alternative mutation testing system. It is envisaged that through monitoring of the development environment, a minimal set of effective mutations and test cases can be developed - a 'vaccine' - that can be applied to the software development process to protect it from errors - from infections.