The strong equivalence principle from gravitational gauge structure
  Gravitational self-interactions are assumed to be determined by the covariant derivative acting on the Riemann-Christoffel field strength. Once imposed on a metric theory, this Yang-Mills gauge constraint extends the equality of gravitational mass and inertial mass to compact bodies with non-negligible gravitational binding energy. Applied to generalized Brans-Dicke theories, it singles out one tensor theory and one scalar theory for gravity but also suggests a way to implement a minimal violation of the strong equivalence principle. 
Jean-Marc Gerard