I am interested in Holder regularity for equations of the form
$$u_t - div A(x,t) \nabla u = 0$$ where $A(x,t)$ is bounded, measurable and elliptic. 

This was proved in the seminal paper of John Nash and later on by J.Moser.

I am looking for references where DiGiorgi's methods are implemented to obtain the same regularity estimates.