General solution of the Wess-Zumino consistency condition for Einstein   gravity
  The Wess-Zumino consistency condition for four-dimensional Einstein gravity is investigated in the space of local forms involving the fields, the ghosts, the antifields and their derivatives. Its general solution is constructed for all values of the form degree and of the ghost number. It is shown in particular that the antifields (= sources for the BRST variations) can occur only through cohomologically trivial terms. 
G. Barnich, F. Brandt and M. Henneaux