There is a prior user defense, see 35 USC 273. Unfortunately, in its current form it is essentially useless, as it only applies to method claims, and nearly all patents contain both product and method claims.
However, the House version of the reform bill expands the defense to cover all types of claims; thus if it survives reconciliation with the Senate bill it will likely become a viable defense.
However, the House version of the reform bill expands the defense to cover all types of claims; thus if it survives reconciliation with the Senate bill it will likely become a viable defense.