How to use mpl sequence as variadic template parameters

Suppose I have a sequence

using r123 = boost::mpl::range_c<int, 1, 3>;

and I want to instantiate a template:

template <typename A, typename B, typename C>
struct abc_ {
     int a = A::value;
     int b = B::value;
     int c = C::value;
};

How does one instantiate such a template with a mpl sequence? If the target class is variadic (c++11), is the technique different?

Thanks.