How do I 'apply' or transform MyVec with MyTraits?

ie. I want the mpl::vector ...

boost::mpl::vector<A<MyTraits>, B<MyTraits>>;

I realise I can do mpl::apply<A<mpl::_>, MyTraits> to get A<MyTraits> but I can't work out how to do the equivalent to the entire vector.

mpl::transform seems like what I should be using. Transform seems to do apply internally, but I can't work out the syntax to do something like:

using substituted = typename boost::mpl::transform<MyVec, boost::mpl::apply<boost::mpl<_>, MyTraits> >::type;

(This isn't right!)

It may be I am confused because inside the transform, boost::mpl::_1 is the item in the vector, not the 'inner' placeholder.

Sorry if this is a basic question ...