I do not have a lot of experience with this particular question.  However,
graft versus host is mediated through lymphocytes.  Though there are lots of
lymphocytes in breastmilk, the numbers decrease as breastfeeding proceeds.
There is no reason to imagine that enough lymphocytes are actually absorbed
from the baby's gut to be clinically significant.

It is incredible that here is the only milk the baby will tolerate, and they
are willing to sacrifice the breastfeeding on a very tenuous theoretical
basis.

Jack Newman, MD, FRCPC