A Bone Marrow Transplant May Not Be Appropriate from a Given

A bone marrow transplant may not be appropriate from a given donor (Jane) to a given recipient (Jane's cousin Bob) , even though Jane has previously given blood for one of Bob's needed transfusions, because

A) even though Jane's blood type is a match to Bob's, her MHC proteins may not be a match.
B) a blood type match is less stringent than a match required for transplant because blood is more tolerant of change.
C) for each gene, there is only one blood allele but many tissue alleles.
D) Jane's class II genes are not expressed in bone marrow.
E) Bob's immune response has been made inadequate before he receives the transplant.