For the Patient's New Immune System to Function Effectively in Bone

For the patient's new immune system to function effectively in bone marrow recipients,some HLA allotypes must be shared because _____.(Select all that apply.)

A) professional antigen-presenting cells are host-derived
B) professional antigen-presenting cells are donor-derived
C) otherwise an autoimmune disease would develop
D) newly generated T cells are positively selected on the recipient's thymic epithelium
E) if all HLA molecules were mismatched,acute rejection of the grafted cells would occur.