Hi Rumble,
Bone marrow donors have to be completely HLA typed.
Since a haplotype is transferred from each parent then the chances of getting a good match is best with twin, then sibling, then parent. Matching HLA types with unrelated individuals is literally a one in a million proposition and thats why marrow data banks/registers have been established. Incomplete matches mean that the recipient then has to been on immunosuppressive drugs for the rest of their lifes. Even then organs will eventually be rejected. Eyes and kidneys are best tolerated transplants when not matched.
I would think that a HLA B27+ individual could be matched to another HLA B27+ individual OK. I wonder though if bone marrow from someone with AS would be a problem and cause AS in the B27 positive recipient, especially since the bone marrow is involved/inflammed in AS?? Although the recipient may not have the other genetic risk factors which contribute to AS so that might be protective.

Without immunosuppression the recipient can develop a condition called Graft Versus Host where the graft takes over and eventually rejects (kills) the recipient - not nice.

Cheers David

Dx Oct 2006 B27+ undifferentiated spondlyarthropathy (uSpA) with mild sebhorrhoeic dermatitis and mild Inflammatory Bowel Disease (IBD) controlled by NSD since 2007.