Jean-Pierre Bosze is not likely to be alive a year from now if he does not receive a bone-marrow transplant. Diagnosed with leukemia in 1988, the 12- year-old boy from Hoffman Estates, Ill., has searched in vain for a suitable donor. His father Tamas, his mother and other relatives have had their blood tested, but none has the right type. His doctors have consulted the National Marrow Donor Program of 180,000 potential donors, but the odds of unrelated people matching are 1 in 20,000.
The chance of a match between siblings or half siblings, however, is higher, which accounts for the...