s immediately following the administration of lethal doses of radiation tended to enhance the animals' survivability.
The bone marrow tissue itself proliferates constantly. Thus, it tends to be extremely sensitive to radiation (3:519). Early investigators found, however, that the transplanted marrow cells could replace those that were destroyed.
Then, in 1957, Mathe and associates attempted these experiments on humans. All six of Mathe et al.'s subjects suffered from accidental radiation exposure. Although each received a bone marrow transplant, the results proved discouraging. In fact, for many years thereafter, progress in bone marrow transplantation techniques was extremely slow.
It wasn't until the discoveries in immunology during the 1960s that any significant advances were achieved. Research in histocompatibility delineated the genetic loci for the transplantation antigens. The four major loci (HLA A, B, C, and DR) all occur on chromosome number 6. Each encodes for cell surface antigens which enable the organism to recognize its own cells (3:518 519).
Normally, the individual has two such antigens (one for each inherited chromosome 6). These two particular major antigens make up a person's specific haplotype. Over 20 different antigen types exist. Thus, there are many possible haplotypes in any given population. Therefore, the chance of a match between nonsiblings is extremely small. Within a single family though there can be, at most, only four different antigens (two from each parent). The probability then, of siblings having identical antigens, is one in four (7:835). In practice, about 30% of siblings actually prove to be antigenically identical. These persons are said to be "genotypically matched."
Such advances in immunology eventually led to the application of bone marrow transplantation in patients with acute leukemia. Thus, during the sixties, several transplantati
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