Q: My suspect had a bone marrow transplant a few years ago. DNA from blood at several crime scenes shows a mixture that is eventually resolved, with both the bone marrow donor and recipient being represented. The CSI investigating the case wishes to use the new antibody profiling assay on the samples in order to distinguish this suspect from the original bone marrow donor (who is also a suspect). Would the antibodies that are tested for in this assay differ between two people who share the same bone marrow and thus the same DNA?
AC, Knoxville, TN
A: Antibody profiling is new, unproven, and has never been used in a court case. So it is as yet not an admissible piece of evidence but that will probably happen before too long if it indeed pans out to be as good as it appears. The science behind it is that when any foreign material enters the body–things such as bacteria and viruses–the body immediately constructs antibodies against this foreign intruder. Remnants of these antibodies remain in the blood system forever. It is these types of antibodies that give us immunity to measles and other infectious diseases once we’ve had them. It is these types antibodies that also make us immune to many of these diseases after a vaccination. Since each of us throughout our lives contact different bacteria and viruses and other foreign materials, we each have an individual pattern of antibodies in our system. No two people have exactly the same antibody profile–or so it seems—and this is the basis for using this profile to identify an individual. If this turns out to be as good as promised it could be as good as DNA and fingerprints.
So an antibody profile could be created from the blood left at the crime scene as well as the two suspects and one would be exonerated while the other would be implicated. The DNA profile and the fact that one of the people had a bone marrow transplant would have nothing to do with this. Antibodies are not part of the DNA profile and they are not created by the blood but rather by immune cells throughout the body.
The bottom line is that even though your two suspects would have the same DNA profile in their blood–but different in every other tissue–they would each have their own individual antibody profile. And even if it has never been used it court, it could easily cause your detectives to focus their attention on one suspect and exclude the other.
