Scientists and detectives share a lot in common.

Both seek answers to unresolved questions. Both combine a systematic approach with intuition.

And both are known as investigators.

David Senitzer (Photo by p.cunningham)

In the case of City of Hope’s Histocompatibility Laboratory, the investigations have high stakes: The work is vital to the outcome of transplants using donated bone marrow and stem cells.

Patients undergo hematopoietic cell transplantation, or HCT, for serious blood-based diseases like leukemia. The procedure reboots a patient’s blood and immune system using healthy blood stem cells.

It all begins with human leukocyte antigens (HLA). The combination of these proteins, which are found on the surface of cells, acts as a tag that tells the immune system, “These cells belong; don’t attack them.”

One of the risks of HCT is graft-versus-host disease, in which the donated cells see the patient’s tissue as foreign and attack it. A patient’s body also may reject donated cells.

A close HLA match between patient and donor is essential to keeping the chances of this transplant rejection down. And that’s where the Histocompatibility Laboratory comes in.

The lab plays the role of matchmaker in the search for a compatible donor, diligently screening samples from potential donors to find the closest match possible.

The lab’s work doesn’t stop there, though. It also helps monitor the success of HCT following the procedure.

Sometimes some of the patient’s original blood cells return after HCT. This increases the threat that disease will return, or it signals that the patient’s body is rejecting the graft.

Physicians test for this early warning sign, which they call chimerism: the mixture of patient cells and donor cells.

Detecting cells early lets physicians adjust treatment to compensate, according to David Senitzer, Ph.D., director of the Histocompatibility Laboratory. “The earlier you catch these problems, the easier they are to deal with,” he said.

To help, HLA researchers adapted methods used by their fellow investigators in police work.

Standard blood tests for chimerism used to take up to six weeks — too long to help patients. In 2004, Senitzer and his colleagues struck upon an idea to speed the process: Use tools from the crime lab.

Police forensic investigators use a special method to compare a person’s unique DNA to evidence found at a crime scene. (It’s also widely used to confirm or deny paternity.) Best of all: It only requires 24 hours.

City of Hope was one of the first in the nation to develop the method for determining chimerism, said Senitzer. In fact, he used to travel extensively to teach it to other labs. Now it’s been adopted by labs all over the U.S. and Europe.

Within the last year or so, the Histocompatibility Laboratory has adopted a test for chimerism that is more sensitive still, by a factor of 100 — and team members vow to keep up their investigations.