Half Matched Yet Perfect

By Medical Discovery News

Dec. 31, 2011

Half Matched Yet Perfect

Americans spend much of their time waiting. Waiting in long traffic delays, waiting in line for coffee, waiting for a call back, but not for a lifeline. Yet everyday tens of thousands of people wait for lifesaving organs and bone marrow. Sadly, most die waiting.

Researchers have developed a new procedure that virtually eliminates the wait time for people who need bone marrow transplants. Called “half-matched donors,” this procedure matches a patient with someone whose tissues are only half identical, yet it works just as well as a complete match.

Right now people with leukemia and lymphoma waiting for bone marrow must find a complete match among family members or from a national registry, but more than half never do. As they wait, their cancer progresses and spreads, and many die.

Not that long ago, half-matched, or haploidentical marrow transplants, were considered impossible because of immune system rejection. So, what changed? Immunosuppressive drugs have improved significantly. But it’s not just the drugs themselves; it’s also how they’re used to prepare a patient for marrow transplantation.

In studies at Johns Hopkins Bone Marrow Transplant Program, patients were first put though six days of chemotherapy before transplantation, just enough to suppress their immune system but not harm their organs. On the day of the procedure, half matched donors, who can be a parent, sibling or child, had their marrow extracted by needle from their hipbone. Those without a blood relative were given half-matched umbilical cord blood cells from donors.

Next, researchers injected the donor marrow into the patient and three days later administered high doses of a drug called cyclophosphamide, which re-boots the immune system. The medication kills off the patient’s immune cells but leaves the donated blood cells intact to create a new immune system that is more likely to accept its new host. The new cells also begin creating cancer-free blood cells within 20 days.

Results of these clinical trials show a one-year survival rate of 62 percent for half-identical marrow transplants and 54 percent for half-matched cord blood cells. That is essentially the same success rate for people who receive complete match transplants.

Doctors at Johns Hopkins speculate half-identical transplants work because the recipient’s immune system reacts more strongly against the cancer and lowers the chance of relapse.

In the study’s final phase, doctors will perform haploidentical transplants on nearly 400 patients.  If the results are as promising, researchers estimate that more than half of sickle cell patients, and nearly all patients with blood cancers or autoimmune disorders, will have potential matches.

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