Fifty years after the world’s first successful transplant of donor bone marrow, performed at the University of Minnesota, doctors marvel at the progress it inspired in the field of regenerative medicine.

Originated as a treatment for the rare “bubble boys,” whose lives were threatened by simple infections, bone marrow and related transplants now occur more than 50,000 times a year to grow new immune systems in patients with aggressive cancers and blood disorders.

In the intervening years, doctors have learned more about protecting recipients from transplant-related complications, which has driven up the survival rate substantially, and how to match bone marrow donors and recipients by their DNA and blood types.

“We’re not at a stage where it’s easy,” said Dr. Daniel Weisdorf, senior research adviser for the U’s Center for International Blood and Marrow Transplant Research. “We’re at a stage where it’s much safer and easier than it use to be. And that’s exciting.”

As doctors reflected last week on the anniversary of one of the U’s signature achievements, they expressed equal excitement about the progress ahead. Two “CAR T” therapies have been approved in the past year to coax the T-cells in patients’ existing immune systems to fight certain cancers, acute lymphoblastic leukemia in children and advanced lymphomas in adults.

Now researchers at the U and other institutions are testing second-generation versions that are “tunable,” meaning they can be turned off if they are too harsh or have eradicated tumors, and turned back on if cancer returns.

It won’t take 50 years to reach the next milestones, Weisdorf said. “That’s not even 20 years away.”

Researchers also are reporting progress in finding new targets on the surfaces of cancer cells that will trigger T-cells to attack. They also are working with “NK,” or natural killer, cells, which play innate roles in the immune system and can attack tumors without those triggers.

Weisdorf said the ability of these new therapies to coax patient’s existing immune systems might replace the use of transplants to grow new systems in many cancer patients. But bone marrow transplants will continue to have a role.

Marking the 50th anniversary was equally important, he said, because it gave the U a chance to inspire today’s patients with stories of transplant recipients who are alive 25 to 30 years later. When such patients come to his clinic, Weisdorf said, he never misses a chance to take them around the waiting room and share their stories. “I make a lot of noise,” he said. “ ‘Look at this! 25 years!’ It's pretty incredible.”