This Christmas morning, Bob Harper gets to have his life back.

As presents under the tree go, that's a pretty big gift, but this one's especially sweet: His kidney transplant last Wednesday was made possible by old friends, whose own son died of kidney failure in 2009.

"I am overwhelmed with gratitude," said Mr. Harper, who is not only close to Nancy and Frank Pfenning of Squirrel Hill, but was a friend to their son Nils, who died at age 21 after two decades of fighting kidney disease.

During his lifetime, Nils Pfenning received two transplants, one from his mother and one from his uncle, and a week ago today, Mr. Harper, 56, of Squirrel Hill received a kidney donated by Nils' sister Marina Pfenning's fiance, Tony Balko.

Mr. Harper was operated on by Amit Tevar, a transplant surgeon at the Thomas E. Starzl Center for Transplantation at UPMC.

"Tony is a real hero," said Marina Pfenning, 28, a student at the Art Institute of Chicago. "It's beautiful and amazing to know he's saved the life of someone who is so close to our family and was so close to my brother."

Mr. Balko, a 31-year-old Smithton native who works as an art professor at the University of St. Francis in Joliet, Ill., said he decided to offer up his kidney because "I was healthy, a good match for Bob, and because it was important to Marina and her family."

He'd never met Nils, who by all accounts was an unusually charismatic, optimistic young man, "but I don't feel totally removed from him. I have a feeling from the stories I'd heard that we had a similar sense of humor. His folks consider me family, so I decided to do it."

"I'm a little out of it, but I'm full of thanks, and in some pain, too, from the incisions. But mostly thanks."

Mr. Harper, a professor of computer science at Carnegie Mellon University, said he spent much of the past two decades in a kind of denial, "my biggest coping mechanism, to be honest."

An avid cyclist, he tried to keep fit, trying to stave off dialysis. That meant more and more dietary restrictions, and more and more medications.

"I was taking about two dozen pills a day, one pill for one problem and another pill to counteract the effects of the pill I was taking," he said, but fatigue became a constant companion.

"We knew he'd gone to a couple of doctors, looking for someone who would tell him he didn't need a transplant," said Marina Pfenning, who added that she grew up calling Mr. Harper Uncle Bob -- her father is also a professor at CMU's computer science department.

Finally, when Mr. Harper's nephrologist told him he must get a transplant, he told the Pfennings, and they immediately swung into action, alerting family and friends. Their daughter -- who had not been a compatible donor to her brother -- offered to be tested, as did Mr. Balko.

The couple -- who are to be married in June -- hope to start a family soon, and "doctors said there might be some complications if I were to get pregnant too quickly after a kidney transplant," said Marina Pfenning. "So Tony decided to volunteer."

Once word got out through the Pfennings' own network of friends, there were three or four other volunteers who immediately stepped forward, "which amazed me," said Mr. Harper, adding that "I didn't think anything would come of it."

Nationally, the wait for a deceased donor's kidney is -- on average -- between two to four years, according to Misty Enos, of the Center for Organ Recovery and Education, an organ procurement organization covering Western Pennsylvania and West Virginia.

Mr. Harper would have had to wait a long time, since he needed a kidney that was compatible with his blood type, O positive.

But living donors are a different story -- if the right one comes forward, a transplant can happen fairly quickly, although thorough evaluations are necessary, not just of medical compatibility, but the physical and mental health of the donor.

Then, one night this summer, the Pfennings took him to dinner with their daughter and future son-in-law, "and they told me that Marina and Tony were both compatible donors, and that Tony was going to do it. It was just humbling."

Living donation is a sensitive situation on both ends, said Ms. Pfenning. The recipient's family and friends "are desperately seeking a way that the transplant can happen in a timely manner ... while the donor's are understandably worried about the health risks, which are remote but do exist," she said.

In the months leading up to the transplant, a delicate balance must be struck between both sides, a consensus by everyone involved that the outcome is well worth the risk, and "when everything falls into place, as it has for our family, it becomes clear that one person saving another's life through organ donation is an act of heroism that all involved will celebrate for the rest of their lives."

Two days after his surgery last week -- as soon as he could get out of bed -- Mr. Harper made the trip to Mr. Balko's room on another floor of UPMC Montefiore, to thank him for saving his life. And within another two days, Mr. Harper was home.

"My head felt clear, so energized," he said. "I wanted to jump up and down and run around. The day before yesterday I had my first banana in 10 years," a food previously prohibited because of high potassium levels in his blood.

"Mr. Harper is what people always called a lovable curmudgeon," said Nancy Pfenning. "As soon as he came out of that operating room, though, it was as though he'd been visited by the ghosts of Christmas past, present and future. He's not a curmudgeon anymore, not really. And all of a sudden he's signing his emails, 'Love, Bob.' "

Still, returning to the transplantation center at UPMC, where Nils fought so long and hard to live, brought back plenty of painful memories for the Pfennings.

"I kept running into ghosts," said Marina Pfenning.

Her brother succumbed to a rare, noncontagious form of meningitis resulting from complications following his second transplant, "but now that we're going through this again, it's a way to relive the experience with the right outcome," said Nancy Pfenning.

"We can't bring our son back, but we can be part of a friend's medical success story, one that we probably wouldn't have participated in if we hadn't had Nils to teach us how important it is to do whatever you can for the people you love."

First Published: December 25, 2013, 2:54 a.m.