Gregg L. Semenza, a University of Pennsylvania alumnus, was sound asleep and missed the first call. He picked up the second time and learned that he was one of three winners of the 2019 Nobel Prize in Physiology or Medicine.

“Certainly nobody expects that, that’s for sure,” Semenza said in a telephone interview with a Nobel Committee representative.

Semenza, now of Johns Hopkins University, William G. Kaelin Jr. of the Dana-Farber Cancer Institute and Harvard University, and Peter J. Ratcliffe of Oxford University and the Francis Crick Institute in England were jointly awarded the prize for their separate work discovering how cells sense and adapt to different oxygen levels.

Semenza earned his M.D. and Ph.D. degrees from Penn in 1984.

For M. Celeste Simon, a cancer biologist at Penn, the award was a vicarious thrill. She studies cellular response to oxygen deprivation, has collaborated with Kaelin, and is friends with all three winners.

“I’ve known Bill since we trained at Harvard in the 1980s and early ’90s,” said Simon, scientific director of Penn’s Abramson Family Cancer Research Institute. “I emailed all three of them today. I’m sure they are deluged” with congratulatory messages.

“This just shows the field is very important,” Simon added.

Indeed, as the Nobel Assembly at Sweden’s Karolinska Institute explained in a news release, “oxygen sensing is central to a large number of diseases," including anemia, cancer, and heart disease. Oxygen’s fundamental importance has been recognized for centuries, but the seminal discoveries of this year’s Nobel laureates have “paved the way for promising new strategies" for treatment.

Two drugs now in clinical trials have built on their discoveries, Simon said. One drug would treat kidney cancer by inhibiting the oxygen sensing pathway. The other would treat renal failure by stimulating the pathway.

Kaelin, who will be speaking at a Penn kidney cancer event on Thursday, began unraveling the molecular mechanics of oxygen sensing by studying a genetic mutation that dramatically increases the chance of kidney cancer and other malignancies.

“Bill in particular — but all three [winners] — approach research with integrity and rigor. He has taken the field to task for floating potential [drug] targets that haven’t held up,” Simon said.

Kaelin has his own research lab at Dana Farber and is a professor at Harvard.

Ratcliffe, a specialist in nephrology, has a research lab at Oxford, where he is a professor. He also directs clinical research at the Crick Institute in London.

Semenza did postdoctoral training at Johns Hopkins, where he now has a research lab and directs the vascular research program.

“Unexpected turns are what makes science so exciting,” Semenza said in the interview, posted on YouTube. “You never know where your studies are going to lead you.”

The prize of nine million Swedish crowns — equivalent to $918,000 — will be shared equally by the three winners.