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Six months to the day after undergoing a life-saving double lung transplant, a Boston school teacher who for his entire life has lived with a disease that robs him of lung capacity is running a 5K charity road race this weekend.

Eamonn Kelly, a science teacher at St. Columbkille Partnership School in the city's Brighton neighborhood, plans to run the race Saturday to raise money for student scholarships and financial aid.

"After the operation I thought this would be a good milestone," said Kelly, 32, who was born with cystic fibrosis. "But this is also a big event for the school, which has been so supportive of me and is such a wonderful community."

Cystic fibrosis is a deadly disease that affects the digestive system and lungs, making it difficult to breathe. About 30,000 Americans have the condition, according to the Cystic Fibrosis Foundation.

Kelly was active as a child growing up in Shrewsbury, New Jersey, but it was never easy running, biking and participating in martial arts.

Getting ready for Saturday's race was physically grueling.

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Kelly, a 2006 graduate of Boston College who is currently pursuing a master's in educational leadership at BC's Lynch School of Education, was encouraged by his doctors the day after the operation to get up out of bed and walk around.

He soon started running for just 15 seconds at a time, and gradually worked his way up to three miles, making him confident he can complete Saturday's run. He figures his lung capacity is at about 85 to 90 percent.

"I know I can do it," he said. "My best time for three miles is about 38 minutes, but I am not so concerned about time. My main goal is to run straight through without stopping to walk."

He'll have help from his wife, Elana, who will run alongside him.

In addition to proving to himself that he can complete the race and raise money for his school, he wants to honor the person who donated their lungs, and spur awareness about organ donation.

"If people see what I am doing, perhaps it will inspire them to become organ donors and give other people the same second chance as me," he said.