A young man from Northwest China lost 17 kilograms of weight in two months in order to donate hematopoietic stem cells to a 2-year-old boy in Wuhan, Hubei province, Changjiang Daily reported Wednesday.

The little boy, who suffered from leukemia, managed to find the matching donor in November 2017 through the China Marrow Donor Program.

On Monday morning, the stem cell collection started. The boy got the bone marrow transplant that night, making it the first case in Wuhan Children’s Hospital that a transplant did not happen between family members.

The young donor, once weighing 100 kilograms, kept exercising to lose weight on hearing that he could save the boy.

He also sent a handwritten letter of 2,000 characters to encourage the boy. The long handwritten letter says, “Little boy, I am glad to be matched with you and doing something for your life. It also gives me the chance to have a special experience that most people in the world could not have.”

The boy’s mother, surnamed Dai, said: “I don’t know the identity of the donor, but I do appreciate him as he brings my child the hope of life.”

Zheng Yumeng contributed to this story.