Cao Yinpeng, eight, stands outside an intensive care unit of the Affiliated Hospital of Xuzhou Medical College to talk with his father Cao Lei in sign language in Xuzhou, Jiangsu province, on July 12, 2016. [Photo/VCG]

An eight-year-old boy gained 11 kilograms within a month in order to receive a hematopoietic stem cell transplantation to save his father in Xuzhou, East China's Jiangsu province, and the surgery was carried out recently.

Cao Yinpeng stood outside an intensive care unit of the Affiliated Hospital of Xuzhou Medical College to talk with his father Cao Lei through sign language on Tuesday, a week after the surgery.

Earlier this year, the father was diagnosed with leukemia, but there was no matched hematopoietic stem cell within the China Marrow Donor Program, a national marrow bank.

Cao Lei is the only child of his parents who are too old to donate. Doctors suggested that they could transplant the son's bone marrow, but the son's weight should be more than 45 kilograms.

Zhang Lin, Cao Yinpeng's mother, said that the son weighed 35.5 kilograms, but after he came to know that he could use his bone marrow to save his father, he ate a lot in a month to reach 46.5 kilograms.

His grandma said that she made all food Cao Yinpeng liked, especially meat. Knowing eating more would be helpful to saving his father, Cao Yinpeng ate a lot in every meal, the grandma said.

On July 6, doctors successfully collected 355 milliliters of hematopoietic stem cell from Cao Yinpeng and transplanted into his father's body.

The boy was happy that his body saved his father, and now he is trying to lose weight. He also dreams of travelling to Australia with his father in the coming winter, a plan that he and his father made before.

The surgery has cost the family more than 400,000 yuan ($59,879), and another 400,000 yuan is needed for future medical treatment, which the family cannot afford, said Zhang. The family has sold their apartment to raise the money for the surgery.