A man in his early 20s has received the world's first sperm-making stem cell transplant in a new procedure that could be groundbreaking for infertility treatment. Until now, the procedure had only been tested in animals. But it successfully allowed male mice and monkeys to father offspring. The patient was diagnosed with azoospermia, a condition that causes no sperm to be present in his ejaculate and makes it impossible to naturally conceive a child, after receiving chemotherapy as a child to treat bone cancer