A team of Scientists of Takuya Sato of the Yokohama City University Graduate School of Medicine in Yokohama, Japan, grew some healthy sperm cells in the laboratory from the testicular tissue of mice and used them to produce fertile offspring. Since decades, the scientists were trying for positive results but failed every attempt.
Fortunately, this time the scientists have marked their success in the discovery, which is surely a nifty technical feat. The study included the spermatogenesis (the multistage process by which spermatogonial stem cells grow to become sperm) in mammals in a lab setting. 
Regarding the results of the study, Dr. Marco Seandel and Dr. Shahin Rafii wrote in a related Nature commentary that this breakthrough may one day help doctors design fertility treatments for men also.
The success of the experiment was marked when the scientists succeeded in growing a sperm in a test tube for the first time. Researchers at Yokohama City University took testis tissue of newborn male mice and fertilized eggs, from which healthy and fertile baby mice were born.
"Until now, none of the attempts have been wholly successful, and when the sperm have been used, the pups born have not been healthy and have soon died," said Dr. Allan Pacey, senior lecturer in andrology at the University of Sheffield, in northern England.