The Artificial Testicle: Centuries in the Making

As I was preparing a recent lecture on Artificial Sperm from Stem Cells for the annual meeting of British urologists, a thought struck me. By no means in pornographic way, the biology of male reproduction has fascinated me for over 20 years. This is different from the usual, casual interest that many men have with their “stuff” since waaaay back when.

Just Add Water

Believe you me, I am not the first to be fascinated by this subject. In fact, Paracelsus first coined the term homunculus in the 15th century when referring to sperm. At that time, it was thought that sperm contained a tiny, but fully formed man or woman just waiting to burst out and grow in the womb. Just add water. This early theory of heredity was termed preformationism for you crossword puzzle buffs.
Then, a century or so later, came Leeuwenhoek. An uneducated tradesman with a keen eye, he created a neat little “microscope” that magnified things 200 fold, and was the first to observe a moving sperm. Incidentally, he was also the first to discover bacteria after looking at the plaque on his teeth. What else was there to do in 17th century Holland?

Turek the Tinkerer

Admittedly a minor leaguer compared to these august figures, I became fascinated by sperm while in medical school. How can these cells, developing well after the immune system has a firm grip on the body, not be rejected by the body as “foreign?” Is this the reason why testicles are walled off from the rest of the body and kept outside of it in a scrotum that is 3 degrees cooler than core temperature? Maybe. We still don’t know for sure.
Fast-forward to my surgical residency training at Penn in the roaring 80s. Still pondering the immunology of sperm, I did bench-top research with Dr. Donna Peehl at Stanford and published a paper about human Sertoli cells, the nurse cells that line the sperm-producing tubules in the testicle. I discovered that Sertoli cells actually do communicate with the body’s immune system, convincing me that the testicles were not simply a “stealth” organ unnoticed by the body. The body clearly “knows” that they are there and that there is foreign sperm within them, but somehow (thankfully) it chooses not to react to them. We still haven’t fully explained how these systems can peacefully coexist.
Creating an artificial human testicle, the topic of my lecture in England, has been a long, hard road to date. Yes, some day, with further persistence and inspiration, we might spin out sperm from a variety of stem cells after using this device. But, this little-engine-that-could may also help us unravel many of the mysteries of sperm biology that have eluded us for generations, nay centuries. In the words of John Lien, the “Whale Professor” at St Johns University, “…the black right whale has 4 kilos of brains and 1,000 kilos of testicles. …we know what it is thinking about!”