After Two Rabbit Studies, Researchers Finally Ready to Regrow Human Penises

Funded by the US Armed Forces Institute of Regenerative Medicine (US-AFIRM), Professor Anthony Atala, MD has been hard at work carving out an unusual niche in the field of tissue engineering — regrowing penises.  As the director of the Wake Forest University’s Institute for Regenerative Medicine (WFIRM) in Winston-Salem, North Carolina, Professor Atala has been working since 1992 to fill what he views as a gaping hole in the literature.
I. Rabbit Penis Transplantation Studies Conclude With Resounding Success
And he’s making serious progress.
After early studies in the 1990s, his team turned last decade to regrowing rabbit penises.  They slowly extended their research into a cohesive blueprint for growing male genitalia.    

Dr. Anthony Atala is a leading surgeon in the field of lab grown penises. [Image Source: Road Trip Nation]
The process began with selecting a donor penis; eventual human studies could come from a deceased organ donor.  The donor penis was processed using various washes and detergents to remove its cells.  What was left behind was a collagen extracellular matrix that formed the structure of the penis.
The researchers then extracted endothelial and smooth muscle cells from the remaining bits of penile tissue in the injured victim.  The endothelial cells populated the interior of the veins, arteries, and capillaries in the scaffold.  The smooth muscle cells covered the outside of the arteries that fill the organ’s spongy tissue with blood to keep it erect.  Additional cells were added to finish the lab-grown penis transplant.
The key advantage of this method over a direct transplant with the organ donor’s cells intact was that the host’s immune system would not attack the organ.  Traditional organ donation involving organs populate by the donor’s cells have been used for decades in heart transplant and kidney transplant surgery.  However, these treatments force the patient to spend the rest of their life on anti-rejection drugs that cripple their immune system, leaving them susceptible to infection.
Dr. Atala’s more advanced strategy paid off in 2008 when he successfully transplanted penises into 12 rabbits.  Of the recipient population, two-thirds were able to ejaculate normally, and one-third actually were able to impregnate a female rabbit.  A second-generation study on rabbits wrapped up this July with a publication in the prestigious peer-reviewed journal PNAS

As seen in these images from Dr. Atala’s 2008 publication, the lab-grown rabbit penises were nearly indistinguishable from nature’s own creation. [Image Source: PNAS/WFU] 
The success stiffened the resolve of Dr. Atala and his staff.  He recalls in an interview with the UK’s Guardian:
  The rabbit studies were very encouraging, but to get approval for humans we need all the safety and quality assurance data, we need to show that the materials aren’t toxic, and we have to spell out the manufacturing process, step by step.  
Now, after years of pounding away at the problem, he’s finally ready to test his penis transplant technique on human volunteers.
II. Human Penis Implant Study is Next
Dr. Atala cautions that his technique requires that the transplant target already have a damaged vestige of a penis, or a malformed organ.  For that reason it won’t be useful for females looking to get a sex change.  However, the therapy could help males who lost their penis in an injury, including wounded vets.  It can also help men with penile cancer, who were forced to have an amputation.  Currently these groups are sometimes equipped with an artificial prosthetic, but these insensitive replacements yield low success rates at ejaculation.

Dr. Atala, seen here walking through his lab at WFU, aims to lead the first research team to achieve a succesful implant of a lab grown human penis. [Image Source: WFU] 
It could also help patients with congenital birth defects.  Some people in the so-called “intersex” community (which covers a variety of medical scenarios where a person is born with atypical sex organs) are sexually males in that they have testicles (sometimes undescended) that produce sperm.  But some are born with no penis or have malformed penis.
As there was previously no way to effectively regrow or transplant a penis, doctors have traditionally tried to make these patients into female, via a mixture of hormone therapy (estrogen injections, etc.) and reconstructive surgery.  While results are expectedly varied, in many cases the male patients suffered serious psychological trauma when doctors tried to reassign their gender to female.  

As many as 1 in 1,000 males may suffer from a severe penis defect at birth.  Some are reassigned to be females.  But by regrowing the heavily vascularized tissue in the lab, Dr. Atala is hoping to provide these patients relief in the near future. [Image Source: Gray’s Anatomy]
More specifically, roughly 1 in 1,000 male babies in the U.S. is born with severe (third degree) Hypospadias [source] — a birth defect in which the urethra is not properly integrated into the penis and opens on the perineum (the base of the penis shaft).  Victims of this condition are often reassigned to be female via surgery [source].  Other more rare conditions such as aphallia also lead to sex reassignment and its associated undesirable outcomes [source].
Dr. Atala remarks:
  Our target is to get the organs into patients with injuries or congenital abnormalities.  Imagine being genetically male but living as a woman.  It’s a firmly devastating problem that we hope to help with.  
His group is now enrolling male patients in a clinical study to test the efficacy of the procedure — a medical first.  

Lab grown penises will begin by decelluarlizing an organ donor’s penis, which will serve as the growth matrix for the patient’s cells to grow on, forming a new penis of their own. [Image Source: WFU]
Medical researchers are praising the work, but also are cautioning the public that while the approach yielded successful erections in rabbits it remains to be seen if it can achieve similar results in human trials, given the neurological complexity of human arousal.  Asif Muneer, a consultant urological surgeon and andrologist at University College hospital, London, comments:
  My concern is that they might struggle to recreate a natural erection.  Erectile function is a coordinated neurophysiological process starting in the brain, so I wonder if they can reproduce that function or whether this is just an aesthetic improvement. That will be their challenge.  
But Professor Atala’s team isn’t letting doubt tie them down.
Professor James Yoo at WFIRM is working to build upon his colleague’s work, using them to penetrate a slightly different medical market — erectile dysfunction treatments.  He believes that in extreme cases of erectile dysfunction where drugs prove ineffective, it may be possible to perform a partial transplant of spongy tissue using a growth strategy similar to that used with the full transplant.  As extreme dysfunction is often related to blockages in the penis itself, this surgical solution seems a promising, if extreme treatment route.
Dr. Atala isn’t solely focused on penises, though.  His team is working to regrow 30 different kinds of organs.  Their greatest success has mostly come in the field of urinary and sex organs.  They became the first to implant a lab grown human bladder in 1999 [paper], the first to transplant a urethra in 2004 [paper], and the first successfully transplant a vagina into a human patient in 2005 [paper].