Researchers who found a way to reach the growth factors that promote cyst growth
in polycystic kidney disease, suggest it opens the possibility for repurposing a large number
of existing drugs to treat the genetic disorder.
A normal kidney is about the size of a fist – a polycystic kidney can grow to the size of an American football.
Image credit: Indiana University School of Medicine
Polycystic kidney disease (PKD) is the world’s most common inherited kidney disease,
affecting around 12 million people. It has no known cure.
In PKD, fluid-filled, benign cysts develop and grow in the kidneys. As they accumulate
more fluid, the cysts get bigger and bigger and destroy healthy tissue. Eventually, this
leads to kidney failure, high blood pressure, and other complications.
The new study, from the University of California Santa Barbara (UCSB), involves the use of
therapeutic antibodies. These biologic therapies are already used extensively to treat
diseases ranging from cancer to autoimmune disorders.
Biologic therapies normally use a class of antibody called immunoglobulin-G (IgG) to bind
to and prevent the activity of specific proteins or growth factors.
But in PKD, the growth factors that drive cyst growth are locked inside the
fluid-filled lumen – the central cavity of the cyst – which IgG antibodies cannot
The UCSB researchers – led by Thomas Weimbs, a professor of molecular, cellular and
developmental biology – found that another class of antibodies called immunoglobulin-A (IgA),
were able to penetrate the cyst wall and enter the lumen.
Study shows IgA can enter PKD cysts and stay there
Three pieces of information came together to spur the discovery made in the study. They
arose in earlier work and observations by Prof. Weimbs, who has been working on PKD for 10
The first piece of information concerned how IgA could cross a cell layer by binding to
polymeric immunoglobulin receptors (pIgR). The second, was that a transcription factor called
STAT6 appears to be overactive in PKD. And the third, was that Prof. Weimbs remembered that
STAT6 had been shown to switch on the expression of pIgRs in other organs.
Prof. Weimbs says the “aha” moment came when he brought the three pieces of information
“I thought if STAT6 is highly active in polycystic kidneys, maybe it also expresses a lot
of pIgR – and that turned out to be the case. So we tested this in mouse models and in human
polycystic kidney tissues, and, in both cases, high levels of pIgR were expressed in kidney
When they injected IgA into mice with polycystic kidneys, the team found around 7%
of the injected IgA stayed inside the cyst lumens.
Prof. Weimbs says this suggests some IgA gets taken into the cysts – and because there is
no way for it to exit – it remains trapped:
“So we end up with a way of exploiting the pIgR system for targeting these antibodies
specifically to the polycystic kidney.”
A key step remains to be tested before the possibility that the method opens up new
treatment avenues for PKD becomes a likelihood – and that is to find a way to reformat IgG
antibodies into IgA types so they can enter the cyst using the pIgR system and target the
Should this step be successful, then, according to Prof. Weimbs:
“Our strategy allows for the repurposing of thousands of existing monoclonal
antibodies that have already been developed, which opens up a whole new class of therapeutics
not previously used for PKD therapy.”
Meanwhile, Medical News Today has learned how another team, reporting in the
Journal of the American Society of Nephrology, may also have developed a new way to
treat PKD by targeting blood vessels surrounding
Written by Catharine Paddock PhD