The number of patients requiring kidney transplants continues to grow, due to the increasing rate of kidney disease and the constant shortage of donor organs. In Canada and the United States, there are currently about 105,000 people in need of a kidney transplant. However, fewer than 20,000 people will receive a new kidney each year. The number of deaths worldwide from chronic kidney disease more than doubled between 1990 and 2013, increasing from 409,000 to 956,000 during that time. Now, two recent studies published in prestigious journals show that it may one day be possible to grow transplantable kidneys from stem cells.
In one study, published in the online edition of Nature, scientists in Australia grew complex groupings of kidney tissue from stem cells derived from human skin. The stem cells were grown in a chemical cocktail which caused the cells to change into kidney cells, and the cells self-organized into groupings of tissue known as organoids. These kidney organoids contained important structural components normally found in kidneys, namely the blood-filtering structures known as nephrons and their associated collecting ducts. Furthermore, the organoids were surrounded by cells which normally form connective tissue and blood vessels in kidneys. The organoids were developmentally similar to human fetal kidneys in the first trimester of gestation.
In another study, published online in Proceedings of the National Academy of Sciences, scientists in Japan overcame a barrier faced by previous attempts at growing functioning kidneys, namely the need for a pathway to drain the urine that is produced. The research group had previously grown kidney structures by using human stem cells transplanted into rat embryos, but these structures lacked a pathway to drain urine, and a build-up of urine limited the development of the kidneys. In the new research, the scientists developed a technique to provide the necessary drainage system, whereby embryonic bladders were transplanted along with developing kidneys into recipient animals. The technique was successfully demonstrated in rats and pigs. The pathways drained urine to the bladders of the host animals, and the kidneys continued to develop.
The kidney is a complex, highly structured organ composed of many distinct cell types performing functions which include removal of metabolic wastes, maintaining acid-base balance and regulating salt and fluid balance. A number of challenges must be overcome to successfully grow a functioning kidney from stem cells. The stem cells must be induced to develop into the various types of kidney cells; the cells must organize into the anatomical structures of the kidney including the waste removal structures and associated drainage paths; and the newly grown kidneys must grow and function in the host patient. The new studies are important advances toward the goal of stem-cell-derived kidneys which may one day alleviate the shortage of transplantable donor kidneys.