Six people were arrested Sunday on suspicion of participating in unauthorized stem cell therapies using blood collected from umbilical cords and placentas after childbirth.

Investigators from the Ehime, Ibaraki, Kochi and Kyoto prefectural police forces suspect doctors in Tokyo and other cities administered cord blood to patients without notifying authorities. They also suspect a man and his employer in Tsukuba, Ibaraki Prefecture, sold cord blood to their clinics while knowing the doctors were providing treatment without reporting it to the government.

It is the first time arrests have been made based on the law on regenerative medicine safety that took force in 2014. Stem cell transplants invite the risk of graft rejection and infection.

Cord blood contains blood-forming stem cells that can be used to treat various diseases. When using stem cells, medical institutions are required to submit treatment plans in advance for review by the health ministry, except when treating leukemia and other designated diseases.

The suspects include Shinsuke Shuto, a 40-year-old Tokyo doctor, and Tsuneo Shinozaki, 52, who runs a company that sells cord blood in Tsukuba, police said.

Shuto allegedly administered cord blood to patients between July 2016 and this April without informing the government, they said.

Between May and June, the ministry ordered 12 clinics in Tokyo and other cities to suspend treatment after they were found to have administered cord blood for cosmetic therapy or cancer treatments without notification. The effectiveness and safety of such therapies has not been proven.