A patient who underwent transplant surgery using retinal cells derived from artificially-derived induced pluripotent stem cells has suffered a swollen retina, according to researchers from Kobe City Medical Center General Hospital and the Japan-government-backed Riken Institute.

The research team said it is the first time a patient has developed a serious adverse reaction during the clinical research to assess the feasibility of using iPSCs.

Surgeons operated on the patient, who is in his 70s, to remove pre-retinal membrane, deemed to be the cause of the retinal oedema. The team was unable to improve the symptoms despite the administration of steroid and anti-VEGF medication.

Dr Masayo Takahashi, MD, a researcher at Riken who heads the team, said: “We cannot deny the causal correlation with iPS cells.”

Dr Takahashi said the symptom falls into the category of serious cases, as it requires hospital admission for treatment, but stressed that it is “neither a matter of great urgency nor life-threatening.”

The incident most likely will not affect future clinical studies on the transplantation of iPS-derived retinal cells in patients with severe eye diseases, Dr Takahashi said.

The patient’s condition improved after the removal of pre-retinal membrane. The team believes the oedema was caused by a reverse in the flow of a liquid solution containing retinal cells derived from iPS cells.

Dr Noriyuki Azuma, MD, chief of the visual science laboratory at the National Center for Child Health and Development, said, the case would not put a stop to regenerative medical techniques and added that it would be important to thoroughly check the pre-retinal membrane taken from the patient to find the cause of the adverse reaction.