The controversial approach aims to rejuvenate old tissue.
The first controlled, but controversial and small, clinical trial of giving young blood to people with dementia has reported that the procedure appears safe. It has also hinted that it may even produce modest improvements in the daily lives of people who have Alzheimer’s disease.
Researchers who conducted the trial and others caution that the results are based on just 18 people and therefore are only a first step in exploring this type of treatment. “This is a really very small trial and the results should not be over-interpreted,” says Tony Wyss-Coray, a neurologist at Stanford University in California who led the study. The trial was conducted by his start-up company Alkahest, which is based in San Carlos, California.
The results suggest the procedure is safe and hint that it could even boost the ability of people with dementia to undertake everyday skills, such as shopping or preparing a meal. The team plans to present the results on 4 November at the 10th Clinical Trials on Alzheimer’s Disease conference in Boston, Massachusetts.
Wyss-Coray and his colleagues tested people aged between 54 and 86 with mild to moderate Alzheimer’s disease. The team gave the 18 subjects weekly infusions for four weeks. They received either a saline placebo or plasma—blood from which the red cells have been removed—from blood donors aged 18–30. During the study, the team monitored the patients to assess their cognitive skills, mood and general abilities to manage their lives independently.
The study detected no serious adverse reactions. It saw no significant effect on cognition, but two different batteries of tests assessing daily living skills both showed significant improvement.
Wyss-Coray, whose group did most of the mouse studies that inspired the clinical trial, now plan to conduct a second, larger trial using plasma from which many proteins and other molecules have been removed.
Blood-transfusion trials are controversial because the active molecules in plasma that seem to lead to the purported effects are unknown.
Irina Conboy, a neurologist at the University of California, Berkeley, and her colleagues have performed extensive parabiosis experiments stitching together young and old mice that have been genetically matched. She has found that young blood clearly rejuvenates mouse tissues such as the heart and the brain. But she says that the effects are probably coordinated by a complex orchestration of factors in the blood that needs to be understood more fully before moving to the clinic.
“The scientific basis for the trial is simply not there,” she says. “The effects of young blood on cognition have not been replicated by an independent group, and there has never been a test with a mouse model of Alzheimer’s.” She says that frequently exposing older people to foreign plasma may be unsafe, because hyperactivation of their immune systems could lead to autoimmune or inflammatory disease.