Pilot study assesses safety and feasibility of young donor plasma replacement in mild cognitive impairment

Heterochronic parabiosis improves physiological and cognitive function in aging rodents; these benefits appear to be derived from the removal of aged blood plasma components and the addition of younger ones. In humans, removing plasma from older individuals with Alzheimer's disease (AD) and replacing it with saline and albumin delayed cognitive deterioration in a large clinical trial. However, mimicking heterochronic parabiosis in humans by removing large volumes of a patient's blood plasma and replacing it with plasma from young and healthy donors has not been tested. Here, we have performed a pilot study to characterize the feasibility and safety of such a procedure, replacing between 16 and 26 L of patient blood plasma with young (ages 18-24) donor blood plasma for twelve patients who recently received a diagnosis of mild cognitive impairment with biomarker evidence of AD. The dose and time interval between plasma exchanges was tailored to maximize equilibration of donor plasma components into the interstitial fluid, achieving what we term interstitial rejuvenation. We explored three permutations of a plasma exchange protocol with different treatment intensities and doses, each performed on three to five patients. We present data on safety, feasibility, patient burden, resource use of the treatments, preliminary measurements of clinical variables and short-term cognitive trajectories in the patients. The procedures were safe and feasible, supporting further investigation of treatment efficacy in a larger controlled trial. This safety and feasibility study was first registered 22 December 2023 at ClinicalTrials.gov and given the identifier NCT06234436.