Young Blood Revisited: Inside the 2026 Trials Testing Plasma Exchange and Rejuvenation Factors

In 2014, three studies published within months of each other set the longevity field ablaze. Researchers in three different labs, led by Amy Wagers at Harvard, Saul Villeda at UCSF, and Tony Wyss-Coray at Stanford, surgically joined the circulatory systems of young and old mice in a procedure called parabiosis. The old mice grew younger. Their muscles regenerated more efficiently. Their hippocampi grew new neurons. Their hearts pumped harder. The young mice grew older. The results were so striking that they implied something extraordinary about blood. There were factors circulating in young plasma that could rejuvenate old tissue, and factors in old plasma that could age young tissue.

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A decade later, the simplest version of this idea has been tempered by harder data and a much more nuanced picture of what blood actually does. The 2026 generation of plasma exchange and rejuvenation factor research is no longer about transfusing teenagers’ blood into wealthy older men. It is about identifying specific proteins, removing inhibitory factors, and testing whether targeted plasma manipulation can move the needle on aging in serious clinical trials. This deep dive walks through the science, the active programs, the recent readouts, and what they mean for how you should think about blood as a longevity target.

The Parabiosis Origin Story

Heterochronic parabiosis, the joining of two animals of different ages, was first performed by physiologist Clive McCay at Cornell in the 1950s. McCay reported that older mice paired with younger ones lived longer, but the technique fell into disrepute because of the surgical complexity and the tendency for paired animals to reject each other.

It returned in 2005, when Amy Wagers and colleagues at Harvard reanimated the technique with modern molecular biology in a Nature paper that has since become foundational. They showed that exposing aged muscle stem cells to young blood circulation restored their proliferative capacity. The same year, Wagers and her collaborators founded the modern field by demonstrating that the rejuvenation effect was systemic and likely mediated by circulating factors.

The next decade brought a flood of follow-up work. In 2014, Saul Villeda at UCSF showed that young blood reversed cognitive aging in mice, increasing dendritic spine density in the hippocampus and improving performance on memory tasks. Tony Wyss-Coray’s lab at Stanford identified specific plasma proteins that increased or decreased with aging and tested individual proteins for their effects. Lee Rubin’s group at Harvard added that it was not just bulk plasma but specific identifiable molecules that drove the effect.

By 2020, the field had a new working model. Aging was not just cellular damage accumulating in tissue. It was a systemic state, broadcast through the bloodstream, in which young tissues secreted pro-regenerative factors that declined with age, and old tissues released pro-inflammatory factors that increased. The question became which factors mattered, and whether any of them could be turned into a therapy.

The First Wave of Candidate Factors

Three molecules dominated the early candidate list, and the trajectory of each tells you something about how scientific consensus moves.

The most famous was GDF11, growth differentiation factor 11, a TGF-beta family protein. In 2013 and 2014, Wagers and her collaborators reported in Cell and Science that GDF11 declined with age and that restoring it to young levels reversed cardiac hypertrophy in old mice. The headlines were immediate and global. Then a 2015 Cell Metabolism paper from David Glass and colleagues at Novartis used a more specific GDF11 assay and reported that GDF11 actually increases with age in humans, that it inhibits muscle regeneration rather than enhancing it, and that the original assays may have been confounded by the closely related protein myostatin. The GDF11 story is now considered an instructive cautionary tale about reagent specificity in biomarker discovery, though some labs still see clinical value in the molecule under specific tissue-restricted conditions.

The second was TIMP2, tissue inhibitor of metalloproteinases 2, identified by Joseph Castellano and Tony Wyss-Coray in a 2017 Nature paper as a young plasma factor that improved hippocampal function and memory in aged mice when delivered intracranially. TIMP2 has held up better than GDF11 and remains an active target in early translational programs, including work at Stanford and at the Buck Institute for Research on Aging.

The third, and perhaps the most underappreciated, was oxytocin. In 2014, Christian Elabd and Irina Conboy at UC Berkeley reported that oxytocin levels decline with age and that restoring oxytocin in old mice rejuvenated muscle stem cell function. Subsequent work has linked oxytocin to a wider range of age-related processes, including bone density and social cognition. Oxytocin is already an FDA-approved drug, used clinically to induce labor, and several investigator-initiated studies are exploring whether intranasal oxytocin in older adults has measurable effects on muscle, cognition, or social engagement.

The Dilution Hypothesis

A subtle but important shift in the field occurred when Irina Conboy at UC Berkeley argued that the dominant effect of young blood may not be the addition of pro-youth factors but the dilution of pro-aging factors. In a 2020 Aging paper, Conboy’s group showed that simply replacing 50 percent of an old mouse’s plasma with saline and albumin produced a rejuvenation effect comparable to receiving young blood. The implication was that aging plasma contains active inhibitors of regeneration, and removing them is sufficient.

This reframed the therapeutic strategy. If the goal is to dilute pro-aging factors, then plasma exchange, also called plasmapheresis or therapeutic plasma exchange (TPE), becomes a plausible intervention. TPE is already an FDA-approved procedure used clinically for autoimmune conditions, neurological diseases like Guillain-Barre syndrome, and certain blood disorders. It involves removing a patient’s plasma, separating the cells, and returning the cells with a substitute fluid such as albumin and saline.

If Conboy’s dilution hypothesis is correct, the same machine that treats myasthenia gravis could, in principle, be repurposed as a longevity intervention.

The AMBAR Trial and the Stanford Program

Several active programs are testing exactly this hypothesis.

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The most prominent is the AMBAR trial, Alzheimer’s Management By Albumin Replacement, run by Grifols, the Spanish plasma products company. AMBAR tested whether monthly therapeutic plasma exchange combined with albumin replacement could slow cognitive decline in patients with mild to moderate Alzheimer’s disease. The Phase 2b/3 results, published in Alzheimer’s and Dementia in 2020 by Mercedes Boada and colleagues, showed a 61 percent reduction in cognitive decline measured by ADAS-Cog 12 in patients receiving the most intensive TPE protocol over fourteen months, with even larger effects on functional measures including the ADCS-ADL. The results were intriguing but did not lead to immediate regulatory approval, in part because the trial design and endpoints did not align cleanly with FDA requirements for Alzheimer’s drugs and the comparator arm received sham apheresis rather than no procedure.

A follow-up trial, AMBAR2, is designed to address those concerns and is enrolling in 2026 with a sharper biomarker package, including plasma amyloid and tau measurements alongside the cognitive endpoints. The Stanford Aging Plasma Project, led by Wyss-Coray and David Furman at the Buck Institute, is running parallel studies on biomarker-defined healthy aging populations to identify which proteins shift with TPE and whether those shifts correlate with measurable healthspan endpoints.

The Diamandis Plasma Exchange Project, founded by Peter Diamandis, has taken a more entrepreneurial approach. The project is running observational and prospective studies on individuals who self-select into TPE protocols at clinics around the world, gathering longitudinal data on epigenetic age clocks, inflammatory biomarkers, and physical function. The data is preliminary and uncontrolled, but it provides one of the few real-world windows into how repeated TPE affects long-term health markers.

A 2023 paper in GeroScience from a multi-site collaboration including Mike Conboy and Irina Conboy at Berkeley reported that a single TPE session in healthy older adults produced measurable shifts in inflammatory biomarkers and a modest reduction in Horvath epigenetic age clock values. The effect size was small, the trial was small, and the durability of the effect remains unknown. But it represents one of the cleanest human data points in the dilution literature.

The CSF Story

The most striking recent advance in the field concerns not blood but cerebrospinal fluid. In 2022, Tal Iram and Tony Wyss-Coray published a Nature paper showing that infusing young CSF into the brains of old mice improved memory function and induced gene expression changes in oligodendrocytes, the cells that produce the myelin sheath wrapping around nerve fibers. The active factor was identified as Fgf17, fibroblast growth factor 17, a protein that declines with age in CSF.

The implication is that the brain has its own rejuvenation pharmacology, distinct from blood-based factors, and that CSF-targeted therapies may eventually be more effective than systemic plasma interventions for cognitive aging. Several preclinical programs are now developing intrathecal Fgf17 delivery, and the broader strategy of identifying tissue-specific rejuvenation factors is gaining momentum.

A 2025 paper in Nature Aging extended this line by showing that the choroid plexus, the structure that produces CSF, undergoes its own characteristic aging signature. Restoring choroid plexus function may amplify the natural rejuvenating signals already produced by the brain, sidestepping the need for exogenous factor delivery entirely. This is a major shift in thinking. The earlier model assumed you would harvest a youth factor, manufacture it as a recombinant drug, and inject it. The newer model asks whether you can persuade the body to start producing the factor again on its own.

The Counterargument

Not every researcher is convinced this line of work will translate. Steven Austad at the University of Alabama at Birmingham, a longtime aging biologist, has argued that the rejuvenation effects observed in parabiosis and TPE studies are real but modest, and that translating mouse data to humans is unusually difficult here because mouse plasma differs from human plasma in important compositional ways.

A second concern is selection. Most young plasma trials use blood from young, healthy donors. The plasma of an actual nineteen year old contains hormones, growth factors, and metabolic signals that depend on circadian state, nutrition, and physical activity at the moment of donation. Standardizing the input is a much harder problem than it appears, and the variability is one reason early trials showed inconsistent effects.

A third concern is duration. The rejuvenation effects of single TPE sessions in mice fade within weeks. Maintaining benefits requires repeated dosing, and the long-term safety of monthly or quarterly TPE in older adults has not been characterized at scale. Plasma exchange carries risks, including hypotension, citrate-related calcium disturbances, infection from venous access, and rare allergic reactions to replacement fluids. The risk-benefit calculus that supports TPE in autoimmune crisis does not automatically extend to elective use in healthy older adults.

A fourth concern, raised by Matt Kaeberlein of Optispan and the Dog Aging Project, is opportunity cost. Resources spent on plasma exchange clinics may displace investment in interventions with stronger evidence and lower complexity, including rapamycin, exercise, sleep, and metabolic interventions like GLP-1 receptor agonists. Kaeberlein has been particularly direct about the gap between the biological plausibility of plasma manipulation and the actual clinical evidence in healthy adults.

The Exercise Connection

A parallel literature, often underappreciated in coverage of plasma exchange, has shown that the body produces its own rejuvenation factors when properly exercised. Saul Villeda’s lab at UCSF reported in 2020 in Science that plasma from exercised mice carried many of the same rejuvenating effects as plasma from young mice, and identified glycosylphosphatidylinositol-specific phospholipase D1, or Gpld1, as one of the factors mediating the effect. Subsequent work from the same group and from Henriette van Praag at Florida Atlantic University has built a list of exercise-induced plasma factors, including irisin, BDNF, clusterin, and several myokines, that converge on neurogenic and anti-inflammatory pathways.

Bente Pedersen’s Copenhagen lab has spent two decades cataloging the muscle secretome during exercise, and the resulting picture is striking. A working muscle is the largest endocrine organ in the body, releasing hundreds of signaling molecules into circulation that act on the brain, the liver, the immune system, and adipose tissue. Many of these molecules overlap with the youth factors identified in parabiosis studies.

The implication is practical. The most reliable way to elevate the concentration of rejuvenation factors in your bloodstream, with the strongest safety record and the lowest cost, is to exercise vigorously and regularly. The plasma of a sixty year old who runs four hours a week resembles the plasma of a forty year old who does not, and is meaningfully different from the plasma of a sedentary peer.

Where the 2026 Field Stands

The field has matured considerably since the parabiosis hype cycle of the mid 2010s. Three observations capture where it sits in 2026.

First, the simplest version of the young blood hypothesis is wrong. There is no single factor in young plasma that, restored to old plasma, reverses aging. The story is multifactorial and probably tissue-specific.

Second, the dilution hypothesis is partially right. Removing pro-aging factors with TPE produces measurable effects in human trials, including the AMBAR data on cognitive decline in Alzheimer’s. Whether this scales into meaningful healthspan extension in healthy older adults remains the empirical question.

Third, the most active translational programs are not pursuing whole plasma at all. They are isolating individual factors, including TIMP2, oxytocin, klotho, Fgf17, and the broader exercise-induced factor set, and developing them as pharmacological products. Five to ten years from now, the practical product of this research may not be a plasma exchange clinic. It may be a recombinant protein injection, an mRNA-encoded factor, or a small molecule that mimics the downstream signaling of one of the major youth factors.

What This Means For You

For most people in 2026, the practical takeaway from young blood research is simple. Do not fly to a clinic for plasma transfusions from teenagers. Do not enroll in unregulated TPE protocols at a wellness center. The data does not support these interventions for healthy adults, and the safety profile of repeated plasma manipulation outside clinical indications is not established. The FDA issued a 2019 safety communication specifically warning against young donor plasma infusions for treatment of aging, and the underlying logic of that warning has not changed.

If you have a defined neurological condition, including Alzheimer’s disease, multiple sclerosis, or chronic inflammatory demyelinating polyneuropathy, plasma exchange may be on the menu of evidence-based options. The decision belongs to you and a neurologist, not a longevity clinic. If you are eligible for the AMBAR2 trial or other rigorously designed studies, that is the appropriate path for accessing TPE in the context of aging.

If you are healthy and interested in elevating your endogenous rejuvenation factor concentrations, the strongest evidence supports vigorous regular exercise. The 2020 Villeda paper and its successors have made it clear that the plasma of an active person is biochemically younger than the plasma of a sedentary peer at the same chronological age. Three sessions a week of resistance training, two sessions of zone two cardio, and one session of high-intensity interval training is the protocol most likely to produce the rejuvenation factor profile you would otherwise be paying tens of thousands of dollars to chase.

Sleep matters as well. Slow wave sleep is when the glymphatic system clears inflammatory metabolites that contribute to the pro-aging plasma signature. Time-restricted eating, with overnight fasting windows of twelve to fourteen hours, supports autophagy and reduces the inflammatory tone of circulating cytokines. Adequate protein intake, anchored at one gram per pound of lean body mass, preserves the muscle that serves as the body’s primary endocrine organ for myokines.

Watch the trial readouts. AMBAR2 is enrolling. The Stanford plasma project is publishing. Several recombinant factor programs are moving toward IND filings. Within five years, the field is likely to deliver either a regulator-approved plasma exchange protocol for a specific aging-related condition or a recombinant protein therapy targeting one of the youth factors. Either outcome would mark a real shift in longevity medicine.

For now, your blood is mostly the product of your behavior. Build the body that produces young plasma, and the chemistry will follow.

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