Partial Reprogramming in Human Testing: Programme Milestones, Safety Questions, and Evidence Gaps

Originally published 10 June 2026. Evidence review: 18 September 2026. Registry information, sponsor-reported milestones and experimental evidence are distinguished below. No clinical efficacy conclusion is drawn from trial entry.

Reader question: Which partial-reprogramming programmes have actually reached human testing, and which translational milestones remain unproven?

Human translation is no longer only a future intention: Life Biosciences has reported dosing a participant with ER-100. The bounded conclusion is narrower than human rejuvenation. A first dose is an operational milestone, not an efficacy result. The reviewed programmes occupy different stages, and the ER-100 registry record does not contain posted clinical results.

What “human testing” actually means

The phrase should identify what was tested, in whom or in what model, and what was measured. Human-derived cells are not treated people. A public registry describes a study; it does not certify a successful treatment. The following ladder is an evidence-reading framework, not a claim that every programme follows an identical sequence.

1. Cultured human cells: an experiment on cells outside a participant; it does not establish clinical delivery.
2. Human tissue or organoids: a tissue-level experimental system, still distinct from administering a candidate to a person.
3. Animal in-vivo evidence: organism-level findings in the stated model, not demonstrated human benefit.
4. Regulatory filing: submission of an application, not permission to begin dosing.
5. Regulatory clearance or authorization: a bounded regulatory milestone, not marketing approval or proof of efficacy.
6. Registered human trial: an identifiable study design and record, not confirmation that a participant has received treatment.
7. Trial recruitment: a dated operational status, not a result.
8. First participant dosed: treatment has begun according to the controlling report; benefit and safety remain to be evaluated.
9. Safety and tolerability results: observed human data requiring denominators, follow-up and adverse-event context.
10. Controlled efficacy signal: a defined outcome interpreted against the study design and comparator.
11. Validated clinical benefit: evidence sufficient to support a specific benefit claim in a defined population, not a general claim of age reversal.

Where partial reprogramming stands now

This is a selected programme map, not an exhaustive trial census. “Not established” means the reviewed material does not establish the milestone; it is not proof that no undisclosed or differently registered activity exists. The comparison includes boundary cases precisely to prevent unrelated programmes from being counted as human partial-reprogramming trials.

ER-100: what has actually crossed into a human trial

The NCT07290244 study record identifies a Phase 1 study with estimated enrollment of 18. Its displayed status is Recruiting; the actual study start is 2 March 2026 and the last update was posted on 19 May 2026. These dates are not interchangeable with a first-dose date. Life Biosciences separately announced IND clearance on 28 January and reported first dosing on 9 June 2026. The regulatory statement is sponsor-attributed, not evidence of FDA approval of efficacy.

The registered intervention is intravitreal AAV delivery of an inducible OSK programme for optic neuropathies, including open-angle glaucoma and non-arteritic anterior ischemic optic neuropathy. The registered design is open-label and sequential, with safety as the primary focus. Its scope is an eye-disease intervention, not a whole-body longevity study.

First dosing establishes that the programme has crossed an operational threshold according to the sponsor. It does not establish that a participant’s vision improved, that the intervention is acceptably safe, or that aging was slowed. The absence of posted registry results is an evidence gap, not a negative trial result.

Safety control is a design problem, not a proven outcome

Inducible expression, exposure control, sentinel/cohort review and extended follow-up are features of the ER-100 risk-management design. They are reasons to examine the eventual data carefully, not reasons to declare the intervention safe before those data exist.

The relevant distinction is between an intended control and a demonstrated consequence. A mechanism intended to regulate expression does not, by itself, establish that all effects are reversible or that a clinically adequate safety margin exists. Exposure, tissue response, durability and adverse findings must be interpreted together. These are evaluation questions, not dosing instructions.

The biological rationale also has a model boundary. Lu and colleagues’ 2020 retinal study tested OSK in mice and reported retinal and visual findings in those models. It supports preclinical rationale; it does not establish restored vision in patients. Neither a compelling animal result nor a carefully designed control system substitutes for human benefit-risk data.

What the other programmes have — and have not — reached

NewLimit’s May–June progress update describes preclinical liver and endothelial work and development of RNA/lipid-particle medicines. Its financing announcement sets out a 2027 clinical ambition. These are company reports and plans, not evidence of human dosing. Exact factors and final programme-specific authorizations are not established in this record.

Shift’s pipeline page distinguishes an AAV strategy for SB000 from RNAi and small-molecule work around SB101. These adjacent cell-state approaches should not be silently relabelled as the same OSK/OSKM intervention. The reviewed page does not establish a treated-human milestone, comparative clinical safety or clinical efficacy.

Junevity’s current homepage identifies JUN_02 as a dual-targeted siRNA obesity programme. Its current pipeline says JUN_02 combines JUN_01 siRNA with an adipose-targeted siRNA and gives a company-planned Phase 1a safety-study start in early 2027 and Phase 2a proof-of-concept target by mid-2028. Those dates are development plans, not evidence of authorization, registry entry, dosing, safety or efficacy. The December 2025 JUN_01 announcement remains historical evidence; the current page does not establish why the programme description changed or whether the earlier standalone framing was renamed, reprioritized or discontinued.

Retro’s programme update separates an autophagy candidate, RTR242, from tissue reprogramming and iPSC-derived cell products. A Phase I statement about the autophagy programme cannot be assigned to tissue reprogramming. Cell replacement and transient in-vivo reprogramming likewise need separate evidence trails. Human reprogramming status remains unestablished in this source set.

What human-cell experiments establish

Gill and colleagues’ transient-reprogramming experiments used cultured human fibroblasts and OSKM factor expression. The study examined molecular and functional cellular measures, with loss and reacquisition of cellular identity in the experimental process. It did not treat patients or establish a clinically usable intervention.

Sarkar and colleagues’ mRNA-factor study examined transient OSKM plus LIN28 and NANOG expression in human cell models. Its cellular findings are a distinct evidence category from treatment outcomes in people. Neither paper establishes a validated clinical surrogate or a human healthspan benefit.

The analytical value of these studies is mechanistic and translational: they make specific experimental effects testable. The limit is equally important. A shift in a molecular age signature is not automatically a measure of clinical repair, and a cell-culture effect does not resolve delivery, persistence or benefit-risk in a participant.

What evidence would materially change the field

The next useful evidence is more specific than a broad claim that reprogramming works. Human safety findings need the number exposed, dose/exposure context, adverse-event detail and follow-up. Durability needs repeated observation rather than a single early measurement. A proposed efficacy signal needs a defined outcome, a suitable comparator and an account of uncertainty.

For this analysis, clinical relevance means connecting the result to the programme’s actual indication and population. An eye-disease result should first be interpreted as an eye-disease result. Extending it to generally healthy people, other organs or lifespan would require additional evidence. This is an assessment standard, not a claim that those later results have been obtained.

What would change this assessment

• Posted ER-100 results or a peer-reviewed human report would move the discussion from operational milestones to observed outcomes.
• A material registry change, safety event or protocol amendment would require a dated reassessment rather than continued reliance on the current status label.
• A programme-specific authorization, registry entry or dosing announcement could change another row’s stage, provided the candidate and modality match. For Junevity, registry, authorization or dosing evidence—or a material revision of the current company timetable—would change its programme stage.
• New controlled evidence could alter the efficacy assessment; an investor presentation or financing announcement alone could not.
• Reproducible clinical benefit with adequate follow-up would support a narrower indication-specific conclusion before any generalized longevity claim.

Sources and evidence

The registry controls study design and posted status; sponsor announcements support attributed operational milestones. Company pipeline pages establish what their developers disclose, not independent clinical validation. The cited experimental papers retain their animal or human-cell classification. Research cutoff: 18 September 2026. This record offers no treatment recommendation.

• ER-100 registry.
• ER-100 IND clearance announcement.
• ER-100 first participant dosed announcement.
• NewLimit Series C and proposed trial timing.
• NewLimit May/June progress update.
• Shift pipeline.
• Junevity homepage — current JUN_02 obesity-programme description; retrieved 18 September 2026.
• Junevity pipeline — current company-reported JUN_01/JUN_02 relationship and JUN_02 development timetable; retrieved 18 September 2026.
• Junevity historical seed announcement.
• Retro financing and programme update.
• Lu et al. mouse OSK vision study.
• Gill et al. transient reprogramming.
• Sarkar et al. non-integrative reprogramming.