T-cell engagers in healthy volunteers
Finding the active dose before the first patient
One of the approaches in the project on speeding up first-in-human T-cell engager studies. The registry and abstract search was run on 2026-09-10. Every source is characterized from a registry record, an abstract or a press release; none has been read, and every entry in the references carries ❌.
In Brief
The idea. Give healthy volunteers (HVs) one or two doses of the T-cell engager (TCE), climbing a dose ladder until the first sign of activity: a grade 1 cytokine release (fever), or peripheral B cells falling by half. That dose, found in weeks in a phase 1 unit, becomes the starting neighbourhood for patients, and the patient study begins where a conventional escalation would have finished.
✅ It has been done. Three healthy volunteer studies of TCEs are registered, all started between December 2025 and July 2026, all in Melbourne, all for autoimmune indications, and all subcutaneous. None has posted a result. Section 2 has the table.
⚠️ It applies to autoimmune programmes only. The three sponsors that dosed volunteers built molecules with a tuned CD3 arm and an extended half-life, for one or two administrations, and a volunteer’s B-cell count is the same measurement as a patient’s. In oncology the target burden that drives cytokine release is absent in a volunteer, so a volunteer’s fever dose says little about a tumour patient’s, and no oncology TCE has been given to volunteers. Section 4 works through the translation.
It saves six months to a year against a conventional escalation in patients, under the assumptions in Section 5, which a programme should replace with its own.
❌ The Ouro question is unresolved. A colleague recalled a Chinese healthy volunteer study of a TCE later acquired by Ouro Medicines. No such study of Ouro’s molecule, CM336, is on ClinicalTrials.gov, and the Chinese registries were not searched. Cizutamig, the molecule that does have a registered volunteer study, is also a Chinese-origin BCMA x CD3 engager, and the two may have been conflated. Section 2 has both. The question to put back to the colleague is the trial identifier.
1. The Idea
Dose healthy volunteers once or twice each, climbing between cohorts, and stop at the first dose that either produces a grade 1 cytokine release syndrome (CRS), which in a volunteer means a fever, or depletes peripheral B cells by 50%. Call that the active dose, and open the patient study with a starting dose and step-up regimen anchored to it.
The claim to test is speed. A phase 1 unit recruits from a standing pool, doses the next cohort within days of the previous readout, and reads a single-dose cytokine and B-cell response inside a week. A conventional oncology escalation waits on accrual of patients with the right disease at the right stage, a 28-day dose-limiting toxicity (DLT) window, and a cohort review. If the volunteer ladder climbs three times faster, the gap between the starting dose and the active dose is crossed before the first patient is enrolled.
2. Studies Found
Registered Healthy Volunteer Studies of T-Cell Engagers
| Study | Molecule | Target | Design | Volunteers | Start | Status | Marker |
|---|---|---|---|---|---|---|---|
| NCT07236411 | Cizutamig (Candid; EMB-06, EpimAb) | BCMA x CD3, 2+2 FIT-Ig | Randomized, double-blind, single IV or SC dose against placebo; absolute bioavailability | 24 healthy adults, all arms | 2025-12-04 | Completed 2026-07-14, no results posted | ❌ |
| NCT07284797 | XmAb657 (Xencor) | CD19 x CD3, 2+1, extended half-life | Open-label first-in-human dose escalation, SC | Healthy adults as the first cohort, then myositis, systemic sclerosis, Sjögren’s | 2026-02-24 | Recruiting; primary completion Oct 2028 | ❌ |
| NCT07712939 | CND319 (Candid) | CD19/CD20 x CD3 | Open-label first-in-human; single ascending dose in volunteers, multiple ascending dose in patients | Healthy adults 18–65 in Part 1 SAD; rheumatoid arthritis and Sjögren’s in MAD and expansion | 2026-07-20 | Recruiting; primary completion Mar 2028 | ❌ |
All three studies started in or after December 2025, all are for autoimmune indications, and none is an oncology TCE. All three molecules were engineered for the setting: a CD3 arm with reduced affinity, a long half-life, subcutaneous administration, and a single dose or short course as the intended regimen.
No registry record shows the readout the idea depends on. The registered primary outcomes are adverse events (XmAb657, CND319) and absolute bioavailability (cizutamig), and the secondary outcomes are serum concentration and anti-drug antibodies. B-cell counts and cytokines will have been measured but are not registered endpoints, so what the volunteer cohorts found will have to come from a presentation. Xencor expects to report on the XmAb657 study in the second half of 2026.
What Is Known About the Molecules From Patients
Cizutamig was dosed in volunteers after its dose range was known from patients. Before the volunteer study it had been given to 40 patients with relapsed or refractory multiple myeloma at weekly doses of 0.2 to 300 mg, with CRS at grade 1 in 18% and grade 2 in 8%, median onset one day, and no immune effector cell-associated neurotoxicity syndrome (ICANS); and to one patient with refractory rheumatoid arthritis, with no cytokine release (entry 24). By January 2026 the sponsor reported 80 patients dosed, half with autoimmune disease, mild cytokine release in fewer than 20%, and no ICANS. That order is the reverse of the idea in Section 1. The study measured bioavailability, and it shows that a volunteer can be dosed, not that the active dose was found that way.
XmAb657 matches the idea: a first-in-human escalation whose first cohort is healthy participants. In cynomolgus monkeys a single dose held B cells below 5 cells/µL for at least 42 days, in lymph node and marrow as well as blood, with no clinical signs of cytokine release and a half-life near 15 days (entry 25). The registry record does not say whether the volunteer cohort climbs to a B-cell-depleting dose or stops at a dose chosen to be subactive. That is the first thing to find out when the study reports.
The Ouro Medicines Molecule
CM336 (gamgertamig) is a BCMA x CD3 engager developed by Keymed Biosciences in Chengdu. It has been in a phase 1/2 in multiple myeloma in China since 2022, and in autoimmune cytopenias, bullous disease, Sjögren’s and several plasma cell disorders since 2025. Keymed licensed rights outside Greater China to Platina Medicines, a unit of Ouro Medicines, in January 2025, and the molecule became OM336. Gilead announced the acquisition of Ouro in March 2026 and completed it in June.
The registered OM336 studies are in autoimmune cytopenias (United States and Australia), Sjögren’s and myositis (New Zealand), and sensitized kidney transplant candidates (Austria and Germany). None enrols healthy volunteers. The one CM336 record carrying the healthy-volunteer flag, NCT06745687, is a study in high-risk smouldering myeloma, and the flag is a registry error.
A Chinese healthy volunteer study of CM336, if one exists, would be on the Center for Drug Evaluation registry (chinadrugtrials.org.cn) or the Chinese Clinical Trial Registry, and neither was searched. Cizutamig is the other candidate for what the colleague recalled: also a Chinese-origin BCMA x CD3 engager, from EpimAb in Shanghai by way of Vignette Bio and Candid Therapeutics. Ask the colleague for the trial identifier or the molecule’s code.
Search Coverage
Searched: ClinicalTrials.gov, by intervention terms (bispecific, trispecific, T-cell engager, CD3) restricted to studies accepting healthy volunteers; Europe PMC for published reports of a CD3-engaging bispecific in healthy subjects, which returned none; and press releases and meeting abstracts for the three molecules found.
Not searched: the Chinese registries, the EU Clinical Trials register, the Australian register (ANZCTR), and the PAGE and ACoP abstract archives.
3. What a Volunteer Study Can Measure
The readouts after a single dose, in the order they arrive:
| Hours after dose | Readout | What it says |
|---|---|---|
| 2–6 | Lymphocyte count falls (T-cell margination) | CD3 was engaged. The earliest pharmacodynamic signal, present at doses well below the active one. |
| 2–24 | IL-6, IFN-γ, TNF in serum | How strongly T cells were activated. A grade 1 CRS is the clinical sign of the same process. |
| 6–48 | Fever | Grade 1 CRS, the first of the two stopping signals in Section 1. |
| 24–72 | Peripheral CD19+ B cells | Depletion, the second stopping signal: depth at nadir and, on later visits, duration. |
| Days to weeks | Serum concentration, anti-drug antibodies | PK, and whether a second dose can be interpreted. |
The two stopping signals will not arrive together. A CD3 arm tuned down, as in all three molecules in Section 2, is tuned to deplete without releasing cytokine. In a volunteer, B cells may fall by half or to zero at a dose that produces no fever, and the first fever may come a log higher or never. The idea as posed treats either signal as “active”, so the design has to choose, because the two name different doses. For an autoimmune programme the answer is depletion, since depletion is the goal and fever the cost. The fever dose then becomes an upper bound the patient study need not approach.
Several volunteers per dose. Volunteers are not scarce, so there is no reason for one person to climb the ladder. A cohort of four to six per dose level, with a sentinel pair dosed a day ahead of the rest, is the ordinary phase 1 shape, and it estimates the between-subject response at each dose, which one person climbing cannot.
A second dose in the same volunteer measures tolerance. Give a priming dose, wait a week, give a higher dose, and compare the cytokine response with a cohort that received the higher dose without priming. That measures the tolerance effect, a primed T-cell pool releasing less cytokine at the next dose, in a system with no tumour and no disease, and a step-up regimen for patients would be designed from it. The confound is that by the second dose the volunteer’s blood B cells are gone, so a lower cytokine response could mean primed T cells or a missing target. Tissue B cells persist longer than blood B cells and make up most of the pool, so the comparison still informs, but the B-cell measurement has to separate the two explanations.
4. Translation From Volunteer to Patient
A volunteer’s active dose is useful to the extent that a patient’s response at the same dose can be predicted from it. Three things differ.
Target burden. Cytokine release scales with the number of target cells the engager finds. A volunteer’s peripheral B-cell count is in the ordinary range, and an autoimmune patient’s is usually similar unless prior rituximab has emptied it; the plasma cell compartment that a BCMA engager targets is larger in a patient with active humoral disease. A patient with a haematological malignancy carries orders of magnitude more target. The volunteer’s fever dose is therefore a lower bound on the fever dose in a low-burden patient, and an overestimate, by an unknown factor, for a patient with a tumour. The B-cell depletion dose translates better, since depleting a normal-sized compartment is the same event in both.
T-cell fitness. An autoimmune patient on glucocorticoids, mycophenolate or methotrexate has a suppressed T-cell response and a volunteer does not. The volunteer dose may over-predict activity in a treated patient, so the patient study would start too low rather than too high: safe, and slow.
Duration. A volunteer given a long-half-life engager loses peripheral B cells for weeks to months (42 days or more in the primate study, entry 25). The volunteer bears that cost for no benefit, which is why all three registered studies are for indications where a single administration is the intended regimen. The ethics review will have weighed it and the consent form will say how; neither document has been read.
The translation holds for autoimmune indications, B-cell or plasma-cell targets, engineered CD3 arms, and a depletion readout rather than a fever readout. Those are the conditions the three registered studies were run under, and the conditions under which the idea in Section 1 works. Outside them, the volunteer dose is a minimal anticipated biological effect level (MABEL) with human data behind it, which still improves on a MABEL without.
5. Where It Applies, and How Much Time It Saves
A volunteer study replaces a prediction of the active dose from primate data with a measurement in humans. What remains uncertain is the volunteer-to-patient translation of Section 4, a factor of a few rather than of tens.
- ✅ B-cell-depleting TCE, autoimmune indication. Run the volunteer study. Start the patient study one or two steps below the volunteer depletion dose, with a step-up regimen designed from the volunteer cytokine data.
- ❌ Solid-tumour or haematological TCE. No volunteer has been dosed with an oncology TCE, the target-burden argument in Section 4 says a volunteer readout would not translate, and depleting a healthy person’s B cells for a lymphoma programme is harder to justify than for an autoimmune one.
The time saving below rests on assumptions, not measurements, and each row is there to be replaced.
| Quantity | Conventional 3+3 in patients | Volunteer single ascending dose |
|---|---|---|
| Recruitment per cohort | Weeks, disease-dependent | Days, from a standing pool |
| Observation before the dose decision | 28-day DLT window | 7 days: CRS window closed, B-cell nadir passed |
| Cohort cadence | 6–8 weeks | 1–2 weeks |
| Dose levels to cross a 3-log gap at 3x steps | 6–7 | 6–7 |
| Time to the active dose | 9–14 months | 2–4 months |
The saving is six months to a year. A saving under about eight weeks, one conventional cohort cycle plus its accrual, would sit inside the noise of ordinary trial execution. This one does not, if the cadence assumptions hold, so check the cadence row first against a real unit’s calendar.
6. Next Steps
- Ask the colleague for the trial identifier behind the Ouro recollection, and search the Chinese registries if it does not come.
- Watch for the XmAb657 volunteer cohort results, expected in the second half of 2026. The dose the volunteers reached, what their B cells did, and whether anyone had a fever answer most of Section 3.
- Read entry 20, the EMA first-in-human guideline, for what it says about healthy volunteers and immunomodulators, since an ethics committee reads that document.
- Set the speed table against a real phase 1 unit’s cohort calendar and a real programme’s escalation history, so both columns become measurements.