Long-Term Cliramitug Exposure Deepens Amyloid Depletion in ATTR-CM
A longer look at cliramitug in ATTR-CM points in the same direction as the first-in-human study: continued treatment was well tolerated, and the biologic signal strengthened rather than fading with time. In the NI006-101 extension cohort, patients who stayed on therapy and, in many cases, moved from lower doses to 30 mg/kg showed further reductions in measures of cardiac amyloid burden alongside improvements in biomarkers, diastolic function, and patient-reported status.
The most clinically important feature of this follow-up is persistence. Antibody-based amyloid depletion has to keep working against a disease process that deposits misfolded transthyretin in the myocardium over years, not weeks. If the target remains accessible and the therapy can be administered without cumulative toxicity, the heart may finally have room to recover some structure and function. This extension provides evidence that the pharmacology of cliramitug still tracks with that logic over a much longer window than the original trial.
A Small but Highly Selected Cohort Stayed on Treatment
Twenty-three participants entered the second open-label extension. All were male, 20 were already receiving background tafamidis, and the median follow-up extended to 29.3 months. Across that period, participants received a median of 10 additional infusions, bringing maximum total exposure to 24 infusions. Thirteen patients who had initially received 10 mg/kg or less were up-titrated to 30 mg/kg during the extension.
Adherence was high at 98%, a useful practical detail in a chronic cardiomyopathy population where repeated infusions can become difficult to sustain. No treatment-related serious adverse events emerged, and no participant discontinued because of treatment-related toxicity. In a disease defined by progressive ventricular stiffening, conduction disease, and relentless biomarker elevation, long-term tolerability is not a side point. It determines whether amyloid depletion can be delivered long enough to matter.
Imaging Showed Continued Reduction in Cardiac Amyloid Signal
The structural and imaging readouts moved in the same favorable direction as the dosing intensified. Continued treatment, especially after up-titration in those with lower prior exposure, was associated with further reductions in cardiac extracellular volume on MRI and lower tracer uptake on bisphosphonate scintigraphy. Those measures matter because they track the burden of infiltrative amyloid within the myocardium rather than a downstream hemodynamic consequence alone.
Cardiac extracellular volume serves as a direct surrogate for tissue infiltration and interstitial expansion. When it falls, the myocardium is not simply behaving better by chance; the tissue environment itself is changing. Bisphosphonate scintigraphy adds another layer by reflecting amyloid signal within the heart, making the convergence of both modalities more persuasive than either test alone. In a cardiomyopathy where wall thickening can reflect protein deposition rather than hypertrophy, imaging that captures clearance is especially valuable.
Biomarkers and Diastolic Physiology Improved in Parallel
The benefits were not confined to imaging. NT-proBNP and troponin T improved, pointing to lower wall stress and less ongoing myocardial injury. Left ventricular relaxation, filling pressures, and wall thickness also improved, suggesting that amyloid depletion translated into measurable hemodynamic relief.
The physiology here is straightforward, even if the disease itself is not. Transthyretin deposits stiffen the ventricle, impair relaxation, raise filling pressures, and drive natriuretic peptide release. They also injure cardiomyocytes, which helps explain persistent troponin elevation in ATTR-CM. If cliramitug lowers the amyloid load, it can plausibly reduce the stiffness that makes the ventricle hard to fill and the biochemical stress that keeps the heart in a chronic state of injury. The observed pattern fits that mechanism.
A single sentence captures the clinical direction of travel: the heart looked less infiltrated, less stressed, and less mechanically constrained after longer exposure.
Patient-Reported Status Moved in the Same Direction
Kansas City Cardiomyopathy Questionnaire scores increased over time, pointing to a possible quality-of-life benefit. In ATTR-CM, symptom change often lags behind biomarker movement, especially when patients are already receiving disease-modifying background therapy. Even so, patient-reported improvement matters because amyloid cardiomyopathy is ultimately a syndrome of exertional limitation, congestion, and loss of reserve.
The score change does not prove broad functional recovery on its own, and the cohort was small. Still, when symptom measures, cardiac biomarkers, and imaging all move together, the story becomes more credible than if one endpoint improved in isolation. The consistency across domains is what gives this extension its weight.
What This Means for Amyloid-Depleting Therapy
Cliramitug is being developed as an amyloid-depleting approach rather than a stabilizer alone. That distinction is central in ATTR-CM, because stabilizing transthyretin slows new deposition, while depletion aims to remove material already lodged in the myocardium. In a chronic infiltrative cardiomyopathy, the possibility of actual clearance is what makes structural reversal biologically plausible.
These data support that premise. Continued exposure and dose escalation were associated with deeper reductions in surrogate markers of amyloid burden, and the safety profile remained favorable over nearly 2.5 years of follow-up. The findings also suggest that lower-dose exposure may not be the ceiling for biologic effect, since participants up-titrated to 30 mg/kg appeared to gain additional benefit.
Still, the study remains a small open-label extension within a narrowly selected group of men who stayed on therapy and tolerated repeated infusions. That makes the results encouraging, but not definitive. The cohort size limits how confidently the field can separate drug effect from selection of more stable survivors, and the absence of a randomized comparator in the extension leaves open how much of the change reflects ongoing natural history under background therapy.
The Remaining Questions Are Dosing, Durability, and Generalizability
Three questions now stand out. First, whether the 30 mg/kg dose should become the preferred long-term regimen for broader use, given the apparent dose-response pattern during follow-up. Second, how durable the amyloid depletion remains once treatment is continued beyond the current observation window. Third, whether the findings extend beyond this all-male cohort and beyond patients already receiving tafamidis.
The next step is not more speculation about mechanism; the mechanism is already biologically coherent. The next step is controlled confirmation in larger and more diverse populations, with hard outcomes that extend beyond surrogate markers. Until then, NI006-101 long-term follow-up leaves cliramitug as one of the clearer examples of an amyloid-depleting strategy that has produced sustained structural and biochemical change without an obvious long-term safety penalty.