Nanjing Leads Biolabs Co., Ltd. has moved opamtistomig, or LBL-024, into formal Chinese regulatory review after the Center for Drug Evaluation of the National Medical Products Administration accepted a marketing application for the company’s PD-L1/4-1BB bispecific antibody as monotherapy in previously treated advanced extrapulmonary neuroendocrine carcinoma. The August 21 filing makes opamtistomig the first PD-L1/4-1BB bispecific antibody to reach this stage of regulatory review globally, according to Leads Biolabs, while the application had already been placed under Priority Review in July.
The regulatory milestone is unusually significant for immuno-oncology because 4-1BB has been regarded as an attractive but difficult therapeutic target for years. Agonizing the receptor can intensify T-cell and natural killer cell activity, potentially strengthening antitumor immunity, but earlier attempts to activate 4-1BB systemically were constrained by either liver toxicity or inadequate therapeutic activity at tolerable doses.
Opamtistomig is designed to address that problem through conditional activation. The bispecific antibody simultaneously targets PD-L1 and 4-1BB, using tumor-associated PD-L1 binding to concentrate 4-1BB stimulation within the tumor microenvironment rather than activating the costimulatory pathway indiscriminately throughout the body. Leads Biolabs describes this architecture as part of its X-Body platform.
If approved, Leads Biolabs says opamtistomig could become the first marketed antibody directly targeting 4-1BB. That remains a prospective distinction because NMPA acceptance and Priority Review do not constitute marketing authorization, while the detailed dataset from the 96-patient registrational study supporting the application has not yet been publicly presented.
Why has 4-1BB been such an attractive but difficult oncology target?
4-1BB, also known as CD137, is a costimulatory receptor expressed on activated immune cells including T cells and natural killer cells. When appropriately stimulated, the receptor can enhance proliferation, survival and cytotoxic activity, providing a powerful theoretical mechanism for strengthening antitumor immunity.
The difficulty has been controlling where and how strongly that activation occurs. First-generation systemic 4-1BB agonist antibodies demonstrated that excessive stimulation could create serious liver toxicity, while approaches using lower systemic activity sometimes failed to generate sufficient antitumor efficacy.
That history turned conditional 4-1BB activation into an important area of bispecific-antibody development. Instead of stimulating the receptor everywhere, newer designs attempt to activate 4-1BB only when the antibody is simultaneously bound to another target enriched within the tumor microenvironment.
Opamtistomig uses PD-L1 as that anchoring target. One side of the molecule blocks the PD-1/PD-L1 immune checkpoint, potentially releasing an inhibitory signal on T cells, while the other activates 4-1BB when the correct spatial conditions are present. The conceptual advantage is therefore dual: remove an immunological brake and provide a localized costimulatory signal through the same molecular construct.
Whether that design produces a clinically superior therapeutic index must ultimately be judged from patient outcomes and safety, not mechanism alone.
What evidence has Leads Biolabs generated in EP-NEC?
Extrapulmonary neuroendocrine carcinoma is an aggressive group of high-grade cancers arising outside the lung. First-line therapy commonly relies on platinum-based chemotherapy, but treatment options become particularly limited once disease progresses, and Leads Biolabs says there is no specifically approved therapy globally for the later-line EP-NEC population targeted by its filing.
The registrational study supporting the Chinese application enrolled 96 patients with third-line or later EP-NEC and completed enrollment in August 2025. Leads Biolabs’ Hong Kong filings describe the study as a single-arm pivotal trial and state that the completed dataset supports the marketing submission.
Detailed results from those 96 patients have not yet been released publicly, creating an important limitation when assessing the filing. Leads Biolabs said the pivotal findings will be presented at a future medical congress, so the regulator currently has access to evidence that external clinicians and investors cannot yet examine fully.
Earlier clinical data nevertheless provide a sense of the activity that prompted the pivotal programme.
In a Phase 1/2a study, 45 evaluable patients with second-line or later EP-NEC included three complete responses and 12 partial responses as of a June 3, 2025 data cutoff. That produced an objective response rate of 33.3% and disease control rate of 51.1%. Median progression-free survival was 2.8 months across the overall population, while median overall survival was 11.9 months.
The presence of complete responses in an aggressive later-line cancer is clinically interesting, but the early study was non-randomized and involved only 45 evaluable patients. Response rate cannot establish a survival advantage, and historical comparisons are particularly vulnerable to differences in patient selection and disease biology.
The 96-patient registrational trial is therefore more important than the earlier signal, even though it too uses a single-arm design.
How should a single-arm pivotal filing be interpreted before the full dataset is public?
China’s regulatory strategy for opamtistomig reflects the severity and unmet need associated with advanced EP-NEC. Leads Biolabs previously disclosed that it had discussed the registrational approach with the Center for Drug Evaluation and designed the pivotal trial around independent-review-committee-assessed objective response rate, with progression-free survival, duration of response and overall survival serving as additional measures relevant to a potential conditional approval.
That design can be appropriate in a rare, aggressive setting lacking established later-line treatment, particularly if tumor responses are large, durable and clearly exceed what would normally be expected. It nevertheless provides less comparative certainty than a randomized trial.
The pivotal population also needs to be examined carefully once the data are presented. Response rate will be more convincing if responses occur across relevant subgroups, last for substantial periods and are accompanied by acceptable safety. Median duration of response will therefore be one of the most important figures to emerge from the complete dataset.
Overall survival should also be interpreted cautiously because a single-arm study cannot isolate the treatment effect from prognostic differences between enrolled patients and historical populations.
The application’s Priority Review status accelerates regulatory consideration but does not change those evidentiary principles. NMPA may still request additional analyses, impose conditions or decline approval if the benefit-risk package is insufficient.
There is also some nomenclature variation in the company’s disclosures. Earlier Leads Biolabs documents described the planned submission as a Biologics License Application, while the August 21 announcement refers to an accepted New Drug Application. The substantive regulatory development is that CDE has accepted the marketing application for review; the terminology difference does not mean two separate applications have been filed.
What has the broader safety experience shown about conditional 4-1BB activation?
The key promise of a PD-L1-dependent 4-1BB bispecific is that tumor-localized activation could avoid the systemic toxicity that complicated earlier 4-1BB programmes.
In the first-in-human Phase 1/2 development programme across solid tumors, Leads Biolabs reported no dose-limiting toxicities and said the maximum tolerated dose had not been reached at doses as high as 25 mg/kg. The company’s 2025 annual report likewise characterized most adverse events in the EP-NEC monotherapy experience as Grade 1 or Grade 2 and manageable.
That is encouraging but does not settle the safety question. The registrational study nearly doubles the size of the earlier evaluable EP-NEC monotherapy population, and detailed rates of treatment-related adverse events, liver abnormalities, discontinuations, serious adverse events and immune-mediated toxicities will need to be reviewed once released.
Combination therapy may introduce another safety profile entirely. Leads Biolabs has been evaluating opamtistomig with platinum-based chemotherapy in first-line EP-NEC, where earlier Phase 1b/2 results showed an objective response rate of 75% and disease control rate of 92.3% among 52 efficacy-evaluable patients across dose levels.
Those results are not part of the monotherapy indication currently under regulatory review, but they demonstrate how the company intends to use opamtistomig as more than a narrowly positioned salvage treatment.
Could EP-NEC approval turn opamtistomig into a broader immuno-oncology platform?
Leads Biolabs has expanded the programme aggressively across solid tumors. Development now includes non-small cell lung cancer, small cell lung cancer, biliary tract cancer, hepatocellular carcinoma, ovarian cancer, esophageal squamous cell carcinoma, gastric or gastroesophageal junction cancer, triple-negative breast cancer and melanoma, among other indications.
The company has also secured US and European regulatory designations around the EP-NEC programme. FDA granted Orphan Drug designation in November 2024 and Fast Track designation in January 2026, while European orphan designation followed in January 2026. These designations support development but should not be confused with approval outside China.
An initial NMPA approval could nevertheless have strategic value beyond immediate EP-NEC sales. It would provide commercial manufacturing experience, real-world safety data and regulatory validation for a 4-1BB bispecific platform whose larger opportunity may ultimately reside in more common cancers.
The first-line EP-NEC programme illustrates that ambition. In May 2026, CDE allowed Leads Biolabs to proceed with a pivotal Phase 3 study of opamtistomig combined with chemotherapy in previously untreated advanced EP-NEC.
The central near-term question, however, remains the narrower one now before Chinese regulators. Opamtistomig has reached marketing review based on a 96-patient single-arm pivotal study in a rare and aggressive cancer with limited later-line options.
Earlier trials show meaningful response activity and an apparently manageable safety profile, but the decisive registrational numbers are still missing from the public record. Until those data are presented and NMPA completes its review, opamtistomig should be viewed as potentially first-in-class rather than an established 4-1BB therapeutic breakthrough.
