FXB0871, a PD-1-Targeted Attenuated IL-2 Fusion Protein, Enters Phase 1 Clinical Testing in China

Fosun Pharma announced on May 29, 2026, that the first participant in mainland China has been dosed in a phase 1 clinical trial of FXB0871, an investigational programmed cell death protein-1 (PD-1)-targeted attenuated interleukin-2 (IL-2) fusion protein immunotherapy (ATTENUKINE) developed in collaboration with Teva Pharmaceutical Industries (Teva).¹

The candidate, designated TEV-56278 outside of Fosun Pharma's licensed territory, is designed to selectively deliver a modified IL-2 signal to PD-1-positive tumor-reactive T cells. This approach is intended to enhance anti-tumor immune activity while limiting the systemic toxicities historically associated with high-dose IL-2 therapy. According to Fosun Pharma, no IL-2–based product with targeted delivery selectively directed to tumor-reactive T cells has been approved globally to date.¹

The China phase 1 trial initiation follows an ongoing international phase 1 study of TEV-56278/FXB0871 in the United States and Canada. Clinical data will be shared between Fosun Pharma and Teva to support joint development.

What is FXB0871’s mechanism of action, and how does it differ from existing IL-2 therapies?

FXB0871 employs the ATTENUKINE platform, which is a fusion protein architecture that links an attenuated IL-2 moiety to a PD-1-targeting domain. The platform’s aim is to concentrate IL-2 signaling at the site of PD-1-expressing, tumor-infiltrating T cells.² A conventional recombinant IL-2, aldesleukin, is approved for metastatic renal cell carcinoma and melanoma but is associated with severe dose-limiting toxicities, including vascular leak syndrome, which limits its clinical utility.³

By attenuating IL-2 receptor binding affinity and directing delivery toward PD-1-positive effector T cells rather than peripheral immune compartments, FXB0871 aims to improve the therapeutic index of IL-2–based immunotherapy. Preclinical data cited by Fosun Pharma indicate tumor regression, increased T-cell infiltration, and durable immune memory,¹ though these findings have not yet been published in peer-reviewed literature.

What is the unmet clinical need driving development of targeted IL-2 therapies in oncology?

IL-2 is a critical cytokine for T-cell proliferation, survival, and effector function, and its immunostimulatory potential has long been recognized in oncology.³ However, the clinical application of IL-2 has been constrained by the toxicity profile of systemic administration and by preferential expansion of immunosuppressive regulatory T cells, which express the high-affinity IL-2 receptor constitutively.⁴

Multiple investigational strategies, including IL-2 conjugates, partial agonists, and fusion proteins, are under clinical evaluation in an effort to decouple anti-tumor efficacy from these limitations.⁴ The PD-1–targeted approach represented by FXB0871 is one of several competing strategies in this space, none of which has yet achieved regulatory approval.

What does the Fosun Pharma–Teva licensing structure mean for FXB0871's global development?

Under an existing agreement between the two companies, Fosun Pharma holds an exclusive license to develop, manufacture, and commercialize FXB0871 in mainland China, Hong Kong special administrative region (SAR), Macau SAR, Taiwan, and select Southeast Asian countries. Teva retains rights in other territories including the US and Canada, where the phase 1 study is ongoing.

The data-sharing arrangement between the two companies is intended to accelerate development across both programs. This regional licensing structure is common in oncology drug development involving Chinese pharmaceutical partners, though it introduces complexity in harmonizing trial design, regulatory strategy, and eventual label negotiations across jurisdictions.⁵

What are the key limitations, and what clinical data are needed to assess FXB0871's potential?

The current announcement pertains solely to first-patient dosing in a phase 1 trial, with no efficacy, pharmacokinetic, or clinical safety data yet available from human studies. Preclinical findings cited, including tumor regression, T-cell infiltration, and immune memory, are mechanistically supportive but not predictive of clinical outcomes.

The competitive landscape for next-generation IL-2 therapies is crowded, with several candidates from other sponsors at comparable or more advanced stages of development.⁴ Tumor type selection, dosing regimen, combination strategies, and biomarker-defined patient populations have not been disclosed for the China phase 1 trial. Phase 1 data from the US and Canada study, when available, will be critical for informing dose selection and early efficacy signals in the China program.

References

1. Fosun Pharma. Fosun Pharma Announces first participant dosed in China phase 1 trial of FXB0871, an innovative immuno-oncology therapy. Published May 29, 2026. Accessed May 29, 2026. https://www.fosunpharma.com/en/content/details37_17365.html
2. Bentebibel S-E, Hurwitz ME, Bernatchez C, et al. A first-in-human study and biomarker analysis of NKTR-214, a novel IL2Rβγ-biased cytokine, in patients with advanced or metastatic solid tumors. Cancer Discov. 2019;9(6):711-721. doi:10.1158/2159-8290.CD-18-1495
3. Fyfe G, Fisher RI, Rosenberg SA, et al. Results of treatment of 255 patients with metastatic renal cell carcinoma who received high-dose recombinant interleukin-2 therapy. J Clin Oncol. 1995;13(3):688-696. doi:10.1200/JCO.1995.13.3.688
4. Mitra S, Ring AM, Amarnath S, et al. Interleukin-2 activity can be fine-tuned with engineered receptor signaling clamps. Immunity. 2015;42(5):826-838. doi:10.1016/j.immuni.2015.04.018
5. Kesselheim AS, Darrow JJ. FDA designations for therapeutics and their impact on drug development and regulatory review. Clin Pharmacol Ther. 2015;97(2):215-223. doi:10.1002/cpt.1