CAMBRIDGE, Mass., ROTTERDAM, Netherlands and SHANGHAI, Oct. 22, 2025 /PRNewswire/ -- Harbour BioMed (HKEX: 02142), a global biopharmaceutical company focused on the discovery and development of novel antibody therapeutics in immunology and oncology, today announced positive Phase II clinical data for porustobart (HBM4003), a next-generation, fully human heavy-chain-only anti-CTLA-4 antibody, in combination with tislelizumab, in patients with microsatellite stable (MSS) metastatic colorectal cancer (mCRC).

The multicenter, open-label Phase II study (NCT05167071) enrolled 24 heavily pretreated patients with non-liver-metastatic (NLM) MSS mCRC. Patients received HBM4003 (0.3 mg/kg) plus tislelizumab (200 mg) every 21 days. The primary efficacy endpoint was objective response rate (ORR) per RECIST 1.1 criteria. The findings showed promising antitumor activity and a manageable safety profile for the combination therapy in this difficult-to-treat population.

Key findings include:

• Baseline: All patients (N=24) had received ≥2 prior lines of therapy; 16/24 (66.7%) had lung metastases.
• Efficacy: Among the 23 evaluable patients, the combination therapy achieved:
  • Objective Response Rate (ORR): 34.8% (8 partial responses)
  • Disease Control Rate (DCR): 60.9% (8 partial responses + 6 stable diseases)
  • Median Progression-Free Survival (mPFS): 4.2 months
• Safety: The regimen was well-tolerated, with no Grade 4 or fatal treatment-emergent adverse events (TEAEs) observed.
  • TRAEs were reported in 87.5% (21/24) of patients, most commonly (incidence ≥20%) liver function test abnormalities, hematological abnormalities, and pyrexia (mostly Grade 1-2).
  • Treatment-related serious adverse events (SAEs) occurred in 37.5% (9/24) of patients.

Dr. Jingsong Wang, Founder, Chairman and CEO of Harbour BioMed commented: "The 2025 Nobel Prize in Physiology or Medicine was awarded to three immunologists for their groundbreaking discoveries in regulatory T cells (Treg cells) and their role in controlling the immune system. HBM4003, a next-generation anti-CTLA-4 antibody discovered through our HCAb Harbour Mice^® platform, is a direct clinical application arising from this foundational research. The positive results from this Phase II clinical study mark an important milestone for Harbour BioMed and underscore the therapeutic potential of HBM4003. We will continue to advance HBM4003 with the goal of delivering transformative immuno-oncology therapies to patients worldwide."

About Porustobart (HBM4003)

Porustobart (HBM4003) is a next-generation, fully human heavy-chain-only anti-CTLA-4 antibody discovered and developed using the HCAb Harbour Mice^® platform. It is also the first fully human heavy-chain-only antibody which entered clinical development globally. Compared with conventional CTLA-4 antibodies, porustobart has unique, favourable properties, including significant Treg cell depletion and optimized pharmacokinetics for improved safety. Additionally, by enhancing antibody-dependent cellular cytotoxicity (ADCC), porustobart increases the potential to selectively deplete intratumoral Treg cells, helping to overcome the efficacy and toxicity bottleneck of current CTLA-4 therapies. The Company has implemented a global development plan for multiple types of solid tumors with an adaptive treatment design for porustobart. Positive efficacy and safety data have been observed in the monotherapy trial targeting advanced solid tumors, as well as in combination trials with PD-1 inhibitors for melanoma, CRC, NEN and HCC. Final data from the study of HBM4003 in combination with toripalimab for advanced HCC were published in Clinical Cancer Research in August 2025.

About Harbour BioMed

Harbour BioMed (HKEX: 02142) is a global biopharmaceutical company committed to the discovery and development of novel antibody therapeutics in immunology and oncology. The company is building a robust and differentiated pipeline through internal R&D capabilities, strategic global collaborations in co-discovery and co-development, and selective acquisitions.

Harbour BioMed's proprietary antibody technology platform, Harbour Mice^®, generates fully human monoclonal antibodies in both the conventional two heavy and two light chain (H2L2) format and the heavy chain-only (HCAb) format. Building upon HCAb antibodies, the HCAb-based immune cell engagers (HBICE^®) bispecific antibody technology enables tumor-killing effects that traditional combination therapies cannot achieve. Additionally, the HCAb-based bispecific immune cell antagonist (HBICA^TM) technology empowers the development of innovative biologics for immunological and inflammatory diseases. By integrating Harbour Mice^®, HBICE^®, and HBICA^TM with a single B-cell cloning platform, Harbour BioMed has built a highly efficient and distinctive antibody discovery engine for developing next-generation therapeutic antibodies. For more information, please visit www.harbourbiomed.com.

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