HBM HOLDINGS-B - VOLUNTARY ANNOUNCEMENT - FIRST PATIENTS DOSED IN PHASE II SIRIUS COPD STUDY OF

HBM9378/WIN378, A FULLY HUMAN ULTRA LONG-ACTING ANTI-TSLP ANTIBODY

和 鉑 醫 藥 控 股 有 限 公 司 HBM Holdings Limited (incorporated in the Cayman Islands with limited liability) (Stock Code: 02142)

VOLUNTARY ANNOUNCEMENT FIRST PATIENTS DOSED IN PHASE II SIRIUS COPD STUDY OF HBM9378/WIN378, A FULLY HUMAN ULTRA LONG-ACTING ANTI-TSLP ANTIBODY

This announcement is made by HBM Holdings Limited (the "Company", together with its subsidiaries, the "Group") on a voluntary basis to inform the shareholders and potential investors

of the Company about the latest business update of the Group.

The board of directors of the Company (the "Board") is pleased to announce that Windward Bio AG ("Windward Bio"), the Company's partner, has dosed the first patients in the Phase II SIRIUS study of HBM9378/WIN378 (also known as SKB378), a fully human ultra long-acting anti-thymic stromal lymphopoietin (TSLP) antibody, in patients with chronic obstructive pulmonary disease (COPD).

SIRIUS is a global, Phase II, randomized, double-blind, placebo-controlled, dose-finding study designed to evaluate the safety, tolerability, pharmacokinetics and pharmacodynamics of HBM9378/WIN378 in patients with moderate-to-severe COPD.

HBM9378/WIN378 is currently also being evaluated in Windward Bio's POLARIS Phase II/III

asthma study, with initial Phase II data expected in the second half of 2026. Windward Bio expects the first Phase III study of HBM9378/WIN378 in asthma to begin in the fourth quarter of 2026. The initiation of the SIRIUS COPD study expands the clinical development of HBM9378/WIN378 into COPD as a second major respiratory disease.

The Board believes that the initiation of the SIRIUS COPD study marks continued clinical advancement of HBM9378/WIN378 and further supports the potential of the molecule as a differentiated, ultra long-acting anti-TSLP antibody for immunological diseases.

About HBM9378/WIN378

HBM9378/WIN378 (also known as SKB378) is a next-generation, fully human monoclonal antibody that potently inhibits the TSLP ligand. This clinically validated target plays a key role in the development and progression of a wide array of immunological diseases, including asthma and COPD. HBM9378/WIN378 has been engineered to achieve half-life extension (HLE) and have a silenced effector function. It has been studied in a Phase I trial, which confirmed an extended half-life suitable for twice-yearly dosing, demonstrated a low rate of antidrug antibodies, and was safe and well tolerated up to the highest dose tested. HBM9378/WIN378 is administered subcutaneously. Windward Bio licensed the global rights (excluding Greater China and several Southeast and West Asian countries) for WIN378 from Harbour BioMed (also known as HBM9378) and Kelun-Biotech (also known as SKB378). HBM9378/WIN378 is currently being evaluated in the POLARIS Phase II/III asthma study with initial readouts expected in the second half of 2026. HBM9378/WIN378 is also being evaluated in the SIRIUS Phase II COPD study. The first Phase III study of HBM9378/WIN378 in asthma is expected to begin in the fourth quarter of

2026.

Cautionary Statement: We cannot guarantee that HBM9378/WIN378 will be successfully developed or ultimately marketed by the Company and/or its collaboration partners. Shareholders and potential investors of the Company are advised to exercise due care when dealing with the shares of the Company.

Forward Looking Statement

There is no assurance that any forward-looking statements regarding the business development of the Group in this announcement or any of the matters set out herein are attainable, will actually occur or will be realized or are complete or accurate. The financial and other data relating to the Group as disclosed in this announcement has also not been audited or reviewed by its auditors.

Shareholders and/or potential investors of the Company are advised to exercise caution when dealing in the shares of the Company and not to place any excessive reliance on the information disclosed herein. Any shareholder or potential investor who is in doubt is advised to seek advice from professional advisors.

By order of the Board HBM Holdings Limited Dr. Jingsong Wang Chairman and Executive Director

Hong Kong, 9 June 2026