SinoMab BioScience Limited — Regulatory Filings 2021

Nov 30, 2021

Hong Kong Exchanges and Clearing Limited and The Stock Exchange of Hong Kong Limited take no responsibility for the contents of this announcement, make no representation as to its accuracy or completeness and expressly disclaim any liability whatsoever for any loss howsoever arising from or in reliance upon the whole or any part of the contents of this announcement.

==> picture [29 x 43] intentionally omitted <==

==> picture [29 x 43] intentionally omitted <==

SinoMab BioScience Limited 中國抗體製藥有限公司

(Incorporated in Hong Kong with limited liability)

(Stock code: 3681)

VOLUNTARY ANNOUNCEMENT SM03 – COMPLETION OF ENROLLMENT IN PHASE III CLINICAL TRIAL IN CHINA

Reference is made to the announcements of SinoMab BioScience Limited (中國抗體製藥有限公 司) (the “ Company ”) dated 7 April 2020, 8 June 2020, 22 June 2020, 28 September 2020 and 27 October 2020 in relation to the latest research and development progress of the Company’s flagship product, SM03.

The board (the “ Board ”) of directors (the “ Directors ”) of the Company is pleased to announce that, on 30 November 2021, SM03 (Suciraslimab) Phase III clinical trial for rheumatoid arthritis (RA) has completed its targeted enrollment of 510 patients. The patients currently in screening will be randomized by end of December 2021, given eligibility criteria are met. The Phase III clinical trial is a multi-center, randomized, double-blind, placebo-controlled, parallel group study to confirm the clinical efficacy and long-term safety in active RA patients receiving methotrexate (MTX).

The efficacy and safety of Suciraslimab was previously evaluated in a phase II clinical study in moderate-to-severely active RA patients. The study results were published recently and shown that Suciraslimab at a dose of 600 mg with 4 and 6 infusions respectively, were both efficacious and well-tolerated throughout the 24 weeks of treatment when compared with the placebo group. Suciraslimab was effective in suppressing disease activity and alleviates symptoms of moderate-toseverely active RA patients receiving stable doses of background MTX.

The Company’s flagship product, SM03 (Suciraslimab), a potential global first-in-target anti-CD22 monoclonal antibody for the treatment of RA and potentially for the treatment of other immunological diseases, is currently in Phase III clinical trials in China.

1

Cautionary Statement required by Rule 18A.05 of the Rules of Governing the Listing of Securities on the Stock Exchange: The Company cannot guarantee that it will be able to ultimately develop and market SM03 (Suciraslimab) successfully. Shareholders of the Company and potential investors are advised to exercise caution when dealing in the shares of the Company.

By Order of the Board SinoMab BioScience Limited Dr. Shui On LEUNG Executive Director, Chairman and Chief Executive Officer

Hong Kong, 30 November 2021

As at the date of this announcement, the executive Director is Dr. Shui On LEUNG, the non-executive Directors are Dr. Haigang CHEN, Mr. Xun DONG, Mr. Senlin LIU, Ms. Wenyi LIU, Mr. Huiyuan MA and Mr. Jing QIANG, and the independent non-executive Directors are Mr. George William Hunter CAUTHERLEY, Mr. Ping Cho Terence HON, Dr. Chi Ming LEE and Mr. Dylan Carlo TINKER.

2