SinoMab BioScience Limited — Regulatory Filings 2020

Oct 27, 2020

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.

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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 UPDATES REGARDING RECENT BUSINESS DEVELOPMENTS

Reference is made to the announcement of SinoMab BioScience Limited (中國抗體製藥有限公 司) (the “ Company ”) dated 28 September 2020 in relation to a recent update in respect of the Company’s flagship product, SM03.

The board of directors (the “ Directors ”) of the Company is pleased to announce that on 26 October 2020, the Company delivered an oral presentation of the results of the clinical immunogenicity study of SM03 against rheumatoid arthritis (“ RA ”) titled “Anti-drug antibody response against SM03, an anti-human CD22 monoclonal antibody, in Chinese rheumatoid arthritis patients” (the “ Abstract ”) at the 22[nd] Asia-Pacific League of Associations for Rheumatology Virtual Congress. The Asia-Pacific League of Associations for Rheumatology is a confederation of various rheumatology associations that represent different countries of the Asia-Pacific region striving to propagate and consolidate rheumatology endeavours in the Asia-Pacific region.

Immunogenicity in RA patients treated with SM03

Abstract number: 264

SM03 is a novel chimeric monoclonal antibody developed for treatment of RA by targeting B cell antigen CD22. In order to assess immunogenicity of SM03 in RA patients, anti-drug antibodies (“ ADAs ”) were detected and measured.

The Bridging Enzyme-Linked Immuno-Sorbent Assay method developed by the Company can specifically detect ADA response against SM03 in RA patients. This study shows that SM03 has mild immunogenicity. In Chinese patients with active RA, SM03 treatment with background methotrexate was efficacious, with infrequent and mild immunogenicity.

The Company’s flagship product, SM03, 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 and expected to be commercialized by the end of 2021.

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The Company may not be able to ultimately develop and market SM03 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 Director

Hong Kong, 27 October 2020

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

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