Spero Therapeutics Appoints Debra Jeske Zack, M.D., Ph.D., as Chief Medical Officer

Dr. Zack brings more than 25 years of leadership in developing therapeutics for immune-mediated diseases

Appointment strengthens Spero's clinical leadership team as the Company advances SP001, a Phase 2-ready third-generation anti-CD40L antibody for IgG4-related disease (IgG4-RD) and other immune-mediated conditions

CAMBRIDGE, Mass., July 27, 2026 (GLOBE NEWSWIRE) -- Spero Therapeutics, Inc. (Nasdaq: SPRO), a clinical-stage biopharmaceutical company focused on advancing next-generation medicines in immunology and inflammation, today announced the appointment of Debra Jeske Zack, M.D., Ph.D., as Chief Medical Officer. Dr. Zack will lead Spero's clinical development strategy and organization as the Company advances its immunology program.

"We are delighted to welcome Deb to Spero at an important time as we initiate clinical development of SP001," said Esther Rajavelu, President and Chief Executive Officer of Spero "She brings deep expertise in rheumatology and immunology along with firsthand experience advancing innovative therapies for autoimmune diseases. Deb's leadership will be invaluable as we advance our clinical strategy with the goal of delivering meaningful therapies for patients with significant unmet medical needs."

Dr. Zack is a board-certified rheumatologist with a Ph.D. in immunology and extensive drug development experience spanning research, clinical development, and medical affairs. At Amgen, she served as Global Development Lead for Enbrel and held additional roles spanning preclinical research, clinical development, and medical affairs. Most recently, Dr. Zack served as Chief Medical Officer of Exagen Inc., and before that she held clinical leadership roles at Xencor Inc., and in the Biotherapeutics Development Unit at Novartis. Before these roles, Dr. Zack served as an associate professor at UCLA for 10 years, treating rheumatology patients and conducting research in molecular immunology. Dr. Zack received her M.D. and Ph.D. from the University of Texas Southwestern Medical School in Dallas, and she completed her residency and rheumatology fellowship at the UCLA School of Medicine.

"I am thrilled to join Spero at such a pivotal time in the Company's evolution," said Dr. Zack. "Spero has set a strong foundation with SP001, targeting CD40 ligand, as its lead asset in immunology. The inhibition of this target, which modulates both B-cell and T-cell activation, has the potential to address multiple drivers of immune-mediated diseases, such as IgG4-RD and the opportunity to evaluate and potentially advance this mechanism is particularly compelling. I look forward to working alongside the talented Spero team to advance SP001 and help shape a disciplined clinical development strategy for this program and future pipeline opportunities in immune-mediated diseases."

About SP001 SP001 is a third-generation, potential best-in-class, fully humanized, Fc-silent IgG1 monoclonal antibody targeting CD40L, an upstream immune activation signal involved in T-cell, B-cell, antigen-presenting cell, and platelet biology. By blocking CD40L, SP001 has the potential to provide a targeted non-B-cell-depleting treatment across multiple immune-mediated diseases where immune-cell interactions drive chronic inflammation, relapse, fibrosis, and additional tissue damage. SP001 is designed to address platelet activation concerns associated with earlier anti-CD40L antibodies, while preserving key monoclonal antibody properties, including FcRn interaction that supports IgG-like half-life.

About Spero Therapeutics Spero Therapeutics is a clinical-stage biopharmaceutical company focused on advancing next-generation medicines in immunology and inflammation for patients with serious diseases and major treatment gaps. The Company's lead program, SP001, is a third-generation, Fc-silent anti-CD40L monoclonal antibody being advanced first in IgG4-related disease, with a broad potential for additional immune-related conditions. For more information, visit www.sperotx.com .

Forward-Looking Statements This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995, as amended. Forward-looking statements include, but are not limited to, statements relating Spero's expectations regarding its ability to advance SP001 into clinical development and the potential benefits thereof. Forward-looking statements are based on Spero's current expectations and assumptions and are subject to risks and uncertainties that could cause actual results to differ materially from those expressed or implied by such statements. These risks and uncertainties include, among others, risks related to the completion and integration of the Innovent transaction; Spero's ability to successfully develop SP001; the timing and outcome of clinical trials and regulatory interactions; the ability to obtain and maintain regulatory approvals; potential safety, efficacy, manufacturing, supply, intellectual property, financing, competitive, and market risks; and other risks described in Spero's filings with the Securities and Exchange Commission. Spero undertakes no obligation to update any forward-looking statements, except as required by law.

Investor Relations Contact: Shai Biran, PhD Spero Therapeutics [email protected]

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