Spero Therapeutics Announces $30 Million Series B Preferred Financing

Funding Supports Development of Novel Therapies To Treat Gram-Negative Bacterial Infections

CAMBRIDGE, Massachusetts, February 2, 2016 – Spero Therapeutics, a biopharmaceutical company founded to develop novel therapies to treat bacterial infections, announced existing Series A investors Atlas Venture, SR One, MRL Ventures, Lundbeckfond Ventures, The Kraft Group and Partners Innovation Fund will provide $30 million in Preferred B funding.

Spero will use proceeds from this financing to further progress its unique therapeutic "Potentiator Platform," intended to improve drug potency and enhance the utility of existing anti-infective medications. Funding will also enable the organization to advance efforts in support of its DHFR program which targets Gram-positive and negative bacteria, fungi and protists. The DHFR program seeks to expand a novel antifolate's antibacterial spectrum to treat trimethoprim-resistant isolates including key Gram-negative pathogens.

"Spero is making excellent progress in its effort to create novel therapies to combat severe infections by reinvigorating existing antibiotics and returning their relevance within the field of anti-infectives," said Jean-François Formela, M.D., Partner at Atlas Venture. "We are excited to continue working with a company doing truly innovative work that has the potential to fulfill such an important unmet medical need."

"We are very privileged to have the strong support of our existing investors to close this Series B financing, which will allow us to continue to advance the important work we are doing to combat the global public health threat of antibiotic resistance.," said Ankit Mahadevia, M.D., President and Chief Executive Officer of Spero. "Humankind is currently losing a race against bacteria now resistant to every known antibiotic—known as 'Superbugs'—with immeasurable healthcare consequences if left unchecked. Spero is executing an aggressive effort to develop important therapies that differ mechanistically and functionally than available treatments in order to address this growing threat."

"The unanimous reinvestment decision among Series A backers is a reflection of the promise and progress made to date," said Rez Halse, Ph.D., Partner at MRL Ventures. "The unique Spero Potentiator Program, and other early stage efforts offer the potential to play a critical role in addressing the growing antibiotic resistance threat."

About Spero
Spero is a biopharmaceutical company developing a pipeline of novel treatments for bacterial infections and is located in Cambridge, Massachusetts. The company's pipeline of anti-infective agents is one of the most unique in the industry – focused on Gram-negative bacterial infections and Gram-positive and negative bacteria, fungi and protists. Spero is pioneering an entirely new therapeutic platform called the Potentiator; this approach has yielded multiple molecules that enhance the utility and potency of many classes of existing drugs to include Gram-negative organisms.

Spero's DHFR program is exploring the expansion of a novel antifolate's antibacterial spectrum to treat trimethoprim resistance isolates including Gram-negative pathogens. And, Spero's MvfR program is exploring the hypothesis of blunting the virulence of bugs, infections, essentially "buying time" so antibiotics can take effect. The investors in Spero include Atlas Ventures, SR One, MRL Ventures, Lundbeckfond Ventures, The Kraft Group and The Partners Innovation Fund. For more information, please visit www.sperotherapeutics.com

About Atlas Venture
Atlas Venture is an early-stage venture capital firm that invests in life sciences startup companies in the U.S. Atlas is headquartered in Cambridge, Massachusetts.

About SR One
SR One is the corporate venture capital arm of GlaxoSmithKline. The firm invests globally in emerging life science companies that are pursuing innovative science which will significantly impact medical care. SR One has a team of investment professionals, located in the US and UK. As a Team, the firm's experience spans basic science, industry and the market. SR One takes an active role in its portfolio companies and works with management teams and its fellow venture investors to create significant value. Celebrating its 30th anniversary in 2015, SR One has invested $1B in more than 170 companies, and its current portfolio includes 40 private and public companies. SR One's expanded remit also focuses on maximizing the value of GSK technological innovation to establish new businesses and revenue opportunities across a range of industries.

MRL Ventures
MRL Ventures Fund, LLC is the therapeutics-focused seed and early-stage corporate venture fund of Merck & Co., Inc. From our headquarters in Kendall Square, Cambridge and with offices in Mission Bay, San Francisco and Central London, MRL Ventures invests globally in innovative science and transformational therapeutics. We are a team of experienced life-sciences venture capital professionals committed to supporting great entrepreneurs in their quest to create value through building companies that have a meaningful impact on health and disease.

About Lundbeckfond Ventures
Lundbeckfond Ventures is a part of the asset management subsidiary of The Lundbeck Foundation which in addition to substantial financial assets has controlling ownerships in H. Lundbeck A/S, ALK-Abelló A/S and Falck A/S. Lundbeckfond Ventures has an evergreen structure and invests around $60 million annually in life science companies. The Lundbeckfond Ventures team is located in Copenhagen, Denmark, and is active in both Europe and USA.

About The Kraft Group
The Kraft Group has grown its portfolio to include investments across many industries and business types. It has combined the Kraft family's entrepreneurial experience with a talented team of professionals made up of financial advisors, legal counsel and tax experts – all trusted, long-standing members of The Kraft Group. This group creates an environment of streamlined due diligence and decision-making.

About Partners Innovation Fund
The Partners Innovation Fund, established in 2007, was launched with a total commitment of $35 million from Brigham and Women's Hospital and Massachusetts General Hospital. It addresses Partners HealthCare's unmet need for funding of early-stage technology to drive improved medical care for patients. The goal of the fund is to provide necessary support to advance innovations in medical systems, therapy, drugs and medical devices.

CONTACT:
Spectrum Science Communications:
Maia Arnold, PhD
Senior Scientific Executive
202-955-6222 x2506
[email protected]