Synlogic Reports Fourth Quarter and Full Year 2021 Financial Results and Provides Business Update - Phenylketonuria (PKU) program on track for Phase 3 trial initiation in H2 2022 - Clinical readouts anticipated for PKU p

Synlogic Reports Fourth Quarter and Full Year 2021 Financial Results and Provides Business Update

- Phenylketonuria (PKU) program on track for Phase 3 trial initiation in H2 2022

- Clinical readouts anticipated for PKU program in H1 2022 and in homocystinuria and enteric hyperoxaluria in H2 2022

- $136.6 million in cash, cash equivalents and marketable securities support projected runway into 2024

- Conference call and webcast at 8:30 a.m. ET today

Cambridge, Mass. March 17, 2022 Synlogic, Inc. (Nasdaq: SYBX), a clinical-stage biotechnology company developing medicines

for metabolic and immunological diseases through its proprietary approach to synthetic biology, today reported financial results for the fourth quarter and full year ending December 31, 2021 and provided an update on pipeline programs.

2021 was a transformational year for Synlogic highlighted by proof of concept for our lead program in phenylketonuria (PKU), said Aoife Brennan,

M.B. Ch.B., Synlogic President and Chief Executive Officer. Despite the devastating burden of this disease, a large majority of people living with PKU remain in need of an efficacious, safe, oral medication. We look forward to sharing Phase 2

data in the first half of this year as we continue plans to initiate Phase 3 later this year. We are also excited for clinical data readouts from our homocystinuria (HCU) and enteric hyperoxaluria programs, as well as research progress including our

ongoing collaborations with Ginkgo Bioworks and Roche.

Recent Portfolio Highlights

SYNB1618 and SYNB1934: In Development for the Treatment of PKU

SYNB1353: In Development for the Treatment of HCU

SYNB8802: In Development for the Treatment of Enteric

Preclinical Pipeline

Anticipated Upcoming Milestones

Rare Metabolic Diseases

Enteric Hyperoxaluria

Earlier this month, the company announced the appointment of Michael Jensen as Chief Financial Officer. Mr. Jensen brings extensive and diversified

experience within global pharmaceutical and medical device companies to Synlogic, spanning analytics, financial management, information systems, and operations. Mr. Jensen was formerly the CFO of Intrinsic Therapeutics.

Fourth Quarter 2021 Financial Results

of December 31, 2021, Synlogic had cash, cash equivalents, and marketable securities of $136.6 million.

Revenue was $0.6 million for the

three months ended December 31, 2021. Revenue in 2021 was associated with the ongoing research collaboration with Roche for the discovery of a novel Synthetic Biotic medicine for the treatment of IBD. There was no revenue for the three months

ended December 31, 2020.

Research and development expenses were $11.9 million for the three months ended December 31, 2021, compared to

$11.4 million for the corresponding period in 2020.

General and administrative expenses for the three months ended December 31, 2021 were

$3.9 million compared to $3.3 million for the corresponding period in 2020.

For the three months ended December 31, 2021, Synlogic reported a consolidated net loss of

$15.1 million, or $0.21 per share, compared to a consolidated net loss of $14.6 million, or $0.39 per share, for the corresponding period in 2020.

Full Year 2021 Financial Results

Revenues were $1.8 million for the year ended December 31, 2021, compared to $0.5 million for the same period in 2020. Revenue in 2021 was

associated with the ongoing research collaboration with Roche for the discovery of a novel Synthetic Biotic medicine for the treatment of IBD. Revenue in 2020 was due to the prior collaboration with AbbVie, which was terminated in May 2020.

Operating expenses were $62.5 million for the year ended December 31, 2021, compared to $61.0 million for the same period in 2020. For the year ended December 31, 2021, consolidated net loss was $60.6 million, or $1.09 per

share, compared to a consolidated net loss of $59.2 million, or $1.65 per share, for the year ended December 31, 2020.

Based upon its current

operating plan and balance sheet as of December 31, 2021, Synlogic expects to have sufficient cash to be able to fund operations into 2024.

Investor Conference Presentation

Synlogic will participate in Oppenheimer s 32nd Annual Healthcare Conference. Dr. Brennan will present virtually at 10:40 am ET.

of the presentation will be accessible under the Event Calendar in the Investors & Media section of the Company s website. An archived version will also be available after the presentation on the Synlogic website.

Conference Call & Webcast Information

Synlogic will host a conference call and live webcast at 8:30 a.m. ET today, March 17, 2022. To access the live webcast, please visit the Event

Calendar page within the Investors and Media section of the Synlogic website. Investors may listen to the call by dialing +1 (844) 815-2882 from locations in the United States or +1 (213) 660-0926 from outside the United States. The conference ID number is 1719849. A replay will be available for 30 days on the Investors and Media section of the Synlogic website.

Synlogic is a clinical-stage biotechnology company developing medicines through its proprietary approach to synthetic biology. Synlogic s pipeline

includes its lead program in phenylketonuria (PKU), which has demonstrated proof of concept with plans to start a pivotal, Phase 3 study in the second half of 2022, and additional novel drug candidates designed to treat homocystinuria (HCU) and

enteric hyperoxaluria. The rapid advancement of these potential biotherapeutics, called Synthetic Biotics, has been enabled by Synlogic s proprietary, reproducible, target-specific drug design. Synlogic uses programmable, precision genetic

engineering of well-characterized probiotics to exert localized activity for therapeutic benefit, with a focus on metabolic and immunologic diseases. Synlogic is also working with Roche in a research collaboration focused on the discovery of a novel

Synthetic Biotic for the treatment of inflammatory bowel disease and with Ginkgo Bioworks to include additional undisclosed preclinical assets, combining Synlogic s approach to Synthetic Biotics with Ginkgo s Codebase and Foundry services.

For additional information visit www.synlogictx.com.

Forward-Looking Statements

This press release contains forward-looking statements that involve substantial risks and uncertainties for purposes of the safe harbor provided by

the Private Securities Litigation Reform Act of 1995. All statements, other than statements of historical facts, included in this press release regarding strategy, future operations, clinical development plans, future financial position, future

revenue, projected expenses, prospects, plans and objectives of management are forward-looking statements. In addition, when or if used in this press release, the words may, could, should, anticipate,

believe, estimate, expect, on track, intend, plan, predict and similar expressions and their variants, as they relate to Synlogic may identify forward-looking

statements. Examples of forward-looking statements, include, but are not limited to, statements regarding the potential of Synlogic s approach to Synthetic Biotics to develop therapeutics to address a wide range of diseases including inborn

errors of metabolism, metabolic diseases, and inflammatory and immune disorders; our expectations about sufficiency of our existing cash balance; the future clinical development of Synthetic Biotics; the approach Synlogic is taking to discover and

develop novel therapeutics using synthetic biology; our research and other collaborations; and the expected timing of Synlogic s clinical trials of SYNB1618, SYNB1934, SYNB1353 and SYNB8802 and availability of clinical trial data. Actual

results could differ materially from those contained in any forward-looking statement as a result of various factors, including: the uncertainties inherent in the clinical and preclinical development process; the ability of Synlogic to protect its

intellectual property rights; and legislative, regulatory, political and economic developments, as well as those risks identified under the heading Risk Factors in Synlogic s filings with the Securities and Exchange Commission. The

forward-looking statements contained in this press release reflect Synlogic s current views with respect to future events. Synlogic anticipates that subsequent events and developments will cause its views to change. However, while Synlogic may

elect to update these forward-looking statements in the future, Synlogic specifically disclaims any obligation to do so. These forward-looking statements should not be relied upon as representing Synlogic s view as of any date subsequent to the

Condensed Consolidated Statements of Operations

Condensed Consolidated Balance Sheets