Seres Therapeutics Presents New Preclinical Data Supporting the Development of SER-401 for Immuno-Oncology at the 2019 American Association for Cancer Research Annual Meeting

Seres
Therapeutics, Inc. (Nasdaq: MCRB) today announced that new
preclinical data supporting the development of microbiome therapeutics
for immuno-oncology (poster title “Leveraging gut microbiota networks to
impact tumor immunotherapy”)¹ will be presented by Sceneay et
al. at the 2019 American Association for Cancer Research Annual Meeting
(AACR) in Atlanta, Georgia. The data presented provide new insights on
the potential mechanism by which Seres’ microbiome therapies, including
the Company’s SER-401 program, could improve outcomes of cancer patients
treated with immune checkpoint inhibitors.

“The novel data presented at AACR provide mechanistic insights into the
biological activity of our microbiome therapeutic candidates to augment
immune checkpoint inhibitors,” said Matthew Henn, Ph.D., Chief
Scientific Officer and Executive Vice President at Seres. “The valuable
learnings obtained from this work have informed the development of
SER-401, which is being evaluated in combination with an FDA approved
immunotherapy in the ongoing MCGRAW Phase 1b study in patients with
metastatic melanoma.”

Seres presented preclinical results evaluating the impact of various
consortia of bacterial species on the anti-tumor immune response in
murine models following treatment with an anti-PD-1 checkpoint
inhibitor. Results demonstrated that germ-free or antibiotic-treated
mice lacking a functional gastrointestinal microbiome failed to mount an
effective anti-tumor response when administered anti-PD-1 checkpoint
inhibitor treatment. The response to anti-PD-1 treatment was restored by
the introduction of a specific consortia of commensal bacteria
rationally designed using insights from both in vivo and human
microbiome signatures of response and the functional properties of
specific bacterial strains in Seres’ strain library of gastrointestinal
bacteria.

These data provide support for the continued development of SER-401, an
oral microbiome therapeutic candidate sourced from screened healthy
individuals who have been identified to have a microbiome bacterial
signature similar to that observed in responders to cancer
immunotherapy. The therapeutic aim of SER-401 is to modify the
microbiome of cancer patients to increase the efficacy of immunotherapy.
SER-401 is being evaluated in a Phase 1b clinical study (NCT03817125)
conducted in collaboration with The University of Texas MD Anderson
Cancer Center and the Parker Institute for Cancer Immunotherapy in
patients with metastatic melanoma. In addition, Seres has an ongoing
collaboration with AstraZeneca to advance the mechanistic understanding
of the microbiome in augmenting the efficacy of cancer immunotherapy,
including in combination with agents in AstraZeneca’s oncology pipeline.

About Seres Therapeutics

Seres Therapeutics, Inc. (Nasdaq: MCRB) is a leading microbiome
therapeutics platform company developing a novel class of biological
drugs that are designed to treat disease by restoring the function of a
dysbiotic microbiome, where the state of bacterial diversity and
function is imbalanced. Seres’ most advanced program, SER-109, has
obtained Breakthrough Therapy and Orphan Drug designations from the U.S.
Food and Drug Administration and is in Phase 3 development for recurrent C.
difficile infection. SER-287 is being evaluated in a Phase 2b study
in patients with active mild-to-moderate ulcerative colitis. Seres is
also developing SER-401 in a Phase 1b study in patients with metastatic
melanoma. For more information, please visit www.serestherapeutics.com.

Forward-looking Statements

This press release contains forward-looking statements within the
meaning of the Private Securities Litigation Reform Act of 1995. All
statements contained in this press release that do not relate to matters
of historical fact should be considered forward-looking statements,
including the potential impact of SER-401, the timing and results of any
collaborations or clinical studies, Seres’ plans for pre-clinical
development, and other statements that are not historical facts.

These forward-looking statements are based on management’s current
expectations. These statements are neither promises nor guarantees, but
involve known and unknown risks, uncertainties and other important
factors that may cause our actual results, performance or achievements
to be materially different from any future results, performance or
achievements expressed or implied by the forward-looking statements,
including, but not limited to, the following: we have incurred
significant losses, are not currently profitable and may never become
profitable; our need for additional funding; our limited operating
history; our unproven approach to therapeutic intervention; the lengthy,
expensive, and uncertain process of clinical drug development; our
reliance on third parties and collaborators to conduct our clinical
trials, manufacture our product candidates, and develop and
commercialize our product candidates, if approved; the success of our
leadership transition; our ability to retain key personnel and to manage
our growth; and our management and principal stockholders have the
ability to control or significantly influence our business. These and
other important factors discussed under the caption “Risk Factors” in
our Annual Report on Form 10-K filed with the Securities and Exchange
Commission, or SEC, on March 6, 2019 and our other reports filed with
the SEC could cause actual results to differ materially from those
indicated by the forward-looking statements made in this press release.
Any such forward-looking statements represent management’s estimates as
of the date of this press release. While we may elect to update such
forward-looking statements at some point in the future, we disclaim any
obligation to do so, even if subsequent events cause our views to
change. These forward-looking statements should not be relied upon as
representing our views as of any date subsequent to the date of this
press release.

Reference

1. Sceneay, Jaclyn et. al., Leveraging gut microbiota networks to impact
tumor immunotherapy. Session title “Inflammation and microbiome”;
section 4, abstract 2839. American Association for Cancer Research
(AACR) Annual Meeting 2019.

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