Seres Therapeutics Overview

Eric Shaff, Chief Executive Officer

Oppenheimer Fall Healthcare Summit

September 23, 2020

Forward looking statements

Some of the statements in this presentation constitute "forward looking statements" under the Private Securities Litigation Reform Act of 1995, including, but not limited to, our development plans, the promise and potential impact of any of our microbiome therapeutics, the ability of our clinical trials to support approval, the timing of clinical studies, the timing and ultimate results of the SER-109 safety data, the size of the market for SER-109, the sufficiency of cash to fund operations, and the potential benefits of Seres' collaborations. Such statements are subject to important factors, risks and uncertainties, such as those discussed under the caption "Risk Factors" in the Company's Quarterly Report on Form 10-Q filed on July 28, 2020, and its other filings with the SEC, that may cause actual results to differ materially from those expressed or implied by such forward looking statements. Any forward looking statements included herein represent our views as of today only. We may update these statements, but we disclaim any obligation to do so.

2

SER-109 Phase 3 success highlights that the time for microbiome therapeutics is now

Seres' mission: To transform the lives of patients worldwide with revolutionary microbiome therapeutics

3

Seres is developing a novel drug modality that modulates the gut microbiome

Ecobiotic® microbiome therapeutics are encapsulated consortia of commensal bacteria with specific pharmacologic properties

Formulated for

Designed to

oral delivery using

target inflammatory

current Good

& immunological

Manufacturing

disease pathways

Practices (cGMP)

simultaneously

Consortia capture

Mechanisms

breadth of

includes microbial

biological &

engraftment in GI

functional diversity

tract to restructure

the microbiome

4

Industry-leading,in-house research engine for drug discovery, development & manufacturing

Disease Target

Identification

Microbiome

Biomarker Discovery

Clinical sample

biorepository

Proprietary genomic

  • metabolomic analytics

World-class

collaborations

Hit-to-Lead

Identification

Consortia Design

Broad strain library & culturing know-how

Genomic & host

function screening

In-silico drug design for functional targets

Lead Optimization

& Bioprocess

Pharmacological

Properties Validation

Ex vivo & in vivo disease modeling

Fermentation &

formulation optimization platforms

End-to-End GMP Manufacturing

Oral formulation

Donor-derived & multi-

strain fermentation

Anaerobic, spore &

lyophilized

technologies

Late clinical stage

drug release assays

5

Broad opportunities for microbiome therapeutics

Infectious Disease

Preclinical

Phase 1b

Phase 2b

Phase 3

Collaborators

SER-109

Recurrent C. difficile

Phase 3

SER-155

Infection, Bacteremia & GvHD in HSCT for cancer

(Rationally-designed, fermented)

Inflammatory

Oncology

SER-287

Ulcerative colitis

SER-301

Ulcerative colitis

(Rationally-designed, fermented)

SER-401

Metastatic melanoma

in combination with anti-PD-1 MAb

Immuno-

Improve response to check-point therapies; potential

Oncology

synergies with AZ pipeline

Phase 2b

Phase 1b

  1. Collaboration with Nestlé Health Science, announced Jan. 11, 2016, regarding C. difficile and IBD programs for markets outside of North America
  2. Collaboration with University of Texas MD Anderson Cancer Center and the Parker Institute for Cancer Immunotherapy, announced Nov. 14, 2017, regarding evaluation of microbiome therapies to improve the outcomes of cancer patients treated with immunotherapy. The Parker Institute is the IND application holder for SER-401.
  3. Collaboration with AstraZeneca, announced Mar. 11, 2019, regarding advancing mechanistic understanding of the microbiome in augmenting the efficacy of cancer immunotherapy, including potential synergy with AstraZeneca compounds.

6

C. difficile Infection

Overview and SER-109 Phase 3 study

August 2020: Positive ECOSPOR III Phase 3 study read-out

  • Multiply recurrent
    C. difficile patients (n=182)
  • All subjects treated with standard of care antibiotics

SER-109 (n = 90)

Primary endpoint:

Safety

C. diff. recurrence,

follow-up to

at up to 8 weeks

24 weeks

Placebo (n = 92)

0 weeks

8 weeks

24 weeks

Toxin testing to ensure

Substantially higher dose vs.

Placebo arm to provide

inclusion of subjects with

Phase 2 designed to result in

invaluable safety and efficacy

active rCDI, and for accuracy

greater and earlier microbiome

data that cannot be obtained in

of endpoint

restoration

open-label trials

8

Topline SER-109 Phase 3 study efficacy results

Primary efficacy endpoint results:

SER-109

Placebo

p-Value

Time point

(N =90)

(N =92)

RR (95%CI)

(p1/p2)

n (%)

n (%)

Week 8

10 (11.1)

38 (41.3)

0.27 (0.15, 0.51)

<0.001 / <0.001

  • Sustained clinical response rate (i.e., percentage of patients who remain free of CDI at 8 weeks): SER-109 was effective in 88.9% of SER-109 subjects vs. 58.7% of subjects in the placebo arm.
  • Results were statistically significant in both age stratified subgroups: 18-64 years old, or 65 and over
    • Highly statistically significant 30.2% absolute reductionin the rate of CDI recurrence compared to placebo
    • Number needed to treat = approximately 3

9

Favorable safety profile observed in Phase 3

  • SER-109was well tolerated, with no treatment-relatedserious adverse events (SAEs) observed in the active arm, and an adverse event profile similar to placebo
  • Overall incidence of patients who experienced AEs during the eight-week study period was similar between SER-109and placebo arms
  • Most commonly observed treatment-related AEs were flatulence, abdominal distention and abdominal pain, which were generally mild to moderate in nature, and these were observed at a similar rate in both the SER-109 and placebo arms

10

Substantial recurrent C. difficile infection market opportunity

Infectious disease caused by toxin-producing bacteria, resulting in diarrhea, abdominal pain, fever and nausea

Leading cause of hospital-acquired infection in the U.S.

  1. ~ 453K cases of primary CDI within the U.S. each year
  1. ~ 170K episodes per year (100K episodes of first recurrence; ~ 73K episodes of 2+ recurrences)
  1. Estimated ~ $5B in healthcare burden each year

25% of primary C. difficile recur

Over 20,000 deaths per year

Potential broad FDA label covering rCDI patients

11 Source: * Desai et al., Epidemiological and economic burden of Clostridium difficile in the United States: estimates from a modeling approach, BMC Infectious Diseases (2016) 16:303; Guh AY et al. NEJM 2020

FMT safety concerns highlight the need for improved, FDA-approved treatment options for C. difficile infection

• In contrast to FMT, SER-109 is comprised of a highly purified consortia of spore-based bacteria manufactured under GMP conditions to ensure product quality and consistency

• Unique manufacturing process to inactivate potential pathogens

• Process inactivates many emerging potential pathogens where diagnostic assays may not yet be widely available, such as SARS-CoV-2

Since July 2020, the largest U.S. provider of FMT has

12

quarantined supply and halted shipments

Amplifying efforts for market preparation and launch

Scaling Market Education

Efforts

Enhancing Understanding of Commercial Opportunity

Building Infrastructure to

Launch

  • Medical communications strategy
  • KOL mapping
  • Develop and deploy payer value proposition
  • Deeper patient journey analysis
  • Pricing analysis
  • Customer segmentation
  • Identify options for go-to-market model
  • Scale Medical Affairs organization and deploy MSL team
  • Hire key commercial leadership roles
  • Key external strategic partners on board

13

SER-109: Investigational, spore-based therapeutic designed to break the cycle of recurrent C. difficile infection

SER-109

Oral formulation of Firmicute bacteria spores

Strong clinical & scientific data

  • Dramatic reduction in CDI recurrence rate
  • Spore-formingFirmicute bacteria prevent C. difficile germination and growth

Oral formulation

  • Spores are resistant to gastric acid, facilitating oral delivery to gastrointestinal tract

Favorable safety profile

  • Favorable tolerability & safety profile with no imbalance in adverse event
  • Spore purification mitigates risk of transmission of known and unknown infectious agents

FDA regulatory designations

  • Breakthrough designation
  • Orphan drug status

14

SER-287 and Ulcerative Colitis

Ulcerative colitis overview

Serious chronic condition characterized by inflammation of the colon and rectum resulting in abdominal pain, bowel urgency and diarrhea

Significant need for improved

therapies - Many drugs are

immunosuppressive, limiting use to

more severe patients

~700K in the United States

Only ~1/3 achieve remission

16

The dysbiotic microbiome may be a trigger of inflammation in ulcerative colitis

Gut Lumen

Gut Epithelium

Lamina Propria

Blood vessel

Microbiome

Steroids

Thiopurines / MTX

Anti-TNFs

JAK Inhibitors

Anti IL12/23

Anti-Integrins S1P1 Agonists

Microbiome therapeutics may drive therapeutic benefit

  • May address drivers of inflammation, barrier integrity, innate immune activation, and adaptive immune education and cell trafficking
  • Effector molecules may include short chain fatty acids, secondary bile acids, tryptophan metabolites, and TLR ligands

Microbial consortia can likely target multiple pathways simultaneously

Opportunity to develop both first-line and combination therapies

17

Published study regarding microbiota transplantation provided clinical proof-of-concept in ulcerative colitis

30%

27%

P= 0.027

25%

20%

15%

8%

10%

5%

0%

Steroid-free clinical remission and endoscopic remission or

response

Microbiota transplant

Placebo

18Note: SER-287 was not involved in this study

SER-287 Phase 1b ulcerative colitis study

Placebo pre-treatment for 6

Placebo once daily for 8

(n=11)

days

weeks

Vancomycin pre-treatment

SER-287 once daily for 8

(n=15)

for 6 days

weeks

58 mild-to-

moderate

WEEKLY

ulcerative

colitis patients

Placebo pre-treatment for 6

SER-287 once weekly for 8

(n=15)

days

weeks

Vancomycin pre-treatment

SER-287 once weekly for 8

(n=17)

for 6 days

weeks

Primary

Objectives

  • Safety and tolerability
  • Change in composition of intestinal microbiome at 8 weeks

19

Phase 1b study results - Statistically significant clinical remission improvement observed in Vanco/SER-287 daily treatment arm

% patients achieving remission

40%

30%

20%

10%

0%

40.0%

(6/15)

p = 0.0237

17.7%

(3/17)

13.3%

(2/15)

0.0%

(0/11)

Placebo

Vancomycin

Placebo

Vancomycin

pretreatment /

pretreatment /

pretreatment /

pretreatment /

Placebo

SER-287 daily

SER-287 weekly

SER-287 weekly

20

Remission = Total Modified Mayo score ≤ 2 AND endoscopic subscore ≤ 1

Note: Missing data treated as failure; statistical significance not found in SER-287 weekly arms

Illustrative endoscopy improvement - Vanco/SER-287 daily treatment

Pre-treatment endoscopy showing

the sigmoid colon with spontaneousPost-treatmentday 64 endoscopy bleeding and ulceration

21

SER-287 Phase 1b safety results show safety profile comparable to placebo

  • SER-287daily arm demonstrated a similar safety profile to placebo
  • No serious drug-related adverse events
  • Reduced gastrointestinal adverse events provide an independent assessment of efficacy as the GI adverse events likely reflect ulcerative colitis disease activity
    SER-287 daily arm GI AEs: 2/15 (13.3%) vs. placebo arm: 5/11 (45.5%)

22

Phase 1b study results - SER-287 bacteria engrafted in subjects and was durable to four weeks after dosing

Henn et al. (in review)

  • Significant engraftment observed starting one week post-dosing
  • Engraftment is significantly higher in arms with vancomycin pre-conditioning
  • Engraftment in vancomycin arms is dose-dependent; significantly greater in daily dosing arm (arm with greatest efficacy)

23

SER-287 Phase 1b study results published

24

Ongoing SER-287ECO-RESET Phase 2b study in patients with mild-to-moderate active ulcerative colitis

10-week induction period

Pbo

pre-

Placebo

treat

Mild to moderate

26-week

Vanco

UC patients with

exploratory

pre-

SER-287 daily high dose

active disease

maintenance

treat

N=201

follow-up

Vanco

SER-287 daily high dose

pre-

followed by step down dose

treat

Primary endpoint:

Clinical remission

  • FDA Fast Track designation
  • FDA feedback: Phase 2b study results, in conjunction with data from a second pivotal study, could support BLA submission

25

Earlier stage development programs: SER-401,SER-301,SER-155

Immuno-oncology - Microbiome signature in melanoma patient responder to anti-PD-1

  • SER-401composition driven by bacteria consistent with responder profile
  • All spore formers that leverage deep Seres expertise in the biology and manufacturing of these organisms

27 Gopalakrishnan et al, Science 2017

Ongoing SER-401 Phase 1b study

Study Objectives

SER-401; biologically sourced

product to match microbiome Primary endpoint = safety and tolerability signature of anti-PD-1 responders

Patients with

(n=20)

All patients = CT scans with RECIST week 12

Secondary endpoints = engraftment,

response and correlative studies

Placebo (n=10)(immune correlates in blood and tumor, metabolites)

metastatic melanoma treated with anti-PD-1 (nivolumab)

Day -14

Day -7

Day 0

Day +7

Day +14

Day +28

Day +56

Day +84

SER-401 / Placebo

Daily dosing

Biospecimens:

Blood

Stool

Biopsy

28

Additional study arm may be added including fecal microbiota obtained from responders

SER-301:Next-generation, rationally designed fermented microbiome therapeutic candidate for ulcerative colitis

  • Reduces induction of pro-inflammatory activity
  • Improves epithelial barrier integrity & TNF-α driven inflammation in IECs
  • Modulates UC-relevantanti-inflammatory, innate & adaptive immune pathways
    • Activities to initiate clinical development ongoing
    • Human Research Ethics Committee approval in Australia

29

SER-155:Rationally-designed, fermented microbiome therapeutic candidate for infection, bacteremia & GvHD

  • Decreases infection by antibiotic resistant bacteria in the gastrointestinal tract that lead to bacteremia
  • Enhances epithelial barrier integrity to prevent bacterial translocation to the blood stream
  • Modulates local and systemic immunomodulatory responses to decrease graft versus host disease
  • Collaboration with:

Catalyzes changes in the microbiome & microbe-derived metabolites to prevent bacteremia

Antibiotic resistant pathogens can dominate the GI microbiome

Compromised epithelial layer with thin mucus layer

Basal

TLRs

  • Lead candidate nominated
  • U.S. regulatory submission preparation in process

30

SER-109 success validates our microbiome therapeutic approach, presenting opportunity in multiple additional areas

  • Deep understanding of the broad role of the microbiome in health:
    • Resistance to pathogens
    • Gut & systemic inflammation
    • Innate & adaptive immunity
    • Regulation of metabolism
  • Novel drug discovery and development platform
  • Option to pursue multiple diseases with high unmet need

Highly productive R&D engine

pursing multiple promising

potential opportunities

Infectious (e.g. Antibiotic resistant

infections)

Inflammatory (e.g. Crohn's, RA)

Oncology (e.g. tumor progression &

bacteremia)

Immune modulation & autoimmune

disease

Metabolic & Cardiovascular (e.g. NASH)

Neurologic & CNS disease

31

Differentiated CMC capabilities producing rationally designed fermented products

Seres in-house GMP manufacturing and quality control capabilities

Cell banking & inoculum

Drug substance

Drug product

Quality control

  • Potential best-in-class clinical profile based on species specific properties
  • Fermented approach enables efficient and highly scalable manufacturing process to serve large markets

32

Broad IP portfolio and regulatory exclusivity

PATENT PORTFOLIO OF OWNED & LICENSED PATENTS AND APPLICATIONS*

  • Have obtained issued patents in the US, demonstrating that rationally designed ecologies of spores and microbes are patentable
  • Portfolio includes composition of matter and method claims, including option to license foundational IP from MD Anderson related to the use of bacteria in combination with checkpoint inhibitors. Portfolio also includes exclusive licenses to Memorial Sloan Kettering Cancer Center IP related to use of bacteria to treat gastrointestinal disorders and cancer relapse.
  • Issued claims related to SER-109/C. difficile & SER-287 /ulcerative colitis lead candidates extend through 2033
  • 13 Issued US Patents obtained

21

Families of Applications

15 Nationalized

1

Pending Provisionals

PROJECTED BIOSIMILAR REGULATORY EXCLUSIVITY

12

years for new

10 drugyears for new

biological composition

33

Seres is well positioned to harness core microbiome capabilities advance pipeline

SER-109

SER-287

SER-401

SER-301

SER-155

Additional R&D opportunities

Positive ECOSPOR III Phase 3 study results expected to serve as single study to support BLA; Plan to meet with FDA to discuss filing

Ulcerative colitis - Phase 2b study ongoing

Metastatic melanoma - Phase 1b study ongoing

Rationally designed fermented composition;

Activities to initiate clinical development ongoing

Rationally designed fermented composition;

Plan to initiate development to prevent infections and GvHD

Multiple earlier stage programs under consideration as new development opportunities

Strong balance sheet, following August 2020

34

capital raise of $264 M

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Seres Therapeutics Inc. published this content on 23 September 2020 and is solely responsible for the information contained therein. Distributed by Public, unedited and unaltered, on 23 September 2020 16:24:02 UTC