UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 10-K (Mark One) ☒ ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31, 2020 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission File Number: 001-37465 Seres Therapeutics, Inc. (Exact Name of Registrant as Specified in Its Charter) (State or Other Jurisdiction of Incorporation or ...

SER-109 for *C. difficile* Infection - SER-109 Phase 3 ECOSPOR III study showed a sustained clinical response rate of 88.9% compared to 58.7% in the placebo arm at 8 weeks[12] - SER-109 demonstrated a 30.2% absolute reduction in the rate of *C. difficile* infection recurrence compared to placebo at 8 weeks[13] - Approximately 453,000 cases of primary *C. difficile* infection occur within the U S each year, leading to an estimated $5 billion in healthcare burden[20] - There are approximately 170,000 episodes of recurrent *C. difficile* infection per year in the U S[20] SER-287 for Ulcerative Colitis - SER-287 Phase 1b study showed a statistically significant clinical remission improvement in the daily treatment arm, with 40% remission compared to 0% in the placebo arm[39, 41] - SER-287 daily arm GI AEs were 13.3% vs 45.5% in the placebo arm[43] - The ECO-RESET Phase 2b study of SER-287 in ulcerative colitis is nearly 90% enrolled, with topline results anticipated in H2 2021[51] Pipeline and Financial Status - Seres Therapeutics had $320 million in cash, cash equivalents, and short and long-term investments as of September 30, 2020[58] - The company is advancing multiple earlier-stage programs, including SER-301, SER-401, and SER-155, targeting ulcerative colitis, metastatic melanoma, and antibiotic-resistant bacterial infections, respectively[6, 53]

Financial Data and Key Metrics Changes - Seres reported a net loss of $30.3 million for Q3 2020, compared to a net loss of $15.4 million for the same period in 2019, indicating a significant increase in losses driven by clinical and development expenses [42][43] - The company ended Q3 2020 with approximately $320 million in cash, cash equivalents, and investments, a substantial increase from $63.9 million at the end of Q2 2020, following a public equity offering and a securities purchase agreement with Nestle that provided approximately $264 million in net proceeds [44][45] Business Line Data and Key Metrics Changes - The SER-109 Phase 3 study demonstrated a 30.2% absolute reduction in recurrences of C. difficile infection compared to placebo at eight weeks post-treatment, showcasing the efficacy of the microbiome therapeutic approach [18][10] - SER-287 is currently in a Phase 2b study for ulcerative colitis, with over 75% enrollment achieved despite challenges posed by the COVID-19 pandemic [25][21] Market Data and Key Metrics Changes - The company is preparing for the anticipated launch of SER-109, conducting market assessments, and engaging in education efforts for healthcare professionals and payers [14][15] - The SER-287 program aims to provide a non-immunosuppressive treatment option for ulcerative colitis, addressing a significant unmet medical need [22] Company Strategy and Development Direction - Seres aims to become the first microbiome company to obtain FDA product approval and bring a drug to market, focusing on SER-109 and other drug candidates to transform disease management [10][11] - The company plans to scale market education efforts in 2021 and expand manufacturing capabilities in preparation for product launch [15][16] Management's Comments on Operating Environment and Future Outlook - Management expressed excitement about the future of Seres and the microbiome space, emphasizing the importance of completing the work needed for SER-109's BLA and preparing for its potential launch [47][48] - The management team acknowledged the challenges posed by the COVID-19 pandemic but noted progress in clinical trial enrollment and operational strategies to mitigate these impacts [25][71] Other Important Information - The company recently appointed a new Chief Technology Officer, Dave Ege, to enhance manufacturing capabilities in anticipation of SER-109's commercialization [16] - The SER-155 program is expected to advance into a Phase 1b study early in 2021, supported by a CARB-X grant [38] Q&A Session Summary Question: Enrollment status for the additional safety cohort - Management confirmed that progress is being made in site activation and enrollment for the open-label study, with enthusiasm from trial sites and physicians [52][53] Question: Treatment paradigm for SER-109 - Management indicated that SER-109 is expected to be applicable for a broad set of patients, including those with first recurrence, pending FDA discussions [61][62] Question: Initial data on SER-287 - Management noted that enrollment is progressing, and they are optimistic about the potential for data updates as the study continues [71] Question: SER-401 study advancement - Management stated that the Phase 1b study of SER-401 is exploratory, and decisions on future studies will be based on the data collected [76] Question: 24-week data from ECOSPOR III - Management is working with the FDA to clarify the schedule for presenting data and expects to have internal data available soon [81] Question: Plans for CMC expansion - Management emphasized the importance of expanding manufacturing capabilities to ensure drug availability and support the growing pipeline [97]

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q (Mark One) ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended September 30, 2020 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 (Exact name of registrant as specified in its charter) Delaware 27-4326290 (State or other jurisdiction of incorporation or organization) 200 Sidney Street - 4th Floor Cambridge, MA 021 ...

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q (Mark One) ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended June 30, 2020 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number: 001-37465 Seres Therapeutics, Inc. (Exact name of registrant as specified in its charter) Delaware 27-4326290 (State or other jurisd ...

April 2020 Seres Therapeutics Overview 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 or clinical trial data, the ability of our clinical trials to support approval, the timing of clinical studies, the sufficiency of cash to fund operations, and the potential ben ...

Seres Therapeutics, Inc. (NASDAQ:MCRB) Q1 2020 Earnings Conference Call May 7, 2020 8:30 AM ET Company Participants Carlo Tanzi - VP of IR & Corporate Communications Eric Shaff - President, CEO & Director Lisa von Moltke - EVP & Chief Medical Officer Matthew Henn - EVP & Chief Scientific Officer Conference Call Participants Chris Shibutani - Cowen Melissa Hilton - Goldman Sachs Matthew Biegler - Oppenheimer Gbola Amusa - Chardan John Newman - Canaccord Vernon Bernardino - H.C. Wainwright Roger Song - Jeffer ...

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q (Mark One) ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended March 31, 2020 OR For the transition period from to Commission file number: 001-37465 Seres Therapeutics, Inc. (Exact name of registrant as specified in its charter) Delaware 27-4326290 (State or other jurisdiction of incorporation or organization) 200 Sidney Street - 4th Floor Cambridge, MA 02139 ...

Seres Therapeutics Overview Eric Shaff, President and Chief Executive Officer Cowen Health Care Conference March 2, 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 or clinical trial data, the ability of our clinical trials to support approval, the timing of c ...

Financial Data and Key Metrics Changes - The company reported a net loss of $70.3 million for Q4 2019, compared to a net loss of $98.9 million for the same period in 2018, indicating a reduction in corporate spending due to refocusing efforts [35] - Cash and cash equivalents at the end of Q4 2019 were approximately $94.8 million, an increase from $83.8 million at the end of Q3 2019 [36] Business Line Data and Key Metrics Changes - SER-109 is in a Phase 3 study (ECOSPOR III) with over 95% enrollment, targeting recurrent C. difficile infection [14][11] - SER-287 is in a Phase 2b study (ECO-RESET) for mild-to-moderate active ulcerative colitis, with a significant 40% remission rate observed in the Phase 1b study [21][20] - SER-301, a next-generation candidate for ulcerative colitis, has initiated clinical development activities, with dosing expected to start later in 2020 [28][29] Market Data and Key Metrics Changes - The company is collaborating with AstraZeneca in immuno-oncology, which includes a $20 million financial support agreement [33] - SER-401 is in a Phase 1b study for metastatic melanoma, with preliminary results expected in the second half of 2020 [31] Company Strategy and Development Direction - The company aims to validate the microbiome therapeutic field through late-stage clinical readouts in 2020 [7] - Focus on developing non-immunosuppressive treatment options for serious diseases like ulcerative colitis [18] Management's Comments on Operating Environment and Future Outlook - Management expressed optimism about 2020 being a transformative year with significant data readouts expected [7] - The company is taking precautions in response to the coronavirus pandemic but remains confident in its clinical supply and study execution [66] Other Important Information - The company has undergone leadership changes, including the departure of the Chief Medical Officer [38] - The manufacturing process for SER-109 is designed to deactivate pathogens, enhancing patient safety [67] Q&A Session Summary Question: What should investors expect regarding the release format for SER-109 data? - Management indicated that a robust set of clinical endpoints would be provided, but microbiome analysis may not accompany the topline clinical analysis due to blinding constraints [43] Question: Are there plans to begin dosing patients for SER-301 this quarter? - Management confirmed that clinical operations have been initiated and expects to start dosing patients later in 2020 [44] Question: What is the power of the Phase 2b trial for SER-287? - Management did not provide specific guidance on power but expressed excitement about replicating positive results from the Phase 1b study in a larger cohort [49] Question: When is the next scheduled meeting with the FDA regarding SER-109? - Management expects to have an end of Phase 3 meeting following the top line results this year [54] Question: How is recurrence defined in the Phase 3 ECOSPOR study? - Recurrence will be based on both positive C. diff toxin tests and symptomatic presentation, with a focus on using cytotoxin as a key differentiator [60]