Seres Therapeutics, Inc.

Previous wording

In the context of preventing infection for patients undergoing allo-HCT for hematological cancer, we believe that our technology may be replicable across different bacterial pathogens with the potential to develop live biotherapeutics to protect a range of medically compromised patients at risk of antimicrobial resistance, or AMR, infections and bloodstream infections, or BSIs, that can result from a compromised mucosal epithelial barrier and that can be a major cause of mortality. SER-155, our most advanced LBP candidate, is an investigational, oral, live biotherapeutic designed to decolonize GI pathogens, improve GI mucosal epithelial barrier integrity, and induce immune homeostasis to prevent bacterial BSIs, including those that can harbor antimicrobial resistance, as well as other pathogen-associated negative clinical outcomes in patients undergoing allogeneic hematopoietic stem cell transplantation, or allo-HCT. In our placebo-controlled Phase 1b study of SER-155 in allo-HCT, SER-155 was associated with a 77% relative risk reduction in bacterial BSIs and a significant reduction in systemic antibiotic exposure as well as a lower incidence of febrile neutropenia, as compared to placebo through day 100 post HCT. SER-155 was generally well tolerated, with no observed treatment-related serious adverse events. Drug pharmacology data demonstrated that SER-155 significantly promoted mucosal epithelial barrier integrity and had a positive impact on biomarkers of systemic inflammation and immune homeostasis. Following advancement of key startup activities for the SER-155 Phase 2 study in allo-HCT, including the submission of a final protocol to the FDA in January 2026, study site evaluation and qualification with our CRO, and manufacturing of drug substance, we have paused additional investment in that program while continuing to seek funding for the Phase 2 study.

Current wording

In the context of preventing infection for patients undergoing allo-HCT for hematological cancer, we believe that our technology may be replicable across different bacterial pathogens with the potential to develop live biotherapeutics to protect a range of medically compromised patients at risk of antimicrobial resistance, or AMR, infections and bloodstream infections, or BSIs, that can result from a compromised mucosal epithelial barrier and that can be a major cause of mortality. SER-155, our most advanced LBP candidate, is an investigational, oral, live biotherapeutic designed to decolonize GI pathogens, improve GI mucosal epithelial barrier integrity, and induce immune homeostasis to prevent bacterial BSIs, including those that can harbor antimicrobial resistance, as well as other pathogen-associated negative clinical outcomes in patients undergoing allogeneic hematopoietic stem cell transplantation, or allo-HCT. In our placebo-controlled Phase 1b study of SER-155 in allo-HCT, SER-155 was associated with a 77% relative risk reduction in bacterial BSIs and a significant reduction in systemic antibiotic exposure as well as a lower incidence of febrile neutropenia, as compared to placebo through day 100 post HCT. SER-155 was generally well tolerated, with no observed treatment-related serious adverse events. Drug pharmacology data demonstrated that SER-155 significantly promoted mucosal epithelial barrier integrity and had a positive impact on biomarkers of systemic inflammation and immune homeostasis. In November 2026, we announced that results from our Phase 1b clinical study of SER-155 in adults undergoing allo-HCT were published in Nature Medicine, marking an important milestone for the program and providing recognition of the innovative science being advanced by the Company. Following advancement of key startup activities for the SER-155 Phase 2 study in allo-HCT, including the submission of a final protocol to the FDA in January 2026, study site evaluation and qualification with our CRO, and manufacturing of drug substance, we have paused additional investment in that program while continuing to seek funding for the Phase 2 study.

Previous wording

We are also evaluating SER-155 in 15 patients with moderate-to-severe (Grade 2- 3) immune checkpoint-related enterocolitis, or irEC, through an investigator-sponsored trial, or IST, with Memorial Sloan Kettering Cancer Center, an institution with whom we have had a decade-long collaboration. irEC is among the most frequent and severe immune-related adverse events, or irAEs, in recipients of immune checkpoint inhibitor, or ICI, therapy and can be observed in up to 50% of patients, with rates varying based on cancer drug and treatment regimen. Moderate to severe irEC occurs in approximately 25% of all ICI therapy recipients in the United States. In 2026, it is estimated that there are a total of 300,000 patients on ICI cancer therapy in the United States, and this figure is increasing as ICI are being used across multiple cancer types, in earlier intervention and in combination with other cancer therapies. ICIs can cause a wide range of irAEs with links to T cell biology and epithelial barrier inflammation, both of which are biological functions shown in our preclinical and clinical pharmacology data to be positively impacted by SER-155. Top-line data from the IST showed that 80% of SER-155 recipients achieved an immunosuppressive-free clinical response of diarrhea (a primary symptom of irEC) at Day 15, which met the primary endpoint, defined as at least a 1-grade improvement in diarrhea symptoms without immunosuppressive therapy (i.e., a corticosteroid and/or biologic immunomodulator drug). All 12 participants with immunosuppressive-free clinical response at Day 15 had the same, or better, diarrhea grade at Day 43. SER-155 was well tolerated, with no drug-related serious adverse events observed. In addition, drug pharmacology translational biomarkers of gastrointestinal inflammation (fecal calprotectin) and of mucosal epithelial barrier integrity (fecal albumin), which were elevated in participants at baseline, prior to SER-155 dosing, both showed decreases post SER-155 treatment, with statistically significant reductions achieved by Day 43, reflecting improvement in two mechanistically linked dimensions of irEC disease. Participants in the study were on a wide range of ICI types, including PD-1 inhibitors (Keytruda®, Opdivo®, Zynyz®), PD-L1 inhibitors (Imfinzi®, Bavencio®), CTLA-4 inhibitors (Yervoy®, Imjudo®), LAG-3 inhibitor (Opdualag®), and combinations thereof. Clinical guidelines for these patients stipulate halting of ICI cancer treatment and initiation of systemic immunosuppressive corticosteroids, which are associated with clinically meaningful toxicities and other negative consequences, including: systemic immunosuppression, increased infection risk, metabolic complications, and potential interference with cancer treatment.

Current wording

SER-155 was evaluated in 15 patients with moderate-to-severe irEC through an investigator-sponsored trial, or IST, with Memorial Sloan Kettering Cancer Center, an institution with whom we have had a decade-long collaboration. Top-line data from the IST showed that 80% of SER-155 recipients achieved an immunosuppressive-free clinical response of diarrhea (a primary symptom of irEC) at Day 15, which met the primary endpoint, defined as at least a 1-grade improvement in diarrhea symptoms without immunosuppressive therapy (i.e., a corticosteroid and/or biologic immunomodulator drug). All 12 participants with immunosuppressive-free clinical response at Day 15 had the same, or better, diarrhea grade at Day 43. SER-155 was well tolerated, with no drug-related serious adverse events observed. In addition, drug pharmacology translational biomarkers of gastrointestinal inflammation (fecal calprotectin) and of mucosal epithelial barrier integrity (fecal albumin), which were elevated in participants at baseline, prior to SER-155 dosing, both showed decreases post SER-155 treatment, with statistically significant reductions achieved by Day 43, reflecting improvement in two mechanistically linked dimensions of irEC disease. Participants in the study were on a wide range of ICI types, including PD-1 inhibitors (Keytruda®, Opdivo®, Zynyz®), PD-L1 inhibitors (Imfinzi®, Bavencio®), CTLA-4 inhibitors (Yervoy®, Imjudo®), LAG-3 inhibitor (Opdualag®), and combinations thereof.

Previous wording

We believe there remains a significant unmet need for systemic immunosuppressive-free therapeutic approaches that reduce gastrointestinal inflammation and diarrhea and may allow patients who develop irEC to avoid disruption of their life-saving ICI cancer treatment and the promising study results support continued development of SER-155 to treat irEC. We are engaging with potential partners, including companies with ICI franchises, as we evaluate next steps for the development of SER-155 in irEC.

Current wording

We believe there remains a significant unmet need for systemic immunosuppressive-free therapeutic approaches that reduce gastrointestinal inflammation and diarrhea and may allow patients who develop irEC to avoid disruption of their life-saving ICI cancer treatment and the promising study results support continued development of SER-155 for irEC patients.

Previous wording

We have built and deploy a reverse translational platform and knowledge base for the discovery and development of live biotherapeutics, and maintain extensive proprietary know-how that may be used to support future research and development efforts. This platform incorporates high-resolution analysis of human clinical data to identify microbiome biomarkers associated with disease and non-disease states; preclinical screening using human cell-based assays and in vitro/ex vivo and in vivo disease models customized for live biotherapeutics; and a strain library and associated microbiological capabilities that span broad biological and functional breadth. This platform and knowledge base are integrated through a proprietary knowledge graph and agentic artificial intelligence, enabling rapid identification of specific microbes, microbial genes, and microbial metabolites/peptides associated with disease and the design of therapeutic consortia of bacteria for specific pharmacological properties to restructure the gut microbiome and modulate functional pathways associated with disease. In addition, we own a valuable intellectual property estate related to the development and manufacture of live biotherapeutics.

Current wording

We have built and deployed a reverse translational platform and knowledge base for the discovery and development of live biotherapeutics and maintain extensive proprietary know-how that may be used to support future research and development efforts. This platform incorporates high-resolution analysis of human clinical data to identify microbiome biomarkers associated with disease and non-disease states; preclinical screening using human cell-based assays and in vitro/ex vivo and in vivo disease models customized for live biotherapeutics; and a strain library and associated microbiological capabilities that span broad biological and functional breadth. This platform and knowledge base are integrated through a proprietary knowledge graph and agentic artificial intelligence, enabling rapid identification of specific microbes, microbial genes, and microbial metabolites/peptides associated with disease and the design of therapeutic consortia of bacteria for specific pharmacological properties to restructure the gut microbiome and modulate functional pathways associated with disease. In addition, we own a valuable intellectual property estate related to the development and manufacture of live biotherapeutics.

Previous wording

Our product candidates are in early-stage clinical or preclinical development. Our ability to achieve profitability will depend heavily on the successful development and eventual commercialization of one or more of our product candidates. Since our inception, we have incurred significant operating losses. Our net loss from operations was $42.2 million for the six months ended June 30, 2026. As of June 30, 2026, we had an accumulated deficit of $987.7 million.

Current wording

Our product candidates are in early-stage clinical or preclinical development. Our ability to achieve profitability will depend heavily on the successful development and eventual commercialization of one or more of our product candidates. Since our inception, we have incurred significant operating losses. Our net loss from operations was $58.3 million for the nine months ended September 30, 2026. As of September 30, 2026, we had an accumulated deficit of $1,004.0 million.

Previous wording

As of June 30, 2026, we had cash and cash equivalents totaling $15.6 million. Based on our currently available cash resources, the $12.5 million Milestone Termination Payment received from SPN in July 2026, and the expected receipt of the additional $12.5 million Milestone Termination Payment due from SPN in October 2026, and considering our future operating plans, we anticipate that we will require additional funding following the first quarter of 2027. In accordance with applicable accounting standards, we evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about our ability to continue as a going concern within 12 months after the date of the issuance of the condensed consolidated financial statements included elsewhere in this Quarterly Report on Form 10-Q. In performing this analysis, we excluded certain elements of our operating plan that cannot be considered probable of occurring. Under the applicable accounting standards, any future transactions or equity issuances cannot be considered probable, as these events are outside our control. Accordingly, management has concluded that substantial doubt exists about our ability to continue as a going concern for 12 months from the date the condensed consolidated financial statements included elsewhere in this Quarterly Report on Form 10-Q are issued. See “Risk Factors— Risks Related to Our Financial Position and Need for Additional Capital —We have identified conditions and events that raise substantial doubt regarding our ability to continue as a going concern.”

Current wording

As of September 30, 2026, we had cash and cash equivalents totaling $17.5 million. Based on our currently available cash resources, the $12.5 million Milestone Termination Payment received from SPN in October 2026, and considering our future operating plans, we anticipate that we will require additional funding following the first quarter of 2027. In accordance with applicable accounting standards, we evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about our ability to continue as a going concern within 12 months after the date of the issuance of the condensed consolidated financial statements included elsewhere in this Quarterly Report on Form 10-Q. In performing this analysis, we excluded certain elements of our operating plan that cannot be considered probable of occurring. Under the applicable accounting standards, any future transactions or equity issuances cannot be considered probable, as these events are outside our control. Accordingly, management has concluded that substantial doubt exists about our ability to continue as a going concern for 12 months from the date the condensed consolidated financial statements included elsewhere in this Quarterly Report on Form 10-Q are issued. See “Risk Factors— Risks Related to Our Financial Position and Need for Additional Capital —We have identified conditions and events that raise substantial doubt regarding our ability to continue as a going concern.”

Previous wording

On February 12, 2026, we announced that we implemented cost reduction actions, including reducing our workforce by approximately 30%. During the three months ended March 31, 2026, we incurred approximately $0.9 million in restructuring costs, primarily related to severance costs, of which $0.7 million was paid during the first quarter of 2026, and the remainder was paid out in the second quarter of 2026.

Current wording

On February 12, 2026, we announced that we implemented cost reduction actions, including reducing our workforce by approximately 30%. During the nine months ended September 30, 2026, we incurred approximately $0.9 million in restructuring costs, primarily related to severance costs, of which $0.7 million was paid during the first quarter of 2026, and the remainder was paid out in the second quarter of 2026.

Previous wording

On June 5, 2026, we announced that we amended our lease with our landlord for a portion of our space in Cambridge, Massachusetts, under which we reduced our leased space, rental rate and facility operating expenses. The restructured lease is expected to materially reduce the Company’s ongoing annual facility-related costs and long-term obligations. Refer to Note 6, Leases, included elsewhere in this Quarterly Report on Form 10-Q for more information.

Current wording

On June 5 and August 5, 2026, we announced that we amended two of our leases for a portion of our space in Cambridge, Massachusetts, under which we reduced our leased space, rental rate and facility operating expenses. The restructured leases are expected to materially reduce our ongoing annual facility-related costs and long-term obligations. On July 31, 2026, we entered into the Third Amendment to Lease and Termination Agreement with BMR-Sidney Research Campus LLC, the purpose of which was to effect an early termination of our lease at 200 Sidney Street, Cambridge, Massachusetts, reducing our ongoing annual facilities costs and materially eliminating our primary restoration obligations. Refer to Note 6, Leases, included elsewhere in this Quarterly Report on Form 10-Q for more information.

Previous wording

We have been collaborating with Memorial Sloan Kettering Cancer Center for over a decade on the impact of the GI microbiome on immune related diseases and cancer; recently this long-standing collaboration included a single arm, open-label Phase 1b investigator-sponsored trial, or IST, evaluating SER-155 as a potential first-line treatment in irEC. The study evaluated SER-155 in 15 patients with moderate-to-severe (Grade 2- 3) irEC. irEC is among the most frequent and severe immune-related adverse events, or irAEs, in recipients of immune checkpoint inhibitor, or ICI, therapy and can be observed in up to 50% of patients, with rates varying based on cancer drug and treatment regimen. Moderate to severe irEC occurs in approximately 25% of all ICI therapy recipients in the United States. ICIs can cause a wide range of irAEs with links to T cell biology and epithelial barrier inflammation, both of which are biological functions shown in our preclinical and clinical pharmacology data to be positively impacted by SER-155. Participants in the study were on a wide range of ICI types, including PD-1 inhibitors (Keytruda®, Opdivo®, Zynyz®), PD-L1 inhibitors (Imfinzi®, Bavencio®), CTLA-4 inhibitors (Yervoy®, Imjudo®), LAG-3 inhibitor (Opdualag®), and combinations thereof. Clinical guidelines for these patients who experience Grade 2-3 irEC stipulate halting of ICI cancer treatment and initiation of systemic immunosuppressive corticosteroids, which are associated with clinically meaningful toxicities and other negative consequences, including systemic immunosuppression, increased infection risk, metabolic complications, and potential interference with cancer treatment. There remains a significant unmet need for systemic, immunosuppressive-free therapeutic approaches that reduce gastrointestinal inflammation and diarrhea and may allow patients who develop irEC to avoid disruption of their life-saving ICI cancer treatment. SER-155 is designed to promote mucosal healing and modulate inflammation without systemic immunosuppressives, which carry the risk of toxicity and ICI efficacy impact.

Current wording

We have been collaborating with Memorial Sloan Kettering Cancer Center for over a decade on the impact of the GI microbiome on immune related diseases and cancer; recently this long-standing collaboration included a single arm, open-label Phase 1b investigator-sponsored trial, or IST, evaluating SER-155 as a potential treatment in irEC. The study evaluated SER-155 in 15 patients with moderate-to-severe (Grade 2- 3) irEC, which affects approximately 25% of all ICI therapy recipients in the United States. Clinical guidelines for patients who experience Grade 2 or higher irEC require treatment, which could include halting of ICI cancer treatment and initiation of systemic immunosuppressive corticosteroids, which are associated with clinically meaningful toxicities and other negative consequences, including systemic immunosuppression, increased infection risk, metabolic complications, and potential interference with cancer treatment. There remains a significant unmet need for systemic, immunosuppressive-free therapeutic approaches that reduce gastrointestinal inflammation and diarrhea and may allow patients who develop irEC to avoid disruption of their life-saving ICI cancer treatment. Participants in the study were on a wide range of ICI types, including PD-1 inhibitors (Keytruda®, Opdivo®, Zynyz®), PD-L1 inhibitors (Imfinzi®, Bavencio®), CTLA-4 inhibitors (Yervoy®, Imjudo®), LAG-3 inhibitor (Opdualag®), and combinations thereof.

Previous wording

We believe data from this IST further supports the potential for live biotherapeutics to address a significant unmet need among the large population of cancer patients receiving ICIs for systemic immunosuppressive-free therapeutic approaches that have the potential to reduce gastrointestinal inflammation and diarrhea and may allow patients who develop irEC to avoid disruption of their life-saving ICI cancer treatment.

Current wording

We believe data from this IST further supports the potential for live biotherapeutics to address a significant unmet need among the large population of cancer patients receiving ICIs for systemic immunosuppressive-free therapeutic approaches that have the potential to reduce gastrointestinal inflammation and diarrhea and may allow patients who develop irEC to avoid disruption of their life-saving ICI cancer treatment. We plan to advance SER-155 into a next study in irEC evaluating prophylactic oral administration and dose optimization in patients initiating ICI cancer therapy. The prevention approach aims to reduce incidence of irEC, keep patients on ICI therapy and avoid immunosuppressive irEC treatments. The study is being designed in consultation with leading oncologists and irEC experts. As part of the development program, we intend to engage with FDA to discuss study design and potential endpoints including incidence of irEC (all grades), ICI administration, and safety. In addition, we intend to seek feedback from FDA on our plans to optimize dosing for prophylaxis, which could include a healthy volunteer study component or a dosing lead-in element, the results of which are expected to inform the prophylactic dosing course before initiating dosing in the broader ICI population. We expect to submit the study design to the FDA in the first quarter of 2027.

Previous wording

We have an extensive patent portfolio directed to rationally designed ecologies of spores and microbes. The portfolio includes both company-owned patents and applications, and those that we have rights to as licensee. The patents and applications included in our portfolio cover both composition of matter and methods (e.g., method of treating). Our intellectual property rights related to SER-155, SER-147 and/or SER-603 extend through at least part of 2046 (not including any potential term extension). We plan on continuing to broaden our patent portfolio. Currently, we have 20 active patent families, which includes 16 nationalized applications, three at the PCT stage, and one at the provisional stage. To date, we have obtained issuance of 33 U.S. patents (which includes three as licensee). Of the issued U.S. patents, 13 U.S. patents (including one as licensee) have been assigned to Nestlé Health Science as part of its purchase of VOWST.

Current wording

We have an extensive patent portfolio directed to rationally designed ecologies of spores and microbes. The portfolio includes both company-owned patents and applications, and those that we have rights to as licensee. The patents and applications included in our portfolio cover both composition of matter and methods (e.g., method of treating). Our intellectual property rights related to SER-155, SER-147, SER-428 and/or SER-603 extend through at least part of 2046 (not including any potential term extension). We plan on continuing to broaden our patent portfolio. Currently, we have 21 active patent families, which includes 16 nationalized applications, three at the PCT stage, and one at the provisional stage. To date, we have obtained issuance of 33 U.S. patents (which includes three as licensee). Of the issued U.S. patents, 13 U.S. patents (including one as licensee) have been assigned to Nestlé Health Science as part of its purchase of VOWST.

Previous wording

We recognized an impairment loss of $5.8 million, related to one of our operating leases and the associated leasehold improvements as an indicator of impairment was deemed to exist and the carrying value of the asset group exceeded its fair value. Refer to Note 6, Leases, included elsewhere in this Quarterly Report on Form 10-Q, for more information.

Current wording

We recognized an impairment loss of $5.7 million and $11.5 million for the three and nine months ended September 30, 2026, respectively, related to our operating leases and the associated leasehold improvements as an indicator of impairment was deemed to exist and the carrying value of the asset group exceeded its fair value. Refer to Note 6, Leases, included elsewhere in this Quarterly Report on Form 10-Q, for more information.

Previous wording

Since our inception in 2010, we have not recorded any U.S. federal or state income tax benefits for the net losses we have incurred in each year or our earned research and development tax credits, due to our uncertainty of realizing a benefit from those items. We did not provide for any income taxes in the three and six months ended June 30, 2026 or 2025.

Current wording

Since our inception in 2010, we have not recorded any U.S. federal or state income tax benefits for the net losses we have incurred in each year or our earned research and development tax credits, due to our uncertainty of realizing a benefit from those items. We did not provide for any income taxes in the three and nine months ended September 30, 2026 or 2025.

Previous wording

Our condensed consolidated financial statements are prepared in accordance with accounting principles generally accepted in the United States. The preparation of these condensed consolidated financial statements requires the application of appropriate technical accounting rules and guidance, as well as the use of estimates. The application of these policies necessarily involves judgments regarding future events. These estimates and judgments, in and of themselves, could materially impact the condensed consolidated financial statements and disclosures based on varying assumptions. The accounting policies discussed in our Annual Report on Form 10-K for the fiscal year ended December 31, 2025, filed with the SEC on March 12, 2026, or the Annual Report, are considered by management to be the most important to an understanding of the consolidated financial statements because of their significance to the portrayal of our financial condition and results of operations. There have been no material changes to that information disclosed in our Annual Report during the three and six months ended June 30, 2026.

Current wording

Our condensed consolidated financial statements are prepared in accordance with accounting principles generally accepted in the United States. The preparation of these condensed consolidated financial statements requires the application of appropriate technical accounting rules and guidance, as well as the use of estimates. The application of these policies necessarily involves judgments regarding future events. These estimates and judgments, in and of themselves, could materially impact the condensed consolidated financial statements and disclosures based on varying assumptions. The accounting policies discussed in our Annual Report on Form 10-K for the fiscal year ended December 31, 2025, filed with the SEC on March 12, 2026, or the Annual Report, are considered by management to be the most important to an understanding of the consolidated financial statements because of their significance to the portrayal of our financial condition and results of operations. There have been no material changes to that information disclosed in our Annual Report during the three and nine months ended September 30, 2026.

Previous wording

Total revenue was $0.7 million for the three months ended June 30, 2026 consisting of costs reimbursable under the CARB-X grant that we were awarded in the third quarter of 2025.

Current wording

Total revenue was $0.6 million and $0.4 million for the three months ended September 30, 2026 and 2025 consisting of costs reimbursable under the CARB-X grant that we were awarded in the third quarter of 2025.

Previous wording

a decrease in personnel-related costs of $2.4 million primarily due to a decrease in salaries, bonuses, employee benefits expenses, and stock-based compensation expense due to lower headcount;

Current wording

a decrease in personnel-related costs of $2.5 million primarily due to a decrease in salaries, bonuses, employee benefits expenses, and stock-based compensation expense due to lower headcount;

Previous wording

a decrease of $0.9 million in expenses related to our live biotherapeutics platform and research and development operations primarily due to the conclusion of the TSA with Nestlé as of December 31, 2025, under which we incurred costs related to inventory shipments and storage of sample material that were reimbursed by Nestlé in 2025, as well as a reduction in facilities costs related to the Lease Amendment that was effective during the second quarter of 2026;

Current wording

a decrease of $3.9 million in expenses related to our live biotherapeutics platform and research and development operations primarily due to the conclusion of the TSA with Nestlé as of December 31, 2025, under which we incurred costs related to inventory shipments and storage of sample material that were reimbursed by Nestlé in 2025, as well as a reduction in facilities costs related to the Lease Amendment that was effective during the second quarter of 2026 and the Termination Agreement that was effective during the third quarter of 2026;

Previous wording

an increase of $0.5 million in expenses related to our early stage programs primarily related to activities associated with the development of SER-428, for which the related reimbursements received from CARB-X are included within grant revenue.

Current wording

an increase of $0.3 million in expenses related to our early stage programs primarily related to activities associated with the development of SER-428, for which the related reimbursements received from CARB-X are included within grant revenue.

Previous wording

General and administrative expenses were $7.1 million for the three months ended June 30, 2026 compared to $10.3 million for the three months ended June 30, 2025. The decrease of $3.2 million was primarily due to the following:

Current wording

General and administrative expenses were $5.4 million for the three months ended September 30, 2026 compared to $9.5 million for the three months ended September 30, 2025. The decrease of $4.0 million was primarily due to the following:

Previous wording

a decrease in personnel-related costs of $1.1 million primarily due to a decrease in salaries, bonuses, employee benefits expenses, and stock-based compensation expenses due to lower headcount;

Current wording

a decrease in personnel-related costs of $1.9 million primarily due to a decrease in salaries, bonuses, employee benefits expenses, and stock-based compensation expenses due to lower headcount;

Previous wording

a decrease in professional fees of $2.2 million due to lower legal and consulting fees, and

Current wording

a decrease in professional fees of $0.3 million due to lower legal fees, and

Previous wording

a decrease in facility-related and other costs of $1.4 million primarily related to information technology costs that were incurred as part of the TSA and reimbursed by Nestlé that did not reoccur in 2026, as well as a reduction in facilities costs related to the Lease Amendment that was effective during the second quarter of 2026.

Current wording

a decrease in facility-related and other costs of $1.8 million primarily related to information technology costs that were incurred as part of the TSA and reimbursed by Nestlé that did not reoccur in 2026, as well as a reduction in facilities costs related to the Lease Amendment that was effective during the second quarter of 2026 and the Termination Agreement that was effective during the third quarter of 2026.

Previous wording

Impairment of long-lived assets was $5.8 million for the three months ended June 30, 2026, consisting of $5.6 million related to right-of-use assets and $0.2 million related to the associated leasehold improvements. Refer to Note 6, Leases, included elsewhere in this Quarterly Report on Form 10-Q, for more information.

Current wording

Impairment of long-lived assets was $5.7 million for the three months ended September 30, 2026, consisting of $3.7 million related to right-of-use assets and $2.0 million related to the associated leasehold improvements. Refer to Note 6, Leases, included elsewhere in this Quarterly Report on Form 10-Q, for more information.

Previous wording

Other income (expense), net was $25.9 million of income and $5.0 million of income for the three months ended June 30, 2026 and 2025, respectively. The increase of $20.8 million in other income, net was primarily due to the $25.0 million Gain on sale of VOWST business related to the Milestone Termination Payment expected to be received from SPN in July and October 2026, partially offset by $3.5 million of reimbursement income associated with the performance of TSA services in the second quarter of 2025 that did not reoccur due to the conclusion of the TSA at the end of 2025, and a decrease in interest income of $0.3 million due to our lower cash balance.

Current wording

Other income (expense), net was $0.1 million of expense and $30.7 million of income for the three months ended September 30, 2026 and 2025, respectively. The decrease of $30.8 million in other income, net was due to the $27.2 million gain on sale of the VOWST business primarily due to the installment payment received from Nestlé in July 2025 that was conditioned on our material compliance with obligations under the TSA, as well as $2.0 million of reimbursement income associated with the performance of TSA services in the third quarter of 2025 that did not reoccur in 2026 due to the conclusion of the TSA at the end of 2025, a decrease in sublease income of $1.1 million, and a decrease in interest income of $0.4 million due to our lower cash balance.

Previous wording

The following table summarizes our results of operations for the six months ended June 30, 2026 and 2025:

Current wording

The following table summarizes our results of operations for the nine months ended September 30, 2026 and 2025:

Previous wording

a decrease in personnel-related costs of $2.6 million primarily due to a decrease in salaries, bonus, employee benefits expenses, and stock-based compensation expense due to lower headcount; and

Current wording

a decrease in personnel-related costs of $5.1 million primarily due to a decrease in salaries, bonus, employee benefits expenses, and stock-based compensation expense due to lower headcount; and

Previous wording

a decrease of $0.9 million in expenses related to our SER-155 program as investment related to preparation for the Phase 2 study of SER-155 in allo-HCT was paused in February 2026; partially offset by

Current wording

a decrease of $1.8 million in expenses related to our SER-155 program as investment related to preparation for the Phase 2 study of SER-155 in allo-HCT was paused in February 2026; and

Previous wording

an increase of $0.5 million in expenses related to our live biotherapeutics platform and research and development operations primarily due to the conclusion of the TSA with Nestlé as of December 31, 2025, under which a portion of our facility costs and other operational costs were included within manufacturing services expenses and were reimbursed by Nestlé in 2025, partially offset by a reduction in facilities costs related to the Lease Amendment that was effective during the second quarter of 2026; and

Current wording

a decrease of $3.4 million in expenses related to our live biotherapeutics platform and research and development operations primarily due to a reduction in facilities costs related to the Lease Amendment that was effective during the second quarter of 2026 and the Termination Agreement that was effective during the third quarter of 2026, partially offset by an increase in facilities costs due to the conclusion of the TSA with Nestlé as of December 31, 2025, under which a portion of our facility costs and other operational costs were included within manufacturing services expenses and were reimbursed by Nestlé in 2025; partially offset by

Previous wording

an increase of $0.6 million in expenses related to our early stage programs primarily related to activities associated with the development of SER-428, for which the related reimbursements received from CARB-X are included within grant revenue.

Current wording

an increase of $0.9 million in expenses related to our early stage programs primarily related to activities associated with the development of SER-428, for which the related reimbursements received from CARB-X are included within grant revenue.

Previous wording

General and administrative expenses were $15.1 million for the six months ended June 30, 2026 compared to $22.1 million for the six months ended June 30, 2025. The decrease of $7.0 million was primarily due to the following:

Current wording

General and administrative expenses were $20.6 million for the nine months ended September 30, 2026 compared to $31.6 million for the nine months ended September 30, 2025. The decrease of $11.0 million was primarily due to the following:

Previous wording

a decrease in personnel-related costs of $1.9 million primarily due to a decrease in salaries, bonus, employee benefits expenses, and stock-based compensation expenses due to the decrease in headcount period over period; and

Current wording

a decrease in personnel-related costs of $3.8 million primarily due to a decrease in salaries, bonus, employee benefits expenses, and stock-based compensation expenses due to the decrease in headcount period over period; and

Previous wording

a decrease in professional fees of $0.7 million due to lower legal and consulting fees, and

Current wording

a decrease in professional fees of $2.5 million due to lower legal and consulting fees, and

Previous wording

a decrease in facility-related and other costs of $2.9 million primarily related to information technology costs that were incurred as part of the TSA and reimbursed by Nestlé that did not reoccur in 2026.

Current wording

a decrease in facility-related and other costs of $4.7 million primarily related to information technology costs that were incurred as part of the TSA and reimbursed by Nestlé that did not reoccur in 2026 and facilities costs associated with the Termination Agreement that was effective during the third quarter of 2026.

Previous wording

Impairment of long-lived assets was $5.8 million for the six months ended June 30, 2026, consisting of $5.6 million related to right-of-use assets and $0.2 million related to the associated leasehold improvements. Refer to Note 6, Leases, included elsewhere in this Quarterly Report on Form 10-Q, for more information.

Current wording

Impairment of long-lived assets was $11.5 million for the nine months ended September 30, 2026, consisting of $9.2 million related to right-of-use assets and $2.3 million related to the associated leasehold improvements. Refer to Note 6, Leases, included elsewhere in this Quarterly Report on Form 10-Q, for more information.

Previous wording

Other income (expense), net was $26.8 million of income and $64.9 million of income for the six months ended June 30, 2026 and 2025, respectively. The decrease of $38.1 million in other income, net was due to the lower gain on sale of VOWST business in 2026 compared to 2025 of $27.4 million, as well as $9.8 million of reimbursement income associated with the performance of TSA services in the first half of 2025 that did not reoccur due to the conclusion of the TSA at the end of 2025, and a decrease in interest income of $0.7 million due to our lower cash balance. The $52.4 million gain on sale of the VOWST business recognized in the six months ended June 30, 2025 was primarily due to the $50.0 million installment payment received from Nestlé in January 2025 that was conditioned on our material compliance with obligations under the TSA, while the $25.0 million gain on sale of VOWST business recognized in the six months ended June 30, 2026 was related to the Milestone Termination Payment expected to be received from SPN in July and October 2026.

Current wording

Other income (expense), net was $26.7 million of income and $95.6 million of income for the nine months ended September 30, 2026 and 2025, respectively. The decrease of $68.9 million in other income, net was due to the lower gain on sale of VOWST business in 2026 compared to 2025 of $54.6 million, as well as $11.8 million of reimbursement income associated with the performance of TSA services in the first half of 2025 that did not reoccur due to the conclusion of the TSA at the end of 2025, and a decrease in interest income of $1.1 million due to our lower cash balance. The $79.6 million gain on sale of the VOWST business recognized in the nine months ended September 30, 2025 was primarily due to the $75.0 million installment payments received from Nestlé in January and July 2025 that were conditioned on our material compliance with obligations under the TSA, while the $25.0 million gain on sale of VOWST business recognized in the nine months ended September 30, 2026 was related to the Milestone Termination Payment received from SPN in July and October 2026.

Previous wording

prepayment of the $60 million Prepaid Milestone tied to the achievement of the First Sales Milestone of worldwide annual net sales of the Product of $150 million, which was paid in cash at Closing, which Prepaid Milestone will accrue interest at a fixed rate of 10% per annum until the First Sales Milestone is achieved and 5% per annum thereafter until the earlier of (x) the date on which the Prepaid Milestone, plus accrued interest thereon, has been repaid in full by set-off and (y) the last day of the Milestone Period; and

Current wording

prepayment of the $60 million Prepaid Milestone, which was paid in cash at Closing; and

Previous wording

future Milestone Payments of (x) $125 million tied to the achievement of worldwide annual net sales of the Product of $400 million and (y) $150 million tied to the achievement of worldwide annual net sales of the Product of $750 million, during the Milestone Period from Closing until December 31 of the calendar year in which the tenth anniversary of Closing occurs.

Current wording

potential future sales milestone payments of $125.0 million and $150.0 million, tied to the achievement of worldwide annual net sales of the Product of $400.0 million and $750.0 million, respectively, during the Milestone Period.

Previous wording

On June 2, 2026, we entered into Amendment No. 1 (the “APA Amendment”) to the Purchase Agreement. Pursuant to the APA Amendment, the parties agreed to terminate SPN’s obligations with respect to the Milestone Payments described above and eliminate the milestone interest payments that would have been due from us to SPN. In consideration for the foregoing, SPN agreed to a one-time payment to us of $25.0 million (the "Milestone Termination Payment"), which amount is payable in two equal installments of $12.5 million, with the first installment paid on July 1, 2026 and the second installment payable on October 1, 2026.

Current wording

On June 2, 2026, we entered into Amendment No. 1 (the “APA Amendment”) to the Purchase Agreement. Pursuant to the APA Amendment, the parties agreed to terminate SPN’s obligations with respect to the Milestone Payments described in clause (iv) above and eliminate the milestone interest payments that would have been due from us to SPN. In consideration for the foregoing, SPN agreed to a one-time payment to us of $25.0 million (the "Milestone Termination Payment"), payable in two equal installments of $12.5 million, with the first installment paid on July 1, 2026 and the second installment paid on October 1, 2026. As a result, no further milestone payments are payable to us under the Purchase Agreement.

Previous wording

In May 2021, we entered into a Sales Agreement, or the Sales Agreement, with Cowen and Company, LLC, or Cowen, to sell shares of our common stock, with aggregate gross sales proceeds of up to $150.0 million, from time to time, through an “at the market” equity offering program under which Cowen acts as sales agent. During the three and six months ended June 30, 2026, we sold 232,286 and 258,082 shares of common stock under the Sales Agreement, at an average price of approximately $7.99 and $8.78 per share, raising aggregate net proceeds of approximately $1.7 million and $2.1 million after deducting an aggregate commission of approximately 3%. During the six months ended June 30, 2025, we sold 54,806 of common stock under the Sales Agreement, at an average price of approximately $18.60 per share, raising aggregate net proceeds of approximately $1.0 million after deducting an aggregate commission of approximately 3% and other issuance costs. As of June 30, 2026, we have sold 2,446,777 shares of common stock under the Sales Agreement, at an average price of approximately $26.16 per share, raising aggregate net proceeds of approximately $61.4 million after deducting an aggregate commission of approximately 3% and other issuance costs.

Current wording

In May 2021, we entered into a Sales Agreement, or the Sales Agreement, with Cowen and Company, LLC, or Cowen, to sell shares of our common stock, with aggregate gross sales proceeds of up to $150.0 million, from time to time, through an “at the market” equity offering program under which Cowen acts as sales agent. During the three and nine months ended September 30, 2026, we sold 113,643 and 371,725 shares of common stock under the Sales Agreement, at an average price of approximately $7.45 and $8.37 per share, raising aggregate net proceeds of approximately $0.7 million and $2.9 million after deducting an aggregate commission of approximately 3%. During the nine months ended September 30, 2025, we sold 54,806 shares of common stock under the Sales Agreement, at an average price of approximately $18.60 per share, raising aggregate net proceeds of approximately $1.0 million after deducting an aggregate commission of approximately 3% and other issuance costs. As of September 30, 2026, we have sold 2,560,420 shares of common stock under the Sales Agreement, at an average price of approximately $25.33 per share, raising aggregate net proceeds of approximately $62.2 million after deducting an aggregate commission of approximately 3% and other issuance costs. On August 13, 2026, we entered into a Sales Agreement, or the 2026 Sales Agreement, with TD Securities (USA) LLC, or TD Cowen, to sell shares of our common stock, with aggregate gross sales proceeds of up to $100.0 million, from time to time, through an "at the market" equity offering program under which TD Cowen acts as sales agent. During the three months ended September 30, 2026, no shares were sold under the 2026 Sales Agreement.

Previous wording

As of June 30, 2026, we had cash and cash equivalents totaling $15.6 million and an accumulated deficit of $987.7 million. For the six months ended June 30, 2026, we incurred a loss from operations of $42.2 million. We expect that our operating losses and negative cash flows will continue for the foreseeable future.

Current wording

As of September 30, 2026, we had cash and cash equivalents totaling $17.5 million and an accumulated deficit of $1,004.0 million. For the nine months ended September 30, 2026, we incurred a loss from operations of $58.3 million. We expect that our operating losses and negative cash flows will continue for the foreseeable future.