Lexeo Therapeutics, Inc.

Previous wording

We are a clinical stage genetic medicine company dedicated to reshaping heart health by applying pioneering science to fundamentally change how cardiovascular diseases are treated. We are advancing a portfolio of therapeutic candidates that take aim at the underlying genetic causes of conditions, including FA cardiomyopathy, plakophilin-2, or PKP2, arrhythmogenic cardiomyopathy, or ACM, and other devastating diseases with high unmet need.

Current wording

We are a clinical stage genetic medicine company dedicated to reshaping heart health by applying pioneering science to fundamentally change how cardiovascular diseases are treated. We are advancing a portfolio of therapeutic candidates that take aim at the underlying genetic causes of conditions, including Friedreich ataxia, or FA, cardiomyopathy, plakophilin-2, or PKP2, arrhythmogenic cardiomyopathy, or ACM, and other devastating diseases with high unmet need.

Previous wording

Our most advanced cardiovascular product candidate, LX2006 for the treatment of FA cardiomyopathy, is currently being evaluated in SUNRISE-FA, our ongoing Phase 1/2 clinical trial, and in a Cornell investigator-initiated trial. In October 2025, we announced progress in regulatory interactions with the FDA on LX2006. In response to questions from us regarding the possibility of a faster path to a Biologics License Application, or BLA, the FDA has indicated openness to a BLA submission for accelerated approval that includes clinical data from our ongoing Phase 1/2 studies of LX2006 pooled with new clinical data to be generated in the planned pivotal study. To enable pooling of these data to support licensure, we will submit enhanced manufacturing comparability data and meet an additional nonclinical requirement, given our intention to leverage our optimized, high-yield Sf9-baculovirus manufacturing platform for future clinical and commercial drug supply, compared to the adherent HEK293 process used for our Phase 1/2 clinical supply. In October 2025, we shared Chemistry, Manufacturing and Controls, or CMC, data for LX2006, which were submitted to the FDA to support analytical comparability between the HEK293 manufacturing process and the Sf9-baculovirus manufacturing platform. These data demonstrate similar frataxin expressionin vitro between the two processes as measured by a quantitative relative potency assay in cardiomyocytes. In November 2025, the FDA approved this analytical comparability report establishing comparability between LX2006 HEK293 and Sf9 manufacturing processes, endorsing use of the optimized, Sf9 final commercial manufacturing process for LX2006 in the planned pivotal study and clearing compatibility requirements to begin dosing patients.

Current wording

LX2006 for the treatment of FA cardiomyopathy

Previous wording

Along with the regulatory announcement, we provided an interim clinical update on LX2006, which included baseline characteristics and safety data from the 17 treated participants across the two studies, and clinical efficacy data from the 16 participants who had reached at least six months of follow up as of that time. These data showed sustained or deepening improvements in the majority of participants across both cardiac and neurologic measures of FA, exceeding the thresholds previously agreed with FDA for co-primary endpoints LVMI and frataxin expression. We shared that the FDA had previously agreed to evaluate the co-primary endpoint of LVMI at a time point earlier than 12 months. LX2006 has been generally well-tolerated across both trials to date, with no clinically significant complement activation. We continue to engage with the FDA on the planned pivotal study protocol and comparability. In discussions to date, there have been no changes to the previously disclosed alignment with the FDA on key parameters related to the LX2006 planned pivotal study.

Current wording

In October 2025, we provided an interim clinical update, which included baseline characteristics and safety data from the 17 treated participants across the two studies, and clinical efficacy data from the 16 participants who had reached at least six months follow-up as of that time. A summary of key observations from the October 2025 interim update is set forth below.

Previous wording

Our second most advanced cardiovascular product candidate, LX2020 for the treatment of ACM caused by mutations in the PKP2 gene, referred to as PKP2-ACM, is currently being evaluated in HEROIC-PKP2, an ongoing Phase 1/2 clinical trial. We have completed enrollment and dosing in this trial, with ten participants dosed: three in the low dose cohort 1 (2×1013 vg/kg), three in the high dose cohort 2 (6×1013 vg/kg), and four in the dose-expansion high dose cohort 3 (6×1013 vg/kg). Across all participants dosed, LX2020 has been generally well-tolerated, with no clinically significant complement activation to date. In October 2025, we reported that one Grade 3 serious adverse event, which was assessed as possibly treatment related, of sustained ventricular tachycardia, or SVT, had been observed three months after dosing in a single participant in the high dose cohort of the HEROIC-PKP2 Phase 1/2 clinical trial. The participant was successfully treated with anti-arrhythmic medication and was discharged with no additional intervention required. This patient had a documented history of prior VTs and had an implantable cardioverter defibrillator in place.

Current wording

Our second most advanced cardiovascular product candidate, LX2020 for the treatment of ACM caused by mutations in the PKP2 gene, referred to as PKP2-ACM, is currently being evaluated in HEROIC-PKP2, an ongoing Phase 1/2 clinical trial.

Previous wording

To date, we have funded our operations primarily through proceeds from the sale of shares of our convertible preferred stock, common stock, and pre-funded warrants and warrants to purchase our common stock, including from our October 2025 Financing Transactions, May 2025 Private Placement, March 2024 Private Placement, IPO and the subsequent partial exercise of the underwriters’ 30-day option to purchase additional shares of common stock. As of September 30, 2025, we had $122.8 million of cash, cash equivalents, and investments in U.S. Treasury securities. We have incurred significant operating losses since the commencement of our operations. Our ability to generate product revenue sufficient to achieve profitability will depend heavily on the successful development and eventual commercialization of one or more of our current gene therapy candidates or any future gene therapy candidates. Our net losses for the nine months ended September 30, 2025 and the year ended December 31, 2024 were $79.0 million and $98.3 million, respectively, and our accumulated deficit was $359.2 million at September 30, 2025. We expect to continue to incur significant losses for the foreseeable future as we advance our current and future product candidates through preclinical and clinical development, continue to build our operations and operate as a public company.

Current wording

To date, we have funded our operations primarily through proceeds from the sale of shares of our convertible preferred stock, common stock, and pre-funded warrants and warrants to purchase our common stock. As of March 31, 2026, we had $227.6 million of cash, cash equivalents, and investments in U.S. Treasury securities. We have incurred significant operating losses since the commencement of our operations. Our ability to generate product revenue sufficient to achieve profitability will depend heavily on the successful development and eventual commercialization of one or more of our current gene therapy candidates or any future gene therapy candidates. Our net losses for the three months ended March 31, 2026 and the year ended December 31, 2025 were $20.2 million and $100.0 million, respectively, and our accumulated deficit was $400.3 million at March 31, 2026. We expect to continue to incur significant losses for the foreseeable future as we advance our current and future product candidates through preclinical and clinical development, continue to build our operations and operate as a public company.

Previous wording

We expense research and development costs as expenses when incurred. Nonrefundable advance payments for goods and services that will be used in future research and development activities are expensed when the activity has been performed or when the goods have been received rather than when the payment is made. When third-party service providers’ billing terms do not coincide with our period-end, we are required to make estimates of our obligations to those third parties incurred in a given accounting period and record accruals at the end of the period. We base these estimates on our knowledge of the research and development programs, services performed for the period, past history for related activities and the expected duration of the third-party service contract, where applicable. If timelines or contracts are modified based upon changes in the scope of work to be performed, we modify our estimates of accrued expenses accordingly on a prospective basis; therefore, actual results could differ from our estimates. Upfront payments under license agreements are expensed upon receipt of the license, and annual maintenance fees under license agreements are expensed in the period in which they are incurred. Milestone payments under license agreements are accrued, with a corresponding expense being recognized, in the period in which the milestone is determined to be probable of achievement and the related amount is reasonably estimable.

Current wording

We record research and development costs as expenses when incurred. Nonrefundable advance payments for goods and services that will be used in future research and development activities are expensed when the activity has been performed or when the goods have been received rather than when the payment is made. When third-party service providers’ billing terms do not coincide with our period-end, we are required to make estimates of our obligations to those third parties incurred in a given accounting period and record accruals at the end of the period. We base these estimates on our knowledge of the research and development programs, services performed for the period, past history for related activities and the expected duration of the third-party service contract, where applicable. If timelines or contracts are modified based upon changes in the scope of work to be performed, we modify our estimates of accrued expenses accordingly on a prospective basis; therefore, actual results could differ from our estimates. Upfront payments under license agreements are expensed upon receipt of the license, and annual maintenance fees under license agreements are expensed in the period in which they are incurred. Milestone payments under license agreements are accrued, with a corresponding expense being recognized, in the period in which the milestone is determined to be probable of achievement and the related amount is reasonably estimable.

Previous wording

We expect that in the near to medium term future our general and administrative expenses will (i) at least approximate those incurred during the three months ended September 30, 2025 on a quarterly basis, and (ii) decrease relative to those incurred during the nine months ended September 30, 2025 on an annualized basis, primarily due to lower anticipated third-party legal fees and related costs, while supporting the continued research and development of our programs and the growth of our business.

Current wording

We expect that in the near to medium term future our general and administrative expenses may increase relative to those incurred during the three months ended March 31, 2026 on a quarterly basis and on an annualized basis, due to anticipated sales and marketing costs as we approach expected commercialization of our product candidates, if approved, while supporting the continued research and development of our programs and the growth of our business.

Previous wording

Other income (expense), net includes foreign exchange gains and (losses).

Current wording

Other expense, net includes foreign exchange gains and (losses).

Previous wording

Amortization of premium on investments consists of amortization of premium on our investments in U.S. Treasury securities.

Current wording

(Amortization of premium) and accretion of discount on investments in U.S. Treasury securities, net consists of amortization of premium and accretion of discount on our investments in U.S. Treasury securities.

Previous wording

The net decrease of $7.7 million in total research and development expenses for the three months ended September 30, 2025 compared to the three months ended September 30, 2024 was primarily due to decreases in (i) milestone expenses of $6.1 million, consisting primarily of a $6.0 million development milestone for our LX2020 program that was achieved during the third quarter of 2024 and subsequently paid to the selling shareholders of Stelios, (ii) employee compensation and stock-based compensation expenses of $1.1 million due to decreased headcount associated with a limited reduction-in-force undertaken in April 2025, and (iii) CMC expenses of $0.9 million. These decreases were partially offset by an increase in clinical trial expenses of $0.5 million.

Current wording

The net decrease of $1.5 million in total research and development expenses for the three months ended March 31, 2026 compared to the three months ended March 31, 2025 was primarily due to decreases in (i) employee and stock-based compensation expenses of $1.5 million primarily due to decreased headcount, (ii) CMC expenses of $0.8 million, and (iii) preclinical and quality expenses of $0.4 million. These decreases were primarily offset by increases in (i) clinical trial expenses of $0.5 million, (ii) milestone expenses of $0.4 million associated with our LX1001 program, and (iii) program and portfolio management expenses of $0.3 million.

Previous wording

The net decrease of $2.2 million in general and administrative expenses for the three months ended September 30, 2025 compared to the three months ended September 30, 2024 was primarily due to a decrease in third-party legal fees and associated costs of $1.6 million, as well as a decrease in stock-based compensation expense of $0.8 million. These decreases were partially offset by increases in capital and franchise tax expenses of $0.2 million.

Current wording

The net decrease of $10.0 million in general and administrative expenses for the three months ended March 31, 2026 compared to the three months ended March 31, 2025 was primarily due to decreases in (i) third-party legal fees and associated costs of $10.5 million, and (ii) employee and stock-based compensation expenses of $0.4 million primarily due to decreased headcount. These decreases were partially offset by increased professional services and consultant expenses of $0.4 million.

Previous wording

We recognized interest income of $1.5 million and $2.1 million for the three months ended September 30, 2025 and September 30, 2024, respectively, primarily related to interest earned on our investments in U.S. government money market funds and our investments in U.S Treasury securities, with the decrease primarily due lower average invested balances, as well as lower interest rates.

Current wording

We recognized interest income of $2.1 million and $1.2 million for the three months ended March 31, 2026 and March 31, 2025, respectively, primarily related to interest earned on our investments in U.S. government money market funds, our investments in U.S Treasury securities, and our interest-bearing demand deposit cash accounts, with the increase due to higher invested balances, which was partially offset by lower interest rates.

Previous wording

Since our inception, we have not generated any revenue from product sales and have incurred significant operating losses and negative cash flows from our operations. We expect to incur significant expenses and operating losses for the foreseeable future as we advance the clinical development of our product candidates. Since our inception through September 30, 2025, we funded our operations primarily through proceeds from the sale of shares of our convertible preferred stock, common stock, and pre-funded warrants and warrants to purchase our common stock, including from our October 2025 Financing Transactions, May 2025 Private Placement, March 2024 Private Placement, IPO and the subsequent partial exercise of the underwriters’ 30-day option to purchase additional shares of common stock, with estimated net proceeds since our inception totaling $594.9 million. As of September 30, 2025 and December 31, 2024, we had cash, cash equivalents, and investments in U.S. Treasury Securities of $122.8 million and $128.5 million, respectively.

Current wording

Since our inception, we have not generated any revenue from product sales and have incurred significant operating losses and negative cash flows from our operations. We expect to incur significant expenses and operating losses for the foreseeable future as we advance the clinical development of our product candidates. Since our inception through March 31, 2026, we funded our operations primarily through proceeds from the sale of shares of our convertible preferred stock, common stock, and pre-funded warrants and warrants to purchase our common stock. As of March 31, 2026 and December 31, 2025, we had cash, cash equivalents, and investments in U.S. Treasury Securities of $227.6 million and $246.6 million, respectively.

Previous wording

On March 24, 2025 we filed a prospectus supplement to the prospectus which forms a part of our effective shelf registration statement on Form S-3, dated December 13, 2024, which registers the offering, issuance, and sale of up to $75.0 million of common stock pursuant to our ATM Program. As of September 30, 2025, we have not sold any shares of common stock pursuant to the ATM Program. In October 2025, we raised $153.8 million in equity capital from the October Financing Transactions, receiving net proceeds of $143.9 million after transaction costs.

Current wording

As of March 31, 2026, we had not sold any shares of common stock pursuant to the ATM Program. In April 2026, we sold 4,424,778 shares of our common stock under the ATM Program for net proceeds of $23.6 million after transaction costs.

Previous wording

The following table summarizes our sources and uses of cash for the nine months ended September 30, 2025 and September 30, 2024 (in thousands):

Current wording

The following table summarizes our sources and uses of cash for the three months ended March 31, 2026 and March 31, 2025 (in thousands):

Previous wording

During the nine months ended September 30, 2025, net cash used in operating activities consisted primarily of our net loss of $79.0 million, which included an unrealized gain of $3.4 million recorded to other non-operating income upon receipt of our long-term investment in convertible preferred stock, in addition to $7.1 million of net cash used in changes in operating assets and liabilities, which were partially offset by $9.4 million of stock-based compensation expense and $1.3 million of depreciation expense and amortization of operating and finance right-of-use assets.

Current wording

During the three months ended March 31, 2026, net cash used in operating activities consisted primarily of our net loss of $20.2 million and $4.2 million of net cash used in changes in operating assets and liabilities, which were partially offset by $2.8 million of stock-based compensation expense and $0.5 million of depreciation expense and amortization of operating and finance right-of-use assets.

Previous wording

During the nine months ended September 30, 2024, net cash used in operating activities consisted primarily of our net loss of $72.4 million, which was partially offset by $9.1 million of net cash provided by changes in operating assets and liabilities, $9.0 million of stock-based compensation expense, and $1.5 million of depreciation expense and amortization of operating and finance right-of-use assets.

Current wording

During the three months ended March 31, 2025, net cash used in operating activities consisted primarily of our net loss of $32.7 million, which was partially offset by $6.7 million of net cash provided by changes in operating assets and liabilities, $3.7 million of stock-based compensation expense, and $0.5 million of depreciation and amortization of operating and finance right-of-use assets.

Previous wording

During the nine months ended September 30, 2025, net cash provided by financing activities consisted primarily of the net proceeds received from the May 2025 Private Placement offering of $73.1 million, as well as proceeds received from common stock issuances under the 2023 ESPP of $0.3 million, which were partially offset by $0.4 million of principal payments made on equipment finance leases.

Current wording

During the three months ended March 31, 2026, net cash provided by financing activities consisted primarily of proceeds received from the exercise of common warrants of $2.4 million, as well as proceeds received from common stock issuances under the 2023 ESPP of $0.1 million, which were partially offset by $0.1 million of principal payments made on equipment finance leases.

Previous wording

During the nine months ended September 30, 2024, net cash provided by financing activities consisted primarily of the net proceeds received from the Private Placement offering of $88.7 million, as well as $0.5 million of proceeds received from the exercise of stock options, which were partially offset by $0.3 million of principal payments made on equipment finance leases.

Current wording

During the three months ended March 31, 2025, net cash provided by financing activities consisted of proceeds received from common stock issuances under the 2023 ESPP of $0.2 million, which was partially offset by $0.2 million of principal payments made on equipment finance leases.