Risk Factors Update Summary

• Net loss increased from $228 million to $276 million for the year ended December 31, 2022.
• Reduction of the workforce by approximately 25% in January 2024, impacting operations and development.
• Revenues from commercialization increased from none to limited to date.
• Total cash, cash equivalents, and short-term investments increased from $242.8 million to $51.7 million as of December 31, 2023.
• Failure to meet Nasdaq listing standards could lead to delisting, affecting liquidity and stock price.
• Addition of a new partner for ATA2271 and/or ATA3271, expanding commercialization potential.
• Cybersecurity incident in November 2023 resulted in unauthorized access, prompting additional IT security measures.
• Anticipated payments of $40.0 million received in January 2023 for milestones under the BLA transfer to Pierre Fabre will fund operations into the second quarter of 2027.
• Workforce reductions of approximately 20%, 30%, and 25% were announced in August 2022, November 2023, and January 2024, respectively.
• Inclusion of partners in the negotiation of pricing with third-party payors and government authorities.
• Increase in compliance obligations and risks due to new state laws on consumer privacy.
• Potential disruption in obtaining clinical supplies due to reliance on third-party manufacturers.
• Reductions in workforce could harm operations and ability to attract talent, impacting product development.
• Fluctuation in the reported sale price of common stock from $20 to $28 per share.