Bruce Booth
About Bruce Booth
Bruce Booth, D.Phil., age 51, has served on Sionna Therapeutics’ board since June 2020. He is a General Partner at Atlas Venture, co-founded Kymera Therapeutics and chairs its board, and chairs Vigil Neuroscience. He holds a B.S. in biochemistry from Penn State and a D.Phil. in molecular immunology from Oxford as a British Marshall Scholar, reflecting deep biotech investing and company-building credentials .
Past Roles
| Organization | Role | Tenure | Committees/Impact |
|---|---|---|---|
| AVROBIO, Inc. (now Tectonic Therapeutic, Inc. NASDAQ: TECX) | Director | Feb 2016 – Jun 2024 | Public company board experience |
| Magenta Therapeutics, Inc. (now Dianthus Therapeutics, Inc. NASDAQ: DNTH) | Director | Feb 2016 – Sep 2023 | Public company board experience |
| Unum Therapeutics, Inc. (now Cogent Biosciences, Inc. NASDAQ: COGT) | Director | Oct 2014 – Jul 2020 | Public company board experience |
| Takeda Pharmaceuticals, UCB Biopharma, Bill & Melinda Gates Foundation | Advisor (various capacities) | Not specified | Strategic advisory roles |
External Roles
| Organization | Role | Tenure | Committees/Impact |
|---|---|---|---|
| Kymera Therapeutics, Inc. | Chairman of the Board | Apr 2016 – present | Board leadership |
| Vigil Neuroscience, Inc. | Chairman of the Board | Jun 2020 – present | Board leadership |
| Nimbus Therapeutics, HotSpot Therapeutics, Arkuda Therapeutics, Matchpoint Therapeutics | Director (private cos.) | Current | Company-building across portfolio |
Board Governance
- Independence: The board determined all directors other than CEO Michael Cloonan are independent under Nasdaq and SEC rules; Booth is independent .
- Committees: Member, Compensation Committee (chair is Dr. Joanne Viney) .
- Attendance: In 2024, each director attended at least 75% of board and applicable committee meetings .
- Tenure on Sionna board: Since 2020; current term up for re-election in 2025 as Class I director .
Fixed Compensation
| Year | Cash Retainer ($) | Committee Fees ($) | Equity Awards ($, grant-date fair value) | Total ($) |
|---|---|---|---|---|
| 2024 | — | — | — | — |
- Note: In 2024, Booth received no cash or equity director compensation due to affiliation with Atlas Venture; as of Dec 31, 2024, he held no outstanding options or unvested stock awards .
- Policy change: Effective Feb 6, 2025, Sionna adopted a non-employee director compensation policy with standard retainers and option grants; per-director post-IPO amounts for Booth are not disclosed in the proxy .
Performance Compensation
| Item | Detail |
|---|---|
| Performance-based director pay metrics | Not disclosed; director equity under the 2025 policy consists of time-based stock options (Initial Grant 39,919 options; Annual Grant 19,959 options) with standard vesting and 10-year term; no performance conditions cited . |
| Clawback | Company maintains a compensation recovery policy applicable to incentive-based compensation upon restatements, aligned with SEC/Nasdaq rules . |
Other Directorships & Interlocks
| Company/Entity | Relationship to SION | Interlock/Ownership Context |
|---|---|---|
| Atlas Venture | Booth is General Partner | Atlas entities beneficially owned >5% of Sionna as of Apr 15, 2025; Atlas purchased shares in the IPO; Booth disclaims beneficial ownership except to pecuniary interest . |
| RA Capital | Fellow director (Resnick) affiliated | RA Capital beneficially owned ~23.7% and purchased IPO shares; overlapping investor-affiliated directors on board . |
| OrbiMed | Fellow director (Thompson) affiliated | OrbiMed beneficially owned ~8.4% and purchased IPO shares . |
| Enavate/Sionna Aggregator | Fellow director (Fleming) affiliated | Sionna Aggregator beneficially owned ~5.6% and purchased IPO shares . |
| TPG Growth | Fellow director (Iancovici) affiliated | TPG affiliated funds beneficially owned ~15.2% and purchased IPO shares . |
- Related party transactions: Atlas, RA Capital, OrbiMed, TPG Growth, Enavate/ Sionna Aggregator, Viking participated in Sionna’s 2024 Series C and 2025 IPO; board members are affiliated with several of these investors .
Expertise & Qualifications
- Venture-backed biotech company formation and governance; chair roles at multiple public biotechs (Kymera, Vigil) .
- Scientific training in molecular immunology; British Marshall Scholar; B.S. biochemistry (summa cum laude), D.Phil. Oxford .
- Advisory experience with large pharma and global foundations (Takeda, UCB, Gates Foundation) .
Equity Ownership
| Holder | Shares Beneficially Owned | % of Outstanding | Notes |
|---|---|---|---|
| Bruce Booth | — | <1% | No beneficial ownership reported; Atlas entities hold 8.4%; Booth is a member of Atlas GP entities and disclaims beneficial ownership except to pecuniary interest . |
- Hedging/pledging: Sionna’s insider trading policy prohibits hedging and pledging of company stock by directors and officers .
Governance Assessment
-
Strengths:
- Independent director with deep biotech governance experience and scientific literacy enhances compensation oversight and strategic alignment .
- Use of independent compensation consultant (Pearl Meyer) and formal committee charters; independence assessed; no consultant conflicts identified .
- Clawback policy, code of ethics, related party transaction policy, and prohibition on hedging/pledging support governance discipline .
-
Concerns/RED FLAGS:
- Investor-affiliated director on Compensation Committee while multiple >5% holders are represented on the board (Atlas, RA, OrbiMed, TPG, Enavate). This presents potential perceived conflicts in pay/strategy decisions despite independence determinations; monitoring of recusal practices and related-party oversight is prudent .
- Minimal personal ownership reported by Booth (no beneficial holdings), which may limit direct alignment with common shareholders; however, firm-level ownership via Atlas is significant and Booth disclaims beneficial ownership .
-
Engagement/Attendance:
- Attendance threshold met (≥75%), but not disclosed as 100%; continued monitoring of committee meeting participation advisable as company matures post-IPO .
-
Compensation signals:
- 2024: No compensation paid due to affiliation; post-IPO policy standardizes cash retainers and time-based options for directors. No performance-linked director equity metrics disclosed, reducing direct pay-for-performance alignment at the board level .