# EDGAR Filing Document

**Accession Number:** 0001732701
**File Stem:** 0001732701-25-000007
**Filing Date:** 2025-11
**Character Count:** 7234
**Document Hash:** e0e20a2f8cb90231b06a8d8f9064b899
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001732701-25-000007.hdr.sgml**: 20251121

**ACCESSION NUMBER**: 0001732701-25-000007

**CONFORMED SUBMISSION TYPE**: 4

**PUBLIC DOCUMENT COUNT**: 1

**CONFORMED PERIOD OF REPORT**: 20251031

**FILED AS OF DATE**: 20251121

**DATE AS OF CHANGE**: 20251121

**REPORTING-OWNER**: 

**OWNER DATA:**
- **COMPANY CONFORMED NAME:** MCDONOUGH GEOFF
- **CENTRAL INDEX KEY:** 0001732701

**ORGANIZATION NAME:**

**FILING VALUES:**
- **FORM TYPE:** 4
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 001-39319
- **FILM NUMBER:** 251508833

**MAIL ADDRESS:**
- **STREET 1:** C/O SURFACE ONCOLOGY, INC.
- **STREET 2:** 50 HAMPSHIRE ST., 8TH FLOOR
- **CITY:** CAMBRIDGE
- **STATE:** MA
- **ZIP:** 02139
**ISSUER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Generation Bio Co.
- **CENTRAL INDEX KEY:** 0001733294
- **STANDARD INDUSTRIAL CLASSIFICATION:** PHARMACEUTICAL PREPARATIONS [2834]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 814301281
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**BUSINESS ADDRESS:**
- **STREET 1:** 301 BINNEY STREET
- **CITY:** CAMBRIDGE
- **STATE:** MA
- **ZIP:** 02142
- **BUSINESS PHONE:** 857-529-5908

**MAIL ADDRESS:**
- **STREET 1:** 301 BINNEY STREET
- **CITY:** CAMBRIDGE
- **STATE:** MA
- **ZIP:** 02142

### UNITED STATES SECURITIES AND EXCHANGE COMMISSION
**Washington, D.C. 20549**

## FORM 4

### STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

[ ] Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

[ ] Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

---

| | | |
|:---|:---|:---|
| **1. Name and Address of Reporting Person**<sup>*</sup><br>MCDONOUGH GEOFF<br><sub>(Last) (First) (Middle)</sub><br>C/O GENERATION BIO CO., 301 BINNEY ST<br><sub>(Street)</sub><br>CAMBRIDGE, MA 02142<br><sub>(City) (State) (Zip)</sub> | **3. Date of Earliest Transaction (Month/Day/Year)**<br>2025-10-31 | **5. Relationship of Reporting Person(s) to Issuer**<br>(Check all applicable)<br>[X] Director [ ] 10% Owner<br>[ ] Officer (give title below) [ ] Other (specify below)<br>_ _ |
| **2. Issuer Name and Ticker or Trading Symbol**<br>Generation Bio Co. [ GBIO ] | **4. If Amendment, Date of Original Filed (Month/Day/Year)**<br>  | **6. Individual or Joint/Group Filing (Check Applicable Line)**<br>[X] Form filed by One Reporting Person<br>[ ] Form filed by More than One Reporting Person |

---

## Table I - Non-Derivative Securities

---

|  |  |  |  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| 1. Title of Security | 2. Transaction Date | 2A. Deemed Execution Date | 3. Transaction Code (V) | 3. Transaction Code (V) | 4. Securities Acquired (A) or Disposed of (D) | 4. Securities Acquired (A) or Disposed of (D) | 4. Securities Acquired (A) or Disposed of (D) | 5. Amount of Securities Beneficially Owned | 6. Ownership Form | 7. Nature of Indirect Beneficial Ownership |
| 1. Title of Security | 2. Transaction Date | 2A. Deemed Execution Date | Code | V | Amount | (A) or (D) | Price | 5. Amount of Securities Beneficially Owned | 6. Ownership Form | 7. Nature of Indirect Beneficial Ownership |
| Common Stock | 2025-10-31 |  | M |  | 659<sup>(1)</sup> | A | <sup>(2)</sup> | 137495 | D |  |
| Common Stock | 2025-10-31 |  | F |  | 293 | D | $5.51 | 137202 | D |  |
| Common Stock |  |  |  |  |  |  |  | 22646 | I | By 2018 Trust<sup>(3)</sup> |
| Common Stock |  |  |  |  |  |  |  | 27500 | I | By 2020 Trust<sup>(4)</sup> |

---

## Table II - Derivative Securities

---

|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| 1. Title of Derivative Security | 2. Conversion or Exercise Price | 3. Transaction Date | 3A. Deemed Execution Date | 4. Transaction Code (V) | 4. Transaction Code (V) | 5. Number of Derivative Securities Acquired (A) or Disposed of (D) | 5. Number of Derivative Securities Acquired (A) or Disposed of (D) | 6. Date Exercisable and Expiration Date | 6. Date Exercisable and Expiration Date | 7. Title and Amount of Underlying Securities | 7. Title and Amount of Underlying Securities | 8. Price of Derivative Security | 9. Number of Derivative Securities Beneficially Owned | 10. Ownership Form | 11. Nature of Indirect Beneficial Ownership |
| 1. Title of Derivative Security | 2. Conversion or Exercise Price | 3. Transaction Date | 3A. Deemed Execution Date | Code | V | (A) | (D) | Date Exercisable | Expiration Date | Title | Amount or Number of Shares | 8. Price of Derivative Security | 9. Number of Derivative Securities Beneficially Owned | 10. Ownership Form | 11. Nature of Indirect Beneficial Ownership |
| Restricted Stock Units | <sup>(2)</sup> | 2025-10-31 |  | M |  |  | 659<sup>(1)</sup> | <sup>(5)</sup> | <sup>(5)</sup> | Common Stock | 527 | $0 | 1977 | D |  |

---

### Footnotes:

(1) Reflects an acceleration of vesting due to the reporting person's resignation as the Issuer's Chief Executive Officer & President.

(2) Each restricted stock unit represents the right to receive one share of the company's common stock.

(3) The securities are directly held by the McDonough Family 2018 Irrevocable Trust, or the 2018 Trust. The reporting person is the settlor of the 2018 Trust, Allison L. McDonough and David S. Grayzel are trustees for the 2018 Trust, and the 2018 Trust is for the benefit of Graeme and Owen McDonough. The reporting person may be deemed to beneficially own the shares of common stock owned by the 2018 Trust.

(4) The securities are directly held by the McDonough Family 2020 Irrevocable Trust, or the 2020 Trust. The reporting person is the settlor of the 2020 Trust, Allison L. McDonough and David S. Grayzel are trustees for the 2020 Trust, and the 2020 Trust is for the benefit of Allison, Graeme and Owen McDonough. The reporting person may be deemed to beneficially own the shares of common stock owned by the 2020 Trust.

(5) On January 20, 2023, the reporting person was granted 8,437 restricted stock units. The shares underlying the restricted stock units vest over two years, with 25% of the shares vesting on July 15, 2022 and the remaining shares vesting in equal quarterly installments thereafter.

**Signature:** /s/ Shawna-Gay White, Attorney-in-Fact  
**Date:** 2025-11-21

### Remarks:

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.

**Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.**