Changes in Beneficial Ownership · 4

TRex Bio, Inc.

TRXBNASDAQEQUITYCurrent

Changes in Beneficial Ownership

Filed Oct 15, 2026Accepted Oct 15, 2026, 4:33 PM EDTFiling CIK 2139097Accession 0001722024-26-000004

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Structured filing — 4

wk-form4_1792096429.xml

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Filing details

Report period: 2026-10-13
Issuer: TRex Bio, Inc.
Issuer CIK: 0002139097
Trading symbol: TRXB
No longer subject to Section 16: Checked

Reporting owner 1

Name: Alexandria Venture Investments, LLC
Reporting owner CIK: 0001722024
Relationship: 10% owner
Address: 26 NORTH EUCLID AVENUE, PASADENA, CA, 91101

Non-derivative transactions

Non-derivative transactions · 2 reported rows
Security	Transaction date	Code	Amount	A / D	Price (USD)	Owned after	Ownership
Common Stock	2026-10-13	C · Form 4	1,167,930	A	^[F1]	1,167,930	D
Common Stock	2026-10-13	P · Form 4	178,571	A	14	1,346,501	D

Table key

C · Form 4: Derivative conversion
A: Acquired
D: Direct
P · Form 4: Purchase on the market or privately

Derivative transactions

Derivative transactions · 2 reported rows
Security	Conversion / exercise price (USD)	Transaction date	Code	Amount	A / D	Price (USD)	Exercisable	Expires	Underlying security	Underlying shares	Owned after	Ownership
Series A-3 Preferred Stock	^[F1]	2026-10-13	C · Form 4	1,033,541	D	0	^[F1]	^[F1]	Common Stock	267,418	0	D
Series B Preferred Stock	^[F1]	2026-10-13	C · Form 4	3,480,387	D	0	^[F1]	^[F1]	Common Stock	900,512	0	D

Table key

C · Form 4: Derivative conversion
D: Direct

Footnotes

F1: Each share of preferred stock automatically converted into the Issuer's common stock at a ratio of 3.8649 shares of preferred stock to 1 share of common stock upon closing of the Issuer's initial public offering on October 13, 2026, for no additional consideration. The shares had no expiration date.↩ 1 ↩ 2 ↩ 3 ↩ 4 ↩ 5 ↩ 6 ↩ 7

Signature 1

Signed: By: /s/ Marc E. Binda, Chief Financial Officer and Treasurer By: ALEXANDRIA REAL ESTATE EQUITIES, INC., a Maryland corporation, managing member
Date: 2026-10-15

Company context

We are a clinical-stage biopharmaceutical company focused on tissue Treg biology for the discovery and development of immunoregulatory medicines designed to restore immune balance and promote tissue repair to address unmet needs of patients with autoimmune and inflammatory diseases. TRexBio was built on a pivotal scientific insight: that regulatory T cells (“Tregs”) in human tissue are not merely passive suppressors of inflammation, but active orchestrators of tissue immune homeostasis and repair. Leveraging our Deep Biology drug discovery and design platform, we integrate tissue-level insights into human biology and Treg function to identify and characterize novel targets and approaches for therapeutic intervention. Our tissue-first conviction and unique insights in Treg biology are the foundation of our pipeline of therapeutic candidates aimed at restoring immune balance and promoting tissue repair for more durable disease control.

Current securities

TRXBNASDAQ · EQUITY · Current

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