EcoR1 Capital, LLC

CIK: 0001587114

Transaction Breakdown

Open Market Buys (P)45 (73.8%)

High conviction signal

Open Market Sales (S)10 (16.4%)

Position reduction

Option Exercises (M)0 (0.0%)

Derivative conversions

Awards (A)0 (0.0%)

Compensation grants

Other (G, F, J, C, D, …)6 (9.8%)

Gifts, tax withholding, conversions, dispositions to the issuer and other codes

Companies & Roles (10)

ATRA

Atara Biotherapeutics, Inc.

10% Owner

TRAX

First Tracks Biotherapeutics, Inc.

10% Owner

AKTS

Aktis Oncology, Inc.

Director

ADAP

Adaptimmune Therapeutics PLC

10% Owner

ZYME

Zymeworks Inc.

Director10% Owner

ITOS

iTeos Therapeutics, Inc.

10% Owner

PRTA

PROTHENA CORP PUBLIC LTD CO

10% Owner

ANAB

ANAPTYSBIO, INC

Director10% Owner

MRSN

Mersana Therapeutics, Inc.

10% Owner

TNGX

Tango Therapeutics, Inc.

10% Owner

Discretionary Trading P&L

Holdings

Transaction History (61 total)

ATRA
Atara Biotherapeutics, Inc.
May 7, 2026
Purchase(P)
Indirect
507.4K shares at avg. $9.35$4.7M
TRAX
First Tracks Biotherapeutics, Inc.
Apr 20, 2026
Sale(S)
Indirect
4.7M shares at avg. $13.81$65.0M
AKTS
Aktis Oncology, Inc.
Jan 12, 2026
Conversion(C)
Indirect
202.9K shares-
AKTS
Aktis Oncology, Inc.
Jan 12, 2026
Conversion(C)
Indirect
128.5K shares-
AKTS
Aktis Oncology, Inc.
Jan 12, 2026
Purchase(P)
Indirect
2.1M shares at avg. $18.00$37.4M
AKTS
Aktis Oncology, Inc.
Jan 12, 2026
Purchase(P)
Indirect
144.4K shares at avg. $18.00$2.6M
AKTS
Aktis Oncology, Inc.
Jan 12, 2026
Conversion(C)
Indirect
2.3M shares-
ADAP
Adaptimmune Therapeutics PLC
Jul 30, 2025
Sale(S)
Indirect
27.4M shares at avg. $0.10$2.8M
ADAP
Adaptimmune Therapeutics PLC
Jul 29, 2025
Sale(S)
Indirect
2.7M shares at avg. $0.10$272K
ADAP
Adaptimmune Therapeutics PLC
Jul 28, 2025
Sale(S)
Indirect
33.9M shares at avg. $0.11$3.8M
ZYME
Zymeworks Inc.
Jun 26, 2025
Tax Payment(F)
Indirect
41 shares at avg. $12.71$521.11
ZYME
Zymeworks Inc.
Jun 26, 2025
In-the-Money(X)
Indirect
5.1M shares at avg. $0.00$508.648
ZYME
Zymeworks Inc.
May 19, 2025
Purchase(P)
Indirect
5.9K shares at avg. $11.78$70K
ZYME
Zymeworks Inc.
May 15, 2025
Purchase(P)
Indirect
49.5K shares at avg. $11.43$566K
ITOS
iTeos Therapeutics, Inc.
May 15, 2025
Purchase(P)
Indirect
3.3M shares at avg. $8.00$26.4M
ITOS
iTeos Therapeutics, Inc.
May 14, 2025
Purchase(P)
Indirect
1.7M shares at avg. $7.41$12.3M
PRTA
PROTHENA CORP PUBLIC LTD CO
May 6, 2025
Sale(S)
Indirect
2M shares at avg. $7.64$15.2M
PRTA
PROTHENA CORP PUBLIC LTD CO
May 5, 2025
Sale(S)
Indirect
977.7K shares at avg. $8.11$7.9M
PRTA
PROTHENA CORP PUBLIC LTD CO
May 2, 2025
Sale(S)
Indirect
3.3M shares at avg. $8.36$27.7M
ZYME
Zymeworks Inc.
Apr 17, 2025
Purchase(P)
Indirect
54.8K shares at avg. $11.52$631K
ZYME
Zymeworks Inc.
Apr 16, 2025
Purchase(P)
Indirect
74K shares at avg. $11.16$826K
ZYME
Zymeworks Inc.
Apr 4, 2025
Purchase(P)
Indirect
196.4K shares at avg. $11.17$2.2M
ZYME
Zymeworks Inc.
Apr 3, 2025
Purchase(P)
Indirect
120.8K shares at avg. $11.84$1.4M
ZYME
Zymeworks Inc.
Apr 2, 2025
Purchase(P)
Indirect
74.4K shares at avg. $11.85$881K
ZYME
Zymeworks Inc.
Apr 1, 2025
Purchase(P)
Indirect
48.7K shares at avg. $11.60$565K

		Type	Shares	Price		Ownership
May 7, 2026	ATRA Atara Biotherapeutics, Inc.	Purchase(P)	507,407	$9.35	$4,744,255	Indirect
Apr 20, 2026	TRAX First Tracks Biotherapeutics, Inc.	Sale(S)	4,705,575	$13.81	$64,999,990	Indirect
Jan 12, 2026	AKTS Aktis Oncology, Inc.	Conversion(C)	202,862	-	$0	Indirect
Jan 12, 2026	AKTS Aktis Oncology, Inc.	Conversion(C)	128,506	-	$0	Indirect
Jan 12, 2026	AKTS Aktis Oncology, Inc.	Purchase(P)	2,077,779	$18.00	$37,400,022	Indirect
Jan 12, 2026	AKTS Aktis Oncology, Inc.	Purchase(P)	144,443	$18.00	$2,599,974	Indirect
Jan 12, 2026	AKTS Aktis Oncology, Inc.	Conversion(C)	2,270,879	-	$0	Indirect
Jul 30, 2025	ADAP Adaptimmune Therapeutics PLC	Sale(S)	27,433,338	$0.10	$2,800,944	Indirect
Jul 29, 2025	ADAP Adaptimmune Therapeutics PLC	Sale(S)	2,687,460	$0.10	$271,971	Indirect
Jul 28, 2025	ADAP Adaptimmune Therapeutics PLC	Sale(S)	33,931,740	$0.11	$3,817,321	Indirect
Jun 26, 2025	ZYME Zymeworks Inc.	Tax Payment(F)	41	$12.71	$521	Indirect
Jun 26, 2025	ZYME Zymeworks Inc.	In-the-Money(X)	5,086,480	$0.00	$509	Indirect
May 19, 2025	ZYME Zymeworks Inc.	Purchase(P)	5,919	$11.78	$69,738	Indirect
May 15, 2025	ZYME Zymeworks Inc.	Purchase(P)	49,502	$11.43	$565,847	Indirect
May 15, 2025	ITOS iTeos Therapeutics, Inc.	Purchase(P)	3,300,000	$8.00	$26,400,000	Indirect
May 14, 2025	ITOS iTeos Therapeutics, Inc.	Purchase(P)	1,658,978	$7.41	$12,285,562	Indirect
May 6, 2025	PRTA PROTHENA CORP PUBLIC LTD CO	Sale(S)	1,984,053	$7.64	$15,164,712	Indirect
May 5, 2025	PRTA PROTHENA CORP PUBLIC LTD CO	Sale(S)	977,693	$8.11	$7,930,166	Indirect
May 2, 2025	PRTA PROTHENA CORP PUBLIC LTD CO	Sale(S)	3,317,938	$8.36	$27,744,929	Indirect
Apr 17, 2025	ZYME Zymeworks Inc.	Purchase(P)	54,760	$11.52	$630,819	Indirect
Apr 16, 2025	ZYME Zymeworks Inc.	Purchase(P)	73,953	$11.16	$825,589	Indirect
Apr 4, 2025	ZYME Zymeworks Inc.	Purchase(P)	196,438	$11.17	$2,193,800	Indirect
Apr 3, 2025	ZYME Zymeworks Inc.	Purchase(P)	120,770	$11.84	$1,430,170	Indirect
Apr 2, 2025	ZYME Zymeworks Inc.	Purchase(P)	74,360	$11.85	$881,017	Indirect
Apr 1, 2025	ZYME Zymeworks Inc.	Purchase(P)	48,658	$11.60	$564,647	Indirect

1-25 of 61 transactions

About EcoR1 Capital, LLC

EcoR1 Capital, LLC (SEC CIK 0001587114) files insider reports with the SEC as 10% Owner of Atara Biotherapeutics, Inc. (ATRA), 10% Owner of First Tracks Biotherapeutics, Inc. (TRAX) and Director of Aktis Oncology, Inc. (AKTS). Signal8 also holds filings tied to 7 other companies.

Signal8 holds 29 ownership filings by EcoR1 Capital, LLC (4 Form 3, 25 Form 4), filed between Nov 8, 2024 and May 11, 2026. Those filings report 61 transactions, from Dec 26, 2023 to May 7, 2026. Signal8's Form 4 history starts in Sep 2024.

The business address on EcoR1 Capital, LLC's filings is in SAN FRANCISCO, CA.

Recent filings by EcoR1 Capital, LLC

May 7, 2026: Open-market purchase of ATRA shares (Form 4, code P).
Apr 20, 2026: Open-market sale of TRAX shares (Form 4, code S).
Jan 12, 2026: Conversions of AKTS shares (2 lines, Form 4, code C).
Jan 12, 2026: Open-market purchases of AKTS shares (2 lines, Form 4, code P).
Jan 12, 2026: Conversion of AKTS shares (Form 4, code C).

Other insiders filing for Atara Biotherapeutics, Inc. (ATRA)

Cherry Brian N, Director
Nguyen AnhCo, President and CEO
Redmile Group, LLC, Director
Sarney Kevin G, Interim CFO
HEIDEN WILLIAM K, Director
Fust Matthew K, Director

How to read Form 4 transaction codes