EcoR1 Capital, LLC
SEC insider (Form 3/4/5 filer). CIK 0001587114. 10% Owner at Atara Biotherapeutics, Inc. (ATRA) and 9 other issuers. 61 reported Form 4/5 transactions since Sep 2024; latest on May 7, 2026. Located in SAN FRANCISCO, CA.
Companies EcoR1 Capital, LLC has filed insider reports for
- Atara Biotherapeutics, Inc. (ATRA): 10% Owner
- First Tracks Biotherapeutics, Inc. (TRAX): 10% Owner
- Aktis Oncology, Inc. (AKTS): Director
- Adaptimmune Therapeutics PLC (ADAP): 10% Owner
- Zymeworks Inc. (ZYME): Director, 10% Owner
- iTeos Therapeutics, Inc. (ITOS): 10% Owner
- PROTHENA CORP PUBLIC LTD CO (PRTA): 10% Owner
- ANAPTYSBIO, INC (ANAB): Director, 10% Owner
- Mersana Therapeutics, Inc. (MRSN): 10% Owner
- Tango Therapeutics, Inc. (TNGX): 10% Owner
EcoR1 Capital, LLC
CIK: 0001587114
Transaction Breakdown
High conviction signal
Position reduction
Derivative conversions
Compensation grants
Gifts, tax withholding, conversions, dispositions to the issuer and other codes
Companies & Roles (10)
Atara Biotherapeutics, Inc.
First Tracks Biotherapeutics, Inc.
Aktis Oncology, Inc.
Adaptimmune Therapeutics PLC
Zymeworks Inc.
iTeos Therapeutics, Inc.
PROTHENA CORP PUBLIC LTD CO
ANAPTYSBIO, INC
Mersana Therapeutics, Inc.
Tango Therapeutics, Inc.
Discretionary Trading P&L
Holdings
Transaction History (61 total)
- May 7, 2026ATRA
Atara Biotherapeutics, Inc.
PurchaseIndirect507.4K shares at avg. $9.35$4.7M - Apr 20, 2026TRAX
First Tracks Biotherapeutics, Inc.
SaleIndirect4.7M shares at avg. $13.81$65.0M - Jan 12, 2026AKTS
Aktis Oncology, Inc.
ConversionIndirect128.5K shares- - Jan 12, 2026AKTS
Aktis Oncology, Inc.
PurchaseIndirect144.4K shares at avg. $18.00$2.6M - Jan 12, 2026AKTS
Aktis Oncology, Inc.
PurchaseIndirect2.1M shares at avg. $18.00$37.4M - Jan 12, 2026AKTS
Aktis Oncology, Inc.
ConversionIndirect2.3M shares- - Jan 12, 2026AKTS
Aktis Oncology, Inc.
ConversionIndirect202.9K shares- - Jul 30, 2025ADAP
Adaptimmune Therapeutics PLC
SaleIndirect27.4M shares at avg. $0.10$2.8M - Jul 29, 2025ADAP
Adaptimmune Therapeutics PLC
SaleIndirect2.7M shares at avg. $0.10$272K - Jul 28, 2025ADAP
Adaptimmune Therapeutics PLC
SaleIndirect33.9M shares at avg. $0.11$3.8M
| Type | Shares | Price | Ownership | |||
|---|---|---|---|---|---|---|
| May 7, 2026 | ATRA Atara Biotherapeutics, Inc. | Purchase | 507,407 | $9.35 | $4,744,255 | Indirect |
| Apr 20, 2026 | TRAX First Tracks Biotherapeutics, Inc. | Sale | 4,705,575 | $13.81 | $64,999,990 | Indirect |
| Jan 12, 2026 | AKTS Aktis Oncology, Inc. | Conversion | 128,506 | - | $0 | Indirect |
| Jan 12, 2026 | AKTS Aktis Oncology, Inc. | Purchase | 144,443 | $18.00 | $2,599,974 | Indirect |
| Jan 12, 2026 | AKTS Aktis Oncology, Inc. | Purchase | 2,077,779 | $18.00 | $37,400,022 | Indirect |
| Jan 12, 2026 | AKTS Aktis Oncology, Inc. | Conversion | 2,270,879 | - | $0 | Indirect |
| Jan 12, 2026 | AKTS Aktis Oncology, Inc. | Conversion | 202,862 | - | $0 | Indirect |
| Jul 30, 2025 | ADAP Adaptimmune Therapeutics PLC | Sale | 27,433,338 | $0.10 | $2,800,944 | Indirect |
| Jul 29, 2025 | ADAP Adaptimmune Therapeutics PLC | Sale | 2,687,460 | $0.10 | $271,971 | Indirect |
| Jul 28, 2025 | ADAP Adaptimmune Therapeutics PLC | Sale | 33,931,740 | $0.11 | $3,817,321 | Indirect |
1-10 of 61 transactions