Spero Therapeutics, Inc. - Common Stock, par value $0.001 per share (SPRO)

Q: What does CUSIP 84833T103 represent in this 13F holders report?

CUSIP 84833T103 is the security identifier for SPRO - Spero Therapeutics, Inc. - Common Stock, par value $0.001 per share used to aggregate holder disclosures.

Q: How many institutions held SPRO - Spero Therapeutics, Inc. - Common Stock, par value $0.001 per share in Q1 2021?

89 institutional investors reported SPRO - Spero Therapeutics, Inc. - Common Stock, par value $0.001 per share for Q1 2021. Use the holders table for investor-level position and value details.

CUSIP: 84833T103

Q1 2021 13F Holders as of 31 Mar 2021

Security type / class: Equity / Common Stock, par value $0.001 per share
Total 13F shares: 18,548,675
Total 13F value: $273,055,350
Share change: +824,228
Put/Call ratio: 201%
SEC-reported price per share: $14.72
Number of holders: 89
Value change: +$11,246,827
Number of buys: 37
Number of sells: 34
Shares outstanding: 55,705,828

Security key

84833T103

Report period

Q1 2021

Institutions

Top holders

SPRO full security history Ownership snapshot Full 13F holder table Newer quarter: Q3 2026 Spero Therapeutics, Inc. SEC filings Spero Therapeutics, Inc. company facts

Broader feeds

Latest 13F filings Latest 13D/G filings Investors directory

Reporting periods

Holder history for CUSIP 84833T103

Newer quarter: Q3 2026

Recent filing periods:

Q3 2026

Ownership snapshot

Top reported holders of SPRO - Spero Therapeutics, Inc. - Common Stock, par value $0.001 per share (13F + 13D/G + 3/4/5)

Grouped by holder across the latest SEC ownership disclosures. Start with comparable ownership when available, then verify the linked 13F, 13D/G, or 3/4/5 evidence.

Comparable stake leader

Aquilo Capital Management...

Disclosed value leader

Aquilo Capital Management...

Comparable rows

0/15

Latest evidence

31 Dec 2020

13F Highest disclosed value: $76,246,000 15 rows are not safely comparable across share classes. Showing 1-6 of 15 holder rows.

Quick read

Aquilo Capital Management, LLC has the largest disclosed position value at $76.25M.

0 of 15 rows have a safely comparable ownership percentage. Use this as a filing-backed starting point, then open the detailed table for source links, reporting role, position value, share count, and filing date.

Open SEC evidence Opens Aquilo Capital Management, LLC's linked filing trail.

Disclosed position value Top 5

Aquilo Capital Management, LLC $76.25M

BVF INC/IL $43.5M

BlackRock Finance, Inc. $33.58M

Atlas Venture Associates IX, LLC $26.7M

Rock Springs Capital Management LP $23.95M

Value bars compare disclosed positions; verify each figure against the linked filing evidence.

Detailed SEC evidence table Showing 1-6 of 15 holder rows

Holder	Evidence	Ownership %	Position	12M Net Δ	As of
Aquilo Capital Management, LLC	13F Company 13F	— denominator unverified	$76,246,000 3,932,209 shares	—	31 Dec 2020
BVF INC/IL	13F Company 13F	— denominator unverified	$43,497,000 2,243,278 shares	—	31 Dec 2020
BlackRock Finance, Inc.	13F Company 13F	— denominator unverified	$33,576,000 1,731,600 shares	—	31 Dec 2020
Atlas Venture Associates IX, LLC	13F Company 13F	— denominator unverified	$26,700,000 1,376,968 shares	—	31 Dec 2020
Rock Springs Capital Management LP	13F Company 13F	— denominator unverified	$23,947,000 1,235,000 shares	—	31 Dec 2020
VANGUARD GROUP INC	13F Company 13F	— denominator unverified	$21,925,000 1,130,730 shares	—	31 Dec 2020

How to read this table

Rows are grouped by holder and ranked first by SEC-reported ownership % when it is safely comparable, then by disclosed holdings value. — indicates unavailable or non-comparable values; "mixed-class rows" means the latest filing spans non-comparable classes.

13F holder rows

Institutional holders as of Q1 2021

Investor-level positions for this CUSIP, loaded as an interactive table.

Institutions

18,548,675

Rows available

Investor	Option	Weight %	Change %	SEC-reported value	* Price	Shares	Share Change	Activity	Report Period

^* SEC-reported price is the security price as of the portfolio date and can indicate the last known price at which the security was still held. The marker flags a reported price that did not pass the local price check.

Compare Q1 2021 vs Q1 2021 Across Filers

Q1 2021 holders

Holder diff

Investor	Q1 2021 Shares	Q1 2021 Shares	Share Diff	Share Chg %	Q1 2021 value	Q1 2021 value	Value change	Value Chg %

Trend: ostatnie 8 kwartałów (+ wybrane okresy porównania).

Quarterly Holders Trend

Quarterly Value Trend

Quarterly Shares Trend