Spero Therapeutics, Inc.
US ˙ NasdaqGS ˙ US84833T1034

SecuritySPRO / Spero Therapeutics, Inc.
InstitutionRenaissance Technologies Llc
ManagerJames Simons
Latest Disclosed Ownership1,189,235 shares
Latest Disclosed Value $ 2,782,810
Renaissance Technologies Llc reports 7.06% decrease in ownership of SPRO / Spero Therapeutics, Inc.

On May 14, 2026 - Renaissance Technologies Llc filed a 13F-HR form disclosing ownership of 1,189,235 shares of Spero Therapeutics, Inc. (US:SPRO) valued at $2,782,810 USD as of March 31, 2026. The entity filed a previous 13F-HR on February 12, 2026 disclosing 1,279,522 shares of Spero Therapeutics, Inc.. This represents a change in shares of -7.06% during the quarter. The current value of the position is $3,353,643 USD.

Institutional Ownership: 13F and NPORT Filings

The Security and Class in the table below are shown exactly as filed by the investor. We do our best to track continuity of investments through acquisitions, and this will be reflected in the table as changes in names. In addition to descriptive data, performance of the investment is shown over time. To calculate quarterly performance, we first calculate cost basis of the shares purchased during the quarter, then use that to calculate gross profit. Quarterly return is Gross Profit / Starting Portfolio value.

Note that cost basis is calculated and stored in thousands, so small quarterly changes in shares frequently result in a cost basis of zero.

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Disclosed Equity Positions (from 13F/NPORT Filings)
File
Date		 Effective
Date		Form Security Class ID Avg Price
Paid (Est)		 Reported
Shares		 ΔShares ΔShares
(%)		 Reported
Value
(x1000)		 ΔValue
(%)		 Alloc
(%)		 ΔAlloc ΔAlloc (%) Cost Basis
(x1000)		 Unrealized
Gain/Loss
(x1000)
2026-05-14 2026-03-31 13F SPERO THERAPEUTICS COM 84833T103 1,189,235 -90,287 -7.06 2,783 -6.68 0.0044
2026-02-12 2025-12-31 13F SPERO THERAPEUTICS COM 84833T103 1,279,522 -173,243 -11.93 2,981 9.15 0.0046
2025-11-13 2025-09-30 13F SPERO THERAPEUTICS COM 84833T103 1,452,765 620,600 74.58 2,731 13.18 0.0036
2025-08-13 2025-06-30 13F SPERO THERAPEUTICS COM 84833T103 832,165 -138,742 -14.29 2,413 245.21 0.0032
2025-05-14 2025-03-31 13F SPERO THERAPEUTICS COM 84833T103 970,907 -134,684 -12.18 699 -38.58 0.0011
2025-02-13 2024-12-31 13F SPERO THERAPEUTICS COM 84833T103 1,105,591 130,938 13.43 1,139 -12.86 0.0017
2024-11-13 2024-09-30 13F SPERO THERAPEUTICS COM 84833T103 974,653 -1,299 -0.13 1,306 3.00 0.0020
2024-08-09 2024-06-30 13F SPERO THERAPEUTICS COM 84833T103 975,952 121,492 14.22 1,269 126,700.00 0.0022
2024-05-13 2024-03-31 13F SPERO THERAPEUTICS COM 84833T103 854,460 306,995 56.08 1 0.0023
2024-02-13 2023-12-31 13F SPERO THERAPEUTICS COM 84833T103 547,465 300 0.05 1 0.0012
2023-11-14 2023-09-30 13F SPERO THERAPEUTICS COM 84833T103 547,165 -46,266 -7.80 1 0.0011
2023-08-11 2023-06-30 13F SPERO THERAPEUTICS COM 84833T103 593,431 183,131 44.63 1 0.0012
2023-05-12 2023-03-31 13F SPERO THERAPEUTICS COM 84833T103 410,300 67,400 19.66 1 0.0008
2023-02-13 2022-12-31 13F SPERO THERAPEUTICS COM 84833T103 342,900 128,200 59.71 1 -100.00 0.0008
2022-11-14 2022-09-30 13F SPERO THERAPEUTICS COM 84833T103 214,700 -724,317 -77.14 429 -38.36 0.0006
2022-08-12 2022-06-30 13F SPERO THERAPEUTICS COM 84833T103 939,017 829,917 760.69 696 -26.66 0.0008
2022-05-13 2022-03-31 13F SPERO THERAPEUTICS COM 84833T103 109,100 109,100 949 0.0011
2021-02-10 2020-12-31 13F SPERO THERAPEUTICS COM 84833T103 0 -153,203 -100.00 0 -100.00
2020-11-13 2020-09-30 13F SPERO THERAPEUTICS COM 84833T103 153,203 -176,700 -53.56 1,710 -61.69 0.0017
2020-08-13 2020-06-30 13F SPERO THERAPEUTICS COM 84833T103 329,903 5,600 1.73 4,464 70.38 0.0039
2020-05-14 2020-03-31 13F SPERO THERAPEUTICS COM 84833T103 324,303 -13,900 -4.11 2,620 -19.43 0.0025
2020-02-13 2019-12-31 13F SPERO THERAPEUTICS COM 84833T103 338,203 85,400 33.78 3,252 21.34 0.0025
2019-11-13 2019-09-30 13F SPERO THERAPEUTICS COM 84833T103 252,803 37,900 17.64 2,680 8.33 0.0023
2019-08-12 2019-06-30 13F SPERO THERAPEUTICS COM 84833T103 214,903 101,600 89.67 2,474 70.50 0.0022
2019-05-14 2019-03-31 13F SPERO THERAPEUTICS COM 84833T103 113,303 70,400 164.09 1,451 449.62 0.0013
2019-02-12 2018-12-31 13F SPERO THERAPEUTICS COM 84833T103 42,903 30,903 257.52 264 109.52 0.0003
2018-11-13 2018-09-30 13F SPERO THERAPEUTICS COM 84833T103 12,000 12,000 126 0.0001
Legend
Shares
The total number of shares held by the institution at the end of the reporting period (the effective date). This is provided in the filing.
Value
The total value of the shares as of the effective date. This is provided in the filing.
Avg. Share Price
The weighted average share price of the shares held by the institution. We use FIFO accounting to determine this price
Class
This is the security class as indicated by the filer. There are a variety of values for this field. Common values include "EC" = equity common, "EP" - equity preferred
Allocation (%)
The percent of the institution's portfolio that this position represents. This is provided in NPORT filings. For 13F filings, we calculate it.
Change in Allocation
The change in allocation from the prior reporting period. This is calculated as current allocation - prior allocation.
Change in Allocation (%)
The percent change in allocation from the prior reporting period. This is calculated as (current allocation - prior allocation) / prior allocation.
Cost Basis
The total cost of the shares held. This is calculated as reported shares * avg. share price
Unrealized Gain/Loss
This is the market value of the position as of the effective date minus the cost basis.