Spero Therapeutics, Inc.
US ˙ NasdaqGS ˙ US84833T1034

SecuritySPRO / Spero Therapeutics, Inc.
InstitutionMorgan Stanley
Latest Disclosed Ownership4,552 shares
Latest Disclosed Value $ 10,651
Morgan Stanley reports 1,354.31% increase in ownership of SPRO / Spero Therapeutics, Inc.

On May 15, 2026 - Morgan Stanley filed a 13F-HR form disclosing ownership of 4,552 shares of Spero Therapeutics, Inc. (US:SPRO) valued at $10,652 USD as of March 31, 2026. The entity filed a previous 13F-HR/A on May 27, 2026 disclosing 313 shares of Spero Therapeutics, Inc.. The current value of the position is $13,565 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)
2026-05-15 2026-03-31 13F SPERO THERAPEUTICS COM 84833T103 4,552 4,239 1,354.31 11 0.0000
2026-05-27 2025-12-31 13F/A-1 SPERO THERAPEUTICS COM 84833T103 313 -43,065 -99.28 1 -100.00 0.0000
2026-02-13 2025-12-31 13F SPERO THERAPEUTICS COM 84833T103 313 -43,065 1 0.0000
2026-05-27 2025-09-30 13F/A-1 SPERO THERAPEUTICS COM 84833T103 43,378 34,157 370.43 82 211.54 0.0000
2025-11-14 2025-09-30 13F SPERO THERAPEUTICS COM 84833T103 43,378 34,157 82 0.0000
2025-08-15 2025-06-30 13F SPERO THERAPEUTICS COM 84833T103 9,221 2,250 32.28 27 420.00 0.0000
2025-05-15 2025-03-31 13F SPERO THERAPEUTICS COM 84833T103 6,971 0 0.00 5 -28.57 0.0000
2025-05-15 2024-12-31 13F/A-1 SPERO THERAPEUTICS COM 84833T103 6,971 0 0.00 7 -22.22 0.0000
2025-02-14 2024-12-31 13F SPERO THERAPEUTICS COM 84833T103 6,971 0 7 0.0000
2025-05-14 2024-09-30 13F/A-2 SPERO THERAPEUTICS COM 84833T103 6,971 0 0.00 9 0.00 0.0000
2025-02-14 2024-09-30 13F/A-1 SPERO THERAPEUTICS COM 84833T103 6,971 0 9 0.0000
2024-11-14 2024-09-30 13F SPERO THERAPEUTICS COM 84833T103 6,971 0 9 0.0000
2025-05-14 2024-06-30 13F/A-2 SPERO THERAPEUTICS COM 84833T103 6,971 -928 -11.75 9 -30.77 0.0000
2024-10-17 2024-06-30 13F/A-1 SPERO THERAPEUTICS COM 84833T103 6,971 -928 9 0.0000
2024-08-14 2024-06-30 13F SPERO THERAPEUTICS COM 84833T103 6,971 -928 9 0.0000
2024-10-17 2024-03-31 13F/A-2 SPERO THERAPEUTICS COM 84833T103 7,899 -4,136 -34.37 14 -23.53 0.0000
2024-08-16 2024-03-31 13F/A-1 SPERO THERAPEUTICS COM 84833T103 7,899 -4,136 14 0.0000
2024-05-15 2024-03-31 13F SPERO THERAPEUTICS COM 84833T103 7,899 -4,136 14 0.0000
2024-08-16 2023-12-31 13F/A-1 SPERO THERAPEUTICS COM 84833T103 12,035 3,047 33.90 18 70.00 0.0000
2024-02-13 2023-12-31 13F SPERO THERAPEUTICS COM 84833T103 12,035 3,047 18 0.0000
2023-11-15 2023-09-30 13F SPERO THERAPEUTICS COM 84833T103 8,988 -542 -5.69 11 -23.08 0.0000
2023-08-14 2023-06-30 13F SPERO THERAPEUTICS COM 84833T103 9,530 -5,700 -37.43 14 -40.91 0.0000
2023-05-15 2023-03-31 13F SPERO THERAPEUTICS COM 84833T103 15,230 -1,847 -10.82 22 -24.14 0.0000
2023-02-14 2022-12-31 13F SPERO THERAPEUTICS COM 84833T103 17,077 -2,177 -11.31 30 -23.68 0.0000
2022-11-14 2022-09-30 13F SPERO THERAPEUTICS COM 84833T103 19,254 -175,177 -90.10 38 -73.61 0.0000
2022-10-27 2022-06-30 13F/A-1 SPERO THERAPEUTICS COM 84833T103 194,431 121,435 166.36 144 -77.32 0.0000
2022-08-15 2022-06-30 13F SPERO THERAPEUTICS COM 84833T103 194,431 121,435 144 0.0000
2022-10-27 2022-03-31 13F/A-1 SPERO THERAPEUTICS COM 84833T103 72,996 22,511 44.59 635 -21.41 0.0001
2022-05-13 2022-03-31 13F SPERO THERAPEUTICS COM 84833T103 72,996 22,511 635 0.0001
2022-02-14 2021-12-31 13F SPERO THERAPEUTICS COM 84833T103 50,485 -6,016 -10.65 808 -22.38 0.0001
2021-11-15 2021-09-30 13F SPERO THERAPEUTICS COM 84833T103 56,501 -13,271 -19.02 1,041 6.88 0.0001
2021-08-23 2021-06-30 13F/A-1 SPERO THERAPEUTICS COM 84833T103 69,772 -119,177 -63.07 974 -64.98 0.0001
2021-08-16 2021-06-30 13F SPERO THERAPEUTICS COM 84833T103 69,772 -119,177 974 0.0000
2021-05-17 2021-03-31 13F SPERO THERAPEUTICS COM 84833T103 188,949 -82,309 -30.34 2,781 -47.12 0.0004
2021-02-16 2020-12-31 13F SPERO THERAPEUTICS COM 84833T103 271,258 248,326 1,082.88 5,259 1,954.30 0.0008
2020-11-13 2020-09-30 13F SPERO THERAPEUTICS COM 84833T103 22,932 -2,838 -11.01 256 -26.44 0.0000
2020-08-14 2020-06-30 13F SPERO THERAPEUTICS COM 84833T103 25,770 24,374 1,745.99 348 3,063.64 0.0001
2020-05-26 2020-03-31 13F/A-1 SPERO THERAPEUTICS COM 84833T103 1,396 -15,158 -91.57 11 -93.08 0.0000
2020-05-15 2020-03-31 13F SPERO THERAPEUTICS COM 84833T103 1,396 -15,158 11 0.8450
2020-02-14 2019-12-31 13F SPERO THERAPEUTICS COM 84833T103 16,554 12,345 293.30 159 253.33 0.0000
2019-11-14 2019-09-30 13F SPERO THERAPEUTICS COM 84833T103 4,209 2,717 182.10 45 164.71 0.0000
2019-08-14 2019-06-30 13F SPERO THERAPEUTICS COM 84833T103 1,492 -1,715 -53.48 17 -58.54 0.0000
2019-05-15 2019-03-31 13F SPERO THERAPEUTICS COM 84833T103 3,207 -23,592 -88.03 41 -75.00 0.0000
2019-02-14 2018-12-31 13F SPERO THERAPEUTICS COM 84833T103 26,799 12,775 91.09 164 11.56 0.0000
2019-04-23 2018-09-30 13F/A-2 SPERO THERAPEUTICS COM 84833T103 14,024 -570 -3.91 147 -31.31 0.0000
2018-11-20 2018-09-30 13F/A-1 SPERO THERAPEUTICS COM 84833T103 14,024 0 147 0.0000
2018-11-14 2018-09-30 13F SPERO THERAPEUTICS COM 84833T103 14,024 147
2019-04-23 2018-06-30 13F/A-1 SPERO THERAPEUTICS COM 84833T103 14,594 3,564 32.31 214 36.31 0.0001
2018-08-14 2018-06-30 13F SPERO THERAPEUTICS COM 84833T103 14,594 214
2019-04-23 2018-03-31 13F/A-1 SPERO THERAPEUTICS COM 84833T103 11,030 477 4.52 157 26.61 0.0000
2018-05-14 2018-03-31 13F SPERO THERAPEUTICS COM 84833T103 11,030 157
2019-04-23 2017-12-31 13F/A-1 SPERO THERAPEUTICS COM 84833T103 10,553 10,553 124 0.0000
2018-02-14 2017-12-31 13F SPERO THERAPEUTICS COM 84833T103 10,553 124 0.0000
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.