Spero Therapeutics, Inc.
US ˙ NasdaqGS ˙ US84833T1034

SecuritySPRO / Spero Therapeutics, Inc.
InstitutionNorthern Trust Corp
Latest Disclosed Ownership120,984 shares
Latest Disclosed Value $ 283,103
Northern Trust Corp ownership in SPRO / Spero Therapeutics, Inc.

On May 14, 2026 - Northern Trust Corp filed a 13F-HR form disclosing ownership of 120,984 shares of Spero Therapeutics, Inc. (US:SPRO) valued at $283,103 USD as of March 31, 2026. The entity filed a previous 13F-HR on February 17, 2026 disclosing 120,984 shares of Spero Therapeutics, Inc.. This represents a change in shares of 0.00% during the quarter. The current value of the position is $360,532 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 120,984 0 0.00 283 0.71 0.0000
2026-02-17 2025-12-31 13F SPERO THERAPEUTICS COM 84833T103 120,984 -8,659 -6.68 282 15.64 0.0000
2025-11-14 2025-09-30 13F SPERO THERAPEUTICS COM 84833T103 129,643 28,812 28.57 244 -16.78 0.0000
2025-08-13 2025-06-30 13F SPERO THERAPEUTICS COM 84833T103 100,831 -93 -0.09 292 305.56 0.0000
2025-05-13 2025-03-31 13F SPERO THERAPEUTICS COM 84833T103 100,924 14,477 16.75 73 -19.10 0.0000
2025-02-14 2024-12-31 13F SPERO THERAPEUTICS COM 84833T103 86,447 -25,050 -22.47 89 -40.27 0.0000
2024-11-13 2024-09-30 13F SPERO THERAPEUTICS COM 84833T103 111,497 -806 -0.72 149 2.76 0.0000
2024-08-14 2024-06-30 13F SPERO THERAPEUTICS COM 84833T103 112,303 -2,256 -1.97 146 -26.40 0.0000
2024-05-14 2024-03-31 13F SPERO THERAPEUTICS COM 84833T103 114,559 25,678 28.89 197 51.54 0.0000
2024-02-13 2023-12-31 13F SPERO THERAPEUTICS COM 84833T103 88,881 0 0.00 131 21.50 0.0000
2023-11-13 2023-09-30 13F SPERO THERAPEUTICS COM 84833T103 88,881 136 0.15 108 -16.41 0.0000
2023-08-11 2023-06-30 13F SPERO THERAPEUTICS COM 84833T103 88,745 2,489 2.89 129 2.40 0.0000
2023-05-15 2023-03-31 13F SPERO THERAPEUTICS COM 84833T103 86,256 16,672 23.96 125 4.17 0.0000
2023-02-13 2022-12-31 13F SPERO THERAPEUTICS COM 84833T103 69,584 -379 -0.54 120 -14.29 0.0000
2022-11-14 2022-09-30 13F SPERO THERAPEUTICS COM 84833T103 69,963 -5 -0.01 140 169.23 0.0000
2022-08-12 2022-06-30 13F SPERO THERAPEUTICS COM 84833T103 69,968 -168,484 -70.66 52 -97.49 0.0000
2022-05-13 2022-03-31 13F SPERO THERAPEUTICS COM 84833T103 238,452 -14,748 -5.82 2,074 -48.84 0.0004
2022-02-08 2021-12-31 13F SPERO THERAPEUTICS COM 84833T103 253,200 -4,739 -1.84 4,054 -14.62 0.0007
2021-11-15 2021-09-30 13F SPERO THERAPEUTICS COM 84833T103 257,939 -2,947 -1.13 4,748 30.37 0.0008
2021-08-13 2021-06-30 13F SPERO THERAPEUTICS COM 84833T103 260,886 21,308 8.89 3,642 3.26 0.0006
2021-05-12 2021-03-31 13F SPERO THERAPEUTICS COM 84833T103 239,578 -26,395 -9.92 3,527 -31.61 0.0007
2021-02-11 2020-12-31 13F SPERO THERAPEUTICS COM 84833T103 265,973 54,896 26.01 5,157 118.89 0.0010
2020-11-16 2020-09-30 13F SPERO THERAPEUTICS COM 84833T103 211,077 1,160 0.55 2,356 -17.04 0.0005
2020-08-14 2020-06-30 13F SPERO THERAPEUTICS COM 84833T103 209,917 46,643 28.57 2,840 115.15 0.0007
2020-05-14 2020-03-31 13F SPERO THERAPEUTICS COM 84833T103 163,274 27,277 20.06 1,320 0.99 0.0004
2020-02-14 2019-12-31 13F SPERO THERAPEUTICS COM 84833T103 135,997 15,913 13.25 1,307 2.67 0.0003
2019-11-13 2019-09-30 13F SPERO THERAPEUTICS COM 84833T103 120,084 26,334 28.09 1,273 17.98 0.0003
2019-08-13 2019-06-30 13F SPERO THERAPEUTICS COM 84833T103 93,750 5,416 6.13 1,079 -4.60 0.0003
2019-05-13 2019-03-31 13F SPERO THERAPEUTICS COM 84833T103 88,334 -8,499 -8.78 1,131 90.08 0.0003
2019-02-12 2018-12-31 13F SPERO THERAPEUTICS COM 84833T103 96,833 1,038 1.08 595 -40.91 0.0002
2018-11-14 2018-09-30 13F SPERO THERAPEUTICS COM 84833T103 95,795 29,145 43.73 1,007 2.97 0.0002
2018-09-18 2018-06-30 13F/A-1 SPERO THERAPEUTICS COM 84833T103 66,650 291 0.44 978 3.49 0.0002
2018-08-14 2018-06-30 13F SPERO THERAPEUTICS COM 84833T103 66,650 978
2018-05-09 2018-03-31 13F SPERO THERAPEUTICS COM 84833T103 66,359 1,234 1.89 945 23.53 0.0002
2018-02-14 2017-12-31 13F SPERO THERAPEUTICS COM 84833T103 65,125 65,125 765 0.0002
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.