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Spero Therapeutics

SPRO on Nasdaq. Market value $68m.

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Should I look at this?

We have not checked this company yet

This is not advice.

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Who owns it

None of the long-term investors we follow own it. 60 funds in all.

Jun '25
Dec '25
Jun '26
Largest holders overall

From 13F filings for the quarter ended 30 June 2026.

Big holders and activists

2 investors own more than 5%.

From Schedule 13D and 13G filings: anyone owning more than 5% must file one.

What insiders did

No insider bought shares on the open market in the last 12 months. 2 sold $552,042.

  • Rajavelu Esther
    See Remarks
    Sold
    Date
    4 May 2026
    Shares
    25,240
    Price
    $2.51
    Value
    $63,352
  • Rajavelu Esther
    See Remarks
    Sold
    Date
    6 February 2026
    Shares
    87,917
    Price
    $2.36
    Value
    $207,484
  • Keutzer Timothy
    Chief Operating Officer
    Sold
    Date
    6 February 2026
    Shares
    18,652
    Price
    $2.36
    Value
    $44,019
  • Keutzer Timothy
    Chief Operating Officer
    Sold
    Date
    4 February 2026
    Shares
    3,471
    Price
    $2.24
    Value
    $7,775
  • Keutzer Timothy
    Chief Operating Officer
    Sold
    Date
    3 February 2026
    Shares
    24,224
    Price
    $2.14
    Value
    $51,839
  • Keutzer Timothy
    Chief Operating Officer
    Sold
    Date
    2 February 2026
    Shares
    18,891
    Price
    $2.20
    Value
    $41,560
  • Rajavelu Esther
    See Remarks
    Sold
    Date
    2 February 2026
    Shares
    18,442
    Price
    $2.20
    Value
    $40,572
  • Rajavelu Esther
    See Remarks
    Sold
    Date
    7 November 2025
    Shares
    40,270
    Price
    $2.37
    Value
    $95,440

From Form 4 filings: insiders must report trades in their own company's shares within two days.

The deep dive

Everything above is arithmetic on public filings. The deep dive reads the last ten years of annual reports, the proxy statements, and the earnings calls, then argues the case the way Buffett, Klarman, and Hohn would, and checks every claim against the source.

  • What the business is worth, as a range, and the margin of safety at today’s price
  • Prices to start buying, buy, and buy hard
  • The three things that would make this a mistake
  • Every number footnoted to the filing it came from
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What a finished deep dive looks like

Not advice. Numbers on this page come from SEC filings and are updated each night; prices are updated again after the US market closes. The five-year figures are rounded.