13G Filing: Biotechnology Value Fund LP and Spero Therapeutics Inc (SPRO)

Partners, as the general partner of
BVF, BVF2, the investment manager of Trading Fund OS, and the sole member of Partners OS, may be deemed to beneficially own the
1,029,185 shares of Common Stock beneficially owned in the aggregate by BVF, BVF2, Trading Fund OS, and certain Partners managed
accounts (the “Partners Managed Accounts”), including 103,997 shares of Common Stock held in the Partners Managed Accounts.

BVF Inc., as the general partner of
Partners, may be deemed to beneficially own the 1,029,185 shares of Common Stock beneficially owned by Partners.

Mr. Lampert, as a director and officer
of BVF Inc., may be deemed to beneficially own the 1,029,185 shares of Common Stock beneficially owned by BVF Inc.

The foregoing should not be construed
in and of itself as an admission by any Reporting Person as to beneficial ownership of any shares of Common Stock owned by another
Reporting Person. Partners OS disclaims beneficial ownership of the shares of Common Stock beneficially owned by Trading Fund OS.
Each of Partners, BVF Inc. and Mr. Lampert disclaims beneficial ownership of the shares of Common Stock beneficially owned by BVF,
BVF2, Trading Fund OS, and the Partners Managed Accounts, and the filing of this statement shall not be construed as an admission
that any such person or entity is the beneficial owner of any such securities.

(b)

Percent of class:

The following percentages are
based on 13,897,684 shares of Common Stock outstanding as disclosed in the Issuer’s prospectus filed with the
Securities and Exchange Commission on November 2, 2017.

As of the close of business on November
9, 2017 (i) BVF beneficially owned approximately 3.7% of the outstanding shares of Common Stock, (ii) BVF2 beneficially owned approximately
2.4% of the outstanding shares of Common Stock, (iii) Trading Fund OS beneficially owned less than 1% of the outstanding shares
of Common Stock (iv) Partners OS may be deemed to beneficially own less than 1% of the outstanding shares of Common Stock, and
(v) each of Partners, BVF Inc. and Mr. Lampert may be deemed to beneficially own approximately 7.4% of the outstanding shares of
Common Stock (less than 1% of which is held in the Partners Managed Accounts).

(c)

Number of shares as to which such person has:

(i)

Sole power to vote or to direct the vote

See Cover Pages Items 5-9.

(ii)

Shared power to vote or to direct the vote

See Cover Pages Items 5-9.

(iii)

Sole power to dispose or to direct the disposition of

See Cover Pages Items 5-9.

(iv)

Shared power to dispose or to direct the disposition of

See Cover Pages Items 5-9.