# EDGAR Filing Document

**Accession Number:** 0001701108
**File Stem:** 0001193125-25-179082
**Filing Date:** 2025-8
**Character Count:** 17426
**Document Hash:** 82c8d5c41c92da54ef15abc3550ac327
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001193125-25-179082.hdr.sgml**: 20250812

**ACCESSION NUMBER**: 0001193125-25-179082

**CONFORMED SUBMISSION TYPE**: S-8

**PUBLIC DOCUMENT COUNT**: 18

**FILED AS OF DATE**: 20250812

**DATE AS OF CHANGE**: 20250812

**EFFECTIVENESS DATE**: 20250812

**FILER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Spero Therapeutics, Inc.
- **CENTRAL INDEX KEY:** 0001701108
- **STANDARD INDUSTRIAL CLASSIFICATION:** PHARMACEUTICAL PREPARATIONS [2834]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 000000000
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** S-8
- **SEC ACT:** 1933 Act
- **SEC FILE NUMBER:** 333-289544
- **FILM NUMBER:** 251207836

**BUSINESS ADDRESS:**
- **STREET 1:** 675 MASSACHUSETTS AVENUE
- **STREET 2:** 14TH FLOOR
- **CITY:** CAMBRIDGE
- **STATE:** MA
- **ZIP:** 02139
- **BUSINESS PHONE:** 857-242-1600

**MAIL ADDRESS:**
- **STREET 1:** 675 MASSACHUSETTS AVENUE
- **STREET 2:** 14TH FLOOR
- **CITY:** CAMBRIDGE
- **STATE:** MA
- **ZIP:** 02139

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** Spero Therapeutics, LLC
- **DATE OF NAME CHANGE:** 20170316

**As filed with the Securities and Exchange Commission on August 12, 2025** 

**Registration No. 333-** 

**UNITED STATES** 

**SECURITIES AND EXCHANGE COMMISSION** 

**WASHINGTON, D.C. 20549** 

**FORM S-8**

**REGISTRATION STATEMENT** 

***UNDER***

***THE SECURITIES ACT OF 1933***

## SPERO THERAPEUTICS, INC.
**(Exact name of registrant as specified in its charter)** 

---

| | |
|:---|:---|
| **Delaware** | **46-4590683** |
| **(State or other jurisdiction of**<br> **incorporation or organization)** | **(I.R.S. Employer**<br> **Identification No.)** |
| **675 Massachusetts Avenue, 14th Floor**<br> **Cambridge, Massachusetts** | **02139** |
| **(Address of Principal Executive Offices)** | **(Zip Code)** |

---

**SPERO THERAPEUTICS, INC. 2017 STOCK INCENTIVE PLAN, AS AMENDED** 

**(Full title of the plan)** 

**Esther Rajavelu, President, Chief Executive Officer, Chief Financial Officer and Treasurer** 

**Spero Therapeutics, Inc.** 

**675 Massachusetts Avenue, 14th Floor** 

**Cambridge, Massachusetts 02139** 

**(Name and address of agent of service)** 

**(857) 242-1600**

**(Telephone number, including area code, of agent for service)** 

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company or an emerging growth company. See the definitions of "large accelerated filer," "accelerated filer," "smaller reporting company," and "emerging growth company" in Rule 12b-2 of the Exchange Act.

---

| | | | |
|:---|:---|:---|:---|
| Large accelerated filer | ☐ | Accelerated filer | ☐ |
| Non-accelerated filer | ☒ | Smaller reporting company | ☒ |
|  |  | Emerging growth company | ☐ |

---

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. ☐

------

**EXPLANATORY NOTE** 

This registration statement registers an aggregate of 3,000,000 additional shares of common stock of Spero Therapeutics, Inc. (the "Registrant") reserved under the Spero Therapeutics, Inc. 2017 Stock Incentive Plan, as amended (the "2017 Plan"), representing an increase of 3,000,000 shares reserved under the 2017 Plan effective June 12, 2025. This registration statement registers additional securities of the same class as other securities for which a registration statement filed on Form S-8 relating to the 2017 Plan has previously been filed and is effective. This registration statement incorporates by reference the contents of (i) the registration statement on Form S-8 (File No. 333-222060), filed with the Securities and Exchange Commission on [December 14, 2017](http://www.sec.gov/Archives/edgar/data/1701108/000119312517369542/d478252ds8.htm) by the Registrant, (ii) the registration statement on Form S-8 (File No. 333-230281), filed with the Securities and Exchange Commission on [March 14, 2019](http://www.sec.gov/Archives/edgar/data/1701108/000119312519074902/d720152ds8.htm) by the Registrant, (iii) the registration statement on Form S-8 (File No. 333-237283), filed with the Securities and Exchange Commission on [March 19, 2020](http://www.sec.gov/Archives/edgar/data/1701108/000119312520079102/d831337ds8.htm) by the Registrant, (iv) the registration statement on Form S-8 (File No. 333-254173), filed with the Securities and Exchange Commission on [March 11, 2021](http://www.sec.gov/Archives/edgar/data/1701108/000119312521077939/d10111ds8.htm) by the Registrant, (v) the registration statement on Form S-8 (File No. 333-259662), filed with the Securities and Exchange Commission on [September 20, 2021](http://www.sec.gov/Archives/edgar/data/1701108/000119312521277265/d110200ds8.htm) by the Registrant, (vi) the registration statement on Form S-8 (File No. 333-268344), filed with the Securities and Exchange Commission on [November 14, 2022](http://www.sec.gov/Archives/edgar/data/1701108/000119312522284615/d421523ds8.htm) by the Registrant, (vii) the registration statement on Form S-8 (File No. 333-275514), filed with the Securities and Exchange Commission on [November 13, 2023](http://www.sec.gov/Archives/edgar/data/1701108/000119312523276127/d568942ds8.htm) by the Registrant, and (viii) the registration statement on Form S-8 (File No. 333-281245), filed with the Securities and Exchange Commission on [August 5, 2024](http://www.sec.gov/Archives/edgar/data/1701108/000119312524193960/d791846ds8.htm) by the Registrant, in each case, except for Item 8, Exhibits.

------

**Item 8. Exhibits.** 

---

| | | | | | |
|:---|:---|:---|:---|:---|:---|
| **Exhibit <br>Number** | **Exhibit Description** | **Filed<br>Herewith** | **Incorporated by<br>Reference<br>herein from<br>Form or<br>Schedule** | **Filing Date** | **SEC File/<br>Reg. Number** |
| 4.1 | [Form of Common Stock Certificate of Registrant.](http://www.sec.gov/Archives/edgar/data/1701108/000119312517305888/d431217dex41.htm) |  | Form S-1<br> (Exhibit 4.1)  | 10/6/2017 | 333-220858 |
| 4.2 | [Amended and Restated Certificate of Incorporation of the Registrant.](http://www.sec.gov/Archives/edgar/data/1701108/000119312517334318/d490191dex31.htm) |  | Form 8-K<br> (Exhibit 3.1)  | 11/6/2017 | 001-38266 |
| 4.3 | [Certificate of Amendment to Amended and Restated Certificate of Incorporation of the Registrant.](http://www.sec.gov/Archives/edgar/data/1701108/000119312521250505/d198322dex31.htm) |  | Form 8-K<br> (Exhibit 3.1)  | 8/18/2021 | 001-38266 |
| 4.4 | [Amended and Restated Bylaws of the Registrant.](http://www.sec.gov/Archives/edgar/data/1701108/000095017023062897/spro-ex3_1.htm) |  | Form 10-Q<br> (Exhibit 3.1)  | 11/13/2023 | 001-38266 |
| 5.1 | [Opinion of Wilmer Cutler Pickering Hale and Dorr LLP.](d24105dex51.htm) | X |  |  |  |
| 23.1 | [Consent of PricewaterhouseCoopers LLP, independent registered public accounting firm.](d24105dex231.htm) | X |  |  |  |
| 23.2 | [Consent of Wilmer Cutler Pickering Hale and Dorr LLP (included in opinion of counsel filed as Exhibit 5.1).](d24105dex51.htm) | X |  |  |  |
| 24.1 | [Power of Attorney (set forth on the signature page of this registration statement).](d24105ds8.htm#sig) | X |  |  |  |
| 99.1 | [2017 Stock Incentive Plan, as amended.](http://www.sec.gov/Archives/edgar/data/1701108/000095017025107388/spro-ex10_1.htm) |  | Form 10-Q<br> (Exhibit 10.1)  | 8/12/2025 | 001-38266 |
| 99.2 | [Form of Stock Option Agreement under the 2017 Stock Incentive Plan, as amended.](http://www.sec.gov/Archives/edgar/data/1701108/000119312521277265/d110200dex46.htm) |  | Form S-8<br> (Exhibit 4.6)  | 9/20/2021 | 333-259662 |
| 99.3 | [Form of Restricted Stock Unit Agreement under the 2017 Stock Incentive Plan, as amended.](http://www.sec.gov/Archives/edgar/data/1701108/000119312521260572/d197711dex101.htm) |  | Form 8-K<br> (Exhibit 10.1)  | 8/30/2021 | 001-38266 |
| 107 | [Filing Fee Table.](d24105dexfilingfees.htm) | X |  |  |  |

---

------

**SIGNATURES** 

Pursuant to the requirements of the Securities Act of 1933, the Registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-8 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Cambridge, Commonwealth of Massachusetts, on August 12, 2025.

---

| | |
|:---|:---|
| **SPERO THERAPEUTICS, INC.** | **SPERO THERAPEUTICS, INC.** |
| By: | /s/ Esther Rajavelu |
|  | Esther Rajavelu |
|  | President, Chief Executive Officer, Chief Financial Officer and Treasurer |

---

**POWER OF ATTORNEY AND SIGNATURES** 

Each person whose signature appears below constitutes and appoints Esther Rajavelu and Timothy Keutzer, and each of them singly, his or her true and lawful attorneys-in-fact and agents, with full power of substitution and resubstitution in each of them singly, for him or her and in his or her name, place and stead, and in any and all capacities, to sign any and all amendments (including post-effective amendments) to this Registration Statement on Form S-8 of Spero Therapeutics, Inc., and to file the same, with all exhibits thereto and other documents in connection therewith, with the Securities and Exchange Commission, granting to the attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done in connection therewith, as fully to all intents and purposes as he or she might or could do in person, hereby ratifying and confirming all that the attorneys-in-fact and agents or any of each of them or their substitute may lawfully do or cause to be done by virtue hereof.

------

Pursuant to the requirements of the Securities Act of 1933, this registration statement has been signed by the following persons in the capacities and on the dates indicated.

---

| | | |
|:---|:---|:---|
| **Signature** | **Title** | **Date** |
| /s/ Esther Rajavelu<br> Esther Rajavelu | President, Chief Executive Officer, Chief Financial Officer and Treasurer<br> *(Principal Executive Officer, Principal Financial Officer and Principal Accounting Officer)* | August 12, 2025 |
| /s/ Frank E. Thomas<br> Frank E. Thomas | Chairman | August 12, 2025 |
| /s/ Milind Deshpande, Ph.D.<br> Milind Deshpande, Ph.D. | Director | August 12, 2025 |
| /s/ Scott Jackson<br> Scott Jackson | Director | August 12, 2025 |
| /s/ Ankit Mahadevia, M.D.<br> Ankit Mahadevia, M.D. | Director | August 12, 2025 |
| /s/ John C. Pottage, M.D.<br> John C. Pottage, M.D. | Director | August 12, 2025 |
| /s/ Cynthia Smith<br> Cynthia Smith | Director | August 12, 2025 |
| /s/ Kathleen Tregoning<br> Kathleen Tregoning | Director | August 12, 2025 |
| /s/ Patrick Vink, M.D.<br> Patrick Vink, M.D. | Director | August 12, 2025 |

---

## Exhibit 5.1

**Exhibit 5.1**![LOGO](g24105g0811220021442.jpg)

+1 617 526 6000 (t)

+1 617 526 5000 (f)

wilmerhale.com

August 12, 2025

Spero Therapeutics, Inc.

675 Massachusetts Avenue, 14th Floor

Cambridge, Massachusetts 02139

Re: 2017 Stock Incentive Plan, as amended

Ladies and Gentlemen:

We have assisted in the preparation of a Registration Statement on Form S-8 (the "Registration Statement") to be filed with the Securities and Exchange Commission (the "Commission") under the Securities Act of 1933, as amended (the "Securities Act"), relating to an aggregate of 3,000,000 shares of common stock, $0.001 par value per share (the "Shares"), of Spero Therapeutics, Inc., a Delaware corporation (the "Company"), issuable under the Company's 2017 Stock Incentive Plan, as amended (the "Plan").

We have examined the Certificate of Incorporation and Bylaws of the Company, each as amended and restated to date, and originals, or copies certified to our satisfaction, of all pertinent records of the meetings of the board of directors and stockholders of the Company, the Registration Statement, the Plan and such other documents relating to the Company as we have deemed material for the purposes of this opinion.

In our examination of the foregoing documents, we have assumed the genuineness of all signatures, the authenticity of all documents submitted to us as originals, the conformity to original documents of all documents submitted to us as certified, photostatic or other copies, the authenticity of the originals of any such documents and the legal competence of all signatories to such documents.

We assume that the appropriate action will be taken, prior to the offer and sale of the Shares in accordance with the Plan, to register and qualify the Shares for sale under all applicable state securities or "blue sky" laws.

We express no opinion herein as to the laws of any state or jurisdiction other than the General Corporation Law of the State of Delaware.

![LOGO](g24105g0811220022670.jpg)

------

![LOGO](g24105g0811220021649.jpg)

August 12, 2025

It is understood that this opinion is to be used only in connection with the offer and sale of the Shares while the Registration Statement is in effect.

Please note that we are opining only as to the matters expressly set forth herein, and no opinion should be inferred as to any other matters.

Based on the foregoing, we are of the opinion that the Shares have been duly authorized for issuance and, when the Shares are issued and paid for in accordance with the terms and conditions of the Plan, the Shares will be validly issued, fully paid and nonassessable.

We hereby consent to the filing of this opinion with the Commission in connection with the Registration Statement in accordance with the requirements of Item 601(b)(5) of Regulation S-K under the Securities Act. In giving such consent, we do not hereby admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the Commission.

Very truly yours,

/s/ Wilmer Cutler Pickering Hale and Dorr LLP

WILMER CUTLER PICKERING HALE AND DORR LLP

![LOGO](g24105g0811220022670.jpg)

## Exhibit 23.1

**Exhibit 23.1** 

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We hereby consent to the incorporation by reference in this Registration Statement on Form S-8 of Spero Therapeutics, Inc. of our report dated March 27, 2025 relating to the financial statements, which appears in Spero Therapeutics, Inc.'s Annual Report on Form 10-K for the year ended December 31, 2024.

![LOGO](g24105dsp1.jpg)

Boston, Massachusetts

August 12, 2025

## Ex-Filing

?xml version='1.0' encoding='ASCII'? EX-FILING FEES

---

| |
|:---|
| **Calculation of Filing Fee Tables**  |
| &nbsp;&nbsp;&nbsp;&nbsp;**S-8**  |
| &nbsp;&nbsp;&nbsp;&nbsp;**Spero Therapeutics, Inc.**  |

---

---

| | | | | | | | | |
|:---|:---|:---|:---|:---|:---|:---|:---|:---|
| | **Security Type**  | **Security Class Title**  | **Fee Calculation Rule**  | **Amount Registered**  | **Proposed Maximum Offering Price Per Unit**  | **Maximum Aggregate Offering Price**  | **Fee Rate**  | **Amount of Registration Fee**  |
| 1 | Equity | Common Stock, par value $0.001 per share | Other | 3000000 | $2.19 | $6570000.00 | 0.0001531 | $1005.87 |
| Total Offering Amounts: | Total Offering Amounts: | Total Offering Amounts: | Total Offering Amounts: | Total Offering Amounts: |  | $6570000.00  |  | $1005.87  |
| Total Fee Offsets:  | Total Fee Offsets:  | Total Fee Offsets:  | Total Fee Offsets:  | Total Fee Offsets:  |  |  |  | $0.00  |
| Net Fee Due:  | Net Fee Due:  | Net Fee Due:  | Net Fee Due:  | Net Fee Due:  |  |  |  | $1005.87  |

---

 **Offering Note** <br>

<sup>1</sup> (1) The number of shares of common stock, par value $0.001 per share ("Common Stock"), of Spero Therapeutics, Inc. (the "Registrant") stated above consists of additional shares of common stock available for issuance under the Spero Therapeutics, Inc. 2017 Stock Incentive Plan, as amended (the "2017 Plan"). The maximum number of shares which may be sold upon the exercise of such options or issuance of stock-based awards granted under the 2017 Plan are subject to adjustment in accordance with certain anti-dilution and other provisions of the 2017 Plan. Accordingly, pursuant to Rule 416 under the Securities Act of 1933, as amended (the "Securities Act"), this registration statement covers, in addition to the number of shares stated above, an indeterminate number of shares which may be subject to grant or otherwise issuable after the operation of any such anti-dilution and other provisions. (2) Estimated solely for the purpose of calculating the amount of the registration fee pursuant to Rule 457(c) and Rule 457(h) promulgated under the Securities Act. The offering price per share and the aggregate offering price for shares reserved for future grant or issuance under the 2017 Plan are based on the average of the high and the low price of the Registrant's Common Stock as reported on The Nasdaq Global Select Market as of a date (August 11, 2025) within five business days prior to filing this registration statement.

---

| | |
|:---|:---|
| | |
| **Rule 457(p)** | **Rule 457(p)** |
| Fee Offset Claims | N/A |
| Fee Offset Sources | N/A |

---