UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 2)*

Selecta Biosciences, Inc.

(Name of Issuer)

Common Stock, $0.0001 par value per share

(Title of Class of Securities)

816212104

(CUSIP Number)

Mark A. Haddad

Foley Hoag LLP

155 Seaport Boulevard

Boston, MA 02210

Tel: (617) 832-1000

Fax: (617) 832-7000

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

September 3, 2019

(Date of Event which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.  ☐

Note: Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See §240.13d-7 for other parties to whom copies are sent.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

This Amendment No. 2 to the statement on Schedule 13D (this “Statement”) with respect to the shares of common stock, par value $0.0001 per share (the “Shares”), of Selecta Biosciences, Inc., a Delaware corporation (the “Issuer”), filed by Timothy A. Springer (“Dr. Springer”), TAS Partners LLC (“TAS”), Leukon Investments, LP (“Leukon”) and Chafen Lu (“Dr. Lu” and, collectively, the “Reporting Persons”) filed on March 27, 2019, as amended by Amendment No. 1 to the statement on Schedule 13D filed on August 23, 2019 (such statement, as amended herein, the “Schedule 13D”), amends the Schedule 13D as set forth below.

All capitalized terms contained herein but not otherwise defined shall have the meanings ascribed to such terms in the Schedule 13D. Except as specifically amended by this Amendment No. 2, items in the Schedule 13D are unchanged.

Item 5. Interest in Securities of the Issuer.

Item 5 of Schedule 13 is hereby amended and restated in full as follows:

The information set forth under Item 3 and the cover page of the Schedule 13D is incorporated herein by reference into this Item 5.

(a) The percentages of beneficial ownership reported in this Item 5, and on each Reporting Person’s cover page to this Statement, are based on a total of 48,141,125 Shares issued and outstanding as of August 20, 2019, which includes 44,962,951 Shares issued and outstanding on August 2, 2019, as reported on the Issuer’s Quarterly Report on Form 10-Q, dated August 8, 2019, as well as an additional 3,178,174 Shares issued to certain investors, including Dr. Springer and TAS, on August 20, 2019 pursuant to the Stock Purchase Agreement, as reported on the Issuer’s Current Report on Form 8-K, dated August 20, 2019. All of the Share numbers reported below, and on each Reporting Person’s cover page to this Statement, are as of September 3, 2019.

The Reporting Persons, in the aggregate, beneficially own 7,784,131 Shares, representing approximately 16.1% of such class of securities.

Dr. Springer is the beneficial owner of a total of 7,784,131 Shares, representing approximately 16.1% of the outstanding Shares and consisting of (i) 6,056,597 Shares held directly, (ii) 79,130 Shares underlying warrants exercisable within 60 days of September 3, 2019 and held directly, (iii) 16,410 Shares issuable upon exercise of outstanding options within 60 days of September 3, 2019 and held directly, (iv) 1,545,576 Shares held by TAS and (v) 86,418 Shares held by Dr. Lu.

TAS is the beneficial owner of a total of 1,545,576 Shares, representing approximately 3.2% of the outstanding Shares. TAS holds all such Shares directly. Dr. Springer is the sole managing member of TAS.

Leukon does not beneficially own any Shares. LKST, Inc. is the general partner of Leukon and Dr. Springer is the president of LKST, Inc.

Dr. Lu is the beneficial owner of a total of 86,418 Shares, representing approximately 0.2% of the outstanding Shares. Dr. Lu holds all such Shares directly. Dr. Lu is the spouse of Dr. Springer.

(b) Dr. Springer exercises sole voting and dispositive power over the Shares held by him directly and the Shares held by TAS. Dr. Springer disclaims beneficial ownership of the Shares held by TAS, except to the extent of his pecuniary interest therein. Dr. Lu exercises sole voting and dispositive power over the Shares held by her directly.

(c) On September 3, 2019, Leukon made a liquidating distribution to its partner, the Springer Charitable Trust (the “Trust”), of the 1,237,028 Shares it beneficially owned for no consideration. Such distribution was made for the purpose of winding up the affairs of Leukon in preparation of the expected dissolution of such entity. Dr. Springer does not, directly or indirectly, have voting power which includes the power to vote, or to direct the voting of, securities held by the Trust, nor investment power which includes the power to dispose, or to direct the disposition of, securities held by the Trust.

The Reporting Persons have not engaged in any transactions with respect to the Shares during the 60 days before the date of this filing, except as described herein and in Item 3 of Schedule 13.

(d) No person other than the Reporting Persons is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the Shares.

(e) Not applicable.

[signature page follows]

SIGNATURES

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Date: September 16, 2019