Under the Securities Exchange Act of 1934
(Amendment No. 4)*

(Name of Issuer)

(Title of Class of Securities)

(CUSIP Number)

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

(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: o

* The remainder of this cover page shall be filled out for a reporting person's initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

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).

* As of the date of this Amendment No. 4 to the Schedule 13D, Roivant Sciences Ltd. (“Roivant”) beneficially owns 16,013,540 common shares, no par value (“Common Shares”), of Arbutus Biopharma Corporation (the “Issuer”). This amount excludes 9,808,386 Common Shares underlying 500,000 shares of the Issuer’s series A participating convertible preferred shares (the “Preferred Shares”) acquired on October 16, 2017, which are not convertible into the Common Shares until they become mandatorily convertible four years after October 16, 2017 (subject to adjustment and subject to limited exceptions in the event of certain transactions or fundamental changes that would permit earlier conversion at Roivant’s option).

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INTRODUCTORY NOTE

Pursuant to Rule 13d-2 under the U.S. Securities Exchange Act of 1934, as amended, this Amendment No. 4 to the Schedule 13D amends certain items of the Schedule 13D for the common shares, no par value (the “Common Shares”), of Arbutus Biopharma Corporation (the “Issuer”), filed with the U.S. Securities and Exchange Commission (the “SEC”) on March 16, 2015, as amended by Amendment No. 1 to the Schedule 13D filed with the SEC on August 25, 2015, Amendment No. 2 to the Schedule 13D filed with the SEC on February 17, 2016 and Amendment No. 3 to the Schedule 13D filed with the SEC on October 3, 2017 (the “Schedule 13D”). This Amendment No. 4 is being filed to report the closing on October 16, 2017 of the first tranche of the Issuer’s series A participating convertible preferred shares (the “Preferred Shares”), pursuant to the subscription agreement, dated October 2, 2017 (the “Subscription Agreement”), previously reported on the Schedule 13D. All capitalized terms contained herein but not otherwise defined shall have the meanings ascribed to such terms in the Schedule 13D.

Item 3.  Source and Amount of Funds or Other Consideration

Item 3 of the Schedule 13D is hereby amended and supplemented as follows:

Pursuant to the Subscription Agreement, following the satisfaction of the applicable closing conditions, at the First Closing on October 16, 2017, the Issuer issued 500,000 Preferred Shares to Roivant for an aggregate purchase price of $50.0 million. The source of the funds for the acquisition was cash on hand.

Item 4.  Purpose of Transaction

Item 4 of the Schedule 13D is hereby supplemented as follows:

Roivant and the Issuer intend to explore working together to leverage Roivant’s infrastructure, including to accelerate more efficient development of the Issuer’s drug pipeline, expand the Issuer’s geographic footprint and enhance the value of the Issuer’s assets.

Item 5.  Interest in Securities of the Issuer

Items 5(a) and 5(b) of the Schedule 13D are hereby amended and restated as follows:

(a)         Following the First Closing on October 16, 2017, Roivant beneficially owns 16,013,540, or 29.1%, of the Common Shares. Roivant will not beneficially own the Common Shares underlying the Preferred Shares acquired in the First Closing or the Common Shares underlying the Preferred Shares to be acquired (subject to the applicable conditions in the Subscription Agreement) in the Second Closing, until the date that is 60 days prior to the date on which the Preferred Shares become convertible into the Common Shares, either automatically or at Roivant’s option pursuant to the terms of the Preferred Shares. As described in Item 6 of the Schedule 13D, the Preferred Shares will mandatorily convert into the Common Shares on the fourth anniversary of the First Closing, subject to limited exceptions in the event of certain transactions or fundamental changes that would permit earlier conversion at Roivant’s option.

(b)         The aggregate number and percentage of the Common Shares beneficially owned by Roivant and, for Roivant, the number of Common Shares as to which there is sole power to vote or to direct the vote, shared power to vote or to direct the vote, sole power to dispose or to direct the disposition, or shared power to dispose or to direct the disposition are set forth on lines 7 through 11 of the cover sheet of this Schedule 13D.

The percentage of outstanding Common Shares that may be deemed to be beneficially owned by Roivant is set forth on line 13 of Roivant’s cover sheet of this Schedule 13D. Such percentage was calculated for Roivant based on an aggregate of 55,051,995 Common Shares issued and outstanding as of October 12, 2017, as provided by the Issuer to Roivant. This amount excludes 9,808,386 Common Shares (subject to adjustment pursuant to the conversion terms of the Preferred Shares, as described in Item 6 of the Schedule 13D) underlying 500,000 Preferred Shares acquired on October 16, 2017, which Common Shares are not deemed beneficially owned as described in Item 5(a).

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Except as disclosed in this Schedule 13D, Roivant does not beneficially own any Common Shares or have the right to acquire any Common Shares.

Except as disclosed in this Schedule 13D, Roivant presently does not have the power to vote or to direct the vote or to dispose or direct the disposition of any of the Common Shares that Roivant may be deemed to beneficially own.

Item 6.  Contracts, Arrangements, Understandings or Relationships with Respect to Securities of the Issuer

Item 6 of the Schedule 13D is hereby amended and supplemented as follows:

The information set forth or incorporated in Item 3 of this Schedule 13D regarding the acquisition of 500,000 Preferred Shares at the First Closing on October 16, 2017 is incorporated herein by reference. Pursuant to the Subscription Agreement, in connection with the First Closing, on October 16, 2017, the Issuer filed the Preferred Shares Article Amendment, and Roivant and the Issuer signed the Amended and Restated Governance Agreement, the Amended Registration Rights Agreement, the Amended and Restated Standstill Agreement and the Amended and Restated Lock-Up Agreement, the forms of which are attached to the copy of the Subscription Agreement, previously filed as Exhibit 7.08 to the Schedule 13D.

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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.

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