Aptevo Therapeutics (NASDAQ: APVO) reports 100% remission in RAINIER AML trial cohort

Rhea-AI Filing Summary

Aptevo Therapeutics Inc. reported new clinical results from its RAINIER study. On September 16, 2025, the company announced a 100% remission rate in Cohort 3 of its Phase 1b/2 RAINIER trial. The study evaluates mipletamig, a first-in-class CD123 x CD3 bispecific antibody, combined with venetoclax and azacitidine in newly diagnosed acute myeloid leukemia patients who are not candidates for intensive chemotherapy.

The company released these data through a press release, which is included as an exhibit to this report, highlighting the importance Aptevo places on this clinical milestone in its oncology pipeline.

Positive

• RAINIER Cohort 3 shows 100% remission rate using mipletamig plus venetoclax and azacitidine in newly diagnosed AML patients unfit for intensive chemotherapy.

Negative

• None.

Insights

Biotech clinical development analyst

Aptevo reports a 100% remission rate in a RAINIER trial cohort, a notably strong early clinical signal.

Aptevo Therapeutics disclosed that Cohort 3 of its Phase 1b/2 RAINIER trial achieved a 100% remission rate using mipletamig in combination with venetoclax and azacitidine. The regimen targets newly diagnosed acute myeloid leukemia patients who are unfit for intensive chemotherapy, a group with high unmet medical need.

These results come from a defined cohort within an ongoing early-stage study, so durability of response, safety, and outcomes in broader populations remain to be characterized. Still, achieving a stated 100% remission rate in any AML cohort is an encouraging development for a first-in-class CD123 x CD3 bispecific antibody.

The company highlighted the data via a dedicated press release on September 16, 2025, signaling strategic importance within its clinical pipeline. Subsequent updates from the RAINIER trial, including additional cohorts and longer follow-up, will help clarify how these findings translate into the overall development path for mipletamig.

8-K Event Classification

2 items: 8.01, 9.01

2 items

Item 8.01 Other Events Other

Voluntary disclosure of events the company deems important to shareholders but not covered by other items.

Item 9.01 Financial Statements and Exhibits Exhibits

Financial statements, pro forma financial information, and exhibit attachments filed with this report.

Understanding 8-K Material Events →

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UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): September 16, 2025

APTEVO THERAPEUTICS INC.

(Exact name of Registrant as Specified in Its Charter)

Delaware			001-37746	81-1567056
(State or Other Jurisdiction of Incorporation)			(Commission File Number)	(IRS Employer Identification No.)
2401 4th Avenue Suite 1050
Seattle, Washington				98121
(Address of Principal Executive Offices)				(Zip Code)

Registrant’s Telephone Number, Including Area Code: (206) 838-0500

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Title of each class		Trading Symbol(s)		Name of each exchange on which registered
Common Stock, $0.001 par value		APVO		The Nasdaq Stock Market LLC

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter).

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 13(a) of the Exchange Act. ☐

Item 8.01 Other Events.

On September 16, 2025, Aptevo Therapeutics Inc. (the "Company") issued a press release announcing a 100% remission rate in Cohort 3 of its Phase 1b/2 RAINIER trial evaluating mipletamig, the Company’s first-in-class CD123 x CD3 bispecific antibody, in combination with venetoclax + azacitidine for newly diagnosed patients with acute myeloid leukemia unfit for intensive chemotherapy.

A copy of the press release is attached hereto as Exhibit 99.1 and is incorporated by reference herein.

Item 9.01 Financial Statements and Exhibits.

(d) Exhibits

The following exhibits are being filed herewith:

Exhibit No.		Description
99.1		Press release of Aptevo Therapeutics Inc. dated September 16, 2025.
104		Cover Page Interactive Data File (embedded within the Inline XBRL document)

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

			APTEVO THERAPEUTICS INC.
Date:	September 16, 2025	By:	/s/ Marvin L. White
			Marvin L. White President and Chief Executive Officer

FAQ

What did Aptevo Therapeutics (APVO) announce in this 8-K?

Aptevo Therapeutics reported that Cohort 3 of its Phase 1b/2 RAINIER trial achieved a 100% remission rate when treating newly diagnosed acute myeloid leukemia patients unfit for intensive chemotherapy with mipletamig plus venetoclax and azacitidine.

What is mipletamig in Aptevo Therapeutics' RAINIER trial?

Mipletamig is described as Aptevo Therapeutics' first-in-class CD123 x CD3 bispecific antibody, evaluated in combination with venetoclax and azacitidine in the Phase 1b/2 RAINIER trial for acute myeloid leukemia.

Which patient population is targeted in Aptevo's RAINIER Cohort 3?

Cohort 3 focuses on newly diagnosed patients with acute myeloid leukemia who are considered unfit for intensive chemotherapy, treated with mipletamig plus venetoclax and azacitidine.

What is the key efficacy result reported for the RAINIER Cohort 3?

The company reported a 100% remission rate in Cohort 3 of the Phase 1b/2 RAINIER trial using mipletamig in combination with venetoclax and azacitidine.

How did Aptevo Therapeutics disclose the RAINIER trial update?

Aptevo issued a press release on September 16, 2025 announcing the RAINIER Cohort 3 remission results and filed it as Exhibit 99.1 to this report.

What exhibit is included with this Aptevo 8-K filing?

The filing includes Exhibit 99.1, which is the press release dated September 16, 2025 detailing the 100% remission rate in Cohort 3 of the RAINIER trial, and Exhibit 104, the cover page Inline XBRL data file.