Arcturus (ARCT) launches KOSTAIVE mRNA vaccine targeting JN.1

Arcturus Therapeutics Holdings Inc. announced on September 26, 2025 the launch of a new presentation of KOSTAIVE®, its self‑amplifying mRNA vaccine candidate against COVID‑19.

Rhea-AI Filing Summary

Arcturus Therapeutics Holdings Inc. announced on September 26, 2025 the launch of a new presentation of KOSTAIVE®, its self‑amplifying mRNA vaccine candidate against COVID‑19. The company said the product is formulated as a two‑dose vial, one vial per carton. In non‑clinical studies it induced neutralizing antibodies against the Omicron sublineage JN.1 and variant XEC, and showed cross‑neutralization versus LP.8.1, XFG and NB.1.8.1. Arcturus also disclosed a distribution and sales agreement with CSL Seqirus for Japan. The filing includes a press release dated September 26, 2025 and a company signature by Joseph E. Payne, Chief Executive Officer. The Item 7.01 disclosure is labeled as Regulation FD information and is not incorporated by reference into other filings unless specifically stated.

Positive

• Launched KOSTAIVE® presentation targeting Omicron JN.1/XEC, showing preclinical neutralization breadth
• Two‑dose vial format noted, which may simplify dosing logistics
• Distribution agreement with CSL Seqirus for Japan provides an established commercialization partner

Negative

• Evidence limited to non‑clinical studies; no human safety or efficacy data disclosed
• No clinical timelines or regulatory milestones were provided in the filing
• Commercial terms for the CSL Seqirus agreement were not disclosed, so near‑term financial impact is unclear

Insights

Biotech Product Specialist

JN.1‑targeted self‑amplifying mRNA vaccine released; only non‑clinical neutralization reported.

The announcement describes a new presentation of KOSTAIVE®, a self‑amplifying mRNA vaccine formulated as a two‑dose vial and engineered to target the SARS‑CoV‑2 Omicron sublineage JN.1 and variant XEC. The disclosed data are non‑clinical neutralization results showing activity against multiple Omicron derivatives, which suggests preclinical breadth but does not include human safety or efficacy data.

Dependencies and near‑term risks include successful transition from non‑clinical to clinical studies and regulatory review pathways in Japan and elsewhere. Watch for initiation of human trials, regulatory submissions, and any disclosed clinical data or timelines in the coming months.

Commercial Partnerships Analyst

Distribution tie‑up with CSL Seqirus provides a Japan commercialization channel.

The company reported a distribution and sales arrangement with CSL Seqirus for Japan, which pairs Arcturus's vaccine candidate with a major local influenza vaccine provider. This agreement could accelerate market access in Japan if clinical and regulatory milestones are met.

Key dependencies include regulatory authorization in Japan and any commercial details (pricing, volumes) not disclosed here. Investors should look for contract terms, regulatory filings, and launch timing that will clarify near‑term commercial impact.

8-K Event Classification

2 items: 7.01, 9.01

2 items

Item 7.01 Regulation FD Disclosure Disclosure

Material non-public information disclosed under Regulation Fair Disclosure, often investor presentations or guidance.

Item 9.01 Financial Statements and Exhibits Exhibits

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

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What did Arcturus (ARCT) announce on September 26, 2025?

Arcturus announced the launch of a new presentation of KOSTAIVE® and a Japan distribution agreement with CSL Seqirus on September 26, 2025.

Does the filing include clinical trial results for KOSTAIVE (ARCT)?

No. The filing reports non‑clinical neutralizing antibody results only; no human clinical data were disclosed.

Which variants did KOSTAIVE neutralize in the non‑clinical studies?

The filing states neutralization against Omicron JN.1 and XEC, plus cross‑neutralization versus LP.8.1, XFG and NB.1.8.1.

What formulation was disclosed for KOSTAIVE in the filing?

The product is supplied as a two‑dose vial, with one vial per carton.

Who will handle distribution and sales of KOSTAIVE in Japan?

CSL Seqirus, part of CSL Limited, was named as the distribution and sales partner for Japan.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Accepted by SEC EDGAR 09/26/2025 - 06:01 AM Learn about SEC filing dates

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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 26, 2025

ARCTURUS THERAPEUTICS HOLDINGS INC.

(Exact name of registrant as specified in its charter)

Delaware		001-38942		32-0595345
(State or other jurisdiction of incorporation)		(Commission File Number)		(I.R.S. Employer Identification No.)

10628 Science Center Drive, Suite 250

San Diego, California 92121

(Address of principal executive offices)

Registrant’s telephone number, including area code: (858) 900-2660

(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, par value $0.001 per share		ARCT		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 7.01 Regulation FD Disclosure.

On September 26, 2025, Meiji Holdings Co., Ltd. announced that its subsidiary, Meiji Seika Pharma Co., Ltd. (“Meiji”), announced today that it launched a new presentation of KOSTAIVE®, a self-amplifying mRNA vaccine against COVID-19. The product targets the SARS-CoV-2 Omicron sub lineage JN.1 variant XEC. In non-clinical studies, it induced neutralizing antibodies not only against Omicron JN.1 and XEC, but also against LP.8.1 and the currently circulating variants XFG and NB.1.8.1. The formulation is supplied as a two-dose vial, with one vial per carton.

As previously announced on April 11, 2023, Meiji entered into a distribution agreement with Seqirus, Inc. (“CSL Seqirus”), a part of CSL Limited, and one of the world’s leading influenza vaccine providers, for the distribution and sales of Arcturus Therapeutics Holdings Inc.’s (the “Company” or “Arcturus”) self-amplifying mRNA vaccine candidate against COVID-19 in Japan.

A copy of Meiji’s press release is furnished herewith as Exhibit 99.1 and is incorporated herein by reference.

The information set forth in this Item 7.01, including Exhibit 99.1, is furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that Section. The information in this Item 7.01 shall not be deemed to be incorporated by reference into any filing of the Company under the Securities Act, or the Exchange Act, whether made before or after the date hereof, except as shall be expressly set forth by specific reference in such a filing.

Cautionary Note Regarding Forward-Looking Statements

This Current Report on Form 8-K contains forward-looking statements that involve substantial risks and uncertainties for purposes of the safe harbor provided by the Private Securities Litigation Reform Act of 1995. Any statements, other than statements of historical fact included in this Current Report on Form 8-K, are forward-looking statements, including those regarding partnered programs (including the COVID-19 and flu programs partnered with CSL Seqirus), the likelihood that non-clinical data will be predictive of future results, the potential supply of KOSTAIVE® in 2025 and timing therefor, and the impact of general business and economic conditions. Arcturus may not actually achieve the plans, carry out the intentions or meet the expectations or projections disclosed in any forward-looking statements such as the foregoing and you should not place undue reliance on such forward-looking statements. These statements are only current predictions or expectations, and are subject to known and unknown risks, uncertainties, and other factors that may cause our or our industry’s actual results, levels of activity, performance or achievements to be materially different from those anticipated by the forward-looking statements, including those discussed under the heading "Risk Factors" in Arcturus’ most recent Annual Report on Form 10-K, and in subsequent filings with, or submissions to, the Securities and Exchange Commission (the “SEC”), which are available on the SEC’s website at www.sec.gov. Except as otherwise required by law, Arcturus disclaims any intention or obligation to update or revise any forward-looking statements, which speak only as of the date they were made, whether as a result of new information, future events or circumstances or otherwise.

Item 9.01 Financial Statements and Exhibits.

(d) Exhibits

Exhibit No.		Description
99.1		Press Release dated September 26, 2025

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.

	Arcturus Therapeutics Holdings Inc.
Date: September 26, 2025
	By:	/s/ Joseph E. Payne
	Name:	Joseph E. Payne
	Title:	Chief Executive Officer