[SCHEDULE 13G/A] Mereo BioPharma Group plc American SEC Filing

Rhea-AI Filing Summary

Janus Henderson Group plc and an affiliated fund report significant passive holdings in Mereo BioPharma Group plc American Depositary Shares. Janus Henderson Group plc beneficially owns 17,688,592 ADS, equal to 11.1% of the class, with shared voting and shared dispositive power only and no sole voting or dispositive power. An affiliated vehicle, Janus Henderson Biotech Innovation Master Fund Ltd, reports 15,203,597 ADS (9.6% of the class), also held with shared voting and dispositive power only.

The filing is a Schedule 13G/A disclosure indicating the holdings are reported as held in the ordinary course of business; the reporting persons certify the securities were not acquired to influence control of the issuer. The filing identifies reporting classifications and a power of attorney authorizing signatories to file required ownership reports.

Positive

• Material ownership disclosed: Janus Henderson Group plc reports beneficial ownership of 17,688,592 ADS (11.1% of class).
• Clear classification and certification: Holdings reported on a Schedule 13G/A and certified as held in the ordinary course, indicating passive intent in this filing.

Negative

• None.

Insights

Financial Analyst

TL;DR: A substantial passive stake (11.1%) disclosed; material ownership but declared passive under Schedule 13G/A.

The filing shows Janus Henderson Group plc beneficially owns 17,688,592 ADS representing 11.1% of the class and an affiliated fund holds 15,203,597 ADS (9.6%). Both positions are reported with shared voting and dispositive power and no sole power, consistent with pooled or managed holdings. As a Schedule 13G/A, the disclosure signals size and transparency without an asserted intent to seek control. For investors, the change in disclosed ownership is material in scale but framed as passive by the filers.

Corporate Governance Expert

TL;DR: Large disclosed ownership is governance-relevant; filer asserts no intent to influence control.

The document identifies reporting classifications (investment adviser and hedge/collective investment types) and confirms that voting and dispositive authority are shared rather than sole. The certification states holdings are in the ordinary course and not for changing control, which aligns with the Schedule 13G/A treatment. From a governance lens, an 11.1% disclosed stake is material and warrants monitoring of any future amendments or conversions to Schedule 13D if intent changes.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 5)

MEREO BIOPHARMA GROUP PLC

(Name of Issuer)

American Depositary Shares

(Title of Class of Securities)

589492107

(CUSIP Number)

06/30/2025

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

Rule 13d-1(b)

Rule 13d-1(c)

Rule 13d-1(d)

SCHEDULE 13G

CUSIP No. 589492107

1

Names of Reporting Persons

JANUS HENDERSON GROUP PLC

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

JERSEY

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 17,688,592.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 17,688,592.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

17,688,592.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

11.1 %

12

Type of Reporting Person (See Instructions)

IA, HC

SCHEDULE 13G

CUSIP No. 589492107

1

Names of Reporting Persons

Janus Henderson Biotech Innovation Master Fund Ltd

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

MASSACHUSETTS

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 15,203,597.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 15,203,597.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

15,203,597.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

9.6 %

12

Type of Reporting Person (See Instructions)

IV

SCHEDULE 13G

Item 1.
(a)	Name of issuer: MEREO BIOPHARMA GROUP PLC
(b)	Address of issuer's principal executive offices: ONE CAVENDISH PLACE, FOURTH FLOOR LONDON, UNITED KINGDOM W1G0QF
Item 2.
(a)	Name of person filing: Janus Henderson Group plc
(b)	Address or principal business office or, if none, residence: 201 Bishopsgate EC2M 3AE, United Kingdom
(c)	Citizenship: Y9
(d)	Title of class of securities: American Depositary Shares
(e)	CUSIP No.: 589492107
Item 3.	If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)	Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)	Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)	Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)	Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)	An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)	An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)	A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)	A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)	A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)	A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J), please specify the type of institution:
(k)	Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
Item 4.	Ownership
(a)	Amount beneficially owned: JHIUS may be deemed to be the beneficial owner of 17,688,592 shares
(b)	Percent of class: 11.1 %
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: 0
	(ii) Shared power to vote or to direct the vote: 17688592
	(iii) Sole power to dispose or to direct the disposition of: 0
	(iv) Shared power to dispose or to direct the disposition of: 17688592
Item 5.	Ownership of 5 Percent or Less of a Class.
Item 6.	Ownership of more than 5 Percent on Behalf of Another Person.
	If any other person 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, such securities, a statement to that effect should be included in response to this item and, if such interest relates to more than 5 percent of the class, such person should be identified. A listing of the shareholders of an investment company registered under the Investment Company Act of 1940 or the beneficiaries of employee benefit plan, pension fund or endowment fund is not required. N/A
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
	If a parent holding company has filed this schedule, pursuant to Rule 13d-1(b)(ii)(G), so indicate under Item 3(g) and attach an exhibit stating the identity and the Item 3 classification of the relevant subsidiary. If a parent holding company has filed this schedule pursuant to Rule 13d-1(c) or Rule 13d-1(d), attach an exhibit stating the identification of the relevant subsidiary. JHIUS, JHIUKL and JHIAIFML are indirect subsidiaries of Janus Henderson and are registered investment advisers furnishing investment advice to Managed Portfolios.
Item 8.	Identification and Classification of Members of the Group.
	If a group has filed this schedule pursuant to §240.13d-1(b)(1)(ii)(J), so indicate under Item 3(j) and attach an exhibit stating the identity and Item 3 classification of each member of the group. If a group has filed this schedule pursuant to §240.13d-1(c) or §240.13d-1(d), attach an exhibit stating the identity of each member of the group. N/A
Item 9.	Notice of Dissolution of Group.
	Notice of dissolution of a group may be furnished as an exhibit stating the date of the dissolution and that all further filings with respect to transactions in the security reported on will be filed, if required, by members of the group, in their individual capacity. See Item 5. N/A

Item 10.

Certifications:

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under § 240.14a-11.

SIGNATURE

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.

JANUS HENDERSON GROUP PLC

Signature:	Kristin Mariani
Name/Title:	Head of North America Compliance, CCO
Date:	08/14/2025

Janus Henderson Biotech Innovation Master Fund Ltd

Signature:	Kristin Mariani
Name/Title:	Head of North America Compliance, CCO
Date:	08/14/2025

Exhibit Information

POWER OF ATTORNEY The undersigned, Janus Henderson Group plc ("the Company"), does hereby make, constitute and appoint each of Kristin Mariani and Caroline Barotti acting severally, as its true and lawful attorneys in-fact, for the purpose of, from time to time, executing in its name and on its behalf, whether the Company individually or as representative of others, any and all documents, certificates, instruments, statements, other filings and amendments to the foregoing (collectively, "documents") determined by such person to be necessary or appropriate to comply with ownership or control-person reporting requirements imposed by any United States or non-United States governmental or regulatory authority, including, without limitation, Forms 13D, 13F, 13G and 13H and any amendments to any of the foregoing as may be required to be filed with the Securities and Exchange Commission, and delivering, furnishing or filing any such documents with the appropriate governmental, regulatory authority or other person, and giving and granting to each such attorney-in-fact power and authority to act in the premises as fully and to all intents and purposes as the Company might or could do if personally present by one of its authorized signatories, hereby ratifying and confirming all that said attorney-in-fact shall lawfully do or cause to be done by virtue hereof. Any such determination by an attorney-in-fact named herein shall be conclusively evidenced by such person's execution, delivery, furnishing or filing of the applicable document. This power of attorney shall be valid from the date hereof and shall remain in full force and effect until either revoked in writing by the Company, or, in respect of any attorney-in-fact named herein, until such person ceases to be an employee of the Company or one of its affiliates. IN WITNESS WHEREOF, the undersigned has caused this power of attorney to be executed as of this 9th day of December, 2022. Janus Henderson Group plc By: /s/ Michelle Rosenberg Name: Michelle Rosenberg Title: General Counsel and Company Secretary

FAQ

How many MREO ADS does Janus Henderson Group plc report owning?

The filing reports 17,688,592 ADS beneficially owned by Janus Henderson Group plc.

What percentage of MREO does that ownership represent?

Janus Henderson Group plc's position represents 11.1% of the class according to the filing.

What stake does Janus Henderson Biotech Innovation Master Fund Ltd report?

The fund reports beneficial ownership of 15,203,597 ADS, equal to 9.6% of the class.

Does the filing indicate an intent to influence control of Mereo BioPharma (MREO)?

No. The filing includes a certification that the securities were acquired and are held in the ordinary course of business and not to change or influence control.

What form was filed for this disclosure?

The reporting persons filed a Schedule 13G/A ownership disclosure.