Positive top-line Phase 1 data for lead clinical program DNTH103 confirm potent classical pathway inhibition, extended half-life, and a potentially differentiated safety profile

Results support DNTH103’s best-in-class potential to be the first subcutaneous, self-administered injection dosed as infrequently as once every two weeks to treat a range of autoimmune disorders

Company plans to initiate multiple Phase 2 trials targeting neuromuscular indications in 2024, starting with generalized Myasthenia Gravis in Q1 2024, followed by Multifocal Motor Neuropathy in Q2 2024, and Chronic Inflammatory Demyelinating Polyneuropathy in second half of 2024

Dianthus Therapeutics, Inc. will begin trading on Nasdaq as DNTH with approximately $184 million of cash runway expected to fund operations into Q2 2026

NEW YORK and WALTHAM, Mass., Sept. 12, 2023 (GLOBE NEWSWIRE) — Dianthus Therapeutics, Inc. (“Dianthus”), a clinical-stage biotechnology company dedicated to advancing the next generation of antibody complement therapeutics to treat severe autoimmune diseases, today announced positive top-line Phase 1 data for DNTH103 validating its best-in-class potential as a selective classical pathway inhibitor targeting only the active form of the C1s protein. Additionally, Dianthus will begin trading on the Nasdaq Capital Market today as DNTH, following the successful completion on September 11, 2023 of the previously announced merger with Magenta Therapeutics (“Magenta”).

The Phase 1 healthy volunteer study was designed to validate the extended half-life, potent classical pathway inhibition, and potentially differentiated safety profile of DNTH103. Top-line data across seven single and multiple ascending dose cohorts with 52 healthy volunteers confirmed its approximately 60-day half-life and highly potent classical pathway inhibition, establishing DNTH103’s best-in-class potential to be the first self-administered subcutaneous injection dosed as infrequently as once every two weeks to treat a range of autoimmune disorders. The results also demonstrated DNTH103 was generally well tolerated with no serious adverse events or complement-related infections. Dianthus plans to initiate multiple Phase 2 studies in 2024 in various neuromuscular indications, starting with generalized Myasthenia Gravis (gMG) in the first quarter of 2024 followed by additional Phase 2 trials for Multifocal Motor Neuropathy (MMN) and Chronic Inflammatory Demyelinating Polyneuropathy (CIDP). Additional information about our Phase 1 data and DNTH103 can be found in our corporate presentation at investor.dianthustx.com.

“This is an exciting and transformative time at Dianthus as we announce top-line Phase 1 data for DNTH103 validating its potential to become a new standard of care with a best-in-class profile for multiple classical pathway-driven autoimmune disorders,” said Marino Garcia, President and Chief Executive Officer of Dianthus Therapeutics. “These results, combined with our transition to the public markets, represent a major milestone in our growth trajectory. We are now well positioned to execute across multiple Phase 2 trials as we continue to maximize the value of DNTH103 as a pipeline-in-a-product.”

“I am very encouraged by the Phase 1 safety and pharmacokinetic/pharmacodynamic data seen with DNTH103, our highly potent and selective upstream classical complement pathway inhibitor. Classical pathway activation plays a significant role in the pathology of various autoimmune disorders such as generalized Myasthenia Gravis, where patients still face significant disease and treatment burden, and we are excited to start the gMG Phase 2 trial early next year,” said Simrat Randhawa, M.D., Chief Medical Officer of Dianthus Therapeutics. “We also look forward to starting Phase 2 trials in both MMN and CIDP in 2024, two neuromuscular autoimmune disorders which currently have no approved targeted biologics and where we believe DNTH103 could benefit patients.”

Concurrent with the closing of the merger, Dianthus completed a $72 million private investment in its common stock and pre-funded warrants from a syndicate of healthcare investors led by Fidelity Management & Research Company, Catalio Capital Management, 5AM Ventures, Avidity Partners, Wedbush Healthcare Partners and founding investors Fairmount, Tellus BioVentures and Venrock Healthcare Capital Partners. The cash and cash equivalents as of the close of the business combination were approximately $184 million, which is expected to provide cash runway into the second quarter of 2026.

About DNTH103
DNTH103 is a clinical-stage, potent monoclonal antibody engineered to selectively target the classical pathway by inhibiting only the active form of the C1s protein, a clinically validated complement target. DNTH103 is enhanced with YTE half-life extension technology designed to enable a more convenient subcutaneous, self-administered injection dosed as infrequently as once every two weeks. Additionally, selective inhibition of the classical complement pathway may lower patient risk of infection from encapsulated bacteria by preserving immune activity of the lectin and alternative pathways. As the classical pathway plays a significant role in disease pathology, DNTH103 has the potential to be a best-in-class pipeline-in-a-product across a range of autoimmune disorders with high unmet need. Dianthus plans to initiate Phase 2 trials in multiple neuromuscular indications in 2024, starting with generalized Myasthenia Gravis in the first quarter of 2024.

About Dianthus Therapeutics
Dianthus Therapeutics is a clinical-stage biotechnology company dedicated to designing and delivering novel, best-in-class monoclonal antibodies with improved selectivity and potency. Based in New York City and Waltham, Mass., Dianthus is comprised of an experienced team of biotech and pharma executives who are leading the development of next-generation antibody complement therapeutics, aiming to deliver transformative medicines for people living with severe autoimmune and inflammatory diseases. To learn more, please visit www.dianthustx.com and follow us on LinkedIn.

Cautionary Statement Regarding Forward-Looking Statements
Certain statements in this press release, other than purely historical information, may constitute “forward-looking statements” within the meaning of the federal securities laws, including for purposes of the safe harbor provisions under the United States Private Securities Litigation Reform Act of 1995, express or implied statements regarding future plans and prospects, including statements regarding the expectations or plans for discovery, preclinical studies, clinical trials and research and development programs, in particular with respect to DNTH103, and any developments or results in connection therewith, including the target product profile of DNTH103; the anticipated timing of the results from those studies and trials; expectations regarding the use of proceeds and the time period over which the Company’s capital resources are expected to be sufficient to fund its anticipated operations; and expectations regarding the market and potential opportunities for complement therapies, in particular with respect to DNTH103. The words “opportunity,” “potential,” “milestones,” “runway,” “will,” “anticipate,” “achieve,” “near-term,” “catalysts,” “pursue,” “pipeline,” “believe,” continue,” “could,” “estimate,” “expect,” “ intend,” “may,” “might,” “plan,” “possible,” “predict,” “project,” “ should,” “strive,” “would,” “aim,” “target,” “commit,” and similar expressions (including the negatives of these terms or variations of them) generally identify forward-looking statements, but the absence of these words does not mean that statement is not forward looking.

Actual results could differ materially from those included in the forward-looking statements due to various factors, risks and uncertainties, including, but not limited to, that preclinical testing of DNTH103 and data from clinical trials may not be predictive of the results or success of ongoing or later clinical trials, that the development of DNTH103 or the Company’s other compounds may take longer and/or cost more than planned, that the Company may be unable to successfully complete the clinical development of the Company’s compounds, that the Company may be delayed in initiating, enrolling or completing its planned clinical trials, and that the Company’s compounds may not receive regulatory approval or become commercially successful products. These and other risks and uncertainties are identified under the headings “Risk Factors—Risks related to Dianthus” and “—Risks Related to the Combined Company” included in the Company’s definitive proxy statement/prospectus that was filed with and declared effective by the SEC on August 1, 2023, and other filings that the Company has made and may make with the SEC in the future. Nothing in this press release should be regarded as a representation by any person that the forward-looking statements set forth herein will be achieved or that any of the contemplated results of such forward-looking statements will be achieved.

The forward-looking statements in this press release speak only as of the date they are made and are qualified in their entirety by reference to the cautionary statements herein. Dianthus undertakes no obligation to publicly update or revise any forward-looking statement, whether as a result of new information, future events or otherwise, except as required by law. 

Media Contact Peg Rusconi Verge Scientific Communications prusconi@vergescientific.com Investor Relations Contact IR@dianthustx.com

The combined company will operate as “Dianthus Therapeutics, Inc.” with its common stock traded on Nasdaq under trading symbol “DNTH” effective Tuesday, September 12, 2023

CAMBRIDGE, Mass., Sept. 11, 2023 (GLOBE NEWSWIRE) — Magenta Therapeutics, Inc. (Nasdaq: MGTA) (“Magenta”) today announced completion of the merger with Dianthus Therapeutics, Inc. (“Dianthus”) following Magenta’s successful receipt of stockholder approval for all proposals related to the merger at a special meeting of stockholders. Magenta effected a reverse stock split of Magenta’s common stock immediately prior to the merger. Magenta following the merger is referred to herein as the “combined company.”

Steve Mahoney, President and Chief Financial and Operating Officer of Magenta said, “We are pleased with the outcome of the special meeting and appreciate our stockholders’ support for the merger with Dianthus.”

To ensure the combined company’s compliance with the minimum bid price requirement of $4.00 per share for initial listing on The Nasdaq Capital Market, Magenta implemented a reverse split of its common stock at a ratio of 1-for-16 shares. In the reverse stock split, every 16 shares of Magenta common stock outstanding was combined and reclassified into 1 share of Magenta common stock. Immediately thereafter, and pursuant to the terms of the previously announced merger agreement, Dianthus became a wholly owned subsidiary of Magenta upon completion of the merger, and each outstanding share of Dianthus common stock was converted into 0.2181 shares of common stock of Magenta. 

Magenta’s stockholders will receive cash in lieu of any fractional shares resulting from the reverse stock split. Stockholders owning shares of common stock via a bank, broker, or other nominee will have their positions automatically adjusted to reflect the reverse stock split and will not be required to take further action in connection with the reverse stock split, subject to their brokers’ particular processes. The new CUSIP number for the combined company following the reverse stock split, merger and other attendant transactions is 252828 108. 

The reverse stock split became legally effective today at 11:13 a.m. Eastern Time, with the merger effective today at 11:15 a.m. Eastern Time.

The combined company will operate under the name, Dianthus Therapeutics, Inc., and its shares will begin trading on The Nasdaq Capital Market on a post-reverse split, post-merger basis under the ticker symbol “DNTH” effective with the open of business on Tuesday, September 12, 2023.

CONTACT
Peg Rusconi
peg.rusconi@vergescientific.com

Experienced life sciences executive brings more than a decade of public company expertise in legal, corporate governance and compliance

New York City and Waltham, Mass., June 20, 2023 – Dianthus Therapeutics, a clinical-stage biotechnology company dedicated to advancing the next generation of antibody complement therapeutics, today announced the appointment of Adam Veness, Esq., as General Counsel.

Joining Dianthus most recently from Cyteir Therapeutics, Veness spent much of his career as Senior Vice President, General Counsel and Secretary at Acceleron Pharma Inc. prior to the acquisition by Merck in November 2021. During his tenure at Acceleron, Veness gained experience in roles of increasing responsibility where he served on the Executive Committee responsible for company strategy, and he led all aspects of global legal and compliance, including capital markets and SEC reporting obligations, corporate governance, contracts, intellectual property, employment matters, and data privacy.

“We are excited to welcome Adam to the Dianthus team at such a pivotal time for the company,” said Marino Garcia, President and Chief Executive Officer of Dianthus Therapeutics. “Adam’s proven track record in helping develop and implement corporate strategy and successfully leading the legal and compliance functions in public life science companies will be invaluable as we expect to transition to a public company in the third quarter of this year. I am looking forward to working with Adam and to his contributions as we continue to build an exciting biotech company.”

Prior to moving in-house to the biotechnology industry, Veness was a corporate and securities attorney at the law firm Mintz Levin where he represented and counseled public and private companies in the biopharmaceutical, technology, and healthcare industries. He began his legal career at a boutique litigation firm representing companies and individuals in a variety of civil litigation matters. Veness earned a B.A. in political science and philosophy from Tulane University, and a J.D. from Boston University School of Law.

“I am thrilled to join Dianthus as the company embarks on this exciting chapter of growth,” said Adam Veness, Esq., General Counsel of Dianthus Therapeutics. “I have been impressed with the quality of the science and the caliber of the Dianthus management team, board of directors, and investors. The team’s dedication to improving the lives of people with severe autoimmune disease has been inspiring, and their impressive achievements over a short period of time exemplify their sense of urgency in bringing potentially best-in-class therapies to these patients with high unmet need. I look forward to working with Marino and the entire Dianthus team as we are poised to cross the threshold into the public markets.”

About DNTH103
DNTH103 is an investigational long-acting classical complement pathway inhibitor designed as a less frequent and convenient subcutaneous injection with the potential to treat people living with severe autoimmune diseases. DNTH103, a fully human monoclonal antibody, is designed to selectively target only the active form of the C1s complement protein, inhibiting only the classical complement pathway, with the aim of treating patients with a lower dosing volume as a convenient subcutaneous injection suitable for a self-administered pre-filled pen. Inhibiting the active form of the complement target seeks to address a critical treatment gap in current complement therapies that do not bind selectively to the active protein, wasting a significant amount of the drug on inert proteins. DNTH103 selective inhibition of the classical pathway is engineered to preserve important immune activity of the lectin and alternative complement pathways needed to protect the body against infections from encapsulated bacteria. DNTH103 is also enhanced with YTE half-life extension technology to further reduce dosing frequency.

DNTH103 has a steady cadence of expected clinical milestones including top-line Phase 1 data aiming to confirm potent classical pathway inhibition and favorable, extended pharmacokinetics expected by the end of 2023, initiation of a Phase 2 trial in generalized Myasthenia Gravis expected in the first quarter of 2024 followed by two additional planned Phase 2 trial initiations in Multifocal Motor Neuropathy (MMN) and Chronic inflammatory demyelinating polyneuropathy (CIDP). Dianthus also plans to initiate an open label proof of efficacy trial in Cold Agglutinin Disease (CAD) with patient data anticipated in the second half of 2024.

About Dianthus Therapeutics

Dianthus Therapeutics is a clinical-stage biotechnology company dedicated to designing and delivering novel, best-in-class monoclonal antibodies with improved selectivity and potency over existing complement therapies. Based in New York City and Waltham, Mass., Dianthus is comprised of an experienced team of biotech and pharma executives who are leading the next generation of antibody complement therapeutics, aiming to deliver transformative medicines for people living with severe autoimmune diseases. In May 2023, Dianthus announced a merger agreement with Magenta Therapeutics and upon completion of the merger, the combined company is expected to operate under the name Dianthus Therapeutics, Inc. and trade on the Nasdaq under the ticker symbol “DNTH”. To learn more, please visit www.dianthustx.com and follow us on LinkedIn.

Forward-Looking Statements

Certain statements in this press release may constitute “forward-looking statements” for purposes of the federal securities laws concerning Dianthus’s expectations with respect to the proposed transaction between Dianthus and Magenta Therapeutics, Inc. (Magenta) announced in May 2023 and its anticipated closing. These forward-looking statements include express or implied statements relating to Dianthus’s management team’s expectations, hopes, beliefs, intentions or strategies regarding the future. In addition, any statements that refer to projections, forecasts or other characterizations of future events or circumstances, including any underlying assumptions, are forward-looking statements. The words “anticipate,” “believe,” “contemplate,” “continue,” “could,” “estimate,” “expect,” “intends,” “may,” “might,” “plan,” “possible,” “potential,” “predict,” “project,” “should,” “will,” “would” and similar expressions may identify forward-looking statements, but the absence of these words does not mean that a statement is not forward-looking. These forward-looking statements are based on current expectations and beliefs concerning future developments and their potential effects. There can be no assurance that future developments affecting Dianthus, Magenta or the proposed transaction will be those that have been anticipated. These forward-looking statements involve a number of risks, uncertainties (some of which are beyond Dianthus’s control) or other assumptions that may cause actual results or performance to be materially different from those expressed or implied by these forward-looking statements. These risks and uncertainties include, but are not limited to, the risk that the conditions to the closing of the transaction are not satisfied, including the failure to obtain stockholder approval for the transaction; the risk that the concurrent financing is not completed in a timely manner or at all; uncertainties as to the timing of the consummation of the transaction and the ability of each of Magenta and Dianthus to consummate the transaction, including the concurrent financing; the occurrence of any event, change or other circumstance or condition that could give rise to the termination of the merger agreement; the effect of the announcement or pendency of the merger on Magenta’s or Dianthus’s business relationships, operating results and business generally; and the outcome of any legal proceedings that may be instituted against Magenta, Dianthus or any of their respective directors or officers related to the merger agreement or the transactions contemplated thereby. The foregoing list of factors is not exhaustive. You should carefully consider the foregoing factors and the other risks and uncertainties described in the “Risk Factors” section of the proxy statement/prospectus included in the registration statement on Form S-4 which was initially filed with the SEC in May 2023 in connection with the transaction and other documents filed by Magenta from time to time with the SEC. Should one or more of these risks or uncertainties materialize, or should any of Dianthus’s assumptions prove incorrect, actual results may vary in material respects from those projected in these forward-looking statements. Dianthus’s forward-looking statements only speak as of the date they are made, and Magenta and Dianthus do not undertake any obligation to update or revise any forward-looking statements, whether as a result of new information, future events or otherwise, except as may be required under applicable securities laws.

Media Contact

Peg Rusconi, Verge Scientific Communications

prusconi@vergescientific.com

Merger to create Nasdaq-listed, clinical-stage biotechnology company focused on advancing Dianthus’ portfolio of next-generation antibody complement therapeutics

Combined company is expected to have approximately $180 million of cash or cash equivalents at close, including approximately $70 million from a concurrent private financing by Dianthus’ new and existing investors, which is expected to provide funding into mid-2026

Cash expected to fund lead program DNTH103 through multiple clinical data catalysts including Phase 1 in healthy volunteers, and Phase 2 trials in generalized Myasthenia Gravis and other indications

Companies will host a joint webcast today, May 3, 2023 at 8:30 a.m. ET

CAMBRIDGE, Mass., May 3, 2023 – Magenta Therapeutics, Inc. (Nasdaq: MGTA) (“Magenta”) and Dianthus Therapeutics, Inc. (“Dianthus”), a privately-held, clinical-stage biotechnology company dedicated to advancing the next generation of antibody complement therapeutics, announced today that they have entered into a definitive merger agreement to combine the companies in an all-stock transaction. The combined company will focus on advancing Dianthus’ pipeline of next-generation complement inhibitors, including DNTH103 currently in a Phase 1 clinical trial. Upon completion of the merger, the combined company is expected to operate under the name Dianthus Therapeutics, Inc. and trade on the Nasdaq under the ticker symbol “DNTH”.

In support of the merger, Dianthus has secured commitments for a $70 million private investment in its common stock and pre-funded warrants from a syndicate of healthcare investors led by Fidelity Management & Research Company, Catalio Capital Management, 5AM Ventures, Avidity Partners, Wedbush Healthcare Partners and founding investors Fairmount, Tellus BioVentures and Venrock Healthcare Capital Partners, that is expected to close immediately prior to completion of the merger. With the cash expected from both companies at closing and the proceeds of the concurrent private financing, the combined company is expected to have approximately $180 million of cash or cash equivalents immediately post-closing. The cash resources are intended to be used to advance Dianthus’ pipeline through multiple clinical data catalysts and is expected to fund operations into mid-2026. The merger and related financing are expected to close in the third quarter of 2023.

“I’m delighted to announce this planned merger with Magenta, which comes at a pivotal moment in the evolution of our company as we advance our pipeline of next-generation complement therapeutics for people living with severe autoimmune diseases,” said Marino Garcia, President and Chief Executive Officer of Dianthus Therapeutics. “Gaining access to the public capital markets can enhance our financial strength and fuel our growth strategy, enabling us to unlock the full potential of our pipeline, including our plans to address multiple autoimmune disorders with our clinical-stage active C1s inhibitor, DNTH103.”

“After a thorough exploration of our strategic alternatives, management and our Board of Directors believe the transaction with Dianthus Therapeutics will culminate in a successful outcome for our stockholders,” said Steve Mahoney, President, Chief Financial and Operating Officer of Magenta. “Dianthus has made rapid progress in developing and advancing DNTH103 into the clinic where it has the potential to be a transformative classical pathway inhibitor for severe autoimmune diseases. We are extremely grateful to our current and former employees who contributed to Magenta’s efforts to develop its programs and we now look forward to the combined company’s advancement on opportunities for value creation for patients.”

Magenta previously announced a comprehensive review of strategic alternatives in February 2023 and has since completed winding down a majority of its activities and costs associated with its research and development initiatives, including the termination of its lease and the sale of key assets.

About DNTH103

DNTH103 is an investigational long-acting classical complement pathway inhibitor designed as a less frequent and convenient subcutaneous injection with the potential to treat people living with severe autoimmune diseases. DNTH103, a fully human monoclonal antibody, is designed to selectively target only the active form of the C1s complement protein, inhibiting only the classical complement pathway, with the aim of treating patients with a lower dosing volume as a convenient subcutaneous injection suitable for a self-administered pre-filled pen. Inhibiting the active form of the complement target seeks to address a critical treatment gap in current complement therapies that do not bind selectively to the active protein, wasting a significant amount of the drug on inert proteins. DNTH103 selective inhibition of the classical pathway is engineered to preserve important immune activity of the lectin and alternative complement pathways needed to protect the body against infections from encapsulated bacteria. DNTH103 is also enhanced with YTE half-life extension technology to further reduce dosing frequency.

DNTH103 has a steady cadence of clinical milestones including top-line Phase 1 data aiming to confirm potent classical pathway inhibition and favorable, extended pharmacokinetics expected by the end of 2023, initiation of a Phase 2 trial in generalized Myasthenia Gravis expected in the first quarter of 2024 followed by two additional planned Phase 2 trial initiations in other neuro indications, and planned initiation of an open label proof of efficacy trial in Cold Agglutinin Disease with patient data anticipated in the second half of 2024.

About the Proposed Transaction, Management and Organization

Pre-merger Dianthus stockholders (including Dianthus stockholders issued shares of Dianthus common stock and pre-funded warrants in the concurrent private financing) are expected to own approximately 78.7% of the combined company and pre-merger Magenta stockholders are expected to own approximately 21.3% of the combined company. The percentage of the combined company that Magenta’s stockholders will own as of the close of the transaction is subject to adjustment based on the amount of Magenta’s net cash at the closing date. Immediately prior to the closing of the proposed merger, Magenta stockholders will be issued contingent value rights representing the right to receive certain payments from proceeds received by the combined company, if any, related to pre-transaction legacy assets.

Following the merger, the combined company will be led by Marino Garcia, the current CEO and President of Dianthus Therapeutics, and the current members of the Dianthus management team. Magenta Therapeutics, Inc. will be renamed “Dianthus Therapeutics, Inc.” and the corporate headquarters will be co-located in New York, NY and Waltham, MA. The merger agreement provides that the Board of Directors of the combined company will be composed of eight board members, including all six current Dianthus board members and two from Magenta. The transaction has been unanimously approved by the Board of Directors of each company and is expected to close in the third quarter of 2023, subject to customary closing conditions, including, the approvals by the stockholders of each company and other customary closing conditions.

Wedbush PacGrow is serving as lead financial advisor, Houlihan Lokey Financial Advisors is serving as co-financial adviser and Goodwin Procter LLP is serving as legal counsel to Magenta Therapeutics. Jefferies, Evercore ISI, Guggenheim Securities and Raymond James are serving as the placement agents to Dianthus Therapeutics, and Gibson, Dunn & Crutcher LLP is serving as legal counsel to Dianthus Therapeutics.

Webcast Presentation

The companies will host a webcast presentation to discuss the proposed transaction as well as Dianthus’ platform and pipeline assets today, May 3, 2023, at 8:30 a.m. ET. The live webcast can be accessed on the Events & Presentations page of Magenta’s website or by using the participant webcast link. A webcast of the presentation and associated slides will be available on the Investors & Media section of Magenta’s website at https://investor.magentatx.com/ and a replay will be archived for one year following the presentation.

About Magenta Therapeutics

Magenta Therapeutics is a biotechnology company focused on improving stem cell transplantation.

About Dianthus Therapeutics

Dianthus Therapeutics is a clinical-stage biotechnology company dedicated to designing and delivering novel, best-in-class monoclonal antibodies with improved selectivity and potency over existing complement therapies. Based in New York City and Waltham, Mass., Dianthus is comprised of an experienced team of biotech and pharma executives who are leading the next generation of antibody complement therapeutics, aiming to deliver transformative medicines for people living with severe autoimmune diseases. Dianthus raised a $100 million Series A in April 2022 co-led by 5AM Ventures, Avidity Partners, and Fidelity Management & Research Company, with participation from additional investors including Wedbush Healthcare Partners and founding investors Fairmount, Tellus BioVentures, and Venrock Healthcare Capital Partners. To learn more, please visit www.dianthustx.com and follow us on LinkedIn.

Forward-Looking Statements

Certain statements in this press release, other than purely historical information, may constitute “forward-looking statements” within the meaning of the federal securities laws, including for purposes of the safe harbor provisions under the United States Private Securities Litigation Reform Act of 1995, concerning Magenta, Dianthus, the proposed concurrent financing and the proposed merger between Magenta and Dianthus (“Proposed Transaction”) and other matters. These forward-looking statements include, but are not limited to, express or implied statements relating to Magenta’s or Dianthus’ management team’s expectations, hopes, beliefs, intentions or strategies regarding the future including, without limitation, statements regarding: the Proposed Transaction and the expected effects, perceived benefits or opportunities and related timing with respect thereto, expectations regarding or plans for discovery, preclinical studies, clinical trials and research and development programs, in particular with respect to DNTH103, and any developments or results in connection therewith, including the target product profile of DNTH103; the anticipated timing of the results from those studies and trials; expectations regarding the use of proceeds and the time period over which Dianthus’ capital resources will be sufficient to fund its anticipated operations; expectations regarding the market and potential opportunities for complement therapies, in particular with respect to DNTH103; and the expected trading of the combined company’s stock on Nasdaq under the ticker symbol “DNTH.” In addition, any statements that refer to projections, forecasts or other characterizations of future events or circumstances, including any underlying assumptions, are forward-looking statements. The words “opportunity,” “potential,” “milestones,” “pipeline,” “can,” “goal,” “aim,” “strategy,” “target,” “seek,” “anticipate,” “achieve,” “believe,” “contemplate,” “continue,” “could,” “estimate,” “expect,” “intends,” “may,” “might,” “plan,” “possible,” “predict,” “project,” “should,” “will,” “would” and similar expressions (including the negatives of these terms or variations of them) may identify forward-looking statements, but the absence of these words does not mean that a statement is not forward-looking. These forward-looking statements are based on current expectations and beliefs concerning future developments and their potential effects. There can be no assurance that future developments affecting Magenta, Dianthus or the Proposed Transaction will be those that have been anticipated. These forward-looking statements involve a number of risks, uncertainties (some of which are beyond Magenta’s control) or other assumptions that may cause actual results or performance to be materially different from those expressed or implied by these forward-looking statements. These risks and uncertainties include, but are not limited to, the risk that the conditions to the closing or consummation of the Proposed Transaction are not satisfied, including the failure to obtain stockholder approval for the Proposed Transaction; the risk that the concurrent financing is not completed in a timely manner or at all; uncertainties as to the timing of the consummation of the Proposed Transaction and the ability of each of Magenta and Dianthus to consummate the transactions contemplated by the Proposed Transaction; risks related to Magenta’s continued listing on Nasdaq until closing of the Proposed Transaction and the combined company’s ability to remain listed following the Proposed Transaction; risks related to Magenta’s and Dianthus’ ability to correctly estimate their respective operating expenses and expenses associated with the Proposed Transaction, as applicable, as well as uncertainties regarding the impact any delay in the closing would have on the anticipated cash resources of the resulting combined company upon closing and other events and unanticipated spending and costs that could reduce the combined company’s cash resources; the occurrence of any event, change or other circumstance or condition that could give rise to the termination of the business combination between Magenta and Dianthus; the effect of the announcement or pendency of the merger on Magenta’s or Dianthus’ business relationships, operating results and business generally; costs related to the merger; the outcome of any legal proceedings that may be instituted against Magenta, Dianthus or any of their respective directors or officers related to the merger agreement or the transactions contemplated thereby; the ability of Magenta or Dianthus to protect their respective intellectual property rights; competitive responses to the Proposed Transaction; unexpected costs, charges or expenses resulting from the Proposed Transaction; potential adverse reactions or changes to business relationships resulting from the announcement or completion of the Proposed Transaction; legislative, regulatory, political and economic developments; and those uncertainties and factors described under the heading “Risk Factors,” “Risk Factor Summary” and “Forward-Looking Statements” in Magenta’s most recent Annual Report on Form 10-K filed with the Securities and Exchange Commission (the “SEC”) on March 23, 2023, as well as discussions of potential risks, uncertainties, and other important factors included in other filings by Magenta from time to time, any risk factors related to Magenta or Dianthus made available to you in connection with the Proposed Transaction, as well as risk factors associated with companies, such as Dianthus, that operate in the biopharma industry. Should one or more of these risks or uncertainties materialize, or should any of Magenta’s or Dianthus’ assumptions prove incorrect, actual results may vary in material respects from those projected in these forward-looking statements. Nothing in this press release should be regarded as a representation by any person that the forward-looking statements set forth herein will be achieved or that any of the contemplated results of such forward-looking statements will be achieved. You should not place undue reliance on forward-looking statements in this press release, which speak only as of the date they are made and are qualified in their entirety by reference to the cautionary statements herein. Neither Magenta nor Dianthus undertakes or accepts any duty to release publicly any updates or revisions to any forward-looking statements. This press release does not purport to summarize all of the conditions, risks and other attributes of an investment in Magenta or Dianthus.

No Offer or Solicitation

This press release and the information contained herein is not intended to and does not constitute (i) a solicitation of a proxy, consent or approval with respect to any securities or in respect of the Proposed Transaction or (ii) an offer to sell or the solicitation of an offer to subscribe for or buy or an invitation to purchase or subscribe for any securities pursuant to the Proposed Transaction or otherwise, nor shall there be any sale, issuance or transfer of securities in any jurisdiction in contravention of applicable law. No offer of securities shall be made except by means of a prospectus meeting the requirements of the Securities Act of 1933, as amended, or an exemption therefrom. Subject to certain exceptions to be approved by the relevant regulators or certain facts to be ascertained, the public offer will not be made directly or indirectly, in or into any jurisdiction where to do so would constitute a violation of the laws of such jurisdiction, or by use of the mails or by any means or instrumentality (including without limitation, facsimile transmission, telephone and the internet) of interstate or foreign commerce, or any facility of a national securities exchange, of any such jurisdiction.

NEITHER THE SEC NOR ANY STATE SECURITIES COMMISSION HAS APPROVED OR DISAPPROVED OF THE SECURITIES OR DETERMINED IF THIS PRESS RELEASE IS TRUTHFUL OR COMPLETE.

Important Additional Information About the Proposed Transaction Will be Filed with the SEC

This press release is not a substitute for the registration statement or for any other document that Magenta may file with the SEC in connection with the Proposed Transaction. In connection with the Proposed Transaction between Magenta and Dianthus, Magenta intends to file relevant materials with the SEC, including a registration statement on Form S-4 that will contain a proxy statement/prospectus of Magenta. MAGENTA URGES INVESTORS AND STOCKHOLDERS TO READ THE REGISTRATION STATEMENT, PROXY STATEMENT/PROSPECTUS AND ANY OTHER RELEVANT DOCUMENTS THAT MAY BE FILED WITH THE SEC, AS WELL AS ANY AMENDMENTS OR SUPPLEMENTS TO THESE DOCUMENTS, CAREFULLY AND IN THEIR ENTIRETY IF AND WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT MAGENTA, DIANTHUS, THE PROPOSED TRANSACTION AND RELATED MATTERS. Investors and stockholders will be able to obtain free copies of the proxy statement/prospectus and other documents filed by Magenta with the SEC (when they become available) through the website maintained by the SEC at www.sec.gov. In addition, investors and stockholders should note that Magenta communicates with investors and the public using its website (www.magentatx.com), the investor relations website (https://investors.magentatx.com/) where anyone will be able to obtain free copies of the proxy statement/prospectus and other documents filed by Magenta with the SEC and stockholders are urged to read the proxy statement/prospectus and the other relevant materials when they become available before making any voting or investment decision with respect to the Proposed Transaction.

Participants in the Solicitation

Magenta, Dianthus and their respective directors and executive officers may be deemed to be participants in the solicitation of proxies from stockholders in connection with the Proposed Transaction. Information about Magenta’s directors and executive officers including a description of their interests in Magenta is included in Magenta’s most recent Annual Report on Form 10-K, including any information incorporated therein by reference, as filed with the SEC. Additional information regarding these persons and their interests in the transaction will be included in the proxy statement/prospectus relating to the Proposed Transaction when it is filed with the SEC. These documents can be obtained free of charge from the sources indicated above.

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Peg Rusconi, Verge Scientific Communications
prusconi@vergescientific.com

Magenta Contact

Investor@magentatx.com

Study of lead program will provide proof-of-concept to enable further clinical development in severe autoimmune diseases; full cohort data available in 2H’23

DNTH103 is a next-generation monoclonal antibody that selectively targets only the active form of the C1s protein in the classical complement pathway

DNTH103 designed as an infrequent and convenient subcutaneous injection to improve upon high dose volume and frequency of currently available complement pathway inhibitors

New York City and Waltham, Mass., November 30, 2022 – Dianthus Therapeutics, a biotechnology company dedicated to advancing the next generation of antibody complement therapeutics, today announced that the first healthy volunteers have been dosed in a Phase 1 clinical trial of its lead monoclonal antibody, DNTH103.

“Today marks a pivotal milestone for Dianthus as we transition into a clinical stage company,” said Marino Garcia, President and Chief Executive Officer, Dianthus Therapeutics. “Data from this Phase 1 study will provide important information about the safety, tolerability, pharmacokinetics and pharmacodynamics of DNTH103 in healthy adult volunteers across single and multiple ascending dose cohorts, demonstrating potential proof-of-concept to advance DNTH103 into severe autoimmune diseases where other modalities have not fully addressed the unmet medical need.”

DNTH103 is a selective inhibitor of the active C1s protein in the complement system’s classical pathway. Classical pathway activity is implicated in driving morbidity in a range of autoimmune disorders. Unlike therapies that broadly inhibit the complement system, selective inhibition of the classical pathway preserves immune activity of the lectin and alternative complement pathways against bacterial infections.

“All currently approved complement antibody therapies indiscriminately bind to both active and inactive complement proteins – meaning a large, sometimes frequent dose must be administered while a significant portion of the drug acts unnecessarily on inert proteins,” said Simrat Randhawa, M.D., Chief Medical Officer, Dianthus Therapeutics. “DNTH103 selectively targets the active form of C1s – allowing more of the drug to have a therapeutic effect so we can potentially reduce dose volume and frequency of administration. In addition, by leaving the lectin and alternative pathways intact, the risk of infection from encapsulated bacteria is lower for DNTH103 versus commonly used C5 and C3 inhibitors.”

About Dianthus Therapeutics

Dianthus Therapeutics is a clinical-stage biotechnology company dedicated to designing and delivering novel, best-in-class monoclonal antibodies with improved selectivity and potency over existing complement therapies. Based in New York City and Waltham, Mass. Dianthus is comprised of an expert team of biotech and pharma executives who are leading the next generation of antibody complement therapeutics to deliver transformative medicines for patients with severe autoimmune diseases. Dianthus raised a $100M Series A in April 2022 co-led by 5AM Ventures, Avidity Partners, and Fidelity Management & Research Company, with participation from additional investors including Wedbush Healthcare Partners and founding investors Fairmount, Tellus BioVentures, and Venrock Healthcare Capital Partners. To learn more, please visit www.dianthustx.com and follow us on Twitter and LinkedIn.

Media Contact

Amanda Sellers, Verge Scientific Communications

asellers@vergescientific.com

Lead program DNTH103 to be accelerated to the clinic this year as a highly differentiated and potent monoclonal antibody designed to selectively target the active form of complement C1s

Led by biotech veterans Marino Garcia as Chief Executive Officer and Lonnie Moulder as Chairman of the Board

Financing co-led by 5AM Ventures, Avidity Partners, and Fidelity Management & Research Company with strong investor syndicate

Waltham, Mass. and New York City, May 3, 2022 – Dianthus Therapeutics, a biotechnology company dedicated to advancing the next generation of antibody complement therapeutics, today announced the completion of its $100 million Series A financing led by 5AM Ventures, Avidity Partners, and Fidelity Management & Research Company, with participation from additional investors including Wedbush Healthcare Partners and founding investors Fairmount, Tellus BioVentures, and Venrock Healthcare Capital Partners. The financing will be used to expand leadership and scientific teams, advance the company’s lead program, DNTH103, to the clinic this year, and to accelerate additional discovery pipeline programs for people living with severe and rare autoimmune diseases. DNTH103 is a potent, next-generation monoclonal antibody that selectively targets the active form of complement C1s, potentially enabling a lower dosing volume and a less frequent subcutaneous administration that is further enhanced with half-life extension technology.

Dianthus also announced the appointment of Marino Garcia as President and Chief Executive Officer, joining in November 2021, and Simrat Randhawa, M.D., M.B.A., as Chief Medical Officer. Mr. Garcia, a veteran dealmaker and strategist, brings more than 25 years of industry experience in business development and operational leadership roles at top biotech and pharma companies, most recently as Senior Vice President, Corporate and Business Development at Zealand Pharma. Dr. Randhawa brings over 20 years of clinical practice and pharmaceutical industry experience to Dianthus, including senior leadership roles focused in the autoimmune and rare disease spaces. He most recently served as Senior Vice President of Clinical and Medical Affairs at Aurinia Pharmaceuticals.

“We are committed to improving the lives of people living with severe and rare autoimmune diseases and are confident that our selective antibodies have the potential to be best-in-class therapeutics,” said Marino Garcia, President and Chief Executive Officer, Dianthus Therapeutics. “We are privileged to have a strong syndicate of leading biotech investors, experienced Board members, and accomplished leaders and scientists as we advance our lead candidate into the clinic later this year, further develop our discovery pipeline, and expand our team in the coming months. Dianthus is positioned to become a leading, next-generation complement company guided by a deep understanding of the needs of patients.”

Dianthus harnesses the power of selectivity in complement pathways to create potent monoclonal antibodies with the potential to overcome the limitations of current complement therapeutics. Unlike current antibody therapies that bind to both inactive and active complement proteins, DNTH103 selectively targets only the active form of the C1s complement protein, enabling a lower dosing volume and less frequent administration. Its half-life extension technology also further reduces dosing frequency. With these differentiated attributes and high potency inhibition of C1s, DNTH103 is designed to relieve the burden of high-volume, frequent administration with IV infusions or inconvenient, frequent subcutaneous dosing. Accelerating the development of a more convenient subcutaneous therapy could be transformative in expanding the potential patient populations that could benefit from complement therapies, while reducing the discomfort and disruptions that pervade the lives of patients today – ultimately allowing more patients to live healthier lives to their fullest potential.

“We are proud to support Dianthus Therapeutics in advancing the discovery and development of next-generation, potent, and highly differentiated antibody complement therapeutics,” said Paula Soteropoulos, Board Director of Dianthus and Strategic Advisor to 5AM Ventures. “With the leadership of the recently appointed President and CEO Marino Garcia, and a talented team of seasoned biotech executives and entrepreneurs who hold an extensive track record of success, we look forward to seeing Dianthus bring their novel therapies to patients living with severe and rare autoimmune diseases.”

Dianthus is currently led by an accomplished team of veteran scientists and biotech entrepreneurs, including:

• Marino Garcia, President and Chief Executive Officer
• Simrat Randhawa, M.D.,Chief Medical Officer
• Evan Thompson, Ph.D.,Chief Operating Officer
• Edward Carr,Chief Accounting Officer
• Rivka Gluck,Senior Vice President, Head of Clinical Operations
• Robert McGarr, Ph.D.,Vice President, Program & Alliance Management
• Kristina Maximenko,Head of Human Resources

Dianthus is also supported by an experienced Board of Directors, including:

• Lonnie Moulder, Chairman of the Board at Dianthus, Founder and Managing Member of Tellus BioVentures
• Paula Soteropoulos, Chairman of the Board at Ensoma and former CEO of Akcea Therapeutics
• Lei Meng, Senior Therapeutics Analyst, Avidity Partners
• Tomas Kiselak, Managing Member of Fairmount
• Jonathan Violin, Ph.D.,Co-founder and Chief Executive Officer of Viridian Therapeutics
• Marino Garcia, President and Chief Executive Officer, Dianthus Therapeutics

Jefferies LLC served as financial advisor to Dianthus.

About Dianthus Therapeutics

Dianthus Therapeutics is a biotechnology company dedicated to designing and delivering novel, best-in-class monoclonal antibodies with improved selectivity and potency over existing complement therapies. Based in Waltham, Mass. and New York City, Dianthus is comprised of an expert team of biotech and pharma executives who are leading the next generation of antibody complement therapeutics to deliver transformative medicines for patients with severe and rare autoimmune diseases. To learn more, please visit www.dianthustx.com.

Media Contact

Amanda Sellers, Verge Scientific Communications
asellers@vergescientific.com