Letermovir

In a subgroup analysis of people living with HIV enrolled in PRIOH-1, pritelivir demonstrated superior lesion healing, achieving 61% complete lesion healing compared with 20% receiving investigator’s choice therapy (ICT) with an adjusted treatment difference of 37% (p = 0.027) in people living with HIV with refractory HSV infections The results were presented as a late-breaking oral presentation at the Conference on Retroviruses and Opportunistic Infections (CROI), which focuses on key clinical and scientific innovations in human retrovirus-associated diseases like HIV Wuppertal, Germany, February 25, 2026 - Aicuris Anti-infective Cures AG (“Aicuris”) today announced superior efficacy results from a subgroup analysis of its pivotal Phase 3 trial (PRIOH-1) evaluating pritelivir vs. investigator’s choice in people living with HIV with refractory herpes simplex virus (HSV) infection. The results were presented as a late-breaking oral presentation at the Conference on Retroviruses and Opportunistic Infections (CROI) on February 25, 2026, in Denver, USA. People living with HIV face a higher risk of severe, refractory HSV infections due to weakened immunity. HSV-2 also increases HIV acquisition risk, and co-infection can cause aggressive, prolonged, painful lesions and may accelerate HIV progression. Repeated antiviral use for treatment of HSV recurrence increases the risk of resistance, underscoring the urgent need for more effective HSV therapies for this vulnerable population. “Patients living with HIV who develop refractory HSV infections with or without acyclovir resistance often present with prolonged, atypical, and clinically challenging disease courses,” said Professor Jean-Michel Molina, University of Paris Cité, Department of Infectious Diseases, Saint-Louis and Lariboisière Hospitals APHP, Paris France , a principal investigator in the PRIOH-1 study who made the presentation at CROI. “The subgroup analysis from this Phase 3 trial provides important evidence that pritelivir can achieve meaningful lesion healing in this population, using an oral treatment option. These data add an important piece to our understanding of how refractory HSV can be managed in people living with HIV.” In the subgroup, people living with HIV represented 37.6% (38/101) of all immunocompromised patients enrolled in the PRIOH-1 Phase 3 trial and had a mean CD4 cell count of 334.8 cells/mm³. Among these patients, 81.6% (31/38) had refractory HSV (no clinical improvement in HSV lesions after ≥ 7 days of treatment), and 18.4% (7/38) had laboratory-confirmed acyclovir resistance. 40% of the study cohort had another underlying immunosuppressive condition. Similar to other subgroups, pritelivir achieved superior lesion healing of 61% (14/23) within up to 28 days of treatment, compared with 20% (3/15) for ICT, with an adjusted treatment difference of 37%, p = 0.027 [95%CI 7.6, 66.8] (post-hoc analysis). The majority (96%) of people living with HIV completed pritelivir treatment compared with 60% in the investigator’s choice treatment group. “People living with HIV often experience more complex clinical manifestations of HSV, which can make infections particularly difficult to treat,” said Cynthia Wat, CMO of Aicuris . “As an antiviral with a novel mechanism of action, pritelivir has shown efficacy in the treatment of refractory HSV infections with or without resistance (R±R) and may offer an important option for people living with HIV facing severe, refractory HSV disease.” Aicuris announced positive efficacy and favorable safety results for pritelivir at the 2026 Tandem Meetings earlier this month. The global, controlled, open-label comparative trial (PRIOH-1, NCT03073967 / Eudra-CT 2023-510088-37-00 ) included 101 randomized patients and 56 non-randomized patients with R±R HSV infection, including patients living with HIV, hematopoietic stem-cell and solid organ transplant patients, and patients with malignancies, autoimmune or inflammatory disorders. Patients were treated with either oral pritelivir or ICT (IV foscarnet, IV/topical cidofovir, or topical imiquimod). Pritelivir demonstrated a favorable safety and tolerability profile. It was associated with fewer renal, electrolyte events and drug-related TEAE discontinuations (2.0%) compared with ICT (20.0%). The most common TEAEs that occurred while receiving pritelivir were headache (13.7%), diarrhea (11.8%), nausea (7.8%), decreased appetite (7.8%), vomiting (5.9%) and dizziness (5.9%). About Herpes Simplex Virus Herpes Simplex Virus (HSV) includes two types, HSV-1 and HSV-2, both of which cause lifelong infections. HSV-1 most commonly causes labial herpes, typically presenting as cold sores, while HSV-2 is the primary cause of genital herpes. HSV infections are characterized by recurrent, painful lesions and sores and, in severe cases, can lead to complications such as encephalitis, meningitis, disseminated disease, keratitis and neonatal herpes. HSV infections represent a substantial global public health burden. According to the World Health Organization, an estimated 3.8 billion people under the age of 50, or 64% of the global population, were infected with HSV-1 in 2020. 520 million people aged 15 to 49 were living with HSV-2. The disease burden is particularly high in immunocompromised patients, who are at increased risk of more severe, more frequent and treatment-refractory HSV infections. About Pritelivir Pritelivir, a novel helicase-primase inhibitor developed by Aicuris, targets both HSV-1 and HSV-2. These viruses are responsible for genital, oral, or disseminated infections with increasing severity and limited treatment options, particularly in immunocompromised patients where being treatment refractory or resistant to existing antivirals is a significant clinical challenge. Unlike traditional antivirals, pritelivir blocks viral DNA synthesis by inhibiting the helicase-primase complex, a mechanism distinct from marketed nucleoside analogues. Because of this distinct mode of action, pritelivir is active against strains resistant to nucleoside analog and foscarnet based therapies. 1 Earlier clinical trials in immunocompetent and immunocompromised individuals showed a favorable safety pro early signals of clinical efficacy compared to standard of care treatments like valacyclovir and foscarnet. Based on these results, pritelivir was granted FDA Breakthrough Therapy designation. In October 2025, Aicuris announced that pritelivir met its primary endpoint in the pivotal Phase 3 trial. About Aicuris Aicuris is meeting the needs of the growing population of immunocompromised people who require precise therapies to effectively treat infection. Our flagship product, PREVYMIS ® , marketed by our partner MSD, prevents CMV in a defined group of transplant recipients. Our pivotal Phase 3 candidate, pritelivir, aims to address refractory HSV infections in a broad population of patients with weakened immune systems. For immunocompromised people, an otherwise manageable infection can mean life or death. Aicuris, with its expertise and growing pipeline, is committed to providing therapeutic solutions for them now and in the future. Contact: Aicuris Anti-infective Cures AG Email: info@aicuris.com Trophic Communications Dr. Stephanie May and Anja Heuer Phone: +49 171 1855 682 Email: aicuris@trophic.eu 1 Sallée, L. and Boutolleau, D. (2024), Management of Refractory/Resistant Herpes Simplex Virus Infections in Haematopoietic Stem Cell Transplantation Recipients: A Literature Review. Rev Med Virol, 34: e2574. Attachment CROI PR

Advancing Expansion in Severe Infectious Disease and Leveraging Existing Global Infrastructure to Drive Long-Term Growth CHELMSFORD, Mass. & TOKYO--(BUSINESS WIRE)-- Asahi Kasei announced it has entered into a definitive agreement to acquire all issued shares of Aicuris Anti-infective Cures AG, a German-based biopharmaceutical company, for approximately €780 million*. This transaction expands Asahi Kasei’s specialty pharmaceutical platform further into severe infectious diseases and is expected to close in the first quarter of fiscal 2026, subject to customary conditions. Asahi Kasei expects the acquisition to contribute positively to operating income after amortization of goodwill and other intangible assets from fiscal 2028 onward. The acquisition advances Asahi Kasei’s strategy to build a focused, sustainable specialty pharmaceutical platform serving immunocompromised and medically complex patient populations. Severe infectious diseases represent an area where Asahi Kasei already maintains a presence and is strategically adjacent to its established core transplant (Veloxis) and nephrology (Calliditas) subsidiaries, where infection-related complications remain a significant clinical concern. By leveraging its established commercial infrastructure across transplant centers and nephrology providers, together with its advanced R&D capabilities, Asahi Kasei expects to accelerate the development and commercialization of Aicuris’s pipeline while enhancing operating efficiency and long-term earnings. “This acquisition strengthens our position across interconnected therapeutic areas, including autoimmune diseases, transplantation, kidney disease, and severe infectious diseases. It enhances our pipeline and reinforces our strategy to build a leading global specialty pharmaceutical company,” stated Ken Shinomiya, Head of Asahi Kasei’s Healthcare Sector. “Given the strategic alignment of this asset and the opportunity to expand within an area where we already have an established presence, we acted in a nimble and disciplined manner to advance our long-term growth objectives. This transaction accords with our capital allocation framework and supports our objective of achieving net sales of ¥300 billion in Pharmaceuticals with an operating margin of 15% or higher by fiscal 2030.” Consistent with this strategic focus, Aicuris adds three compounds that complement Asahi Kasei’s existing treatment portfolio and expand its presence in infectious diseases: Product / Mechanism Target Indication Key Characteristics Stage (1) Prevymis ® (letermovir) / Cytomegalovirus (CMV) terminase inhibitor Prevention of CMV infection in transplant recipients Royalty income as the originator of the drug Marketed (licensed to Merck & Co., Inc. [known as MSD outside the US and Canada]) (2) Pritelivir / Herpes simplex virus (HSV) helicase-primase inhibitor Treatment of HSV infection in immunocompromised patients Oral drug with a new mechanism of action specifically for HSV Phase III completed (FDA approval targeted for 2026) (3) AIC468 / mRNA splicing inhibitor Treatment of BK Virus (BKV) infection in kidney transplant patients Antisense oligonucleotide (ASO) targeting BKV following kidney transplantation Phase I completed (commercialization targeted for 2030 Pritelivir represents a significant near-term value driver and is being evaluated for the treatment of HSV infection in immunocompromised patients. These patients are commonly seen in transplant centers and specialized hospital settings where Asahi Kasei maintains established commercial relationships and infrastructure. This alignment enables efficient market access and targeted uptake within a defined patient population. AIC468 is in development for the treatment of BK virus (BKV) infection in kidney transplant recipients. This directly intersects with both Asahi Kasei’s transplant franchise and renal-disease network. BKV remains a significant post-transplant complication with limited approved treatment options. By leveraging its established clinical, regulatory, and commercial capabilities, Asahi Kasei is positioned to efficiently advance development and commercialization. The portfolio also enhances Asahi Kasei’s financial profile, combining immediate royalty income from Prevymis ® with near-term commercial upside from pritelivir, for which approval is targeted in fiscal 2026. Together with the longer-term potential of AIC468, the acquisition delivers a layered growth pro supports revenue durability and margin expansion over time. This acquisition represents one of a series of strategic investments and portfolio transformations that are reshaping Asahi Kasei into a more focused enterprise. Asahi Kasei has positioned Pharmaceuticals as a First Priority business under its current medium-term management plan “Trailblaze Together,” and is actively capitalizing on high-growth areas. Through structural transformation and disciplined investment, the company is optimizing its portfolio and accelerating its transition toward a more capital-efficient structure. * Approximately $919 million at exchange rate of $1.178/€ as of February 25, 2026 About Asahi Kasei Asahi Kasei is a diversified global company that contributes to life and living for people around the world. Since its foundation in 1922, with businesses in ammonia and cellulose fiber, Asahi Kasei has consistently grown through proactive portfolio transformation to meet the evolving needs of every age. With 50,000 employees worldwide, the company contributes to sustainability by providing solutions to the world’s challenges across its three business sectors: Healthcare, Homes, and Material. For more information, visit . Contacts North America Contact: Asahi Kasei America Inc. Christian OKeefe christian.okeefe@ak-america.com Europe Contact: Asahi Kasei Europe GmbH Sebastian Schmidt sebastian.schmidt@asahi-kasei.eu