LEO Pharma Acquires Replay's HSV Gene Therapy

Denmark-based LEO Pharma has entered into a definitive agreement to acquire San Diego-based Replay, a private gene therapy company, for USD 50 million upfront plus undisclosed milestone payments and tiered single-digit royalties. The acquisition of gene therapy assets from Replay adds an engineered herpes simplex virus (HSV) delivery platform to LEO Pharma's rare dermatology pipeline, with the lead program targeting dystrophic epidermolysis bullosa (DEB) in preclinical studies.

The transaction is structured as a full corporate acquisition, conveying global rights to Replay's HSV platform and all associated programs. Beyond the USD 50 million upfront payment to Replay's equity holders, the financial terms do not disclose individual milestone triggers or other specifics.

The Replay gene therapy platform is built on engineered HSV vectors, which carry a substantially larger genetic payload than adeno-associated virus (AAV) vectors — a property relevant to skin diseases caused by mutations in large structural genes such as COL7A1, which encodes type VII collagen and is deficient in DEB. The platform is formulated as a topical gel applied directly to affected skin, enabling localized delivery and, according to the company, the capacity for repeat dosing over time due to HSV's natural tropism for epithelial cells. Replay's lead program for dystrophic epidermolysis bullosa treatment remains in preclinical studies; no investigational new drug application filing timeline was disclosed.

The HSV gene therapy rare skin disease space has one validated regulatory precedent. Krystal Biotech's Vyjuvek (beremagene geperpavec), an HSV-1 vector-based topical gel delivering functional COL7A1 to wound sites, received US FDA approval in May 2023 for DEB, establishing the first approved redosable gene therapy and directly validating the delivery modality and disease target that underpin Replay's platform. On the M&A side, Castle Creek Pharmaceutical Holdings previously acquired Fibrocell Science to obtain FCX-007, an autologous cell-based gene therapy also targeting COL7A1 deficiency in recessive DEB, demonstrating acquirer appetite for genetic skin disease therapy assets at various stages of clinical development.

The rare dermatology innovation rationale for LEO Pharma centers on combining Replay's HSV design and manufacturing capabilities with LEO Pharma's existing dermatology commercial infrastructure and regulatory experience. DEB is caused by mutations in COL7A1 and results in severe skin fragility, chronic wound formation, and elevated risk of squamous cell carcinoma; no curative systemic therapy is currently approved beyond Vyjuvek's topical indication. LEO Pharma's acquisition of gene therapy capability at the preclinical stage provides optionality across DEB subtypes and potentially other large-gene dermatological conditions addressable by high-payload HSV vectors.

The genetic skin disease therapy field has seen structured acquisition activity as larger dermatology-focused companies seek to internalize platform technologies rather than rely on licensing arrangements. The full acquisition structure here, rather than an option or co-development agreement, reflects a decision to retain control over manufacturing scale-up and clinical development timing — both of which are operationally complex for topical gene therapy products. Whether the milestone payment structure is weighted toward development or commercial triggers was not disclosed, leaving the total deal value indeterminate from public filings alone.

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