One To Watch

Replay

A San Diego-based gene-therapy biotech using engineered herpes-simplex-virus (HSV) vectors to deliver therapies for rare genetic skin diseases; LEO Pharma announced its acquisition of Replay's gene-therapy arm on 30 April 2026.

Company Overview

Headquarters and Global Presence

Replay is headquartered in San Diego, California, with an additional presence in London, UK, reflecting its international founding footprint. The company's dual-location structure supports both its US biotech ecosystem ties and European investor and partnership relationships.

Founding and History

Replay launched publicly in June 2024, announcing $55 million in seed financing at its inception — an unusually large seed round reflecting strong investor conviction in its HSV-vector gene therapy platform. Shortly after launch, the company spun out Kaleibe, an HSV-based gene therapy company targeting genetic brain disorders, signaling a strategy of building focused subsidiaries around distinct therapeutic applications. Within two years of founding, Replay attracted acquisition interest from LEO Pharma, which agreed to pay $50 million to bring Replay's rare skin disease gene therapy capabilities in-house.

Therapy Areas and Focus

Replay's primary focus is rare genetic dermatological conditions — a space characterized by severe unmet need, limited treatment options, and patient populations underserved by conventional small-molecule or biologic approaches. Genetic skin diseases such as epidermolysis bullosa and related genodermatoses often require correction of large or complex gene defects, making Replay's big DNA delivery capability particularly relevant. Through its spinout Kaleibe, the company also addresses rare genetic brain disorders, extending the HSV-vector gene therapy platform into the central nervous system.

Technology Platforms and Modalities

Replay's core platform is built around HSV-vector gene therapy — the ability to write and deliver large DNA sequences into target cells, going beyond the payload constraints of adeno-associated virus (AAV)-based approaches. The company uses herpes simplex virus (HSV) as a delivery vehicle, a modality capable of carrying significantly larger genetic payloads than AAV, making it well suited to conditions caused by large or multi-exon gene defects. This approach positions Replay in a differentiated segment of the gene therapy landscape, addressing disease targets that have historically been out of reach for smaller-vector platforms.

Key Pipeline and Programs

Replay's lead program is a preclinical gene therapy for a rare genetic skin disease, the specific indication undisclosed at the time of the LEO Pharma acquisition announcement. The program is built on HSV-mediated delivery of large DNA constructs, targeting the underlying genetic cause of the condition rather than symptom management. Through Kaleibe, the HSV gene therapy platform is being extended to rare genetic brain disorders, with that spinout pursuing its own development pathway independently. Replay's product company Syena, announced through a partnership with JURA Bio, is developing T cell receptor NK therapies in oncology, leveraging JURA Bio's VISTA-TCR platform with AI and machine learning to identify targets in cancer — broadening the company's modality base beyond pure gene correction into cell and receptor engineering.

Recent Developments

In June 2024, Replay launched publicly with $55 million in seed financing and simultaneously announced the spinout of Kaleibe to pursue HSV-based gene therapy for genetic brain disorders. A partnership between Replay's product company Syena and JURA Bio was announced to advance T cell receptor NK therapies in cancer, incorporating AI-driven target discovery. In April 2026, LEO Pharma entered into a definitive agreement to acquire Replay for $50 million, with LEO citing Replay's rare genetic skin disease program as a strategic fit for its medical dermatology portfolio.

Key Personnel

Jason Laster serves as Chief Executive Officer of Replay, leading the company since its 2024 launch. Brian Hackett serves as Chief Technology Officer, overseeing the HSV-vector gene therapy and HSV delivery platform that underpins the company's pipeline. Both executives were part of the founding team that secured the $55 million seed round and defined Replay's multi-program strategy at launch.

Strategic Partnerships

Replay's product company Syena has entered into a partnership with JURA Bio to develop T cell receptor NK therapies, applying JURA Bio's VISTA-TCR platform and AI capabilities to cancer target discovery. The April 2026 acquisition agreement with LEO Pharma for $50 million represents the company's most significant strategic transaction, bringing Replay's dermatology gene therapy program into a dedicated global dermatology organization.

FAQ Section

LEO Pharma, a global leader in medical dermatology, agreed to acquire Replay for $50 million in April 2026 to bolster its rare skin disease capabilities with gene therapy. Replay's preclinical program targeting a rare genetic dermatological condition represents a potentially transformative treatment modality that complements LEO's existing biologics and small-molecule portfolio. The deal gives Replay's technology a well-resourced commercial and clinical development home with deep dermatology expertise.

Herpes simplex virus can carry DNA payloads far larger than those accommodated by adeno-associated virus, the most widely used gene therapy vector. Many rare genetic diseases — particularly genodermatoses and neurogenetic conditions — are caused by defects in large genes that exceed AAV's packaging capacity, making HSV a practically necessary alternative. Replay's ability to write and deliver big DNA directly addresses this biological bottleneck, opening therapeutic possibilities that smaller-vector approaches cannot reach.

Replay's HSV-vector gene therapy framing positions it around the ability to construct and deliver large, complex DNA sequences — not merely correct point mutations or deliver small transgenes. This distinguishes the company from AAV-focused peers and from base or prime editing approaches that operate at the single-nucleotide level. The spinout model — creating Kaleibe for neurological applications and Syena for oncology cell therapy — also reflects a platform-first strategy that extracts multiple product lines from a single core technology.

At the time of the LEO Pharma acquisition announcement in April 2026, the lead program was described as preclinical, targeting a rare genetic dermatological condition. The specific indication had not been publicly named, though the program is built on Replay's HSV-mediated large DNA delivery platform. Under LEO Pharma's ownership, the program is expected to advance toward IND-enabling studies and eventual clinical development within LEO's dermatology infrastructure.

Through Kaleibe, Replay's HSV gene therapy platform is being applied to rare genetic brain disorders, representing a significant CNS extension of the core technology. Through Syena, the company has entered oncology via T cell receptor NK therapies developed in partnership with JURA Bio, using AI-driven target discovery. This three-pronged spread — dermatology, neurology, and oncology — reflects Replay's strategy of using a single delivery platform across multiple disease domains.

Replay is an early-stage company, founded and launched in June 2024, with its primary dermatology program at preclinical stage at the time of the LEO Pharma acquisition in 2026. The company moved from a $55 million seed financing to an acquisition within approximately two years — an unusually rapid trajectory reflecting both the platform's strategic appeal and the competitive dermatology M&A environment. Its spinouts Kaleibe and Syena remain in earlier discovery and partnership stages.

Key watchpoints for Replay — now within LEO Pharma's structure — include:

Progression of the lead rare skin disease program from preclinical toward IND filing and Phase I entry under LEO Pharma's development resources.
Clinical and operational momentum at Kaleibe, particularly whether the CNS HSV gene therapy program advances to IND application.
Syena's JURA Bio partnership delivering on AI-driven TCR NK target identification and early oncology data.
Regulatory and safety considerations specific to HSV-based delivery in skin and brain tissues, which remain relatively early in clinical validation.
LEO Pharma's ability to integrate Replay's platform culture and pipeline ambition within a larger, commercially oriented dermatology organization.

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