What Replay does

Replay is a San Diego–based gene therapy platform company founded in July 2022 that develops engineered herpes simplex virus (HSV) viral vectors capable of delivering genetic payloads up to approximately 150 kilobases — roughly 30 times the cargo capacity of adeno-associated virus (AAV) vectors, which are limited to about 5 kb. The company was built to address the roughly 83% of human genes that are too large to fit inside AAV, the dominant delivery vehicle in approved gene therapies. Its core technology is a high-payload HSV delivery platform, and its lead drug candidate is a preclinical topical HSV-based gene therapy gel that delivers a healthy COL7A1 gene into skin cells to treat Dystrophic Epidermolysis Bullosa (DEB), a rare genetic skin disorder. At launch, Replay also framed itself more broadly as a "genome writing company" spanning three platform pillars: viral delivery vectors, cell sources, and gene synthesis platforms.

The company's commercialization model was an enterprise out-licensing / M&A motion rather than independent product commercialization. Replay launched in July 2022 with a $55 million seed financing led by KKR and OMX Ventures (with participation from Artis Ventures, Axial VC, DeciBio Ventures, Lansdowne Partners, and Salt Ventures), and operated with a lean team of approximately 12 named members covering R&D, gene therapy, CMC, legal, and finance. In May 2026, the Danish dermatology-focused pharmaceutical company LEO Pharma signed a definitive agreement to acquire Replay for $50 million upfront plus potential milestone payments and tiered royalties, integrating the HSV platform and the preclinical DEB program into LEO Pharma's rare dermatology pipeline. The company was led by CEO and co-founder Lachlan MacKinnon (formerly of Oxford Science Enterprises) and Executive Chairman Robert Coffin, the inventor of T-VEC (Imlygic) and former Replimune CEO, with co-founder Adrian Woolfson providing scientific leadership.

Name

Replay

Legal name

Replay Holdings, Inc.

Website

https://replay.bio

Company type

Private

Founded year

2022

Operating status

Acquired

Headcount range

11–50 employees

Short description

Replay is a San Diego gene therapy company developing engineered herpes simplex virus (HSV) vectors that deliver genetic payloads up to ~150 kb — roughly 30x AAV capacity — to treat rare genetic diseases. Its preclinical lead program is a topical gene therapy for Dystrophic Epidermolysis Bullosa, and the company was acquired by LEO Pharma in May 2026.

Ownership category

akta.pro rank

Product category

Gene Therapy Platform

NAICS

Research and Development in Biotechnology (except Nanobiotechnology) (541714), Scientific Research and Development Services (5417)

SIC

Biological Products, (No Disgnostic Substances) (2836)

akta.pro primary industry

Gene Therapy for Rare/Monogenic Diseases (HLAAACAE)

akta.pro secondary industries

Gene Therapy CMC/Process Development Platforms (capsid engineering, producer cell lines, plasmids, upstream/downstream) (HLAAACAN), Gene Therapy Delivery Devices & Administration Systems (catheters, intrathecal, ocular delivery) (HLAAACAL), Vaccine Technology Platforms (mRNA, viral vector, protein subunit, inactivated/live-attenuated, VLP, DNA) (HLAAAEAD), Lentiviral Vector Gene Therapy Developers (HLAAACAB)

Keywords

• Gene therapy platforms
• Viral vector delivery
• HSV-based therapeutics
• Rare genetic diseases
• Genome writing

Headquarters

HQ city

San Diego

HQ country

United States

HQ region

North America

Offices1 record

Markets served

GTM type

B2B

Offering type

Services

Cost components

Personnel, Technology or R&D, Operations, Supply Chain, Marketing or Sales, Others

Revenue model

1. Acquisition upfront and milestone payments: Replay's commercial outcome was a corporate acquisition by LEO Pharma for $50 million upfront plus undisclosed future milestone payments and single-digit (tiered) royalties on future products arising from the HSV gene therapy platform.
2. Seed equity financing: Pre-acquisition funding of $55 million in seed funding led by KKR and OMX Ventures when Replay launched as a genome writing company. This represented equity capital rather than operating revenue.

Go-to-market motion2 records

Distribution channels1 record

Marketing channels3 records

Core offering

Replay develops a high-payload herpes simplex virus (HSV) viral vector platform for gene therapy, capable of delivering genetic payloads up to 150kb (roughly 30x the capacity of AAV vectors), addressing the approximately 83% of human genes too large for conventional AAV-based delivery. The company's lead preclinical program is a topical HSV gene therapy gel delivering the COL7A1 gene to treat dystrophic epidermolysis bullosa (DEB), and the broader platform encompasses delivery vectors, cell sources, and gene synthesis technologies for rare genetic disease therapeutics.

Product overview

Replay's offering is a single unified platform-plus-program architecture: the company is built around an HSV (herpes simplex virus) viral vector gene-therapy platform that addresses the ~83% of human genes too large for AAV, and against which a specific lead preclinical program — a topical HSV gene-therapy gel delivering COL7A1 for dystrophic epidermolysis bullosa (DEB) — has been advanced. The HSV Gene Therapy Platform is the core technology, while the DEB program is the lead clinical-stage asset, and the broader Genome Writing Platform (encompassing delivery vectors, cell sources, and gene synthesis) represents the underlying platform suite announced at company launch. The DEB program and the HSV platform together are what was acquired by LEO Pharma in May 2026 for $50 million upfront plus milestones and royalties.

Differentiator

Problem solved

Functional benefit

Products and services

• HSV Gene Therapy Platform Replay's core viral gene therapy platform uses engineered herpes simplex virus (HSV) vectors to deliver large genetic payloads (up to ~150 kb, roughly 30x the capacity of AAV at ~5 kb) into cells, addressing the ~83% of human genes that are too large to fit inside AAV vectors and enabling treatment of rare genetic diseases out of reach for conventional AAV gene therapy.
• HSV-based topical gene therapy for Dystrophic Epidermolysis Bullosa (DEB) Preclinical topical HSV-based gene therapy gel that delivers a healthy COL7A1 gene into skin cells to treat dystrophic epidermolysis bullosa (DEB), a rare genetic skin disorder causing extremely fragile skin and persistent wounds. The program was advanced through preclinical evaluation and was the lead asset underpinning LEO Pharma's acquisition of Replay.
• Genome Writing Platform (delivery vectors, cell sources, gene synthesis) At launch, Replay positioned itself as a "genome writing company" built around three platform technologies: viral delivery vectors, cell sources, and gene synthesis platforms, framed as the foundation for tackling genomic-medicine challenges beyond what existing gene-therapy delivery systems (e.g., AAV) can address.

Named customers1 record

Technology focussed Yes

API detail

Has API

No

API docs

API detail

Core technology

AI maturity

App detail

Feature3 records

Partnerships

Two partnerships are on record, tiered flagship / core acquirer and ad-hoc / deal-specific.

• LEO Pharmaflagship / core acquirerStrategic or Co-development PartnerLEO Pharma entered into a definitive agreement to acquire Replay, a gene therapy company developing treatments for rare genetic dermatological conditions. Replay equity holders receive $50 million upfront plus potential milestone payments and tiered royalties. The deal adds Replay's high-payload herpes simplex virus (HSV) delivery vector platform and preclinical DEB gene therapy program to LEO Pharma's dermatology pipeline.
• Latham & Watkins LLPad-hoc / deal-specificImplementation/ SI/ Consulting PartnerLatham & Watkins LLP served as legal counsel to LEO Pharma on the cross-border acquisition of Replay's gene therapy platform. The firm is referenced as deal counsel rather than an ongoing strategic partner.

Scale indicators6 records

Recent moves5 records

Expansion highlights4 records

Direct peers

• Replimune Group: Replimune is the most directly comparable peer — it develops oncolytic and gene therapy programs using engineered HSV vectors, was co-founded and led as CEO by Robert Coffin (now Replay's Executive Chairman), and advances multiple RPx HSV programs through clinical trials; the two companies share platform technology, executive DNA, and HSV therapeutic category.
• Krystal Biotech: Krystal Biotech developed and commercialized Vyjuvek, the FDA-approved topical gene therapy for dystrophic epidermolysis bullosa (DEB) — the exact indication Replay's lead program targets — and is a former employer of Replay's VP of CMC; it represents the most direct competitive peer for Replay's DEB program and shares the topical gene therapy approach.
• Abeona Therapeutics: Abeona Therapeutics developed EB-101, an autologous gene-corrected cell therapy for recessive dystrophic epidermolysis bullosa (R-DEB), directly competing in the DEB treatment space with Replay's COL7A1 program and sharing the rare dermatology gene therapy focus.

Emerging players

• Castle Creek Biosciences: Castle Creek Biosciences develops gene and cell therapies for rare dermatological conditions including epidermolysis bullosa, making it a direct clinical competitor to Replay's DEB program in the rare skin genetic disease space.
• Poseida Therapeutics: Poseida Therapeutics develops non-viral and viral vector gene therapies and cell therapies (CAR-T, iPSC-based) for rare diseases and oncology; it is a former employer of Replay's VP of Gene Therapy and shares the rare disease gene therapy development focus as an emerging player with overlapping platform science.
• Taysha Gene Therapies: Taysha Gene Therapies is a clinical-stage gene therapy company focused on AAV-based treatments for rare monogenic diseases of the central nervous system; it is an emerging peer with comparable rare genetic disease targeting and viral vector platform approach, though focused on CNS rather than dermatology indications.

Broad incumbents

• BioMarin Pharmaceutical: BioMarin is an established rare disease biotech with multiple approved gene therapies (e.g., Roctavian for hemophilia A) and a broad pipeline addressing genetic conditions that AAV and other viral vector platforms can target — overlapping with Replay's rare genetic disease focus as a larger, capitalized incumbent.
• uniQure: uniQure is a clinical-stage gene therapy company using AAV-based vectors for rare diseases including hemophilia and Huntington's disease; it represents a broader incumbent gene therapy platform peer with comparable target patient populations and regulatory pathway experience to Replay.
• Regenxbio: Regenxbio is an established gene therapy platform company developing AAV-based therapeutics for rare diseases and licensing its NAV technology platform to multiple partners; it is broadly comparable to Replay as a viral vector gene therapy platform company targeting rare genetic conditions.
• Sarepta Therapeutics: Sarepta Therapeutics is a leading gene therapy company with multiple approved and clinical-stage AAV-based treatments for rare neuromuscular diseases (e.g., Elevidys for Duchenne muscular dystrophy); it is a broad incumbent peer in gene therapy for rare genetic diseases using viral vector delivery.

Market position

Strengths5 records

Weaknesses5 records

Competitive moat3 records

Key highlights7 records

Customer concentration

• Xx.com/replaybio

Compliance1 record

Revenue estimate

Valuation estimate

Number of profiles

Funding overview

Funding rounds3 records

Investors7 records

Funding detail is available on the Subscription and Enterprise plan.Contact sales →

M&A

Investments

M&A and investment is available on the Subscription and Enterprise plan.Contact sales →

Frequently asked questions about Replay