What ExcepGen does

ExcepGen is a San Francisco-based genetic medicine startup developing the RNAx platform, a nucleic acid therapeutics technology that addresses a core limitation of existing RNA medicines—the excessive innate immune response triggered by RNA and lipid nanoparticles (LNPs). Rather than engineering nucleic acid chemistry or delivery (the focus of prior advances in capping, manufacturing, and non-natural nucleosides), RNAx encodes an mRNA-based "shield" protein that modulates how cells respond to RNA, dampening overactive innate immunity with the goal of producing RNA-based vaccines with tolerability approaching the standard of care. The technology is supported by peer-reviewed research published in PubMed (ID: 40301369).

The company's platform is structured around three parallel vaccine initiatives: self-amplifying mRNA vaccines, trans-amplifying mRNA vaccines, and standard mRNA vaccines. ExcepGen operates as a B2B platform company targeting pharmaceutical and biotechnology partners that seek to improve the tolerability and efficacy of their nucleic acid therapeutic and vaccine pipelines. As a pre-revenue startup with 1-10 employees, the company has no commercial products, no disclosed customers, and no licensing deals; its current activity centers on research, platform development, and scientific publication.

ExcepGen has raised $14 million in cumulative seed funding across multiple rounds, including an early round led by Y Combinator in 2019, a Hydrazine Capital-led round in 2021, and a $4 million extension in August 2023 led by RA Capital Management with ZAKA VC as a co-investor. The 6-person leadership and R&D team is anchored by co-founders Thomas Folliard (CEO) and Barbara Mertins (CSO), with functional leadership across operations, vaccine development, and research. The company is headquartered at 780 Bryant St. in San Francisco.

Name

ExcepGen

Legal name

ExcepGen

Website

https://excepgen.com

Company type

Private

Founded year

2021

Operating status

Operating

Headcount range

1–10 employees

Short description

ExcepGen is a San Francisco-based biotech developing the RNAx platform—an mRNA-encoded shield protein that dampens excessive innate immune responses to improve tolerability of RNA-based vaccines. It targets pharmaceutical and biotech partners across self-amplifying, trans-amplifying, and standard mRNA vaccine programs.

Ownership category

akta.pro rank

Product category

Nucleic Acid Therapeutics Platform

NAICS

Research and Development in Biotechnology (except Nanobiotechnology) (541714)

SIC

Biological Products, (No Disgnostic Substances) (2836)

akta.pro primary industry

Vaccine Technology Platforms (mRNA, viral vector, protein subunit, inactivated/live-attenuated, VLP, DNA) (HLAAAEAD)

akta.pro secondary industries

RNA Therapeutics Platforms & Design (sequence design, target ID/validation, AI/bioinformatics) (HLAAADAG), mRNA Therapeutics (vaccines, protein replacement, immuno-oncology) (HLAAADAA), Protein Engineering & Directed Evolution Platforms (enzyme/therapeutic protein optimization) (HLAAAIAC)

Keywords

• Nucleic acid therapeutics
• MRNA vaccine platform
• RNA-based medicines
• Biotech R&D services
• Innate immune modulation

Headquarters

HQ city

San Francisco

HQ country

United States

HQ region

North America

Offices1 record

Markets served

GTM type

B2B

Offering type

Services

Cost components

Technology or R&D, Personnel, Operations, Infrastructure, Marketing or Sales

Marketing channels2 records

Core offering

ExcepGen develops the RNAx platform, an mRNA-encoded shield protein technology that alters how cells respond to RNA and lipid nanoparticles (LNPs) by dampening overactive innate immune responses. The platform is designed to enable more tolerable RNA-based vaccines and nucleic acid therapeutics, with application across self-amplifying mRNA, trans-amplifying mRNA, and standard mRNA vaccines intended for licensing and partnership with pharmaceutical and biotechnology companies.

Product overview

ExcepGen offers the RNAx Platform, a nucleic acid therapeutics platform designed to improve RNA-based medicines. The platform works by encoding a shield protein that modulates how cells respond to RNA and lipid nanoparticles (LNPs), addressing the excessive innate immune response that limits current nucleic acid therapeutics. The company focuses on three core vaccine initiatives: self-amplifying mRNA vaccines, trans-amplifying mRNA vaccines, and standard mRNA vaccines.

Differentiator

Problem solved

Functional benefit

Brands

• RNAx: ExcepGen's mRNA encoded protein platform that alters the way cells respond to RNA and LNPs by dampening an overactive innate immune response.

Products and services

• RNAx Platform A nucleic acid therapeutics platform that encodes an mRNA-based shield protein to alter cellular response to RNA and lipid nanoparticles (LNPs) by dampening overactive innate immune responses, thereby improving efficacy and tolerability of RNA medicines for pharmaceutical and biotechnology partners.

Quantifiable outcome

• RNA-based vaccines with tolerability close to the standard of care

Segments1 record

Ideal customer profiles1 record

Technology focussed Yes

API detail

Has API

No

API docs

API detail

Core technology

AI maturity

App detail

Feature2 records

Scale indicators2 records

Recent moves4 records

Expansion highlights4 records

Direct peers

• Arcturus Therapeutics: Clinical-stage mRNA medicines company developing self-amplifying and conventional mRNA vaccines with proprietary delivery technology. Directly comparable as an mRNA vaccine platform pursuing improved efficacy and tolerability, though more advanced and better capitalized.
• Replicate Bioscience: Developer of self-amplifying RNA (saRNA) vaccines and therapeutics. Closely comparable to ExcepGen's sa-mRNA initiative and shares the platform-strategy approach of improving RNA medicines through novel molecular engineering.
• Strand Therapeutics: Synthetic biology company developing self-amplifying mRNA therapies for oncology and other diseases. Comparable as an early-stage programmable mRNA platform company focused on extending mRNA therapeutic applications.
• Translate Bio (Sanofi): mRNA therapeutics platform acquired by Sanofi, developed vaccines and therapeutics using lipid nanoparticle delivery. Comparable as a mRNA platform company focused on therapeutic and vaccine applications.

Emerging players

• Laronde (Lilly acquisition): Pioneered endless RNA (eRNA), a circular RNA platform for therapeutic protein expression. Comparable as an early-stage RNA therapeutics platform company seeking to expand the addressable applications of RNA medicines.
• Tessera Therapeutics: Genetic medicine company developing RNA-based gene writing technology. Comparable as an early-stage platform company leveraging novel RNA mechanisms to expand the therapeutic scope of nucleic acid medicines.
• Capstan Therapeutics: In vivo cell engineering company using mRNA-LNP delivery to reprogram immune cells. Comparable as an early-stage biotech applying novel mRNA delivery and cellular-response strategies to expand nucleic acid therapeutic applications.
• Gritstone bio: Clinical-stage biotechnology company developing self-amplifying mRNA vaccines for oncology and infectious disease. Comparable as a platform mRNA vaccine company pursuing improved immune response through novel RNA designs.

Broad incumbents

• Moderna: Dominant commercial-stage mRNA vaccine and therapeutics company with broad pipeline across infectious disease, oncology, and rare diseases. Sets the benchmark for mRNA vaccine tolerability and efficacy that ExcepGen's platform seeks to improve upon.
• BioNTech: Commercial-stage mRNA therapeutics company with leading COVID-19 vaccine franchise and broader pipeline in oncology and infectious disease. Represents the incumbent standard against which ExcepGen's improved-tolerability positioning must compete.

Market position

Strengths5 records

Weaknesses5 records

Competitive moat3 records

Key risks5 records

Key highlights6 records

Customer concentration

Revenue estimate

Valuation estimate

Number of profiles

Profiles6 records

Funding overview

Funding rounds4 records

Investors9 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 ExcepGen