Principal Scientist - HSV‑1 Viral Vector Analytical Development

About Replay, now part of LEO Pharma

Replay Holdings, Inc. ("Replay"), now part of LEO Pharma, is advancing the future of gene therapy for patients with rare disease. Originally built as a preclinical gene therapy company focused on HSV-based vectors for topical dermatology applications, Replay combines the agility of a small, high-impact team with the global reach and patient commitment of LEO Pharma.

Together, we are building the CMC capabilities needed to advance our lead program from pre-clinical development through IND submission and GMP clinical manufacturing. Our platform leverages the large payload capacity of HSV vectors (up to 150 kb) to deliver complex therapeutic genes, with the goal of bringing meaningful new treatment options to patients with high unmet needs.

Your Role

As a Principal Scientist you will be empowered to build an entire Analytical Development and QC function, laying the foundations for robust GMP analytics, and playing a critical role in regulatory submissions, all within a fast-paced and highly collaborative environment. You will directly influence product quality, regulatory readiness, and operational success as we transition from early-stage development to clinical manufacturing.

Reporting into the Vice President of CMC, you’ll be an effective and confident technical contributor with visibility across development and manufacturing functions.

Key responsibilities will include:

Method Qualification & Validation

• Leading development, qualification and validation of analytical methods for GMP release and characterization assays.
• Defining method suitability, system suitability, and acceptance criteria.
• Developing comparability protocols to support process changes, scale-up, and site transfers.
• Establishing analytical control strategies, including CQAs and specifications.

QC System Buildout

• Designing QC systems from scratch, including release panels for drug substance/product, process testing, and raw/excipient testing.
• Implementing stability programs across multiple storage conditions.
• Establishing reference standard programs, environmental monitoring, and equipment qualification plans.

Regulatory & Documentation

• Authoring analytical sections for FDA & EMA IND/CTA submissions.
• Preparing method validation reports, analytical development reports, and method transfer protocols.
• Developing specifications and justification documents for regulatory filings.

CDMO Interface & Method Transfer

• Leading analytical method transfers to CDMO laboratories, ensuring equivalence and integrity.
• Reviewing and approving CDMO QC data packages for lot release.
• Providing on-site analytical support during GMP campaigns.

Team Leadership

• Mentoring junior scientists, fostering career development within AD/QC.
• Prioritising concurrent analytical workstreams across multiple CDMOs.
• Collaborating effectively with process development, formulation, and R&D teams.

What success looks like:

• Analytical Development and QC function and systems are operational, compliant, and delivering timely, high-quality analytical data to support GMP manufacturing.
• Analytical strategies, control systems, and regulatory documentation are robust, enabling smooth IND/CTA submissions and regulatory interactions.
• Effective CDMO partnerships are resulting in seamless analytical method transfers, high data integrity, and on-time lot releases.

Your Qualifications

• Ph.D. in Biochemistry, Molecular Biology, Virology, Analytical Chemistry, or related field; or M.S. with 10+ years of directly relevant industry experience
• Progressive experience in analytical development for viral vector or gene therapy biologics programs
• Proven track record of qualifying and validating analytical methods for IND-enabling programs
• Demonstrated ability to build QC systems and release-testing frameworks - ideally in a small biotech where you established them from the ground up
• Experience authoring analytical sections of IND or CTA submissions for FDA or EMA
• Hands-on expertise with PCR-based (qPCR, ddPCR, RT-qPCR), cell-based (plaque assay, potency assays), and protein-based (ELISA, SDS-PAGE, western blot, SEC, DLS) analytical methods
• People management experience, with the ability to coach, mentor and develop others.

Desirable

• Direct experience with HSV vector analytical characterization and release testing is a major differentiator
• Familiarity with HSV-specific assay challenges (e.g., plaque assay variability, qPCR/ddPCR quantification for large genomes, HCP ELISA for novel producer lines, residual host-cell DNA sizing)
• Experience supporting analytical development for topical gene therapy products, including excipient compatibility testing and formulation-specific stability methods
• Experience supporting CDMO QC method transfer and providing on-site analytical oversight for viral vector programs
• Successful track record in small biotech/start-up environments, establishing new systems and frameworks

Technical Skills

• PCR assay design and validation (qPCR, ddPCR, RT-qPCR)
• Cell-based potency and reporter assay development and standardization
• Protein analytics using ELISA, SDS-PAGE, western blot, SEC-HPLC, DLS
• Impurity and residuals testing, including host-cell DNA quantitation, endotoxin (LAL/rFC), and protein (micro-BCA)
• Management of release testing, stability programs, method lifecycle, and OOS/OOT investigations
• Regulatory writing: method validation to ICH Q2(R2)/Q14, IND/CTA authorship, and generating certificates of analysis

Success in this role requires excellent communication skills to clearly convey complex technical information to diverse audiences. Advanced analytical thinking with data-driven decision making is a must, as is a proactive, collaborative approach to problem-solving.

You are someone you will thrive in a fast-paced, cross-functional environment!

Compensation

The base salary range for this position is $160,000 - $210,000. The base salary range represents the anticipated low and high of the range for this position. Salary will vary based on several factors such as the candidates qualifications, skills, competencies and proficiency for the role. In addition, some positions may include eligibility to earn commissions/bonus based on company and/or individual performance.

Your Application

You do not need to upload a cover letter, but feel free to add a few sentences in your resume on why this position sparked your interest. Please refrain from including a photograph.

Beyond the skin

Become part of Replay and the LEO Pharma partnership, as we go beyond the skin to make a lasting impact. We are the legacy-builders of the future – enabling people to have a better today and tomorrow. Through collaboration and partnerships, we can do much more. 

For certain positions, you may be required to complete a background check conducted by a third party.

Join us and make an impact - Together, we reach far beyond the skin