Legend Biotech is seeking an Principal Scientist, Vector Biology as part of the Vector Biology Upstream team based in Philadelphia, PA.

Role Overview

Legend Biotech seeks a highly experienced and scientifically driven Principal Scientist to join the Vector Biology Upstream team in Philadelphia, with a strategic focus on early process development and the establishment of a manufacturable lentiviral vector (LVV) platform in support of in-vivo CAR-T programs. This senior individual contributor role will serve as a scientific cornerstone within R&D, leading the early-stage definition, interrogation, and optimization of upstream LVV processes from molecular construct design through scalable bioreactor manufacturing with the deliberate intent of building a robust, developable process foundation that can be advanced into late-stage development and commercialization. The Principal Scientist will bring a rare combination of molecular biology depth and bioprocess engineering breadth, functioning as a key technical authority who bridges construct-level design decisions with upstream process outcomes, while closely interfacing with Downstream, Analytical, and Technical Development partners to ensure end-to-end process coherence and readiness for technology transfer.

Key Responsibilities

• Establish and optimize early-stage seed train strategies from shake flask through bench-scale bioreactor, defining the foundational process parameters, cell culture conditions, and operational ranges that will underpin a scalable and manufacturable LVV platform.
• Apply molecular biology expertise to evaluate LVV constructs encompassing plasmid architecture, packaging system selection, promoter and transgene configuration, and transfer vector optimization to establish high-performing, platform-compatible vectors that meet manufacturability and potency requirements for in-vivo CAR-T applications.
• Design and optimize LVV production workflows, including transient transfection systems and emerging stable producer cell line platforms, to systematically improve vector yield, product quality attributes, and process robustness as part of an integrated early process development strategy.
• Conduct systematic media optimization, feeding strategy evaluation, and bioreactor process control development to define process setpoints, identify critical process parameters (CPPs), and establish the mechanistic understanding needed to support scale-up to 40-L and beyond.
• Partner closely with Downstream colleagues to understand purification process constraints and integrate upstream design decisions including harvest conditions, clarification approaches, and vector quality attributes that enable a cohesive, end-to-end manufacturable process. 
• Design and execute fit-for-purpose early process development studies to generate the foundational data packages required for process lock, comparability assessments, and downstream regulatory filings; apply structured Design of Experiments (DoE) and risk-based approaches to maximize information yield.
• Serve as the upstream scientific lead within Vector Biology, providing authoritative technical input to cross-functional forums on construct-process relationships, early development strategy, and the stage-appropriate advancement of research findings into formal process development programs aligned with IND-enabling timelines.
• Exercise a high degree of scientific independence in designing and executing complex experiments; proactively identify technical risks, generate mechanistic hypotheses, and implement data-driven solutions with minimal oversight to keep early development programs on track.
• Synthesize complex experimental datasets into clear, structured data packages and deliver evidence-based technical recommendations that drive go/no-go decisions, inform process development strategy, and support program progression within Vector Biology and across R&D functional teams.
• Author high-caliber technical reports, early process development summaries, and stage-gate presentations that communicate scientific progress, key process decisions, and development risk assessments to Vector Biology leadership and cross-functional R&D stakeholders.
• Operate in full adherence to BSL-2 biosafety requirements and Legend Biotech’s research policies; maintain rigorous, contemporaneous electronic laboratory notebook records that meet scientific reproducibility standards and support future transition into GxP-aligned development stages.
• Champion experimental reproducibility and data integrity through rigorous, organized documentation practices that meet the highest standards of scientific rigor and regulatory traceability.
• Apply molecular biology expertise to design, engineer, and evaluate LVV constructs encompassing plasmid architecture, packaging system selection, promoter and transgene configuration, and transfer vector optimization to establish high-performing, platform-compatible vectors that meet manufacturability and potency requirements for in-vivo CAR-T applications.

Requirements

• MS degree with 10+ years; or PhD degree with ~5-8+ years of progressive industry experience in Bioengineering, Cell Biology and Chemical Engineering, or a closely related discipline. Advanced degree (PhD) with a molecular biology or virology foundation is preferred for this Principal Scientist role in early process development.
• Demonstrated hands-on expertise in viral vector production, upstream process development, and characterization across multiple development scales, with a clear track record of translating early research-stage processes toward manufacturable, scalable platforms (required).
• Substantial experience in mammalian suspension cell culture and upstream bioprocessing, with meaningful exposure to molecular biology workflows relevant to viral vector construct engineering.
• Experience with bioreactor operations (up to 50 L preferred) and familiarity with downstream processing operations including clarification, chromatographic purification, and tangential flow filtration with the ability to apply downstream process constraints to upstream design decisions is a strong differentiator. 
• Meaningful early process development experience within gene therapy or viral vector platforms, with direct hands-on contribution to defining manufacturable upstream processes from concept through bioreactor scale.
• Exceptional analytical acumen and structured scientific reasoning; experienced in the application of Design of Experiments (DoE), multivariate data analysis, and risk-based decision frameworks to accelerate early process development and maximize learning efficiency.
• Demonstrated commitment to scientific rigor and research data integrity, with proficiency in maintaining meticulous, contemporaneous electronic laboratory notebook records that ensure experimental reproducibility and are structured to support future GxP-aligned technology transfer activities.
• Highly organized and execution-oriented, with demonstrated capacity to manage multiple concurrent early development workstreams, prioritize effectively in a fast-paced R&D environment, and deliver scientifically sound results within program-driven timelines.
• Exemplary oral and written communication skills, with the ability to translate complex early process development findings into compelling scientific narratives for diverse audiences including R&D leadership, CMC colleagues, and cross-functional program teams while operating with equal effectiveness as a self-directed scientific contributor and an engaged collaborative partner
• Proficiency in molecular biology techniques central to viral vector construct design, including plasmid architecture and engineering, packaging system configuration, promoter selection and regulatory element optimization, transgene design, and transfer vector development to support LVV platform optimization (preferred).
• Working knowledge of downstream processing operations —encompassing harvest and clarification strategies, affinity and ion-exchange chromatography, and tangential flow filtration — with the scientific acuity to incorporate purification process requirements and vector quality attribute targets into upstream process design; experience in integrated upstream-downstream process development is preferred.

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About the Role:

We are looking for experienced Mid-level (Full Stack, Backend, Frontend) Engineers passionate about building an excellent user experience up and down the layers of an application. The ideal candidate has contributed to features on at least one sizable production application using modern frameworks within the past year. An experienced Mid-level Engineer at Perpay will spend their time writing code, reviewing PRs, and helping scope & design new features. We value Engineers who demonstrate excitement around solving tough problems and delivering solutions in a fast-paced environment.

We aim for our Engineering team to be a place that Mid-level Engineers can push our quick-growing startup forward, and grow into future Senior Engineers and Engineering leaders. The significant projects and initiatives available to our Mid-level Engineers provide opportunities to expand experience, ownership, and business value.

Much of our team is full stack, so we look for team members excited to learn new technologies and work across all stacks, even if it’s not something you’ve done before! Our tech stack: Javascript, Typscript, React, React Native, Python, Django, Flask, Kubernetes, AWS, Docker and more.

Our greatest strength is our people and we’d love for you to be one of them!

Responsibilities:

• Collaborate closely with the development team, including UX designers, product managers, and other Engineers, to implement solutions that meet business needs and provide the best user experience
• Work with stakeholders to design, build, test, and release new features for our platform
• Write clean, efficient, and maintainable code. Break down code contributions into reviewable, shippable chunks
• Contribute to the Engineering design process by bringing forward tradeoffs and opinions
• Identify opportunities to reduce technical debt and implement changes to improve developer experience and team velocity
• Participate independently in on-call rotation and coordinate incident response

What You’ll Bring:

• Minimum of 2 years experience as a Software Engineer (excluding internships or coop experiences) with a focus on full stack development
• Strong proficiency in at least one backend application framework such as Django or Flask and experience with frontend technologies such as React, Angular, or Vue.js
• Proven experience building, deploying and maintaining scalable web applications, with knowledge of database design and management
• Knowledge of RESTful API design and integration
• Experience working with cloud infrastructure and containerization technologies such as AWS, Docker, and Kubernetes is preferred
• Passion for learning new technologies and keeping up with industry trends
• Ability to collaborate with cross-functional teams, including UX designers, product managers, and other Engineers
• Strong communication skills and ability to articulate technical concepts to non-technical stakeholders

Hey, we know not everybody checks all the boxes, so if you’re interested, please apply because you could be just what we’re looking for!

About the Role:

We are looking for senior backend engineers passionate about backend technology, excellent user experience and system reliability. The ideal candidate has helped lead the technical design and implementation of backend features on at least one sizable production application within the past year. A senior backend engineer at Perpay will spend their time writing code, reviewing PRs, mentoring engineers, and helping scope & design new features. We are looking for people who can bring backend technical expertise to push our technology forward — whether it’s hosting a lunch-and-learn on a new backend technology or directing a large refactor. We value engineers who demonstrate excitement around solving tough problems and delivering solutions in a fast-paced environment.

Much of our team is fullstack, so we look for team members excited to learn new technologies and work across all stacks, even if it’s not something you’ve done before! Our tech stack: Javascript, React, React Native, Redux, Python, Django, Flask, Kubernetes, AWS, Docker and more.

Our greatest strength is our people and we’d love for you to be one of them!

Responsibilities:

• Design and evolve RESTful APIs used by our frontend and internal systems
• Own data modeling decisions across our relational databases with an eye toward performance and maintainability
• Improve reliability, observability, and operational excellence of our backend systems (metrics, logging, tracing, alerting)
• Participate in architectural decisions around service boundaries, asynchronous workflows, and distributed system tradeoffs
• Diagnose and resolve production issues across multiple services
• Contribute to infrastructure-as-code and CI/CD improvements to increase developer velocity and system stability
• Partner with product and stakeholders to translate complex business rules into maintainable backend systems

What You’ll Bring

• 5+ years of experience building web applications at scale in at least one modern language / framework (e.g. Python/Django, Rails, etc.)
• 2+ years of experience leading technical teams and large, complex projects
• Deep understanding of relational databases (e.g., Postgres), query optimization, indexing strategies, and schema evolution
• Experience operating production systems in a large cloud provider (e.g. AWS)Familiarity with containerized environments (Docker) and orchestration systems (Kubernetes)
• Experience with background job systems and message queues (e.g. Celery)
• Working knowledge of caching strategies (e.g. Redis)
• Experience with monitoring/observability tooling (e.g. Datadog, CloudWatch)
• Strong understanding of system reliability, failure modes, and operational tradeoffs
• Ability to communicate complex system behavior clearly to non-technical stakeholders
• A solutions-oriented mindset, willing to step outside your primary domain to unblock teammates and ensure successful delivery

NYC-level total cash-comp (base $160k into the $200’s, plus equity and a discretionary cash bonus)

We know not everybody checks all the boxes, so if you’re interested, please apply because you could be just what we’re looking for!

About the Role:

We are looking for senior frontend engineers passionate about frontend technology and excellent user experience. The ideal candidate has helped lead the technical design and implementation of frontend features on at least one sizable production application within the past year. A senior frontend engineer at Perpay will spend their time writing code, reviewing PRs, mentoring engineers, and helping scope & design new features. We are looking for people who can bring frontend technical expertise to push our technology forward — whether it’s hosting a lunch-and-learn on a new frontend technology or directing a large refactor. We value engineers who demonstrate excitement around solving tough problems and delivering solutions in a fast-paced environment.

Much of our team is fullstack, so we look for team members excited to learn new technologies and work across all stacks, even if it’s not something you’ve done before! Our tech stack: Javascript, React, React Native, Redux, Python, Django, Flask, Kubernetes, AWS, Docker and more.

Our greatest strength is our people and we’d love for you to be one of them!

Responsibilities:

• Collaborate closely and communicate with other members of the development team, including UX designers, product managers, and other engineers, to ensure that the frontend meets the needs of the business and provides an excellent user experience
• Ensure our application is responsive and accessible across different devices and platforms
• Write clean, efficient, and maintainable code
• Contribute to the engineering design process by bringing forward tradeoffs and opinions on how to weigh them
• Leverage continued research around the changing frontend landscape to bring best practices and innovation to our code, developer experience, and user experience

What You’ll Bring:

• 5+ years of experience delivering commercial products to market
• 2+ years of experience leading technical teams and large, complex projects
• Significant experience with React and the React ecosystem and unidirectional data flow patterns, preferably Redux
• Strong knowledge of JavaScript, including the latest ECMAScript standards
• Understanding of RESTful APIs
• Experience with optimizing web applications for performance and accessibility
• Product focus and a passion for UX/UI design or familiarity with UX/UI principles
• Strong curiosity about industry trends
• Ability to pick up new technologies quickly, with software engineering best practices prioritized over familiarity with specific tools or languages
• History of cross-functional collaboration on mission-critical projects
• Experience with React Native, AWS, Docker, and Kubernetes is nice to have
• Experience standing up a design system is also a nice to have

NYC-level total cash-comp (base $160k into the $200’s, plus equity and a discretionary cash bonus)

We know not everybody checks all the boxes, so if you’re interested, please apply because you could be just what we’re looking for!

About the Role:

We’re searching for an experienced and owner-minded Software Engineer to join Perpay and contribute to our culture of technical excellence. You will lead large-scale projects from start-to-finish, working across multiple teams (analytics, commerce, product, design, operations) while providing guidance to junior-level engineers. As we’re a growing engineering team, you’ll also have the opportunity to make an impact on our tech and our team. Given our people-first approach, your elevated level of contribution will strengthen our culture of inclusion, mentorship, and continuous learning.

As a leader of Perpay’s engineering team, you’ll collaborate with stakeholders ranging from entry-level contributors to senior-level executives. This opportunity is both unique and pivotal, as it offers the chance to provide leadership to a rapidly growing team. Our tech stack: Typescript, Javascript, React, Redux, Python, Django, Flask, Kubernetes, AWS, Docker and more

Our greatest strength is our people and we’d love for you to be one of them!

We highly value product-mindset, experience building production web apps for real users, and ability to coach and support junior engineers. An ownership mentality is a must, along with empathy and low ego. We’re building to win, and are eager to find more team members to help us get there.

You Will:

• Be a leader our team looks to as a model of execution, accountability, and technical expertise
• Lead the implementation of large scale features for our customers and our internal finance, operations, and risk teams
• Develop technical requirements alongside our Product team
• Solve problems that span multiple interconnected systems with distributed architectures and scaling systems
• Execute on the full lifecycle of new features with fellow engineers
• Continue to improve how we build, test, and deliver software

What You’ll Bring

• 5+ years of experience building web applications at scale in at least one modern language / framework (Python/Django, React/Typescript, Rails, etc.)
• 2+ years of experience leading technical teams and large, complex projects
• Experience working on consumer-facing products and demonstrating empathy for end-users
• Excellent at unblocking yourself and those around you, and an ability to design, analyze, and debug distributed systems and services.
• Significant experience with operating large scale services with AWS, Docker, and/or Kubernetes
• Excellent communication skills, including the ability to explain highly technical subject matter to a nontechnical audience

NYC-level total cash-comp (base $160k into the $200’s, plus equity and a discretionary cash bonus)

We know not everybody checks all the boxes, so if you’re interested, please apply because you could be just what we’re looking for!

About the Role:

As an Intern at Perpay, we want you to grown with us. Your primary responsibilities are going to be collaborating with your team to ship features, learning how to approach your work with a product mindset, and demonstrating the grit that will get you through challenging projects.

We understand the value of mentorship and offer students an opportunity to gain real work experience before graduation. In the 10-12 weeks we’ll be together, you’ll be like any other member of the engineering team working on features within our existing product roadmap. You’ll be contributing to our codebase, test & release features into production, partner with our other teams like product, design, data science & analytics, operations, and other stakeholders to ship new features and products. All while developing the skills to succeed in a fast-paced tech start-up environment and experiencing and contributing to our unique culture.
Our tech stack: Javascript, React, Redux, Python, Django, Flask, Kubernetes, AWS, Docker and more

Our greatest strength is our people and we’d love for you to be one of them!

What You’ll Bring:

• Currently enrolled in or will receive a Bachelor’s or higher in Computer Science, Mathematics, or related technical discipline with an expected graduation date between winter 2026 – summer 2027
• Cumulative GPA of 3.0 or better
• Knowledge and experience with some if not all of our stack
• Ability to pick up new technologies quickly, with software engineering fundamentals being valued more than familiarity with specific tools or languages
• A strong focus on writing and deploying clear, readable, testable code

Bonus:

• Enrolled in a Master’s Degree or advanced technical degree
• Previous work experience in a technical field

Hey, we know not everybody checks all the boxes, so if you’re interested, please apply because you could be just what we’re looking for!

What We’ll Bring For Internship: 

• Hourly compensation
• Espresso bar, full kitchen, weekly catered lunches, snacks, beverages, & everyday lunch essentials
• One of a kind office with comfortable work/lounge spaces and pleasant riverfront setting
• Opportunity to gain experience at one of the fastest-growing financial startups in the country in both e-commerce & fintech working cross functionally.
  

About the Role:

We are looking for motivated graduates to join our Software Engineering team in 2026! You’ll contribute to our codebase, test & release features into production, and collaborate with other teams like product, design, data science, analytics, and operations. The ideal candidate has software development internship experience and is enthusiastic about learning and growing! We're particularly interested in working with candidates excited about joining a mission-driven startup. On our team, you’ll sharpen your skills, learn new tools alongside other new graduates, and learn from experienced engineers. Plus, our team organizes events and social gatherings outside of work hours. We believe having a fun and engaging work environment is essential to fostering a positive company culture and creating a strong foundation for career growth.

Much of our team is fullstack, so we look for team members excited to learn new technologies and work across all stacks, even if it’s not something you’ve done before! Our tech stack: Javascript, React, React Native, Redux, Python, Django, Kubernetes, AWS, Docker, Terraform, and more.

Our greatest strength is our people, and we’d love for you to be one of them!

Responsibilities:

• Develop, test, and release features for our customer-facing and internal platforms alongside the engineering team
• Write clean, efficient, and maintainable code
• Collaborate cross-functionally to develop efficient and user-friendly solutions to support the complex needs of our business
• Actively participate in design reviews, code reviews, and discussions to improve our software architecture and implement efficient processes within our engineering team

What You’ll Bring:

• Currently pursuing a Bachelor’s degree or higher or a recent graduate studying Computer Science, Mathematics, or a related technical field 
• 1 to 2 previous Software Engineering internships with a focus on fullstack software development
• Experience with at least one backend application framework such as Django or Flask
• Experience with frontend technologies such as React, Angular, or Vue.js
• Knowledge of RESTful API design and integration
• Experience with Python or another dynamically typed language
• A strong focus on writing and deploying clear, readable, testable code
• Ability to pick up new technologies quickly, with software engineering fundamentals being valued more than familiarity with specific tools or languages
• Eagerness to learn, grow, and seek feedback from team members
• Strong communication skills

Even if you don't check all the boxes, please apply if interested. You might be exactly what we're looking for!