PDA Letter Article

Seven Key Takeaways from PDA’s Viral Safety for ATMPs Workshop and Virus Conference Events Seven Key Takeaways from PDA’s Viral Safety for ATMPs Workshop and Virus Conference Events

by Alison Armstrong, PhD, Merck KGaA, Andy Bailey, ViruSure, Sean O’ Donnell, PhD, Eli Lily, and Sebastian Teitz, Biopharma Excellence

The advanced therapies medicinal products (ATMPs) class of therapeutics does not only comprise cell and gene therapies, as one familiar with the topic would assume, but also medical devices comprised of animal/human-derived starting materials and other products that are notoriously challenging to produce safely.

In June, PDA Europe hosted two events in the lovely city of Madrid, Spain, with over 200 attendees: the 2023 PDA Viral Safety for ATMPs Workshop and the PDA Virus Conference. While the latter is a recurring and popular subject, according to the PDA’s annual event calendar, the first event revolved around the innovative and unique class of therapeutics involving ATMPs. Together, both events gave deep insights into the current state of pathogen safety for biopharmaceuticals, and they have been, in attendee numbers but also content, one of the most successful events on this topic in PDA’s history, despite numerous competing events that happened around the same time.

Various industry experts, along with current regulators from the European Union (EU) and U.S. FDA, gave different presentations, sharing their knowledge and insights on developments within the arena of virus safety of biopharmaceuticals. Each session culminated with an interactive question and answer period that allowed participants the opportunity to ask and challenge the panel of experts about the topics they presented. Attendees were also afforded the opportunity to speak to different vendors in the exhibition area to learn more about industrial advancements in new methods, innovative tools, and emerging developments in new technologies, equipment, and utilities.

Above all, the events allowed attendees to share their interpretations, challenges, and possible solutions for the implementation of the new revision of ICH Q5A with their peers from the industry. The event was deemed a success based on the high level of interaction and engagement with presenters and the number of questions asked during the interactive questionnaire sessions.

Key Takeaways from the ATMP Workshop and Conference

The ICH Q5A (R2) revision, which promotes the wider application of next-generation sequencing (NGS) and polymerase chain reaction (PCR)- based technologies for the detection of potential virus contamination, is expected to be adopted in late 2023 or early 2024, and it proved to be a key point of discussion.

It was surprising to learn through responses shared at the conference that some organizations are still in the early phases of preparing for implementation of the revision with some of them not really being aware of the intricacies and content of the revised guideline. Fortunately, there will be some more time before adoption and implementation begins.

1. Challenges in Manufacture of Cell and Gene Therapies

The PDA Viral Safety for ATMPs Workshop focused on the viral safety of raw materials for cell therapy in the first session and downstream virus removal for viral vector products in the second session.

During the workshop, an interactive Mentimeter questionnaire posed the question, “What do you see as the challenges for downstream processing for gene therapy vectors?” Unsurprisingly, the event attendants identified viral clearance, in general, as the highest concern, with scalability coming in second and most other answers (consistency, characterization, testing, and others) being mentioned once or twice. The same question posted in a social media poll resulted in a very different weighting of answers, with scalability coming in before yield, followed by virus clearance and purity, which may represent the broader reach of the platform (further lively discussions on this topic are guaranteed to come!).

For the viral safety of cell therapy products, an important focus lies on safe raw materials, as viral clearance steps are not feasible. Highlighted during the conference was that human blood products derived from raw materials are not necessarily better or worse than, for instance, bovine products from a safety perspective. Here, the profile of raw materials concerning species barriers, transmissible spongiform encephalopathy (TSE) risk, testing, and procurement strategies must be assessed individually. In that regard, small pools of human sera are preferable, and the use of inactivated serum/human platelet lysate (HPL) is also preferable. The second part of the PDA Viral Safety for ATMPs Workshop shed light on downstream virus removal for viral vector products. Importantly, the revision of ICH Q5A incorporates viral vector-derived products in its scope, which proved to be a fertile basis for presentations and discussions.

One important idea to make raw materials safe is the implementation of well-known and well-characterized virus clearance steps on the materials side rather than downstream on the cell product itself, where inactivation technologies are normally not feasible. Evolving by these means toward safer ancillary materials, two presentations showcased the viral clean-up of HPL. Technologies that can be utilized and are indeed feasible are solvent-detergent (S/D), gamma-irradiation, and virus filtration (nanofiltration). The cases presented for nanofiltration, S/D treatment, and gamma-irradiation showed very good logarithmic reduction values over 4log with the model viruses tested, significantly contributing to safety, although also with a loss in cell growth-promoting activity. However, it should be noted that treated HPL outperformed even untreated fetal bovine serum in this respect, thereby making it a viable option for manufacturing cell therapies.

Three dedicated topics were presented that covered various areas of interest in mitigating virus risk for vector-based products. Talks covered the prevention, detection, and removal aspects of a multistep risk mitigation strategy for viral vectors.

The presentation on the safety of adeno-associated virus (AAV) vector products (virus clearance and testing for helper viruses) highlighted the high risk of contamination by raw materials and that mitigation of risks from helper viruses can be challenging in production systems where they are utilized. Also, the downstream purification schemes are very heterogeneous, and not all make good enough use of feasible clearance steps such as virus filtration.

A deep concern with gene therapy vectors is the occurrence of recombination events that would generate a replication-competent virus, potentially harmful to the patient. While there is no prescription on the type of test, current legislation rightfully demands extremely high safety margins and sensitive enough assays for replication-competent viruses, with one example being that a maximum of one replication-competent adenovirus may be present in 3x1010 vector particles. Thus, one presentation provided a summary of replication-competent viral vector assays, their development, validation, and use.

The last presentation then provided a summary of biosafety risk mitigation strategies for raw and starting materials used in ATMPs' manufacturing. Again, emphasis was put on the fact that when the removal of viral contaminants is not feasible, there is a need to bolster the prevention and detection of contamination.

2. International Regulatory Update

Regulators from three regions (EU/global, U.S. FDA, and China FDA) provided their overview of the current regulatory landscape relevant to virus safety. The speakers touched on key points from the draft revision of ICH Q5A (R2) and provided an up-to-date understanding of viral risk mitigation. One speaker discussed the ability to use novel molecular-based technologies to address virus detection, and the impact of a more flexible approach, including platform validation and continuous viral inactivation for viral clearance, was discussed. It was a great achievement of the organizer and committee to welcome a regulatory speaker from the Chinese FDA, Sai Wenbo, from the Center for Drug Evaluation, for the first time. He gave valuable insight from his regional regulations. Mr. Wenbo spoke about technical requirements for platform validation of virus clearance in clinical trial applications and strategies for virus safety re-evaluation of process changes. The open and fruitful exchanges with Mr. Wenbo were warmly welcomed, and we sincerely hope for more to come.

Regarding the ICH Q5A revision, attendees learned about key components of the document. It will please many industry stakeholders to learn that the revision gives good guidance on many aspects of virus safety and facilitates implementation in numerous ways. For instance, we learned that “classical” tests may be readily replaced by molecular methods, and the good news is that these alternate tests do not need to go through a head-to-head comparison with animal tests, thereby reducing ethical and sustainability concerns by sparing numerous animal lives. The panel discussions were also highly valuable in enabling some of the regulators involved in the ICH Q5A revision to share some background on why comparisons between next-generation sequencing (NGS) and in vivo or in vitro assays are unnecessary. The different nature of the tests makes such comparisons difficult to interpret. As long as the NGS or PCR methods are suitably controlled, their suitability as a direct replacement or supplement to in vivo or in vitro assays is considered demonstrated.

Also, the leverage of prior knowledge (PK) gains more weight regarding the following:

a) End-of-use studies for chromatography resins (most notably Protein A) will not be mandated in many cases, thereby relieving developers of new biologicals of a big process development burden.

b) Virus filtration validation is alleviated by just studying the worst-case virus models in virus clearance studies.

c) Having enough supporting data for other chromatography methods can also make end of lifecycle resin validation obsolete.

d) Advanced concepts like continuous manufacturing are reflected in the revision as well.

3. Updates on Viral Clearance

The session on viral clearance explored new approaches toward the measurement and detection of virus particles in the context of virus clearance studies. Also, it dived into the implementation and validation of virus filters into continuous processes. Attendees learned about advanced technology in the context of the detection and measurement of virus particles to facilitate simplified virus clearance studies and the applicability of virus filtration in continuous processes.

Another presentation during this session discussed the implementation of virus filtration into a continuous process with stable filterability and high parvovirus removability in an end-to-end continuous process. Innovative solutions for the application of retrovirus-like particles (RVLPs) in virus clearance studies were also discussed. Based on accumulated data for multiple separation steps, compatibility of RVLPs was shown. The last podium contribution showed an improved method for detecting non-cytopathic viruses that enables sensitive detection, and we expect to see more application case studies using this technology in virus clearance studies.

4. Round Table Discussion Summary

In the afternoon of the first day, attendees were afforded the opportunity to choose from a list of four different topics in round table discussions:

(a) Virus clearance: The questions and discussions revolved around the implementation of clearance steps in challenging products such as exosomes and using clearance steps for raw materials in products where no downstream clearance is possible.

(b) Testing for residual helper viruses in the context of viral vector manufacture: Here, discussed what types of tests are suitable for the detection of helper viruses, at which stage to test (bulk or drug substance), and the regulatory background according to the United States Pharmacopoeia.

(c) New product types/gene therapies and vaccines: The questions focused on raw material qualification, how raw materials will be regulated, and their use in several production systems.

(d) Adventitious agent testing: The discussion focused on the use of NGS in raw material qualification, testing requirements for raw materials used in ATMP manufacture, and the comparability of different methods.

Overall, this new format turned out to be interactive and productive, and the organizers and committee are favorably considering making it a standing part of the event.

5. Virus Detection

The session explored how NGS can be effectively implemented in any adventitious agent testing program and how this technology compares with more traditional, infectivity-based approaches. Moreover, the session demonstrated that NGS is sensitive to a broad range of potential contaminants is key, and the case studies addressed these key aspects. One particular interest is the Advanced Virus Detection Interest Group (AVDTIG), a multidisciplinary, international effort focusing on developing standards and conducting collaborative studies for performance evaluation and qualification of NGS technologies for adventitious virus detection in biologics. The group provided background, ongoing activities, and achievements of the Interest Group, as well as the status of ongoing collaborative studies for evaluating virus detection using short-read and long-read NGS technologies.

A comparison of NGS proved to have higher sensitivity vs. “standard” in vivo testing. On the notoriously challenging aspect of bioinformatics, we learned about the necessity of accurately curated databases and the removal of non-viral sequences during analysis and optimization of workflows. Here, targeted vs. agnostic approaches were compared, and the use of the Word Health Organization reference standards was explained.

Furthermore, the AVDTIG gave a presentation on detection in cellular and viral seed backgrounds, transcriptome studies for virus detection, and pre-treatment methodologies. Numerous publications are expected in late 2023, giving the community further solid guidance on the “how to” for the implementation of novel detection methods.

6. Manufacturing Related Aspects

Biopharmaceutical manufacturers are continually looking for ways to rapidly detect and prevent adventitious virus contamination and remove endogenous viruses in the manufacturing processes. High-temperature short-time (HTST) is a common method that manufacturers employ to inactivate any potential contamination in cell culture media and feeds, but implementation can be costly and take a lot of development time. The session reflected on the use of upstream virus barriers and on the use of PCR to detect endogenous viral loads in unprocessed bulk harvests, including removal during the Protein A column chromatography unit operation.

For instance, we learned that PCR could be used as a replacement for transmission electron microscopy (TEM) in determining the number of RVLPs in unprocessed bulks and that PCR detects about 1-1.5 logs more RVLPS than TEM does. On the topic of upstream barrier technologies for reducing virus risk, it was made clear that upstream viral filters are an easy and robust method to filter media or feeds, adding significantly to the facility’s safety, and that upstream filters can be an easy and cost-effective alternative to HTST.

7. Current Strategies and Challenges in the Future

Just like the Challenges in Manufacture of Cell and Genes Therapy session, this session started with an interactive Mentimeter poll relevant to virus safety. The ICH Q5A R2 draft presents several new facets and challenges for meeting the regulatory requirements around virus safety, which is much of what the industry has learned in more than 30 years of performing virus clearance studies and is reflected in the ICH Q5A R2 document. Presentations and discussions explored how virus clearance studies (VCS) are impacted and how testing strategies for well-known manufacturing platforms, such as Chinese hamster ovary cell lines, may benefit from leveraging PK generated in the past.

The audience learned about several aspects that can simplify VCS and lower those costs, for instance, by co-spiking two or more viruses in clearance studies and automation solutions. Validation efforts are expected to be significantly lowered thanks to increased flexibilities offered in the ICH Q5A revision. Furthermore, leveraging PK, platform validation approaches, and use of alternative models, such as RVLPs, will increase speed through clinics but will also help in designing VCS for new modalities.


The PDA Virus Safety Conference remains one of the most important events in PDA's annual event calendar for the pathogen safety of biological medicinal products. It covers topics from blood products, ATMPs, and biologics products and brings together suppliers, service companies, authorities, and manufacturers. In addition, interaction with the most senior Pathogen Safety Managers is basically guaranteed.

With a record attendance number of 260, this year’s agenda was one of the strongest yet, with a lot of great content and inspiration about the revision of ICH Q5A R2 and how we put PK forward into a new era of biopharmaceutical development and manufacturing.

We look forward to deepening the discussions and learnings at the 2024 PDA Virus Conference on June 26-27 in The Netherlands. Save the date!

About the Authors

Alison Armstrong, PhD, started her career in academic research with a strong interest in the role of viruses in various pathogenic conditions. Moving to the contract testing sector in the late 1990s, Armstrong led many teams in different divisions within Merck and currently holds the position of Global Head of Technical and Scientific Solutions. During her career, Armstrong has authored many articles on trends in biosafety testing and is a member of industry forums on virology methods and alternate and rapid technologies.

Andy Bailey is a protein chemist and experienced virologist who served nine years at the MRC Virology Unit in Glasgow. In 1995, Bailey moved to the industry sector, initially as Director of Virus Validation services with Q-One Biotech Ltd, then as Manager at the Global Pathogen Safety group of Baxter Healthcare in Vienna, Austria. Bailey has been the CEO of ViruSure for the last 17 years and is now a part of the Asahi Kasei Medical group. Over the last 27 years, Bailey has been actively involved in the virus and prion safety field, presenting at numerous regulatory agencies for either support of products or as an invited speaker at expert workshops.

Sean O’Donnell, PhD, is a Senior Director in the Virology and purification development group at Eli Lilly and Company. O’Donnell has been a member of this department since 2012 and has been responsible for cell bank testing and viral clearance studies to support manufacturing. O’Donnell has over 16 years of industry experience, working in various aspects of viral research and viral safety.

Sebastian Teitz graduated from the University of Cologne with a diploma in Genomic Imprinting. Teitz followed this with a PhD in the Analysis of O-glycosylated Proteins. Teitz has previously worked at Fred Hutchinson Cancer Research Center (Seattle, WA), looking into Cytomegalovirus and its Role in Graft vs. Host Disease and Transplant Rejection, and at NewLab BioQuality / Charles River as the Project Manager of Virus Clearance Studies. Within Asahi, Teitz focuses on virus and pathogen safety, supporting customers and internal entities technically and scientifically, and liaising with authorities, CROs, and industry consortiums of the biopharmaceuticals industry. At Biopharma Excellence, he is now consulting developers of new drugs in scientific and regulatory affairs during all stages of market access.