Boehringer Ingelheim Vetmedica’s Dr Randolph Seidler discusses the emerging trends in veterinary vaccines
Veterinary vaccines are an important arrow in the quiver of the veterinarian and are arguably one of the most powerful tools in keeping animals healthy and well. Recent advances in technologies and our improved understanding of pathogenicity, immunology and epidemiology have opened new opportunities for preventing infectious diseases at an unprecedented level.
In this article we want to outline some of the advances that we consider amongst the most impactful, including advances in delivering and presenting antigens to the immune system, platforms enabling an improved response to emerging diseases and progress in manufacturing.
Current veterinary vaccines substantially contribute to animal welfare and healthy food, but many have their limitations
Infectious diseases remain a major challenge in veterinary and human medicine, and the interaction and interdependence between both is increasingly being recognised through the concept of ‘One Health’. Veterinary vaccines based on inactivated and conventionally attenuated pathogens have made substantial contributions to keeping animals and humans healthy.
However, in many instances vaccines based on conventional technologies also have their limitations. For example, the immunogenicity of many bacterial pathogens is complex and can frequently only incompletely be imitated in inactivated vaccines (so-called ‘bacterins’). Often it is not fully understood what triggers a protective immune response in the host, but the ability of many bacterial species to express a large number of genes and their capability to evolve in ‘serovars’ is thought to play an important role. Viral pathogens evade the immune system through different mechanisms, including the shutdown of the cellular interferon response and high mutation rates (especially in RNA viruses).
Generating attenuated live bacterial vaccines (so-called attenuated live cultures or ALCs) has proven to be a successful strategy in some of those cases and the vaccine against Lawsonia intracellularis (Enterisol Ileitis®) is one example. But the conventional attenuation method through repeated passaging in vitro is a time-consuming, cumbersome and somewhat unpredictable process and defining the right balance between attenuation and immunity is challenging.
As a consequence, for a number of the clinically relevant diseases more or less satisfactory vaccine solutions are available; however, there are still many diseases where verterinary vaccines are either not available at all, have substantial weaknesses or a very narrow spectrum of protection, necessitating the application of different technologies to fill the gaps.
Innovation drives the quest for new and better solutions
Over the last decade progress in biomedical research, virology and microbiology has also fuelled the innovation of vaccine research, including better understanding of the interaction between pathogens and the host immune system, the continuous improvement in the deciphering of the immune response and its components in domestic animals.
Subunit and virus-like particle (VLP)-based vaccines
Improved understanding of the immunogenic and protective antigens of pathogens as well as the ability to produce recombinant proteins cost-effectively and at high quality have opened the door to vaccines that are based on relevant antigens only. Conceptually the advantages of this approach over conventional inactivated pathogens are:
1) that the immune system can focus its response to the most ‘relevant’ antigen(s) rather than producing antibodies against a large number of different and potentially irrelevant proteins;
2) subunit proteins can be modified from the wild type structure to increase immunogenicity and thus, potentially broaden the spectrum of protection;
3) reduction of unwanted or unnecessary proteins can improve tolerability of the vaccine; and
4) the exclusion of potentially immune suppressive proteins can improve the efficacy of the vaccine.
Some viral proteins can spontaneously assemble into biological nanoparticles, so-called ‘virus-like particles’. VLPs mimic viral structures but cannot cause a productive infection and are readily recognised by the immune system, triggering an enhanced B and T cell immune response. Prominent examples of VLP-based vaccines are some baculovirus/insect cell-expressed veterinary vaccines against Porcine circovirus 2 (PCV2), Ingelvac CircoFLEX® for example.
The immune responses to those vaccines can be further boosted by the use of immune stimulators or adjuvants. With the more frequent usage of recombinant vaccine antigens and the increasing emphasis on safety and tolerability of veterinary vaccines for the sake of animal welfare, those compounds are predicted to gain more importance in the future.
Vaccines using targeted deletions and modifications
Live vaccines maintain beneficial features for veterinary medicine due to their powerful stimulation of the immune system in relevant tissues, typically alleviating the need for ‘boosting’ of vaccination and leading to robust immune responses especially in cases, where inactivated vaccines show limited protection.
Conventional modified live vaccines (MLVs) are typically attenuated through multiple passages in culture, followed by selection of a clone that demonstrates the desired properties. While multiple examples exist that this can lead to very good or at least acceptable vaccines, one downside of this approach is that the underlying mechanism for attenuation is often poorly understood.
Recent improvements in the understanding of virulence and pathogenicity combined with effective molecular biological methods have given way to rational design of vaccines, where virulence factors have selectively been eliminated or functionally silenced. This has led to vaccines that maintain the beneficial properties of live vaccines, while reducing the risk for a potential reversion of virulence.
An example of this technology is a vaccine against Bovine viral diarrhoea virus (BVDV) recently introduced in the EU (Bovela®), where deletion and modification of two non-structural proteins allowed combining safety of an inactivated vaccine with the efficacy of a MLV.
Vector-based veterinary vaccines
Insertion of protective antigens into a live but apathogenic vector organism is a strategy that has been successfully applied to experimental and commercial vaccines. However, while vector-based veterinary vaccines are ‘coming of age’ for viral diseases, they are still only emerging for bacterial diseases. Besides conceptually combining the advantages of a live vaccine with its potent immune system stimulation with the high degree of safety of an avirulent carrier, they also allow for a potentially faster regulatory review. Additional advantages of some vector systems is their limited or even abortive replication competence in the host animal, substantially reducing the risk for shedding and recombination.
Finally, vector-based veterinary vaccines are typically excellent candidates for so-called ‘DIVA’ (differentiation of vaccinated from naturally infected animals) vaccines a key tool for the eradication of infectious diseases.
Merial has been a pioneer in this field and has introduced some of the earliest vector-based vaccines in veterinary medicine, inducing a canarypox-vectored rabies vaccine for cats (Purevax®) and a herpes-based infectious bursal disease virus (vHVT-IBD) vaccine for chickens (Vaxxitek®).
Much current research focuses on the identification and optimisation of additional vector systems optimally suited for different species and applications as well as on identification of optimised antigens potentially allowing for faster and longer lasting immune responses or for broader protection across different clades or serotypes.
Using DNA for vaccination represents a relatively new technology and its swift accessibility and well controlled production makes it a potentially interesting solution for the future. DNA vaccines currently suffer from some drawbacks, including: 1) relatively high costs; 2) strict requirements for intramuscular administration, which is a limitation in many domestic animal species; and 3) incompatibility with other classical vaccines leading to a barrier for the easy development of combination vaccines.
Even higher expectations are on the use of RNA for vaccination; however, there are still technical hurdles to overcome before it will be widely used as vaccine, including the development of commercially viable formulations of mRNA. Both, DNA and RNA vaccines are able to broadly stimulate the immune system and are addressing the humoral and cellular immunity.
In addition, nanotechnology has found its way into vaccinology; particles either produced by protein expression systems or made synthetically are used as carriers for vaccine antigens which can be linked to the surface of the support particle. These systems have the potential to be used as a platform technology for vaccine production.
The first DNA/RNA-based vaccines have recently been approved for the use in veterinary medicine. The veterinary vaccine industry has been at the forefront in developing commercial DNA vaccines including a vaccine against Salmon Pancreas Disease (Clynav®), a currently not commercialised West Nile virus (WNV) vaccine for horses or a canine melanoma vaccine (Oncept®).
Shortening the response time to emerging diseases will be key to protect livestock and humans
Recent emerging viral disease events in livestock in Europe (i.e. Bluetongue virus and Schmallenberg virus diseases) as well as in humans in Africa (i.e. Ebola virus) have shown that response times to develop a vaccine is of essence for an effective response, but that current development and marketing authorisation models are still too slow for a swift response, especially when diseases are insect-borne as they can spread very fast over long distances.
Currently, the extensive work packages and review time required to arrive at a marketing authorisation limit the response time. A solution could be platform technologies e.g. in vitro systems for antigen expression.
The development of a vaccine against a new infectious disease, using the well-established pathways for inactivated veterinary vaccines, or well-known viral vectored vaccine platforms, such as the non-replicative canarypox virus, still takes a minimum of four years if a full marketing authorisation is required.
Consequently, there is a need to rethink the way we design ‘optimal vaccines’ for these unexpected (re-)emerging diseases. The first objective is to deliver a vaccine product in the shortest time possible and to scale up production in order to supply very large populations of either animals or humans. For zoo(anthropo)notic viruses, it is more efficient to block the outbreak first in animals in order to control the virus reservoir and consequently the transmission to humans by contact.
The EU-supported Innovative Medicines Initiative (IMI) Zoonoses Anticipation and Preparedness Initiative (ZAPI) project was launched two years ago with the intention of designing a methodology that will support the very rapid and large scale manufacturing of key control tools (both vaccines and therapeutic neutralising antibodies) against new or existing zoonotic pathogens. This unique One Health project brings together representatives of the animal health industry, the human health industry and key academic centres for developing completely new approaches to define, manufacture and release vaccine batches.
An important additional objective for ZAPI is to avoid the need for using animals for the quality control of vaccines, since the in vivo phase can significantly impact the manufacturing cycle time before release and a key target for reduction of animal use (3R).
The ZAPI ambition is to achieve a cycle time of a few weeks instead of several months. The final achievements of ZAPI will be known in approximately three years’ time. It is expected that key learnings will be applicable at multiple levels in our industry and will thus contribute to the faster development of veterinary vaccines in emergency situations.
The role of modern vaccines in the effort for prudent use of antibiotics
The growing prevalence of bacterial strains resistant against a broad spectrum of antibiotics poses a substantial problem in the treatment of bacterial diseases. While the prudent use of antibiotics is a shared responsibility between the medical and veterinary community, the use of antibiotics in livestock husbandry has received substantial criticism in the public debate.
Bacterial diseases remain a key challenge in veterinary practice and responsible use of antibiotics is presently an important tool to overcome these diseases, prevent suffering of animals and thus improve animal welfare. However, there is a growing understanding that – while antibiotics use cannot fully be avoided – increased efforts are needed to prevent disease through better hygiene measurements and vaccines.
Many bacterial diseases can be found in different serotypes and cross-protection between serotypes is often poor. The consequence is that vaccination against a certain serotype will not sufficiently protect the animal from infection of other serotypes. At the same time a combination of different serotypes can be limited by interference in the immune response between different strains, tolerability issues due to increased side effects, and/or production costs.
In addition, for many bacterial diseases inactivated vaccines themselves are not sufficiently protective.
Research into the function of individual genes within bacteria and their role in the pathology of bacterial disease in order to identify cross-protective immunogen subunits is now progressing faster through the combined use of large scale (deep) sequencing, bioinformatics and predictive software. However, targeted changes to arrive at effective and safe vaccines is still a mid- to long-term objective for many bacterial diseases requiring substantial additional basic research.
Innovation in manufacturing will drive quality, supply, and cost effectiveness
Capital investment into manufacturing facilities continues to be a limiting factor in the expansion of commercial manufacturing of veterinary vaccines and is a key driver of cost of goods. While the intrinsic properties of newly developed vaccines such as production yields and minimum immunising dose (MID) play a key role for the capacity requirements and cost in commercial manufacturing, technology advances in manufacturing technologies and processes have increased flexibility, lowered cost and increased response time to changing market demands.
Such advances include:
1) the use of modular facilities, for example through utilisation of a ‘ballroom’ concept and of single-use technology, which can lower initial investment cost and decrease changeover time, therefore increasing flexibility, response time and overhead cost;
2) the use of high-density cell banking systems can shorten the seed-train and therefore the overall production cycle;
3) inline measurement of key process parameters allow for a better controlled manufacturing process, optimisation of yields, reduction in batch-by-batch variability and product quality attributes and therefore optimised cost and improved quality;
4) advancements in the formulation of vaccines have enabled the manufacturing of more stable vaccines with the ultimate goal of thermostable and liquid vaccine presentations; and
5) the development of in vitro product release assays can reduce assay variability, reduce the number of animals used in commercial manufacturing, thereby serving the ‘3R’ ambition, reduce cost and shorten production cycle times.
Innovation is driven through collaboration, partnering, and strategic alliances
As outlined in this article, technological advances have enabled the (veterinary) medical community to tackle vaccines against infectious disease at an unprecedented level. It can be expected that a number of these advances will translate into products that will improve prevention of disease and enable veterinarians and animal owners in their effort to keep animals healthy, improve their wellbeing and reduce the use of antibiotics in livestock. At the same time the need for breakthrough innovations often requires pursuing multiple approaches in parallel, makes identification of the best approach more unpredictable, and requires a plethora of skills and scientific disciplines that are unlikely to be found in one place.
Academic research in universities and government research institutions provide the optimal environment to develop an understanding of the basic mechanisms of infectious diseases, host-pathogen interactions and novel vaccine concepts. Small and mid-sized companies dedicated to the identification and development of veterinary medicines have recently emerged and have shown significant progress and agility.
Finally, large animal health companies possess a unique institutional knowledge about the successful development of veterinary vaccines for all major regions, regulatory authority requirements and access to global markets.
Different models of collaboration have successfully been deployed in the past and have proven their effectiveness. Among those, sponsored research collaborations and licensing of technology have been most common. A special case has been consortial research endeavours that have proven to provide a good basis for scientific progress in specific areas and to de-risk early approaches. For example, the Horizon 2020 framework programme and its Innovative Medicines Initiative, supported by the European Union, have set a high standard.
However, a number of collaboration models such as open innovation, crowd-sourcing of technology and pre-competitive collaborations have just recently emerged and are not yet utilised to their potential as research tools by companies and academia.
The changes in innovation models have led to the realisation that building alliances between partners of complementary skills and capabilities will become a key success factor in effectively identifying innovation and implementing it in well-defined applications for our end users in the market.
Most large companies, including one of the authors, have implemented dedicated resources for alliance management, ensuring the maximisation of value for all involved partners of mid- and long-term alliances. For the control of zoonotic diseases a closer collaboration between the human and the animal health sector in the development of vaccines seems prudent. Examples of such diseases including Hepatitis E, MERS, Rift Valley Fever, etc. However, for some of those vaccines the economic reward is low and shared financing between the private and the public sector appears rational.
In summary, we predict that – driven by new technology and approaches – veterinary vaccines will see a wave of innovation in the coming years to the benefit of veterinarians, animals, animal owners and ultimately the research-driven manufacturing companies. New models of better working collaboratively between different stakeholders in this area will be a key driver for innovation.
Konrad Stadler, Boehringer Ingelheim Veterinary Research Center GmbH & Co. KG
Jean-Christophe Audonnet, Merial S.A.S.
Randolph Seidler, Boehringer Ingelheim Vetmedica GmbH