Chapter 1
History of Vaccine Process Development

NARAHARI S. PUJAR AND SANGEETHA L. SAGAR

Merck & Co., Inc. West Point, PA, USA

ANN L. LEE*

Genentech, South San Francisco, CA, USA

1.1 Introduction

The goal of vaccine process development is to develop a manufacturing process that can consistently produce a vaccine that is safe and efficacious. During vaccine discovery, the etiologic agent is identified, the immunogen, adjuvant (if applicable), and administration regimens are developed in animal models such that the vaccine candidate produces a prophylactic immune response that is safe and effective. A requirement of the manufacturing process is to preserve the immunological properties innate to the molecular/biological architecture defined in vaccine discovery and enable production of the vaccine in increasingly larger quantities for use in human clinical studies and later commercial supplies. These activities of vaccine discovery and process development must be well integrated, require collaborative efforts and iterative refinements. The safety and efficacy of the vaccine gets proven though phases of clinical studies with increasing number of subjects. The final process developed and used to produce the vaccine for pivotal clinical trials becomes the manufacturing process which is licensed by regulatory authorities for full-scale production to supply the market.

Unlike for many other pharmaceutical drugs, the manufacturing process used to produce the vaccine is still frequently tied to the definition of the product. While many modern vaccines are highly purified biomolecules, others are complex preparations, such as live viral vaccines or multivalent conjugate vaccines, consisting of the antigen, trace levels of cellular and process residuals, excipients, as well as adjuvants. For some types of vaccines the "product-is-the-process" interdependence can be greatly alleviated by modern process and analytical technology. This approach is built upon much greater scientific understanding of the process and product characteristics which allows greater process control and performance.

Generally speaking, the immunogen is generated via a cultivation process (also referred to as the upstream process) and is characterized by an appropriate choice of cell substrate, growth media and a fermentation or cell culture conditions that reproducibly produce the antigen in large quantities (note that in the rest of the chapter, the word antigen is used as a synonym for immunogen). The vaccine purification process (also referred to as the downstream process) maybe designed to remove host cell impurities, as well as process additives and yields a bulk vaccine (drug substance). The bulk vaccine is converted into a final vaccine product (drug product) in the formulation, fill, and finish processes. Through this stage, the vaccine is formulated into a final composition that imparts long-term stability, whether in liquid or lyophilized form, and then presented in an appropriate final container, such as vials or prefilled syringes. An adjuvant may or may not be used as part of the drug product depending on the type of the vaccine.

This chapter outlines the history of vaccine manufacturing from a bioprocess development perspective. With the maturation of the biotechnology industry, vaccine manufacturing has evolved significantly over the years. An understanding of the evolution of vaccine manufacturing processes can be instructive in the development of future generations of vaccines. There have been previous reviews on various aspects of vaccine bioprocessing. An excellent review on viral vaccine production is presented by Aunins ((2000), 2009). Other viral vaccine production reviews have been written by Shevitz et al. (1990), Ellis (2001), Bailey (2007), and Genzel and Reichl ((2007a); (2007b)), which also include production of viral vectors. Bacterial vaccine production has been reviewed by Liljeqvist and Stahl ((1999a); (1999b)) and Ellis (2001). Broader reviews of vaccine bioprocessing include those by Aunins et al., (2010), Dekleva ((1999a); (1999b)), and Josefsberg and Buckland (2012). This chapter encompasses a broad range of vaccine bioprocesses including whole-viral and -bacterial vaccines, as well as subunit and conjugate vaccines. This chapter is focused on drug substance processes; the area of drug product manufacturing processes, including the topic of adjuvants, is quite rich in its own right, but is beyond the scope of this chapter.

1.2 Vaccines Bioprocess Evolution

Vaccines and vaccine candidates have been directed at infectious (bacteria, viruses, and fungi), parasitic, and non-infectious diseases, such as cancer and Alzheimer's disease. They can be largely classified as either live, attenuated, inactivated (or killed), or subunit. Production can be in the native organism or in a heterologous host. Recombinant vaccines have been in the form of protein subunit vaccines and modern live viral vaccines (Nkolola and Hanke, (2004); Polo and Dubensky, (2002); Ellis; (2003)). Genetic and peptide vaccines are some other categories, which could be considered subcategories of the aforementioned broad categories. Genetic vaccines are those where the immunogen is delivered in the form of a gene via a naked DNA or a viral vector. The evolution in vaccinology has taken vaccines from complex preparation of undefined contents to whole organisms to highly purified whole organisms and subunit components. This evolution of vaccines is directly related to the development of bioprocess technologies. At the outset, identification of the etiologic agent requires bioprocessing, albeit at a much smaller scale and without the worry of scalability or manufacturability. Although the long-held goal of vaccine innovation would not include any whole organisms (live, attenuated, or inactivated) it is not currently possible nor necessary, particularly in the case of some viral vaccines. Further simplification via reverse vaccinology (Hilleman, (2002); Rappuoli, 2007) leading to genetic or peptide-based vaccines is certainly an attractive goal from the bioprocess technology perspective. If these approaches can be established, they will represent a powerful step change not only in vaccinology, but also in the ease of vaccine bioprocessing because they can consistently be based on well-defined platform technologies.

Although contemporary vaccine history is known to start with Edward Jenner, who developed the small pox vaccine in 1796 using the pus of patients with cowpox with a predecessor, variolation, was known to have been practiced much earlier in China, India, Turkey, Persia, and Africa (Behbehani, (1893)). Nevertheless, Jenner is credited for initiating this safer approach in vaccine development, as well as coining the term vaccine from vacca (Latin for cow). This early history has been reviewed quite extensively (e.g., Galambos, (1999); Hilleman, (2000); Plotkin and Plotkin, (1999); Lederberg, (2000); Plotkin, (2009)). Since the days of Jenner, vaccinology has proven to be a tremendous benefit to all mankind. In particular, vaccines have had a significant impact on increasing life expectancy since dawn of the twentieth century. With modern molecular techniques, the molecular architecture of the etiologic agent and the antigen continues to be better defined, and consequently, vaccine manufacturing processes are more capable of producing better defined antigens, in many cases rivaling the production of therapeutic proteins where the concept of a "well-characterized" biologic is well established.

1.3 Live Attenuated and Inactivated Virus Vaccines

The earliest vaccines were live attenuated organisms - e.g. smallpox vaccine by Jenner and rabies vaccine by Pasteur. Live vaccines have complex upstream cultivation processes and undergo minimal downstream processing. Because they are live, the degree of attenuation and genetic stability is particularly important, as it relates to the reversal of virulence. Furthermore, the choice of the host can have an impact on vaccine safety and reactogenicity because of potential host cell residuals, growth media components, as well as the potential for adventitious agents. The production system, in the case of Jenner's smallpox vaccine was patients with cowpox. Pasteur used rabbits as the bioreactor to produce the immunogen for the rabies vaccine. This type of in vivo production is still in use for the production of a Japanese encephalitis (JE) vaccine. JE-VAX®, licensed in 1954 in Japan and in 1992 in the United States, was derived from mouse brain (in this case, the vaccine is administered as an inactivated virus) and was being supplied in the United States until it was discontinued in 2007. Other mouse-brain-derived JE vaccines are still being manufactured in South Korea, Taiwan, Thailand, and Vietnam but are slowly being replaced by cell-culture derived vaccines. (www.path.org, JE vaccines at a glance; Zanin et al., (2003)). In vivo production continues to be widely used in veterinary vaccines (Aunins, (2000)).

In 1931, Ernest Goodpasture discovered that a hen's egg was an ideal sterile production system for fowl pox virus, and a whole new, enduring bioreactor system was born (Woodruff and Goodpasture, (1931)). This led to the licensure of the first influenza vaccine in 1945 (Salk and Francis, (1946)). Also, in the 1930s, a yellow fever vaccine based on the 17D strain was developed (Vainio and Cutts, (1998)). In ovo production is still widely practiced today for the production of both of these vaccines. Scale-up of...