Recent trends in cell substrate considerations for continuous cell lines.

Product development activity in the past five to ten years has reconstituted a version of an old debate on the safety assessment of biological products, namely whether the use of some types of continuous cell lines (CCLs) is appropriate in the preparation of some types of biological products. Since 1987, dozens of purified recombinant DNA products derived from CCLs have been developed and have received regulatory approval. In addition, several live attenuated and inactivated viral vaccines manufactured in CCLs were approved after thorough review of product safety and manufacturing issues. The current discussion revolves around the potential use of CCLs (human or not) to prepare purified protein subunit vaccines, such as for HIV, and the use of human CCLs to prepare purified protein products.

International acceptance of blood and blood products.

International agreement on the standardisation of blood and blood products is of crucial importance in helping to ensure that those biological medicines are safe and effective. International efforts to establish norms for the acceptability of biological products are accomplished primarily through the WHO, and many international reference materials needed for calibration, such as standards for blood grouping and hepatitis C virus RNA have been established by WHO. In addition to coordinating the development of physical standards, WHO also has been the major player in attempting to generate an international consensus on the basic criteria for the acceptability of biological products. However, requirements for safe blood and blood products are fluid because new risks or new infectious agents continue to be identified. For all those reasons, worldwide harmonization of the quality of blood and blood products remains an elusive goal. However, opportunities to move forward exist, and WHO is in a good position to act as a catalyst for progress.

Cell substrates: lessons learned and challenges remaining.

The history of cell substrates for the manufacture of biological products is directly related to a series of technical advances and challenges to the status quo, some of which were accepted quickly while others took more than a decade to resolve. The development of cell culture techniques in the 1950s opened the door to the manufacture of a wide range of biological products. The first major challenge occurred in the late 1960s when human diploid cells (HDCs) were developed and proposed as an alternative to primary cell cultures for the production of live viral vaccines such as polio, which up to that point had been produced in primary cells of various species. In the 1970s, attention was focussed on the use of continuous cell lines (CCLs) for the production of non-replicating biological products such as interferon (IFN). The next significant technical advance and challenge was the development of recombinant DNA and monoclonal antibody technologies in the 1980s, both of which required the use of CCLs. Although most of the issues relating to CCLs in the manufacture of biological products have been resolved, issues related to their use as substrates for live viral vaccines remain to be fully addressed. Those experiences in the past teach us clearly that a system in which regulatory authorities, industry, and the general biomedical community cooperate in finding solutions to problems and in reaching consensus on issues raised by technical advances is ultimately in everyone's best interest. The World Health Organization has played a major role in that regard, and it should continue to provide leadership in this area.

Karyology and tumorigenicity testing requirements: past, present and future.

At the present time, karyology and tumorigenicity are applied to primary, diploid, and continuous cell systems in an uneven and inappropriate manner, largely for historical reasons. It is a significant anomaly that such rigorous requirements are applied only to diploid cells when, of all three cell types, they represent the category with the least potential problems. During the 1992 presidential campaign in the U.S., a very direct and telling slogan was used to the advantage of Mr. Clinton: <>. That message was meant to have the effect of focusing on the real issue that was of concern to the electorate. The other topics were of secondary significance and tended to act as distractions from the central issue. In a very similar sense, one could say: <>. In other words, we should be focussing our time and attention on the characteristics of the biological product manufactured in a given cell system that has been well characterized rather than continue to belabour the issue of cell substrates. To a large degree, this has already been initiated with the recommendations of various groups already mentioned. However, current diploid cell quality control regulations stand out as a peculiar throwback to an earlier era. HDCs should be treated on a par with primary and continuous cells. There are three basic questions related to the routine use karyology that need to be addressed: (i) is the original rationale for requiring cytogenetic analysis of a diploid cell substrate still valid; (ii) is there a new rationale that would warrant its continued use; and (iii) if there is a continuing need for karyology, is it unique to diploid cell cultures or does it need to be extended to all types of cell systems? The original rationale was that karyology provided evidence of the normal character of WI-38 cells and therefore supported its acceptability as a cell substrate for vaccine production. Karyology essentially has remained as a legacy of the intense debate that led to the acceptance of WI-38 cells. There is no new information over the past 30 years to suggest that there is a new rationale for instituting chromosomal analysis of cell substrates. If there were, however, it is difficult to imagine why it should not be applied to all types of cell substrates (primary, diploid, and continuous). Taking all the above into consideration, there would seem to be no rationale for continuing to single out diploid cell cultures as the only cell type for which karyology is required on a routine basis. As stated above, the initial characterization of a new diploid cell line should include karyology. Like karyology, tumorigenicity testing was incorporated into the assessment of diploid cells in an attempt to persuade regulatory authorities that the cells were normal and acceptable. Again, after 30 years of testing, there has never been an instance of normal diploid fibroblasts generating a tumour in any in vitro or in vivo assays. The futility of continuing to do these tests is obvious. A description of the tumorigenic potential of a cell substrate should be an element in the characterization of a new cell line; but it has little if any value as a routine test. If history teaches us anything at all about risk, it is that we need to focus serious attention on contaminants rather than be diverted to remote theoretical issues that may be interesting to discuss and argue about, but which pale in the face of the potential impact on public health of viral and viral-like contaminants of biological products. One has only to recall the transmission of SV-40 from primary monkey kidney cells that were used to produce polio vaccine, or more recently the transmission of Creutzfeld-Jacob disease to recipients of human growth hormone derived from human pituitaries and of HIV to recipients of blood and blood derivatives. (ABSTRACT TRUNCATED)

An overview of viral and viral-like agents in cell culture systems.

The first recognition of seriously contaminated biological products occurred almost 100 years ago. More recently, in the second half of this century, the potential for contamination by viral and viral-like agents became obvious when the SV-40 virus was identified as an endogenous agent in the cell cultures used to produce polio vaccines. The history of major contamination incidents is reviewed, and current issues are discussed.

Administration of tumor cell chromatin to immunosuppressed and non-immunosuppressed non-human primates.

For decades, developers and regulators of vaccines and other biological products have been concerned about the theoretical risk to patients posed by contaminants derived from the cell substrates used to produce those products. The present study addresses the issue of how risky DNA may be as a residual impurity by injecting both normal and immunosuppressed monkeys with 10(8) genome equivalents of DNA from a human tumor cell line. After more than eight years of observation, none of the animals shows evidence of neoplastic disease. The results of this study along with clinical experiences with already approved products derived from continuous cell lines suggest that he benefits of using such cells for the production of biologicals far outweigh any theoretical risks associated with DNA.

The acceptability of continuous cell lines: A personal & historical perspective.

In the 1950s, only primary cell cultures were acceptable for the production of human biological products. This position was challenged in the late 1960s by human diploid cells (HDCs), and again in the 1980s by continuous cell lines (CCLs). The history of the HDC controversy is reviewed and lessons from that era that are relevant to the use of CCLs are pointed out. It became apparent in the early days of recombinant DNA technology in the 1980s that CCLs were needed for the development of some products. CCL acceptability therefore became more urgent, and several attempts were made to reach a consensus on regulatory issues. In 1986, the World Health Organization convened a Study Group to review the safety issues related to products derived from CCLs. The Study Group made a clear recommendation to pursue CCLs in product development because of the demonstrated capability of modern manufacturing processes to cope with contaminants. Issues such as acceptable levels of cellular DNA in products and the relationship of purity to safety are discussed in the context of the need for regulatory authorities, industry, and the general biomedical community to cooperate in addressing problems in a rational scientific manner.

Global HIV vaccines: economic considerations.

PIP: Information and education programs have had only very limited success in modifying sex behavior. It may therefore be that the development and widespread dissemination of an HIV vaccine through a global immunization program is the world's best hope for controlling the spread of HIV infection and AIDS. It is conservatively estimated that there would be 100 million initial recipients worldwide of an HIV vaccine. Even under the most optimistic circumstances, the cost of procuring and delivering the drug or drugs would be at least several billion dollars, the majority of which would be spent upon immunizing people in the developing world. Annual per capita financial resources allocated to medical care in developing countries are, however, often less than $10. Developed countries will most likely have to cover a substantial proportion of the costs of any eventual global HIV immunization strategy. Strategies must be developed now to deal with the issues of accessibility and use of HIV vaccines throughout the world. Policymakers in developed countries should therefore begin to give serious consideration to how to finance the procurement and distribution of HIV vaccines so that one or more systems can be put into place in anticipation of the approval of HIV vaccines.^ieng

Global immunization against AIDS: economic considerations.

Many knowledgeable people believe that the only real hope for halting the AIDS pandemic rests with safe and effective HIV vaccines that are delivered through a global immunization programme. When such vaccines become a reality, the size of potential target populations for HIV vaccines may well be over 100 million. The costs associated with such a large vaccination programme probably reach the multi-billion dollar level. An international consideration of financing strategies should begin in the near future in order to avoid a repetition of the lag between vaccine availability and widespread use that accompanied the introduction of hepatitis B vaccine.

Cell line issues: historical and future perspectives.

The initial decision to use only primary cell cultures for the production of human biological products was challenged in the late 1960s by the introduction of human diploid cells (HDCs), and again in the 1980s by continuous cell lines (CCLs). The history of the HDC controversy is reviewed and lessons from that era that are relevant to the use of CCLs are pointed out. With the introduction of recombinant DNA technology in the 1980s, and the potential usefulness of CCLs in product development, the issue of cell acceptability became more urgent, and several attempts were made to reach a consensus on regulatory issues. In 1986, the World Health Organization convened a Study Group to review the safety issues related to products derived from CCLs. The Study Group made a clear recommendation to pursue CCLs in product development because of the demonstrated capability of modern manufacturing processes to cope with contaminants. Issues such as acceptable levels of cellular DNA in products, the relationship of purity to safety, and the relevance of the genetic stability of recombinant cells to product consistency are current examples of areas in need of discussion and agreement. A system in which regulatory authorities, industry, and the general biomedical community cooperate in finding solutions is ultimately in everyone's best interest.

Regulatory philosophy and acceptability of cells for the production of biologicals.

The issue of what types of cells should be considered acceptable for use in manufacture of biologicals dates back to the early 1950s. One of the central points in the discussions and debates over the past 35 years has been the possibility that the use of a given type of cell would result in unsafe products. Of the possible sources of risk, the presence of endogenous viruses in cell substrates has been the only one with realistic and practical implications for public health. The discovery of SV-40 in polio vaccines derived from primary Rhesus kidney cells made the issue of viral contaminants a very real one. Avian leukosis viruses have also been identified as endogenous agents that were carried over into products derived from chicken eggs. It is now important for regulatory policy to continue to be flexible, and to be guided by our technological capabilities in addressing safety issues associated with endogenous viral contaminants.

Vaccines: obstacles and opportunities from discovery to use.

Since smallpox, vaccine-development programs have varied, yet common elements exist. Investment in vaccine research and development depends on epidemiology, market size, funding, and liability. Fear of liability inhibits innovation, adaptation of existing methods, and regulatory decision-making. Vaccine evaluation proceeds from animal and in vitro studies to controlled human clinical trials. Successive stages provide the information base necessary for decisions on vaccine approval for general use, but sociopolitical forces can affect the process. The World Health Organization establishes nonbinding international norms for vaccine acceptability that are adopted by many countries. Concerns for purity and safety need to be addressed along with cost and vaccine availability. For example, replacement of brain tissue-derived rabies vaccine in developing countries with a continuous cell line-derived vaccine is possible if purity is balanced in relation to safety. Substantially reducing the toll of infectious diseases will require cooperation and common-sense decisions.