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.