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)