Collaborative study on test systems to assess toxicity of whole cell pertussis vaccine

A collaborative study has been carried out to establish the precision and accuracy of five test systems for the assessment of the toxicity of whole cell pertussis vaccine. To this end, six vaccines, including both "normal" and "abnormal" products with respect to arbitrary levels of Pertussis toxin and/or potency were tested. The study included in vivo test systems as the Mouse Weight Gain (MWG) test; the current WHO-recommended bioassay to evaluate overall pertussis toxicity and four specific test systems; the Leukocytosis Promotion (LP) test, the Histamine Sensitization (HS) test and in vitro the Chinese Hamster Ovary (CHO) clustering test to estimate pertussis toxin (PT) levels, and the Limulus Amoebocyte Lysate (LAL) test to evaluate endotoxin levels. In addition, participants were also asked to estimate potency by the Mouse Protection test according to Kendrick (MP). Fourteen laboratories in various countries participated in the study. In almost all participating laboratories, the MWG test was not very accurate in evaluating the overall toxicity of whole cell pertussis vaccines. In addition, statistical significant interlaboratory variation was frequently seen. The specific toxicity tests (LP, HS, CHO and LAL test) appeared to be more accurate, but large interlaboratory variation was seen, statistically significant at P < 0.05 for LP test, CHO test and LAL test. Significant variation in test results also occurred in the potency test. Furthermore, the discriminative power of the MP test between different levels of potency was low. It was concluded that, on the condition of optimization and stringent standardisation, HS and CHO test and in particular LP test might be more appropriate to assess PT activity than the MWG test provided that the tests are optimised and stringently standardized. An inhibition ELISA was used to estimate levels of PT. This test could be of value for prescreening purposes. The LAL test should be used to estimate endotoxin activity. The value of the MP test, as a model to assess potency, is disputed.