[Alternative for the neurovirulence test]
For safety testing and release for attenuated oral poliomyelitis virus (OPV) vaccine lots, national and international authorities require the in vivo neurovirulence test (NVT). This test is extremely expensive, time consuming and is carried out in socially sensitive monkeys. In this test the test vaccine is injected into the spinal chord of monkeys and the mean lesion score of neurovirulence is evaluated and compared to that of a reference vaccine. If the test vaccine is not significantly different from the reference, the vaccine passes the test. Data from several investigations suggest that the accumulation of distinct reversions in a vaccine lot correlate with an increased mean lesion score of neurovirulence in the monkey test, and thus are the causa sine qua non of reversion of attenuation to wild type. The relevant reversions are for serotype 1, 480 G to A and 525 U to C, for serotype 2, 481 A to G, and for serotype 3, 472 U to C. To quantify these reversions on a relative basis in vitro, the MAPREC test (Mutation Analysis by PCR and Restriction Enzyme Cleavage), developed by Chumakov et al. (FDA), seems to be the only suitable test. For serotype 3 it could be demonstrated, that vaccine lots failing the NVT comprise a reversion rate >/= 0.9%. For serotypes 1 and 2 such a limit could not yet clearly be defined. MAPREC quantifies only single mutations, which have been shown to be important for neurovirulence. There is a possibility, however, that also other mutations/reversions, not yet identified, could principally contribute to neurovirulence, but would not be detected by MAPREC. Therefore, at date, there is no scientific basis to replace the monkey NVT by MAPREC. Howeser, MAPREC can be used to check the consistence of reversion rates in vaccine lots under current production conditions, and the impact of changed production conditions on the reversion rates, and thus can be used to get more and more experience. It further ongoing studies and analyses of manufacturers and national and international control laboratories will show that the predictions of the MAPREC results on the outcome of the monkey NVT are sufficiently safe, this in vitro test would be an excellent alternative for the monkey test.
Dörsam
Volker
Chiron-Behring GmbH & Co., D-Marburg.
Schmeel
Andreas
A
Chumakov
Konstantin
K
Fibi
Mathias R.
MR