Brownie C, Statt J, Bauman P, Buczynski G, Skjolaas K, Lee D, Hotta J, Roth N J
Statistical Consultant, Raleigh, NC 27627, USA.
Biologicals. 2011 Jul;39(4):224-30. doi: 10.1016/j.biologicals.2011.06.007. Epub 2011 Jul 23.
An important consideration in the manufacture of products derived from animal or human sources is the virus reduction capacity of the manufacturing process as estimated using validated bench-scale models of relevant manufacturing steps. In these studies, manufacturing process intermediates are spiked with virus and processed using the bench-scale model and the resulting viral titres of input and output samples are typically determined using cell-based infectivity assays. In these assays, the Spearman-Kärber (SK) method is commonly used to estimate titres when there is one or more positive observation (i.e., the presence of any viral cytopathic effect). The SK method is most accurate when the proportion of positive observations ranges from <0.1 to >0.9 across dilutions but can be biased otherwise. Maximum likelihood (ML) based on a single-hit Poisson model is an alternative widely used estimation method. We compared SK with ML and found the methods to have similar properties except for situations in which the concentration of virus is low but measurable. In this case, the SK method produces upwardly biased estimates of titres. Based on our results, we recommend the use of either ML or SK at most virus concentrations; however, at low virus concentrations ML is preferred.
在生产源自动物或人类的产品时，一个重要的考量因素是生产过程的病毒清除能力，这是通过相关生产步骤经过验证的实验室规模模型来估算的。在这些研究中，将病毒添加到生产过程中间体中，并使用实验室规模模型进行处理，输入和输出样本的最终病毒滴度通常使用基于细胞的感染性测定法来确定。在这些测定中，当存在一个或多个阳性观察结果（即存在任何病毒细胞病变效应）时，常用Spearman-Kärber（SK）方法来估算滴度。当阳性观察结果的比例在各稀释度范围内从<0.1到>0.9时，SK方法最为准确，否则可能会有偏差。基于单击泊松模型的最大似然法（ML）是另一种广泛使用的估算方法。我们将SK与ML进行了比较，发现除了病毒浓度较低但可测量的情况外，这两种方法具有相似的特性。在这种情况下，SK方法会产生向上偏差的滴度估计值。根据我们的结果，我们建议在大多数病毒浓度下使用ML或SK；然而，在低病毒浓度下，首选ML。
