A validation protocol and evaluation algorithms to determine compatibility of cell therapy product matrices in microbiological testing

As part of product release testing, sterility of cellular therapy products, using formally validated methods, must be demonstrated, irrespective of whether products are released and administered while microbiological results are pending or whether these can be awaited. Components of the matrix, i.e. the carrier fluid and the therapeutic cells, could potentially inhibit bacterial growth and may thus obscure their presence, resulting in false-negative data. The European Pharmacopoeia and equivalent guidelines therefore specify that for each cell therapy product the specific matrix' compatibility with validated detection methods is formally established. There for, matrix is spiked with known numbers of representative aerobic and anaerobic agents, cultured in automated systems such as BacT/ALERT, followed by microbiological species identification from culture-positive bottles. We here propose an easy-to-follow protocol for matrix validation and demonstrate its successful execution with a panel of novel advanced therapy medicinal products and standard cell therapy products, as well as algorithms for interpretation of conflicting results between BacT/Alert and culture methods. This protocol can serve as a basis for microbiological method (matrix) validations for cellular preparations.