Attachment IV - Page 27 
-5- DRAFT 
NOVEMBER 7, 1983 
tumor igenicity should be obtained. Various methods can be utilized to transfer 
an expression vector Into Its host, such as transfection, transduction. 
Infection, mlcrolnjectlon, etc. The mechanism of transfer, copy number, and the 
physical state of the vector Inside the host cell; Integrated or extrachromosomal, 
should be provided. In most cases, a single host cell containing the expression 
vector should be cloned to give rise to the Master Cell Bank. The cloning 
history and methodology should be described. If new Master Cell Banks are to be 
generated periodically by expression vector transfer and cloning, acceptance 
criteria for both the new clones and the product produced by these clones should 
be described. 
IV. Master Cell Bank 
Host cells chosen to express recombinant DNA products should be 
maintained In seed lot aliquots under storage conditions which ensure genetic 
stability. The stability of both the host cell and expression vector should 
be Investigated. In particular, the fidelity of the nucleotide sequence 
encoding the expression product present in each seed lot should be verified. 
The purity of the cells in the seed lot should be assured by. Isoenzyme 
analysis, suxotrophy, antibiotic resistance, and karyology, as appropriate. 
The seed lot should be free of adventitious agents Including mycoplasma, 
bacteria, yeast, viruses, and vlrus-llke particles. At a minimum, mammalian 
host cells should be analyzed for reverse transcriptase and detection of 
virus-like structures by electron microscopy. 
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