When used in conjunction with or in reference to cell cultures, which may be referred to as tissue cultures, the following terms shall mean:

1. (a) Batches of primary cells. A pool of original cells derived from normal tissue up to and including the 10th subculture.
2. (b) Cell line. A pool of cells which are 11 or more subcultures from the tissue of origin.
3. (c) Subculture. Each flask to flask transfer or passage regardless of the number of cell replications.
4. (d) Master Cell Stock (MCS). The supply of cells of a specific passage level from which cells for production of biologics originate.

[38 FR 8426, Apr. 2, 1973, as amended at 40 FR 45419, Oct. 2, 1975; 49 FR 22624, May 31, 1984]