9 CFR § 101.6 - Cell cultures.
---
identifier: "/us/cfr/t9/s101.6"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "9 CFR § 101.6 - Cell cultures."
title_number: 9
title_name: "Animals and Animal Products"
section_number: "101.6"
section_name: "Cell cultures."
chapter_name: "ANIMAL AND PLANT HEALTH INSPECTION SERVICE, DEPARTMENT OF AGRICULTURE"
subchapter_number: "E"
subchapter_name: "VIRUSES, SERUMS, TOXINS, AND ANALOGOUS PRODUCTS; ORGANISMS AND VECTORS"
part_number: "101"
part_name: "DEFINITIONS"
positive_law: false
currency: "2026-03-24"
last_updated: "2026-03-24"
format_version: "1.1.0"
generator: "[email protected]"
authority: "21 U.S.C. 151-159; 7 CFR 2.22, 2.80, and 371.4."
regulatory_source: "38 FR 8426, Apr. 2, 1973, unless otherwise noted."
cfr_part: "101"
---
# 101.6 Cell cultures.
When used in conjunction with or in reference to cell cultures, which may be referred to as tissue cultures, the following terms shall mean:
(a) *Batches of primary cells.* A pool of original cells derived from normal tissue up to and including the 10th subculture.
(b) *Cell line.* A pool of cells which are 11 or more subcultures from the tissue of origin.
(c) *Subculture.* Each flask to flask transfer or passage regardless of the number of cell replications.
(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]