started from the liquid nitrogen stock.

Выражение встречается в следующем контексте:

To test immunomodulatory properties of β-glucans THP-1 monocytes were used. The THP-1 is a human leukemic cell line cultured from the blood of a boy with acute monocytic leukemia (Tsuchiya S, et al., 1980). The cell culture was started from the liquid nitrogen stock. The cells were grown in IMDM +10% FCS+ 50 μg/ml penicillin-streptomycin in small flasks (medium volume 8 cm3) until sufficient cells were obtained.

Заранее спасибо