Collins J K, Chesebro B
J Natl Cancer Inst. 1980 May;64(5):1153-9.
Cell line Y57, obtained from a (C57BL/10 X A.BY)F1 mouse made leukemic with Friend virus complex (FV), spontaneously ceased FV production in vitro after 20 passages. By limiting dilution cloning, the incidence of non-virus-producing cells was found to increase with sequential passage. Nonproducer cells apparently arose spontaneously and were able to increase in number relative to producer cells because the growth rate of nonproducer cells was more rapid than the rate at which virus could reinfect them. Nonproducer clones all contained the defective spleen focus-forming virus in a latent but rescuable form but showed defects in helper virus env and gag gene product synthesis. Stable long-term virus-producing clones were obtained both by cloning at early in vitro passages or by cloning immediately after reinfection of nonproducer cells with FV.
细胞系Y57源自一只感染了弗瑞德病毒复合物（FV）而患白血病的（C57BL/10×A.BY）F1小鼠，在体外传代20次后自发停止产生FV。通过有限稀释克隆发现，不产生病毒的细胞的发生率随着连续传代而增加。不产生病毒的细胞显然是自发产生的，并且相对于产生病毒的细胞数量能够增加，因为不产生病毒的细胞的生长速率比病毒再次感染它们的速率更快。不产生病毒的克隆均含有潜伏但可拯救形式的缺陷型脾集落形成病毒，但在辅助病毒env和gag基因产物合成方面存在缺陷。通过在体外传代早期进行克隆或在用FV再次感染不产生病毒的细胞后立即进行克隆，均获得了稳定的长期产生病毒的克隆。
