My HGF cell line was working fine when suddenly every cryovial i thawed started to show a pattern of cell death, i.e. after one subculture. Contamination comes out of nowhere and i am losing valuable cell stock. The incubator has been cleaned , all plastic ware changed and reagents changed as well. The aseptic technique is spot on and frankly was working fine before. I am at a loss to understand why this is happening. The media i use is alpha-mem, P-strep 1% and FBS 10%. Filtered FBS stock after throwing away previous and got new P-strep and alpha-mem as well. Any ideas or suggestions because this is hindering my entire study.