Being immortalized ?

[Moens William]

Hello Netters,

Primary cultures of mammalian cells usually die after a certain number of passag
es in vitro. In rodent primaries, some cells may survive to the crisis and behav
e as "immortal". This extremely rarely happens with human primaries.
Therefore "immortalisation" vectors are used to get immortalisation of human 
primary cultures.
In fact I have difficulties to catch exactly on which physiological/molecular fa
cts one can declare a successful "immortalisation" of such cultures.
Are they mutants of apoptosis, then which are the criteria to check?
Are they surviving cells with or without normal cell cycling rates?