Hello. I am involved in an effort to develop an ontology describing cell cultures and cell lines. A key goal here is to provide clear and precise definitions of key concepts in this domain and the terms used to refer to these concepts. As you know, terms such as 'cell line' and 'primary culture' are used differently by different people. I am a cell biologist myself, so I have my own view of all this. But I am hoping to use this forum to get broader feedback from experts in the community about concepts and terms that are ambiguous or variably applied, so that our ontology might best reflect the consensus in the domain.
My first question concerns when a 'primary cell culture' becomes a 'cell line'? To clarify our definitions for these terms:
<*>a 'primary cell culture' is a cell culture comprised of cells expanded directly from living tissue prior to being passaged
<*>a 'cell line' is a cell culture comprised of a stable and homogeneous population of cells of common biological origin, derived through the passaging of a primary cell culture or the alteration of an existing cell line (e.g. a stable genetic alteration)
Note that cell lines as defined here are not necessarily immortal (we call these 'immortal cell lines'). Rather, the notion of attaining a degree of 'stability and homogeneity' is central to defining a cell line. Many textbooks are content to say that the first passage of a primary culture is sufficient to achieve this (see refs below), such that the output culture qualifies as a 'cell line'. But in the real world, many biologists we have talked with say that this is not always the case - that several passages, or additional selective procedures, may be required for a primary culture to be considered a cell line. To reflect this view, our model currently holds that when a 'primary cell culture' is passaged, it becomes what we are calling a 'secondary cell culture', but is not necessarily a 'cell line' until some degree of homogeneity and stability are reached. The question is, Can we establish some criteria or metrics for describing when this degree of homogeneity is reached, and when a cell line is established? Or is the consensus out there simply that a primary culture always becomes a line after its first passage?
If you are a biologist with experience establishing or using cell cultures and lines, your feedback here would be much appreciated. We are trying here to focus on defining the concepts and not getting hung up on their labels - so keep this in mind as you reply. Thanks everyone!
Interesting work, I think these sorts of things are good, though dissemination of the work so as to become standard will be much much harder than it might seem.
To my way of thinking, a cell line is a group of cells that have been established in culture and exhibit defined properties. This would include any immortal cell line and many cell lines that are not immortalized, but are well established (e.g. stem cells). A primary culture (for me) is any culture derived from a tissue that exhibits cell senescence (i.e. Hayflick limit) or death in a time dependent manner.
However, I don't bother with secondary culture descriptions, as it seems to me to be a waste of time, as usually the amount of cells you get from a primary culture (under your definition) is not enough to do much with that couldn't have been done with the tissue directly.