Primary cells differ from cell lines in many ways.  Here’s what you should know about primary cells:

1.  Primary cells have a finite life span. They are exactly like the cells that you would find in your own body, so they do die after a certain period of time in culture. The amount of time primary cells survive in culture varies according to cell type.  
2.  Primary cells can be diverse. Cancer cell lines often come from a single patient – for example, HeLa cells came from one woman, Henrietta Lacks. Primary cells, on the other hand, can come from a variety of people. Having a variety of primary cell types from many different donors is especially useful when carrying out early drug testing— it’s important to ensure that the drug is effective for everyone. Before testing the drug in human patients, researchers can use primary cells from different donors to verify that the same effects are observed. 
3. Primary cells can change in culture.  For this reason, and because primary cells do not live forever, Lifeline Cell Technology strongly suggests carrying out experiments on primary cells using earlier passages.
4. Primary cells have not been modified in any way. Except for the enzymatic and/or physical dissociation required for extracting the cells from their tissue of origin, primary cells are not altered in any way. Immortalized cell lines, on the other hand, are often transformed either with cancer genes, viruses or other inducible modifications, which could alter the outcome of experiments.
5. Primary cells are finicky. Cell lines are hardy, mostly because they have to last a long time in culture, and be capable of surviving multiple rounds of cryopreservation and thawing. Primary cells, on the other hand, tend to be more difficult to maintain in culture.