Cell culture is fundamental to a huge amount of biological research. Although technically cells from any animals can be grown, human cells are one of the most useful to learn about human disease and test new medicines.
There two different kinds of cell culture:
1) Culturing cells that have been directly extracted from a bit of the body e.g. during an operation, and grown in the lab. These cells are called primary cells. Primary cells can be difficult to grow, and even with all the right media and temperature they normally don't last very long. This means scientists have to plan their experiments around when they might get new samples (e.g. when operations are planned) which can be complicated and difficult as sometimes for medical reasons or consent reason the scientist might not get the cells they thought they would.
2) Some cells have been growing in the lab for years. They are called immortalised cell lines. An example of one of the oldest and most used cell line is HeLa cells, that were originally from the cervical cancer of Henrietta Lacks in 1951. Sadly in the 1950s, it was not common to inform the patient or even ask the patient if it was OK to take cells, and Henrietta died without knowing about how her cells will one day help us develop vaccines against polio and HPV and figure out how cells age and develop drugs against cancer - just to name a few.The drawback of cell lines is that they have to be from a cancer or somehow modified in the lab to let them grow so easily, so they are not as similar to the cells in a healthy human body.
Both primary cells and cell lines are often originally from humans.
These days, the ethics behind using human cells is part of an open discussion between patients, doctors and scientists. There are very strict rules on what can be used from patients for research, whether that is data or cells. A lot has changed since the 1950s, the time of Henrietta Lacks and scientists are becoming more and more engaged in ethical discussions around human samples. Although a lot of work and discussion is needed to ensure human cells are collected and used in an ethical and appropriate way that protects patient data and rights, it is worth the time and effort because using human cells is one of the only ways to learn about many biological processes and test new life-saving medicines without harming animals or humans.