In biomedical research and development, scientists mostly use cultured cell lines as models because they offer easy, inexpensive, and stable platforms. However, cell lines fail to grasp the microenvironment physiology that occurs in vivo. Human primary cells come to the rescue in this situation! Primary cell culture portrays the complex physiological cell behavior and therefore represents the in vivo microenvironment better. Once you decide on your hypothesis, it is up to your research requirement whether to use human primary cells or immortal cell lines to achieve the required research efficacy.
Human primary cells closely represent the human in vivo physiology and in the case of establishing experiment results, human primary cells offer a better and relevant cell culture model.