There are no rules in this regard. Try to make the appropriate choice for each situation.
If you are introducing a broad area/concept, for example a cell type, or a form of therapy or a disease, you can reference a review article. In this case, you should ensure that it is a recently written one (refer to several reviews, if appropriate).
If you are referring to the demonstration of a result, a specific finding/discovery, then ideally you should refer to the original research paper, even if it is old.
For example: "Cell transplantation is a potential therapeutic approach to treat neurodegenerative diseases (reviews). It is possible to transplant embryonic stem cells without adverse immune responses (specific research papers)."
There are no rules in this regard. Try to make the appropriate choice for each situation.
If you are introducing a broad area/concept, for example a cell type, or a form of therapy or a disease, you can reference a review article. In this case, you should ensure that it is a recently written one (refer to several reviews, if appropriate).
If you are referring to the demonstration of a result, a specific finding/discovery, then ideally you should refer to the original research paper, even if it is old.
For example: "Cell transplantation is a potential therapeutic approach to treat neurodegenerative diseases (reviews). It is possible to transplant embryonic stem cells without adverse immune responses (specific research papers)."
I usually use to cite a review if there is a long list of references to cite for a topic. It help to short the reference list keeping the support to the information you are writing about.
quote research articles there where you want to compare your results with previous findings, use review articles for generalized findings and statements.
I think both of them are necessary, but research papers have more importance because you can exactly referance the similar results which scientists acquierd before you and compare all the investigated results in your field of study with others.