Which of the following is NOT a type of cell culture commonly used in research?

Prokaryotic cells are not classified as a type of cell culture commonly used in research in the same way that HeLa cells, CHO cells, and Vero cells are. HeLa cells are derived from cervical cancer cells and are widely used for cancer research and vaccine development due to their ability to divide indefinitely in culture. CHO (Chinese Hamster Ovary) cells are used extensively in biopharmaceutical production because of their capability to post-translationally modify proteins, making them invaluable for producing therapeutic proteins. Vero cells, derived from the kidney of an African green monkey, are important in virology and vaccine development as they can support the replication of various viruses.

In contrast, prokaryotic cells, which include bacteria and archaea, are generally not used in the same cell culture context as these eukaryotic cells. They are usually grown in a different setting that involves distinct culturing techniques, primarily for studying their biology or for applications like cloning and plasmid propagation. This fundamental difference in the type of organisms and their applications in research firmly establishes prokaryotic cells as outside the common types of cell cultures that researchers typically utilize.