Did you know that Cells at work had a number of Spin offs. At time of writing this there is four different ones, the newest being Cells At Work Friend. In every case Akane Shimizu is supervising it. He is the person who made the original Cell at Work Manga Story and Art. Below is a quick bit of information about each. As of now I haven't herd of any of these coming state side.
Bacteria at Work
Likely the most different on this list, Bacteria at Work focus on anthropomorphic bacteria that lives in a high school girl intestines. This one is also different as it focus on peaceful community instead of invading alien bodies
Cells at Work! BLACK
The most popular it seems on this list, it has a similar focus as the normal Cells at Work but the body is a middle age and poorly maintained. The person has issues with stress, smoking, drinking, and the like which causes complications on the body which is the world the cells live in.
Cells that Don't Work
A different take on Cells at Work, with it lead being a Macrophage that works in a Red Bone Marrow and a older Erythroblast that refuses to undergo erythropoiesis because he does not want to work as a Erythrcyte (AKA Red blood Cell).
An Erythroblast is a immature cell red blood cell. In this story the lead Erythroblast is the oldest in the Bone Marrow and much rather become a White Blood Cell so he can fight different cells and bacteria. Unlike the original, cells in this series display disinterest towards their supposed functions.
Cells at Work! Friend
Focus of Cells at Work! FRIEND spin off is on will star the aggressive Killer T as he takes down foreign bodies and unhealthy cells. It should start coming out In February in japan but I find calling it Friend is a odd choice.
Where to Enjoy
State Side you can watch and Read just the main work that had an anime adaption.