This app gives you a heat map of gene expression in different immune cells. Not all of you will have use for this app, but if you work in oncologic ID or see a lot of patients who are on immunomodulating meds, you might find it helpful. You might wonder if a new anti CD-XYZ drug will have immunosuppressive effects, and in the absence of any hard data this helps you reason it out. Combine that with a knowledge of what cell line deficiencies lead to which kinds of infections, and you can alter the way you think about opportunistic infections.
Going with ImmGen is the CD Antigens app. It gives essentially the same information but in a more narrative way. Instead if immune cells as the starting point, it starts with the CD antigen. Between ImmGen and this app, you can make a reasoned prediction about how a new drug may affect immune cells (in the absence of more concrete clinical data).