Following. Myelosuppressive chemotherapy, the bone marrow will be compromised in its ability to make neutrophils (a type of WBC that protects against bacterial infections). Since a neutrophil only lasts 24hrs after it's made, you quickly run out if you aren't making them efficiently. To facilitate recovery after chemo, we use a gcsf, which stimulates neutrophil production to mitigate infection risk.
Chemotherapy. There is nothing you can do. Watching your white blood cells is one of the main things your cancer specialist will do and they will react as needed.