Yes I do mean leukopenia. If a said person has a viral infection that causes a decrease in wbc count, why would chemotherapy be used as a treatment? The virus is yet unknown. Other treatments have been unsuccessful and thus chemo is being used as a resort. cancer has been ruled out.
Do you mean leukopenia secondary to hemophagocytosis? Some viral infections can manifest like a malignant disease with pancytopenia and chemotherapy may help. I have not taken care of hemophagocytosis patients for decades and can not remember the name of chemotherapeutic agents. Yu should be able to find them in literature.