With our identification of vIRF3 as an IRF4 co-TF, it is apparent that each of the three human viruses linked to hematologic malignancy (EBV, KSHV, and HTLV-1) encodes at least one protein that usurps IRF4 and/or BATF family members to promote the survival and proliferation of infected cells. Here, IRF4 is linked to hematologic disorder.