Since single-round infectivity assay to determine the potential role of IFN-α could not provide useful information on viral resistance, replication, and productivity of TF and NT viruses, we performed a multiple round infection assay in primary CD4+ T cells in the presence and absence of IFN-α to compare the resistance, replication kinetics and productivity of TF and NT viruses over a period of time up to 12 days. The gene discussed is CD4; the disease is infection.