CD4 and viral infectious disease: However, these approaches showed a high variability in the expansion of the different γδ-T cell subpopulations (CD4, CD8, CD4–/CD8–, Vδ1, Vδ2, and Vδ1–/Vδ2–) and feasibility of gene-modification in order to improve persistence and efficacy against a broad range of tumours and viral infections.