TNFRSF9 and infection: CD137+ and CD137− Vγ9Vδ2-T cell subsets were sorted after activation by an anti-γδ-TCR antibody in vitro, and then highly purified (>95%) CD137+, CD137− or whole Vγ9Vδ2-T cells were adoptively transferred into the influenza virus-infected mice on days 2, 4, and 6 post infection (Fig. 3a).