TNFRSF9 and infection: This also correlated with a requirement for 4-1BB in the T cell response to the former, whereas 4-1BB was dispensable for the response to the less virulent strain.Similarly, anti-4-1BB was previously shown to enhance primary T cell responses to influenza virus delivered by the non-productive i.p. route of infection, in which there is minimal viral replication, but had little effect on the accumulation of T cells at later times (Bertram et al., 2004).