PDPN and infection: Immortalized lnFRCs (ilnFRCs), which are PDPN+ CD31− and mediate trans-infection of A3.01 T cells in 2D conditions like parental primary lnFRCs (Supplementary Fig. 5B–D), were encapsulated in a PEG gel and allowed to grow into a 3D network (Supplementary Fig. 5E).