Functional CD4 T cells after intercellular molecular transfer of OX40 ligand

OX40/OX40 ligand (OX40L) proteins play critical roles in the T cell-B cell and T cell-dendritic cell interactions. Here we describe the intercellular transfer of OX40L molecules by a non-Ag specific manner. After 2-h cocultur e of activated CD4(+) T cell (OX40L(-), OX40(+)) with FLAG peptide-tagged O X40L (OX40L-flag) protein-expressing COS-1 cells, the OX40L-flag protein wa s detected on the cell surface of the CD4(+) T cells by both anti-OX40L and anti-FLAG mAbs. The intercellular OX40L transfer was specifically abrogate d by pretreatment of the COS-1 cells with anti-OX40L mAb, 5A8. The OX40L tr ansfer to OX40-negative cells was also observed, indicating an OX40-indepen dent pathway of OX40L transfer. HUVECs, allostimulated monocytes, and human T cell leukemia virus type I-infected T cells, which all express OX40L, ca n potentially act as the donor cells of OX40L. The entire molecule of OX40L was transferred and stabilized on the recipient cell membrane with discret e punctate formation. The transferred OX40L on normal CD4(+) T cells was fu nctionally active as they stimulated latent HIV-1-infected cells to produce viral proteins via OX40 signaling. Therefore, these findings suggest that the intercellular molecular transfer of functional OX40L may be involved in modifying the immune responses.