CONSTRUCTION, PURIFICATION, AND FUNCTIONAL INCORPORATION ON TUMOR-CELLS OF GLYCOLIPID-ANCHORED HUMAN B7-1 (CD80)

To generate a potent cell-mediated immune response, at least two signa ls are required by T cells. One is engagement of the T cell receptor w ith peptide-bearing major histocompatibility complex molecules. The ot her signal can be delivered by various molecules on the antigen-presen ting cell, such as B7-1 (CD80). Many tumor cells escape immune recogni tion by failing to express these costimulatory molecules, Transfection of the B7 gene into some murine tumor cells allows for immune recogni tion and subsequent rejection of the parental tumor. We have studied a n alternative approach for the introduction of B7-1 onto the surface o f tumor cells. This method involves purified glycosyl-phosphatidylinos itol (GPI)-anchored proteins which can spontaneously incorporate their lipid tail into cell membranes. We have created and purified a GPI-an chored B7-1 molecule (called GPI-B7) which is able to bind its cognate ligand, CD28, and incorporate itself into tumor cell membranes after a short incubation. Tumor cells that have been reconstituted with GPI- B7 can provide the costimulatory signal needed to stimulate T cells. T hese findings suggest an approach for the introduction of new proteins onto cell membranes to create an effective tumor vaccine for potentia l use in human immunotherapy.