T-CELL ACTIVATION VIA THE DISIALOGANGLIOSIDE GD3 - ANALYSIS OF SIGNAL-TRANSDUCTION

The monoclonal antibody (mAb) R24 is a murine immunoglobulin G(3) (IgG (3)) that reacts with the GD3 disialoganglioside present on melanoma c ells as well as a subset of T cells. R24 mAb has induced antitumor res ponses both alone and in combination with interleukin-2 (IL-2) in clin ical trials. We have reported T cell activation via GD3 as measured by the induction of tyrosine phosphorylation. In this study a more detai led analysis of signal transduction after ligation of GD3 was performe d in an attempt to understand the mechanism of in vivo therapeutic ben efits observed, Analysis of subsequent events indicated that GD3 engag ement resulted in phospholipase C gamma phosphorylation and calcium fl ux, When ras-associated events were examined, GD3 signaling resulted i n ras activation as determined by GDP/GTP conversion as well as dose- and time-dependent IP3 activation, In addition, the majority of the IP 3 activation by GD3 was inhibited by herbimycin A pretreatment. Elucid ation of the nature and potential role of this moiety in GD3 signal tr ansduction should be useful. Collectively, these data suggest a novel mechanism of T cell activation via a single, non-protein, surface moie ty, This novel form of T cell-mediated activation may permit the deliv ery and local activation of effector cells at the tumor resulting in s ite-specific activation of the immune system.