Data from Suppression of Proximal T Cell Receptor Signaling and Lytic Function in CD8<sup>+</sup> Tumor-Infiltrating T Cells

Abstract

<div>Abstract<p>CD8<sup>+</sup> tumor-infiltrating lymphocytes (TIL) lack <i>in vivo</i> and <i>in vitro</i> lytic function due to a signaling deficit characterized by failure to flux calcium or activate tyrosine kinase activity upon contact with cognate tumor cells. Although CD3ζ is phosphorylated by conjugation <i>in vitro</i> with cognate tumor cells, showing that TIL are triggered, PLCγ-1, LAT, and ZAP70 are not activated and LFA-1 is not affinity-matured, and because p56<sup>lck</sup> is required for LFA-1 activation, this implies that the signaling blockade is very proximal. Here, we show that TIL signaling defects are transient, being reversed upon purification and brief culture <i>in vitro</i>, implying a fast-acting “switch”. Biochemical analysis of purified nonlytic TIL shows that contact with tumor cells causes transient activation of p56<sup>lck</sup> (∼10 s) which is rapidly inactivated. In contrast, tumor-induced activation of p56<sup>lck</sup> in lytic TIL is sustained coincident with downstream TCR signaling and lytic function. Shp-1 is robustly active in nonlytic TIL compared with lytic TIL, colocalizes with p56<sup>lck</sup> in nonlytic TIL, and inhibition of Shp-1 activity in lytic TIL <i>in vitro</i> blocks tumor-induced defective TIL cytolysis. Collectively, our data support the notion that contact of nonlytic TIL with tumor cells, and not with tumor-infiltrating myeloid-derived suppressor cells, causes activation of Shp-1 that rapidly dephosphorylates the p56<sup>lck</sup> activation motif (Y394), thus inhibiting effector phase functions. [Cancer Res 2007;67(23):11447–54]</p></div>