A novel co-stimulatory T cell antigen co-expressed on renal cell carcinoma

The A6H mAb raised primarily against human renal cell carcinoma(RCC) has previously been shown to bind strongly to RCC, tosome degree to colon carcinoma but only marginally to a varietyof normal tissues. Immunohlstochemical analysis of RCC tissuescontaining tumor-Infiltrating lymphocytes revealed that A6Hstained both tumor cells and lymphocytes. FACS analysis of humanperipheral blood cells demonstrated that A6H mAb stained 85-90%of both CD4⁺ and CD8⁺ T cells, but not granulocytes, monocytes,NK cells or B cells. Furthermore, 85-90% of naive and memoryT helper cells were stained with A6H suggesting that the A6HmAb defines unique subsets within these T cell populations.Dual staining showed that A6H mAb bind to an antigen that isclearly distinct from other cell surface molecules on T cells,including CD28, CD29, CD26, CD44 and ICAM-2. A6H mAb bindinginduced a second signal in anti-CD3 mAb activated T cells, resultingIn cell proliferation, IL-2 receptor expression and vigorousproduction of IFN_- and TNF, and production of minor amountsof IL-2. Immunoprecipitatlon with A6H mAb indicated a molecularweight of 120-140 kDa on both T cells and RCC. We suggest thatthe A6H mAb defines a unique T cell surface antigen which isinvolved in signal transduction and is expressed on subsetsof human T cells. The co-expression of A6H on T cells and tumorcells suggests a possible function related to common propertiesof these cells.