Human gamma delta T lymphocytes exert natural and IL-2-induced cytotoxicity to neuroblastoma cells

Human gamma delta T lymphocytes play an important role in nonadaptive react ions to infection and early tumor defense. This is the first report that fr eshly isolated, native gamma delta T cells of some healthy donors can kill human neuroblastoma cells to varying degrees. Their killing ability was inc reased and maintained during expansion and cultivation with interleukin-2 ( IL-2; 400 IU/mL) for as long as 30 days (100% specific lysis at an effector -to-target cell (E:T) ratio of 20:1). gamma delta T lymphocytes without thi s spontaneous killing ability gained a specific cytolytic activity of 81% /- 10.4% SD after stimulation with IL-2 for 24 hours. gamma delta cells wer e isolated from peripheral blood by positive enrichment (using a magnetic c ell sorting system; purity, 95.2% +/- 3.2% SD, n = 21). High natural cytoto xic activity against human neuroblastoma cell lines (>50% specific lysis at an E:T ratio of 20:1) was exhibited by one of 11 donors, whereas two of 11 showed medium cytotoxicity (30% to 50% specific lysis). Eight of 11 donors showed very slight or no lytic activity against human neuroblastoma cells (<30% specific lysis), gamma delta T cells were also cytotoxic against Daud i (32.7% specific lysis at an E:T ratio of 20:1), Raji (10.3%), Colo 205 (2 3.1%), A 204 (54%), K 562 (100%), and SK-N-MC (100%) cells. Isolated gamma delta T cells were grown in Iscove modified Dulbecco medium with IL-2 (400 IU/mL). Increased cell proliferation (38.5% to 182%) was induced with phyto hemagglutinin, IL-15, Clodronat, OKT3, or various combinations of these. Re sults of cold target inhibition assays suggest a natural killer-like activi ty of the gamma delta T-cell killing mechanism. Peptidase or papain render neuroblastoma cells unsusceptible to gamma delta T-cell killing, suggesting the involvement of antigen peptide(s) in the process of neuroblastoma cell killing. Treatment with acid phosphatase reduced specific lysis by 66.5% /- 34.1% SD, which suggests a binding to phosphorylated neuroblastoma cell- surface structures in the killing mechanism of gamma delta T cells. Heat sh ock did not affect the extent of neuroblastoma killing by gamma delta cells . Recognition of neuroblastoma cells by gamma delta cytotoxic T lymphocytes is negatively regulated by major histocompatibility complex I receptors. E vidence for natural and inducible cell cytotoxicity of gamma delta T cells against human neuroblastoma cells, easy propagation, purification, and miss ing alloreactivity in mixed lymphocytes cultures indicates a role for this subpopulation of T lymphocytes in adoptive immunotherapy.