Human NKT cells recognize the glycolipid antigen, a-galactosylceramide (aGalCer), presented in the context of the non-classical antigen-presenting molecule, CD Id. However, NKT cells exposed to aGalCer can lyse a number of CD Id-negative tumor-derived ;ell lines. Lysis of these tumor targets in the absence of CDld suggests that aGalCer-activuted NKT cells may release soluble mediators. One possible mediator is granulysin, a newly described component of cytolytic granules present in activated cytotoxic T cells and NK cells. Granulysin is a member of the saposin-like protein family that has direct antimicrobial activity and that can activate caspase 9 to induce apoptosis in nucleated cells. In the present study, immunofluorescent staining demonstrated a granular pattern of granulysin expression in NKT cells. Purified granulysin protein was tested against a number of ta'get cells and correlated with results of cytotoxicity assays. The CDld-positive Molt-3 T cell acute lymphoblastic leukemia (ALL) cell line was specifically lysed by an NKT cell clone derived from a normal donor at the effector to target ratio of 5:1 (40% specific lysis) and was sensitive to lysis by granulysin (30% increase in propidium iodide-staining cells;. In contrast, a recently derived CD Id-negative T cell leukemia cell line was resistant to both lysis by NKT cells (3% specific lysis) and to lysis by granulysin (10% lysis). This cell line was established from a patient with chemo-refractory disease and contairs a chromosomal rearrangement at Ip36.1, the location of the caspase 9 gene. Caspase 9 is required for apoptosis induced by chemotherapeutic agents, as well as by granulysin. Loss of caspase 9 activity in this cell line is being investigated. Finally, primary ALL cells from an untreated patient were sensitive to granulysin (30% lysis). Overall, these studies suggest that the tumorolytic effect of aGalCer-activated NKT cells may be mediated through the release of soluble cytotoxic mediators, such as granulysin, and that the optima) timing of immunotherapy using the NKT cell/aGalCer system is early in disease, before resistance emerges.
|Original language||English (US)|
|Issue number||11 PART I|
|State||Published - Dec 1 2000|
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