Studies of the mechanism of cytolysis by tumour-infiltrating lymphocytes

Abstract

SUMMARYIn order to determine the mechanism of tumour destruction by tumour-infiltrating lymphocytes (TIL), we examined the ability of both CD4 þ and CD8 þ effector TIL, and TIL clones, to manifest granzymemediated and Fas-mediated destruction of tumour targets. In many in vitro studies TIL have been shown to manifest anti-tumour reactivity, yet many tumours escape immunological destruction. To investigate the role of Fas expression and the concomitant sensitivity to the inducibility of apoptotic death, we derived TIL from four melanomas and one glioma. The glioma, and all but one of the melanomas, expressed Fas, but Fas-mediated apoptosis could only be detected if the targets were treated with cyclohexamide. The melanomas and the glioma all expressed detectable cytoplasmic Bcl-2 protein, known to exert anti-apoptotic activity. Lysis of tumours by CD8-enriched cultures and CD8 þ clones was Ca 2þ -dependent and could not be modified by an anti-Fas MoAb. In CD4-enriched cultures or CD4 þ clones with cytotoxic potential against tumour cells, cytotoxicity was also Ca 2þ -dependent. As Ca 2þ -dependent cytotoxicity is usually the result of secretion of perforin/granzyme-B, we investigated the presence of perforin in cytotoxic CD4 þ clones and demonstrated the presence of granular deposits of this enzyme in some of the CD4 þ clones. Although an anti-Fas MoAb did not block the lysis of melanoma targets by CD4 þ clones, the examination of Fas-dependent targets demonstrated that these clones also had the potential to kill by the Fas/Fas ligand system. These data suggest that the predominant mechanism in tumour killing by TIL appears to be perforin-granzyme-dependent, and that the solid tumour cell lines we studied are less susceptible to Fas-mediated apoptosis. As non-apoptotic pathways may enhance tumour immunogenicity, exploitation of the perforin-granzyme-dependent cytotoxic T lymphocyte (CTL) pathways may be important for achieving successful anti-tumour responses.

Glucocorticoid-Induced TNF Receptor Family Related Gene Activation Overcomes Tolerance/Ignorance to Melanoma Differentiation Antigens and Enhances Antitumor Immunity

“…Studies have shown that CD4 ϩ T cells that infiltrate tumors contain perforin granules and have the potential to kill by Fas/FasL system (36,37). Because class II Ags are expressed in different solid malignancies including melanoma (38,39), CD4…”

Role of the Mitogen-Activated Protein Kinase Signaling Pathway in the Regulation of Human Melanocytic Antigen Expression

“…4). 6 The different MITF isoforms are transcribed from different promoters, with isoform-specific 5 ¶ exons spliced onto common 3 ¶ exons (25), and the respective isoforms are, therefore, subject to divergent transcriptional controls. Significant suppression of MITF-M expression by MEK inhibitors would seem unlikely to be correlated with increased MITF-M function.…”

“…The products of many of these genes are localized in the melanosome, and some are directly linked to melanin synthesis (1)(2)(3). Importantly, with respect to immunotherapy, several melanocytic gene products have been directly shown to function as target antigens for CTLs (4)(5)(6)(7)(8)(9). Loss of such antigen expression by target melanoma cells is thus a mechanism for escape from immune recognition (10)(11)(12)(13)(14)(15).…”

Activated cytotoxic lymphocytes promote tumor progression by increasing the ability of 3LL tumor cells to mediate MDSC chemoattraction via Fas signaling

“…15 In Fas-sensitive tumor cells, CTLs can induce tumor cell apoptosis by FasL, which is one of the mechanisms by which CTLs kill tumor cells. 16 It is not clear whether the activation of Fas signaling initiated by FasL on CTLs affects apoptosis-resistant tumor cells. We questioned whether CTLs could improve tumor escape via the activation of Fas-induced non-apoptotic signaling in Fas-resistant tumor cells.…”