Rescuing Melanoma Epitope-Specific Cytolytic T Lymphocytes from Activation-Induced Cell Death, by SP600125, an Inhibitor of JNK: Implications in Cancer Immunotherapy

Abstract

Activation-induced cell death (AICD) as well as programmed cell death (PCD) serve to control the expansion of activated T cells to limit untoward side effects of continued effector responses by T cells and to maintain homeostasis. AICD of T cells in tumor immunotherapy can be counterproductive particularly if the activated T cells undergo apoptotic death after the very first secondary encounter of the specific epitope. We examined the extent to which tumor epitope-specific CTLs that are activated and expanded in an in vitro-matured dendritic cell-based primary stimulation protocol undergo AICD following their first secondary encounter of the cognate epitope. Using the MART-127–35 epitope as a prototype vaccine epitope, we also examined whether these CTLs could be rescued from AICD. Our results demonstrate that a substantial fraction of MART-127–35 epitope-specific primary CTLs undergo AICD upon the very first secondary encounter of the cognate epitope. The AICD in these CTLs is neither caspase dependent nor is it triggered by the extrinsic death signaling pathways (Fas, TNFR, etc.). These CTLs, interestingly, could be rescued from AICD by the JNK inhibitor, SP600125. We also found that SP600125 interferes with their IFN-γ response but does not block their cytolytic function. The rescued CTLs, however, regain their capacity to synthesize IFN-γ if continued in culture without the inhibitor. These observations have implications in tumor immunotherapy and in further studies for regulation of AICD in CTLs.

Activation‐induced cell death of human melanoma specific cytotoxic T lymphocytes is mediated by apoptosis‐inducing factor

“…We have recently shown that melanoma epitopespecific primary CTL undergo AICD after encountering the cognate antigen in an external DR-and caspaseindependent manner and that these CTL can be rescued from AICD by the c-jun N terminal kinase (JNK) inhibitor, SP600125 [12]. While our findings are in agreement with recent observations on a DR-independent and caspase-independent mechanism of AICD of CTL, the molecular mechanism behind the caspaseindependent mechanism of AICD of primary CTL remains poorly understood.…”

“…1 recapitulates our basic observation of the protective affect of the JNK inhibitor SP600125 on AICD in MART-1 [27][28][29][30][31][32][33][34][35] epitope-specific CTL [12]. A fraction of in vitro expanded CTL dies upon encountering the cognate antigen for the second time (Fig.…”

“…1B), and SP600125 blocked this c-Jun activation. We have previously reported that AICD of primary CTL does not involve cleavage of PARP [12]. We now find that neither caspase-8 nor caspase-3 are activated in these CTL encountering the cognate epitope (Fig.…”

“…It is widely believed that apoptosis of T cells results from the ligation of death receptors (such as Fas and TNFR) and is mediated by the activation of caspases. A universal role for Fas and TNF family receptor-driven signaling in T cell apoptosis has, however, come into question by recent observations [8,[10][11][12]. Caspase-independent apoptosis, in general [11], and a DR-independent and caspaseindependent mechanism of AICD of CTL, in particular, have been described [8,12], but the molecular mechanism behind this process remains unclear.…”

“…A universal role for Fas and TNF family receptor-driven signaling in T cell apoptosis has, however, come into question by recent observations [8,[10][11][12]. Caspase-independent apoptosis, in general [11], and a DR-independent and caspaseindependent mechanism of AICD of CTL, in particular, have been described [8,12], but the molecular mechanism behind this process remains unclear. We have recently shown that melanoma epitope-specific primary CTL undergo AICD after encountering the cognate antigen in an external DR-and caspaseindependent manner, and that these CTL can be rescued from AICD by the c-jun N-terminal kinase (JNK) inhibitor, SP600125 [12].…”