IRX-2, a novel immunotherapeutic, protects human T cells from tumor-induced cell death

Abstract

IRX-2 is a cytokine-based biologic agent that has the potential to enhance antitumor immune responses. We investigated whether IRX-2 can protect T cells from tumor-induced apoptosis. Tumor-derived microvesicles (MV) expressing FasL were purified from supernatants of tumor cells and incubated with activated CD8+ T cells. MV induced significant CD8+ T-cell apoptosis, as evidenced by Annexin binding (64.4±6.4%), caspase activation (58.1±7.6%), a loss of mitochondrial membrane potential (82.9±3.9%) and DNA fragmentation. T-cell pretreatment with IRX-2 prevented apoptosis. IRX-2-mediated cytoprotection was dose and time dependent and was comparable to effects of IL-2, IL-7 or IL-15. IRX-2 prevented MV-induced downregulation of JAK3 and TCRζ chain and induced STAT5 activation in T cells. IRX-2 prevented MV-induced Bax and Bim upregulation (P<0.005–0.05), prevented cytochrome c release and Bid cleavage, and concurrently restored the expression of Bcl-2, Bcl-xL, FLIP and Mcl-1 (P<0.005–0.01) in T cells. In addition, IRX-2 reversed MV-induced inhibition of the PI3K/Akt pathway. An Akt inhibitor (Akti-1/2) abrogated protective effects of IRX-2, suggesting that Akt is a downstream target of IRX-2 signaling. Thus, ex vivo pretreatment of CD8+ T cells with IRX-2 provided potent protection from tumor-induced apoptosis. IRX-2 application to future cancer biotherapies could improve their effectiveness by bolstering T-cell resistance to tumor-induced immunosuppression.

Exosomes and tumor-mediated immune suppression

“…Thus, TEX induce apoptosis of activated CD8 + T cells by engaging extrinsic and intrinsic apoptosis pathways (60). The in vitro data discussed above are consistent with reports of similar changes in the expression of the pro-or antiapoptotic family members in circulating T cells of patients with cancer (61,63).…”

“…TEX-mediated signals leading to apoptosis of activated CD8 + T cells were associated with early membrane changes (i.e., annexin V binding) in target cells, caspase 3 cleavage, cytochrome C release from mitochondria, loss of the mitochondrial membrane potential (MMP), and, finally, DNA fragmentation (60). The PI3K/AKT pathway is a key target of TEX in activated CD8 + T cells (60,61). Recently, phosphatase and tensin homolog (PTEN), which regulates PI3K/AKT signaling, was found to be a component of the TEX cargo and to mediate phosphatase activity in recipient cells (62).…”

Tumor-Derived Exosomes and Their Role in Tumor-Induced Immune Suppression

“…We found that TEX produced by tumor cells may exert direct or indirect effects on human immune cells. TEX induce apoptosis of activated anti-tumor effector T cells [28,29]; TEX inhibit functions necessary for sustaining anti-tumor responses such as activation, proliferation and cytotoxicity [28]; TEX interfere with normal differentiation of immune cells [26,30]; TEX polarize immune cells to tumor-promoting phenotypes and regulate mobilization of immune cells to the tumor [31,32]. Indirectly, TEX expand proliferation of Treg and myeloid-derived suppressor cells (MDSC) and up-regulate suppressor activity of these cells thus contributing to tumor-induced immune suppression and the tumor immune escape [33,34].…”

“…These data suggest that TEX induce apoptosis in activated CD8+ T cells by engaging extrinsic as well as intrinsic apoptotic cascades. Further, the PI3K/AKT pathway is the key target for TEX in activated CD8+ T cells: dramatic, time-dependent AKT dephosphorylation and concomitant decreases in expression levels of BCL-2, BCL-xL and MCL-1 accompanied by an increase in levels of pro-apoptotic BAX were observed in these cells during co-incubation with TEX [29]. …”

Biological markers of prognosis, response to therapy and outcome in ovarian carcinoma

“…Exosome cargos include proteins, such as enzymes, cytokines, growth factors, lipids and nucleic acids, including mRNA or microRNA and ncRNA [75–77]. It has been shown that tumor cells are avid producers of exosomes, which play a role in many aspects of tumor progression including: degradation of the extracellular matrix [78]; angiogenesis [79]; suppression of immune cell functions [56,80,81] and drug resistance [82]. …”