Activated T cells Inhibit NK Cell-mediated Tumour Rejection

A novel inhibitor of proteasome deubiquitinating activity renders tumor cells sensitive to TRAIL-mediated apoptosis by natural killer cells and T cells

The proteasome inhibitor bortezomib simultaneously renders tumor cells sensitive to killing by natural killer (NK) cells and resistant to killing by tumor-specific T cells. Here, we show that b-AP15, a novel inhibitor of proteasome deubiquitinating activity, sensitizes tumors to both NK and T cell-mediated killing. Exposure to b-AP15 significantly increased the susceptibility of tumor cell lines of various origins to NK (p < 0.0002) and T cell (p = 0.02)-mediated cytotoxicity. Treatment with b-AP15 resulted in increased tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptor-2 expression (p = 0.03) and decreased cFLIP expression in tumor cells in vitro. In tumor-bearing SCID/Beige mice, treatment with b-AP15 followed by infusion of either human NK cells or tumor-specific T cells resulted in a significantly delayed tumor progression compared with mice treated with NK cells (p = 0.006), T cells (p < 0.0001) or b-AP15 alone (p = 0.003). Combined infusion of NK and T cells in tumor-bearing BALB/c mice following treatment with b-AP15 resulted in a significantly prolonged long-term survival compared with mice treated with b-AP15 and NK or T cells (p ≤ 0.01). Our findings show that b-AP15-induced sensitization to TRAIL-mediated apoptosis could be used as a novel strategy to augment the anticancer effects of adoptively infused NK and T cells in patients with cancer.

Role of stress-induced NKG2D ligands in liver diseases

Cell death by apoptosis is a prominent feature in a variety of liver diseases. It is likely that apoptosis is the initial cellular response to hepatocyte and biliary injury, which then leads to the initiation of cellular and cytokine cascades culminating in hepatocyte death with subsequent fibrosis and cirrhosis. This sequence of events is of paramount clinical importance. Recently, soluble forms of the major histocompatibility complex class I-related chains A and closely related B (MIC A and B) were reported to be increased in patients with a variety of liver diseases. MIC A and B are cell surface glycoproteins that function as indicators for cellular stress and thus activate circulating cytotoxic natural killer (NK) cells. The interaction between MIC A and B with their cognate receptor natural killer group 2 member D (NKG2D) culminates in enhanced liver cell death, which is mediated in part by apoptotic mechanisms. The present overview focuses on the role of the stress-induced NKG2D ligands MIC A and B in diverse liver diseases. Critical insights into these complex relations may help to promote rationally based therapies in liver diseases. Importantly, we hope that this overview will help to stimulate further studies into mechanisms by which stress ligands mediate cell death and its sequale.