Balancing STAT Activity as a Therapeutic Strategy

Driven by dysregulated IL-6 family member cytokine signaling in the tumor microenvironment (TME), aberrant signal transducer and activator of transcription (STAT3) and (STAT5) activation have been identified as key contributors to tumorigenesis. Following transformation, persistent STAT3 activation drives the emergence of mesenchymal/cancer-stem cell (CSC) properties, important determinants of metastatic potential and therapy failure. Moreover, STAT3 signaling within tumor-associated macrophages and neutrophils drives secretion of factors that facilitate metastasis and suppress immune cell function. Persistent STAT5 activation is responsible for cancer cell maintenance through suppression of apoptosis and tumor suppressor signaling. Furthermore, STAT5-mediated CD4+/CD25+ regulatory T cells (T_regs) have been implicated in suppression of immunosurveillance. We discuss these roles for STAT3 and STAT5, and weigh the attractiveness of different modes of targeting each cancer therapy. Moreover, we discuss how anti-tumorigenic STATs, including STAT1 and STAT2, may be leveraged to suppress the pro-tumorigenic functions of STAT3/STAT5 signaling.

Identification of cancer-stem cell antigens and development of CTL-mediated cancer immunotherapy

Cancer-stem cells (or cancer-stem like cells, CSC) play an indispensable role in tumor initiation or tumor development in vivo. However, CSCs are resistant to conventional therapies including chemo/radiotherapy and a certain molecularly-targeted therapy, thereby are responsible for tumor relapse or metastasis in clinical settings. In this review, we focus on cytotoxic T-cell mediated immune responses against CSCs and discuss a challenge of targeting CSCs as well as the development of CSC-based cancer immunotherapy, which is an emerging and promising strategy toward a complete cure of quite a few types of cancers.