Background: In accord with the cancer stem cell (CSC) theory, only a small subset of cancer cells are capable of forming tumors. We previously reported that CD44 isolates tumorigenic cells from head and neck squamous cell cancer (HNSCC). Recent studies indicate that aldehyde dehydrogenase (ALDH) activity may represent a more specific marker of CSCs.Methods: Six primary HNSCCs were collected. Cells with high and low ALDH activity (ALDH^high/ALDH^low) were isolated. ALDH^high and ALDH^low populations were implanted into NOD/SCID mice and monitored for tumor development.Results: ALDH^high cells represented a small percentage of the tumor cells (1% to 7.8%). ALDH^high cells formed tumors from as few as 500 cells in 24/45 implantations, whereas only 3/37 implantations of ALDH^low cells formed tumors.Conclusions: ALDH^high cells comprise a subpopulation cells in HNSCCs that are tumorigenic and capable of producing tumors at very low numbers. This finding indicates that ALDH activity on its own is a highly selective marker for CSCs in HNSCC. © 2010 Wiley Periodicals, Inc. Head Neck, 2010

The incidence of human papillomavirus–positive (HPV⁺) head and neck squamous cell carcinoma (HNSCC) has surpassed that of cervical cancer and is projected to increase rapidly until 2060. The coevolution of HPV with transforming epithelial cells leads to the shutdown of host immune detection. Targeting proximal viral nucleic acid–sensing machinery is an evolutionarily conserved strategy among viruses to enable immune evasion. However, E7 from the dominant HPV subtype 16 in HNSCC shares low homology with HPV18 E7, which was shown to inhibit the STING DNA-sensing pathway. The mechanisms by which HPV16 suppresses STING remain unknown. Recently, we characterized the role of the STING/type I interferon (IFN-I) pathway in maintaining immunogenicity of HNSCC in mouse models. Here we extended those findings into the clinical domain using tissue microarrays and machine learning–enhanced profiling of STING signatures with immune subsets. We additionally showed that HPV16 E7 uses mechanisms distinct from those used by HPV18 E7 to antagonize the STING pathway. We identified NLRX1 as a critical intermediary partner to facilitate HPV16 E7–potentiated STING turnover. The depletion of NLRX1 resulted in significantly improved IFN-I–dependent T cell infiltration profiles and tumor control. Overall, we discovered a unique HPV16 viral strategy to thwart host innate immune detection that can be further exploited to restore cancer immunogenicity.

Appropriate treatment of head and neck squamous cell cancer (HNSCC) remains one of the most difficult challenges in head and neck oncology. Overall survival of patients with HNSCC remains at approximately 50% at 5 years. Surgical therapy can be mutilating and often has significant effects on swallowing, speech, and physical appearance. The addition of chemotherapy to radiation treatment has shown efficacy in organ preservation in some sites in the head and neck, but has resulted in limited improvement in survival rates. HNSCC resistance to chemotherapy has limited the usefulness of chemotherapy in the treatment of this disease. We have recently demonstrated that human head and neck squamous cell cancers contain a tumorigenic, so-called cancer stem cell, subpopulation of cells that can self-renew and produce differentiated cells that form the bulk of the tumor. These tumorigenic HNSCC cells have a distinct phenotype and can be identified by a surface marker. Current treatment for HNSCC regimens may selectively kill the differentiated cancer cells, producing tumor regression while sparing the cancer stem cells, leading to tumor regrowth and relapse. It is important for us to understand why HNSCC does not respond to chemotherapy and to identify new targeted treatments that can overcome resistance and improve patient outcomes. Further study of HNSCC stem cells will increase our knowledge of this devastating disease and allow us to develop novel treatments.

Worldwide, malignant neoplasms of the head and neck account for approximately 500 000 new cases of cancer annually.¹ Despite an ever-expanding fund of knowledge regarding the etiology and pathophysiology of malignant neoplasms, head and neck squamous cell carcinoma (HNSCC) continues to be a disfiguring and deadly disease. For patients with squamous cell carcinoma of the oral cavity or oropharynx, the 5-year survival is a dismal 56%, which has remained relatively unchanged in recent years.² This poor prognosis reflects the fact that most patients present with advanced-stage disease, often making a complete cure a seemingly unattainable goal. In fact, just 46% of oral cavity and 16% of oropharyngeal cancers are diagnosed when there is only local disease.²

Objectives: To determine if the behavior of cancer stem cells (CSCs) is affected by human papillomavirus (HPV) status.Study Design: An in vitro and in vivo analysis of HPV and CSCs.Setting: University laboratory.Subjects and Methods: We isolated CSCs from HPV‐positive and HPV‐negative cell lines. Two HPV‐negative cell lines underwent lentiviral transduction of E6/E7. Chemoresistence was determined using colony formation assays. Native HPV‐positive and HPV E6/E7‐transduced cells were compared for lung colonization after tail vein injection in NOD/SCID mice.Results: The proportion of CSC is not significantly different in HPV‐positive or HPV‐negative head and neck squamous cell carcinoma (HNSCC) cell lines. The HNSCC CSCs are more resistant to cisplatin than the non‐CSCs, but there were no significant differences between HPV‐positive and HPV‐negative cells. The HPV‐negative cancer cells yielded low colony formation after cell sorting. After transduction with HPV E6/E7, increased colony formation was observed in both CSCs and non‐CSCs. Results from tail vein injections yielded no differences in development of lung colonies between HPV E6/E7‐transduced cells and nontransduced cells.Conclusions: Human papillomavirus status does not correlate with the proportion of CSCs present in HNSCC. The HPV‐positive cells and those transduced with HPV E6/E7 have a greater clonogenicity than HPV‐negative cells. The HNSCC CSCs are more resistant to cisplatin than non‐CSCs. This suggests that common chemotherapeutic agents may shrink tumor bulk by eliminating non‐CSCs, whereas CSCs have mechanisms that facilitate evasion of cell death. Human papillomavirus status does not affect CSC response to cisplatin therapy, suggesting that other factors explain the better outcomes for patients with HPV‐positive cancer.