In this report, we describe the establishment and characterization of USC-HN2, a novel cell line derived from a patient with recurrent, invasive HPV− buccal SCC with a past medical history significant for a 50-pack-year history of tobacco smoking and no pre-operative chemotherapy or radiation therapy. USC-HN2 cultured cells and heterotransplanted tumors closely resembled the original tumor biopsy specimen with respect to morphology, HNSCC-associated markers (keratin, E-cadherin, FABP5), HPV infection, and cytogenetic abnormalities. One difference noted was the outgrowth of a highly proliferative, EGFR+ subclone from a largely EGFR− original tumor during establishment of the cell line. Overall, USC-HN2 showed similar morphology, growth rate, phenotype, and tumor suppressor and oncogene expression to the previously established HNSCC cell line SCCL-MT1.
Immune evasion and suppression are two mechanisms by which tumors escape immune destruction and evidence exists for the employment of both by HNSCC tumors10,11
. The results of this study revealed USC-HN2 and SCCL-MT1 to be highly immunogenic tumor models with strong immune suppression capacity. Additionally, the USC-HN2 cultured cells and heterotransplants, as well as the SCCL-MT1 cells, showed strong positivity for the cancer stem cell marker CD44v6. Cancer stem cell populations within tumors are reported to have greater expression of immunogenic tumor-associated antigens27,28
, a hypothesis that was supported here by microarray data demonstrating significant up-regulation of antigen-presentation-related genes in USC-HN2 and SCCL-MT1. In order for immunogenic tumor cells to persist in the face of infiltrating host immune cells, they must adapt to acquire immunosuppressive capabilities, such as the release of immune-inhibitory factors or the recruitment of immune suppressor cells11
. In this study we demonstrate that both USC-HN2 and SCCL-MT1 have strong immunosuppressive capabilities, including elevated expression of inflammatory and Th2 cytokines IL-1β, IL-6, IL-8, GM-CSF, and VEGF. Previously, we have identified IL-1β, IL-6, and GM-CSF as key factors for the induction of myeloid-derived suppressor cells, a population of innate immune suppressor cells that mediate direct suppression of effector T cells and expand regulatory T cell populations22
. Indeed, co-culture of USC-HN2 and SCCL-MT1 with normal healthy donor PBMC generated functionally suppressive MDSC and Treg in vitro.
Of note, when compared to six other established HNSCC cell lines (SCC-4, FaDu, Cal27, SW2224, Sw451, RPMI 2650) USC-HN2 and SCCL-MT1 were found to be the most potent inducers of suppressive MDSC, a finding which correlated with their high expression of immune modulatory cytokines23
Immunotherapy seeks to overcome tumor-mediated immune dysfunction and activate a cell-mediated immune response against cancer cells. Such an approach holds great promise for reducing damage to collateral tissue by taking advantage of the inherent specificity of the human immune system. Systemic trafficking and monitoring by immune cells also provides for superior treatment of metastatic and inoperable lesions compared with external beam irradiation and surgical therapies. Perhaps most importantly, the generation of immunologic memory following a robust anti-tumor immune response prevents the recurrence of tumors. While immune stimulatory treatment strategies have shown success in a variety of solid tumors, immunotherapeutic approaches in HNSCC have proven difficult perhaps in part due to the profound immune suppression generated by these tumors11
. New pre-clinical models are needed with which to study the mechanisms of immune suppression in HNSCC and develop new targeted immunotherapies. USC-HN2 and SCCL-MT1 appear to model highly immunogenic cancers with robust cytokine production and strong induction of suppressor cell populations as compared with other available HNSCC cell lines. Based upon these results, USC-HN2 and SCCL-MT1 provide excellent models for the development of new suppressor cell-targeted therapies for these difficult to treat tumors.