Podocalyxin protects high grade serous ovarian cancer spheroids from NK cell infiltration and spheroid destruction.

BACKGROUND: High grade serous carcinoma (HGSC) is the most common and lethal subtype of ovarian cancer, yet its prognosis has remained unchanged in the past 3 decades. HGSC is known to have evolved immune evasion strategies to promote survival, but these mechanisms are not well understood. Podocalyxin (PODXL), a CD34-related sialomucin, is often expressed in HGSC patients with poor prognosis. We have recently reported that PODXL promotes the formation of compact and chemoresistant HGSC spheroids to boost their survival. METHODS: In this current study, we investigated whether PODXL may also influence HGSC spheroid susceptibility to NK cell infiltration and cytotoxicity. We co-cultured HGSC spheroids with primary human NK cells isolated from peripheral blood mononuclear cells (PBMCs) and examined the impact on these spheroids following 24, 48 and 72 h of co-culture. We first used a cell line model of HGSC spheroids employing Kuramochi cells, which express the highest level of PODXL among known HGSC cell lines. To study the impact of PODXL levels, we compared spheroids of control and PODXL knockout (PODXL-KO) cells that we have previously engineered. We then validated the data in primary cancer spheroids derived from ascites of HGSC patients that express high and low levels of PODXL. RESULTS: In both the cell line and primary HGSC spheroid models, co-culture of spheroids expressing lower levels of PODXL resulted in more NK cell infiltration and cytotoxicity, while spheroids expressing higher levels of PODXL were resistant to destruction and showed more proliferation. CONCLUSIONS: Collectively, these data suggest that PODXL may play an important role in aiding immune evasion in HGSC, at least partly by conferring resistance to NK cell infiltration and the related cytotoxicity.