Abstract 2749: The unique tumor immune microenvironment of clear cell ovarian carcinoma
Authors: Cun Han T. , Zhu Ying , Ferri-Borgogno Sammy , Sheng Jianting , Cheng Rita , Kim Jae-hoon , Han Gwan Hee , Wong Stephen T. , Lu Karen H. , Mok Samuel C. 
Published: July 2021

Abstract
Based on differences in chemosensitivity and clinical outcomes, we hypothesize that clear cell ovarian carcinoma (CCCO) displays a unique tumor immune microenvironment (TIME) compared to high grade serous ovarian carcinoma (HGSOC). Microsatellite instability and ARID1DA mutations are more common in clear cell ovarian carcinoma suggesting improved outcomes with checkpoint blockade immunotherapy use. Our objective is to compare the TIME of CCCO to HGSOC using imaging mass cytometry (IMC).
Primary untreated ovarian tumors were collected under an IRB-approved protocol. Formalin fixed paraffin embedded (FFPE) tissue sections were stained with 34 metal-tagged antibodies to detect various cell specific and immune related markers using the Fluidigm protocol. IMC data was obtained by the Fluidigm Helios CyTOF instrument utilizing the Hyperion Imaging System laser ablation module. Images from a 1mm2 area of each tissue section were processed and converted to tiff files using MCD Viewer (Fluidigm). Images were analyzed using a deep learning based data analytic pipeline beginning with cell segmentation then multiple rounds of phenotype clustering for cell type annotation. Various cell phenotypes were then measured for cell density analysis within a tumor enriched area. Spearman correlation was performed between cell densities of CCCO and HGSOC.
Samples from 51 patients were used for the study: 10 with CCCO and 41 with HGSOC. In the CCCO group, stage of disease ranged from stage I (70%) to III (10%), but all the HGSOC had stage III (92.7%) or IV (7.3%) disease (p&lt;0.001).
Images were analyzed using 18 markers based on high signal-to-noise ratios. Following cell segmentation and phenotype clustering, 39 cell subtype clusters were identified including 6 macrophage cell subtypes, 11 T cell subtypes, and 12 tumor cell subtypes.
CCCO had a lower density of intratumoral activated CD8+ T cells (CD44+CD8a+CD45RO+) than the HGSOC (p=0.048). Tumor cell subtypes in the tumor-enriched areas differed between the two groups. CCCO had a higher density of B7-H4midKi67hi tumor cells (p=0.004), but had a lower density B7-H4hiKi67midKeratin8_18+ (p=0.027), B7-H4hiKeratin8_18+ (p=0.004), and B7-H4hiKi67midKeratin8_18+ tumor cells (p=0.007). CCCO had a lower density of CD31+CD73mid cells (p=0.034) but higher density of CD73hi (p=0.024) compared to HGSOC.
CCCO have a distinct TIME compared to HGSOC. In our cohort, despite most having stage I disease, CCCO showed features associated with poor prognosis including decreased intratumoral CD8+ T cells, higher density of a subtype of actively dividing B7-H4mid ki67hi cancer cells, and higher density of CD73hi cells. Since B7-H4 and CD73 both act as immune checkpoint inhibitors that can confer chemoresistance, therapeutic strategies to target these molecules may enhance CD8+ T cell mediated anti-tumor immune response and chemosensitivity to improve survival in patients with CCCO.
Citation Format: Han T. Cun, Ying Zhu, Sammy Ferri-Borgogno, Jianting Sheng, Rita Cheng, Jae-hoon Kim, Gwan Hee Han, Stephen T. Wong, Karen H. Lu, Samuel C. Mok. The unique tumor immune microenvironment of clear cell ovarian carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2749.