Immune markers of response to pembrolizumab and guadecitabine in platinum resistant ovarian cancer utilizing multiplex immunohistochemistry (mIHC)

Abstract

<h3>Objectives:</h3> Treatment options for platinum-resistant ovarian cancer (PROC) are limited by poor response (poor response) rates and short progression-free survival. Immune checkpoint inhibitors induce modest response rates (8-11%) in phase II trials for PROC, although responders can have prolonged disease control. An immunoreactive subtype of ovarian cancer (OC) was proposed from TCGA genomic analysis and susceptibility to immune checkpoint blockade seems to correlate with specific populations of tumor infiltrating lymphocytes (TILs). This study sought to identify potential markers of response to immunotherapy by using multiplex immunohistochemical staining (mIHC) to phenotype TILs in ovarian tumors obtained before and after treatment with guadecitabine and pembrolizumab in a phase II clinical trial (NCT02901899). <h3>Methods:</h3> OC core needle biopsies were obtained at baseline and after 2 cycles of treatment from patients with PROC enrolled in a phase 2 trial testing the combination of guadecitabine and pembrolizumab. The Opal Multiplex IHC kit (Akoya Biosciences) was used to identify the TIL markers CD3, CD8, CD20, CD68 and FoxP3, and the epithelial marker pan-cytokeratin. A total of 12 paired (pre- and post-treatment) specimens from responders (PR or stable disease > 4 months, n=6, R) vs. non-responders (progression <4 months, n=6, NR) were stained and scanned by using the Vectra digital laser microscope and analyzed with the inForm software. The following lymphocytes were phenotyped and analyzed for spatial relationships to each other and to epithelial tumor nests: T cells, cytotoxic T cells, B cells, macrophages, and T regulatory cells (Tregs) in relationship to response to treatment. Additionally, archival tissue from 36 patients enrolled in this trial was stained with the monoclonal antibody 22C3 to assess PD-L1 expression. <h3>Results:</h3> In this study, 48 pts were enrolled, 43 were treated, and 33 were evaluable for response. Overall, there were 3 PRs (RR=9.9%) and 16 pts had stable disease (SD) [48%]. The clinical benefit rate (PR + SD > 3 months) was 27%. Analysis of TILs in the tumor microenvironment identified an increased total and stromal numbers of CD8 cells in baseline biopsies in R vs. NR (p=0.05). Likewise the total and stroma-infiltrating numbers of CD8 cells post-treatment were higher in R vs. NR (p=0.05). The total, tumor, and stromal numbers of B cells at baseline and after treatment were increased in R vs. NR (p<0.05). The numbers of total, stromal, and tumor infiltrating macrophages post-treatment samples were increased in R vs. NR (p<0.05). There were no differences in numbers of Tregs between R and NR at baseline of after treatment. Of the 36 archival specimens, 16 (45.7%) showed PD-L1 tumor modified H score/modified percent score staining greater than 0; 20 specimens (59%) had present staining at the tumor/stroma interface. <h3>Conclusions:</h3> Immunophenoyping using mIHC identified treatment induced changes in immune cell subpopulations predictive of response to immunotherapy in PROC.