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532 Characterization of PD-1 and PD-L1 expression in the tumour microenvironment of ovarian cancer using fluorescence immunohistochemistry: results from the TRIOC trial
  1. Hossameldin Attia1,2 and
  2. Agnieszka Michael1,2
  1. 1University of Surrey, Guildford, UK
  2. 2Royal Surrey County Hospital, Guildford, UK


Introduction/Background The role of immunotherapy in ovarian cancer remains limited despite reported evidence of better survival in the presence of tumour-infiltrating lymphocytes as well as in a clearly defined immune reactive molecular subtype of ovarian cancer. We conducted a vaccine study using Modified Vaccinia Ankara Virus containing the gene encoding for 5T4 (MVA-5T4) in asymptomatic relapsed ovarian cancer. we used fluorescence multiplex immunohistochemistry to characterize and better understand these patients‘ tumour immune environment.

Methodology 48 biopsies from patients with relapsed ovarian cancer recruited for the TRIOC trial were analysed for PD-L1, PD1, CD8, CD68, FOXP3 and a pan-cytokeratin marker. The samples were obtained at initial diagnosis and retrospectively collected when patients were recruited. Initial validation and optimization of all antibodies was performed by chromogen-based IHC analysis. Immunofluorescent staining was performed manually using the Opal 7 kit (Akoya Biosciences).

Results 40 cases (83%) showed intratumoral infiltration by CD 8 +ve T-lymphocytes. While PD-1 +ve lymphocytes infiltrated the tumours and the stroma in an even manner, they were only present in 7 (14.5%) cases. Most CD8+ve T-cells lacked PD-1 expression and were restricted to the peritumoural stroma. CD 68 + PD-L1 -ve tumour-associated macrophages (TAMs) infiltrated the stroma and the tumours equally while PD-L1 + TAMs found in only 25% of cases were restricted to the peritumoural stroma. Tumour cells showed PD-L1 expression in 29% of cases which was concordant with the presence of PD-L1 expressing peritumoural TAMs. We also studied the significance of PD-1 expression by the T-lymphocytes and PD-L1 expression by either tumor cells or TAMs of which none was associated with significant differences in survival. Figure 1 shows an example of multiplex staining demonstrating the presence of PDL1 expression.

Conclusion The expression of PD-L1, PD-1, and CD8, in ovarian tumour tissue, does not correlate with clinical response to the MVA-5T4 vaccination.

Disclosures H. Attia has no disclosures

A. Michael has received research support and educational events sponsorship from GSK, CLOVIS, BMS, IPSEN and MECK.

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