AB016. Different pattern of indoleamine 2,3-dioxygenase 1 (IDO1) and PD-L1 immunoexpression in thymomas
Abstract

AB016. Different pattern of indoleamine 2,3-dioxygenase 1 (IDO1) and PD-L1 immunoexpression in thymomas

Surabhi Jain1, Aruna Nambirajan1, Rajinder Parshad2, Deepali Jain1

1Department of Pathology, All India Institute of Medical Sciences, New Delhi, India; 2Department of Surgery, All India Institute of Medical Sciences, New Delhi, India

Correspondence to: Deepali Jain, MD. Department of Pathology, All India Institute of Medical Sciences, New Delhi, India. Email: deepalijain76@gmail.com.

Background: Indoleamine 2,3-dioxygenase 1 (IDO1), a heme enzyme has been implicated in acquisition of peripheral immune tolerance in the tumor microenvironment as well as peripheral blood. It decreases antitumor response by suppressing T cell activation. Thymomas show strong expression of PD-L1 with highest positivity in type B thymomas. With increased advances in immunotherapy, expression of IDO1 in thymomas may have translational relevance and hence the need for this study.

Methods: This was a retrospective study in a tertiary care center including 60 morphologically confirmed cases of thymoma. Tissue microarrays were prepared and immunohistochemistry was performed for PD-L1 (SP263) and IDO1 (V1NC3IDO). Cases with immunopositive aggregates of tumor or other cells (immune cells, mesenchymal cells, endothelial cells) (≥2/low power field) were considered as IDO1 positive. Immunostaining of >25% in the thymic epithelial cells was considered positive for PD-L1. The results were compared with clinical parameters and statistical analysis was performed.

Results: Of 60 cases of thymoma, 27 (45%) showed IDO1 immunopositivity in the stromal endothelial cells, immune cells, fibroblasts, and tumor cells. IDO1 expression was observed in all the subtypes including 25% of type A, 53.49% of type B (B1/B2/B3) and 25% of type AB (P value =0.199). Most of the IDO1 positive cases did not have myasthenia gravis (MG) (77.78%) (P value =0.053). No significant association was observed between IDO1 positive tumors and clinical parameters like age, sex and Masaoka Koga stage. PD-L1 immunopositivity showed significant association with type B thymomas (P value =0.001).

Conclusions: IDO1 is expressed in a substantial number of thymomas and show maximum expression in type B thymomas similar to PD-L1. Although immunoreactivity of PD-L1 and IDO1 is seen in different types of cells, both showed maximum expression in type B thymomas. PD-L1 is expressed mostly by thymic epithelial cells whereas IDO1 mostly stains peritumoral stromal endothelial cells, immune cells, and mesenchymal cells. It is possible that the PD-L1-IDO1 axis plays an important role in immune regulation and pathogenesis of thymic epithelial tumors which can be explored in further studies.

Keywords: Thymomas; indoleamine 2,3-dioxygenase 1 (IDO1); PD-L1

Acknowledgments

Funding: None.

Footnote

Conflicts of Interest: The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

doi: 10.21037/med.2021.ab016
Cite this abstract as: Jain S, Nambirajan A, Parshad R, Jain D. AB016. Different pattern of indoleamine 2,3-dioxygenase 1 (IDO1) and PD-L1 immunoexpression in thymomas. Mediastinum 2021;5:AB016.

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