Evaluation of PD1/PDL1 Expression and Their Clinicopathologic Association in EBV-associated Lymphoproliferative Disorders in Nonimmunosuppressed Patients.

Epstein-Barr virus (EBV)-associated lymphoproliferative disorders (LPD)/lymphomas in nonimmunosuppressed patients represent a unique entity and have been proposed to be related to immune senescence. Engagement of programmed cell death 1 (PD1) by its ligand programmed death ligand 1 (PDL1) inhibits T-cell activation, and leads to T-cell exhaustion. In clinical trials, therapeutic antibodies that block the PD1-PDL1 axis have shown promising therapeutic activity in certain types of lymphomas. Although PD1/PDL1 has been extensively studied in variety of lymphomas, there are few reports characterizing their expression in EBV-positive LPD. As these group of patients are presumed to be associated with immunosenescence/immune dysregulation, we hypothesize that the immune checkpoint pathway might be relevant in this entity. We explored the expression of PD1, PDL1 and its clinicopathologic association in 6 patients with a total of 8 independent specimens of EBV-positive LPD/lymphomas. We also applied proximity assay, a novel technique, which can identify intermolecular interaction, to evaluate physical interaction or in situ engagement of PD1 and PDL1. We found that the malignant cells in the EBV-positive LPDs express PDL1. PD1-positive tumor-infiltrating lymphocytes can be seen in these tumors. Proximity assay suggests there is active engagement between PD1 and PDL1. To our knowledge, this is the first report on the utility of proximity assay to test the active engagement between PD1 and PDL1 in lymphomas. As some EBV-positive LPDs were positive for PDL1, this subgroup of EBV-positive LPDs might be suitable for PD1/PDL1 antibody therapies.