Strong Expression of the Immune Checkpoint Regulators LAG3 and Tim3 in Hodgkin Lymphoma
Authors: el Halabi Layal , Adam Julien , Marty Virginie , Bosq Jacques , Lazarovici Julien , Danu Alina , Ribrag Vincent , Ghez David 
Published: October 2019

Abstract
Background: Recent results of immune checkpoint blockade trials have provided a proof of concept for immunotherapy in classical Hodgkin lymphoma (cHL) with more than two third of relapsed/refractory patients responding to blockade of the PD1/PDL1 axis. Unfortunately, there is still a proportion of patients who will present primary or secondary resistance to immunotherapy. Besides the PD1/PDL1 axis, several other molecules are critical regulators of the immune response and may be the target of therapeutic intervention. Combined immune checkpoint targeting has shown interesting results in preclinical and clinical trials in several types of tumors.
Methods: Patients with initially diagnosed or relapsed cHL for whom formalin fixed paraffin embedded (FFPE) tissue was available at our institution were identified. Fifty-seven cases were selected depending solely on the availability and the quality of the FFPE blocks. Expression of the following immune checkpoints PD1, PDL1, LAG3, TIM3 was assessed using immunohistochemical methods with a threshold of 5% set for positivity.
Results: Complete results for 25 cases were available at the time the abstract was written. Hodgkin and Reed Sternberg cells (HRS) were identified morphologically upon microscopic examination. Consistently with data published in the literature, HRS stained positively and intensely for PDL1 in 100% of the cases (25/25). HRS were positive for Tim3 in 36% (9/25) of cases but with more varying intensities. No PD1 or LAG3 expression was found on HRS cells except for a single case where 5% of HRS stained weakly for LAG3. In the tumor microenvironment, PD1 expression was detected in 65% of cases (15/23) and PDL1 in 60% of cases (15/25). Impressively, LAG3 and TIM3 stained positively in 96% (23/24) and 92% (24/25) of cases respectively. Lymphocyte-rosetting was present in 9/25 cases. These CD4+ FoxP3- T cells surrounding HRS were positive for PD1 in 5 cases, for LAG3 in 2 cases and for both PD1 and LAG3 in 2 cases, suggesting they represented exhausted T-cells. Concomitant expression of PD1 and PDL1 in the tumor microenvironment was present in 43% of cases (10/23).
Conclusion: LAG3 and TIM3 are nearly universally expressed in the tumor microenvironment of cHL. These findings provide a strong rationale for their blockade alone or in combination in relapsed/refractory patients with cHL. The role of TIM3 expression by HRS remains unclear. Correlation of these findings with clinical data and survival outcome of the patients will be done for the whole sample.

Disclosures
Ribrag: NanoString: Membership on an entity's Board of Directors or advisory committees; Esai: Membership on an entity's Board of Directors or advisory committees; ArgenX: Research Funding; Gilead: Membership on an entity's Board of Directors or advisory committees; Infinity: Membership on an entity's Board of Directors or advisory committees; Pharmamar: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees; Incyte: Membership on an entity's Board of Directors or advisory committees.