PD1 in Sézary syndrome: a repressor of cell survival sometimes lost during progression, but a new target using depleting antibodies?

Oral presentation

Nicolas Ortonne

(Research team Ortonne - NFL, IMRB, INSERM U955 Henri Mondor hospital, Paris | Pathology department, APHP, Henri Mondor hospital, Paris)

Introduction

PD1 is known to be expressed by tumor cells from Sézary syndrome (SS). In a mouse model of T-cell lymphoma (ITK-SYK), it has been shown that PD1 may be a haplo-insufficient tumor suppressor and one of the PDCD1 alleles is often deleted in cutaneous T –cell lymphomas. In some T-cell lymphomas, anti-PD1 immunotherapy appears to worsen the disease, but depleting targeting of PD1 has never been studied so far.

Material and Methods

Study of PD1 and PDL1 expression using immuohistochemistry (IHC) in 45 biopsies from 24 patients sith SS (8 women and 16 men) at diagnosis or under treatment (skin biopsies (n=41), compared to a control group of inflammatory dermatoses , and lymph node (n=4)), and by flow cytometry (FCM) in 8 blood samples and 5 SS cell lines, including one produced in the laboratory (RM231152 line). Tissue expression of PD1 was assessed using IHC semi-quantitatively (intensity x proportion of labeled CD3 + T cells).

Functional studies of a case of SS with maintenance of Sézary cells (Sc) in primary culture, including:

The effect of commercially available anti-PD1 blocking IgG4 antibodies (pembolizumab [PLZ] and Nivolumab) on the survival of Sc in vitro, assessed with CMF (n=2).
The ability of humanized anti-PD1 IgG1 antibodies (PLZ – IgG1) to kill Sc in vitro (n=5), compared to normal PBMC, by ADCC and ADCP mechanisms: co-cultures of primary Sc labeled with Viability Dye and NK cells or macrophages, respectively, from healthy donors.

Results

We observed a significant expression of PD1 in most SS samples (skin: 31/41, 76%, nodes: 2/4 and blood: 7/8), more intense than in the inflammatory control infiltrates in the skin (p<0.0001). PDL1 was expressed by tumor micro-environment cells in all cases and by tumor cells (5/5 in the blood, figure A). Three SS were PD1 negative, either at diagnosis or during evolution (lymph node [n=1], tumor [n=1] and skin lésions with large cell transformation [n=1]). All the SS cell lines studied expressed neither PD1 nor PDL1, including the RM231152 line (transformed SS). Incubation of primary Sc with blocking anti-PD1 antibodies significantly reduced spontaneous or stimulated Sc mortality (CD3 / CD28 and IL2, figure B) or had no effect. PLZ-IgG1 achieved significant lysis of fresh Ss, either by ADCC or ADCP in vitro (n=5, figure C).

Discussion

The PD1 receptor could act as a repressor of Sc survival in some patients, through its inhibitory T cell co-receptor functions, and could be engaged by PDL1 tumor cells themselves in vivo. PD1 expression can be lost during tumor progression but may represent a new therapeutic target of interest unsing depleting antibodies, al the more that its expression seems more intense than in normal activated T cells in the skin.