ALBERT

Description: Programmed Death Ligand 1 (PD-L1) is expressed on antigen presenting cells and serves to inhibit activation of T cells through its receptor, Programmed Death 1 (PD-1). PD-L1 is aberrantly expressed on epithelial malignancies and may prevent an effective host antitumor immune response. However, the pattern of expression and function of PD-L1 in non-Hodgkin lymphoma (NHL) is largely unknown. We examined 77 primary NHL tissue specimens and 16 NHL cell lines for expression of PD-L1. PD-L1 was detected by immunohistochemical staining in all 14 anaplastic large cell lymphoma (ALCL) specimens (both ALK+ and ALK-), and in 18 of 22 diffuse large B cell lymphomas (DLBCL). PD-L1 was expressed in all cases of Hodgkin’s, mediastinal B cell, and grey zone lymphoma, 50% of peripheral T cell lymphomas, 15% of follicular lymphomas, and 33% of mantle cell lymphomas. Among DLBCL cases subtyped into germinal-center B (GCB) and non-GCB using CD10, BCL-6, and MUM-1 (Hans et al, Blood2004;103:275), 8 of 12 (66%) GCB cases expressed PD-L1, compared to 10 of 11 (91%) of non-GCB cases (p=0.31). Among NHL cell lines, all 9 B cell lines were negative for PD-L1, as measured by flow cytometry, but all 5 ALCL cell lines were strongly positive. Therefore, we chose to focus on ALCL to study the role of PD-L1 in modulating anti-lymphoma T cell activity. PD-L1 expressed by ALCL was biologically active in that proliferation of allogeneic T cells co-cultured with Karpas 299 ALCL cells was significantly enhanced by blocking PD-L1 with monoclonal antibodies. To further study tumor-T cell interactions, malignant ascites from a patient with newly diagnosed ALK+ ALCL, containing approximately equivalent proportions of PD-L1-expressing tumor cells and tumor-associated T cells, was used as an autologous system. Secretion of interferon-γ after 3- or 5-day incubation of the T cell/tumor mixture with phytohemagglutinin (a polyclonal T cell activator) was increased four-fold in the presence of anti-PD-L1 antibody, as compared with control antibody or media alone. Secretion of other inflammatory cytokines, including IL-1, TNFα, IL-5, IL-13, and MIP1α, was also markedly increased with the addition of anti-PD-L1 antibody to the mixture of tumor cells and lymphocytes. In conclusion, PD-L1 is expressed in a broad array of non-Hodgkin lymphomas, particularly in ALCL. Blockade of tumor-associated PD-L1 promoted activation of adjacent T cells. PD-L1 may play a role in thwarting an effective antitumor immune response, and thus represents an attractive target for lymphoma immunotherapy using anti-PD-L1 or anti-PD-1 monoclonal antibodies. Heterogeneity of PD-L1 expression among DLBCLs may be related to GCB subtype or other biological properties, and these associations are being explored in a larger set of DLBCL cases. Table 1. PD-L1 expression by lymphoma subtype. Subtype Number PD-L1+ % Anaplastic large cell lymphoma 14 14 100% Diffuse large B cell lymphoma 22 18 82% T cell rich DLBCL 7 4 57% Follicular lymphoma 13 2 15% Mantle cell lymphoma 6 2 33% Mediastinal DLBCL 2 2 100% Hodgkin lymphoma 5 5 100% Grey zone lymphoma 1 1 100% Peripheral T cell lymphoma 7 4 57%