PD-L1 expression in metastatic neuroblastoma as an additional mechanism for limiting immune surveillance

Abstract

The prognosis of high-risk neuroblastoma (NB) remains poor, although immunotherapies with anti-GD2 antibodies have been reported to provide some benefit. Immunotherapies can be associated with an IFNγ storm that induces in tumor cells the "adaptive immune resistance" characterized by the expression of Programmed Death Ligands (PD-Ls). Tumor cells can also constitutively express PD-Ls in response to oncogenic signaling. Here, we analyze the constitutive and the inducible surface expression of PD-Ls in NB cells. We show that virtually all HLA class I NB cell lines constitutively express PD-L1, whereas PD-L2 is rarely detected. IFNγ upregulates or induces PD-L1 both in NB cell lines and in NB engrafted nude/nude mice. Importantly, after IFNγ stimulation PD-L1 can be acquired by NB cell lines, as well as by metastatic neuroblasts isolated from bone marrow aspirates of high-risk NB patients, characterized by different amplification status. Interestingly, in one patient NB cells were poorly responsive to IFNγ stimulation, pointing out that responsiveness to IFNγ might represent a further element of heterogeneity in metastatic neuroblasts. Finally, we document the presence of lymphocytes expressing the PD-1 receptor in NB-infiltrated bone marrow of patients. PD-1 cells are mainly represented by αβ T cells, but also include small populations of γδ T cells and NK cells. Moreover, PD-1 T cells have a higher expression of activation markers. Overall, our data show that a PD-L1-mediated immune resistance mechanism occurs in metastatic neuroblasts and provide a biological rationale for blocking the PD-1/PD-Ls axis in future combined immunotherapeutic approaches.

PD-1 signaling modulates interferon-γ production by Gamma Delta (γδ) T-Cells in response to leukemia

“…PD-L1 upregulation can be triggered by the early proinflammatory cytokine IFN-γ, for example in monocytes but also in cancer cells. 7,13,14 In T-cells upregulating PD-L1 has been implicated to protect γδ T-cells from fratricide. 5 We did not detect changes in PD-L1 MFI following stimulation, but the fraction of PD-L1 positive cells increased significantly (Figure 1(b)).…”

PD-L1 Is a Therapeutic Target of the Bromodomain Inhibitor JQ1 and, Combined with HLA Class I, a Promising Prognostic Biomarker in Neuroblastoma

“…Few studies have investigated PD-L1 and PD-1 expression in neuroblastoma with discordant results. Some authors detected a high frequency of PD-L1 þ tumor cells (31/43 samples) in high-risk neuroblastoma (14), whereas others reported no expression of PD-L1 in 18 primary and 4 metastatic neuroblastoma lesions tested (15,16). A detailed description of the functional status of tumor-infiltrating immune cells in a larger cohort of neuroblastoma samples is not currently available.…”

Anti-GD2 MABS and Next-Generation mAb-Based Agents for Cancer Therapy

“…The expression of these surface molecules on the tumor cells is required for the success of this therapeutic strategy. Therefore, the fact that there is evidence demonstrating that PD-L1 is upregulated in NB cell lines [155] as well as in tumor cells isolated from NB patients [156], supports the use of this strategy in the clinic. In contrast, patients whose tumors show little evidence for an ongoing adaptive immune response are less likely to benefit from checkpoint blockade [157].…”