Immunoprofiling in Neuroendocrine Neoplasms Unveil Immunosuppressive Microenvironment

SIMPLE SUMMARY: Immunotherapy with checkpoint inhibitors targeting the programmed cell death protein 1 (PD-1)/programmed death-ligand 1 (PD-L1) axis or Cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) has shown only modest activity in neuroendocrine tumors (NET) and neuroendocrine carcinomas (NEC). By investigating the tumor immune microenvironment in NET/NEC with immunohistochemistry (IHC) and mRNA immunoprofiling, we found that they lack signs of an activation of an antitumor immune response like intratumoral T cell infiltration and expression of IFNγ regulated genes. But NET and NEC expressed several immunosuppressive genes. This included chemokines, known to attract immunosuppressive myeloid cells but not antitumor effector cells, or genes with immunosuppressive functions. Some of those might be expressed by both tumor cells and immune cells, such as CD74, and represent potential therapeutic targets for immunomodulation. ABSTRACT: Checkpoint inhibitors have shown promising results in a variety of tumors; however, in neuroendocrine tumors (NET) and neuroendocrine carcinomas (NEC), low response rates were reported. We aimed herein to investigate the tumor immune microenvironment in NET/NEC to determine whether checkpoint pathways like programmed cell death protein 1 (PD-1)/programmed death-ligand 1 (PD-L1) might play a role in immune escape and whether other escape mechanisms might need to be targeted to enable a functional antitumor response. Forty-eight NET and thirty NEC samples were analyzed by immunohistochemistry (IHC) and mRNA immunoprofiling including digital spatial profiling. Through IHC, both NET/NEC showed stromal, but less intratumoral CD3+ T cell infiltration, although this was significantly higher in NEC compared to NET. Expression of PD1, PD-L1, and T cell immunoglobulin and mucin domain-containing protein 3 (TIM3) on immune cells was low or nearly absent. mRNA immunoprofiling revealed low expression of IFNγ inducible genes in NET and NEC without any spatial heterogeneity. However, we observed an increased mRNA expression of chemokines, which attract myeloid cells in NET and NEC, and a high abundance of genes related to immunosuppressive myeloid cells and genes with immunosuppressive functions like CD47 and CD74. In conclusion, NET and NEC lack signs of an activation of the adaptive immune system, but rather show abundance of several immunosuppressive genes that represent potential targets for immunomodulation.