B7 immune-checkpoints as targets for the treatment of neuroendocrine tumors

Abstract

The B7 family, and their receptors, the CD28 family, are major immune checkpoints that regulate T-cell activation and function. In the present study, we explore the role of two B7 immune-checkpoints: HERV-H LTR-Associating Protein 2 (HHLA2) and B7 Family Member, H4 (B7x), in the progression of gastrointestinal and pancreatic neuroendocrine tumors (GINETs and PNETs). We demonstrated that both HHLA2 and B7x were expressed to a high degree in human GINETs and PNETs. We determined that the expression of B7x and HHLA2 correlates with higher grade and higher incidence of nodal and distant spread. Furthermore, we confirmed that HIF-1 overexpression is associated with the upregulation of B7x both in our in vivo (animal model) and in vitro (cell culture) models. When grown in vitro, islet tumor β-cells lack B7x expression, unless cultured under hypoxic conditions, which results in both hypoxia inducible factor 1 subunit alpha (HIF-1α) and B7x upregulation. In vivo, we demonstrated that Men1/B7x double knockout (KO) mice (with loss of B7x expression) exhibited decreased islet β-cell proliferation and tumor transformation accompanied by increased T-cell infiltration compared with Men1 single knockout mice. We have also shown that systemic administration of a B7x mAb to our Men1 KO mice with PNETs promotes an antitumor response mediated by increased T-cell infiltration. These findings suggest that B7x may be a critical mediator of tumor immunity in the tumor microenvironment of NETs. Therefore, targeting B7x offers an attractive strategy for the immunotherapy of patients suffering from NETs.

Pancreatic Neuroendocrine Tumors: Molecular Mechanisms and Therapeutic Targets

“…Demonstrated the cooperative role of tumor suppressor genes, Men1, Rb1, Pten, and Trp53 in pNET suppression [76] RIP-Tag2; Rabl6 m/m C57BL/6N Insulinoma Loss of oncogenic RABL6A attenuates pNET progression and angiogenesis in RIP-Tag2 mice [77] Pdx1-Cre; Men1 f/f ; B7x KO C57BL/6 Insulinoma Loss of B7x, an immune-checkpoint ligand, reduces islet β-cell proliferation and pNET formation consistent with increased T-cell infiltration [78] (Abbreviations: RIP = rat insulin promoter, MIP = mouse insulin promoter, Tag = T-antigen).…”

“…pNETs have low mutational burden and as such, are traditionally perceived to be 'cold' tumors offering limited scope for immunotherapy. Notably, a recent study by Yuan et al, demonstrates that B7x, an immune-checkpoint ligand expressed by tumor cells, suppresses anti-tumor immunity in pNETs and as such, could be an attractive target for (p)NET immunotherapy [78]. The authors demonstrated that genetic ablation or administration of B7x antibody in Men1-deficient mice with insulinomas results in reduced islet cell proliferation and pNET development accompanied by increased T-cell infiltration (Table 2).…”

Human endogenous retrovirus-H long terminal repeat-associating 2: The next immune checkpoint for antitumour therapy

“…Overexpressed in multiple human cancer types, the prognostic role of HHLA2 remains controversial ( Table 1 ). Several studies indicated that overexpression of HHLA2 in tumour cells was associated with unfavorable clinical outcomes and shorter survival rate in patients with prostate cancer, 26 neuroendocrine tumours, 27 hepatocellular carcinoma, 28 , 29 , 30 lung adenocarcinoma, 31 , 32 , 33 , 34 gastric cancer, 35 oral squamous cell carcinoma, 36 bladder urothelial carcinoma, 37 intrahepatic cholangiocarcinoma, 38 colorectal carcinoma, 39 , 40 osteosarcoma, 41 and triple negative breast cancer. 17 On the contrary, HHLA2 was a protective factor predicting low mortality rate in patients with pancreatic cancer, 14 , 42 , 43 epithelial ovarian cancer, 44 malignant glioma, 45 and recurrent or unresectable advanced gastric cancer.…”

“… Tumour type Year Research object/Numbers HHLA2 expression Conclusions Refs. Prostate cancer 2021 Patient tumour samples, N = 239 Tumour cells High HHLA2 expression was an independent prognostic predictor for prostate cancer, and was negatively correlated with CD TILs 26 Neuroendocrine tumours 2021 Patient tumour samples, N = 37 Tumour cells High HHLA2 expression was correlated with high tumour grade and metastasis 27 Colorectal cancer 2021 Patient tumour samples, N = 214 Tumour cells HHLA2 expression was low in colorectral cancer and appeared to have no influence on clinical outcomes. 40 Hepatocellular carcinoma 2021 Patient tumour samples, N = 205 Peri-tumour region of HCC tissues HHLA2 expression in the peri‑tumour region was an independent prognostic factor for OS, and was negatively correlated with PD-L1 28 Patient tumour samples, N = 55 Tumour cells Higher expression of HHLA2 protein was associated with advanced cancer stage, tumour differentiation, and invasion of adjacent structures 29 Patient tumour samples, N = 202 Tumour cells HHLA2 level was a independent worse prognostic factor and affected the tumour microenvironment 30 Epithelial ovarian cancer 2021 Patient tumour samples, N = 64 Tumour cells HHLA2 was correlated with high CD TIL levels and tumour differentiation; and predicted improved survival in ovarian cancer 44 Lung adenocarcinoma 2021 …”

The Landscape and Clinical Application of the Tumor Microenvironment in Gastroenteropancreatic Neuroendocrine Neoplasms

“…Currently, more immune checkpoints are being elaborated upon in tumor studies, such as the B7 family, T cell immunoglobulin, and mucin domain-containing protein 3 (TIM-3), CD47, and CD74. HERV-H LTR-associating protein 2 and B7 family member H4, as two B7 family immune checkpoints, are richer in GEP-NETs and are associated with a high tumor grade and lymph node metastasis rate [ 76 ]. Additionally, CD47 and CD74 are highly abundant, but PD1, PD-L1, and TIM-3 are lacking in ileal NENs [ 45 ].…”