Clinical Relevance of CD4 Cytotoxic T Cells in High-Risk Neuroblastoma

Abstract

Neuroblastoma is the most common extracranial childhood solid tumor. The majority of high-risk neuroblastoma is resistant/refractory to the current high intensity therapy, and the survival of these patients remains poor for the last three decades. To effectively treat these extremely unfavorable neuroblastomas, innovative immunotherapy approaches would be the most promising. In this article, we discuss the identity of tumor-infiltrating effector cells and immunosuppressive cells in high-risk neuroblastoma. Neuroblastoma is unique in that it expresses little or no classical HLA Class I and II. In contrast, high-risk neuroblastomas express the stress-responsive non-classical Class I, HLA-E molecule. HLA-E is the ligand of activating receptors NKG2C/E that are expressed on memory NK cells, CD8+T cells and CD4 CTLs. By examining a comprehensive RNA-seq gene expression dataset, we detected relatively high levels of CD4 expression in high-risk neuroblastoma tissues. The majority of CD4+ cells were CD3+, and thus they were likely tumor-associated CD4+T cells. In addition, high-level of both CD4 and NKG2C/E expression was associated with prolonged survival of the high-risk neuroblastoma patients, but CD8 levels were not, further suggesting that the CD4+ NKG2C/E+ T cells or CD4 CTL conferred cytotoxicity against the neuroblastoma cells. However, this T cell mediated- “protective effect” declined over time, in part due to the progressive formation of immunosuppressive tumor microenvironment. These observations suggest that to improve survival of high-risk neuroblastoma patients, it is essential to gain insights into how to enhance CD4 CTL cytotoxicity and control the immunosuppressive tumor microenvironment during the course of the disease.

Macrophage-mediated anti-tumor immunity against high-risk neuroblastoma

“…We previously reported that macrophages were predominant PD-L1+ cells in neuroblastoma tissues at diagnosis based on multiplex IHC analysis [ 5 ]. In this report, we further extended this observation by examining the prognostic effect of PD-L1 expression in two large neuroblastoma gene expression datasets, including SEQC-498 (Cohort 1) and Kocak-649 (Cohort 2) [ 30 , 31 ] (Fig.…”

“…CD8 CTLs are thus expected to play little role in the anti-neuroblastoma immune response. Our previous study suggests that CD4 CTLs are important effector cells against high-risk neuroblastoma, but the CD4 CTL mediated-“protective effect” declines over time, in part due to the progressive formation of an immunosuppressive tumor microenvironment (TME) [ 5 ] and/or chemotherapy-induced suppression of hematopoiesis [ 6 ].…”

“…PD-L1 expression is also found on other immune cells (dendritic cells, B cells, T cells) [ 14 ] and some tumor cells [ 15 ]. However, based on our multiplex immunohistochemistry (IHC) analysis, neuroblastoma cells do not express PD-L1, and PD-L1+ cells detected in neuroblastoma tissues are predominantly macrophages [ 5 ]. In fact, this study revealed that high-level expression of macrophage-derived PD-L1 was significantly associated with better patient outcome, including those with high-risk neuroblastoma.…”

The Era of Cytotoxic CD4 T Cells

“…Whether these cells exacerbate, or counter tumour progression or metastasis formation remains to be fully elucidated and might depend on the tumour type and/or stage. Recently, CD4 T cells displaying a cytotoxic gene signature were reported in children with high-risk neuroblastoma and were associated with a putative protective effect that declined over time due to the progressive formation of an immunosuppressive tumour microenvironment ( 74 ). CD4 CTLs were also observed in B-cell chronic lymphocytic leukaemia (B-CLL), where they were able to kill autologous B-CLL cells ex vivo in a perforin-mediated mechanism ( 75 , 76 ).…”

Exploring and Targeting the Tumor Immune Microenvironment of Neuroblastoma

“…Our group and others have shown that there are different subtypes of TMEs found in neuroblastoma and that the TME of pediatric neuroblastoma is not only associated but plays an active role in the clinical outcomes of these patients [ 10 , 12 , 50 , 51 ]. A variety of therapeutic approaches to harness a patient’s immune system to target the tumor have been developed.…”