Hepatoblastoma exhibits a predominantly myeloid immune landscape and reveals opportunities for macrophage targeted immunotherapy

Abstract

Background & Aims: Hepatoblastoma (HB) is a rare form of pediatric liver cancer which is currently treated with chemotherapy and surgery. The side effects of chemotherapy pose a major problem in HB and underline the need for an alternative treatment option. We aimed to characterize the immune landscape of HB to improve our understanding of the immunologic contribution to this disease and explore immunotherapeutic options. Methods: An imaging mass cytometry panel of 36 antibodies was used on tissue of treatment-naive HB (n=5), and chemotherapy-treated HB (n=3), with paired distal normal liver tissue. Immunofluorescence was used to stain HB and normal liver tissue for Kupffer cell marker MARCO. A public single-cell RNA-sequencing (scRNA-seq) dataset was analyzed consisting of 9 chemotherapy-treated HB and paired normal liver tissue. Results: HB showed a heterogeneous immune landscape predominantly comprising macrophages and monocytes with high expression of immune checkpoints CD47, SIRPa, and VISTA, whereas T cells were limited. Chemotherapy increased influx of macrophages and CD8+ T cells in HB. Transcriptome profiling demonstrated an early activated phenotype of CD8+ T cells in chemotherapy-treated HB and absence of an exhaustion signature and immune checkpoint expression. Furthermore, tumor-associated macrophages had low MARCO expression, upregulated inflammatory markers and a high liver tissue residency score while expressing other Kupffer cell markers, such as CD5L, to a variable degree. Conclusions: The absence of immune checkpoints and exhaustion markers in CD8+ T cells prohibits T cell-targeting by immune checkpoint blockade in HB patients. Instead, HB tumors contain a large myeloid compartment which provide opportunities for macrophage targeting, thereby paving the way for the development of improved treatment strategies for HB patients.

Tumor‐associated macrophages: The key player in hepatoblastoma microenvironment and the promising therapeutic target

“…A recent publication showed that chemotherapy increased influx of TAMs and CD8 + T-cells in the HB-treated group. 7 On the other hand, our recent studies showed that chemotherapeutics induced overexpression of immunosuppressive IL-32 22 and SerpinB9 26 in different HB cell lines, which might be included in tumor invasion and chemoresistance. Thus, the abovementioned crosstalk is not a mere dual conversation between TAMs and HB in an isolated TME, but a multifactorial noise.…”

“…14 IL-34, which is another ligand of M-CSFR, was found to be expressed in the tumor cells of the embryonal and recurrent HB as well, and thought to be associated with tumor cell proliferation, chemoresistance, and TAMs infiltration. 13 Krijgsman et al 7 also showed that TAMs infiltrating the resected HB specimens lack the expression of the Kupffer cell marker (MARCO), suggesting that HB TAMs are monocyte-derived cells, rather than embryonic-derived macrophages. Furthermore, TAMs express myeloid checkpoint molecules such as CD47, SIRPα, and VISTA, making their targeting possible, unlike T-cells that lack the mentioned molecules' expression.…”

“…Furthermore, TAMs express myeloid checkpoint molecules such as CD47, SIRPα, and VISTA, making their targeting possible, unlike T-cells that lack the mentioned molecules' expression. 7 THE CROSSTALK BETWEEN TAMs AND HB CELLS TAMs are involved not only in promoting tumor growth and proliferation but also in immune invasion and initiation of tumorigenesis. A previous study has shown that the TAMs cytokine (IL-6) induces the expression of the hepatocyte growth factor-like protein (HGFLP) gene in HB cells.…”

“…27 scRNAseq recently showed other immune checkpoints highly expressed by TAMs: (CD47, SIRPα, and VISTA), which are supposed to be promising therapeutic targets in the future. 7 Targeting MIF, 23 TIM3 in HB cases with EIs, 21 and GM-CSF in HB cases showing higher expression of the receptor 14 were tried experimentally. For the time being, Macrophagemediated, antibody-dependent cellular phagocytosis (ADCP) using Codrituzumab, a monoclonal antibody against glypican-3 (GPC3), is investigated in preclinical studies of adult HCC, and currently, a phase I trial is recruiting for relapsed or refractory extracranial solid tumors in children and adolescents, including HB, [ClinicalTrials.gov (US) ID: NCT04928677].…”

“…6 This may explain the predominant myeloid nature of HB TME. In addition, Krijgsman et al 7 demonstrated that HB TME exhibits a predominantly myeloid immune landscape with higher infiltration of TAMs and limited infiltration of T-cells after mass cytometry and single-cell analysis of specimens from 8 HB patients. All mentioned studies highlighted the key role of TAMs in HB TME.…”