Tumour-associated CD204+ microglia/macrophages accumulate in perivascular and perinecrotic niches and correlate with an interleukin-6-enriched inflammatory profile in glioblastoma

Aims Glioblastomas are heterogeneous tumours with a rich tumour microenvironment particularly comprised of tumour-associated microglia/macrophages (TAMs), but also containing a population of dedifferentiated/stem-like glioblastoma cells. Both cell populations contribute to tumour aggressiveness and immune evasion through the actions of various signalling molecules. The scavenger and pattern recognition receptor CD204 is associated with a pro-tumourigenic phenotype of TAMs and has a negative prognostic value. Our objective was to investigate the possible interaction between TAMs and dedifferentiated glioblastoma cells and characterise the myeloid phenotype of CD204-enriched glioblastomas. Methods Double immunohistochemistry and cell counting was performed on eight glioblastoma samples to estimate the expression and interaction level between dedifferentiated/stem-like tumour cells and TAMs. Using the NanoString technology, myeloid transcriptome profiling was performed on 46 glioblastomas, which had been selected based on their protein expression levels of CD204 and ionised calcium-binding adaptor molecule-1 (IBA1). The results were validated by immunohistochemistry and in silico gene expression analyses. Results TAMs especially CD204(+) TAMs accumulated in perivascular and perinecrotic niches in close proximity to podoplanin(+) glioblastoma cells. Gene profiling revealed that CD204-enriched glioblastoma has a unique signature with upregulation of genes related to hypoxia, angiogenesis and invasion, including interleukin-6. The gene signature favoured a poor prognosis in patients with glioblastoma. Conclusions This is the first study to characterise the role of CD204 in the myeloid microenvironment of glioblastoma. Our results support the unfavourable prognostic impact of CD204 and suggest that CD204 and interleukin-6 could serve as targets for re-education of TAMs and potentiation of current anti-glioma therapy.