Abstract Background Early clinical promises have led to the recent FDA approval of GD2 chimeric antigen receptor (CAR) T-cell therapy for DMG. However, the response is transitory (extended survival of 2 years) indicating the need to further explore DMG immune microenvironment to better understand tumor microenvironment (TME). Method Whole brains (49 DMGs, 20 non-DMG, 10 non-malignant) from 79 pediatric patients were used to establish a tissue microarray (918 cores) representing primary, metastatic, and adjacent healthy sites. We multiplexed probing for 33 immune and cell type markers (CellDIVE MxIF) followed by signal quantification (QuPath). Bulk RNA sequencing was (n = 62 patients) performed to define additional immune signatures. Immune signature was correlated to patient clinical management. Findings were validated using patient plasma and DMG PDX models. Results Multiplex immunofluorescent probing for 33 antigens revealed enrichment of M1-activated microglia in primary versus adjacent healthy tissue. PD1 positive cells were significantly (p 0.01) higher in primary and metastatic sites compared to adjacent controls. mRNA profiling validated upregulation of immune markers in primary versus metastatic DMG sites further indicating two distinct groups with top 35 significant (p 0.05) genes revealing synaptic signature in metastatic cohort. We stratified the patient cohort by treatment immunotherapy (n = 9), imipridone, a known immune activator drug (n = 5), immuno/imipridone combination (n = 7) and immuno/imipridone naïve (n = 17). Imipridone cohort was void of progenitor (Nestin+, Vimentin+, and SOX2+) cells as well as increased macrophages/microglia infiltration. Increased T and B cells was validated in patient plasma following imipridone therapy. Combination therapy cohort exhibited increased myeloid (Iba1, CD68, CD163) and lymphoid (CD3, CD8) cells. Enhanced immune engagement was validated in DMG PDX models. Conclusion DMG tumors maintain a cold immune microenvironment, which is nevertheless dynamic and responsive to therapy. Our observation that DMG TME responds to imipridone, and immunotherapy indicated the need to explore combination therapies that will enhance clinical response in this patient population.
Laternser et al. (Fri,) studied this question.