Abstract Diffuse midline glioma (DMG) is a lethal pediatric and adolescent high-grade glioma. DMG patients harbor a cold tumor immune microenvironment (TIME), similar to adult glioblastoma patients, who also suffer from systemic lymphopenia. In glioblastoma, lymphopenia is linked to T-cell sequestration in the bone marrow, caused by T-cell internalization of S1PR1, limiting trafficking. The DRD2 antagonist/ClpP agonist ONC201 is currently in clinical trials for DMG and has reported immunomodulatory effects in other cancers, thus we aimed to investigate ONC201’s immunomodulatory effects in DMG. Flow cytometry of peripheral blood from DMG patients at diagnosis showed low levels of lymphocytes (CD4+, CD8+, and NK cells) compared to the reference range (n = 9). This was also seen in immunocompetent C57BL/6 DMG-engrafted mice (known as ‘PPK’ harboring PdgfraD842V, DNp53, and H3f3aK27M mutations) compared to tumor-naïve, sham-engrafted mice (n = 3). Vehicle-treated PPK-engrafted mice showed increased numbers of T cells in the bone marrow compared to sham-engrafted mice (log2FC:-1.28, p-value:0.0367), suggesting T-cell sequestration. ONC201 treatment (125 mg/kg B.I.W.) increased S1PR1 surface expression on T cells (log2FC:0.73, p-value=0.0005), reducing sequestration in the bone marrow. Immunohistochemistry identified increased levels of tumor-infiltrating lymphocytes (TILs) within the TIME of ONC201-treated mice, including CD45+ and CD3+ T cells (log2FC:2.38 and 1.94, p-value:0.0275 and 0.0103). ONC201 also promoted increased expression of the MHC I subunit B2M (log2FC:1.67, p-value:0.0281), suggesting enhanced antigen presentation. Despite warming the TIME, no survival benefit was seen using immunocompetent mice (n = 10). scRNAseq of PPK tumors +/-ONC201 identified increased infiltration of immunosuppressive myeloid-derived macrophages (MDMs). These MDMs showed upregulation of CD74, known to be expressed on tumor-associated macrophages favoring a tumor-permissive TIME, revealing a possible therapeutic vulnerability. In conclusion, DMG tumors contribute to systemic lymphopenia, partially reversed by ONC201. While ONC201 promotes antigen presentation and TIL recruitment, killing efficacy may be limited by tumor-promoting CD74+ MDMs, highlighting future combination strategies.
Persson et al. (Fri,) studied this question.