Abstract Background Glioblastoma (GBM) is an aggressive brain cancer infiltrated by immunosuppressive myeloid-derived suppressor cells (MDSCs) and confers poor prognosis. To address this, our group developed an adoptive cellular therapy platform specifically for primary CNS malignancies that yielded significant survival benefits against multiple brain cancer models. Pre-clinically, this platform establishes proof-of-concept for lymphodepletion achieved through host conditioning with total body irradiation (TBI). While host conditioning is thought to remove immunosuppressive elements, the aim of this study was to determine how immune recovery is impacted by adoptive cellular therapy. Methods The adoptive cellular therapy platform includes myeloablative TBI, hematopoietic stem cell rescue, tumor-specific T-cells, and dendritic cell vaccines. KR158B glioma-bearing mice were treated with adoptive cellular therapy and secondary lymphoid organs were evaluated using flow cytometry, spatial genomics and multiplex protein analysis. Single cell transcriptomics and trans-well migration assay evaluated the role of CCL12 on MDSC migration. Results We show that adoptive cellular therapy allows for reconstitution of MDSC and tumor-associated macrophages in secondary lymphoid organs but prevents their accumulation in the TME. This allows for the increased engraftment and activation of T-cells within the TME. Next, we show that adoptive cellular therapy decreases CCL12 in the TME and neutralization of TAM-derived CCL12 in vitro inhibits MDSC migration in glioma. Conclusion These findings suggest a previously unrecognized association between both loss of intratumoral immunosuppressive elements after immunotherapy and TAM-derived CCL12, a chemokine that promotes MDSC migration. Future in vivo studies will evaluate the causal role of CCL12 on MDSC recruitment in glioma.
Figg et al. (Sat,) studied this question.