TAMI-78. STEM CELL IMMUNOTHERAPY MODULATES IMMUNOREGULATORY PATHWAYS IN THE TUMOR MICROENVIRONMENT

Abstract

Abstract INTRODUCTION A major obstacle in efficacious therapeutics against high-grade gliomas has been an inability to overcome powerful regulatory mechanisms within the TME that hamper immune activation. Fortunately, immunotherapy has enabled the enhancement of immune activation within the TME through adoptive immunotherapy and checkpoint inhibition. We found that co-transfer of hematopoietic stem cells (HSCs) with either adoptive immunotherapy or PD-1 blockade significantly improves therapeutic outcomes by manipulating the cellular components that make up the TME in high-grade gliomas. HSC co-transfer with immunotherapy leads to increased in situ downregulation of multiple immune regulatory pathways, activation of tumor-reactive T cells, and significant reduction in the frequency of MDCs and TAMs within the TME. METHODS C57BL/6 mice with orthotopic KR158B-gliomas received either adoptive immunotherapy using activated tumor-reactive T cells or αPD-1, either with or without HSC co-transfer. After treatment of late-stage tumors, brains were sectioned and digital spatial profiling (NanoString GeoMx) of the TME was conducted in situ. Briefly, tumor-bearing brain sections were stained for nuclei, CD3, CD45, and GFP (HSC-derived cells); regions of interest (ROIs) containing 200 nuclei were selected and processed for whole genome sequencing. Areas rich in immune cells within the TME were chosen as ROIs and compared between groups. Results were corroborated with flowcytometry and PCR. RESULTS Mice that received HSCs with either adoptive cellular therapy or αPD-1 had reductions in expression of multiple regulatory markers in the TME including iNOS, TGFβ, and PD-L1. This was accompanied by reductions in the frequencies of MDSCs and TAMs. An increased relative abundance of activated CD8+ T cells within the TME was also observed. Interestingly, we found that HSC-derived cells provided rich amounts of dendritic cells at the TME when co-transferred with immunotherapy. Host-derived myeloid cells were significantly displaced from the TME in mice receiving HSC plus adoptive cellular therapy or αPD-1.