Blocking ITGA5 potentiates the efficacy of anti-PD-1 therapy on glioblastoma by remodeling tumor-associated macrophages.

Background: Glioblastoma (GBM) is largely refractory to antibodies against programmed cell death 1 (anti-PD-1) therapy. Fully understanding the cellular heterogeneity and immune adaptations in response to anti-PD-1 therapy is necessary to design more effective immunotherapies for GBM. This study aimed to dissect the molecular mechanisms of specific immunosuppressive subpopulations to drive anti-PD-1 resistance in GBM.

Methods: We systematically analysed single-cell RNA sequencing and spatial transcriptomics data from GBM tissues receiving anti-PD-1 therapy to characterize the microenvironment alterations. The biological functions of a novel circular RNA (circRNA) were validated both in vitro and in vivo. Mechanically, co-immunoprecipitation, RNA immunoprecipitation and pull-down assays were conducted.

Results: Mesenchymal GBM (MES-GBM) cells, which were associated with a poor prognosis, and secreted phosphoprotein 1 (SPP1)+ myeloid-derived macrophages (SPP1+ MDMs), a unique subpopulation of MDMs with complex functions, preferentially accumulated in non-responders to anti-PD-1 therapy, indicating that MES-GBM cells and SPP1+ MDMs were the main anti-PD-1-resistant cell subpopulations. Functionally, we determined that circular RNA succinate dehydrogenase complex assembly factor 2 (circSDHAF2), which was positively associated with the abundance of these two anti-PD-1-resistant cell subpopulations, facilitated the formation of a regional MES-GBM and SPP1+ MDM cell interaction loop, resulting in a spatially specific adaptive immunosuppressive microenvironment. Mechanically, we found that circSDHAF2 promoted MES-GBM cell formation by stabilizing the integrin alpha 5 (ITGA5) protein through N-glycosylation. Meanwhile, the N-glycosylation of the ITGA5 protein facilitated its translocation into exosomes and subsequent delivery to MDMs to induce the formation of SPP1+ MDMs, which in turn maintained the MES-GBM cell status and induced T-cell dysfunction via the SPP1-ITGA5 pathway, ultimately promoting GBM immune escape. Importantly, our findings demonstrated that antibody-mediated ITGA5 blockade enhanced anti-PD-1-mediated antitumor immunity.

Conclusions: This work elucidated the potential tissue adaptation mechanism of intratumoral dynamic interactions between MES-GBM cells, MDMs and T cells in anti-PD-1 non-responders and identified the therapeutic potential of targeting ITGA5 to reduce anti-PD-1 resistance in GBM.