The Transcriptional Landscape Of Tumor-Infiltrated Leukocytes Upon anti-OX40 Antibody Treatment

By engagement of OX40L with OX40, Antigen-presenting cells (APCs) provide a co-stimulatory signal to T-cells. In clinical trials, OX40 agonist antibodies (αOX40) have been used to enhance specific anti-tumoral immune response. Whereas monotherapy did not induce clinical benefit, combination with Immune checkpoint blockade (ICB) resulted in reduced tumor growth, suggesting a synergistic effect between αOX40 agonist and ICB. Here, we aim to deeper our understanding of the immediate effects of αOX40 agonist therapy on tumor-infiltrating leukocytes. We used a melanoma mouse model treated with OX40 agonist antibody or its isotype control. Single-cell tumor-infiltrating leukocytes were then isolated and sequenced for further bioinformatic analysis. We found that while OX40 agonist treatment mostly affected T-cells, which up-regulated the OX40 pathway, subsequent changes could already be observed across other immune subsets. CD8+ T-cells activation was accompanied by the upregulation of the transcriptional programs of cytotoxicity, co-stimulation and co-inhibition. Regulatory T-cells (Tregs) expressed a greater suppressive phenotype. An indirect effect of the treatment was observed in several subpopulations of dendritic cells and macrophages, which shifted towards a more pro-inflammatory state, antigen processing and presentations and increased chemotaxis. Finally, our data points to specific compensatory mechanisms which regulate T-cell activation such as Ctla4 and Havcr2 (Tim3). Put together, our findings provide further understanding for αOX40 treatment and rationale for combination therapy in ongoing and future clinical trials.