Single-cell RNA seq-derived signatures define response patterns to atezolizumab + bevacizumab in advanced hepatocellular carcinoma.

Background & Aims
The combination of atezolizumab and bevacizumab (atezo+bev) is the current standard of care for advanced hepatocellular carcinoma (HCC), providing a median overall survival (OS) of 19.2 months. Here, we aim to uncover the underlying cellular processes driving clinical benefit versus resistance to atezo+bev.Methods
We harnessed the power of single-cell RNA sequencing in advanced HCC to derive gene expression signatures recapitulating 21 cell phenotypes. These signatures were applied to 422 RNA-sequencing samples of advanced HCC patients treated with atezo+bev (n=317) versus atezolizumab (n=47) or sorafenib (n=58) as comparators.Results
We unveiled two distinct patterns of response to atezo+bev. First, an immune-mediated response characterized by the combined presence of CD8+ T effector cells and pro-inflammatory CXCL10+ macrophages, representing an immune rich microenvironment. Second, a non-immune, angiogenesis-related response distinguishable by a reduced expression of the VEGF co-receptor neuropilin-1 (NRP1), a biomarker that specifically predicts improved OS upon atezo+bev vs sorafenib (p = 0.039). Primary resistance was associated with an enrichment of immunosuppressive myeloid populations, namely CD14+ monocytes and TREM2+ macrophages, and Notch pathway activation. Based on these mechanistic insights we define "Immune-competent" and "Angiogenesis-driven" molecular subgroups, each associated with a significantly longer OS with atezo+bev versus sorafenib (p of interaction = 0.027), and a "Resistant" subset.Conclusion
Our study unveils two distinct molecular subsets of clinical benefit to atezolizumab plus bevacizumab in advanced HCC ("Immune-competent" and "Angiogenesis-driven") as well as the main traits of primary resistance to this therapy, thus providing a molecular framework to stratify patients based on clinical outcome and guiding potential strategies to overcome resistance.