The cellular actors of the tumor microenvironment: a single-cell atlas perspective on specialized subtypes, coordinated networks, and immunotherapy

The tumor microenvironment (TME) is a multicellular ecosystem composed of immune and stromal compartments, together with vascular and neural–glial components, that coevolve with malignant cells and collectively shape tumor initiation, progression, and therapeutic responses. In this review, we integrate recent advances from single-cell and spatial transcriptomic atlases of the TME, which have delineated a set of tumor-enriched, specialized cell populations, including CXCL13⁺ T cells, SPP1⁺ tumor-associated macrophages (SPP1⁺ TAM), LAMP3⁺ dendritic cells, tumor-associated natural killer (TaNK) cells, tumor-associated atypical B (TAAB) cells, and LRRC15⁺ cancer-associated fibroblasts (LRRC15⁺ CAF). Notably, these subsets do not function independently but instead assemble into coordinated cellular networks, such as cell modules and immunity hubs, that shape antitumor immunity and clinical outcomes. However, existing conceptual frameworks still fall short of capturing the full complexity of immune regulation within the TME, underscoring the need to systematically integrate artificial intelligence (AI) into TME research. We therefore highlight how AI-driven “virtual cell” and “virtual laboratory” platforms can integrate multimodal omics with clinical data to simulate cellular dynamics, predict the therapeutic benefit, and accelerate drug discovery through human–AI collaboration. Building on these advances, we further propose the concept of a “virtual tumor” to encompass AI-constructed computational models of the TME. Finally, we summarize the recent progress in cancer immunotherapy—including immune checkpoint blockade, engineered T-cell and macrophage therapies, and personalized cancer vaccines—and discuss emerging strategies that target specific TME components to overcome primary and acquired resistance. Together, these developments outline a roadmap that unites atlas-era TME biology, next-generation immunotherapies, and AI-guided modeling to advance mechanism-based precision cancer immunotherapy.