Spatiotemporal CD8+ T-Cell Dynamics: Clonal Replacement and Expansion as Determinants of Sustainable Antitumor Response.

The clinical success of immune checkpoint inhibitors (ICI) has shifted the paradigm of cancer treatment, yet the fundamental mechanisms governing the long-term sustainability of antitumor T-cell responses remain elusive. Emerging evidence suggests that the efficacy of ICI depends not only on the reinvigoration of pre-existing tumor-infiltrating lymphocytes but also on the continuous mobilization and replacement of T-cell clones from systemic reservoirs. In this review, we propose a "spatiotemporal ecosystem model" of the antitumor T-cell response. We first delineate the spatial dynamics of T-cell clones, where tumor-reactive progenitors primed in the tumor-draining lymph nodes (dLN) circulate through the peripheral blood to replenish the tumor microenvironment (TME). We highlight that TCR avidity emerges as a key determinant of clonal fate; while high-avidity clones provide potent early cytotoxicity, their susceptibility to accelerated terminal exhaustion eventually creates an available niche that allows for the subsequent expansion of intermediate-avidity successor clones. Furthermore, we discuss how single-cell multi-omics integration (transcriptome, TCR repertoire, and epigenome) reveals that clonal fate is functionally encoded in the molecular and metabolic poise of T cells prior to their expansion. Finally, we discuss the potential of monitoring these clonal dynamics through liquid biopsy as a non-invasive window into the resilience of the immune ecosystem, distinguishing responders with sustainable, polyclonal mobilization from non-responders with frustrated, oligoclonal responses. By integrating clonal evolution, metabolic fitness, and inter-organ crosstalk, this ecosystem perspective offers a comprehensive framework for predicting therapeutic outcomes and developing next-generation precision immunotherapies.