T-cell immunity in anti-tumor battle

The clinical success of T-cell-based immunotherapies has transformed oncology, yet tumor immune evasion remains a formidable barrier. In this review, we delineate the developmental and molecular landscapes that shape antitumor T-cell immunity. Following a brief overview of CD4⁺ helper T-cell contributions, we focus primarily on CD8⁺ cytotoxic lineages. Rather than a passive loss of effector function, CD8⁺ T-cell exhaustion is increasingly recognized as functional attrition and profound oligoclonality. In the immunosuppressive tumor microenvironment (TME), unremitting antigenic pressure drives an iterative selection process that` narrows a highly diverse T-cell pool into a constricted, oligoclonal population, a phenomenon termed "clonal contraction". We expand the conceptual scale of T-cell clonal selection during the immune response, tracing this clonal evolution from early thymic selection and primary antigen priming to exhaustive terminal differentiation. We further propose a structural model demonstrating how the biophysical constraints of a fixed T-cell receptor (TCR) repertoire create a profound imbalance against rapidly diversifying tumor antigens. Within this framework, we highlight tissue-resident memory (Trm) as a crucial spatial reservoir that safeguards the host against the depletion of functional clones. Finally, we contextualize the therapeutic paradigm of immune checkpoint inhibition (ICI) and note that, under some circumstances, durable clinical efficacy can be driven by systemic "clonal replacement". Ultimately, we argue that next-generation T-cell-based immunotherapies may shift `from attempting only to reverse functional exhaustion to actively engineering continuous clonal selection and preserving TCR repertoire diversity.