Immunotherapy for pediatric solid tumors: overcoming biological barriers through rational multimodal combinations

Pediatric solid tumors remain among the most treatment-refractory childhood malignancies, defined by biological features that have largely resisted the immunotherapeutic advances transforming adult oncology. Exceptionally low tumor mutational burden, sparse neoantigen landscapes, and profoundly immunosuppressive tumor microenvironments collectively undermine the T cell-dependent mechanisms on which most current immunotherapies depend. Yet the field is undergoing a meaningful shift. Anti-GD2 monoclonal antibodies have established a survival benchmark in high-risk neuroblastoma, and next-generation antibody-drug conjugates and bispecific T cell engagers targeting GD2, B7-H3, and GPC2 are extending the reach of antibody-based approaches across pediatric histologies. CAR T cell therapies have demonstrated clinical feasibility against multiple targets, with advanced engineering strategies, including cytokine armoring, bispecific constructs, and locoregional delivery, beginning to address fundamental barriers such as poor tumor infiltration, limited persistence, and antigen escape. Immune checkpoint inhibitors, while largely ineffective as monotherapy in unselected populations, induce durable responses in molecularly defined subsets such as mismatch repair-deficient and hypermutated tumors. Emerging platforms, including oncolytic virotherapy, NK cell engagers, and neoantigen vaccines, offer rational strategies to convert immunologically cold tumors into treatment-responsive phenotypes. Together, these advances point toward a future of combination immunotherapy tailored to the distinct immune biology of childhood cancers.