Abstract
Cancer immunotherapy has revolutionized oncology by leveraging the immune system’s ability to recognize and eliminate tumor cells. Among the most impactful advances are immune checkpoint inhibitors that target the programmed death-1 (PD-1) receptor and its ligand PD-L1, which can restore T cell activity and generate durable responses across several cancer types. However, their effectiveness is limited by both primary and acquired resistance, restricting long-term benefit to a subset of patients. This review highlights current progress in cancer immunotherapy and explores emerging strategies beyond PD-1/PD-L1 blockade. Novel inhibitory and co-stimulatory immune checkpoints such as lymphocyte activation gene-3 (LAG-3), T cell immunoglobulin mucin-3 (TIM-3), T cell immunoreceptor with Ig and ITIM domains (TIGIT), OX40, CD137 (4-1BB), and CD40 are examined for their potential to enhance anti-tumor immunity. The rationale for combining immunotherapy with chemotherapy, radiotherapy, targeted therapies, oncolytic viruses, and neoantigen vaccines is discussed in the context of overcoming resistance. Additional emphasis is placed on modifying the tumor microenvironment, targeting tumor metabolism, and overcoming stromal barriers. Advanced delivery systems such as chimeric antigen receptor (CAR) T cells, bispecific antibodies, and nanoparticle-based platforms offer improved specificity and reduced toxicity. Biomarker-guided precision immuno-oncology using tumor mutational burden, microsatellite instability, and immune gene signatures is advancing clinical decision-making. Gut microbiota modulation and artificial intelligence-based tools are also emerging as critical components in optimizing therapeutic outcomes. Collectively, this review proposes a multidimensional and personalized immunotherapy paradigm aimed at broadening clinical efficacy and overcoming resistance beyond conventional PD-1/PD-L1 inhibition. GRAPHICAL ABSTRACT: [Image: see text]