Nanotechnology-Enabled Immunotherapy for Colorectal Cancer: Overcoming the "Cold" Tumor Microenvironment in...

Immune checkpoint inhibitors (ICIs) have transformed the management of mismatch repair-deficient/microsatellite instability-high (dMMR/MSI-H) colorectal cancer (CRC), yet the ~95% of patients with mismatch repair-proficient/microsatellite-stable (pMMR/MSS) disease derive little benefit owing to an immunologically "cold" tumor microenvironment (TME), poor T-cell infiltration, myeloid dominance, TGF-β-enriched stroma, and the systemically immunosuppressive milieu imposed by hepatic metastases. Clinically tested combinations-multikinase inhibitor plus anti-PD-1, Fc-enhanced dual checkpoint blockade, chemotherapy- or antiangiogenic-ICI regimens-have so far produced modest, largely non-durable response rates that are further attenuated in liver-metastatic disease, motivating approaches that pharmacologically remodel the TME rather than only release checkpoint restraint.

To provide an evidence-stratified synthesis of nanotechnology-enabled immunotherapy in CRC that explicitly separates (a) clinically established evidence, (b) strategies under early-phase clinical investigation, and (c) concepts that remain preclinical or are extrapolated from other tumor types, and to derive from this appraisal a biomarker-enriched translational research agenda.

Narrative, integrative (non-systematic) review. PubMed, Embase, Web of Science, ClinicalTrials.gov, and ASCO/ESMO/AACR proceedings were searched from January 2010 through April 2026. Each strategy was appraised according to the highest available level of evidence, the tumor type and model system in which the evidence was generated, and its demonstrated CRC specificity.

In current clinical practice, nanomedicine in CRC is essentially limited to nanoparticle-formulated cytotoxics exploited for pharmacokinetic advantage (e.g. liposomal irinotecan), whereas nano-enabled immunotherapy is confined to a small number of early-phase trials-most notably lipid nanoparticle (LNP)-formulated individualized neoantigen mRNA vaccines in ctDNA-positive resected CRC and hafnium-oxide nanoparticle radioenhancers-none of which has yet demonstrated a progression-free or overall survival benefit in MSS CRC. Against this background we critically appraise six classes of strategy: (i) LNP-based mRNA neoantigen vaccines; (ii) polymeric and inorganic nanocarriers for STING and TLR agonists; (iii) tumor-associated macrophage-repolarizing nanoparticles; (iv) nano-radiosensitizers and photothermal/photodynamic platforms priming immunogenic cell death; (v) nano-formulated checkpoint inhibitor delivery; and (vi) locoregional nano-strategies directed at hepatic metastasis-specific immunosuppression. For categories (ii)-(vi) the supporting evidence is predominantly murine (largely subcutaneous CT26/MC38 models) or extrapolated from immunologically "hot" tumors such as melanoma and non-small-cell lung cancer, in which both the underlying biology and the checkpoint backbone differ materially from MSS CRC. Recurrent translational barriers include low, highly heterogeneous nanoparticle accumulation in human tumors, dense TGF-β-rich stroma and elevated interstitial pressure, mononuclear phagocyte system clearance, liver-metastasis-specific tolerance that subcutaneous models do not reproduce, unresolved manufacturing/CMC and regulatory pathways, and the absence of validated pharmacodynamic biomarkers of intratumoral immune conversion.

Nanotechnology offers a mechanistically coherent and experimentally testable-but at present clinically unproven-set of strategies for converting "cold" MSS CRC into immune-responsive disease. We therefore position nano-enabled immunotherapy as a research priority rather than an imminent standard of care, and argue that its clinical value can only be established through biomarker-enriched, paired-biopsy early-phase trials with pharmacodynamic endpoints of immune conversion and prospective stratification by metastatic site (particularly hepatic involvement) and consensus molecular subtype.

This is a narrative rather than systematic review; it is therefore subject to selection and publication bias, and much of the evidence synthesized is preclinical and of limited direct translational certainty.