Cryoablation remodels the immune microenvironment in hepatocellular carcinoma: From mechanistic insights to clinical translation in combination immunotherapy

Table 1 Dual immunomodulatory effects of cryoablation on the hepatocellular carcinoma microenvironment

Immunomodulatory direction	Core mechanisms and events	Key effects/findings
Positive immune activation	Induction of immunogenic cell death: Releases intact tumor antigens and DAMPs via unique physical injury (ice crystal formation, cell rupture)[30-33,35]	Functions as an in situ vaccine, initiating systemic anti-tumor immunity. Antigen accumulation within DCs may be higher than with thermal ablation
	DAMP release and antigen-presenting cell activation: Releases key DAMPs (high mobility group box 1, adenosine triphosphate, calreticulin, heat shock proteins), promoting DC maturation and antigen presentation via receptors like Toll-like receptor 4 and P2X7[19,32,34,36]	Provides “danger signals”, bridging innate and adaptive immunity
	Initiation of adaptive immunity: DCs capture antigens, migrate to lymph nodes, and activate tumor-specific CD4+ and CD8+ T cells[13,14,20,35]	Preclinical models confirm increased numbers and activity of T cells and NK cells locally and systemically, with tumor-specific antibody production
	Effector T cell infiltration and abscopal effect: Activated CTLs home to tumors. Enrichment of CD8+ T cells and NK cells is also observed in untreated distant lesions[27,37-39]	Combination with immune adjuvants or anti-PD-L1 significantly enhances T cell infiltration and function, yielding synergistic activity
	Formation of immunological memory: Induces expansion of effector memory T cell and central memory T cell, particularly potent neoantigen-specific CD4+ T-cell responses[40-46]	Clinical studies show increased memory T cell subsets in peripheral blood post-procedure. Combination with immune checkpoint inhibitors or adjuvants significantly enhances the strength and durability of memory responses
Potential immunosuppression	Release of immunosuppressive cytokines: Necrotic areas release TGF-β, interleukin-10, vascular endothelial growth factor, etc. May induce more intense pro-inflammatory cytokine release compared to MWA/radiofrequency ablation[30,47-50]	TGF-β strongly inhibits CTL/NK function, promotes Treg differentiation, and M2 macrophage polarization
	Recruitment of immunosuppressive cells: Recruits myeloid-derived suppressor cells, M2-type tumor-associated macrophages, and regulatory T cells to the tumor site. May polarize tumor-associated neutrophils to an immunosuppressive N2 phenotype, forming physical barriers via NETs[20,37,50-53]	These cells inhibit effector T cells via mechanisms like depletion of essential amino acids and secretion of inhibitory factors. NET formation is a novel mechanism limiting efficacy
	Upregulation of immune checkpoints: As an adaptive resistance mechanism, induces upregulation of checkpoint molecules (e.g., programmed death-1/PD-L1) in distant tumor tissues[54]	May lead to rapid T cell exhaustion and limit the abscopal effect. Studies show it may induce higher PD-L1 upregulation than MWA
	Antigen overload and immune tolerance[55,56]	Massive short-term antigen release in a suppressive milieu may lead to T cell deletion/anergy, inducing immune tolerance

CTL: Cytotoxic T lymphocyte; DAMP: Damage-associated molecular pattern; DC: Dendritic cell; MWA: Microwave ablation; NET: Neutrophil extracellular trap; NK: Natural killer; PD-L1: Programmed death-ligand 1; TGF-β: Transforming growth factor-beta; Treg: Regulatory T cell.