Immunoregulatory effects of liver ablation therapies for the treatment of primary and metastatic liver malignancies

Ablation of liver tissue produces in situ tumoural antigens and elicits specific immune responses. The aim of this review is to examine the available data about the local and systemic responses produced and to compare differences between the methods available. A literature search was undertaken for all papers focusing on immune responses following ablative therapy of the liver, including experimental and clinical studies. Following ablative procedures, the cellular response is elicited by the presentation of antigens by dendritic cells to specific CD4(+) T cells, which in turn stimulate natural killer or CD8(+) cytotoxic cells. The local release of intracellular debris activates Kupffer cells to produce cytokines, which, in the immediate vicinity, activate monocytes/macrophages or specific T cells that respond and produce systemic reactions such as fever, thrombocytopaenia or shock. The immune responses elicited by cryotherapy, both cellular and cytokine, seem far greater than those produced by radiofrequency or microwave ablation, probably as a consequence of the peculiar mechanism of cell death of the former (disruptive necrosis). This mechanism is considered central to the pathogenesis of cryoshock. Ablative techniques stimulate the immune system and provide an easy way to achieve in vivo vaccination against tumoural antigens. Immunomodulatory approaches have the potential to augment the initial immune stimulation and this combined approach could pave the way to a more selective and specific method of treating liver tumours.