In this prospective cohort, we analysed the key immune cytokines/chemokines in HCC patients (n = 22) before and after thermal ablation. Our results showed that there were many cytokines/chemokines (12 of 27) that were lower in HCC patients before ablation than in healthy controls, whereas only MCP-1 was higher. This result suggested that early HCC (BCLC stage 0-B) developed a complex immunosuppressive environment, especially Th1/Th2 cytokine network imbalance.
In addition to local tumour tissue necrosis, our study provides evidence that thermal ablation could induce a systemic antitumor immune response. We found that IL-6 was markedly elevated and that there was a significant positive correlation between ALT and WBC and IL-6 levels at week 1 after thermal ablation. IL-6 is a pleiotropic cytokine involved not only in the immune response but also in inflammation by stimulating signal transducer and activator of transcription 3 (STAT3) [15, 16]. Some studies have reported that the IL-6 level is significantly elevated at 3–15 days post-ablation [17–19]. Therefore, we hypothesized that IL-6 is a biomarker reflecting the degree of hepatic trauma and inflammation caused by thermal ablation and can be used as a biomarker to diagnose complications early. We also found that IL-10, an anti-inflammatory Th2 cytokine that promotes immunosuppression, was decreased dramatically from baseline to week 4 after ablation, while the Th1 cytokine TNF-α was first decreased at week 1 and then elevated at week 4, but there was no significant difference between baseline and week 4. Our findings indicated that thermal ablation may offset the Th1/Th2 balance, which was reshaped and polarized to the Th1 status, thus alleviating HCC tumour-induced immune suppression. In addition, MCP-1 and MIP-1β showed similar dynamics to TNF-α. IL-17, PDGF-BB and RANTES showed the same dynamic changing trends and were significantly elevated at week 4 compared with baseline and week 1. Taken together, our data showed the different dynamic changing trends of cytokines/chemokines after ablation, which could be caused by different mechanisms. First, thermal ablation may cause trauma to the liver, and the wound healing process may result in alterations in some cytokines/chemokines. Second, heat-induced injury could promote acute thermal coagulative necrosis and apoptosis in liver and tumour tissues. The ablated tissue or tumour cells release cytokines/chemokines. Third, importantly, tumour antigens that are released after necrosis drain to antigen-presenting cells, which further stimulate nonspecific and specific immune responses. In conclusion, cytokine expression affected by wound healing, ablated tissue and nonspecific immune responses lasts for a shorter duration than that affected by specific immune responses [20], which may be the reason why the cytokine/chemokine changes lasted for different durations. Therefore, we concluded that thermal ablation induced specific immune cytokine/chemokine changes at week 4.
Interestingly, we further observed that IL-10, TNF-α, PDGF-BB and RANTES were associated with tumour recurrence. IL-10 may contribute to a tumour microenvironment promoting HCC carcinogenesis and progression. Our study showed that a high level of IL-10 at baseline but not after thermal ablation was easily associated with tumour recurrence. This is consistent with the finding of a previous study describing IL-10 as a major biomarker of poor prognosis in HCC [21]. We also observed that the levels of TNF-α, PDGF-BB and RANTES were significantly lower at week 4 and were closely linked with an unfavourable prognosis. The results further indicated that thermal ablation induced antitumor immune function at week 4. TNF-α is one of the most important proinflammatory cytokines and has been demonstrated to be an antitumor cytokine that activates NF-κB formation. Some studies have shown that HCC patients with high expression of TNF-α and NF-κB have longer survival times. The level of TNF-α was higher after ablation and was associated with a good prognosis in patients with cancer [22–24].
PDGF-BB is a pluripotent angiogenic ligand that is present in platelets and released upon degranulation and plays a biological function by activating PDGFR-α and PDGFR-β [25]. PDGF-BB has roles in tumour growth, invasion and metastasis [26–27]. A study revealed that in HCC patients after curative resection, PDGF-BB was lower in the recurrence group than in the nonrecurrence group both before surgery and at 4 weeks post-operation [28]. In a previous study [29], after sorafenib treatment, PDGF-BB was significantly lower in non-long survivors than in long survivors (overall survival ≥ 2 years). We showed for the first time that depleted serum concentrations of PDGF-BB may be associated with tumour recurrence after ablation. In patients with recurrence, the molecular mechanism involved in the exhaustion of serum PDGF-BB concentrations is unknown. The reason could be that platelet dysfunction is already known to contribute to cancer progression [30–31], and therefore. our hypothesis was that the depletion of serum PDGF-BB might be attributed to platelet exhaustion.
The CC-chemokine RANTES (CCL5) is a T-cell chemoattractant and an immunoregulatory molecule. RANTES can be expressed by a number of cell types, including T lymphocyte cells, macrophages, platelets and tubular epithelium [32]. Nevertheless, the role of RANTES in tumour development remains controversial. Some studies have shown that RANTES overexpression facilitates tumour progression and metastasis via the RANTES/CCR5 axis [33–34]. In addition, other studies have reported that increased RANTES expression, which chemotactically attracts a substantial number of immunocytes to tumour tissues to exert antitumor efficacy, may be associated with favourable outcomes in some diseases [35]. In our study, elevated serum levels of RANTES were observed in nonrecurrence patients compared with recurrence patients at week 4 after ablation. This could imply a protective role of RANTES for antitumor immune responses to prevent tumour recurrence.
Our study found immune mediators associated with tumour recurrence and used large panels of 27 cytokines/chemokines, immune mediators and growth factors at three time points before and after ablation, which has rarely been reported in the existing literature. We also recognize that this study has several limitations. First, the sample size was relatively small, and larger cohorts are needed to validate these findings. Second, we merely evaluated circulating cytokines/chemokines, and further studies on their association with the immune response in the ablation zone microenvironment should be conducted.