Reduced IL-37 gene expression and CD8 T lymphocytes in patients with metastatic breast cancer

The normal distribution of data was assessed by the Kolmogorov–Smirnov normality test. One way ANOVA test was used to compare means between the different groups. Significant levels were considered less than 0.05. Statistical tests were performed in SPSS version 16.0 (SPSS, Inc., Chicago, IL, USA). Graph Pad Prism software (version 6.0) was used for graph drawing.

OPEN IN VIEWER

Fig. 2.

Comparison of IL-37 gene expression in ER⁺/PR⁺/HER2⁺ subgroups of breast cancer. (A) Non-metastatic and (B) metastatic breast cancer. *; P < 0.05, **; P < 0.01, ***; P < 0.001.

The results of the present studies are in agreement with the other clinical studies in which showed that the expression of the IL-37 gene was significantly decreased in patients with a different type of cancer. On the other hand, statistical analysis of the relationship between the expression of IL-37 gene and metastasis showed that the expression of this gene in breast cancer with or without metastasis was not significantly different. Also, the results showed that the number of CD8 T lymphocytes in the samples of patients including non-metastatic and metastatic breast cancer was significantly decreased compared to the healthy individuals [15–17].

In this respect, studies by Cavalli et al. confirmed that IL-37 gene expression was significantly decreased in patients with kidney cancer. This decrease is associated with disease progression because IL-37 acts as an immune suppressor in advanced kidney cancer using the IL-6/STAT3 signaling pathway [18]. In 2003, Gao and colleagues reported that fibrosarcoma growth was suppressed by injecting IL-37 into mice [17]. Zhao et al. reported in 2014 that IL-37 expression levels were negatively correlated with tumor size in hepatocellular carcinoma (HCC) [19]. Wang et al. showed that IL-37 can suppress cell proliferation and metastasis in HCC through the STAT3 pathway [20].

The previous studies showed that IL-37 acts as a tumor suppressor in lung cancer and exerts its antitumor action by inhibiting angiogenesis that can be used as a promising therapeutic target for lung cancer [21]. Previous research has shown that there is a negative correlation between IL-37 expression and angiogenesis in different cancers; however, the exact mechanisms are not depicted [21,22]. Chen and colleagues found that IL-37 stimulates apoptosis and inhibits the migration and proliferation of cancer cells [23]. On the other hand, in vivo experiments showed that IL-37 suppresses tumor growth as well as the expression of the IL-6 and hypoxia-inducible factor 1-alpha (HIF-1α) genes [23].

In addition to studies on IL-37 in humans, numerous studies have shown that the effects of IL-37 in mice are comparable to those on humans. The results confirmed that IL-37 caused significant inhibition of tumor growth in the RCC (renal cell carcinoma) mouse model [23]. Recently, IL-37 has been shown to play an important role in mouse models not only in the innate immune response but in the acquired immunity [24].

In our study, IL-37 gene expression was evaluated in different breast sub-classes of breast cancer. As a result, IL-37 was increased in the ER⁺/PR⁺/HER2⁺ patients with non-metastatic breast cancer compared to HER2⁺ patients. Baker et al. in 2019 has sown that HER2 expression in breast cancer patients is directly related to inflammatory cytokines such as IL-1 and IL-6 [25]. Previous studies have shown that ER/HER2 and HER2 breast cancer show different metastatic patterns, in which patients with HER2 breast cancer that more likely to metastases to bone and show lower survival and may need more aggressive treatment [26]. So, an increase of IL-37 may prevent metastasis in breast cancer that should be elucidated in the future.

In our study, the results showed that the number of TCD8 in the samples of patients including non-metastatic and metastatic breast cancer was significantly decreased compared to the healthy individuals. As a result, the presentation of antigen to lymphocytes is decreased, and eventually, cytokines such as IL-2, IL-12, IFN-α, and IFN-γ that affect the killing of tumor cells are reduced; however, decreased number of TCD8 in the peripheral blood may show the recruitment of these cells into the tumor site.

In tumor tissues, expression of IL-37 was positively correlated with density of CD57 NK cell. In vitro studies showed that IL-37 was able to attract CD57 NK cells and delays tumor growth [19]. Also, IL-37 cytokine can mediate the effects of IL-12 and IL-18, which perform their antitumor function through the expression of perforin and FAS-L, respectively [12].

According to previous research, IL-37 promotes NK cell activity and anti-tumor cytokines like IL-12 and IL-18. All of the above results suggest that IL-37 cytokine may be a potential activator for cytotoxic T cells in breast cancer; however, identification of the molecular mechanisms of IL-37 on cytotoxic T lymphocytes still need further studies.

In summary, our results suggest that cytokines can promote cell proliferation and invasion through signaling pathways, contribute to cancer metastasis, or prevent cancer progression. The present study showed that IL-37 gene expression and TCD8 count decreased in the new breast cancer patients. Since IL-37 increases the maturation of dendritic cells and induces the secretion of cytokines to increase the antitumor effect, there may be a direct link between IL-37 expression and the count of CD8 T lymphocytes that mediate antitumor responses. Considering the possible effects of IL-37 on TCD8 cells in tumor immune responses, although there are no sufficient studies in this regard, more research will be done to benefit from the therapeutic effects of this cytokine in the future.