Blood cell and hematopoietic stem cell progenitors found in the medullary cavities are susceptible to their environment. Cytokines play a fundamental role in transducing extracellular signals and impulses by binding to their respective receptors on the cell surface [11].
In the context of leukemia, abnormal cytokine levels and aberrant response to them result in perturbed bone marrow niche architecture, which enhances leukemogenesis and disease progression [12]. In AML, these events are well documented [11].
Deregulated cytokine production is attributed to polymorphisms and VNTRs in cytokine genes. These polymorphisms critically influence genetic susceptibility to cancers in several ways, such as affecting the level and the function of cytokines engaged in immune responses, disrupting nuclear factor binding to targeted genes, and altering apoptosis [13,14,15].
IL-4 is a crucial cytokine that controls proliferation, differentiation, and apoptosis in hematopoietic and non-hematopoietic cell lineages. Recent investigations have confirmed the essential role of IL4 in the survival of AML cells [16].
The polymorphism of the minisatellite region in the third intron of the IL-4 gene has attracted increased attention due to its role in changing gene expression. Thus, the amount of IL4 produced [16]. Currently, this IL4 gene polymorphism has been identified as a risk factor affecting susceptibility to carcinogenesis [15]. However, its role as a genetic marker in AML is still undetermined. To date, it is still unknown whether this polymorphism has prognostic value in the stratification of AML risk, as it highlights the factors contributing to the provocation and impairment of blast cells, which are the fundamental basics in AML cell biology with potential treatment outcomes [11].
Therefore, we performed this work to reveal its role and provide a deeper evaluation of its association with clinical and laboratory data and its potential prognostic impact on AML patients.
There are three alleles for IL4 gene VNTR polymorphism, namely, P1 allele, three repeats; P2 allele, two repeats; and P3 allele, four repeats. The P1 allele is the most standard allele, and the P3 allele is the rarest one [17].
In the current study, P1/P2 and P2/P2 genotypes were frequently detected in leukemic patients, and the P2 allele was significantly associated with the disease. These findings are inconsistent with a study by Ahmed et al. [4], in which patients of different kinds of leukemias have been recruited. They observed a higher incidence of allele loss in leukemic patients, and they concluded that P1/P1 and P1/P2 genotypes are collectively associated with leukemogenesis. Moreover, their study confirmed a higher frequency of P1 allele in leukemic patients. This difference stems from the observed heterogeneity of various types of leukemia in the patients enrolled in their study.
Duan et al. [15] performed a meta-analysis to investigate IL-4 intron 3 VNTR polymorphism and its relationship to cancer risk. They concluded that the P2 allele might be linked to a lower risk of cancer compared to the P1 allele. However, some reservations were raised regarding that meta-analysis. The pooled data were obtained from studies on different cancer types, accounting for heterogeneity. Various types of malignancies might trigger different host responses, and the interplay between environmental factors and the host might also affect susceptibility to different types of cancer [18].
In the present work, patients with the P2P2 genotype had higher leukocytosis, moderate anemia, marked thrombocytopenia, and higher blast percentages compared to heterozygous and non-carriers of the P2 allele. They also had inferior disease outcomes than the other group since they were less responsive to therapy and had a higher incidence of relapse.
It has been evidenced that the IL-4 intron 3 VNTR variant can alter messenger ribonucleic acid splicing resulting in different splice variants. There is strong evidence that IL4 VNTR polymorphism may alter IL-4 synthesis, with the P1 allele boosting IL-4 expression compared to the P2 allele [19].
Together with ours, this finding raises questions regarding the mechanism by which IL4 affects leukemic cells growth and survival and whether a P2P2 genotype with lower IL4 expression causes more malignant clone and resistant disease.
According to a recent study, IL4 is an inhibitor of AML cells that appears as the first hit to leukemic cells because it showed the most selective suppression of their growth while retaining normal bone marrow cells. The authors of this study referred to its antileukemic effect to STAT6 being a downstream mediator of IL4 signaling and a crucial signaling pathway in macrophage function and activation. In a STAT 6-dependent manner, IL4 selectively triggers programmed cell death of AML cells [20].
Indeed, our patients with the P2P2 genotype and lower IL4 expression had higher blast percentages, increased therapy resistance, a higher incidence of relapse, shorter OS, and a worse disease outcome when compared to the heterozygous and non-carrier of the P2 allele.
Several reports indicate that IL-4 is the central cytokine of T-helper 2 cells that enhances the differentiation and function of CD4 and CD8-T cells [21]. Moreover, some tumors contained IL4 in their microenvironment, primarily expressed by tumor-infiltrating leucocytes [22, 23].
In support of these reports, IL-4 expressed by tumors or T cells had been observed to improve tumor elimination with innate immunity acting in synergy with CD8 + T cells to decrease tumor load [24].
Similarly, Gitlitz et al. [25] concluded that IL-4 with granulocyte macrophage-colony stimulating factor (GM-CSF) boosts the quantity and performance of antigen-presenting cells in cancer patients. Moreover, the anti-tumor activity of IL4 has been shown in experiments on various cancers such as colon, breast, and renal carcinoma [26, 27].
In contrast to the findings above, other studies indicated that IL-4 produced by the tumor hinders apoptosis, causing the immortalization of malignant cells [16]. It has been reported that IL-4 induces the development and metastasis of head and neck squamous carcinoma [28,29,30].
Based on previous findings, it can be confirmed that IL-4 is a potent tumor immune modulator with both tumor-promoting and tumor-suppressing features. How IL-4 will interact either way is primarily determined by the type of tumor-clearing effector cell (adaptive/innate) and the kind of tumor cell studied. That is why a single molecule can adversely influence different tumor models and how innate and adaptive immunity will respond [24].
Since IL4 has contradictory effects on tumor immunity, gene sequence variations can still affect gene expression and function. It will significantly benefit investigating the association between IL-4 polymorphism variants and the risk of several human cancers. In addition to determining the molecular mechanisms underlying cell responses to IL-4 in various cancer types, it may provide valuable information for designing new risk stratification models and novel treatments for cancer patients.
