The relationship between polymorphisms in the promoter region of Tim-3 and unexplained recurrent spontaneous abortion in Han Chinese women

Next generation of immune checkpoint molecules in maternal-fetal immunity

Successful pregnancy is a unique situation requires the maternal immune system to recognize and tolerate a semi-identical fetus and allow normal invasion of trophoblast cells. Although efforts have been made, the deep mechanisms of the maternal-fetal crosstalk have not yet been fully deciphered. Immune checkpoint molecules (ICMs) are a group of negative modulators of the immune response that avoid immune damage. They have been extensively studied in the fields of oncology and transplantation, while the latest evidence suggests that they are closely associated with pregnancy outcomes via multiple inhibitory mechanisms. Although studies have mostly demonstrated the regulatory role of the well-known PD-1, CTLA-4 at the maternal-fetal interface, what is unique about the newly discovered multiple ICMs remains a mystery. Here, we review the latest knowledge on ICMs, focusing on the first generation of checkpoints (PD-1, CTLA-4) and the next generation (Tim-3, Tigit, Lag-3, VISTA) highlighting their immunoregulatory roles in maternal-fetal tolerance and decidual vascular remodeling, and their involvement in pathological pregnancies. The content covers three aspects: the characteristics they possess, the dynamic expression profile of their expression at the maternal-fetal interface, and their involvement in pathological pregnancy. In immunotherapy strategies for pregnancy complications, upregulation of immune checkpoints may play a role. Meanwhile, the impact on pregnancy outcomes when using ICMs in clinical cancer treatment during pregnancy is a topic worth exploring. These may serve as a guide for future basic research and clinical applications of maternal-fetal immunity.

Immune checkpoints and reproductive immunology: Pioneers in the future therapy of infertility related Disorders?

As co-stimulatory receptors, immune checkpoint molecules are found on the surface of various immune cells and transduce inhibitory signals following ligand binding. The most studied members in this regard include PD-1, TIM-3, and CTLA-4. The physiological part immune checkpoints possess is the prevention of dangerous immune attacks towards self-antigens throughout an immune response, which takes place through the negative regulation of the effector immune cells, through the induction of T-cell exhaustion, for instance. It has recently been suggested that each checkpoint reduces immunoactivation via distinct intracellular mechanisms of signaling. Regulators of immune checkpoints are supposed to participate actively in immune defense mechanisms against infections, preventing autoimmunity, transplantation, and tumor immune evasion. In pregnancy, as an active immunotolerance mechanism which is also natural, the maternal immune system encounters two simultaneous challenges; in addition to accepting the semi-allogeneic fetus, the maternal immune system should also prevent infections. In this regard, the part immune checkpoint molecules possess is particularly interesting. Herein, the current understanding of such part in reproductive immunology is described.

Immune Checkpoint Molecules in Reproductive Immunology

Immune checkpoint molecules, like CTLA-4, TIM-3, PD-1, are negative regulators of immune responses to avoid immune injury. Checkpoint regulators are thought to actively participate in the immune defense of infections, prevention of autoimmunity, transplantation, and tumor immune evasion. Maternal-fetal immunotolerance represents a real immunological challenge for the immune system of the mother: beside acceptance of the semiallogeneic fetus, the maternal immune system has to be prepared for immune defense mostly against infections. In this particular situation, the role of immune checkpoint molecules could be of special interest. In this review, we describe current knowledge on the role of immune checkpoint molecules in reproductive immunology.

Tim-3: Expression on immune cells and roles at the maternal-fetal interface

Successful pregnancy relies on the accurate regulation of the maternal-fetal immune system. Without enough tolerance in the uterine microenvironment, the mother and the hemiallogeneic fetus could not peacefully coexist. T cell immunoglobulin and mucin domain (Tim)-3 is a molecule originally regarded as to be expressed on terminally differentiated IFN-γ expressing CD4⁺ T cells (Th1). The engagement of Tim-3 with its ligand, galectin-9 (Gal-9) could induce the exhaustion or apoptosis of effector T cells, and thus might regulate the tolerance. Tim-3 pathway also participates in regulating the activities of CD4⁺ regulatory T cells, monocyte-macrophages, dendritic cells and natural killer cells. Dysregulation of Tim-3 expression can elicit excessive or inhibited inflammatory responses and ultimately result in autoimmune diseases, viral or tumor evasion and pregnancy complications. In this review, we will mainly focus on the expression of Tim-3 on local immune cells and its function in pregnancy. In addition, meaningful questions that need further investigation and the potential roles of Tim-3 in fetal tolerance will be discussed. Deeper understanding of the immune checkpoint receptor Tim-3 will shed new light on exploring the pathogenesis of some pregnancy complications, including pre-eclampsia, intrauterine growth restriction, recurrent spontaneous abortion and preterm birth. Tim-3 pathway might be a new target of immune therapy for pregnancy complications in the future.

Soluble costimulatory molecule sTim3 regulates the differentiation of Th1 and Th2 in patients with unexplained recurrent spontaneous abortion

This study is to investigate the mechanism of unexplained recurrent spontaneous abortion (URSA). A total of 35 cases of URSA patients (URSA group), 20 cases with normal pregnancy (normal pregnancy group) and 20 healthy non-pregnancy candidates (healthy control group) were enrolled in this study. Enzyme linked immunosorbent assay (ELISA) method was used for detection of serum soluble Tim-3 (sTim3) and Galectin-9. Cytokine bead array (CBA) determination method was used to detect IFN-γ and IL-4 expression levels. Compared with the healthy control group, sTim-3 levels in normal pregnancy group and URSA group increased, and URSA group had significantly higher sTim-3 levels than normal pregnancy group (P < 0.05). Compared with the healthy control group, Galectin-9 levels in normal pregnancy group and URSA group also increased. However, the normal pregnancy group had significantly higher Galectin-9 level than URSA group (P < 0.05). IFN-γ levels in normal pregnancy group and URSA group were lower than those in healthy control group, and IFN-γ levels in the normal pregnancy group were significantly lower than those in URSA group (P < 0.05). Levels of IL-4 in normal pregnancy group and URSA groups increased compared with the healthy control group, and the IL-4 levels in normal pregnancy group were significantly higher than those in URSA group (P < 0.05). Th1/Th2 imbalance, sTim-3 and Galectin-9 expression increase are found in the patients with URSA, ant this might be involved in the regulation of immunity in pregnancy.

Association between polymorphisms in the promoter region of T cell immunoglobulin and mucin domain-3 and myasthenia gravis-associated thymoma

Thymoma is a type of benign or low-grade malignant tumor, occurring on the thymic epithelium. Patients with thymoma may also suffer from myasthenia gravis (MG), presenting MG-associated thymoma. T cell immunoglobulin and mucin domain-3 (Tim-3), a subtype of the Tim protein family, may be an important immune regulatory and pivotal molecule associated with tumor development. In order to understand the etiology and pathogenesis of MG-associated thymoma in the Han population of North China, the present study investigated the association between a polymorphism on the -574 locus in the promoter of Tim-3 and the risk of MG-associated thymoma in the Han Chinese population. In total, 116 patients with thymoma and MG were enrolled into the MG-associated thymoma group, while 124 patients with thymoma, but without MG, were enrolled into the non-MG-associated thymoma group. Examinations were conducted to reach a definite diagnosis of thymoma and MG and rule out other autoimmune diseases. Allele-specific polymerase chain reaction (AS-PCR) was performed to determine the polymorphism on the -574 locus of Tim-3 in all the subjects. PCR products were randomly selected for sequencing. Statistically significant differences were detected between the distribution frequencies of the GT+TT genotype and T allele on the -574 locus of the MG-associated thymoma group (31.03 vs. 12.90%, respectively; χ²=11.609, P=0.001) and the non-MG-associated thymoma group (15.52 vs. 6.45%, respectively; χ²=10.198, P=0.001). In conclusion, the present study indicated that an association may exist between the polymorphism of the -574 locus in the Tim-3 promoter and MG-associated thymoma.