The amelioration of composite tissue allograft rejection by TIM-3-modified dendritic cell: Regulation of the balance of regulatory and effector T cells

Highlights

• TIM-3 can mitigate allograft rejection and enhance immune tolerance in CTA.

• TIM-3 can induce lymphocyte hyporesponsiveness in CTA.

• TIM-3 can regulate the balance of regulatory and effector T cells in CTA.

Abstract

T cell-dependent immune responses play a central role in allograft rejection. Exploring ways to disarm alloreactive T cells represents a potential strategy to promote long-term allograft acceptance and survival. T cell Ig domain and mucin domain 3 (TIM-3) has previously been demonstrated as a central regulator of T helper 1 (Th1) responses and immune tolerance. Hence, TIM-3 may be an important molecule for decreasing immunological rejection during composite tissue allotransplantation (CTA). In this study, BALB/c and C57BL/6 mice were chosen as the experimental animals. The effects of TIM-3 on allograft rejection were explored using TIM-3-modified mature dendritic cells (TIM-3 mDCs). A laser speckle blood flow (LSBF) imager was used to evaluate blood distribution of the BALB/c mice. ELISA, MTT, ELISPOT assays and flow cytometry analysis were carried out for further researches. We found that TIM-3 could obviously prolong the survival time of the transplanted limbs. And TIM-3 could mitigate the immune response and thus enhance immune tolerance after CTA. Also, TIM-3 can induce lymphocyte hyporesponsiveness, including facilitating lymphocyte apoptosis, decreasing lymphocyte proliferation, and influencing the secretion of inflammatory cytokines by CD4⁺ T cells. Furthermore, TIM-3 overexpression could induce CD4⁺ T cells to differentiate into regulatory T cells (Tregs), which recalibrate the effector and regulatory arms of the alloimmune response. In summary, we concluded that TIM-3 can mitigate allograft rejection and thus enhance immune tolerance by inducing lymphocyte hyporesponsiveness and increasing the number of Tregs of the alloimmune response. TIM-3 may be a potential therapeutic molecule for allograft rejection in CTA.

Introduction

Understanding the immunology of tolerance and rejection has allowed composite tissue allotransplantation (CTA) to progress [1]. CTA has been introduced as a potential clinical treatment for complex reconstructive procedures [2]. At present, a particularly large number of people have been suffering from the loss of limbs, and CTA has tremendous potential for the reconstruction of such physiological defects [3]. However, CTA is considered to elicit a stronger response compared with solid organ transplants for the reason that CTA consists of heterogeneous tissues [2]. Hence, it is important to inhibit immunological rejection after CTA.

Previous research has shown that current immunosuppressive agents, including cyclosporine [4], rapamycin [5], and FK506 [6], prolong the survival of rat limb allografts [3]. Also, in order to reduce the degree of immunological rejection, recipients often have to take immunosuppressive agents after transplantation for a long time, which inevitably results in serious side effects, including drug toxicity, infection, malignancy, and even life-threatening side effects [3], [7]. Thus, long-term use of immunosuppressive agents for CTA recipients should be avoided, and a new therapeutic strategy should be established.

It has been confirmed that T cell-dependent immune responses play a central role in allograft rejection, and the balance between T cell activation and inhibition determines the ultimate fate of allografts [8], [9]. To be specific, complete T cell activation includes T cell proliferation, differentiation into effector or memory T cells, and cytokine release, which might finally result in allograft rejection [9]. Thus, exploring ways to disarm alloreactive T cells is crucial to survival of allograft, and manipulating activating or inhibiting signals to T cells represents a potential strategy to promote long-term allograft acceptance and survival [10], [11].

T cell Ig domain and mucin domain (TIM)-3, a transmembrane protein, is constitutively expressed on CD4⁺ Th1 and CD8⁺ Tc1 cells [12]. TIM-3 has previously been demonstrated as a central regulator of Th1 responses and immune tolerance. Research by the OB and FDA has reported that TIM-3 is a key regulatory molecule of alloimmunity through its ability to broadly modulate CD4⁺ T cell differentiation. Also, they found that blockade of TIM-3 increased allospecific effector T cells, enhanced Th1 and Th17 polarization, and resulted in a decrease in the overall number of allospecific Tregs [10]. Hence, TIM-3 may be an important molecule for decreasing immunological rejection during CTA. Also, it remains unknown whether TIM-3 overexpression can prolong allograft survival time by influencing leukomonocytes.

The family of TIMs has been described in mice [13]. In this study, we chose mice as the research model. Our results suggest that TIM-3 can prolong the survival time of allografts by inducing lymphocyte hyporesponsiveness. Furthermore, TIM-3 overexpression can induce CD4⁺ T cells to differentiate into Tregs. Hence, TIM-3 may be a potential therapeutic molecule for allograft rejection in CTA.