Rejection of xenogeneic porcine islets in humanized mice is characterized by graft-infiltrating Th17 cells and activated B cells

Preclinical models for Type 1 Diabetes Mellitus - A practical approach for research

Numerous preclinical models have been developed to advance biomedical research in type 1 diabetes mellitus (T1DM). They are essential for improving our knowledge of T1DM development and progression, allowing researchers to identify potential therapeutic targets and evaluate the effectiveness of new medications. A deeper comprehension of these models themselves is critical not only to determine the optimal strategies for their utilization but also to fully unlock their potential applications in both basic and translational research. Here, we will comprehensively summarize and discuss the applications, advantages, and limitations of the commonly used animal models for human T1DM and also overview the up-to-date human tissue bioengineering models for the investigation of T1DM. By combining these models with a better understanding of the pathophysiology of T1DM, we can enhance our insights into disease initiation and development, ultimately leading to improved therapeutic responses and outcomes.

Mouse models and human islet transplantation sites for intravital imaging

Human islet transplantations into rodent models are an essential tool to aid in the development and testing of islet and cellular-based therapies for diabetes prevention and treatment. Through the ability to evaluate human islets in an in vivo setting, these studies allow for experimental approaches to answer questions surrounding normal and disease pathophysiology that cannot be answered using other in vitro and in vivo techniques alone. Intravital microscopy enables imaging of tissues in living organisms with dynamic temporal resolution and can be employed to measure biological processes in transplanted human islets revealing how experimental variables can influence engraftment, and transplant survival and function. A key consideration in experimental design for transplant imaging is the surgical placement site, which is guided by the presence of vasculature to aid in functional engraftment of the islets and promote their survival. Here, we review transplantation sites and mouse models used to study beta cell biology in vivo using intravital microscopy and we highlight fundamental observations made possible using this methodology.

Cellular Immune Responses in Islet Xenograft Rejection

Porcine islets surviving the acute injury caused by humoral rejection and IBMIR will be subjected to cellular xenograft rejection, which is predominately mediated by CD4⁺ T cells and is characterised by significant infiltration of macrophages, B cells and T cells (CD4⁺ and CD8⁺). Overall, the response is different compared to the alloimmune response and more difficult to suppress. Activation of CD4⁺ T cells is both by direct and indirect antigen presentation. After activation they recruit macrophages and direct B cell responses. Although they are less important than CD4⁺ T cells in islet xenograft rejection, macrophages are believed to be a major effector cell in this response. Rodent studies have shown that xenoantigen-primed and CD4⁺ T cell-activated macrophages were capable of recognition and rejection of pancreatic islet xenografts, and they destroyed a graft via the secretion of various proinflammatory mediators, including TNF-α, reactive oxygen and nitrogen species, and complement factors. B cells are an important mediator of islet xenograft rejection via xenoantigen presentation, priming effector T cells and producing xenospecific antibodies. Depletion and/or inhibition of B cells combined with suppressing T cells has been suggested as a promising strategy for induction of xeno-donor-specific T- and B-cell tolerance in islet xenotransplantation. Thus, strategies that expand the influence of regulatory T cells and inhibit and/or reduce macrophage and B cell responses are required for use in combination with clinical applicable immunosuppressive agents to achieve effective suppression of the T cell-initiated xenograft response.

Xenogeneic Sertoli cells modulate immune response in an evolutionary distant mouse model through the production of interleukin-10 and PD-1 ligands expression

BACKGROUND

Immunomodulatory mechanisms of Sertoli cells (SCs) during phylogeny have not been described previously. This study attempted to reveal mechanisms of SC immune modulation in an evolutionary distant host.

METHODS

The interaction of the SC cell line derived from Xenopus tropicalis (XtSC) with murine immune cells was studied in vivo and in vitro. The changes in the cytokine production, the intracellular and surface molecules expression on murine immune cells were evaluated after co-culturing with XtSCs. Migration of XtSCs in mouse recipients after intravenous application and subsequent changes in spleen and the testicular immune environment were determined by flow cytometry.

RESULTS

The in vitro co-culture model was established, allowing the study of XtSCs interaction with murine immune cells. Intracellular staining of interleukin (IL-)10 revealed a significant increase in its expression in macrophages and B cells co-cultured with XtSCs, compared to both unstimulated cells and xenogeneic control. On the contrary, a significant decrease in Th lymphocytes expressing interferon-gamma was observed. The expression of both PD-1 ligands (PD-L1 and PD-L2) was upregulated on the macrophage surfaces after co-culture with XtSCs, but not with the controls. XtSCs migrated specifically to testes when administered intravenously and modulated systemic and local testicular microenvironment; this was detected by the expression of molecules associated with suppressive phenotype by CD45⁺ cells in both spleen and testes.

CONCLUSION

We have demonstrated for the first time that SCs can migrate and modulate immune response in a phylogenetically distant host. It was further observed that SCs induce expression of molecules associated with immunosuppression, such as IL-10 and PD-1 ligands.

Clinically available immunosuppression averts rejection but not systemic inflammation after porcine islet xenotransplant in cynomolgus macaques

A safe, efficacious, and clinically applicable immunosuppressive regimen is necessary for islet xenotransplantation to become a viable treatment option for diabetes. We performed intraportal transplants of wild-type adult porcine islets in 25 streptozotocin-diabetic cynomolgus monkeys. Islet engraftment was good in 21, partial in 3, and poor in 1 recipient. Median xenograft survival was 25 days with rapamycin and CTLA4Ig immunosuppression. Adding basiliximab induction and maintenance tacrolimus to the base regimen significantly extended median graft survival to 147 days (p < .0001), with three animals maintaining insulin-free xenograft survival for 265, 282, and 288 days. We demonstrate that this regimen suppresses non-Gal anti-pig antibody responses, circulating effector memory T cell expansion, effector function, and infiltration of the graft. However, a chronic systemic inflammatory state manifested in the majority of recipients with long-term graft survival indicated by increased neutrophil to lymphocyte ratio, IL-6, MCP-1, CD40, and CRP expression. This suggests that this immunosuppression regimen fails to regulate innate immunity and resulting inflammation is significantly associated with increased incidence and severity of adverse events making this regimen unacceptable for translation. Additional studies are needed to optimize a maintenance regimen for regulating the innate inflammatory response.

Preclinical Models to Evaluate the Human Response to Autoantigen and Antigen-Specific Immunotherapy in Human Type 1 Diabetes

Type 1 Diabetes (T1D) is an autoimmune disease that results from the destruction of pancreatic islet β-cells by auto-reactive T cells. The clinical management of T1D faces the lack of fully predictive biomarkers in its preclinical stage and of antigen-specific therapies to induce or re-induce immune tolerance to β-cell autoantigens and prevent its development. From a therapeutic standpoint, preclinical models of T1D have fallen short of directly translating into humans. To circumvent this limitation, preclinical models are being optimized to allow defining autoantigen epitopes that are presented to T cells and directly apply to the human. In this review, we propose to make a point on the latest available models such as humanized immunodeficient NOD mice models and HLA and autoantigen transgenic mice and their application in the context of T1D.

Particulate-Based Single-Dose Local Immunosuppressive Regimen for Inducing Tolerogenic Dendritic Cells in Xenogeneic Islet Transplantation

Recent studies emphasize on developing immune tolerance by an interim administration of various immunosuppressive drugs. In this study, a robust protocol is reported for local immunomodulation using a single-dose of FK506 microspheres and clodronate liposomes (mFK+CLO) in a xenogeneic model of islet transplantation. Surprisingly, the single-dose treatment with mFK+CLO induce tolerance to the islet xenograft. The recipient mice display tolerogenic dendritic cells (tDCs) with decreased antigen presenting ability and T cell activation capacity. Furthermore, a reduced percentage of CD4⁺ and CD8⁺ T cells and an impaired differentiation of naïve CD4⁺ T cells into interferon-γ producing Th1 and interleukin-17 producing Th17 cells are observed. In addition, the immunosuppressive protocol leads to the generation of Foxp3⁺ regulatory T cells (Tregs) which are required for the long-term graft survival. The enhanced generation of tDCs and Tregs by the single treatment of mFK+CLO cause xenograft tolerance, suggesting a possible clinical strategy which may pave the way towards improving therapeutic outcomes of clinical islet transplantation.