An immunosufficient murine model for the study of human islets

In vivo induction of regulatory T cells by anti-CD45RB antibody causes transferable tolerance to discordant human xenogenic islets

BACKGROUND

The treatment of diabetes by islet cell transplantation has become an accepted therapy, with transplantation of xenogeneic islet cells an attractive alternative to the problem. Previous studies in mice have demonstrated that anti-CD45RB induce immune tolerance in human pancreatic islet cells. The current study was to define the mechanism of action of anti-CD45RB induced nonspecific immune tolerance to heteroantigens.

METHODS

A total of 1500 IEQ human islets were transplanted to diabetic B6μMT-/- mice, B6 mice, and μMT-/- diabetic mice undergoing thymectomy. These mice were treated short-term with doses of anti-CD45RB. CD4+Foxp3+Tregs were detected in the blood, peripheral lymphatic organs by flow cytometry, and immunohistochemistry. In addition, anti-CD25 mAb was administered to tolerant human islet cells B6μMT-/-mice. Mice then were transplanted with other human islet cells and received CD4+CD25+Tregs isolated from tolerant human islets mice to observe islet destruction.

RESULTS

Anti-CD45RB treatment-induced tolerance to islets in both immunocompetent and B-cell-deficient mice (μMT-/- mice) by processes that were dependent on CD25+ Tregs, but not B cells. Anti-CD45RB treatment increased the number of CD4+Foxp3+Tregs cells. Anti-CD45RB treatment-induced immune tolerance that was antigen nonspecific, with Tregs playing an important role. Anti-CD45RB treatment-induced tolerance generated Tregs that could be transferred to another individual to manifest nonspecific immune tolerance.

CONCLUSION

The results of the experiment suggest that anti-CD45RB induced tolerance to human islet xenografts is mediated by the proliferation of Tregs. These tolerogenic Tregs can be transferred to other mice and induce nonspecific immune tolerance.

Mettl14-mediated m6A modification enhances the function of Foxp3+ regulatory T cells and promotes allograft acceptance

N6-methyladenosine (m6A), the most prevalent form of internal mRNA modification, is extensively involved in Treg cells differentiation and function. However, the involvement of m6A in functional Treg cells for transplantation tolerance remains to be elucidated. By using an experimental transplantation mouse model, we found that m6A levels in Treg cells were altered during the induction of transplant tolerance by performing a dot blotting assay. Subsequently, we used the heterogenic Treg-specific Mettl14 knockout mice (Foxp3-Mettl14^f/+ cKO) to reduce METTL14 expression and performed islets allograft transplantation. Our result revealed that reduced expression of METTL14 prevented Treg cells expansion and promoted the infiltration of CD4⁺ and CD8⁺ T cells around the allograft, which led to rapid allograft rejection in Foxp3-Mettl14 ^f/+ cKO mice. The expression of regulatory cytokines including IL-10 and TGF-β was significantly decreased in Foxp3-Mettl14 ^f/+ cKO mice, and the suppressive function of Treg cells was also abrogated. In addition, an analysis of RNA-seq data revealed that the SOCS family (SOCS1, SOCS2 and SOCS3) is the subsequent signaling pathway affected by the METTL14 mediated m6A modification in Treg cells to modulate the suppressive function after transplantation. Taken together, our study showed for the first time that the METTL14-mediated m6A modification is essential for the suppressive function of Treg cells in transplantation and may serve as a regulatory element of Treg cell-based therapy in transplant medicine.

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.

E Pluribus Unum: 50 Years of Research, Millions of Viruses, and One Goal--Tailored Acceleration of AAV Evolution

Fifty years ago, a Science paper by Atchison et al. reported a newly discovered virus that would soon become known as adeno-associated virus (AAV) and that would subsequently emerge as one of the most versatile and most auspicious vectors for human gene therapy. A large part of its attraction stems from the ease with which the viral capsid can be engineered for particle retargeting to cell types of choice, evasion from neutralizing antibodies or other desirable properties. Particularly powerful and in the focus of the current review are high-throughput methods aimed at expanding the repertoire of AAV vectors by means of directed molecular evolution, such as random mutagenesis, DNA family shuffling, in silico reconstruction of ancestral capsids, or peptide display. Here, unlike the wealth of prior reviews on this topic, we especially emphasize and critically discuss the practical aspects of the different procedures that affect the ultimate outcome, including diversification protocols, combinatorial library complexity, and selection strategies. Our overall aim is to provide general guidance that should help users at any level, from novice to expert, to safely navigate through the rugged space of directed AAV evolution while avoiding the pitfalls that are associated with these challenging but promising technologies.