Generation of adaptive regulatory T cells by alloantigen is required for some but not all transplant tolerance protocols

Regulatory B cells require antigen recognition for effective allograft tolerance induction

Through multiple mechanisms, regulatory B cells (Breg) have been shown to play an important role in the development of allograft tolerance. However, a careful understanding of the role of antigen-specificity in Breg-mediated allograft tolerance has remained elusive. In experimental models of islet and cardiac transplantation, it has been established that Bregs can be induced in vivo by anti-CD45RB ± anti-TIM1antibody treatment, resulting in prolonged, Breg-dependent allograft tolerance. The importance of Breg antigen recognition has been suggested but not confirmed through adoptive transfer experiments, using tolerant WT C57BL/6 animals challenged with either BALB/c or C3H grafts. However, the importance of receptor-specificity has not been formally tested. Here, we utilize the novel ovalbumin-specific B cell receptor transnuclear (OBI) mice in multiple primary tolerance and adoptive transfer experiments to establish that Breg-dependent allograft tolerance relies on antigen recognition by B cells. Additionally, we identify that this Breg-dependent tolerance relies on the function of transforming growth factor-β. Together, these experiments mark important progress toward understanding how best to improve Breg-mediated allograft tolerance.

Coaggregates of Regulatory T Cells and Islet Cells Allow Long-term Graft Survival in Liver Without Immunosuppression

BACKGROUND

Transplantation of islets of Langerhans (islets) has been investigated in the clinic to treat patients with insulin-dependent diabetes mellitus. Islet grafts have been maintained by administering immunosuppressive drugs, which can lead to complications in the long term. Alternatives to immunosuppressive therapy are eagerly desired. In this study, we examined the transplantation of coaggregates of CD4CD25 regulatory T (Treg) cells.

METHODS

Coaggregates of Treg cells from C57BL/6 mice and islet cells from BALB/c mice were prepared on agarose hydrogel with small round-bottomed wells. Four hundred coaggregates were transplanted into the livers of streptozotocin-induced diabetic C57BL/6 mice without systemic immunosuppression.

RESULTS

The Treg cells and islet cells were distributed randomly in the coaggregates. When 400 coaggregates were transplanted into 9 C57BL/6 mice via the portal vein, 6 of the 9 recipients demonstrated blood glucose less than 250 mg/dL for more than 100 days. A number of insulin-positive cells were observed in the livers at 120 days after transplantation.

CONCLUSIONS

The Treg cells and islet cells were distributed randomly in the coaggregates. After intraportal transplantation of the coaggregates, Treg cells in the aggregates enabled the long-term survival of allogeneic islet cell grafts in the liver without the use of immunosuppressive drugs.

Immunosuppression: trends and tolerance?

Advances in pharmacologic immunosuppression are responsible for the excellent outcomes experienced by recipients of liver transplants. However, long-term follow-up of these patients reveals an increasing burden of morbidity and mortality that is attributable to these drugs. The authors summarize the agents used in contemporary liver transplantation immunosuppression protocols and discuss the emerging trend within the community to minimize or eliminate these agents from use. The authors present recently published data that may provide the foundation for immunosuppression minimization or tolerance induction in the future and review studies that have focused on the utility of biomarkers in guiding immunosuppression management.

Coating human pancreatic islets with CD4(+)CD25(high)CD127(-) regulatory T cells as a novel approach for the local immunoprotection

OBJECTIVES

To develop a novel approach for local immunoprotection using CD4(+)CD25(high)CD127(-) T regulatory cells (Tregs) attached to the surface of the islets before transplantation.

BACKGROUND

Tregs expanded ex vivo can control allo and autoreactivity, therefore, Treg-based therapy may offer more effective protection for transplanted islets from immunologic attack than currently used immunosuppression. Local application of Tregs can make such therapy more clinically feasible and efficient.

METHODS

Human islets were isolated and coated with allogeneic ex vivo expanded Tregs using biotin-poly(ethylene glycol)-N-hydroxysuccinimide ester (biotin-PEG-NHS) and streptavidin as binding molecules.

RESULTS

Coating pancreatic islets with Tregs did not affect islet viability (>90% fluorescein diacetate/propidium iodide) or the insulin secretion profile in dynamic islet perifusion assays. After in vitro incubation with allogeneic T effector cells, Treg-coated islets revealed preserved function with higher insulin secretion compared with controls-native islets, coated islets with T effector cells or when Tregs were added to the culture, but not attached to islets (P < 0.05). In addition, the Enzyme-linked immunosorbent spot (ELISPOT) assay revealed suppression of interferon (IFN)-γ secretion, when T effector cells were challenged with Treg-coated islets comparing to controls (99 ± 7 vs 151 ± 8 dots, respectively; P < 0.01).

CONCLUSIONS

We demonstrated, for the first time, the ability to bind immune regulatory cells to target cells with preservation of their viability and function and protective activity against immune attack. If successfully tested in an animal model, local delivery of immunoprotective Tregs on the surface of transplanted pancreatic islets may be an alternative or improvement to the currently used immunosuppression.