Importance of B cells to development of regulatory T cells and prolongation of tissue allograft survival in recipients receiving autologous bone marrow transplantation

B cell-T cell interplay in immune regulation: A focus on follicular regulatory T and regulatory B cell functions

B cells are the core components of humoral immunity. A mature B cell can serve in multiple capacities, including antibody production, antigen presentation, and regulatory functions. Forkhead box P3 (FoxP3)-expressing regulatory T cells (Tregs) are key players in sustaining immune tolerance and keeping inflammation in check. Mounting evidence suggests complex communications between B cells and Tregs. In this review, we summarize the yin-yang regulatory relationships between B cells and Tregs mainly from the perspectives of T follicular regulatory (Tfr) cells and regulatory B cells (Bregs). We discuss the regulatory effects of Tfr cells on B cell proliferation and the germinal center response. Additionally, we review the indispensable role of B cells in ensuring homeostatic Treg survival and describe the function of Bregs in promoting Treg responses. Finally, we introduce a new subset of Tregs, termed Treg-of-B cells, which are induced by B cells, lake the expression of FoxP3 but still own immunomodulatory effects. In this article, we also enumerate a sequence of research from clinical patients and experimental models to clarify the role of Tfr cells in germinal centers and the role of convention B cells and Bregs to Tregs in the context of different diseases. This review offers an updated overview of immunoregulatory networks and unveils potential targets for therapeutic interventions against cancer, autoimmune diseases and allograft rejection.

Autologous Hematopoietic Stem Cell Transplantation for Liver Transplant Recipients With Recurrent Primary Sclerosing Cholangitis: A Pilot Study

BACKGROUND

Primary sclerosing cholangitis (PSC) is an indication for liver transplantation, but recurrence after liver transplantation is associated with poor outcomes often requiring repeat transplantation. We investigated whether autologous hematopoietic stem cell transplantation (aHSCT) could be used to stop progression of recurrent PSC and promote operational tolerance.

METHODS

Twelve patients with recurrent PSC were fully evaluated and 5 were selected for aHSCT. Autologous hematopoietic stem cells were collected, purified by CD34 immunomagnetic selection, and cryopreserved. Immunoablation using busulfan, cyclophosphamide, and rabbit antithymocyte globulin was followed by aHSCT. The primary endpoint of the study was the establishment of operational tolerance defined as lack of biochemical, histologic, and clinical evidence of rejection while off immunosuppression at 2 y post-aHSCT.

RESULTS

Two of the 5 patients achieved operational tolerance with no clinical or histologic evidence of PSC progression or allorejection. A third patient developed sinusoidal obstruction syndrome following aHSCT requiring repeat liver transplantation but has no evidence of PSC recurrence while on sirolimus monotherapy now >3 y after aHSCT. A fourth patient was weaned off immunosuppression but died 212 d after aHSCT from pericardial constriction. A fifth patient died from multiorgan failure. Immunosuppression-free allograft acceptance was associated with deletion of T-cell clones, loss of autoantibodies, and increases in regulatory T cells, transitional B cells, and programmed cell death protein-1 expressing CD8+ T cells in the 2 long-term survivors.

CONCLUSIONS

Although operational tolerance occurred following aHSCT, the high morbidity and mortality observed render this specific protocol unsuitable for clinical adoption.

Progress in Liver Transplant Tolerance and Tolerance-Inducing Cellular Therapies

Liver transplantation is currently the most effective method for treating end-stage liver disease. However, recipients still need long-term immunosuppressive drug treatment to control allogeneic immune rejection, which may cause various complications and affect the long-term survival of the recipient. Many liver transplant researchers constantly pursue the induction of immune tolerance in liver transplant recipients, immunosuppression withdrawal, and the maintenance of good and stable graft function. Although allogeneic liver transplantation is more tolerated than transplantation of other solid organs, and it shows a certain incidence of spontaneous tolerance, there is still great risk for general recipients. With the gradual progress in our understanding of immune regulatory mechanisms, a variety of immune regulatory cells have been discovered, and good results have been obtained in rodent and non-human primate transplant models. As immune cell therapies can induce long-term stable tolerance, they provide a good prospect for the induction of tolerance in clinical liver transplantation. At present, many transplant centers have carried out tolerance-inducing clinical trials in liver transplant recipients, and some have achieved gratifying results. This article will review the current status of liver transplant tolerance and the research progress of different cellular immunotherapies to induce this tolerance, which can provide more support for future clinical applications.

The advantage of Sirolimus in amplifying regulatory B cells and regulatory T cells in liver transplant patients

Sirolimus has been shown to ameliorate steroid-resistant rejection and induce long-term immune tolerance among liver transplant patients. However, the detailed mechanism of how Sirolimus achieve these advantages is still lacking. This study attempts to reveal some possible mechanisms by investigating regulatory B cells (Bregs), regulatory T cells (Tregs) and some cytokines in liver transplant recipients whose Tacrolimus was partially converted to Sirolimus. The results showed that CD19⁺CD24⁺CD38⁺Bregs and CD4⁺CD25⁺FoxP3⁺Tregs increased significantly during the first month after drug conversion (P < 0.01 and P < 0.05). The percentages of IL-10⁺Bregs and TGF-β₁⁺Bregs were also elevated (P < 0.05 and P < 0.01), and the same trend was observed in the levels of IL-10 and TGF-β₁ (P < 0.01 and P < 0.01). However, in the observation period, these investigated lymphocyte subsets and cytokines didn't change significantly in patients without Sirolimus usage. The incidence of biliary stenosis in the conversion group were significantly lower than that in the control group (P < 0.05). At the same time, in vitro experiments showed that Sirolimus could significantly amplify Bregs and Tregs (P < 0.01 and P < 0.01) while Tacrolimus did not show the amplifications effects. Sirolimus' function of amplifying Bregs was weakened, and its function of amplifying Tregs even disappeared after IL-10 and TGF-β₁ were neutralized. In conclusion, Sirolimus could amplify Bregs and Tregs among liver transplant recipient, which might be benefit to mitigate the immune response, decrease chances of rejection and alleviate biliary complication. IL-10 and TGF-β₁ may play important roles during this process.

Mechanism(s) of prolonged attenuation of allergic responses after modulation of idiotypic regulatory network

BACKGROUND

We showed previously that allergic reactivity to ovalbumin (OVA) could be regulated in mice following perturbation of immune networks using combinations of an immune Ig along with anti-idiotypic Ig. We have explored features of this regulation including: its persistence after cessation of administration of combined Igs; the ability of heterologous Igs to produce immunoregulation; a role for Treg induction in regulation; and the ability to attenuate responses in mice pre-sensitized to an allergic stimulus.

METHODS

BALB/c mice were sensitized to OVA. Mice also received 5 weekly injections of immune Ig or anti-idiotype Ig (at separate sites) from either homologous (mouse) or heterologous (human) sources. In the latter case pooled IVIG (given IM, hence hereafter IMIG) was used as a source of anti-idiotype Ig, and human anti-Tet as immune Ig. Injections of the Ig were given from the time of OVA sensitization (to attenuate development of immunity), or after pre-sensitization of mice (to attenuate existing allergic responses). All mice were assayed for development of OVA-specific serum IgE and IgG, as well as the production of OVA-induced IL-2, IL-4, IL-13, IL-31 and IL-33 in splenocytes cultured for 72 h. In studies examining possible mechanism(s) responsible for inhibition of immunity mice received, in addition to the Ig treatments described, infusion of depleting anti-CD4, and/or anti-CD8 antibodies, or a mAb to TNFSFR25, known to expand Tregs implicated in regulation of Allo immunity.

RESULTS

Combinations of both heterologous and homologous immune Igs and anti-idiotype Igs attenuated OVA allergic responses in both naïve and pre-sensitized mice. This attenuation persisted in mice greater than 14 weeks after cessation of treatment with the Igs used. Finally, depletion of either CD4 or CD8 cells ameliorated the suppressive effect seen, while the combination of anti-CD4 and anti-CD8 essentially abolished suppression. Suppression was further enhanced by anti-TNFSFR25 mAb.

CONCLUSIONS

We conclude that the combine Ig treatment protocols used produced a long-lasting suppression of allergic immunity, even in pre-sensitized animals. The effects seem to depend upon induction and expansion of Tregs and represents a novel approach to treatment of allergic disease in humans and other animals.