Effect of triple costimulation blockade on islet allograft survival in sensitized mice

Transition from preclinical to clinical application of CTLA4-Ig co-stimulation blockage in beta-cell replacement therapy

Beta-cell replacement therapies, including islet and pancreas transplantation, offer promising results in term of glycemic control for patients with type 1 diabetes experiencing high glycemic variability and severe hypoglycemia. However, long-term insulin independence remains challenging due to progressive graft function decline. Immunosuppressive regimens, especially calcineurin inhibitors such as tacrolimus, are known to be diabetogenic, contributing to the paradox of impaired beta-cell function in a diabetes treatment setting. Recent studies have focused on CTLA4-Ig (e.g., belatacept) as a potential alternative to calcineurin inhibitors, showing promising results in preclinical and clinical models. This review summarizes key advancements and remaining challenges in CTLA4 applications for beta-cell replacement. First, genetic engineering approaches aiming for CTLA4 expression in islets demonstrated initial success in delaying rejection but remain hindered by immune escape and limited integration efficacy. Coating techniques and exogenous CTLA4-Ig administration offer simpler, albeit transient, immunosuppressive effects, which, combined with encapsulation technologies, can improve graft survival. In non-human primate models, islet transplantation with immunosuppressant regimen using CTLA4-Ig combined with agents such as sirolimus or anti-CD154 has shown extended insulin independence, though full immune tolerance remains elusive. A limited number of human studies using belatacept for beta-cell replacement indicate reduced HbA1c levels and avoidance of severe hypoglycemia, yet consistent absence of rejection remains unachieved. Future research on BCR with CTLA4-Ig should explore graft survival in human islets transplantation and refine immunosuppressive protocols to leverage CTLA4-Ig potential in improving long-term graft function, thus enhancing the sustainability of CTLA4-Ig in clinical beta-cell replacement approach.

Role of myeloid-derived suppressor cells in mouse pre-sensitized cardiac transplant model

Harness of sensitized transplantation remains a clinical challenge particularly in parallel with prolonged cold ischemia time (PCI)-mediated injury. Our present study was to test the role of myeloid-derived suppressor cells (MDSCs) in mouse pre-sensitized transplantation. Our findings revealed that CD11b+Gr1(low) MDSC was shown to have strong suppressive activity. MDSCs subsets from the tolerated mice exhibited higher suppressive capacities compared with counterparts from naive (untreated) mice. Depletion of Tregs could not affect splenic CD11b+Gr1(-low) MDSC frequency, but increase peripheral and intragraft CD11b+Gr1(-low) frequency. Intriguingly, boost of Tregs remarkably caused an increase of CD11b+Gr1(-low) frequency in the graft, peripheral blood, and spleen. Furthermore, peripheral CD11b+Gr1(-low) cells were massively accumulated at the early stage when allogeneic immune response was enhanced. Taken together, MDSCs could prevent grafts from PCI-mediated injury independent on Tregs in the pre-sensitized transplant recipients. Utilization of MDSC subset particularly CD11b+Gr1(-low) might provide a novel insight into improving graft outcome under such clinical scenarios.

Immune rejection after pancreatic islet cell transplantation: in vivo dual contrast-enhanced MR imaging in a mouse model

PURPOSE

To detect adoptively transferred immune attack in a mouse model of islet cell transplantation by using a long-circulating paramagnetic T1 contrast agent, a protected graft copolymer (PGC) that is covalently linked to gadolinium-diethylenetriaminepentaacetic acid with fluorescein isothiocyanate (Gd-DTPA-F), which accumulates in the sites of inflammation that are characterized by vascular disruption.

MATERIALS AND METHODS

All animal experiments were performed in compliance with institutional guidelines and approved by the subcommittee on research animal care. Six nonobese diabetic severe combined immunodeficiency mice received transplanted human islet cells under the kidney capsule and adoptively transferred 5 × 10(6) splenocytes from 6-week-old nonobese diabetic mice. These mice also served as control subjects for comparison of pre- and postadoptive transfer MR imaging results. Mice that received phosphate-buffered saline solution only were included as nonadoptive-transfer control subjects (n = 2). In vivo magnetic resonance (MR) imaging was performed before and 17 hours after intravenous injections of PGC-Gd-DTPA-F, followed by histologic examination. Statistical differences were analyzed by means of a paired Student t test and repeated two-way analysis of variance.

RESULTS

MR imaging results showed significantly greater accumulation of PGC-Gd-DTPA-F in the graft area after immune attack initiated by adoptive transfer of splenocytes compared with that of the same area before the transfer (T1, 137.2 msec ± 39.3 and 239.5 msec ± 17.6, respectively; P < .001). These results were confirmed at histologic examination, which showed considerable leakage of the contrast agent into the islet cell interstitium.

CONCLUSION

PGC-Gd-DTPA-F-enhanced MR imaging allows for the in vivo assessment of vascular damage of the graft T cell challenge.

Inhibition of recall responses through complementary therapies targeting CD8+ T-cell- and alloantibody-dependent allocytotoxicity in sensitized transplant recipients

Allospecific T memory cell responses in transplant recipients arise from environmental exposure to previous transplantation or cross-reactive heterologous immunity. Unfortunately, these memory responses pose a significant barrier to the survival of transplanted tissue. We have previously reported that concurrent inhibition of CD154 and LFA-1 suppresses primary CD8-dependent rejection responses that are not controlled by conventional immunosuppressive strategies. We hypothesized that CD154- and LFA-1-mediated inhibition, by targeting activation as well as effector functions, may also be efficacious for the control of alloreactive CD8+ T-cell responses in sensitized hosts. We found that treatment with anti-LFA-1 mAb alone enhanced transplant survival and reduced CD8-mediated cytotoxicity in sensitized CD4 KO recipients. However, treatment with anti-CD154 mAb alone did not have an effect. Notably, when both CD4- and CD8-dependent rejection pathways are operative (wild-type sensitized recipients), LFA-1 significantly inhibited CD8-mediated in vivo allocytotoxicity but did not correspond with enhanced hepatocyte survival. We hypothesized that this was due to alloantibody-mediated rejection. When anti-LFA-1 mAb treatment was combined with macrophage depletion, which we have previously reported impairs alloantibody-mediated parenchymal cell damage, in vivo cytotoxic effector function was significantly decreased and was accompanied by significant enhancement of hepatocyte survival in sensitized wild-type recipients. Therefore, LFA-1 is a potent therapeutic target for reduction of CD8-mediated cytotoxicity in sensitized transplant recipients and can be combined with other treatments that target non-CD8-mediated recall alloimmunity.