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In the past decade, the power of harnessing T-cell co-signaling pathways has become increasingly understood to have significant clinical importance. In cancer immunotherapy, the field has concentrated on two related modalities: First, targeting cancer antigens through highly activated chimeric antigen T cells ( CAR-Ts) and second, re-animating endogenous quiescent T cells through checkpoint blockade. In each of these strategies, the therapeutic goal is to re-ignite T-cell immunity, in order to eradicate tumors. In transplantation, there is also great interest in targeting T-cell co-signaling, but with the opposite goal: in this field, we seek the Yin to cancer immunotherapy's Yang, and focus on manipulating T-cell co-signaling to induce tolerance rather than activation. In this review, we discuss the major T-cell signaling pathways that are being investigated for tolerance induction, detailing preclinical studies and the path to the clinic for many of these molecules. These include blockade of co-stimulation pathways and agonism of coinhibitory pathways, in order to achieve the delicate state of balance that is transplant tolerance: a state which guarantees lifelong transplant acceptance without ongoing immunosuppression, and with preservation of protective immune responses. In the context of the clinical translation of immune tolerance strategies, we discuss the significant challenge that is embodied by the fact that targeted pathway modulators may have opposing effects on tolerance based on their impact on effector vs regulatory T-cell biology. Achieving this delicate balance holds the key to the major challenge of transplantation: lifelong control of alloreactivity while maintaining an otherwise intact immune system. [ABSTRACT FROM AUTHOR]

Belatacept was developed to minimize cardiovascular risk and nephrotoxicity associated with calcineurin inhibitor (CNI)- based immunosuppression. Recently, 7-year data from the Belatacept Evaluation of Nephroprotection and Efficacy as First-line Immunosuppression Trial (BENEFIT), a phase III study comparing belatacept with cyclosporine, have been published. While during the first year of belatacept the risk of acute rejection episodes was elevated, this seemingly had marginal consequences for long-term graft survival and function as well as patient survival. For patients at a low-immunological risk, this drug seems to be a safe and effective alternative to CNI-based immunosuppression. Whether the higher rates of acute rejection episodes in the first year outweigh the gain in long-term graft function is still debated. In particular, the lower incidence of donor-specific antibodies indicates that belatacept should not be considered as lower intensity immunosuppression over the long term. Therefore, should belatacept be the centrepiece of immunosuppression for renal patients?. All randomized trials so far have focussed on patients at a low immunological risk. Furthermore, cyclosporine A (CsA), the comparator of belatacept in BENEFIT and the Belatacept Evaluation of Nephroprotection and Efficacy as First-line Immunosuppression Trial-EXTended criteria donors (BENEFIT-EXT), is not the CNI of choice in modern transplantation. Furthermore, while at Year 7 the rate of cancer and infections was comparable with the CsA group, long-term data are missing on safety issues for a large number of patients. Thus, currently belatacept may be the drug of choice for a select group of patients, but not for everyone. This review highlights the benefits and uncertainties of the use of belatacept in kidney transplantation. [ABSTRACT FROM AUTHOR]

Phelps CJ, Ball SF, Vaught TD, Vance AM, Mendicino M, Monahan JA, Walters AH, Wells KD, Dandro AS, Ramsoondar JJ, Cooper DKC, Ayares DL. Production and characterization of transgenic pigs expressing porcine CTLA4-Ig. Xenotransplantation 2009; 16: 477–485. © 2009 John Wiley & Sons A/S. Inhibition of the T-cell-mediated immune response is a necessary component of preventing rejection following xenotransplantation with pig α1,3-galactosyltransferase gene-knockout (GTKO) organs. Cytotoxic T lymphocyte-associated antigen (CTLA4) is a co-stimulatory molecule that inhibits T-cell activity and may be useful in prolonging graft rejection. Methods: An expression vector was built containing the extracellular coding region of porcine (p) CTLA4 fused to the hinge and CH2/CH3 regions of human IgG1 (pCTLA4-Ig). Pigs transgenic for pCTLA4-Ig, on either a GTKO or wild-type (WT) genetic background, were produced by nuclear transfer and characterized using Western blot analysis, immunofluorescence, ELISA, and necropsy. Results: Fifteen pCTLA4-Ig-transgenic piglets resulted from five pregnancies produced by nuclear transfer. All transgenic pigs exhibited robust expression of the pCTLA4-Ig protein and most expressed the transgene in all organs analyzed, with significant levels in the blood as well. Despite initial good health, these pigs exhibited diminished humoral immunity, and were susceptible to infection, which could be managed for a limited time with antibiotics. Conclusions: Viable pigs exhibiting robust and ubiquitous expression of pCTLA4-Ig were produced on both a WT and GTKO background. Expression of pCTLA4-Ig resulted in acute susceptibility to opportunistic pathogens due at least in part to a significantly compromised humoral immune status. As this molecule is known to have immunosuppressive activity, high levels of pCTLA4-Ig expression in the blood, as well as defective development related to exposure to pCTLA4-Ig in utero, may contribute to this reduced immune status. Prophylactic treatment with antibiotics may promote survival of disease-free transgenic pigs to a size optimal for organ procurement for transplantation. Additional genetic modifications and/or tightly regulated expression of pCTLA4Ig may reduce the impact of this transgene on the humoral immune system. [ABSTRACT FROM AUTHOR]