Anti-LFA-1 therapy induces long-term islet allograft acceptance in the absence of IFN-gamma or IL-4

Islet beta-cells and intercellular adhesion molecule-1 (ICAM-1): Integrating immune responses that influence autoimmunity and graft rejection

Type 1 diabetes (T1D) develops due to autoimmune targeting of the pancreatic islet β-cells. Clinical symptoms arise from reduced insulin in circulation. The molecular events and interactions between discrete immune cell populations, infiltration of such leukocytes into pancreatic and islet tissue, and selective targeting of the islet β-cells during autoimmunity and graft rejection are not entirely understood. One protein central to antigen presentation, priming of immune cells, trafficking of leukocytes, and vital for leukocyte effector function is the intercellular adhesion molecule-1 (ICAM-1). The gene encoding ICAM-1 is transcriptionally regulated and rapidly responsive (i.e., within hours) to pro-inflammatory cytokines. ICAM-1 is a transmembrane protein that can be glycosylated; its presence on the cell surface provides co-stimulatory functions for immune cell activation and stabilization of cell-cell contacts. ICAM-1 interacts with the β2-integrins, CD11a/CD18 (LFA-1) and CD11b/CD18 (Mac-1), which are present on discrete immune cell populations. A whole-body ICAM-1 deletion protects NOD mice from diabetes onset, strongly implicating this protein in autoimmune responses. Since several different cell types express ICAM-1, its biology is fundamentally essential for various physiological and pathological outcomes. Herein, we review the role of ICAM-1 during both autoimmunity and islet graft rejection to understand the mechanism(s) leading to islet β-cell death and dysfunction that results in insufficient circulating quantities of insulin to control glucose homeostasis.

Immunosuppressive PLGA TGF-β1 Microparticles Induce Polyclonal and Antigen-Specific Regulatory T Cells for Local Immunomodulation of Allogeneic Islet Transplants

Allogeneic islet transplantation is a promising cell-based therapy for Type 1 Diabetes (T1D). The long-term efficacy of this approach, however, is impaired by allorejection. Current clinical practice relies on long-term systemic immunosuppression, leading to severe adverse events. To avoid these detrimental effects, poly(lactic-co-glycolic acid) (PLGA) microparticles (MPs) were engineered for the localized and controlled release of immunomodulatory TGF-β1. The in vitro co-incubation of TGF-β1 releasing PLGA MPs with naïve CD4⁺ T cells resulted in the efficient generation of both polyclonal and antigen-specific induced regulatory T cells (iTregs) with robust immunosuppressive function. The co-transplantation of TGF-β1 releasing PLGA MPs and Balb/c mouse islets within the extrahepatic epididymal fat pad (EFP) of diabetic C57BL/6J mice resulted in the prompt engraftment of the allogenic implants, supporting the compatibility of PLGA MPs and local TGF-β1 release. The presence of the TGF-β1-PLGA MPs, however, did not confer significant graft protection when compared to untreated controls, despite measurement of preserved insulin expression, reduced intra-islet CD3⁺ cells invasion, and elevated CD3⁺Foxp3⁺ T cells at the peri-transplantation site in long-term functioning grafts. Examination of the broader impacts of TGF-β1/PLGA MPs on the host immune system implicated a localized nature of the immunomodulation with no observed systemic impacts. In summary, this approach establishes the feasibility of a local and modular microparticle delivery system for the immunomodulation of an extrahepatic implant site. This approach can be easily adapted to deliver larger doses or other agents, as well as multi-drug approaches, within the local graft microenvironment to prevent transplant rejection.

Molecular Aspects of Volatile Anesthetic-Induced Organ Protection and Its Potential in Kidney Transplantation

Ischemia reperfusion injury (IRI) is inevitable in kidney transplantation and negatively impacts graft and patient outcome. Reperfusion takes place in the recipient and most of the injury following ischemia and reperfusion occurs during this reperfusion phase; therefore, the intra-operative period seems an attractive window of opportunity to modulate IRI and improve short- and potentially long-term graft outcome. Commonly used volatile anesthetics such as sevoflurane and isoflurane have been shown to interfere with many of the pathophysiological processes involved in the injurious cascade of IRI. Therefore, volatile anesthetic (VA) agents might be the preferred anesthetics used during the transplantation procedure. This review highlights the molecular and cellular protective points of engagement of VA shown in in vitro studies and in vivo animal experiments, and the potential translation of these results to the clinical setting of kidney transplantation.

Thalidomide with blockade of co-stimulatory molecules prolongs the survival of alloantigen-primed mice with cardiac allografts

Background

Miscellaneous memory cell populations that exist before organ transplantation are crucial barriers to transplantation. In the present study, we used a skin-primed heart transplantation model in mouse to evaluate the abilities of Thalidomide (TD), alone or in combination with co-stimulatory blockade, using monoclonal antibodies (mAbs) against memory T cells and alloantibodies to prolong the second cardiac survival.

Results

In the skin-primed heart transplantation model, TD combined with mAbs significantly prolonged the second cardiac survival, accompanied by inhibition of memory CD8⁺ T cells. This combined treatment enhanced the CD4⁺Foxp3⁺ regulatory T cells ratio in the spleen, restrained the infiltration of lymphocytes into the allograft, and suppressed the allo-response of spleen T cells in the recipient. The levels of allo-antibodies also decreased in the recipient serum. In addition, we detected low levels of the constitutions of the lytic machinery of cytotoxic cells, which cause allograft damage.

Conclusions

Our study indicated a potential synergistic action of TD in combination with with mAbs to suppress the function of memory T cells and increase the survival of second allografts in alloantigen-primed mice.

Peritransplant VLA-4 blockade inhibits endogenous memory CD8 T cell infiltration into high-risk cardiac allografts and CTLA-4Ig resistant rejection

Recipient endogenous memory CD8 T cells expressing reactivity to donor class I MHC infiltrate MHC-mismatched cardiac allografts within 24 hours after reperfusion and express effector functions mediating graft injury. The current study tested the efficacy of Very Late Antigen-4 (VLA-4) blockade to inhibit endogenous memory CD8 T cell infiltration into cardiac allografts and attenuate early posttransplant inflammation. Peritransplant anti-VLA-4 mAb given to C57BL6 (H-2b ) recipients of AJ (H-2a ) heart allografts completely inhibited endogenous memory CD4 and CD8 T cell infiltration with significant decrease in macrophage, but not neutrophil, infiltration into allografts subjected to either minimal or prolonged cold ischemic storage (CIS) prior to transplant, reduced intra-allograft IFN-γ-induced gene expression and prolonged survival of allografts subjected to prolonged CIS in CTLA-4Ig treated recipients. Anti-VLA-4 mAb also inhibited priming of donor-specific T cells producing IFN-γ until at least day 7 posttransplant. Peritransplant anti-VLA plus anti-CD154 mAb treatment similarly prolonged survival of allografts subjected to minimal or increased CIS prior to transplant. Overall, these data indicate that peritransplant anti-VLA-4 mAb inhibits early infiltration memory CD8 T cell infiltration into allografts with a marked reduction in early graft inflammation suggesting an effective strategy to attenuate negative effects of heterologous alloimmunity in recipients of higher risk grafts.

The Costimulatory Pathways and T Regulatory Cells in Ischemia-Reperfusion Injury: A Strong Arm in the Inflammatory Response?

Costimulatory molecules have been identified as crucial regulators in the inflammatory response in various immunologic disease models. These molecules are classified into four different families depending on their structure. Here, we will focus on various ischemia studies that use costimulatory molecules as a target to reduce the inherent inflammatory status. Furthermore, we will discuss the relevant role of T regulatory cells in these inflammatory mechanisms and the costimulatory pathways in which they are involved.

Disruption of Transplant Tolerance by an "Incognito" Form of CD8 T Cell-Dependent Memory

Several approaches successfully achieve allograft tolerance in preclinical models but are challenging to translate into clinical practice. Many clinically relevant factors can attenuate allograft tolerance induction, including intrinsic genetic resistance, peritransplant infection, inflammation, and preexisting antidonor immunity. The prevailing view for immune memory as a tolerance barrier is that the host harbors memory cells that spontaneously cross-react to donor MHC antigens. Such preexisting "heterologous" memory cells have direct reactivity to donor cells and resist most tolerance regimens. In this study, we developed a model system to determine if an alternative form of immune memory could also block tolerance. We posited that host memory T cells could potentially respond to donor-derived non-MHC antigens, such as latent viral antigens or autoantigens, to which the host is immune. Results show that immunity to a model nonself antigen, ovalbumin (OVA), can dramatically disrupt tolerance despite undetectable initial reactivity to donor MHC antigens. Importantly, this blockade of tolerance was CD8⁺ T cell-dependent and required linked antigen presentation of alloantigens with the test OVA antigen. As such, this pathway represents an unapparent, or "incognito," form of immunity that is sufficient to prevent tolerance and that can be an unforeseen additional immune barrier to clinical transplant tolerance.

The impact of cell surface PEGylation and short-course immunotherapy on islet graft survival in an allogeneic murine model

Islet transplantation is a promising therapy for Type 1 diabetes mellitus; however, host inflammatory and immune responses lead to islet dysfunction and destruction, despite potent systemic immunosuppression. Grafting of poly(ethylene glycol) (PEG) to the periphery of cells or tissues can mitigate inflammation and immune recognition via generation of a steric barrier. Herein, we sought to evaluate the complementary impact of islet PEGylation with a short-course immunotherapy on the survival of fully-MHC mismatched islet allografts (DBA/2 islets into diabetic C57BL/6J recipients). Anti-Lymphocyte Function-associated Antigen 1 (LFA-1) antibody was selected as a complementary, transient, systemic immune monotherapy. Islets were PEGylated via an optimized protocol, with resulting islets exhibiting robust cell viability and function. Following transplantation, a significant subset of diabetic animals receiving PEGylated islets (60%) or anti-LFA-1 antibody (50%) exhibited long-term (>100d) normoglycemia. The combinatorial approach proved synergistic, with 78% of the grafts exhibiting euglycemia long-term. Additional studies examining graft cellular infiltrates at early time points characterized the local impact of the transplant protocol on graft survival. Results illustrate the capacity of a simple polymer grafting approach to impart significant immunoprotective effects via modulation of the local transplant environment, while short-term immunotherapy serves to complement this effect.

STATEMENT OF SIGNIFICANCE

We believe this study is important and of interest to the biomaterials and transplant community for several reasons: 1) it provides an optimized protocol for the PEGylation of islets, with minimal impact on the coated islets, which can be easily translated for clinical applications; 2) this optimized protocol demonstrates the benefits of islet PEGylation in providing modest immunosuppression in a murine model; 3) this work demonstrates the combinatory impact of PEGylation with short-course immunotherapy (via LFA-1 blockage), illustrating the capacity of PEGylation to complement existing immunotherapy; and 4) it suggests macrophage phenotype shifting as the potential mechanism for this observed benefit.

Sodium Iodide Symporter PET and BLI Noninvasively Reveal Mesoangioblast Survival in Dystrophic Mice

Muscular dystrophies are a heterogeneous group of myopathies, characterized by muscle weakness and degeneration, without curative treatment. Mesoangioblasts (MABs) have been proposed as a potential regenerative therapy. To improve our understanding of the in vivo behavior of MABs and the effect of different immunosuppressive therapies, like cyclosporine A or co-stimulation-adhesion blockade therapy, on cell survival noninvasive cell monitoring is required. Therefore, cells were transduced with a lentiviral vector encoding firefly luciferase (Fluc) and the human sodium iodide transporter (hNIS) to allow cell monitoring via bioluminescence imaging (BLI) and small-animal positron emission tomography (PET). Non-H2 matched mMABs were injected in the femoral artery of dystrophic mice and were clearly visible via small-animal PET and BLI. Based on noninvasive imaging data, we were able to show that co-stim was clearly superior to CsA in reducing cell rejection and this was mediated via a reduction in cytotoxic T cells and upregulation of regulatory T cells.

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Longitudinal monitoring of murine mesoangioblasts with BLI and small-animal PET

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Noninvasive evaluation of immune suppressant efficacy

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Inhibition of co-stimulation outperformed cyclosporin

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Inhibition of co-stimulation reduced cytotoxic and upregulated regulatory T cells

Anti-OX40L monoclonal antibody prolongs secondary heart allograft survival based on CD40/CD40L and LFA-1/ICAM-1 blockade

BACKGROUND

Memory T cells (Tms) form a barrier against long-term allograft survival; however, CD4(+)Foxp3(+) regulatory T cells (Tregs) can suppress allograft rejection. The OX40/OX40L pathway is critical to the generation of Tms and turns off Treg suppressor function.

METHODS

B6 mice that rejected BALB/c skin grafts after 4 weeks were used as the secondary heart transplant recipients. The skin recipient mice, termed S0, S2 and S3, were treated with the isotype antibodies, anti-CD40L/LFA-1 or anti-OX40L combined with anti-CD40L/LFA-1 mAbs, respectively. The secondary heart recipients, termed H0 and H2, received anti-CD40L/LFA-1 mAbs or not, respectively (Fig. 1).

RESULTS

Four weeks after primary skin transplantation, the Tms in the S3 group that received anti-OX40L with anti-CD40L/LFA-1 mAbs were reduced compared to those in the S2 group (CD4(+) Tm: 32.61 ± 2.20% in S2 vs. 25.36 ± 1.16% in S3; CD8(+) Tm: 27.76 ± 1.96% in S2 vs. 20.95 ± 1.30% in S3; P < 0.01). Meanwhile, the proportions of Tregs in S3 increased compared to those in S2 (P < 0.05). The anti-OX40L with anti-CD40L/LFA-1 mAbs group (S3H2) prolonged the mean survival time (MST) following secondary heart transplantation from 9.5 days to 21 days (P < 0.001). Furthermore, allogeneic proliferation of recipient splenic T cells and graft-infiltrating lymphocytes were significantly inhibited in the S3H2 group. Additionally, a higher level of IL-10 was detected in sera and allografts.

CONCLUSIONS

Anti-OX40L mAb could prolong secondary heart allograft survival based on CD40/CD40L and LFA-1/ICAM-1 blockade. The mechanism of protecting allografts using anti-OX40L mAb involved impairing the generation of Tm and up-regulating IL-10 producing Tregs, inhibiting the function of T cells.

Long-term survival of allograft murine islets coated via covalently stabilized polymers

Clinical islet transplantation (CIT) has emerged as a promising treatment option for type 1 diabetes mellitus (T1DM); however, the antirejection drug regimen necessary to mitigate allograft islet rejection is undesirable. The use of polymeric coatings to immunocamouflage the transplant from host immune attack has great potential. Alginate and poly(ethylene glycol) (PEG)-based polymers, functionalized with azide and phosphine, respectively, which form spontaneous and chemoselective crosslinks via the bioorthogonal Staudinger ligation scheme, were recently developed. Here, the utility of these polymers to form immunoprotective, ultrathin coatings on murine primary pancreatic islets is explored. Resulting coatings are nontoxic, with unimpaired glucose stimulated insulin secretion. Transplantation of coated BALB/c (H-2(d) ) islets into streptozotozin-induced diabetic C57BL/6 (H-2(b) ) results in prompt achievement of normoglycemia, at a rate comparable to controls. A significant subset of animals receiving coated islets (57%) exhibits long-term (>100 d) function, with robust islets observed upon explantation. Control islets rejected after 15 d (±9 d). Results illustrate the capacity of chemoselectively functionalized polymers to form coatings on islets, imparting no detrimental effect to the underlying cells, with resulting coatings exhibiting significant protective effects in an allograft murine model.

Endogenous memory CD8 T cells directly mediate cardiac allograft rejection

Differences in levels of environmentally induced memory T cells that cross-react with donor MHC molecules are postulated to account for the efficacy of allograft tolerance-inducing strategies in rodents versus their failure in nonhuman primates and human transplant patients. Strategies to study the impact of donor-reactive memory T cells on allografts in rodents have relied on the pretransplant induction of memory T cells cross-reactive with donor allogeneic MHC molecules through recipient viral infection, priming directly with donor antigen or adoptive transfer of donor antigen primed memory T cells. Each approach accelerates allograft rejection and confers resistance to tolerance induction, but also biases the T cell repertoire to strong donor reactivity. The ability of endogenous memory T cells within unprimed mice to directly reject an allograft is unknown. Here, we show a direct association between increased duration of cold ischemic allograft storage and numbers and enhanced functions of early graft infiltrating endogenous CD8 memory T cells. These T cells directly mediate rejection of allografts subjected to prolonged ischemia and this rejection is resistant to costimulatory blockade. These findings recapitulate the clinically significant impact of endogenous memory T cells with donor reactivity in a mouse transplant model in the absence of prior recipient priming.

Costimulation-adhesion blockade is superior to cyclosporine A and prednisone immunosuppressive therapy for preventing rejection of differentiated human embryonic stem cells following transplantation

RATIONALE

Human embryonic stem cell (hESC) derivatives are attractive candidates for therapeutic use. The engraftment and survival of hESC derivatives as xenografts or allografts require effective immunosuppression to prevent immune cell infiltration and graft destruction.

OBJECTIVE

To test the hypothesis that a short-course, dual-agent regimen of two costimulation-adhesion blockade agents can induce better engraftment of hESC derivatives compared to current immunosuppressive agents.

METHODS AND RESULTS

We transduced hESCs with a double fusion reporter gene construct expressing firefly luciferase (Fluc) and enhanced green fluorescent protein, and differentiated these cells to endothelial cells (hESC-ECs). Reporter gene expression enabled longitudinal assessment of cell engraftment by bioluminescence imaging. Costimulation-adhesion therapy resulted in superior hESC-EC and mouse EC engraftment compared to cyclosporine therapy in a hind limb model. Costimulation-adhesion therapy also promoted robust hESC-EC and hESC-derived cardiomyocyte survival in an ischemic myocardial injury model. Improved hESC-EC engraftment had a cardioprotective effect after myocardial injury, as assessed by magnetic resonance imaging. Mechanistically, costimulation-adhesion therapy is associated with systemic and intragraft upregulation of T-cell immunoglobulin and mucin domain 3 (TIM3) and a reduced proinflammatory cytokine profile.

CONCLUSIONS

Costimulation-adhesion therapy is a superior alternative to current clinical immunosuppressive strategies for preventing the post-transplant rejection of hESC derivatives. By extending the window for cellular engraftment, costimulation-adhesion therapy enhances functional preservation following ischemic injury. This regimen may function through a TIM3-dependent mechanism.

Transient combination therapy targeting the immune synapse abrogates T cell responses and prolongs allograft survival in mice

T cells play a major role in allograft rejection, which occurs after T cell activation by the engagement of several functional molecules to form an immune synapse with alloantigen presenting cells. In this study, the immune synapse was targeted using mAbs directed to the TCR beta-chain (TCRβ) and lymphocyte function-associated antigen−1 (LFA1) to induce long-term allograft survival. Evaluation of antigen-specific T cell responses was performed by adoptively transferring CFSE labeled transgenic OT-II cells into wild-type mice and providing OVA peptide by intravenous injection. Graft survival studies were performed in mice by transplanting BALB/c ear skins onto the flanks of C57BL/6 recipients. The anti-TCRβ plus anti-LFA1 mAb combination (but not either mAb alone) abrogated antigen-specific T cell responses invitro and invivo. Transient combination therapy with these agents resulted in significantly prolonged skin allograft survival in mice (51±10 days; p<0.01) when compared to treatment with either anti-TCRβ mAb (24±5 days) or anti-LFA1 mAb (19±3 days) alone or no treatment (10±1 days). When lymphoid tissues from these mice were analyzed at different times post-transplant, only those receiving the combination of anti-TCRβ and anti-LFA1 mAbs demonstrated long-lasting reductions in total T cell numbers, cellular and humoral anti-donor responses, and expression of CD3 on the surface of T cells. These results demonstrate that transient anti-TCRβ and anti-LFA1 mAb combination therapy abrogates antigen-reactive T cell responses with long-lasting effects that significantly prolong allograft survival.

Costimulation blockade: current perspectives and implications for therapy

T cells must be activated before they can elicit damage to allografts, through interaction of their T cell receptor (TCR) with peptide-MHC complex and through accessory molecules. Signaling through accessory molecules or costimulatory molecules is a critical way for the immune system to fine tune T cell activation. An emerging therapeutic strategy is to target selective molecules involved in the process of T cell activation using biologic agents, which do not impact TCR signaling, thus only manipulating the T cells, which recognize alloantigen. Costimulatory receptors and their ligands are attractive targets for this strategy and could be used both to prevent acute graft rejection as well as for maintenance immunosuppression. Therapeutic agents targeting costimulatory molecules, notably belatacept, have made the progression from the bench, through nonhuman primate studies and into the clinic. This overview describes some of the most common costimulatory molecules, their role in T cell activation, and the development of reagents, which target these pathways and their efficacy in transplantation.

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.

Clinical islet transplantation: where immunity and metabolism intersect?

PURPOSE OF REVIEW

The dramatic results of the Edmonton Protocol in 2000 triggered tremendous excitement over the application of pancreatic islet transplantation as a viable approach to achieving consistent insulin independence in type 1 diabetic patients. However, this optimism in the field was tempered by follow-up studies showing frequent attrition of graft function commonly requiring a return to exogenous insulin therapy within 1-3 years after transplant. The purpose of this review is to put these initial studies in perspective and to highlight progress and challenges in this important field.

RECENT FINDINGS

Recent clinical and experimental findings demonstrate a progressive improvement in the function and durability of islet allografts. Induction therapies targeting T lymphocytes and costimulatory pathways have been highly effective at promoting islet transplant function. It is also apparent that islet injury associated with metabolic distress provides a nonimmune barrier to islet transplant outcomes.

SUMMARY

Newer therapeutic interventions show great promise for attenuating the adaptive immune response to islet allografts. Also, clarifying the mechanisms of metabolic-related tissue distress may provide additional potential targets for improving islet graft outcomes.

Combined costimulatory and leukocyte functional antigen-1 blockade prevents transplant rejection mediated by heterologous immune memory alloresponses

BACKGROUND

Recent evidence suggests that alloreactive memory T cells are generated by the process of heterologous immunity, whereby memory T cells arising in response to pathogen infection crossreact with donor antigens. Because of their diminished requirements for costimulation during recall, these pathogen-elicited allocrossreactive memory T cells are of particular clinical importance, especially given the emergence of costimulatory blockade as a transplant immunosuppression strategy.

METHODS

We used an established model of heterologous immunity involving sequential infection of a naïve C57BL/6 recipient with lymphocytic choriomeningitis virus and vaccinia virus, followed by combined skin and bone marrow transplant from a BALB/c donor.

RESULTS

We demonstrate that coupling the integrin antagonist anti-leukocyte functional antigen (LFA)-1 with costimulatory blockade could surmount the barrier posed by heterologous immunity in a fully allogeneic murine transplant system. The combined costimulatory and integrin blockade regimen suppressed proliferation of alloreactive memory T cells and attenuated their cytokine effector responses. This combined blockade regimen also promoted the retention of FoxP³⁺ Tregs in draining lymph nodes. Finally, we show that in an in vitro mixed lymphocyte reaction system using human T cells, the combination of belatacept and anti-LFA-1 was able to suppress cytokine production by alloreactive memory T cells that was resistant to belatacept alone.

CONCLUSIONS

As an antagonist against human LFA-1 exists and has been used clinically to treat psoriasis, these findings have significant translational potential for future clinical transplant trials.

Protection of porcine islet xenografts in mice using sertoli cells and monoclonal antibodies

BACKGROUND

To remedy the shortage of human donor islets, xenotransplantation of neonatal porcine islets (NPI) provides an attractive alternative source of donor tissue so long as graft rejection can be circumvented. Thus, in this study, we sought to determine whether cotransplantation of NPI with Sertoli cells (SC) combined with a short-course treatment of monoclonal antibody (mAb) could provide long-term islet xenograft survival.

METHODS

NPI alone or NPI cotransplanted with neonatal porcine SC were transplanted into diabetic C57BL/6 mice. These mice were left untreated or were treated with a short course of antileukocyte function associated antigen-1 (LFA-1), anti-CD154, or anti-CD45RB mAb. Blood glucose levels were monitored twice a week to assess graft function. At more than 100 days posttransplantation or on the day of rejection, graft-bearing kidneys were collected for characterization using immunohistochemistry.

RESULTS

None of the untreated control mice transplanted with NPI alone (0/5) or NPI cotransplanted with SC (0/8) achieved normoglycemia. However, of the mice receiving NPI alone, 3 of 7 treated with anti-LFA-1 mAb, 2 of 7 treated with anti-CD154 mAb, and 1 of 7 treated with anti-CD45RB mAb achieved long-term graft survival (>100 days). These proportions improved considerably when NPI were cotransplanted with SC, as 15 of 15 mice treated with anti-LFA-1 mAb, 7 of 8 mice treated with anti-CD154 mAb, and 4 of 9 mice treated with anti-CD45RB mAb achieved long-term graft survival.

CONCLUSIONS

These results show that transient administration of anti-LFA-1 mAb or anti-CD154 mAb is efficacious in prolonging NPI xenograft survival when islets are cotransplanted with SC. Interleukin-4 and Serpina3n may be important mediators of protection observed in this model.

Integrin antagonists prevent costimulatory blockade-resistant transplant rejection by CD8(+) memory T cells

The success of belatacept in late-stage clinical trials inaugurates the arrival of a new class of immunosuppressants based on costimulatory blockade, an immunosuppression strategy that disrupts essential signals required for alloreactive T-cell activation. Despite having improved renal function, kidney transplant recipients treated with belatacept experienced increased rates of acute rejection. This finding has renewed focus on costimulatory blockade-resistant rejection and specifically the role of alloreactive memory T cells in mediating this resistance. To study the mechanisms of costimulatory blockade-resistant rejection and enhance the clinical efficacy of costimulatory blockade, we developed an experimental transplant system that models a donor-specific memory CD8(+) T-cell response. After confirming that graft-specific memory T cells mediate costimulatory blockade-resistant rejection, we characterized the role of integrins in this rejection. The resistance of memory T cells to costimulatory blockade was abrogated when costimulatory blockade was coupled with either anti-VLA-4 or anti-LFA-1. Mechanistic studies revealed that in the presence of costimulatory blockade, anti-VLA-4 impaired T-cell trafficking to the graft but not memory T-cell recall effector function, whereas anti-LFA-1 attenuated both trafficking and memory recall effector function. As antagonists against these integrins are clinically approved, these findings may have significant translational potential for future clinical transplant trials.

Composite islet-kidneys from single baboon donors cure diabetes across fully allogenic barriers

We have previously reported that transplantation (Tx) of prevascularized donor islets as composite islet-kidneys (IK) reverses diabetic hyperglycemia in miniature swine. In order to test the potential clinical applicability of this strategy, we have extended it to a fully allogeneic nonhuman primate model. IKs were prepared in baboons by isolating islets from 50% to 70% partial pancreatectomies and injecting them under the autologous renal capsule, allowing vascularization before allogeneic Tx. Baboons with diabetes induced by stereptozotocin or total pancreatectomy, received composite IKs (n = 3) or free islets under the renal capsule or intraportally (n = 3), across fully allogeneic barriers with an immunosuppressive regimen consisting of ATG followed by MMF and tacrolimus. FBS of two of IK recipients decreased immediately after Tx and no insulin therapy was required throughout the experimental period (225 and 301 days). In contrast, all recipients of allogeneic free islets showed unstable FBS levels and required insulin within 2 months. We conclude that in addition to maintaining creatinine in the normal range, fully allogeneic IKs from single primate donors can achieve glucose regulation without insulin therapy, while free islets do not. These results support the feasibility of composite allogeneic IK Tx as a potential cure for end-stage diabetic nephropathy.

LFA-1 blockade induces effector and regulatory T-cell enrichment in lymph nodes and synergizes with CTLA-4Ig to inhibit effector function

Despite encouraging results using lymphocyte function antigen-1 (LFA-1) blockade to inhibit BM and solid organ transplantation rejection in nonhuman primates and humans, the precise mechanisms underlying its therapeutic potential are still poorly understood. Using a fully allogeneic murine transplantation model, we assessed the relative distribution of total lymphocyte subsets in untreated versus anti-LFA-1-treated animals. Our results demonstrated a striking loss of naive T cells from peripheral lymph nodes, a concomitant gain in blood after LFA-1 blockade, and a shift in phenotype of the cells remaining in the node to a CD62LloCD44hi profile. We determined that this change was due to a specific enrichment of activated, graft-specific effectors in the peripheral lymph nodes of anti-LFA-1-treated mice compared with untreated controls, and not to a direct effect of anti-LFA-1 on CD62L expression. LFA-1 blockade also resulted in a dramatic increase in the frequency of CD4+ FoxP3+ regulatory T cells in graft-draining nodes. Our results suggest that the differential impact of LFA-1 blockade on the distribution of naive versus effector and regulatory T cells may underlie its ability to inhibit alloreactive T-cell responses after transplantation.

Specificity and detection of insulin-reactive CD4+ T cells in type 1 diabetes in the nonobese diabetic (NOD) mouse

In the nonobese diabetic (NOD) mouse model of type 1 diabetes (T1D), an insulin peptide (B:9-23) is a major target for pathogenic CD4(+) T cells. However, there is no consensus on the relative importance of the various positions or "registers" this peptide can take when bound in the groove of the NOD MHCII molecule, IA(g7). This has hindered structural studies and the tracking of the relevant T cells in vivo with fluorescent peptide-MHCII tetramers. Using mutated B:9-23 peptides and methods for trapping the peptide in particular registers, we show that most, if not all, NOD CD4(+) T cells react to B:9-23 bound in low-affinity register 3. However, these T cells can be divided into two types depending on whether their response is improved or inhibited by substituting a glycine for the B:21 glutamic acid at the p8 position of the peptide. On the basis of these findings, we constructed a set of fluorescent insulin-IA(g7) tetramers that bind to most insulin-specific T-cell clones tested. A mixture of these tetramers detected a high frequency of B:9-23-reactive CD4(+) T cells in the pancreases of prediabetic NOD mice. Our data are consistent with the idea that, within the pancreas, unique processing of insulin generates truncated peptides that lack or contain the B:21 glutamic acid. In the thymus, the absence of this type of processing combined with the low affinity of B:9-23 binding to IA(g7) in register 3 may explain the escape of insulin-specific CD4(+) T cells from the mechanisms that usually eliminate self-reactive T cells.

Costimulatory pathways in transplantation

Secondary, so-called costimulatory, signals are critically required for the process of T cell activation. Since landmark studies defined that T cells receiving a T cell receptor signal without a costimulatory signal, are tolerized in vitro, the investigation of T cell costimulation has attracted intense interest. Early studies demonstrated that interrupting T cell costimulation allows attenuation of the alloresponse, which is particularly difficult to modulate due to the clone size of alloreactive T cells. The understanding of costimulation has since evolved substantially and now encompasses not only positive signals involved in T cell activation but also negative signals inhibiting T cell activation and promoting T cell tolerance. Costimulation blockade has been used effectively for the induction of tolerance in rodent models of transplantation, but turned out to be less potent in large animals and humans. In this overview we will discuss the evolution of the concept of T cell costimulation, the potential of 'classical' and newly identified costimulation pathways as therapeutic targets for organ transplantation as well as progress towards clinical application of the first costimulation blocking compound.

LFA-1 antagonism inhibits early infiltration of endogenous memory CD8 T cells into cardiac allografts and donor-reactive T cell priming

Alloreactive memory T cells are present in virtually all transplant recipients due to prior sensitization or heterologous immunity and mediate injury undermining graft outcome. In mouse models, endogenous memory CD8 T cells infiltrate MHC-mismatched cardiac allografts and produce IFN-γ in response to donor class I MHC within 24 h posttransplant. The current studies analyzed the efficacy of anti-LFA-1 mAb to inhibit early CD8 T cell cardiac allograft infiltration and activation. Anti-LFA-1 mAb given to C57BL/6 6 (H-2(b)) recipients of A/J (H-2(a)) heart grafts on days -1 and 0 completely inhibited CD8 T cell allograft infiltration, markedly decreased neutrophil infiltration and significantly reduced intragraft expression levels of IFN-γ-induced genes. Donor-specific T cells producing IFN-γ were at low/undetectable numbers in spleens of anti-LFA-1 mAb treated recipients until day 21. These effects combined to promote substantial prolongation (from day 8 to 27) in allograft survival. Delaying anti-LFA-1 mAb treatment until days 3 and 4 posttransplant did not inhibit early memory CD8 T cell infiltration and proliferation within the allograft. These data indicate that peritransplant anti-LFA-1 mAb inhibits early donor-reactive memory CD8 T cell allograft infiltration and inflammation suggesting an effective strategy to attenuate the negative effects of heterologous immunity in transplant recipients.

Targeting the CXCR4-CXCL12 axis mobilizes autologous hematopoietic stem cells and prolongs islet allograft survival via programmed death ligand 1

Antagonism of CXCR4 disrupts the interaction between the CXCR4 receptor on hematopoietic stem cells (HSCs) and the CXCL12 expressed by stromal cells in the bone marrow, which subsequently results in the shedding of HSCs to the periphery. Because of their profound immunomodulatory effects, HSCs have emerged as a promising therapeutic strategy for autoimmune disorders. We sought to investigate the immunomodulatory role of mobilized autologous HSCs, via target of the CXCR4-CXL12 axis, to promote engraftment of islet cell transplantation. Islets from BALB/c mice were transplanted beneath the kidney capsule of hyperglycemic C57BL/6 mice, and treatment of recipients with CXCR4 antagonist resulted in mobilization of HSCs and in prolongation of islet graft survival. Addition of rapamycin to anti-CXCR4 therapy further promoted HSC mobilization and islet allograft survival, inducing a robust and transferable host hyporesponsiveness, while administration of an ACK2 (anti-CD117) mAb halted CXCR4 antagonist-mediated HSC release and restored allograft rejection. Mobilized HSCs were shown to express high levels of the negative costimulatory molecule programmed death ligand 1 (PD-L1), and HSCs extracted from wild-type mice, but not from PD-L1 knockout mice, suppressed the in vitro alloimmune response. Moreover, HSC mobilization in PD-L1 knockout mice failed to prolong islet allograft survival. Targeting the CXCR4-CXCL12 axis thus mobilizes autologous HSCs and promotes long-term survival of islet allografts via a PD-L1-mediated mechanism.

LFA-1-specific therapy prolongs allograft survival in rhesus macaques

Outcomes in transplantation have been limited by suboptimal long-term graft survival and toxicities associated with current immunosuppressive approaches. T cell costimulation blockade has shown promise as an alternative strategy to avoid the side effects of conventional immunosuppressive therapies, but targeting CD28-mediated costimulation alone has proven insufficient to prevent graft rejection in primates. Donor-specific memory T (TM) cells have been implicated in costimulation blockade-resistant transplant rejection, due to their enhanced effector function and decreased reliance on costimulatory signaling. Thus, we have tested a potential strategy to overcome TM cell-driven rejection by targeting molecules preferentially expressed on these cells, such as the adhesion molecule lymphocyte function-associated antigen 1 (LFA-1). Here, we show that short-term treatment (i.e., induction therapy) with the LFA-1-specific antibody TS-1/22 in combination with either basiliximab (an IL-2Rα-specific mAb) and sirolimus (a mammalian target of rapamycin inhibitor) or belatacept (a high-affinity variant of the CD28 costimulation-blocker CTLA4Ig) prolonged islet allograft survival in nonhuman primates relative to control treatments. Moreover, TS-1/22 masked LFA-1 on TM cells in vivo and inhibited the generation of alloproliferative and cytokine-producing effector T cells that expressed high levels of LFA-1 in vitro. These results support the use of LFA-1-specific induction therapy to neutralize costimulation blockade-resistant populations of T cells and further evaluation of LFA-1-specific therapeutics for use in transplantation.

Transplant long-surviving induced by CD40-CD40 ligand costimulation blockade is dependent on IFN-γ through its effect on CD4(+)CD25(+) regulatory T cells

BACKGROUND

IFN-γ was documented to be commonly associated with acute rejection. In the present study, we investigated the role of IFN-γ in the transplant long-surviving induced by blocking CD40-CD40 ligand (CD40-CD40L) costimulation and its mechanisms.

METHODS

IFN-γ expression in cardiac allografts and spleens from syngeneic and allogeneic recipients with or without anti-CD40L monoclonal antibody (MR-1) treatment was examined by real-time RT-PCR. The grafts survival time in Wild type (IFN-γ(+/+)) and IFN-γ deficient (IFN-γ(-/-)) recipients was investigated. Mixed lymphocyte reaction (MLR) of CD4(+) T cells and cytotoxic T lymphocyte (CTL) assay of CD8(+) T cells were also studied. FoxP3 expression in allografts and spleens from IFN-γ(+/+) or IFN-γ(-/-) recipients with MR-1 treatment was examined. Furthermore, FoxP3, IL-10 and CTLA-4 expressions and the suppressive capability of CD4(+)CD25(+) regulatory T cells were examined.

RESULTS

Rejected allografts showed significantly higher IFN-γ expression than long-surviving allografts. Allograft survival was not prolonged in nonimmunosuppressed IFN-γ(-/-) mice. Administration of MR-1 induced long-term survival in 90.1% of IFN-γ(+/+) recipients (98±6.6 days) but failed to do so in IFN-γ(-/-) group (16.2±4.0 days). IFN-γ(-/-) recipients facilitated the proliferation and CTL generation of T cells. The allografts and spleens from IFN-γ(+/+) recipients contained higher FoxP3 expression than IFN-γ(-/-) recipients. Moreover, CD4(+)CD25(+) T cells from IFN-γ(+/+) recipients displayed a higher FoxP3 and IL-10 expression and suppressive capability.

CONCLUSION

IFN-γ plays an important role in the long-surviving induced by blocking CD40-CD40L through inhibiting the function of activated T cells and increasing suppressive capability of CD4(+)CD25(+) regulatory T cells.

Inhibition of TLR4 signaling prolongs Treg-dependent murine islet allograft survival

Toll-like receptors (TLRs) provide an important link between innate and adaptive immune system. We hypothesized that the recognition of endogenous TLR4 ligands is occurring at the time of transplantation, and these innate signals drive the inflammation and affect alloimmune responses. We confirmed that early after transplantation of allogenic islets, transcripts for TLR4 as well as potential ligands were released or up-regulated. In an allogenic islet transplantation model, genetic disruption of TLR4 on donor islets had no effect on allograft survival, whereas TLR4 deficiency in recipients lead to prolonged graft survival. Low dose rapamycin-treatment of TLR4(-/-) recipients induced permanent engraftment of 45% islet graft (p=0.005) compared to WT recipients. This prolonged graft survival was dependent on the presence of CD4(+)CD25(+)Foxp3(+) Treg. Naïve CD4(+)CD25(-) T cells cultured with the TLR4 ligand lipopolysaccharide showed enhanced IL-4, IL-6, IL-17, IFN gamma secretion and inhibited TGFbeta induced Foxp3(+)Treg generation. Thus, inhibition of recipient TLR4 activation at the time of transplantation decreases proinflammatory signals and allows Treg generation.

Pig embryonic pancreatic tissue as a source for transplantation in diabetes: transient treatment with anti-LFA1, anti-CD48, and FTY720 enables long-term graft maintenance in mice with only mild ongoing immunosuppression

OBJECTIVE

Defining an optimal costimulatory blockade-based immune suppression protocol enabling engraftment and functional development of E42 pig embryonic pancreatic tissue in mice.

RESEARCH DESIGN AND METHODS

Considering that anti-CD40L was found to be thrombotic in humans, we sought to test alternative costimulatory blockade agents already in clinical use, including CTLA4-Ig, anti-LFA1, and anti-CD48. These agents were tested in conjunction with T-cell debulking by anti-CD4 and anti-CD8 antibodies or with conventional immunosuppressive drugs. Engraftment and functional development of E42 pig pancreatic tissue was monitored by immunohistology and by measuring pig insulin blood levels.

RESULTS

Fetal pig pancreatic tissue harvested at E42, or even as early as at E28, was fiercely rejected in C57BL/6 mice and in Lewis rats. A novel immune suppression comprising anti-LFA1, anti-CD48, and FTY720 afforded optimal growth and functional development. Cessation of treatment with anti-LFA1 and anti-CD48 at 3 months posttransplant did not lead to graft rejection, and graft maintenance could be achieved for >8 months with twice-weekly low-dose FTY720 treatment. These grafts exhibited normal morphology and were functional, as revealed by the high pig insulin blood levels in the transplanted mice and by the ability of the recipients to resist alloxan induced diabetes.

CONCLUSIONS

This novel protocol, comprising agents that simulate those approved for clinical use, offer an attractive approach for embryonic xenogeneic transplantation. Further studies in nonhuman primates are warranted.

Translating costimulation blockade to the clinic: lessons learned from three pathways

SUMMARY

As the recognition that costimulatory signals are critical for optimal T-cell activation, proliferation, and differentiation, there has been an explosion in the study of costimulatory molecules and their roles in enhancing anti-donor T-cell responses following transplantation. Here, we focus on the bench-to-beside translation of blocking agents designed to target three critical costimulatory pathways: the CD28/CD80/CD86 pathway, the CD154/CD40 pathway, and the lymphocyte function associated antigen-1/intercellular adhesion molecule pathway. While blockade of each of these pathways proved promising in inhibiting donor-reactive T-cell responses and promoting long-term graft survival in murine models of transplantation, the progression of development of therapeutic agents to block these pathways has each taken a slightly different course. Both logistical and biological pitfalls have accompanied the translation of blockers of all three pathways into clinically applicable therapies, and the development of costimulatory blockade as a substitute for current standard-of-care calcineurin inhibitors has by no means reached completion. Collaboration between both the basic and clinical arenas will further propel the development of costimulation blockers currently in the pipeline, as well as of novel methods to target these critical pathways during transplantation.

CD4+CD25+ T cells alloactivated ex vivo by IL-2 or IL-4 become potent alloantigen-specific inhibitors of rejection with different phenotypes, suggesting separate pathways of activation by Th1 and Th2 responses

CD4(+)CD25(+)Foxp3(+) T cells are regulatory/suppressor cells (Tregs) that include non-antigen (Ag)-specific as well as Ag-specific Tregs. How non-Ag-specific naive CD4(+)CD25(+) Treg develop into specific Tregs is unknown. Here, we generated adaptive Tregs by culture of naive CD4(+)CD25(+)Foxp3(+) T cells with allo-Ag and either interleukin-2 (IL-2) or IL-4. Within days, IL-2 enhanced interferon-gamma receptor (Ifngammar) and Il-5 mRNA and IL-4 induced a reciprocal profile with de novo IL-5Ralpha and increased IFN-gamma mRNA expression. Both IL-2- and IL-4-alloactivated CD4(+)CD25(+) Tregs within 3 to 4 days of culture had enhanced capacity to induce tolerance to specific donor but not to third-party cardiac allografts. These hosts became tolerant as allografts functioned more than 250 days, with a physiologic ratio of less than 10% CD4(+)CD25(+)Foxp3(+) T cells in the CD4(+) population. CD4(+)CD25(+) T cells from tolerant hosts given IL-2-cultured cells had increased Il-5 and Ifngammar mRNA. Those from hosts given IL-4-cultured cells had enhanced IL-5Ralpha mRNA expression and IL-5 enhanced their proliferation to donor but not third-party allo-Ag. Thus, IL-2 and IL-4 activated allo-Ag-specific Tregs with distinct phenotypes that were retained in vivo. These findings suggested that T-helper 1 (Th1) and Th2 responses activate 2 pathways of adaptive Ag-specific Tregs that mediate tolerance. We propose they be known as T-suppressor 1 (Ts1) and Ts2 cells.

Redox modulation inhibits CD8 T cell effector function

The evolutionary preservation of reactive oxygen species in innate immunity underscores the important roles these constituents play in immune cell activity and as signaling intermediates. In an effort to exploit these pathways to achieve control of aberrant immune activation we demonstrate that modulation of redox status suppresses cell proliferation and production of IL-2, IFN-gamma, TNF-alpha, and IL-17 in two robust CD8 T-cell-dependent in vitro mouse models: (1) response to alloantigen in an mixed leukocyte reaction and (2) CD8 T cell receptor transgenic OT-1 response to cognate peptide (SIINFEKL). To correlate these findings with cytotoxic lymphocyte (CTL) function we performed cytotoxicity assays and found that redox modulation diminishes the ability of alloantigen-specific and antigen-specific OT-1 CTLs to kill their corresponding antigen-expressing target cells. To further examine the mechanisms of redox-mediated repression of CTL target cell lysis, we analyzed the expression of the effector molecules IFN-gamma, perforin, and granzyme B and the degranulation marker CD107a (LAMP-1). In both models, redox modulation reduced the expression of these effector components by at least fivefold. These results demonstrate that redox modulation quells the CD8 T cell response to alloantigen and the T cell receptor transgenic CD8 T cell response to its cognate antigen by inhibiting proliferation, proinflammatory cytokine synthesis, and CTL effector mechanisms.

Monotherapy with anti-LFA-1 monoclonal antibody promotes long-term survival of rat islet xenografts

Previously we demonstrated that anti-LFA-1 monoclonal (mAb) could promote long-term survival of discordant porcine islet xenografts in mice. The aim of this study, therefore, was to determine whether a shortterm administration of anti-LFA-1 mAb would promote long-term survival of concordant rat islet xenografts in mice, and whether combining short-term administration of anti-LFA-1 mAb therapy with an immunosuppressive drug, rapamycin, would facilitate islet xenograft survival. Streptozotocin-induced diabetic BALB/c mice were transplanted with 500 Wistar-Furth rat islets under the kidney capsule and were either left untreated or treated with short-term administration of rapamycin (0.2 mg/kg) alone, anti-LFA-1 mAb (0.2 mg/ dose) alone, or a combination of rapamycin and anti-LFA-1 mAb using the same doses. All untreated mice rejected their grafts by 24 days posttransplantation with a mean graft survival time of 18.8 +/- 2.5 days posttransplantation (n = 5). All mice treated with rapamycin alone had prolonged islet graft survival but eventually rejected their islet grafts by 81 days posttransplantation. In contrast, the majority of the mice (27/ 28) treated with anti-LFA-1 mAb alone maintained long-term normoglycemia (>100 days). Rapamycin in combination with anti-LFA-1 mAb proved equally effective with 29 of 30 mice maintaining normoglycemia for more than 100 days posttransplantation. Low levels of mouse anti-rat antibodies, as well as a decrease in the degree of mononuclear cell infiltration of the islet graft, closely correlated with long-term islet xenograft survival. These results demonstrate that monotherapy with anti-LFA-1 mAb is highly effective in promoting long-term survival of rat islet xenografts and that combination of anti-LFA-1 mAb with rapamycin does not facilitate nor abrogate the induction of long-term xenograft survival by anti-LFA-1 mAb therapy in BALB/c mice. Our study indicates that immunomodulation through mAb therapy could form a significant component of future antirejection therapies in clinical islet xenotransplantation.

Alloreactive (CD4-Independent) CD8+ T cells jeopardize long-term survival of intrahepatic islet allografts

Despite success of early islet allograft engraftment and survival in humans, late islet allograft loss has emerged as an important clinical problem. CD8+ T cells that are independent of CD4+ T cell help can damage allograft tissues and are resistant to conventional immunosuppressive therapies. Previous work demonstrates that islet allografts do not primarily initiate rejection by the (CD4-independent) CD8-dependent pathway. This study was performed to determine if activation of alloreactive CD4-independent, CD8+ T cells, by exogenous stimuli, can precipitate late loss of islet allografts. Recipients were induced to accept intrahepatic islet allografts (islet 'acceptors') by short-term immunotherapy with donor-specific transfusion (DST) and anti-CD154 mAb. Following the establishment of stable long-term islet allograft function for 60-90 days, recipients were challenged with donor-matched hepatocellular allografts, which are known to activate (CD4-independent) CD8+ T cells. Allogeneic islets engrafted long-term were vulnerable to damage when challenged locally with donor-matched hepatocytes. Islet allograft loss was due to allospecific immune damage, which was CD8- but not CD4-dependent. Selection of specific immunotherapy to suppress both CD4- and CD8-dependent immune pathways at the time of transplant protects islet allografts from both early and late immune damage.

LFA-1-mediated T cell costimulation through increased localization of TCR/class II complexes to the central supramolecular activation cluster and exclusion of CD45 from the immunological synapse

T cell activation is associated with a dramatic reorganization of cell surface proteins and associated signaling components into discrete subdomains within the immunological synapse in T cell:APC conjugates. However, the signals that direct the localization of these proteins and the functional significance of this organization have not been established. In this study, we have used wild-type and LFA-1-deficient, DO11.10 TCR transgenic T cells to examine the role of LFA-1 in the formation of the immunological synapse. We found that coengagement of LFA-1 is not required for the formation of the central supramolecular activation cluster (cSMAC) region, but does increase the accumulation of TCR/class II complexes within the cSMAC. In addition, LFA-1 is required for the recruitment and localization of talin into the peripheral supramolecular activation cluster region and exclusion of CD45 from the synapse. The ability of LFA-1 to increase the amount of TCR engaged during synapse formation and segregate the phosphatase, CD45, from the synapse suggests that LFA-1 might enhance proximal TCR signaling. To test this, we combined flow cytometry-based cell adhesion and calcium-signaling assays and found that coengagement of LFA-1 significantly increased the magnitude of the intracellular calcium response following Ag presentation. These data support the idea that in addition to its important role on regulating T cell:APC adhesion, coengagement of LFA-1 can enhance T cell signaling, and suggest that this may be accomplished in part through the organization of proteins within the immunological synapse.

Spontaneous allograft tolerance in B7-deficient mice independent of preexisting endogenous CD4+CD25+ regulatory T-cells

BACKGROUND

Acute cardiac allograft rejection requires host, but not donor, expression of B7-1/B7-2 costimulatory molecules. However, acute cardiac rejection requires direct antigen presentation by donor-derived antigen presenting cells to CD4 T-cells and does not require indirect antigen presentation to CD4 T-cells. Given this discrepancy in the literature and that the consequence of allograft exposure in B7-deficient mice is unknown; the goal of the study was to examine the antidonor status of allografted B7-1/B7-2-deficient hosts.

METHODS

C57Bl/6 B7-1/B7-2-/- mice were grafted with heterotopic BALB/c hearts. Recipients bearing long-term surviving allografts were used to examine the status of antidonor reactivity in vitro and in vivo. Tolerance was examined in vivo through adoptive transfer of splenocytes from graft-bearing animals to secondary immune-deficient Rag-1-/- hosts bearing donor-type or third-party cardiac allografts and by regulatory T-cell depletion with anti-CD25 antibody.

RESULTS

When transferred to B7-replete Rag-1-/- recipients, cells from naïve B7-1/B7-2-/- mice readily initiated cardiac allograft rejection. However, splenocytes transferred from long-term allograft acceptor B7-1/B7-2-/- hosts failed to reject donor-type hearts but acutely rejected third-party allografts. In addition, such cells did not reject (donorxthird-party) F1 allografts. Finally, in vivo depletion of regulatory T-cells did not prevent long-term acceptance.

CONCLUSIONS

Results demonstrate that B7-deficient T-cells are capable of acute cardiac allograft rejection in a B7-replete environment. Importantly, results also show that B7-deficient hosts do not simply ignore cardiac allografts, but rather spontaneously develop transferable, donor-specific tolerance and linked suppression in vivo. Interestingly, this tolerant state does not require endogenous CD4+CD25+ regulatory T-cells.

A phase I/II randomized open-label multicenter trial of efalizumab, a humanized anti-CD11a, anti-LFA-1 in renal transplantation

Leukocyte function associated antigen-1 (LFA-1) has a multifaceted role in the immune response, including adhesion and trafficking of leukocytes, stabilizing the immune synapse of the MHC-TCR complex and providing costimulation signals. Monoclonal antibodies to the CD11a chain of LFA-1 have been seen to result in effective immunosuppression in experimental models. Efalizumab, a humanized IgG1 anti-CD11a, is approved for use in psoriasis and may provide effective immunosuppression in organ transplantation. Thirty-eight patients undergoing their first living donor or deceased renal transplant were randomized to receive efalizumab 0.5 or 2 mg/kg weekly subcutaneously for 12 weeks. Patients were maintained on full dose cyclosporine, mycophenolate mofetil and steroids or half dose cyclosporine, sirolimus and prednisone. At 6 months following transplant patient survival was 97% and graft survival was 95%. Clinical biopsy-proven acute rejection in the first 6 months after transplantation was confirmed in 4 of 38 patients (11%). Three patients (8%) developed post transplant lymphoproliferative disease, all treated with the higher dose efalizumab and full dose cyclosporine. The two doses of efalizumab resulted in comparable saturation and modulation of CD11a. This phase II trial suggests that efalizumab may warrant further investigation in transplantation.

Diabetes induces rapid suppression of adaptive immunity followed by homeostatic T-cell proliferation

Surprisingly, the effect of acute diabetes on immunity has not been examined in detail. We, herein, show for the first time that untreated acute diabetes causes rapid lymphopenia followed by homeostatic T-cell proliferation. The diabetes-induced lymphopenia was associated with an immunosuppressed state that could be sufficiently strong to allow engraftment of fully allogeneic beta-cells or block rejection of islet transplants. In contrast, homeostatic proliferation and recovery of T-cell numbers were associated with islet rejection. Thus, the timing of islet transplant challenge in relation to diabetes induction was critical in determining whether islets were accepted or rejected. In addition, we tested whether diabetes-related immunosuppression could result in an overestimation of the efficacy of a tolerance-inducing protocol. Consistent with this possibility, a protocol targeting CD40L and ICOS that we have shown induces tolerance in diabetic recipients was unable to induce tolerance in non-diabetic recipients. The data uncover a previously unrecognized suppressive effect of diabetes on adaptive immunity. Furthermore, they suggest that the standard methods of testing new tolerance-inducing protocols in islet transplantation require modification and that diabetes itself can contribute to homeostatic proliferation, a process associated with autoimmunity and a resistance to tolerance induction.

Differential role of ICAM ligands in determination of human memory T cell differentiation

Background

Leukocyte Function Antigen-1 (LFA-1) is a primary adhesion molecule that plays important roles in T cell activation, leukocyte recirculation, and trans-endothelial migration. By applying a multivariate intracellular phospho-proteomic analysis, we demonstrate that LFA-1 differentially activates signaling molecules.

Results

Signal intensity was dependent on both ICAM ligand and LFA-1 concentration. In the presence of CD3 and CD28 stimulation, ICAM-2 and ICAM-3 decreased TGFβ1 production more than ICAM-1. In long-term differentiation experiments, stimulation with ICAM-3, CD3, and CD28 generated IFNγ producing CD4+CD45RO+CD62L-CD11a^BrightCD27- cells that had increased expression of intracellular BCL2, displayed distinct chemokine receptor profiles, and exhibited distinct migratory characteristics. Only CD3/CD28 with ICAM-3 generated CD4+CD45RO+CD62L-CD11a^BrightCD27- cells that were functionally responsive to chemotaxis and exhibited higher frequencies of cells that signaled to JNK and ERK1/2 upon stimulation with MIP3α. Furthermore, these reports identify that the LFA-1 receptor, when presented with multiple ligands, can result in distinct T cell differentiation states and suggest that the combinatorial integration of ICAM ligand interactions with LFA-1 have functional consequences for T cell biology.

Conclusion

Thus, the ICAM ligands, differentially modulate LFA-1 signaling in T cells and potentiate the development of memory human T cells in vitro. These findings are of importance in a mechanistic understanding of memory cell differentiation and ex vivo generation of memory cell subsets for therapeutic applications.

Anti-LFA-1 antibody postpones T-cell receptor triggering while preserving generation of regulatory T cells in T-cell receptor anti-HY transgenic mice

BACKGROUND

Anti-LFA-1 (CD11a) antibody increases allograft survival and/or induces tolerance in murine models, but its mechanisms of action remain to be elucidated.

METHODS

Rag-2-/- H-2b recipient mice, bearing a transgenic T-cell receptor specific for the male antigen HY presented by MHC class II molecule, were transplanted with a C57BL/6 (H-2b) male heart with or without administration of anti-LFA-1 antibody from days -1 to 9.

RESULTS

Treatment prevented the transient episode of acute graft rejection observed in nontreated mice and maintained a naive phenotype and proliferative characteristics comparable to that of naive transgenic lymphocytes on day 7 during treatment, with decreased IFN-gamma mRNA and increased IL-4 mRNA. On day 14, phenotype and proliferative response of lymphocytes in treated mice was comparable to those of untreated animals. Furthermore, treatment did not interfere with the generation of CD4+Vbeta6+CD25+ (Foxp3) cells that were observed in long-term nontreated tolerant mice.

CONCLUSIONS

This in vivo model demonstrates that anti-LFA-1 treatment induced a transient blockade of antigen recognition, which inhibited and postponed induction of signal 1 via the TCR and decreased the intensity of the Th1 response. Importantly, LFA-1 blockade did not disturb spontaneous generation of regulatory mechanism. This treatment would be compatible in clinical settings with other therapeutics inducing regulatory mechanisms.

Biological and Biomaterial Approaches for Improved Islet Transplantation

Islet transplantation may be used to treat type I diabetes. Despite tremendous progress in islet isolation, culture, and preservation, the clinical use of this modality of treatment is limited due to post-transplantation challenges to the islets such as the failure to revascularize and immune destruction of the islet graft. In addition, the need for lifelong strong immunosuppressing agents restricts the use of this option to a limited subset of patients, which is further restricted by the unmet need for large numbers of islets. Inadequate islet supply issues are being addressed by regeneration therapy and xenotransplantation. Various strategies are being tried to prevent beta-cell death, including immunoisolation using semipermeable biocompatible polymeric capsules and induction of immune tolerance. Genetic modification of islets promises to complement all these strategies toward the success of islet transplantation. Furthermore, synergistic application of more than one strategy is required for improving the success of islet transplantation. This review will critically address various insights developed in each individual strategy and for multipronged approaches, which will be helpful in achieving better outcomes.

LFA-1 (CD11a) as a therapeutic target

Leukocyte function associated antigen-1 (LFA-1) was one of the earliest of cell-surface molecules identified by monoclonal antibodies generated against leukocyte immunogens. This integrin heterodimer is perhaps best known as a classic adhesion molecule facilitating the interaction between T cells and antigen-presenting cells. However, varied studies indicate that LFA-1 has multi-faceted roles in the immune response including adhesion, activation and trafficking of leukocyte populations. While there has been long-standing interest in LFA-1 as a therapeutic target for regulating immunity, anti-LFA-1 therapy is still not a first-line indication for any clinical condition. Antagonism of LFA-1 with monoclonal antibodies, either alone or in combination with other agents, can result in regulatory tolerance in vivo. Furthermore, new generation humanized anti-LFA-1 monoclonal antibodies (Efalizumab) show at least modest promise for continued application in clinical trials. Thus, anti-LFA-1 forms a potential, but still largely unexploited, immunotherapy which may find its greatest application as an agent which augments other therapies.

Perturbation of Leukocyte Function-Associated Antigen-1/Intercellular Adhesion Molecule-1 Results in Differential Outcomes in Cardiac Vs Islet Allograft Survival

BACKGROUND

Various studies indicate the requirements for tolerance induction may vary between different transplanted tissues and organs. Consequently, we compared the efficacy of anti-leukocyte function-associated antigen-1 (LFA-1)/anti-intercellular adhesion molecule-1 (ICAM-1) monoclonal antibody therapy for facilitating cardiac vs islet long-term allograft acceptance in mice.

METHODS

BALB/c (H-2d) mouse cardiac or islet allografts were transplanted into recipient CBA/J (H-2k) mice. Monoclonal anti-body therapy with anti-LFA-1, anti-ICAM-1, the combination, or control rat immunoglobulin (Ig) was administered intraperitoneally on Days 0 to 5. Cardiac allograft function was assessed by palpation and islet graft function by blood glucose monitoring. Mixed lymphocyte assays were performed to assess proliferation of CD4 and CD8 T-cells under conditions of stimulator-cell ICAM-1 and/or LFA-1 deficiency.

RESULTS

Anti-ICAM-1 therapy resulted in a modest prolongation of cardiac allografts but in pronounced survival of islet allografts. Anti-LFA-1 therapy promoted significant long-term survival of both cardiac and islet allografts. Surprisingly, combined anti-LFA-1/anti-ICAM-1 therapy abrogated long-term islet, but not cardiac, allograft acceptance relative to either monotherapy. Mixed lymphocyte reactions demonstrated complete blockade of CD4 and CD8 T-cell proliferation under conditions of ICAM-1 deficiency alone or in combination with anti-LFA-1 therapy.

CONCLUSION

These results indicate that optimal therapies for some allografts (vascularized-heart) may not translate to other types of allografts (cellular-islet). Thus, the type of transplant represents an independent variable for optimizing strategies to promote indefinite allograft acceptance. Complete inhibition of CD4 and CD8 T-cell proliferation during ICAM-1/LFA-1 blockade suggests a threshold signal may be dependent upon ICAM-1/LFA-1 for regulatory tolerance to occur and that this signal may be lost under conditions of minimal graft cellular mass.

Simultaneous LFA-1 and CD40 ligand antagonism prevents airway remodeling in orthotopic airway transplantation: implications for the role of respiratory epithelium as a modulator of fibrosis

Airway remodeling is a prominent feature of certain immune-mediated lung diseases such as asthma and chronic lung transplant rejection. Under conditions of airway inflammation, the respiratory epithelium may serve an important role in this remodeling process. Given the proposed role of respiratory epithelium in nonspecific injury models, we investigated the respiratory epithelium in an immune-specific orthotopic airway transplant model. MHC-mismatched tracheal transplants in mice were used to generate alloimmune-mediated airway lesions. Attenuation of this immune injury and alteration of antidonor reactivity were achieved by the administration of combined anti-LFA-1/anti-CD40L mAbs. By contrast, without immunotherapy, transplanted airways remodeled with a flattening of respiratory epithelium and significant subepithelial fibrosis. Unopposed alloimmune injury for 10 days was associated with subsequent epithelial transformation and subepithelial fibrosis that could not be reversed with immunotherapy. The relining of donor airways with recipient-derived epithelium was delayed with immunotherapy resulting in partially chimeric airways by 28 days. Partial chimerism was sufficient to prevent luminal fibrosis. However, epithelial chimerism was also associated with airway remodeling. Therefore, there appears to be an intimate relationship between the morphology and level of chimerism of the respiratory epithelium and the degree of airway remodeling following alloimmune injury.