Traumatic brain injury does not disrupt costimulatory blockade-induced immunological tolerance to glial-restricted progenitor allografts.

BACKGROUND: Cell transplantation-based treatments for neurological disease are promising, yet graft rejection remains a major barrier to successful regenerative therapies. Our group and others have shown that long-lasting tolerance of transplanted stem cells can be achieved in the brain with systemic application of monoclonal antibodies blocking co-stimulation signaling. However, it is unknown if subsequent injury and the blood-brain barrier breach could expose the transplanted cells to systemic immune system spurring fulminant rejection and fatal encephalitis. Therefore, we investigated whether delayed traumatic brain injury (TBI) could trigger graft rejection. METHODS: Glial-restricted precursor cells (GRPs) were intracerebroventricularly transplanted in immunocompetent neonatal mice and co-stimulation blockade (CoB) was applied 0, 2, 4, and 6 days post-grafting. Bioluminescence imaging (BLI) was performed to monitor the grafted cell survival. Mice were subjected to TBI 12 weeks post-transplantation. MRI and open-field test were performed to assess the brain damage and behavioral change, respectively. The animals were decapitated at week 16 post-transplantation, and the brains were harvested. The survival and distribution of grafted cells were verified from brain sections. Hematoxylin and eosin staining (HE) was performed to observe TBI-induced brain legion, and neuroinflammation was evaluated immunohistochemically. RESULTS: BLI showed that grafted GRPs were rejected within 4 weeks after transplantation without CoB, while CoB administration resulted in long-term survival of allografts. BLI signal had a steep rise following TBI and subsequently declined but remained higher than the preinjury level. Open-field test showed TBI-induced anxiety for all animals but neither CoB nor GRP transplantation intensified the symptom. HE and MRI demonstrated a reduction in TBI-induced lesion volume in GRP-transplanted mice compared with non-transplanted mice. Brain sections further validated the survival of grafted GRPs and showed more GRPs surrounding the injured tissue. Furthermore, the brains of post-TBI shiverer mice had increased activation of microglia and astrocytes compared to post-TBI wildtype mice, but infiltration of CD45+ leukocytes remained low. CONCLUSIONS: CoB induces sustained immunological tolerance towards allografted cerebral GRPs which is not disrupted following TBI, and unexpectedly TBI may enhance GRPs engraftment and contribute to post-injury brain tissue repair.

Personalized Tumor RNA Loaded Lipid-Nanoparticles Prime the Systemic and Intratumoral Milieu for Response to Cancer Immunotherapy.

Translation of nanoparticles (NPs) into human clinical trials for patients with refractory cancers has lagged due to unknown biologic reactivities of novel NP designs. To overcome these limitations, simple well-characterized mRNA lipid-NPs have been developed as cancer immunotherapeutic vaccines. While the preponderance of RNA lipid-NPs encoding for tumor-associated antigens or neoepitopes have been designed to target lymphoid organs, they remain encumbered by the profound intratumoral and systemic immunosuppression that may stymie an activated T cell response. Herein, we show that systemic localization of untargeted tumor RNA (derived from whole transcriptome) encapsulated in lipid-NPs, with excess positive charge, primes the peripheral and intratumoral milieu for response to immunotherapy. In immunologically resistant tumor models, these RNA-NPs activate the preponderance of systemic and intratumoral myeloid cells (characterized by coexpression of PD-L1 and CD86). Addition of immune checkpoint inhibitors (ICIs) (to animals primed with RNA-NPs) augments peripheral/intratumoral PD-1+CD8+ cells and mediates synergistic antitumor efficacy in settings where ICIs alone do not confer therapeutic benefit. These synergistic effects are mediated by type I interferon released from plasmacytoid dendritic cells (pDCs). In translational studies, personalized mRNA-NPs were safe and active in a client-owned canine with a spontaneous malignant glioma. In summary, we demonstrate widespread immune activation from tumor loaded RNA-NPs concomitant with inducible PD-L1 expression that can be therapeutically exploited. While immunotherapy remains effective for only a subset of cancer patients, combination therapy with systemic immunomodulating RNA-NPs may broaden its therapeutic potency.

A monoclonal antibody against CD86 and its protection in a murine lupus nephritis model of chronic graft-versus-host disease.

CONTEXT: Lupus nephritis is the most common complication that causes the death of systemic lupus erythematosus patients. CD28/CTLA4 and their ligands CD80 or CD86 costimulatory pathway play a pivotal role in autoimmune disease and organ transplantation. OBJECTIVES: We generated a monoclonal antibody (clone 1D1) against human CD86 (1D1) that could recognize both human and mouse CD86, and blocked the CD86/CD28 costimulatory pathway with our mAb on a murine lupus nephritis model induced with chronic graft-versus-host disease (cGVHD). MATERIALS AND METHODS: Experimental lupus nephritis mice were induced with cGVHD, and splenocyte population were analyzed by flow cytometry. Autoantibodies and proteinuria were detected to evaluate the severity of lupus nephritis. The change of histopathology was observed by microscopy, fluorescence microscopy and electron microscopy. RESULTS: we successfully generated a monoclonal antibody against human CD86(1D1). 1D1 mAb could recognize not only human CD86, but also mouse CD86. 1D1 was applied to the cGVHD-induced experimental lupus nephritis model, and our study found the production of ANA and anti-dsDNA in the 1D1-treated group was lower than those in IgG-treated group after four weeks. The pathological injure of kidney in the 1D1-treated group was lighten than that in IgG-treated group. DISCUSSION AND CONCLUSIONS: Our data showed that blockade of CD86/CD28 with 1D1 induced a significant remission of proteinuria, production of autoantibodies, immune complex deposition and renal parenchyma lesions in experimental mice. Anti-CD86 Abs might be a potential method for immune therapy in autoimmune diseases and transplantation.

Prevention of lupus nephritis development in NZB/NZW mice by selective blockade of CD28.

Systemic lupus erythematosus (SLE) is a chronic systemic inflammatory disease. Autoantibodies (autoAbs) against double-stranded DNA (ds DNA), the hallmark of lupus, are produced and maintained by the interaction between auto-reactive B cells and CD4+ T cells. This interplay is controlled by the CD28/CD80-86/CTLA-4 axis. Here we investigated whether selective blockade of CD28-CD80/86 co-stimulatory interactions abrogates lupus nephritis development in a murine model of SLE. To this aim, NZB/NZW F1 mice were treated for 3 months, either with an anti-CD28 Fab' fragment or a control Fab'-IgG. The effect of CD28 blockade on lupus nephritis onset, survival, production of anti-ds DNA antibodies and costimulatory molecules was evaluated. CD28 blockade prevented the development of lupus nephritis and prolonged survival during the 3-month treatment and 12 weeks after. Furthermore, the production of anti-ds DNA autoAbs was decreased. Lastly, the protective effect of CD28 blockade was associated with increased intrarenal expression of the immunoregulatory molecule, Indoleamine 2, 3-dioxygenase, of the co-inhibitory receptor programmed cell-Death - 1 (PD-1) and of its ligand programmed death ligand - 1 (PDL-1).In conclusion, CD28 blockade prevented the development of lupus nephritis in NZB/NZW F1 mice. This immunomodulatory strategy is a promising candidate for SLE therapy in humans.

Direct suppression of autoaggressive CD8+ T cells with CD80/86 blockade in CD8+ T cell-mediated polymyositis models of mice.

OBJECTIVES: CD80/86 blockade to inhibit CD28 costimulation suppressed alloreactive human and murine CD4+ T cells but not alloreactive CD8+ T cells. In contrast, CD28 costimulation augments CD8+ T cell-mediated cell lysis in antigen-nonspecific stimulation. The present study was conducted to discern whether the CD80/86 blockade exerts therapeutic effects on CD8+ T cell-mediated polymyositis (PM) models of mice and whether the effects could be attributable to direct suppression of autoantigen-specific CD8+ T cells. METHODS: C protein-induced myositis (CIM) was induced in mice with intradermal injection of C protein fragments. C protein peptide-induced myositis (CPIM), in which autoaggressive CD8+ T cells are activated without CD4+ T cell help, was induced in mice with intravenous injection of dendritic cells (DCs) loaded with CD8+ T cell-epitope peptides derived from the C protein fragment. The immunised mice were treated with CTLA4-Ig or anti-CD80 and anti-CD86 antibodies (anti-CD80/86 Abs). The muscles were evaluated histologically 21 days after the C protein immunisation or 7 days after the DC injection. RESULTS: CIM was suppressed in the mice treated with CTLA4-Ig or anti-CD80/86 Abs administered prophylactically from the day of immunisation and therapeutically after the disease onset. CPIM was suppressed when CTLA4-Ig was administered concurrently with the DC injection. CONCLUSIONS: The CD80/86 blockade was effective in PM models of mice. Amelioration of CPIM indicates direct suppression of CD8+ T cells by the CD80/86 blockade. CTLA4-Ig should be a potential therapeutic agent of PM and other CD8+T cell-mediated diseases by suppressing both autoantigen-specific CD4+ and CD8+ T cells.

Costimulation Blockade in Kidney Transplantation: An Update.

In the setting of solid-organ transplantation, calcineurin inhibitor (CNI)-based therapy remains the cornerstone of immunosuppression. However, long-term use of CNIs is associated with some degree of nephrotoxicity. This has led to exploring the blockade of some costimulation pathways as an efficient immunosuppressive tool instead of using CNIs. The only agent already in clinical use and approved by the health authorities for kidney transplant patients is belatacept (Nulojix), a fusion protein that interferes with cytotoxic T lymphocyte-associated protein 4. Belatacept has been demonstrated to be as efficient as cyclosporine-based immunosuppression and is associated with significantly better renal function, that is, no nephrotoxicity. However, in the immediate posttransplant period, significantly more mild/moderate episodes of acute rejection have been reported, favored by the fact that cytotoxic T lymphocyte-associated protein pathway has an inhibitory effect on the alloimmune response; thereby its inhibition is detrimental in this regard. This has led to the development of antibodies that target CD28. The most advanced is FR104, it has shown promise in nonhuman primate models of autoimmune diseases and allotransplantation. In addition, research into blocking the CD40-CD154 pathway is underway. A phase II study testing ASK1240, that is, anti-CD40 antibody has been completed, and the results are pending.

High intensity focused ultrasound enhances anti-tumor immunity by inhibiting the negative regulatory effect of miR-134 on CD86 in a murine melanoma model.

HIFU has been demonstrated to enhance anti-tumor immunity, however, the mechanism of which has not been well elucidated. Emerging evidence indicates that miRNAs play important roles in immune response. In this study, we used the B16F10 melanoma allograft mouse model to investigate the role of miRNAs in HIFU-enhanced anti-tumor immunity. We found that HIFU treatment decreased circulating B16F10 cells and pulmonary metastasis nodules while increased IFN-γ and TNF-α in the peripheral blood and cumulative mouse survival, which was associated with inhibition of miR-134 expression and activation of CD86 expression in tumor tissues. Further, we determined that miR-134 directly binds to the 3'UTR of CD86 mRNA to suppress its expression in B16F10 cells. When B16F10 cells transfected with miR-134 were co-cultured with normal splenic lymphocytes, the secretion of IFN-γ and TNF-α from lymphocytes was reduced and B16F10 cell survival was increased. HIFU exposure efficiently decreased miR-134 while increased CD86 expression in B16F10 cells in vitro. CD86 knockdown with siRNA markedly rescued the viability of HIFU-treated B16F10 cells that co-cultured with lymphocytes. Altogether, our results suggest that HIFU down-regulates miR-134 to release the inhibition of miR-134 on CD86 in melanoma cells, thereby enhancing anti-tumor immune response.

Impact of soyasaponin I on TLR2 and TLR4 induced inflammation in the MUTZ-3-cell model.

Previous studies have demonstrated that soyasaponin (SoSa) possesses anti-inflammatory properties in lipopolysaccharide (LPS)-stimulated immune cells by influencing the immune sensing of toll-like receptor (TLR) 4. The aim of this study was to investigate the immune modulatory effect of SoSa I on TLR2- and TLR4-induced inflammation within the monocytic MUTZ-3-cell model. MUTZ-3 cells were stimulated with gram-negative (Escherichia coli) or gram-positive (Staphylococcus aureus) bacteria or bacterial pathogen-associated molecular patterns (PAMPs) such as LPS or peptidoglycans (PGN) alone or in combination with SoSa I. Cell morphology was characterized by raster scanning and light microscopy. Cytokine production (IL-1ß, IL-6, TNF-α, IP-10, RANTES and IL-8) was measured by cytometric bead array and the expression of surface markers was assessed by flow cytometry. MUTZ-3 cells revealed a cell maturation-like alteration in morphology and increased expression of CD80, CD86, TLR2 and TLR4 after stimulation with either gram-negative and gram-positive bacteria or bacterial PAMPs. The addition of SoSa I suppressed pro-inflammatory cytokine and chemokine secretions in a dose-dependent manner regardless of TLR2 or TLR4 stimulation. Interestingly, E. coli- and S. aureus-induced inflammation was always inhibited better by SoSa I than that induced by LPS and PGN. Additionally, SoSa I reduced the expression of CD86 in PGN- or LPS-stimulated cells. This study demonstrated that the anti-inflammatory capacity of SoSa I is based on influencing both monocytic TLR2 and TLR4 and that SoSa I inhibits more effectively whole bacteria compared to solely LPS or PGN what points to a broader role of SoSa I in the down-regulation of inflammation.

Personalized medicine in rheumatoid arthritis: is the glass half full or half empty?

The care of patients with rheumatoid arthritis (RA) has been revolutionized since the 1990s. Strict monitoring and disease control based on measurement of signs and symptoms towards a target of low disease activity have improved outcome of patients enormously. As a result of treatment strategies based upon individualized measurement of disease activity, the clinical view of RA has changed from a destructive autoimmune disease (with a median joint damage of >10 Sharp units per year) to a condition in which significant damage can be prevented in the majority of patients. Moreover, a large number of targeted therapies (tumour necrosis factor, IL6, CD80/CD86 and CD20 inhibitors) have become available to better treat the underlying disease process. However, identification of the underlying pathways that drive the disease process in an individual patient has been relatively unsuccessful, implying that no predictive factors have been identified to guide the choice of a specific treatment. Distinct subsets of RA patients have been identified, based on the presence or absence of anticitrullinated protein antibodies (ACPAs). These two subsets are associated with different environmental and genetic risk factors, histology and disease outcome (a more destructive disease course with more persistent joint inflammation is observed when ACPAs are present). Therefore, it is recommended that treatment should be guided towards a more consistently low level of disease activity in the presence of ACPAs than in the absence of the antibodies.

Use of belatacept to maintain adequate early immunosuppression in calcineurin-mediated microangiopathic hemolysis post-renal transplant.

We report a 17-yr-old boy who developed a microangiopathic hemolytic anemia presumed secondary to tacrolimus shortly following a living-related donor renal transplant. This was initially managed by plasmapheresis. Reinstitution of calcineurin inhibition using cyclosporine led to recurrence of hemolysis, so an alternative agent was needed. He was commenced on monthly intravenous belatacept, with no further recurrence of the hemolysis, and subsequent stable graft function. Modulation via CTLA-4 offers an alternative immunosuppressive tactic if current regimens produce graft threatening adverse effects. The method of administration and frequency of dosage of belatacept also lends itself well to the high-risk period of adolescence and transition. We propose that belatacept may therefore also have utility in difficult cases complicated by poor concordance, common in the adolescent age group.

Targeting CD28, CTLA-4 and PD-L1 costimulation differentially controls immune synapses and function of human regulatory and conventional T-cells.

CD28, CTLA-4 and PD-L1, the three identified ligands for CD80/86, are pivotal positive and negative costimulatory molecules that, among other functions, control T cell motility and formation of immune synapse between T cells and antigen-presenting cells (APCs). What remains incompletely understood is how CD28 leads to the activation of effector T cells (Teff) but inhibition of suppression by regulatory T cells (Tregs), while CTLA-4 and PD-L1 inhibit Teff function but are crucial for the suppressive function of Tregs. Using alloreactive human T cells and blocking antibodies, we show here by live cell dynamic microscopy that CD28, CTLA-4, and PD-L1 differentially control velocity, motility and immune synapse formation in activated Teff versus Tregs. Selectively antagonizing CD28 costimulation increased Treg dwell time with APCs and induced calcium mobilization which translated in increased Treg suppressive activity, in contrast with the dampening effect on Teff responses. The increase in Treg suppressive activity after CD28 blockade was also confirmed with polyclonal Tregs. Whereas CTLA-4 played a critical role in Teff by reversing TCR-induced STOP signals, it failed to affect motility in Tregs but was essential for formation of the Treg immune synapse. Furthermore, we identified a novel role for PD-L1-CD80 interactions in suppressing motility specifically in Tregs. Thus, our findings reveal that the three identified ligands of CD80/86, CD28, CTLA-4 and PD-L1, differentially control immune synapse formation and function of the human Teff and Treg cells analyzed here. Individually targeting CD28, CTLA-4 and PD-L1 might therefore represent a valuable therapeutic strategy to treat immune disorders where effector and regulatory T cell functions need to be differentially targeted.

T-cell co-stimulatory blockade in transplantation: two steps forward one step back!

INTRODUCTION: The concern about nephrotoxicity with calcineurin inhibitors led to the search of novel agents for immunosuppression. Based on the requirement of T-cell co-stimulatory signals to fully activated naïve T cells, it became clear that blocking these pathways could be an appealing therapeutic target. However, some unexpected findings were noticed in the recent clinical trials of belatacept, including a higher rate of rejection, which warranted further investigation with some interesting concepts emerging from the bench. AREAS COVERED: This article aims to review the literature of the B7:CD28 co-stimulatory blockade in transplantation, including the basic immunology behind its development, clinical application and potential limitations. EXPERT OPINION: Targeting co-stimulatory pathways were found to be much more complex than initially anticipated due to the interplay between not only various co-stimulatory pathways but also various co-inhibitory ones. In addition, co-stimulatory signals have different roles in diverse immune cell types. Therefore, targeting CD28 ligands with cytotoxic T lymphocyte antigen-4 (CTLA4)-Ig may have some deleterious effects, including the inhibition of regulatory T cells, blockade of co-inhibitory signals (CTLA4) and promotion of Th17 cells. Co-stimulatory independence of memory T cells was another unforeseen limitation. Learning how to better integrate co-stimulatory targeting with other immunosuppressive agents will be critical for the improvement of long-term graft survival.

CD86 expression as a surrogate cellular biomarker for pharmacological inhibition of the histone demethylase lysine-specific demethylase 1.

There is a lack of rapid cell-based assays that read out enzymatic inhibition of the histone demethylase LSD1 (lysine-specific demethylase 1). Through transcriptome analysis of human acute myeloid leukemia THP1 cells treated with a tranylcypromine-derivative inhibitor of LSD1 active in the low nanomolar range, we identified the cell surface marker CD86 as a sensitive surrogate biomarker of LSD1 inhibition. Within 24h of enzyme inhibition, there was substantial and dose-dependent up-regulation of CD86 expression, as detected by quantitative polymerase chain reaction, flow cytometry, and enzyme-linked immunosorbent assay. Thus, the use of CD86 expression may facilitate screening of compounds with putative LSD1 inhibitory activities in cellular assays.

B7-1/B7-2 blockade overrides the activation of protective CD8 T cells stimulated in the absence of Foxp3+ regulatory T cells.

Although T cell activation has been classically described to require distinct, positive stimulation signals that include B7-1 (CD80) and B7-2 (CD86) costimulation, overriding suppression signals that avert immune-mediated host injury are equally important. How these opposing stimulation and suppression signals work together remains incompletely defined. Our recent studies demonstrate that CD8 Teff activation in response to cognate peptide stimulation is actively suppressed by the Foxp3(+) subset of CD4 cells, called Tregs. Here, we show that the elimination of Treg suppression does not bypass the requirement for positive B7-1/B7-2 costimulation. The expansion, IFN-γ cytokine production, cytolytic, and protective features of antigen-specific CD8 T cells stimulated with purified cognate peptide in Treg-ablated mice were each neutralized effectively by CTLA-4-Ig that blocks B7-1/B7-2. In turn, given the efficiency whereby CTLA-4-Ig overrides the effects of Treg ablation, the role of Foxp3(+) cell-intrinsic CTLA-4 in mitigating CD8 Teff activation was also investigated. With the use of mixed chimera mice that contain CTLA-4-deficient Tregs exclusively after the ablation of WT Foxp3(+) cells, a critical role for Treg CTLA-4 in suppressing the expansion, cytokine production, cytotoxicity, and protective features of peptide-stimulated CD8 T cells is revealed. Thus, the activation of protective CD8 T cells requires positive B7-1/B7-2 costimulation even when suppression by Tregs and in particular, Treg-intrinsic CTLA-4 is circumvented.

Co-stimulatory molecules as targets for treatment of lupus.

Co-stimulatory molecules help to regulate interactions between T cells and antigen-presenting cells and may play an important role in the pathogenesis of lupus. Both work in murine models and some early studies in human lupus support further examination of these molecules as therapeutic targets. Complexities of lupus clinical trial variables may have hampered progress in this area but recent developments in the field may make interventional trials more feasible in the near future. To date biologics which provide direct blockade of interactions between CD40 and CD154, B7RP-1 and ICOS, and CD80 or CD86 with CD28 have been assessed in multicenter clinical trials. These data will be reviewed and critiqued.

Divergent effects of T cell costimulation and inflammatory cytokine production on autoimmune peripheral neuropathy provoked by Aire deficiency.

Chronic inflammatory demyelinating polyneuropathy results from autoimmune destruction of the peripheral nervous system and is a component of the multiorgan autoimmunity syndrome that results from Aire gene mutations in humans. In parallel, peripheral nervous system autoimmunity resembling chronic inflammatory demyelinating polyneuropathy develops spontaneously in NOD mice with a partial loss of Aire function (NOD.Aire(GW/+) mice) and is a T cell-mediated disease. In this study, we analyze how key aspects of T cell activation and function modulate disease development in Aire-deficient mice. We show that genetic ablation of the Th1 cytokine IFN-γ completely prevents clinical and electrophysiological evidence of neuropathy in NOD.Aire(GW/+) mice. IFN-γ deficiency is associated with absence of immune infiltration and decreased expression of the T cell chemoattractant IP-10 in sciatic nerves. Thus, IFN-γ is absolutely required for the development of autoimmune peripheral neuropathy in NOD.Aire(GW/+) mice. Because IFN-γ secretion is enhanced by B7-CD28 costimulation of T cells, we sought to determine the effects of these costimulatory molecules on neuropathy development. Surprisingly, B7-2 deficiency accelerated neuropathy development in NOD.Aire(GW/+) mice, and Ab blockade of both B7-1 and B7-2 resulted in fulminant, early-onset neuropathy. Thus, in contrast to IFN-γ, B7-2 alone and B7-1/B7-2 in combination function to ameliorate neuropathy development in NOD.Aire(GW/+) mice. Together, these findings reveal distinct and opposing effects of the T cell costimulatory pathway and IFN-γ production on the pathogenesis of autoimmune peripheral neuropathy.

Generation and evaluation of the efficacy of rhesus monkey soluble cytotoxic T lymphocyte-associated antigen-4 in the allogeneic mixed lymphocyte reaction.

Cytotoxic T lymphocyte-associated antigen-4 (CTLA-4; CD152) is a transmembrane protein that is structurally similar to CD28. As CTLA-4 has a much higher binding affinity to B7 than CD28, several approaches using soluble CTLA-4 have been tried to down-regulate T cell activity by blocking the interaction between CD28 and B7. We constructed soluble rhesus monkey CTLA-4 immunoglobulin (CTLA-4Ig) containing a critical binding site to B7 combined with a constant Ig heavy chain region in a mammalian system. Flow cytometry analyses indicated that soluble rhesus monkey CTLA-4Ig bound to rhesus monkey CD86 (B7.2). Moreover, soluble rhesus monkey CTLA-4Ig more effectively blocked the rhesus monkey-rhesus monkey allogeneic mixed lymphocyte reaction compared with that of humans. These results indicate that soluble rhesus monkey CTLA-4Ig may be useful in preclinical trials in a rhesus monkey model.

Affinity and cross-reactivity engineering of CTLA4-Ig to modulate T cell costimulation.

CTLA4-Ig is an Fc fusion protein containing the extracellular domain of CTLA-4, a receptor known to deliver a negative signal to T cells. CTLA4-Ig modulates T cell costimulatory signals by blocking the CD80 and CD86 ligands from binding to CD28, which delivers a positive T cell costimulatory signal. To engineer CTLA4-Ig variants with altered binding affinity to CD80 and CD86, we employed a high-throughput protein engineering method to map the ligand binding surface of CTLA-4. The resulting mutagenesis map identified positions critical for the recognition of each ligand on the three CDR-like loops of CTLA-4, consistent with the published site-directed mutagenesis and x-ray crystal structures of the CTLA-4/CD80 and CTLA-4/CD86 complexes. A number of single amino acid substitutions were identified that equally affected the binding affinity of CTLA4-Ig for both ligands as well as those that differentially affected binding. All of the high-affinity variants showed improved off-rates, with the best one being a 17.5-fold improved off-rate over parental CTLA4-Ig binding to CD86. Allostimulation of human CD4(+) T cells showed that improvement of CD80 and CD86 binding activity augmented inhibition of naive and primed T cell activation. In general, increased affinity for CD86 resulted in more potent inhibition of T cell response than did increased affinity for CD80. Optimization of the affinity balance to CD80 and CD86 to particular disease settings may lead to development of a CTLA4-Ig molecule with improved efficacy and safety profiles.