Co-stimulatory pathway competitive assay development using Liquid chromatography-tandem mass spectrometry (LC-MS/MS)

T-cells play a significant role in the development of autoimmune diseases. The CD28-B7 costimulatory pathway is crucial for activating T-cells, and blocking this pathway is essential for treating autoimmune diseases. Therapeutic antibodies and fusion proteins that target costimulatory molecules like CD80, CD86, CTLA-4, and CD28 have been developed to explore the costimulation process and as targeted treatments. To advance our understanding of costimulation in autoimmunity and the inhibition of the costimulatory pathway, it is crucial to have an accurate, precise, and direct method for detecting and quantifying the soluble form of these molecules in body fluids and various biological systems. Herein, we developed a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for quantifying the four costimulatory proteins depending on the signature peptides derived from the soluble isoform of these proteins in multiple reaction monitoring (MRM) mode. The method was validated using the US FDA guidelines. The LOQ was determined as ∼0.5 nM for the four analytes, with quantification extended to 20 nM with a correlation coefficient of R2>0.998. The developed MRM method was used to analyze on-bead digested protein mixtures to establish a competitive assay for the CD28-B7 costimulatory pathway using CTLA4-Ig (Abatacept ™) as an FDA-approved drug for rheumatoid arthritis. The IC50 was determined to be 2.99 and 159.8 nM for sCD80 and sCD86, respectively. A straightforward MRM-based competitive assay will advance the knowledge about the costimulatory role in autoimmunity and the autoimmune therapeutic drug discovery, with the need for broad application on different in vitro and in vivo models to discover new targeted inhibitors.

CTLA4-Ig-Based Bifunctional Costimulation Inhibitor Blocks CD28 and ICOS Signaling to Prevent T Cell Priming and Effector Function

CTLA4-Ig/abatacept dampens activation of naive T cells by blocking costimulation via CD28. It is an approved drug for rheumatoid arthritis but failed to deliver efficacy in a number of other autoimmune diseases. One explanation is that activated T cells rely less on CD28 signaling and use alternate coreceptors for effector function. ICOS is critical for activation of T-dependent humoral immune responses, which drives pathophysiology of IgG-mediated autoimmune diseases. In this study, we asked whether CD28 and ICOS play nonredundant roles for maintenance of T-dependent responses in mouse models. Using a hapten-protein immunization model, we show that during an ongoing germinal center response, combination treatment with CTLA4-Ig and ICOS ligand (ICOSL) blocking Ab completely dissolves ongoing germinal center responses, whereas single agents show only partial activity. Next, we took two approaches to engineer a therapeutic molecule that blocks both pathways. First, we engineered CTLA4-Ig to enhance binding to ICOSL while retaining affinity to CD80/CD86. Using a library approach, binding affinity of CTLA4-Ig to human ICOSL was increased significantly from undetectable to 15-42 nM; however, the affinity was still insufficient to completely block binding of ICOSL to ICOS. Second, we designed a bispecific costimulation inhibitor with high-affinity CTLA4 extracellular domains fused to anti-ICOSL Ab termed bifunctional costimulation inhibitor. With this bispecific approach, we achieved complete inhibition of CD80 and CD86 binding to CD28 as well as ICOS binding to ICOSL. Such bispecific molecules may provide greater therapeutic benefit in IgG-mediated inflammatory diseases compared with CTLA4-Ig alone.

Combinatorial engineering of N-TIMP2 variants that selectively inhibit MMP9 and MMP14 function in the cell

Developing selective inhibitors for proteolytic enzymes that share high sequence homology and structural similarity is important for achieving high target affinity and functional specificity. Here, we used a combination of yeast surface display and dual-color selective library screening to obtain selective inhibitors for each of the matrix metalloproteinases (MMPs) MMP14 and MMP9 by modifying the non-specific N-terminal domain of the tissue inhibitor of metalloproteinase-2 (N-TIMP2). We generated inhibitor variants with 30- to 1175-fold improved specificity to each of the proteases, respectively, relative to wild type N-TIMP2. These biochemical results accurately predicted the selectivity and specificity obtained in cell-based assays. In U87MG cells, the activation of MMP2 by MMP14 was inhibited by MMP14-selective blockers but not MMP9-specific inhibitors. Target specificity was also demonstrated in MCF-7 cells stably expressing either MMP14 or MMP9, with only the MMP14-specific inhibitors preventing the mobility of MMP14-expressing cells. Similarly, the mobility of MMP9-expressing cells was inhibited by the MMP9-specific inhibitors, yet was not altered by the MMP14-specific inhibitors. The strategy developed in this study for improving the specificity of an otherwise broad-spectrum inhibitor will likely enhance our understanding of the basis for target specificity of inhibitors to proteolytic enzymes, in general, and to MMPs, in particular. We, moreover, envision that this study could serve as a platform for the development of next-generation, target-specific therapeutic agents. Finally, our methodology can be extended to other classes of proteolytic enzymes and other important target proteins.

The Effect of ASP2409, a Novel CD86-Selective Variant of CTLA4-Ig, on Renal Allograft Rejection in Nonhuman Primates

BACKGROUND

Blockade of CD28-mediated T cell costimulation by a modified cytotoxic T lymphocyte-associated antigen 4 (CTLA4-Ig), belatacept, is a clinically effective immunosuppressive therapy for the prevention of renal allograft rejection. Use of belatacept-based calcineurin inhibitor-free immunosuppression, however, has demonstrated an increased frequency of cellular rejection episodes and immunosuppression-related safety issues relative to conventional regimens. Furthermore, belatacept typically requires infusion for its administration chronically, which may present an inconvenience to patients. To address these issues, a novel CTLA4-Ig variant, ASP2409, with improved CD86 binding selectivity and affinity relative to belatacept was created using DNA shuffling directed evolution methods.

METHODS

We evaluated the immunosuppressive effect of ASP2409 on in vitro alloimmune T cell responses, in vivo tetanus toxoid (TTx)-induced immunological responses and renal transplantation in cynomolgus monkeys.

RESULTS

ASP2409 had 6.1-fold higher and 2.1-fold lower binding affinity to monkey CD86 and CD80 relative to belatacept, respectively. ASP2409 was 18-fold more potent in suppressing in vitro alloimmune T cell responses relative to belatacept. In a cynomolgus monkey TTx immunization model, ASP2409 inhibited anti-TTx immune responses at a 10-fold lower dose level than belatacept. In a cynomolgus monkey renal transplantation model, subcutaneous injection of 1 mg/kg ASP2409 prevented allograft rejection through complete CD86 and partial CD80 receptor occupancies and dramatically prolonged renal allograft survival in combination with tacrolimus or mycophenolate mofetil/methylprednisolone.

CONCLUSIONS

These results support the potential of ASP2409 as an improved CTLA4-Ig for maintenance immunosuppression in organ transplantation.

Belatacept after kidney transplantation in adolescents: a retrospective study

Regardless of recipient age at kidney transplantation (KTx), patients are at greatest risk for graft loss in adolescence, partly due to nonadherence to an oral immunosuppressive regimen. Belatacept, a non-nephrotoxic, first-in-class immunosuppressant that inhibits costimulation of T cells requires intravenous application only every 4 weeks, potentially leading to better adherence. However, it is only approved for use in adults. We report here the findings of the first study of belatacept in adolescents, comprising all patients in our department switched to belatacept post-KTx. Six patients (median age 15.5 years) were switched after a median of 7.5 months (range 23 days to 12 years), treatment range 3-28 months (cumulative 83 months): Three patients switched early (<3 months after KTx) had increased estimated glomerular filtration rate (GFR); one patient switched 12 years post-KTx has stable GFR; two patients were switched following rapid decline of and with markedly impaired GFR, changing slope in one patient. One patient had one acute rejection. In addition of two patients who received belatacept for other conditions, the only relevant adverse event was neutropenia (after a cumulative 109 months). Belatacept as primary immunosuppression is an option in Epstein-Barr virus-seropositive nonadherent adolescents if administered sufficiently early before deterioration of graft function.

ASP2409, A Next-Generation CTLA4-Ig, Versus Belatacept in Renal Allograft Survival in Cynomolgus Monkeys

Belatacept is the first costimulatory blockade agent approved for maintenance immunosuppression in kidney transplant recipients. Clinical results have indicated that belatacept is associated with superior renal function and improved metabolic profile; however, higher incidence of acute rejection and posttransplant lymphoproliferative disorder are the shortcomings of this agent. In this study, ASP2409, a new cytotoxic T-lymphocyte associated protein 4-immunoglobulin possessing 14-fold higher in vitro CD86 binding affinity than belatacept, was tested for renal allograft survival in cynomolgus monkeys. ASP2409 monotherapy dose-dependently prolonged renal allograft survival. Low-dose ASP2409 in combination with a subtherapeutic dose of tacrolimus showed much longer median survival time than monotherapy. Similar allograft survival results were observed in regimens based on high-dose ASP2409, belatacept, and therapeutic-dose tacrolimus. The results of renal allograft histopathology with high-dose ASP2409-based regimens were not inferior to the belatacept-based regimen. Moreover, higher frequencies of FoxP3-positive regulatory T cells in renal allografts were observed in ASP2409- and belatacept-based regimens compared with tacrolimus-based regimens. No serious side effects related to ASP2409 administration were found during the study. These data suggest that ASP2409 is a promising candidate for calcineurin inhibitor-sparing or -avoidance regimens.