CTLA4Ig Research Articles

Abatacept Enhances Natural Killer Cell Cytotoxicity Following Haploidentical HCT: A Novel Platform to Dissociate GVL from Gvhd

Background: Abatacept (Abata, CTLA4 Ig), has been explored for the past 3 decades for blockade of CD28-B7 costimulation pathway in organ transplantation. One of the disadvantages of Abata has been its sparing effect on natural killer (NK) cells, resulting in NK-mediated rejection in preclinical models. However, we explored this caveat of abatacept to augment NK cell mediated anti-leukemia effect without invoking T cell mediated GVHD, where unmodified donor lymphocyte infusions (DLI) were administered 6 hours following administration of abatacept in-vivo (Abata-DLI) to patients with advanced malignancies undergoing haploidentical (Haplo)-HCT on days +7, +21 and +35. An early and rapid proliferation of mature NK cells was observed, which correlated with an improved relapse-free survival, without an increase in GVHD. To explore the mechanistic pathway behind this phenomenon, we studied the effect of Abata on cytotoxicity as well as cytokine profile of NK cells both in-vitro as well as in-vivo (CTRI:REF/2021/08/046552). Methods: NK cells and monocytes were isolated from PBMC of healthy donors. NK cells ± monocytes, were incubated with IL2, IL15 and IL12/15/18 with or without Abata for 72 hours and 7 days. They were assessed for cytotoxicity and IFN-g and perforin expression against K562 cell lines at effector: target (E:T) ratio of 5:1 and 1:1 . In HCT recipients, samples were obtained at day +20 (baseline), +30, +45, +60, and 6, 12 and 18 months. The samples were cryopreserved and both cytotoxicity and cytokine assays were carried out in batches after thawing. Cytokine profile was analysed in total NK cells and in NKG2A+ and NKG2C+ subsets. Results: The study was carried out on 11 healthy donors and 20 haplo-HCT recipients (15 with malignant diseases receiving Abata-DLI and 5 with non-malignant diseases receiving Abata without DLI). NK cells from healthy donors showed significant increase in cytotoxicity at 72 hours in presence of Abata with IL2 and IL15 (Figure1, p<0.01) at E:T ratio of 5:1 as well as 1:1 at both 72 hours as well as 7 days, but not with IL12/15/18. The effect was independent of monocytes. Perforin tended to be upregulated at both 72 hours and 7 days with Abata and IL15. In patients receiving Abata-DLI, cytotoxicity of NK cells was significantly increased at all time points compared to baseline at E:T ratio of 5:1 and 1:1 (Fig 2, P < 0.01). NK-cytotoxicity was significantly higher than the corresponding donor samples at days +45 and +60 (p<0.05). This was particularly so in 11 patients without any event compared to 4 patients with relapse/GVHD. To evaluate if Abata-DLI had greater impact on NK-cytotoxicity, the data was compared with 5 patients who received Abata alone. This showed significantly greater cytotoxicity at days +45 and +60 in the Abata-DLI group, which was more pronounced, when only those without events were analysed from the Abata-DLI group (p<0.01). There was no significant change in cytokine profile in those receiving Abata alone, but in Abata-DLI group, IFN-g was significantly upregulated in the NKG2C+ subset at day +60 at 1:1 ratio. Perforin expression was significantly higher at days+45 and +60 at both 5:1 and 1:1 in the Abata-DLI cohort, for both NKG2C+ and NKG2A+ subsets. In the Abata-DLI group NKG2C+ subset showed significantly higher IFN-g at days+45 and +60 and upregulation of perforin at all time points. 3 patients transplanted with active leukemia, assessed beyond day +60, showed greater cytotoxicity compared to the corresponding donors at 6-18 months. Conclusion: In this study, Abata was shown to increase cytotoxicity of NK cells, independent of monocytes, in the presence of IL2 and IL15, but not with IL12/15/18. This was observed at both high as well as low E:T ratios, with significant upregulation of perforin. In Haplo-HCT with Abata-DLI, there was marked increase in NK-cytotoxicity with upregulation of both IFN-g and Perforin, when compared to baseline as well as in comparison to those receiving Abata without DLI. Our findings suggest that Abatacept directly augments NK-cytotoxicity and provides rationale for exploring Abata-augmented NK cell therapy as a novel approach to augment NK-mediated GVL effect without invoking T cell mediated GVHD

Factors associated with COVID-19 breakthrough infection among vaccinated patients with rheumatic diseases: A cohort study

ObjectiveRheumatic disease patients on certain immunomodulators are at increased risk of impaired humoral response to SARS-CoV-2 vaccines. We aimed to identify factors associated with breakthrough infection among patients with rheumatic diseases. MethodsWe identified patients with rheumatic diseases being treated with immunomodulators in a large healthcare system who received at least two doses of either the mRNA-1273 (Moderna) or BNT162b2 (Pfizer-BioNTech) vaccines or one dose of the Johnson & Johnson-Janssen (J&J) vaccine. We followed patients until SARS-CoV-2 infection, death, or December 15, 2021, when the Omicron variant became dominant in our region. We estimated the association of baseline characteristics with the risk of breakthrough infection using multivariable Cox regression. ResultsWe analyzed 11,468 patients (75% female, mean age 60 years). Compared to antimalarial monotherapy, multiple immunomodulators were associated with higher risk of infection: anti-CD20 monoclonal antibodies (aHR 5.20, 95% CI: 2.85, 9.48), CTLA-4 Ig (aHR 3.52, 95% CI: 1.90, 6.51), mycophenolate (aHR 2.31, 95% CI: 1.25, 4.27), IL-6 inhibitors (aHR 2.15, 95% CI: 1.09, 4.24), JAK inhibitors (aHR 2.02, 95% CI: 1.01, 4.06), and TNF inhibitors (aHR 1.70, 95% CI: 1.09, 2.66). mRNA-1273 recipients had a lower risk of breakthrough infection compared to BNT162b2 recipients (aHR 0.66, 95% CI: 0.50, 0.86). There was no association of sex, body mass index, smoking status, race, or ethnicity with risk of breakthrough infection. ConclusionAmong patients with rheumatic diseases, multiple immunomodulators were associated with increased risk of breakthrough infection. These results highlight the need for additional mitigation strategies in this vulnerable population.

Abstract 662: Late CTLA-4 Ig treatment improves antitumor efficacy of immunotherapy

Abstract The promising approach of combining immune checkpoint therapies such as anti-CTLA-4 and anti-PD-1 increases antitumor response and overall survival rate relative to single treatments. However, it also increases the frequency and severity of immune-related adverse events (irAEs), such as cardiotoxicity. Our previous results showed that CTLA-4 Ig (abatacept), an inhibitor of T cell costimulation through CD28, can reverse those irAEs in patients with cancer, however, its effect on the antitumor response remains unclear. In the B16F10 melanoma model, we injected mice with CTLA-4 Ig antibody when: 1) mice were first treated with anti-CTLA-4, anti-PD-1, or combination (early time point) and 2) the immunotherapy was finished (late time point). We demonstrated that CTLA-4 Ig at the early time point compromised the antitumor efficacy of the immunotherapy. In contrast, the antitumor efficacy of the immunotherapy was improved if mice were treated with CTLA-4 Ig at the late time point. We also found that the antitumor response induced by CTLA-4 Ig (late) was dependent on CD80/86. Interestingly, the frequency of ICOS+ Foxp3+ Tregs was significantly reduced by CTLA-4 Ig at the late time point. Thus, we treated B16F10 tumors in Foxp3DTR mice with anti-CTLA-4 and then with CTLA-4 Ig (late). The antitumor tumor efficacy was similar between mice treated with or without Diphtheria toxin (DT) at the late time point. This suggests that the improved antitumor efficacy of CTLA-4 Ig at the late time point was Treg dependent. Collectively, we show that CTLA-4 Ig treatment has a differential role throughout the time course of immunotherapy treatments, and this work suggests a potential combination treatment strategy with checkpoint blockade and late CTLA-4 Ig treatment. Citation Format: Stephen Mok, James P. Allison. Late CTLA-4 Ig treatment improves antitumor efficacy of immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 662.

Tumor-associated Tregs obstruct antitumor immunity by promoting T cell dysfunction and restricting clonal diversity in tumor-infiltrating CD8+ T cells

BackgroundAccumulation of regulatory T cells (Treg) has been described to often correlate with poor prognosis in many solid tumors. How Treg presence impinges on limited functionality and clonal composition of...

Inborn errors of immunity and immunodeficiencies: Antibody-mediated pathology and autoimmunity as a consequence of impaired immune reactions.

B-cell tolerance to self-antigen is an active process that requires the temporal and spatial integration of signals of defined intensity. In common variable immune deficiency disorders, CTLA-4 deficiency, autoimmune lymphoproliferative syndrome, or in collagen VII deficiency, genetic defects in molecules regulating development, activation, maturation, and ECM composition alter the generation of B cells, resulting in immunodeficiency. Paradoxically, at the same time, the defective immune processes favor autoantibody production and immunopathology through impaired establishment of tolerance. The development of systemic autoimmunity in the framework of defective BCR signaling is relatively unusual in genetic mouse models. In sharp contrast, such reduced signaling in humans is clearly linked to pathological autoimmunity. The molecular mechanisms by which tolerance is broken in these settings are only starting to be explored resulting in novel therapeutic interventions. For instance, in CTLA-4 deficiency, homeostasis can be restored by CTLA-4 Ig treatment. Following this example, the identification of the molecular targets causing the reduced signals and their restoration is a visionary way to reestablish tolerance and develop novel therapeutic avenues for immunopathologies.

Overexpression of PD-1 on T cells promotes tolerance in cardiac transplantation via ICOS-dependent mechanisms.

The programmed death 1/programmed death ligand 1 (PD-1/PD-L1) pathway is a potent inhibitory pathway involved in immune regulation and is a potential therapeutic target in transplantation. In this study, we show that overexpression of PD-1 on T cells (PD-1 Tg) promotes allograft tolerance in a fully MHC-mismatched cardiac transplant model when combined with costimulation blockade with CTLA-4–Ig. PD-1 overexpression on T cells also protected against chronic rejection in a single MHC II–mismatched cardiac transplant model, whereas the overexpression still allowed the generation of an effective immune response against an influenza A virus. Notably, Tregs from PD-1 Tg mice were required for tolerance induction and presented greater ICOS expression than those from WT mice. The survival benefit of PD-1 Tg recipients required ICOS signaling and donor PD-L1 expression. These results indicate that modulation of PD-1 expression, in combination with a costimulation blockade, is a promising therapeutic target to promote transplant tolerance.

ACTH treatment promotes murine cardiac allograft acceptance.

Heart transplantation is the optimal therapy for patients with end-stage heart disease, but its long-term outcome remains inadequate. Recent studies have highlighted the importance of the melanocortin receptors (MCRs) in inflammation, but how MCRs regulate the balance between alloreactive T cells and Tregs, and whether they impact chronic heart transplant rejection, is unknown. Here, we found that Tregs express MC2R, and MC2R expression was highest among all MCRs by Tregs. Our data indicate that adrenocorticotropic hormone (ACTH), the sole ligand for MC2R, promoted the formation of Tregs by increasing the expression of IL-2Rα (CD25) in CD4+ T cells and activation of STAT5 in CD4+CD25+ T cells. ACTH treatment also improved the survival of heart allografts and increased the formation of Tregs in CD28KO mice. ACTH treatment synergized with the tolerogenic effect of CTLA-4–Ig, resulting in long-term survival of heart allografts and an increase in intragraft Tregs. ACTH administration also demonstrated higher prolongation of heart allograft survival in transgenic mouse recipients with both complete KO and conditional KO of PI3Kγ in T cells. Finally, ACTH treatment reduced chronic rejection markedly. These data demonstrate that ACTH treatment improved heart transplant outcomes, and this effect correlated with an increase in Tregs.

TET2 Driven Clonal Hematopoiesis Promotes Allograft Tolerance in a Mouse Heart Transplant Model

Purpose Clonal hematopoiesis (CH) is the result of clonal expansion of hematopoietic progenitors within the bone marrow (BM) that harbor mutations that confer fitness advantage relative to the background population. These clones can expand to become a dominant source of peripheral blood cells. Clonal mutations in TET2 (chromatin demethylase) have the strongest association with cardiovascular mortality and are prevalent in heart failure patients. Increased production of cytokines (i.e., interleukin-1β) by monocytes and macrophages may represent the underlying mechanism by which TET2 CH contributes to accelerated atherosclerosis and heart failure progression. The impact of TET2 CH on heart transplantation remains unexplored. Methods We established an adoptive BM transplantation CH model. Unfractionated BM (1.5 × 107cells) harvested from C57/B6 control or TET2-/- mice was injected into syngeneic C57/B6 UBC-GFP animals on three consecutive days. The extent of peripheral chimerism was assessed by flow cytometry 4-8 weeks after adoptive transfer. We then transplanted Balb/c donor hearts into chimeric C57/B6 recipient mice. All mice received CTLA4 Ig (days 0, 2 4, 6) for immunosuppression. The primary endpoint was a time to event analysis of allograft survival assessed by daily palpation. Secondary endpoints included histology, immunohistochemistry, and measurement of donor alloreactive T-cells and antibodies. Results Adoptive transfer of C57/B6 control BM into C57/B6 UBC-GFP mice led to diminished chimerism (0.6% - 3.6%) compared to adoptive transfer of C57/B6 TET2-/- BM into C57/B6 UBC-GFP mice (32 - 34.6%). We observed marked differences in donor heart survival between experimental groups. Following transplantation, recipient mice that received control BM displayed an average survival of 18 days, whereas recipient mice that received TET2-/- BM demonstrated evidence of long-term survival with 2/3 of mice surviving beyond 60 days (p Conclusion TET2 driven CH confers protection from allograft rejection and promotes long-term allograft acceptance in mice.

A Genetic Mouse Model Recapitulates Immune Checkpoint Inhibitor-Associated Myocarditis and Supports a Mechanism-Based Therapeutic Intervention.

Immune checkpoint inhibitors (ICI) targeting CTLA4 or PD-1/PD-L1 have transformed cancer therapy but are associated with immune-related adverse events, including myocarditis. Here, we report a robust preclinical mouse model of ICI-associated myocarditis in which monoallelic loss of Ctla4 in the context of complete genetic absence of Pdcd1 leads to premature death in approximately half of mice. Premature death results from myocardial infiltration by T cells and macrophages and severe ECG abnormalities, closely recapitulating the clinical and pathologic hallmarks of ICI-associated myocarditis observed in patients. Using this model, we show that Ctla4 and Pdcd1 functionally interact in a gene dosage-dependent manner, providing a mechanism by which myocarditis arises with increased frequency in the setting of combination ICI therapy. We demonstrate that intervention with CTLA4-Ig (abatacept) is sufficient to ameliorate disease progression and additionally provide a case series of patients in which abatacept mitigates the fulminant course of ICI myocarditis. SIGNIFICANCE: We provide a preclinical model of ICI-associated myocarditis which recapitulates this clinical syndrome. Using this model, we demonstrate that CTLA4 and PD-1 (ICI targets) functionally interact for myocarditis development and that intervention with CTLA4-Ig (abatacept) attenuates myocarditis, providing mechanistic rationale and preclinical support for therapeutic clinical studies.See related commentary by Young and Bluestone, p. 537.This article is highlighted in the In This Issue feature, p. 521.

At the Heart of Immune Checkpoint Inhibitor-Induced Immune Toxicity.

Wei and colleagues showcase a genetic mouse model of immune-mediated myocarditis that shares homology with immune checkpoint inhibitor (CPI)-induced myocarditis in patients with cancer. They demonstrate that abatacept (CTLA4-Ig) limits cardiac toxicity in the mouse model and, thus, may ameliorate the CPI-induced myocarditis in patients with cancer while potentially maintaining antitumor activity.See related article by Wei et al., p. 614.

Follicular helper T cells and follicular regulatory T cells in the immunopathology of primary Sjögren's syndrome.

Primary Sjögren's syndrome (pSS) is a chronic autoimmune disease, characterized by lymphocytic infiltration into exocrine glands, which causes dry eyes, dry mouth, and systemic damage. Although the precise etiology of pSS is not clear yet, highly activated B cells, abundant anti-SSA/Ro, and anti-SSB/La autoantibodies are the hallmarks of this disease. Follicular helper T cells (Tfh), a subset of CD4+ T cells, with cell surface receptors PD-1 and CXCR5, express ICOS, transcription factor Bcl-6, and a cytokine IL-21. These cells help in the differentiation of B cells into plasma cells and stimulate the formation of germinal center (GC). Previous studies have demonstrated abundant Tfh cells in the peripheral blood and salivary glands (SGs) of the patients with pSS, correlated with extensive lymphocytic infiltration of the SGs and high disease activity scores. Patients with pSS who are treated with abatacept (CTLA-4 Ig) show fewer circulating Tfh cells, reduced expression of ICOS, and lower disease activity scores. Recently identified follicular regulatory T (Tfr) cells, a subset of regulatory T cells, control the function of Tfh cells and the GC reactions. Here, we summarize the observed alterations in Tfh and Tfr cell numbers, activation state, and circulating subset distribution in pSS. Our goal is to improve the understanding of the roles of Tfh and Tfr cells (surface marker expression, cytokine production, and transcription factors) in the pathogenesis of pSS, thus contributing to the identification of candidate therapeutic agents for this disease.

Circulating TFH cells as a marker for early therapeutic intervention in T1D.

Costimulatory blockade via the CTLA-4–Ig fusion protein abatacept is beneficial in patients with early-onset type 1 diabetes, but some individuals benefit more than others. A new study reports that the pretreatment abundance of T follicular helper (TFH) cells could predict clinical responses to abatacept.

Development of an intravital imaging system for the synovial tissue reveals the dynamics of CTLA-4 Ig in vivo

There have been many attempts to visualize the inflamed joints using multiphoton microscopy. However, due to the hypervascular and multilayered structure of the inflamed synovium, intravital imaging of the deep synovial tissue has been difficult. Here, we established original intravital imaging systems to visualize synovial tissue and pathological osteoclasts at the pannus–bone interface using multiphoton microscopy. Combined with fluorescence-labeling of CTLA-4 Ig, a biological agent used for the treatment of rheumatoid arthritis, we identified that CTLA-4 Ig was distributed predominantly within the inflamed synovium and bound to CX3CR1+ macrophages and CD140a+ fibroblasts 6 h after injection, but not to mature osteoclasts. Intravital imaging of blood and lymphatic vessels in the inflamed synovium further showed that extravasated CTLA-4 Ig was immediately drained through lymphatic vessels under acute arthritic conditions, but the drainage activity was retarded under chronic conditions. These results indicate that this intravital synovial imaging system can serve as a platform for exploring the dynamics of immune cells, osteoclasts, and biological agents within the synovial microenvironment in vivo.

Cellular Mechanisms of Rejection of Optic and Sciatic Nerve Transplants: An Observational Study.

Background.Organ transplantation is a standard therapeutic strategy for irreversible organ damage, but the utility of nerve transplantation remains generally unexplored, despite its potential benefit to a large patient population. Here, we aimed to establish a feasible preclinical mouse model for understanding the cellular mechanisms behind the rejection of peripheral and optic nerves.Methods.We performed syngenic and allogenic transplantation of optic and sciatic nerves in mice by inserting the nerve grafts inside the kidney capsule, and we assessed the allografts for signs of rejection through 14 d following transplantation. Then, we assessed the efficacy of CTLA4 Ig, Rapamycin, and anti-CD3 antibody in suppressing immune cell infiltration of the nerve allografts.Results.By 3 d posttransplantation, both sciatic and optic nerves transplanted from BALB/c mice into C57BL/6J recipients contained immune cell infiltrates, which included more CD11b+ macrophages than CD3+ T cells or B220+ B cells. Ex vivo immunogenicity assays demonstrated that sciatic nerves demonstrated higher alloreactivity in comparison with optic nerves. Interestingly, optic nerves contained higher populations of anti-inflammatory PD-L1+ cells than sciatic nerves. Treatment with anti-CD3 antibody reduced immune cell infiltrates in the optic nerve allograft, but exerted no significant effect in the sciatic nerve allograft.Conclusions.These findings establish the feasibility of a preclinical allogenic nerve transplantation model and provide the basis for future testing of directed, high-intensity immunosuppression in these mice.

Investigating the Roles of Donor Macrophages after Cardiac Transplantation

Heart transplantation is limited by donor availability, immune mediated rejection, and unintended adverse effects from immunosuppression. Expanding donor availability and immunologic compatibility are priorities. Donor-organ directed therapies have the potential to improve allograft survival while minimizing patient harm. The heart contains 2 ontogenically distinct tissue resident macrophage populations (CCR2- and CCR2+ macrophages) with divergent inflammatory and reparative functions. The exact role of donor macrophages after cardiac transplant remains unexplored. A better understanding of how donor intrinsic immunity influences allograft acceptance and survival may provide new opportunities to improve the outcomes of transplant recipients. We utilized a fully HLA-mismatched mouse heart transplant model in combination with two differing immunosuppression regimens: CTLA4-Ig (acute rejection model) and CTLA4 Ig + anti-CD40L Ab (graft tolerance model). We assessed donor macrophage composition, location, and dynamics at various time points following transplantation using genetic lineage tracing and imaging. The functional requirements for CCR2- and CCR2+ donor macrophages was assessed using transgenic mice that facilitate selective depletion of CCR2- or CCR2+ macrophages. We show that donor CCR2- and CCR2+ macrophages persist in the heart following transplantation. We demonstrate that donor CCR2- and CCR2+ macrophages display dynamic responses following IRI and rejection. Co-labelling with CD68 highlights the later composition of donor-derived CCR2+ macrophages, donor-derived CCR2- macrophages, and resident monocyte derived macrophages in the transplanted heart. Depletion of CCR2+ macrophages prior to transplantation resulted in prolonged allograft survival and reduced cardiomyocyte cell death. In contrast, deletion of CCR2- macrophages led to accelerated rejection, increased cardiomyocyte cell death, and exaggerated leukocyte infiltration. Donor-derived CCR2+ macrophages and donor-derived CCR2- macrophages persist in the cardiac transplant. Depletion of donor-derived CCR2+ macrophages led to graft rejection whereas removal of donor-derived CCR2- macrophages promoted graft survival. These data indicate that donor macrophages play key roles in acute cellular rejection after cardiac transplantation.

CD28-Dependent CTLA-4 Expression Fine-Tunes the Activation of Human Th17 Cells.

SummaryPrevious work has demonstrated that Th17 memory cells but not Th1 cells are resistant to CD28/CTLA-4 blockade with CTLA-4 Ig, leading us to investigate the individual roles of the CD28 and CTLA-4 cosignaling pathways on Th1 versus Th17 cells. We found that selective CD28 blockade with a domain antibody (dAb) inhibited Th1 cells but surprisingly augmented Th17 responses. CD28 agonism resulted in a profound increase in CTLA-4 expression in Th17 cells as compared with Th1 cells. Consistent with these findings, inhibition of the CD28 signaling protein AKT revealed that CTLA-4 expression on Th17 cells was more significantly reduced by AKT inhibition relative to CTLA-4 expression on Th17 cells. Finally, we found that FOXO1 and FOXO3 overexpression restrained high expression of CTLA-4 on Th17 cells but not Th1 cells. This study demonstrates that the heterogeneity of the CD4+ T cell compartment has implications for the immunomodulation of pathologic T cell responses.

Abatacept Is Effective for Gvhd Prophylaxis after Unrelated Donor Stem Cell Transplantation (URD SCT) for Severe Sickle Cell Disease (SCD)

Background In 2016, results from the first URD SCT for SCD (the SCURT Trial) revealed a 2-year overall survival (OS) and event-free survival (EFS) of 79% (95% CI 59-90) and 69% (95% CI, 48-82) respectively following reduced intensity conditioning (RIC).1 Though the RIC approach provided successful engraftment in the majority, the transplant approach was not considered safe for widespread adoption due to high rates of graft-versus-host disease (GVHD) especially in children >13 years, a predominant cause of mortality. Strategies to minimize GVHD were essential if URD SCT was to be considered with curative intent in SCD. Aim/Method Multicenter trial (NCT03128996) with the primary objective of determining EFS in non-malignant disorders at one-year was amended as follows. The phase I SCD cohort included conditioning with hydroxyurea, proximal alemtuzumab, fludarabine, and melphalan in patients with 8/8 HLA-matched URD (-A, -B, - C and -DRB1).1 Thiotepa (8 mg/kg) was added in 7/8 HLA-mismatched SCT. GVHD prophylaxis included a calcineurin inhibitor and methotrexate as previously described. Abatacept (10 mg/kg) was administered on days -1, +5, +14, +28, +60, +100, +180, +270 and +365 based on efficacy described against acute GVHD with early dosing after SCT for malignant disorders.2,3 The latter 3 doses were omitted in cord transplant recipients. Result Thirteen children (7-21 years) underwent SCT (8/8 URD marrow- 7; 7/8 URD marrow or cord-6) primarily for stroke (N=6), ≥3 severe vaso-occlusive pain crises (N=4) or ≥2 acute chest syndrome episodes per year (N=3). The conditioning regimen was well tolerated. One patient had primary graft rejection after CMV infection (7%) and had autologous recovery. All other patients engrafted; neutrophils at median of 18 days (10-24), platelets at median of 28 days (16-39) and are surviving free of SCD with median follow-up of 12 months (range 4-59). Myeloid lineage donor chimerism was >95% and lymphoid was 39%- 100% at day+100. Two-year OS and EFS was 100% and 92.3% (95% CI, 6.57-35.7), respectively. The day+100 incidence of grade II-IV and III-IV acute GVHD incidence was 23% and 15% respectively. One-year incidence of chronic GVHD was 38%. However, only one patient (7%) developed extensive cGVHD. One patient (7%) developed posterior reversible encephalopathy syndrome and recovered. Viral replication in blood was detected in 7 of 13 patients (7 CMV, 1 EBV reactivation). No patient developed EBV PTLD or required EBV-related intervention. Conclusion In comparison to previous experience1 with RIC and URD SCT, our early observations are (1) a lower incidence of PRES (7 vs 34%) (2) low incidence of severe acute GVHD (15% vs 17% grade III -IV) despite mismatched donors, (3) low incidence of extensive chronic GVHD (7% vs 38%) and (4) no mortality despite patient age (10/13 were >13 years old). We attribute this gain to avoiding steroid use, and the benefit of including abatacept into the treatment regimen. The engraftment, safety, and immune reconstitution profile continue to be monitored in this ongoing trial now accruing in a Phase II cohort. As we and others work toward expanding donor options for SCD transplants, we submit that all alternate donor transplants for severe SCD are experimental and should be performed on clinical trials that track success and pitfalls. Reference: 1. Shenoy S et al. A trial of unrelated donor marrow transplantation for children with severe sickle cell disease. Blood. 2016 Nov 24; 128(21): 2561-2567. 2. Koura et al. In vivo T cell costimulation blockade with abataceptfor acute graft-versus-host disease prevention: a first-in-disease trial. Biol Blood Marrow Transplant. 2013 Nov; 19(11): 1638-49. 3. Watkins BK et al. T cell co-stimulation blockade with CTLA-4 Ig (Abatacept) for acute GVHD prevention in HLA-matched and mismatched unrelated donor transplantation: Results of a Phase 2 trial. Abstract 65. ASTCT Meetings, Houston 2019. Figure Disclosures Shah: Jazz pharmaceuticals: Speakers Bureau. OffLabel Disclosure: Abatacept, FDA approved for rheumatoid arthritis is a fusion protein that inhibits T-cell activation by binding to CD80/CD86 on antigen-presenting cells (APCs).It is used for acute graft-versus-host disease (aGVHD) prevention during unrelated-donor hematopoietic cell transplantation in this study

Abatacept modulates CD80 and CD86 expression and memory formation in human B-cells

BackgroundCytotoxic T lymphocyte antigen-4 (CTLA-4) limits T-cell activation and is expressed on T-regulatory cells. Human CTLA-4 deficiency results in severe immune dysregulation. Abatacept (CTLA-4 Ig) is approved for the treatment of rheumatoid arthritis (RA) and its mechanism of action is attributed to effects on T-cells. It is known that CTLA-4 modulates the expression of its ligands CD80 and CD86 on antigen presenting cells (APC) by transendocytosis. As B-cells express CD80/CD86 and function as APC, we hypothesize that B-cells are a direct target of abatacept. ObjectivesTo investigate direct effects of abatacept on human B-lymphocytes in vitro and in RA patients. MethodsThe effect of abatacept on healthy donor B-cells’ phenotype, activation and CD80/CD86 expression was studied in vitro. Nine abatacept-treated RA patients were studied. Seven of these were followed up to 24 months, and two up to 12 months only and treatment response, immunoglobulins, ACPA, RF concentrations, B-cell phenotype and ACPA-specific switched memory B-cell frequency were assessed. ResultsB-cell development was unaffected by abatacept. Abatacept treatment resulted in a dose-dependent decrease of CD80/CD86 expression on B-cells in vitro, which was due to dynamin-dependent internalization. RA patients treated with abatacept showed a progressive decrease in plasmablasts and serum IgG. While ACPA-titers only moderately declined, the frequency of ACPA-specific switched memory B-cells significantly decreased. ConclusionsAbatacept directly targets B-cells by reducing CD80/CD86 expression. Impairment of antigen presentation and T-cell activation may result in altered B-cell selection, providing a new therapeutic mechanism and a base for abatacept use in B-cell mediated autoimmunity.

Abstract 3: Ex Vivo Expanded Regulatory T Cells Combined With Short-term Costimulation Blockade Prevent Rejection Of Vascularized Composite Allografts

PURPOSE: Reconstructive transplantation represents a valid therapeutic option after devastating tissue loss. Routine clinical application, however, is hampered by the toxicity of long-term maintenance immunosuppression. The current study investigates a novel approach using ex vivo expanded regulatory T cells combined with a short-term immunomodulatory strategy in a murine hind limb transplantation model. METHODS: Fully MHC-mismatched orthotopic hind limb transplants were performed from Balb/C to C57BL/6 mice. Recipients in the experimental groups received a combination regimen consisting of 0.5mg CTLA4 Ig on day 0, 2, 4 and 6 post-transplant, 20mg/kg anti-Thy 1.2 mAb on POD-1, and 1mg/kg Rapamycin (POD 0–9), and in one group, 1 wk expanded CD4+CD25+ Treg cells. Allograft survival was monitored and flow cytometric analysis was performed to evaluate mixed chimerism and clonal deletion of alloreactive T cells. Treg activity was assessed in vitro using suppression assays in order to support and supplement in vivo data. RESULTS: Combination of T cell depletion and CTLA4-Ig plus short course of Rapamycin increased VCA survival significantly while untreated controls rejected their allografts (MST 105 days; Untreated, MST 9 days; CTLA4 Ig only, MST 17 days, Rapamycin, MST 20 days; T cell depletion, 20 days; p<0.01). Mixed chimerism was detected in recipients receiving this combined treatment protocol with 5.013 ± 1.23 % of CD11b+ cells being donor-derived on POD 55. Vβ - TCR staining profiles in recipients after full treatment showed 1.570 ± 0.3700 % of νβ5+CD4+ T cells, while naïve C57BL/6 express 3.567 ± 0.3690 % of νβ5+CD4+ T cells, suggesting the actuation of central deletion of developing donor-reactive T cells. In order to further prolong allograft survival, one week expanded Tregs were then included in the combination therapy. The suppressive activity of the CD4+CD25+ Tregs was confirmed with in vitro suppression assays. The addition of ex vivo expanded regulatory T cells further increased VCA survival to >200 days and induced long-term stable mixed chimerism with 16.7 ± 1.5 % of CD11b cells being donor-derived on POD 55 after administration of expanded Treg cells. CONCLUSION: The combination of T cell depletion, costimulation blockade, and a short-course of Rapamycin prevents VCA rejection and significantly prolongs graft survival without the need for myeloablative conditioning or maintenance therapy. Moreover, regulatory T cells added in the early post-transplant period further optimize immune regulation by inducing sustained mixed chimerism.

Ex vivo Expanded Regulatory T cells Combined with Short-term Costimulation Blockade Prevent Rejection of Vascularized Composite Allografts

Background Reconstructive transplantation represents a valid therapeutic option after devastating tissue loss. Routine clinical application, however, is hampered by the toxicity of long-term maintenance immunosuppression. The current study investigated a novel approach using ex vivo expanded regulatory T cells combined with a short-term immunomodulatory strategy in a murine hind limb transplantation model. Methods Fully MHC-mismatched orthotopic hind limb transplants were performed from Balb/C to C57BL/6 mice. Recipients in the experimental groups received a combination regimen consisting of 0.5mg CTLA4 Ig on day 0, 2, 4 and 6 post-transplant, 20mg/kg anti-Thy 1.2 mAb on POD-1, and 1mg/kg Rapamycin (POD 0-9), and in one group, 1 wk expanded CD4+CD25+ Treg cells. Allograft survival was monitored and flow cytometric analysis was performed to evaluate mixed chimerism and clonal deletion of alloreactive T cells. Treg activity was assessed in vitro using suppression assays in order to support and supplement in vivo data. Results Combination of T cell depletion and CTLA4-Ig plus short-course of Rapamycin increased VCA survival significantly while untreated controls rejected allografts (MST 105 days; Untreated, MST 9 days; CTLA4 Ig only, MST 17 days, Rapamycin, MST 20 days; T cell depletion, 20 days; p<0.01[GB1]). [GB2] Mixed chimerism was detected in recipients receiving this combined treatment protocol with 5.013 ± 1.23 % of CD11b+ cells being donor-derived on POD 55. Vβ – TCR staining profiles in recipients after full treatment showed 1.570 ± 0.3700 % of νβ5+CD4+ T cells, while naïve C57BL/6 express 3.567 ± 0.3690 % of νβ5+CD4+ T cells, suggesting the actuation of central deletion of developing donor-reactive T cells. In order to further prolong allograft survival, one week expanded Tregs were then included in the combination therapy. The suppressive activity of the CD4+CD25+ Tregs was confirmed with in vitro suppression assays. The addition of ex vivo expanded regulatory T cells further increased VCA survival to >200 days and induced long-term stable mixed chimerism[GB3] with 16.7±1.5 % of CD11b cells being donor-derived on POD 55 after administration of expanded Treg cells. Conclusion The combination of T cell depletion, costimulation blockade, and a short-course of Rapamycin prevents VCA rejection and significantly prolongs graft survival without the need for myeloablative conditioning or maintenance therapy. Moreover, regulatory T cells added in the early post transplant period further optimize immune regulation by inducing sustained mixed chimerism.