Abatacept Exposure Research Articles

Abatacept Pharmacokinetics and Exposure Response in Patients Hospitalized With COVID-19

The pharmacokinetics of abatacept and the association between abatacept exposure and outcomes in patients with severe COVID-19 are unknown. To characterize abatacept pharmacokinetics, relate drug exposure with clinical outcomes, and evaluate the need for dosage adjustments. This study is a secondary analysis of data from the ACTIV-1 (Accelerating COVID-19 Therapeutic Interventions and Vaccines) Immune Modulator (IM) randomized clinical trial conducted between October 16, 2020, and December 31, 2021. The trial included hospitalized adults who received abatacept in addition to standard of care for treatment of COVID-19 pneumonia. Data analysis was performed between September 2022 and February 2024. Single intravenous infusion of abatacept (10 mg/kg with a maximum dose of 1000 mg). Mortality at day 28 was the primary outcome of interest, and time to recovery at day 28 was the secondary outcome. Drug exposure was assessed using the projected area under the serum concentration time curve over 28 days (AUC0-28). Logistic regression modeling was used to analyze the association between drug exposure and 28-day mortality, adjusted for age, sex, and disease severity. The association between time to recovery and abatacept exposure was examined using Fine-Gray modeling with death as a competing risk, and was adjusted for age, sex, and disease severity. Of the 509 patients who received abatacept, 395 patients with 848 serum samples were included in the population pharmacokinetic analysis. Their median age was 55 (range, 19-89) years and most (250 [63.3%]) were men. Abatacept clearance increased with body weight and more severe disease activity at baseline. Drug exposure was higher in patients who survived vs those who died, with a median AUC0-28 of 21 428 (range, 8462-43 378) mg × h/L vs 18 262 (range, 9628-27 507) mg × h/L (P < .001). Controlling for age, sex, and disease severity, an increase of 5000 units in AUC0-28 was associated with lower odds of mortality at day 28 (OR, 0.52 [95% CI, 0.35-0.79]; P = .002). For an AUC0-28 of 19 400 mg × h/L or less, there was a higher probability of recovery at day 28 (hazard ratio, 2.63 [95% CI, 1.70-4.08] for every 5000-unit increase; P < .001). Controlling for age, sex, and disease severity, every 5000-unit increase in AUC0-28 was also associated with lower odds of a composite safety event at 28 days (OR, 0.46 [95% CI, 0.33-0.63]; P < .001). Using the dosing regimen studied in the ACTIV-1 IM trial, 121 of the 395 patients (30.6%) would not achieve an abatacept exposure of at least 19 400 mg × h/L, particularly at the extremes of body weight. Using a modified, higher-dose regimen, only 12 patients (3.0%) would not achieve the hypothesized target abatacept exposure. In this study, patients who were hospitalized with severe COVID-19 and achieved higher projected abatacept exposure had reduced mortality and a higher probability of recovery with fewer safety events. However, abatacept clearance was high in this population, and the current abatacept dosing (10 mg/kg intravenously with a maximum of 1000 mg) may not achieve optimal exposure in all patients. ClinicalTrials.gov Identifier: NCT04593940.

Cancer risk with tocilizumab/sarilumab, abatacept, and rituximab treatment in patients with rheumatoid arthritis: a Danish cohort study.

To investigate cancer risk in rheumatoid arthritis (RA) patients treated with tocilizumab/sarilumab, abatacept, or rituximab compared with those who received tumour necrosis factor inhibitors (TNFi) and compared with biological disease-modifying anti-rheumatic drugs (bDMARD) naïve RA patients. Nationwide registry-based cohort study of RA patients initiating treatment with tocilizumab/sarilumab, abatacept, rituximab, TNFi, and bDMARD-naive patients their second type of conventional synthetic DMARD (csDMARD). Patients were identified in DANBIO and followed for cancer from 2006-2020. Patients could contribute multiple treatments, with person years (PYRS), deaths, and cancers allocated to each treatment group in a 'latest type of treatment' manner. Inverse probability of treatment weighting and weighted cause-specific Cox models were used to calculate hazard ratios (HRs) for cancer in each tocilizumab/sarilumab, abatacept, and rituximab group compared with TNFI and bDMARD naïve groups, respectively. In total, 21 982 treatment initiations, 96 475 PYRS, and 1423 cancers were identified. There were no statistically significant increased HRs for overall cancer in tocilizumab/sarilumab, abatacept, or rituximab treatment groups (HRs ranged from 0.7-1.1). More than five years of abatacept exposure showed a non-significantly increased HR compared with TNFi (HR 1.41, 95% confidence intervals CI 0.74-2.71). For hematological cancers, rituximab treatment showed non-significantly reduced HRs: vs TNFi (HR 0.09; 95%CI 0.00-2.06) and bDMARD-naïve (HR 0.13; 95%CI 0.00-1.89). Treatment with tocilizumab/sarilumab, abatacept, or rituximab in RA patients was not associated with increased risks of cancer compared with TNFi-treated and with bDMARD-naïve RA patients in a real-world setting.

Abatacept and non-melanoma skin cancer in patients with rheumatoid arthritis: a comprehensive evaluation of randomised controlled trials and observational studies

ObjectivesThis study aims to evaluate non-melanoma skin cancer (NMSC) risk associated with abatacept treatment for rheumatoid arthritis (RA).MethodsThis evaluation included 16 abatacept RA clinical trials and 6 observational studies. NMSC...

Higher abatacept exposure after transplant decreases acute GVHD risk without increasing adverse events

AbstractIn the ABA2 study, the T-cell costimulation blockade agent, abatacept, was safe and effective in preventing acute graft-versus-host disease (aGVHD) after unrelated-donor hematopoietic cell transplant (HCT), leading to US Food and Drug Administration approval. Here, we performed a determination of abatacept pharmacokinetics (PK), which enabled an examination of how abatacept exposure-response relationships affected clinical outcomes. We performed a population PK analysis of IV abatacept using nonlinear mixed-effect modeling and assessed the association between abatacept exposure and key transplant outcomes. We tested the association between the trough after dose 1 (Ctrough_1) and grade (GR) 2 or 4 aGVHD (GR2-4 aGVHD) through day +100. An optimal Ctrough_1 threshold was identified via recursive partitioning and classification tree analysis. This demonstrated that abatacept PK was characterized by a 2-compartment model with first-order elimination. The ABA2 dosing regimen was based on previous work targeting a steady-state abatacept trough of 10 μg/mL. However, a higher Ctrough_1 (≥39 μg/mL, attained in ∼60% of patients on ABA2) was associated with a favorable GR2-4 aGVHD risk (hazard ratio, 0.35; 95% confidence interval, 0.19-0.65; P < .001), with a Ctrough_1 <39 μg/mL associated with GR2-4 aGVHD risk indistinguishable from placebo (P = .37). Importantly, no significant association was found between Ctrough_1 and key safety indicators, including relapse, and cytomegalovirus or Epstein-Barr virus viremia. These data demonstrate that a higher abatacept Ctrough_1 (≥39 μg/mL) was associated with a favorable GR2-4 aGVHD risk, without any observed exposure-toxicity relationships. This trial was registered at www.clinicaltrials.gov as #NCT01743131.

Efficacy of COVID-19 mRNA vaccination in patients with autoimmune disorders: humoral and cellular immune response

BackgroundThe impact of immunosuppressive therapies on the efficacy of vaccines to SARS-CoV-2 is not completely clarified. We analyzed humoral and T cell-mediated response after COVID-19 mRNA vaccine in immunosuppressed patients and patients with common variable immunodeficiency disease (CVID).PatientsWe enrolled 38 patients and 11 healthy sex- and age-matched controls (HC). Four patients were affected by CVID and 34 by chronic rheumatic diseases (RDs). All patients with RDs were treated by corticosteroid therapy and/or immunosuppressive treatment and/or biological drugs: 14 patients were treated with abatacept, 10 with rituximab, and 10 with tocilizumab.MethodsTotal antibody titer to SARS-CoV-2 spike protein was assessed by electrochemiluminescence immunoassay, CD4 and CD4-CD8 T cell-mediated immune response was analyzed by interferon-γ (IFN-γ) release assay, the production of IFN-γ-inducible (CXCL9 and CXCL10) and innate-immunity chemokines (MCP-1, CXCL8, and CCL5) by cytometric bead array after stimulation with different spike peptides. The expression of CD40L, CD137, IL-2, IFN-γ, and IL-17 on CD4 and CD8 T cells, evaluating their activation status, after SARS-CoV-2 spike peptides stimulation, was analyzed by intracellular flow cytometry staining. Cluster analysis identified cluster 1, namely the “high immunosuppression” cluster, and cluster 2, namely the “low immunosuppression” cluster.ResultsAfter the second dose of vaccine, only abatacept-treated patients, compared to HC, showed a reduced anti-spike antibody response (mean: 432 IU/ml ± 562 vs mean: 1479 IU/ml ± 1051: p = 0.0034), and an impaired T cell response, compared with HC. In particular, we found a significantly reduced release of IFN-γ from CD4 and CD4-CD8 stimulated T cells, compared with HC (p = 0.0016 and p = 0.0078, respectively), reduced production of CXCL10 and CXCL9 from stimulated CD4 (p = 0.0048 and p = 0.001) and CD4-CD8 T cells (p = 0.0079 and p = 0.0006). Multivariable General Linear Model analysis confirmed a relationship between abatacept exposure and impaired production of CXCL9, CXCL10, and IFN-γ from stimulated T cells. Cluster analysis confirms that cluster 1 (including abatacept and half of rituximab treated cases) showed a reduced IFN-γ response, as well as reduced monocyte-derived chemokines All groups of patients demonstrated the ability to generate specific CD4 T activated cells after spike proteins stimulation. After the third dose of vaccine, abatacept-treated patients acquired the ability to produce a strong antibody response, showing an anti-S titer significantly higher compared to that obtained after the second dose (p = 0.0047), and comparable with the anti-S titer of the other groups.ConclusionsPatients treated with abatacept showed an impaired humoral immune response to two doses of COVID-19 vaccine. The third vaccine dose has been demonstrated to be useful to induce a more robust antibody response to balance an impaired T cell-mediated one. All patients, exposed to different immunosuppressive drugs, were able to produce specific CD4-activated T cells, after spike proteins stimulation.Trial registrationLocal Ethical Committee NP4187.

Safety outcomes in patients with rheumatoid arthritis treated with abatacept: results from a multinational surveillance study across seven European registries

BackgroundPatients with rheumatoid arthritis (RA) have an increased risk of infection and malignancy compared with the general population. Infection risk is increased further with the use of disease-modifying antirheumatic drugs (DMARDs), whereas evidence on whether the use of biologic DMARDs increases cancer risk remains equivocal. This single-arm, post-marketing study estimated the incidence of prespecified infection and malignancy outcomes in patients with RA treated with intravenous or subcutaneous abatacept.MethodsData were included from seven European RA quality registries: ATTRA (Anti-TNF Therapy in Rheumatoid Arthritis [Czech Republic]), DANBIO (Danish Rheumatologic Database), ROB-FIN (National Registry of Antirheumatic and Biological Treatment in Finland), ORA (Orencia and Rheumatoid Arthritis [France]), GISEA (Italian Group for the Study of Early Arthritis), BIOBADASER (Spanish Register of Adverse Events of Biological Therapies in Rheumatic Diseases), and the SCQM (Swiss Clinical Quality Management) system. Each registry is unique with respect to design, data collection, definition of the study cohort, reporting, and validation of outcomes. In general, registries defined the index date as the first day of abatacept treatment and reported data for infections requiring hospitalization and overall malignancies; data for other infection and malignancy outcomes were not available for every cohort. Abatacept exposure was measured in patient-years (p-y). Incidence rates (IRs) were calculated as the number of events per 1000 p-y of follow-up with 95% confidence intervals.ResultsOver 5000 patients with RA treated with abatacept were included. Most patients (78–85%) were female, and the mean age range was 52–58 years. Baseline characteristics were largely consistent across registries. Among patients treated with abatacept, IRs for infections requiring hospitalization across the registries ranged from 4 to 100 events per 1000 p-y, while IRs for overall malignancy ranged from 3 to 19 per 1000 p-y.ConclusionsDespite heterogeneity between registries in terms of design, data collection, and ascertainment of safety outcomes, as well as the possibility of under-reporting of adverse events in observational studies, the safety profile of abatacept reported here was largely consistent with previous findings in patients with RA treated with abatacept, with no new or increased risks of infection or malignancy.

341 - Mechanism of Success of Abatacept in Hematopoietic Stem Cell Transplantation: Pharmacokinetic-Pharmacodynamic (PK-PD) Analysis Demonstrates Greater Abatacept Exposure Decreases Acute Gvhd (AGVHD) Risk without Increasing Adverse Events

341 - Mechanism of Success of Abatacept in Hematopoietic Stem Cell Transplantation: Pharmacokinetic-Pharmacodynamic (PK-PD) Analysis Demonstrates Greater Abatacept Exposure Decreases Acute Gvhd (AGVHD) Risk without Increasing Adverse Events

Risk of hepatitis B virus reactivation following treatment with abatacept: A retrospective study of international pharmacovigilance databases

SummaryBackgroundAbatacept is a selective T-cell costimulation modulator approved for the treatment of rheumatoid arthritis, juvenile idiopathic arthritis, and psoriatic arthritis. Reports were recently published on hepatitis B virus reactivation (HBVr) in patients who were treated with abatacept. However, the literature is limited to case reports and series, and no study has investigated the relationship between HBVr and abatacept using extensive population-based databases.MethodsUsing the United States Food and Drug Administration Adverse Event Reporting System (FAERS) database, we collected all cases of HBVr between Jan 1, 2006 and June 30, 2021, for abatacept and other drugs. Disproportionality was analysed using the reporting odds ratio (ROR), which was considered significant when the lower limit of the 95% CI was >1. We also conducted a confirmatory analysis in the European pharmacovigilance database, EudraVigilance.FindingsDuring the study period, 77,669 adverse cases were reported for abatacept use. There were 2889 reports of HBVr with any drug during this period, of which 55 were reported with abatacept. The ROR for HBVr with abatacept was significantly elevated at 4·80 (95% CI 3·68–6·27). All 55 cases of HBVr with abatacept were reported as serious adverse events. Of them, six individuals were hospitalised and four died. Among 832 reports of HBVr with any drug in EudraVigilance, 43 were reported with abatacept; the ROR was 8·99 (95% CI 6·61–12·23).InterpretationWe identified a positive signal between abatacept exposure and HBVr. Future prospective studies should further confirm the relationship and provide evidence to develop strategies involving pre-treatment screening, monitoring, and utilisation of antiviral prophylaxis when using abatacept in patients with rheumatic diseases.FundingThis work was supported by the Fundamental Research Funds for Central Universities (xjh012019063).

Absence of Association Between Abatacept Exposure and Initial Infection in Patients With Juvenile Idiopathic Arthritis

To assess the relationship between infection risk and abatacept (ABA) exposure levels in patients with polyarticular-course juvenile idiopathic arthritis (pJIA) following treatment with subcutaneous (SC) and intravenous (IV) ABA. Data from 2 published studies (ClinicalTrials.gov: NCT01844518, NCT00095173) of ABA treatment in pediatric patients were analyzed. One study treated patients aged 2-17 years with SC ABA and the other treated patients aged 6-17 years with IV ABA. Association between serum ABA exposure measures and infection was evaluated using Kaplan-Meier plots of probability of first infection vs time on treatment by ABA exposure quartiles and log-rank tests. Number of infections by ABA exposure quartiles was investigated. Overall, 343 patients were included in this analysis: 219 patients received SC ABA and 124 patients received IV ABA. Overall, 237/343 (69.1%) patients had ≥ 1 infection over 24 months. No significant difference in time to first infection across 4 quartiles of ABA exposure levels was observed in the pooled (P = 0.45), SC (2-5 yrs: P = 0.93; 6-17 yrs: P = 0.48), or IV (P = 0.50) analyses. Concomitant use of methotrexate and glucocorticoids (at baseline and throughout) with ABA did not increase infection risk across the ABA exposure quartiles. There was no evidence of association between number of infections and ABA exposure quartiles. No opportunistic infections related to ABA were reported. In patients aged 2-17 years with pJIA, no evidence of association between higher levels of exposure to IV ABA or SC ABA and incidence of infection was observed.

Risk of opportunistic infections in patients with rheumatoid arthritis initiating abatacept: cumulative clinical trial data

BackgroundTo evaluate incidence of opportunistic infections (OIs) in patients with rheumatoid arthritis (RA) treated with abatacept in clinical trials.MethodsThis pooled analysis of 16 randomized, double-blind/open-label trials, with ≥ 1 abatacept (intravenous or subcutaneous) arm, and with/without placebo control covered cumulative (controlled short-term and open-label long-term) abatacept exposure periods. OIs were analyzed separately in controlled (abatacept and placebo individually) and cumulative periods. OIs were identified using a prespecified list; events were independently adjudicated. Unadjusted incidence rates (IRs; per 100 patient-years) with 95% confidence intervals (CIs) were calculated.ResultsIn cumulative periods, 7044 patients received abatacept, with a mean (standard deviation) duration of exposure of 36.9 (26.2) months (21,274 patient-years of exposure). IRs (95% CIs) of OIs were 0.17 (0.05–0.43) for abatacept and 0.56 (0.22–1.15) for placebo during the controlled periods and 0.21 (0.15–0.28) for abatacept during the cumulative periods. There was 1 case of tuberculosis in both the abatacept (IR [95% CI] 0.04 [0.00–0.24]) and placebo (IR [95% CI] 0.08 [0.00–0.44]) groups during the controlled periods; 13 verified tuberculosis cases (IR [95% CI] 0.06 [0.03–0.10]) were reported in the cumulative period. Herpes zoster was reported numerically more often with abatacept (IR 1.9 [1.4–2.5]), versus placebo (1.7 [1.1–2.6]) in the controlled periods; within the cumulative period, herpes zoster IR (95% CI) was 1.53 (1.36–1.71) for abatacept-treated patients.ConclusionIn controlled periods of the clinical trials, abatacept-treated patients had similarly low rates of OIs compared with placebo-treated patients. Overall, OI rates were similar among abatacept-treated patients in the controlled and cumulative periods and consistent with the ranges reported in the literature.

Risk of malignancy with non-TNFi biologic or tofacitinib therapy in rheumatoid arthritis: A meta-analysis of observational studies

ObjectivesTo assess the risk of developing cancer in patients with rheumatoid arthritis (RA) exposed to non-TNF inhibitors (TNFi) biologics or tofacitinib therapy. MethodsSystematical search of PubMed, EMBASE and Cochrane Library plus a hand search of conference proceedings were performed. Observational studies that reported cancer incidence in patients with RA treated with biologics or tofacitinib with active comparator of conventional synthetic disease-modifying anti-rheumatic drugs (csDMARDs) or TNFi were eligible for inclusion. The pooled relative risk (RR) and 95% confidence interval (CI) were calculated with fix-effects or random-effects model. ResultsOf 2,819 identified articles, a total of 10 studies involving over 40,587 patients with more than 87,622 patient-years of exposure to non-TNF inhibitors (TNFi) biologics and 2,221 patients with more than 4,506 patient-years of exposure to tofacitinib were included. Pooled analysis showed there was no increased risk of developing cancer in general or specific cancer types in RA patients receiving treatment with rituximab (pooled RR 0.87, 95% CI 0.74–1.03), tocilizumab (pooled RR 0.92, 95% CI 0.79–1.06), or tofacitinib, compared with those receiving csDMARDs or TNFi. But abatacept was associated with a slightly increased overall cancer risk (pooled RR 1.13, 95% CI 1.02–1.24) and non-melanoma skin cancer (pooled RR 1.26, 95% CI 1.09–1.45), relative to csDMARDs or TNFi in RA patients. ConclusionAmong RA patients, a small statistically significant increase in developing cancer was observed for abatacept exposure, while no increased cancer risk for rituximab, tocilizumab or tofacitinib, in comparison with csDMARDs or TNFi.

Maintenance of antibody response to diphtheria/tetanus vaccine in patients aged 2\u20135\u2009years with polyarticular-course juvenile idiopathic arthritis receiving subcutaneous abatacept

BackgroundPatients with polyarticular-course juvenile idiopathic arthritis (pJIA), receiving disease-modifying anti-rheumatic drugs with immunosuppressive effects, may be at increased risk of vaccine-preventable infections. This substudy assessed protective antibody responses to diphtheria and tetanus vaccination given prior to study enrolment in patients with pJIA.FindingsThis was a substudy of a 24-month, single-arm, open-label, multicenter, Phase III trial (NCT01844518) of subcutaneous abatacept in children with active pJIA (N = 219). Patients aged 2–5 years, with ≥2 continuous months of weekly weight-tiered (10–< 25 kg [50 mg], 25–< 50 kg [87.5 mg]) subcutaneous abatacept treatment (with/without methotrexate and/or low-dose corticosteroids), who received diphtheria/tetanus vaccine prior to enrolment, were eligible. Protective antibody levels to diphtheria/tetanus (> 0.1 IU/mL), and safety, were assessed.Overall, 29 patients were analyzed: 19 (65.5%), 1 (3.4%) and 9 (31.0%) patients had > 12, 6–12 and 2–< 6 months of abatacept exposure, respectively. All patients had protective antibody levels to tetanus and 26 (89.7%) patients had protective antibody levels to diphtheria. Of the 3 patients without protective antibody levels to diphtheria, each had an antibody level of 0.1 IU/mL, bordering the lower threshold of protection. Concomitant use of methotrexate and/or low-dose corticosteroids had no evident effect on antibody levels. No unexpected adverse events, including cases of diphtheria or tetanus, were reported during the 24-month period.ConclusionsPatients aged 2–5 years with pJIA who received 2–24 months of weekly subcutaneous abatacept, with or without concomitant methotrexate and/or low-dose corticosteroids, maintained effective diphtheria and tetanus vaccination protection without new safety signals.Trial registrationClinicalTrials.gov (NCT01844518); registered May 1, 2013; https://clinicaltrials.gov/ct2/show/NCT01844518?term=NCT01844518&rank=1

FRI0191 Immunogenicity is low and transient with intravenous abatacept therapy

BackgroundImmunogenicity with therapeutic proteins has been linked to reduction in both efficacy and safety in patients (pts) with RA.1,2 We previously reported in clinical trials that IV abatacept (ABA) demonstrated...

FRI0312 Abatacept exposure-response analysis and its impact on dose selection in lupus nephritis

BackgroundRecent post-hoc analyses of patients participating in a trial of abatacept (ABA) vs. placebo, in combination with mycophenolate mofetil and corticosteroids for treatment of active lupus nephritis (IM101075) have provided...

THU0246 Subcutaneous Abatacept: Long-Term Data From the Acquire Trial

BackgroundThe Abatacept (ABA) Comparison of Sub[QU]cutaneous (SC) versus Intravenous (IV) in Inadequate Responders to MethotrexatE (MTX) (ACQUIRE) study showed comparable efficacy and safety of SC vs IV ABA over 6...

Model-based determination of abatacept exposure in support of the recommended dose for Japanese rheumatoid arthritis patients

The objective of this study was to provide support for a body weight-tiered dosing regimen by characterizing abatacept pharmacokinetics (PK) and the relationship between exposure and the ACR20 (American College of Rheumatology criteria for 20% improvement) response in Japanese patients with rheumatoid arthritis (RA). A population PK model was developed using NONMEM with 2,535 samples from 344 Japanese RA patients in two clinical trials. The exposure-response relationship was characterized using a Generalized Estimating Equation (GEE) logistic regression model, with time-varying actual trough concentrations and ACR20 responder rates over 6months in a randomized, placebo-controlled phase 2 trial for stable methotrexate. Abatacept exposure was well characterized using a linear, two-compartment model, in which body weight and the empirically calculated glomerular filtration rate were significant covariates for clearance. The ACR20 response model was developed by examining the quasi-likelihood information criterion, and the cumulative logit in the final model was specified by the log-transformed trough concentration. The predicted ACR20 responder rate was consistent with the actual values in the clinical trial and this model revealed trough concentrations higher than the recommended body weight-tiered dose are unlikely to result in substantial increases in clinical efficacy. Considering that ACR20 is a longitudinal binary variable and the response to RA treatment is delayed, the GEE model was useful for predicting the probability of an ACR20 response. In conclusion, the same dosing regimen as non-Japanese patients is recommended because a body weight-tiered dosing regimen achieves similar exposures across the wide range of body weight.

Modeling and Simulation of Abatacept Exposure and Interleukin‐6 Response in Support of Recommended Doses for Rheumatoid Arthritis1

Abatacept is a recombinant soluble fusion protein that inhibits the CD80/CD86:CD28 costimulatory signal required for T cell activation and has demonstrated efficacy in the treatment of rheumatoid arthritis. The objectives of this analysis were to provide support for a body weight-tiered dosing regimen approximating 10 mg/kg by (1) quantifying the effect of body weight on exposure and (2) characterizing the relationship between exposure and serum interleukin (IL)-6 concentration. The abatacept exposure and exposure-response models were developed with 2148 abatacept serum concentrations (from 388 subjects) and 1894 IL-6 serum concentrations (from 799 subjects), respectively, followed by simulation with these models to address the above objectives. Abatacept exposure was characterized by a linear 2-compartmental model, in which clearance was linearly related to body weight. The IL-6 response was characterized by an indirect-response model, in which the IL-6 production rate increased with baseline C-reactive protein levels. Model-based simulations demonstrated that body weight-tiered dosing was desirable to ensure consistent steady-state abatacept trough concentrations across a range of body weights; doses approximating 10 mg/kg (500, 750, 1000 mg for subjects weighing <60, 60-100, and >100 kg, respectively) provided consistent exposure across the body weight groups. In addition, doses >10 mg/kg did not result in further increases in IL-6 suppression. These modeling and simulation results indicate that the body weight-tiered abatacept therapeutic doses approximating 10 mg/kg will ensure consistent abatacept exposure and optimal IL-6 suppression.