| Pharmacotherapeutic group: selective immunosuppressants, ATC code: L04AA24Abatacept is a fusion protein that consists of the extracellular domain of human cytotoxic T lymphocyte associated antigen 4 (CTLA 4) linked to a modified Fc portion of human immunoglobulin G1 (IgG1). Abatacept is produced by recombinant DNA technology in Chinese hamster ovary cells.Mechanism of action Abatacept selectively modulates a key costimulatory signal required for full activation of T lymphocytes expressing CD28. Full activation of T lymphocytes requires two signals provided by antigen presenting cells: recognition of a specific antigen by a T cell receptor (signal 1) and a second, costimulatory signal. A major costimulatory pathway involves the binding of CD80 and CD86 molecules on the surface of antigen presenting cells to the CD28 receptor on T lymphocytes (signal 2). Abatacept selectively inhibits this costimulatory pathway by specifically binding to CD80 and CD86. Studies indicate that naive T lymphocyte responses are more affected by abatacept than memory T lymphocyte responses.Studies in vitro and in animal models demonstrate that abatacept modulates T lymphocyte dependent antibody responses and inflammation. In vitro, abatacept attenuates human T lymphocyte activation as measured by decreased proliferation and cytokine production. Abatacept decreases antigen specific TNFα, interferon γ, and interleukin 2 production by T lymphocytes.Pharmacodynamic effects Dose dependent reductions were observed with abatacept in serum levels of soluble interleukin 2 receptor, a marker of T lymphocyte activation; serum interleukin 6, a product of activated synovial macrophages and fibroblast like synoviocytes in rheumatoid arthritis; rheumatoid factor, an autoantibody produced by plasma cells; and C reactive protein, an acute phase reactant of inflammation. In addition, serum levels of matrix metalloproteinase 3, which produces cartilage destruction and tissue remodelling, were decreased. Reductions in serum TNFα were also observed.Clinical efficacy and safety The efficacy and safety of abatacept were assessed in randomised, double blind, placebo controlled clinical trials in adult patients with active rheumatoid arthritis diagnosed according to American College of Rheumatology (ACR) criteria. Studies I, II, III, and V required patients to have at least 12 tender and 10 swollen joints at randomization. Study IV did not require any specific number of tender or swollen joints.In Studies I, II, and V the efficacy and safety of abatacept compared to placebo were assessed in patients with an inadequate response to methotrexate and who continued on their stable dose of methotrexate. In addition, Study V investigated the safety and efficacy of abatacept or infliximab relative to placebo. In Study III the efficacy and safety of abatacept were assessed in patients with an inadequate response to a TNF blocking agent, with the TNF blocking agent discontinued prior to randomization; other DMARDs were permitted. Study IV primarily assessed safety in patients with active rheumatoid arthritis requiring additional intervention in spite of current therapy with non biological and/or biological DMARDs; all DMARDs used at enrollment were continued.Study I patients were randomized to receive abatacept 2 or 10 mg/kg or placebo for 12 months. Study II, III, and IV patients were randomized to receive a fixed dose approximating 10 mg/kg of abatacept or placebo for 12 (Studies II and IV) or 6 months (Study III). The dose of abatacept was 500 mg for patients weighing less than 60 kg, 750 mg for patients weighing 60 to 100 kg, and 1 gram for patients weighing greater than 100 kg. Study V patients were randomized to receive this same fixed dose of abatacept or 3 mg/kg infliximab or placebo for 6 months. Study V continued for an additional 6 months with the abatacept and infliximab groups only.Studies I, II, III, IV, and V evaluated 339, 638, 389, 1,441, and 431 patients, respectively.Clinical response ACR response The percent of abatacept treated patients achieving ACR 20, 50, and 70 responses in Study II (patients with inadequate response to methotrexate) and Study III (patients with inadequate response to TNF blocking agent) are shown in Table 3.In abatacept treated patients in Studies II and III, statistically significant improvement in the ACR 20 response versus placebo was observed after administration of the first dose (day 15), and this improvement remained significant for the duration of the studies. In Study II, 43% of the patients who had not achieved an ACR 20 response at 6 months developed an ACR 20 response at 12 months.Table 3: ACR Responses in Placebo Controlled Trials | | Percent of Patients | | Inadequate Response to Methotrexate (MTX) | Inadequate Response to TNF Blocking Agent | Study II | Study III | Response Rate | Abatacepta +MTX n = 424 | Placebo +MTX n = 214 | Abatacepta + DMARDsb n = 256 | Placebo + DMARDsb n = 133 | ACR 20 | | | | | Day 15 | 23%* | 14% | 18%** | 5% | Month 6 | 68%*** | 40% | 50%*** | 20% | Month 12 | 73%*** | 40% | NAd | NAd | ACR 50 | | | | | Month 6 | 40%*** | 17% | 20%*** | 4% | Month 12 | 48%*** | 18% | NAd | NAd | ACR 70 | | | | | Month 6 | 20%*** | 7% | 10%** | 2% | Month 12 | 29%*** | 6% | NAd | NAd | Major Clinical Responsec | 14%*** | 2% | NAd | NAd | * p < 0.05, abatacept vs. placebo.** p < 0.01, abatacept vs. placebo.*** p < 0.001, abatacept vs. placebo.a Fixed dose approximating 10 mg/kg (see section 4.2).b Concurrent DMARDs included one or more of the following: methotrexate, chloroquine/hydroxychloroquine, sulfasalazine, leflunomide, azathioprine, gold, and anakinra.c Major clinical response is defined as achieving an ACR 70 response for a continuous 6 month period.d After 6 months, patients were given the opportunity to enter an open label study.In the open label extension of Studies I, II, and III durable and sustained ACR 20, 50, and 70 responses have been observed through 48, 24, and 18 months, respectively, of abatacept treatment. In study I, ACR 20 responses were observed in 71% (42/59) of patients, ACR 50 in 41% (24/59), and ACR 70 in 31% (18/58) at 48 months. In study II, ACR 20 responses were observed in 88% (291/332) of patients, ACR 50 in 62% (205/332), and ACR 70 in 38% (127/334) at 24 months. In study III, ACR 20 responses were observed in 70% (118/167) of patients, ACR 50 in 43% (73/168), and ACR 70 in 22% (37/169) at 18 months.Greater improvements were seen with abatacept than with placebo in other measures of rheumatoid arthritis disease activity not included in the ACR response criteria, such as morning stiffness.DAS28 response Disease activity was also assessed using the Disease Activity Score 28 (DAS28 ESR). There was a significant improvement of DAS in Studies II, III, and V as compared to placebo.Study V: abatacept or infliximab versus placebo A randomized, double blind study was conducted to assess the safety and efficacy of abatacept or infliximab versus placebo in patients with an inadequate response to methotrexate (Study V). The primary outcome was the mean change in disease activity in abatacept treated patients compared to placebo treated patients at 6 months with a subsequent double blind assessment of safety and efficacy of abatacept and infliximab at 12 months. Greater improvement (p < 0.001) in DAS28 was observed with abatacept and with infliximab compared to placebo at six months in the placebo controlled portion of the trial; the results between the abatacept and infliximab groups were similar. The ACR responses in Study V were consistent with the DAS28 score. Further improvement was observed at 12 months with abatacept. At 6 months, the incidence of AE of infections were 48.1% (75), 52.1% (86), and 51.8% (57) and the incidence of serious AE of infections were 1.3% (2), 4.2% (7), and 2.7% (3) for abatacept, infliximab and placebo groups, respectively. At 12 months, the incidence of AE of infections were 59.6% (93), 68.5% (113), and the incidence of serious AE of infections were 1.9% (3) and 8.5% (14) for abatacept and infliximab groups, respectively.Radiographic response Structural joint damage was assessed radiographically over a two year period in Study II. The results were measured using the Genant modified total Sharp score (TSS) and its components, the erosion score and joint space narrowing (JSN) score. The baseline median TSS was 31.7 in abatacept treated patients and 33.4 in placebo treated patients. Abatacept/methotrexate reduced the rate of progression of structural damage compared to placebo/methotrexate after 12 months of treatment as shown in Table 4. The rate of progression of structural damage in year 2 was significantly lower than that in year 1 for patients randomized to abatacept (p < 0.0001).Table 4: Mean Radiographic Changes Over 12 Months in Study II | Parameter | Abatacept/MTX n = 391 | Placebo/MTX n = 195 | P valuea | Total Sharp score | 1.21 | 2.32 | 0.012 | Erosion score | 0.63 | 1.14 | 0.029 | JSN score | 0.58 | 1.18 | 0.009 | a Based on non parametric analysis.Physical function response Improvement in physical function was measured by the Health Assessment Questionnaire Disability Index (HAQ DI) in Studies II, III, IV and V and the modified HAQ DI in Study I. The results from Studies II and III are shown in Table 5. Table 5: Improvement in Physical Function in Placebo Controlled Trials | | Inadequate Response to Methotrexate | Inadequate Response to TNF Blocking Agent | | | Study II | Study III | HAQc Disability Index | Abatacepta +MTX | Placebo +MTX | Abatacepta +DMARDsb | Placebo +DMARDsb | Baseline (Mean) | 1.69 (n = 422) | 1.69 (n = 212) | 1.83 (n = 249) | 1.82 (n = 130) | Mean Improvement from Baseline Month 6 | 0.59*** (n = 420) | 0.40 (n = 211) | 0.45*** (n = 249) | 0.11 (n = 130) | Month 12 | 0.66*** (n = 422) | 0.37 (n = 212) | NAe | NAe | Proportion of patients with a clinically meaningful improvementd Month 6 | 61%*** | 45% | 47%*** | 23% | Month 12 | 64%*** | 39% | NAe | NAe | *** p < 0.001, abatacept vs. placebo.a Fixed dose approximating 10 mg/kg (see section 4.2).b Concurrent DMARDs included one or more of the following: methotrexate, chloroquine/hydroxychloroquine, sulfasalazine, leflunomide, azathioprine, gold, and anakinra.c Health Assessment Questionnaire; 0 = best, 3 = worst; 20 questions; 8 categories: dressing and grooming, arising, eating, walking, hygiene, reach, grip, and activities.d Reduction in HAQ DI of 0.3 units from baseline.e After 6 months, patients were given the opportunity to enter into an open label study.In Study II, among patients with clinically meaningful improvement at month 12, 88% retained the response at month 18, and 85% retained the response at month 24. During the open label period of Studies I, II, and III, the improvement in physical function has been maintained through 48, 24, and 18 months, respectively.Health related outcomes and quality of life Health related quality of life was assessed by the SF 36 questionnaire at 6 months in Studies I, II, and III and at 12 months in Studies I and II. In these studies, clinically and statistically significant improvement was observed in the abatacept group as compared with the placebo group in all 8 domains of the SF 36 (4 physical domains: physical function, role physical, bodily pain, general health; and 4 mental domains: vitality, social function, role emotional, mental health), as well as the Physical Component Summary and the Mental Component Summary. | |