Here is the design of a clinical trial:

Official Title: Efficacy and Safety of Belimumab for Prevention of Disease Flares in SLE Patients With Low Disease Activity

Included conditions:
- Systemic Lupus Erythematosus

Study Armgroups:
- {'label': 'Belimumab 2mg/kg', 'type': 'EXPERIMENTAL', 'description': 'Eligible patients were randomized in a 1:1 ratio to belimumab/placebo on the background of standard therapy. Belimumab 2mg/kg is administered intravenously at week 0, week 2, week 4 and then every 4 weeks until 48 weeks.', 'interventionNames': ['Biological: Belimumab']}
- {'label': 'Placebo', 'type': 'PLACEBO_COMPARATOR', 'description': 'Eligible patients were randomized in a 1:1 ratio to belimumab/placebo on the background of standard therapy. Placebo (normal saline) is administered intravenously at week 0, week 2, week 4 and then every 4 weeks until 48 weeks.', 'interventionNames': ['Biological: Placebo']}

Interventions:
- {'type': 'BIOLOGICAL', 'name': 'Belimumab', 'description': 'Belimumab 2mg/kg intravenously', 'armGroupLabels': ['Belimumab 2mg/kg'], 'otherNames': ['BENLYSTA™']}
- {'type': 'BIOLOGICAL', 'name': 'Placebo', 'description': 'Placebo intravenously', 'armGroupLabels': ['Placebo']}

Primary Outcomes:
- {'measure': 'Percentage of patients with disease flares', 'description': 'Disease flare is defined by modified SELENA-SLEDAI SLE flare index (SFI).', 'timeFrame': '52 weeks'}

Please estimate the sample size based on the assumption: 
The trial assumes an 80% power at a two-sided alpha error of 0.05, with an estimated 10% drop-out rate.
Sample size calculation
        The NEA study showed that 10âmg/kg belimumab reduced the severe flare rates in patients with active SLE significantly better than placebo (22% vs 12%, p=0.0004). Besides, according to the BLISS-52, BLISS-76 and the post hoc analysis, 1âmg/kg belimumab helped patients achieve comparable endpoints with 10âmg/kg group. Therefore, low-dose belimumab (120âmg per infusion, about 2âmg/kg) is chosen for the trial to prevent lupus flares among patients with low-grade SLE.
        The sample size estimation was thus carried out with the reference to the flare rate of the placebo arm in our previous âMet Lupusâ trial enrolling similar population12 and the reduction magnitude of flare rate borrowed from the NEA trial.
        A sample size of 167 participants per group including an estimated 10% drop-out would provide the trial with 80% power at a two-sided alpha error of 0.05, yielding a minimum required enrolment of 334 participants.