Here is the design of a clinical trial:

Official Title: Safety, Tolerability and Efficacy of Anti-IL-6 Antibody Clazakizumab in Late Antibody-Mediated Rejection After Kidney Transplantation - a Pilot Trial

Included conditions:
- Antibody-mediated Rejection

Study Armgroups:
- {'label': 'Clazakizumab / Clazakizumab', 'type': 'ACTIVE_COMPARATOR', 'description': 'Monthly subcutaneous injections of 25mg clazakizumab for three months (after completion of part A, monthly injection of 25mg clazakizumab for nine months).', 'interventionNames': ['Drug: Clazakizumab / Clazakizumab']}
- {'label': 'Placebo / Clazakizumab', 'type': 'PLACEBO_COMPARATOR', 'description': 'Monthly subcutaneous injections of placebo (saline) for three months (after completion of part A, monthly injection of 25mg clazakizumab for nine months).', 'interventionNames': ['Drug: Placebo / Clazakizumab']}

Interventions:
- {'type': 'DRUG', 'name': 'Clazakizumab / Clazakizumab', 'description': 'Humanized monoclonal anti-IL-6 antibody', 'armGroupLabels': ['Clazakizumab / Clazakizumab'], 'otherNames': ['Anti-IL-6 antibody']}
- {'type': 'DRUG', 'name': 'Placebo / Clazakizumab', 'description': '0.9% Saline', 'armGroupLabels': ['Placebo / Clazakizumab'], 'otherNames': ['Saline']}

Primary Outcomes:
- {'measure': "Number of adverse events and severe adverse events (AE's, SAE's)", 'description': 'Serious and Non-Serious adverse events probably or possibly attributable to clazakizumab', 'timeFrame': '12 months'}

Please estimate the sample size based on the assumption: 
The primary endpoint will be safety and tolerability. Preliminary assessment of efficacy outcomes will be conducted.
Sample size calculation
        For this pilot study, no exact sample size estimation has been performed, because the effect size is unknown (there is no prior information to base a sample size on). The primary endpoint will be safety and tolerability. A preliminary assessment of efficacy outcomes in 20 kidney transplant recipients with late ABMR will provide first data on the effect of clazakizumab on clinical, morphological, immunological, and molecular endpoints. The respective results (e.g. comparison between clazakizumab and placebo with respect to microcirculation inflammation and molecular rejection scores), including an assessment of variability, can be expected to provide a valuable foundation of the design of future trials.