Given that the human C5aR1-specific antagonist PMX53 has already undergone phase Ib/IIa clinical trials to treat psoriasis and rheumatoid arthritis and has passed safety and tolerability testing (69), this raises hope for a clear path for trials of PMX53, or other C5a-targeted therapeutics (70), to block the devastating outcome of invasive meningococcal disease. This evidence concerns the gene C5 and rheumatoid arthritis.