Abstract: The present invention relates to a polynucleotide comprising a Complement Factor I (CFI) nucleotide sequence encoding a CFI polypeptide or a fragment thereof. The invention further relates to a viral particle comprising a recombinant genome comprising the polynucleotide of the invention, and a composition comprising the polynucleotide or viral particle of the invention. The invention also relates to methods of using, and uses of, the polynucleotide, viral particle and/or composition of the invention. The invention also relates to methods of using, and uses of, a polynucleotide comprising a CFI nucleotide sequence, a viral particle comprising a recombinant genome comprising the polynucleotide, or a composition comprising the polynucleotide or viral particle.