Aspects of the disclosure relate to compositions comprising a plurality of complexes comprising an
antibody (e.g., anti-TfRI
antibody) covalently linked to one or more oligonucleotides (e.g. a DMPK targeting
oligonucleotide), each
oligonucleotide being covalently linked at a linkage site represented by a
lysine (K) residue of the
antibody. In some embodiments, the antibody comprises a
heavy chain comprising a
heavy chain variable region (VH) and a
heavy chain constant region, and a light chain comprising a light chain variable region (VL) and a light chain
constant region, wherein at least 80% (e.g., 80%-98%, 80%-95%, 80%-90%, 85%-98%, 85%-95%, 85%-90%, 90%-98%, 90%-95%, 95%-97%, or more) of the light chain constant regions of the antibodies of the complexes in the composition are independently covalently linked to an
oligonucleotide at a linkage site represented by K188 (based on Kabat
numbering) and / or a linkage site represented by K190 (based on Kabat
numbering) of the light chain constant regions of the antibodies.