The present disclosure relates to modified proteins and peptides that have reduced ability to bind to pre-existing antibodies. Such modified protein/peptide molecules can comprise C-terminal additions, extensions or tags and/or certain amino acid substitutions. Such modified molecules (e.g., fusions and conjugates) comprise proteins, peptides, antigen binding molecules, antibodies or antibody fragments such as single variable domains. The disclosure further relates to uses and formulations of compositions comprising such modified C-terminally extended and/or amino acid substituted molecules and also to methods of production and expression of these.