The Humanness of Macaque Antibody Sequences

Chimeric, humanized and human antibodies have successively been exploited as therapeutics because their increasing human (‘self’) character is expected to correspond with decreased immunogenicity, which is critical for their clinical development. Thus, humanness has been inferred to predict antibody immunogenicity. Humanness of antibody variable regions (V-regions) has recently been studied using a parameter (here referred to as the H-score) that evaluates similarity to expressed human sequences. Macaque (Macaca fascicularis) antibody sequences are of particular interest because they have been suggested to have extremely human-like character and, recently, macaque single-chain variable fragments with very high affinity for various antigens have been isolated. In this study, the H-scores of all macaque antibody V-regions available in sequence data banks were compared with those of their human counterparts using statistical tests. The results were found to be influenced by the relative size of the human families to which the macaque V-regions are related. As the relevance of families to immunogenicity is suspected but unproven, a new parameter (the ‘G-score’) was derived from the H-score to avoid this influence, and macaque V-region sequences were reanalyzed using the G-score. Both parameters show that these regions cannot be regarded as human when they derive from heavy chains, but the humanness of light chains is variable. It was shown that ‘germline humanization’ of a macaque V-region favourably influenced its humanness, as evaluated by both H-score and G-score. In addition, the humanness of macaque sequences presented in patents has been analyzed. The H-score and G-score define objectively the humanness of antibody V-regions, and their use is exemplified here.