Quantitative analysis of the CD4 T-cell repertoire specific to therapeutic antibodies in healthy donors

Therapeutic antibodies are generally partially to fully humanized, yet they can show unwanted immunogenicity and lead to antibody response and adverse effects when administered to humans. As immunogenicity relies on a T-cell-dependent mechanism, we have evaluated in vitro the size of the preexisting CD4 T-cell repertoire specific to therapeutic antibodies in healthy donors. Specific CD4 T cells of individuals with different HLA-DR allotypes were amplified by in vitro stimulation and quantified. Well-known immunogenic proteins, KLH and a murine antibody, exhibited a strong in vitro T-cell response characterized by a mean of preexisting T cells >1 cell/106 cells. In contrast, the preexisting CD4 T-cell repertoires specific to 2 chimeric, 2 humanized, and 2 fully human antibodies remained generally inferior to this value, confirming the role of species-specific sequences in their shaping. Mean values ranged from 0.01 to 0.3 cell/106 cells and varied not necessarily in relationship with the humanization level...