Biophysical Properties of Human Antibody Variable Domains

There are great demands on the stability, expression yield and resistance to aggregation of antibody fragments. To untangle intrinsic domain effects from domain interactions, we present first a systematic evaluation of the isolated human immunoglobulin variable heavy (VH) and light (VL) germline family consensus domains and then a systematic series of VH–VL combinations in the scFv format. The constructs were evaluated in terms of their expression behavior, oligomeric state in solution and denaturant-induced unfolding equilibria under non-reducing conditions. The seven VH and seven VL domains represent the consensus sequences of the major human germline subclasses, derived from the Human Combinatorial Antibody Library (HuCAL®). The isolated VH and VL domains with the highest thermodynamic stability and yield of soluble protein were VH3 and Vκ3, respectively. Similar measurements on all domain combinations in scFv fragments allowed the scFv fragments to be classified according to thermodynamic stability and in vivo folding yield. The scFv fragments containing the variable domain combinations H3κ3, H1bκ3, H5κ3 and H3κ1 show superior properties concerning yield and stability. Domain interactions diminish the intrinsic differences of the domains. ScFv fragments containing Vλ domains show high levels of stability, even though Vλ domains are surprisingly unstable by themselves. This is due to a strong interaction with the VH domain and depends on the amino acid sequence of the CDR-L3. On the basis of these analyses and model structures, we suggest possibilities for further improvement of the biophysical properties of individual frameworks and give recommendations for library design.