The scientific community is well-aware that these specific constraints can be satisfied for human membrane proteins only by expression in human or animal cells. Therefore, most human membrane proteins produced either synthetically, or in E. coli, or yeast, or insect cells do not present a fully native conformation. In addition, membrane proteins produced in human cells extracted by detergents (even when reinserted in liposomes) lose their native conformations.
Until now, the best source of native membrane proteins for the development of antibodies is whole cells expressing these proteins, or membranes purified from these cells, or VLPs (Viral Like Particles containing HIV or MuLV capsids). Unfortunately, the low concentration of membrane proteins and the high amount of other proteins (like those of viral capsids) are major drawbacks for developing strong and specific immune responses targeting membrane proteins that are generally poor immunogens.