The reason the antibody needs to be humanized is that monoclonal antibodies taken from mice will be seen by the human body as foreign matter, triggering an immunological reaction that neutralizes it. Therefore it's necessary to apply genetic engineering to convert most of the molecular structure into a human gene sequence for the human body to accept it and allow it to work.
而抗體之所以要人源化，是因為從小鼠身上取得的單株抗體，會被人體視為外來物，引發免疫反應將它中和掉，所以必須以遺傳工程的方式進行基因剪貼，將大部分的分子結構置換成人類的基因序列，才能為人體接受，並發揮作用。