A method for separating cells capable of producing target antigen-specific monoclonal antibodies (TASMAs) wherein a cell group including antibody-producing cells is immobilized using a reversible crosslinking agent having cell membrane-permeating properties. The immobilized cell group is subjected to cell membrane dissolution using a surface active agent; and the cell group is reacted with a labeling target antigen. In the stained cell group a that has reacted with the labeling target antigen is separated. A method to produce TASMAs by separating mRNA from the cell separated using the method; preparing cDNA and preparing antigen-specific monoclonal antibodies or fragments thereof from the prepared cDNA. Also provided are a method whereby at least one cell capable of producing TASMAs is separated and a method whereby said antibodies can be produced by using the separated cell. Threonine 18 phosphorylated p53 (pT18-p53) and threonine 68 phosphorylated CHK2 (pT68-CHK2) specific monoclonal antibodies are also disclosed.