CIRCUMVENTION OF TOLERANCE FOR THE NUCLEAR T-CELL PROTEIN TCF-1 BY IMMUNIZATION OF TCF-1 KNOCK-OUT MICE

Molecular events that underlie the well-defined phenotypic changes of the differentiating thymocyte are poorly understood. A candidate gene to control thymocyte differentiation, T cell factor-1 (TCF-1) encodes a DNA-binding protein. Its mRNA expression pattern is complex during embryogenesis, yet restricted to lymphocytes postnatally. Expression s tudies on TCF-1 protein have been hampered by the difficulty to raise antibodies due to extreme evolutionary conservation. TCF-1 knock-out m ice, generated recently in our laboratory, have strongly decreased num bers of thymocytes, but are otherwise normal. We have used these mice to generate anti-TCF-1 antibodies. By immunization with a recombinant fusion protein, we show that TCF-1 knock-out mice readily yield antise rum titers against human and mouse TCF-1 protein. Wild-type littermate s remain unresponsive to TCF-1 while they mount a high-titer antibody response to the fusion protein, Maltose Binding Protein (MBP). Subsequ ently, TCF-1-specific hybridomas could be prepared from the spleens of immunized knock-out mice. This study illustrates the almost complete tolerance of mice for human TCF-1 and demonstrates that this tolerance is readily broken by gene knock-out. Furthermore, the usefulness of k nock-out mice for the generation of monoclonal antibodies against the gene product of interest is underscored.