Somatic cell nuclear transfer (SCNT) may be used to clone mice from lymphocytes of defined specificity. By harvesting as few as 200 primary lymphocytes from animals that are at the peak of an immune response, and by transfer of the nucleus from such antigen specific lymphocytes into an enucleated oocyte, embryonic stem cells that harbor the genetic rearrangements encoding the original antigen receptor may be obtained and used for the construction of transnuclear mice. These animals contain T or B cells of the appropriate specificity, have no genetic alterations other than the physiological TCR/BCR rearrangements and are the closest approximation of physiological immune responses to date. Importantly, the generation of transnuclear mice is rapid, requiring approximately 6 weeks from T cell harvest to obtaining chimeric animals.

We use the Cas9-CRISPR system to directly modify genes in fertilized mouse zygotes. We have optimized the process to increase the frequency of homologous recombination, thereby generating precise genome edits and decreasing off-target effects.