A Bcl11b N797K variant isolated from an immunodeficient patient inhibits early thymocyte development in mice

BCL11B is a transcription factor with six C H -type zinc-finger domains. Studies in mice have shown that Bcl11b plays essential roles in T cell development. Several germline heterozygous BCL11B variants have been identified in human patients with inborn errors of immunity (IEI) patients. Among these, two mis-sense variants cause asparagine (N) to lysine (K) replacement in distinct zinc-finger domains, BCL11B and BCL11B . To elucidate the pathogenesis of the BCL11B variant, we generated a mouse model of BCL11B by inserting the corresponding mutation, , into the mouse genome. In mice, the proportion of immature CD4 CD8 single-positive thymocytes was increased, and the development of invariant natural killer cells was severely inhibited in a T-cell-intrinsic manner. Under competitive conditions, γδT cell development was outcompeted by control cells. mice died within one day of birth. Recipient mice reconstituted with fetal liver cells nearly lacked CD4 CD8 double-positive thymocytes, which was consistent with the lack of their emergence in culture from fetal liver progenitors. Interestingly, progenitors gave rise to aberrant c-Kit and CD44 cells both and . The increase in the proportion of immature CD8 single-positive thymocytes in the Bcl11b mutants is caused, in part, by the inefficient activation of the gene due to the attenuated function of the two enhancers via distinct mechanisms. Therefore, we conclude that immunodeficient patient-derived Bcl11b mutant mice elucidated a novel role for Bcl11b in driving the appropriate transition of CD4 CD8 into CD4 CD8 thymocytes.