A mutant BCL11B-N440K protein interferes with BCL11A function during T lymphocyte and neuronal development.

Genetic studies in mice have shown that the zinc finger transcription factor BCL11B has an essential role in regulating early T cell development and neurogenesis. A de novo heterozygous missense BCL11B variant, BCL11BN441K, was isolated from a patient with T cell deficiency and neurological disorders. Here, we show that mice harboring the corresponding Bcl11bN440K mutation show the emergence of natural killer (NK)/group 1 innate lymphoid cell (ILC1)-like NKp46+ cells in the thymus and reduction in TBR1+ neurons in the neocortex, which are observed with loss of Bcl11a but not Bcl11b. Thus, the mutant BCL11B-N440K protein interferes with BCL11A function upon heterodimerization. Mechanistically, the Bcl11bN440K mutation dampens the interaction of BCL11B with T cell factor 1 (TCF1) in thymocytes, resulting in weakened antagonism against TCF1 activity that supports the differentiation of NK/ILC1-like cells. Collectively, our results shed new light on the function of BCL11A in suppressing non-T lymphoid developmental potential and uncover the pathogenic mechanism by which BCL11B-N440K interferes with partner BCL11 family proteins.