LCK and immunodeficiency disease: The T cell receptor (TCR) ‐CD3 complex formed by CD3E and TCR plays a key role in antigen recognition, linking downstream signalling pathways and T cell maturation.52 Besides, the mutation or non‐expression of CD3E is closely related to immunodeficiency.53 LCK belongs to the Src family of tyrosine protein kinases, which are involved in T cell maturation and proliferation, and mediate the key downstream molecules of MAPK and NFKB through TCR‐CD3 complex.54, 55 CD3E and LCK are upstream molecules of the T cell receptor pathway.