Co‐existence of clonal expanded autologous and transplacental‐acquired maternal T cells in recombination activating gene‐deficient severe combined immunodeficiency

Summary It is commonly accepted that the presence of high amounts of maternal T cells excludes O menn syndrome ( OS ) in severe combined immunodeficiency ( SCID ). We report a SCID patient with a novel mutation in the recombination activating gene ( RAG )1 gene (4‐ BP DEL .1406 TTGC ) who presented with immunodeficiency and OS . Several assays, including representatives of specific T cell receptors ( TCR ), V β families and TCR ‐γ rearrangements, were performed in order to understand more clearly the nature and origin of the patient's T cells. The patient had oligoclonal T cells which, based on the patient–mother human leucocyte antigen ( HLA )‐ B 50 mismatch, were either autologous or of maternal origin. These cell populations were different in their numbers of regulatory T cells ( T reg ) and the diversity of TCR repertoires. This is the first description of the co‐existence of large amounts of clonal expanded autologous and transplacental‐acquired maternal T cells in RAG 1‐deficient SCID .