Significant impairment in B- and T-cell development in older RAG1-S723C heterozygous mice. Flow cytometric analyses were performed on RAG1^+/+, RAG1^+/S723C, and RAG1^S723C/S723C mice at 12 months of age. (A) Thymocytes and splenocytes were stained with αCD4 and αCD8 antibodies. (B) Bone marrow cells and splenocytes were stained with antibodies against the indicated cell-surface markers.