Identification of revertant cells in patient's T-lymphocytes. (A) FACS analysis showing presence of WASp in approximately 14% of patient's lymphocytes. (B) FACS analysis showing presence of WASp-expressing cells at 21% frequency in CD4⁺ and 44% frequency in CD8⁺ lymphocyte populations. The top right quadrants contain WASp⁺ cells coexpressing CD4 or CD8. (C) Schematic of WAS gene structure and relevant genotypes. The 995C>T>A reversion introduces a novel XbaI restriction enzyme site allowing detection of revertant genotype. (D) Examination of 995C>T>A revertant genotype in lymphocyte populations. XbaI digestion confirmed the presence of the 995C>T>A revertant in CD8⁺ and CD3⁺/CD8⁻ T cells. The 1.3 kb PCR product for the 995C>T>A genotype yields 2 bands (0.86 kb, 0.44 kb) when digested with XbaI. (E) Class I revertants, identified in allospecific T-cell clones, involved single base pair substitutions (positions 995-997) resulting in replacement of the mutant 321stop codon with either the wild-type arg321 or the other amino acids indicated. (F) Schematic of class II (intron 9 base pair substitutions just upstream of the beginning of exon 10), class III (single or double base pair substitutions within exon 10), and class IV revertants (deletions of various size in intron 9 and/or exon 10).