Severe combined immunodeficiency caused by deficiency in either the delta or the epsilon subunit of CD3

Abstract

We investigated the molecular mechanism underlying a severe combined immunodeficiency characterized by the selective and complete absence of T cells. The condition was found in 5 patients and 2 fetuses from 3 consanguineous families. Linkage analysis performed on the 3 families revealed that the patients were carrying homozygous haplotypes within the 11q23 region, in which the genes encoding the gamma, delta, and epsilon subunits of CD3 are located. Patients and affected fetuses from 2 families were homozygous for a mutation in the CD3D gene, and patients from the third family were homozygous for a mutation in the CD3E gene. The thymus from a CD3delta-deficient fetus was analyzed and revealed that T cell differentiation was blocked at entry into the double positive (CD4+CD8+) stage with the accumulation of intermediate CD4-single positive cells. This indicates that CD3delta plays an essential role in promoting progression of early thymocytes toward double-positive stage. Altogether, these findings extend the known molecular mechanisms underlying severe combined immunodeficiency to a new deficiency, i.e., CD3epsilon deficiency, and emphasize the essential roles played by the CD3epsilon and CD3delta subunits in human thymocyte development, since these subunits associate with both the pre-TCR and the TCR.

Figure 1

Pedigree and linkage analysis of the 3 families studied. Haplotype analysis of polymorphic markers spanning the CD3G/D/E locus on chromosome 11q23 revealed homozygous haplotype segregations in the patients studied. Polymorphic markers were ordered according to the National Center for Biotechnology Information Homo sapiens map (35). The phase in the patients was determined by analysis of parental genotype.

Figure 2

Schematic representation of the CD3D and CD3E gene mutations. The extracellular (EC), transmembrane (TM), and intracellular (IC) regions, the leader peptide (LP), and the glycosylation sites (G) are shown. X, stop codon; fs, frameshift.

Figure 3

Immunohistology of the thymus from PIII-3 (a 22-week-old fetus) and a control fetus. Sections from the PIII-3 and control thymus were stained with H&E (A), and with antibodies to cytokeratin (KL1) (B), CD3ε (C), CD4 (D), CD8α (E), CD45RO (F), and Ki67 (G). Similar results were obtained for both PIII-3 and PIII-2, with the exception that the Ki67 antibody labeled more cells in PIII-3 than in PIII-2 (a 24-week-old fetus) (see Figure 4). Magnification, ×40.

Figure 4

CD3⁺ thymocyte counts and their proliferation in the thymi from PIII-2 and PIII-3 compared with the thymus from the control fetus. (A) Number of CD3⁺ thymocytes per high-power field (HPF; magnification, ×40). Fields were chosen at random from CD3ε antibody–labeled sections of PIII-3, PIII-2, and control thymi. CD3 antibody–labeled cells were counted on photographs of 3 fields per sample. The results are presented as the mean and SD of the 3 measurements. (B) Percentage of Ki67⁺ thymocytes among the CD3⁺ thymocytes. Fields were photographed at random from Ki67 antibody–labeled sections of PIII-3, PIII-2, and control thymus (magnification, ×40). Ki67 antibody–labeled cells were then counted in 3 fields per sample. The results were plotted against the values obtained for CD3.

Figure 5

Immunohistology of a lymph node from the PIII-2 (24-week-old) fetus and a control (24-week-old) fetus. Peripancreatic lymph node sections from PIII-3, PIII-2, and control thymi were labeled with anti-CD20 mAb and anti-CD3ε mAb. Magnification, ×40.