Characterization of the gammac chain among 27 unrelated Japanese patients with X-linked severe combined immunodeficiency (X-SCID)

Progressive B Cell Loss in Revertant X-SCID

We report the case of a patient with X-linked severe combined immunodeficiency (X-SCID) who survived for over 20 years without hematopoietic stem cell transplantation (HSCT) because of a somatic reversion mutation. An important feature of this rare case included the strategy to validate the pathogenicity of a variant of the IL2RG gene when the T and B cell lineages comprised only revertant cells. We studied the X-inactivation of sorted T cells from the mother to show that the pathogenic variant was indeed the cause of his SCID. One interesting feature was a progressive loss of B cells over 20 years. CyTOF (cytometry time of flight) analysis of bone marrow offered a potential explanation of the B cell failure, with expansions of progenitor populations that suggest a developmental block. Another interesting feature was that the patient bore extensive granulomatous disease and skin cancers that contained T cells, despite severe T cell lymphopenia in the blood. Finally, the patient had a few hundred T cells on presentation but his TCRs comprised a very limited repertoire, supporting the important conclusion that repertoire size trumps numbers of T cells.

Molecular assessment of thymus capabilities in the evaluation of T-cell immunodeficiency

T-cell immunodeficiency may pose a diagnostic challenge to clinicians, especially when the basic T-cell immune workup is not sufficiently informative. An intensive assessment of thymus capabilities that involves either measuring the recent thymic emigrant cells or analyzing the T-cell receptor (TCR) repertoire is often required to estimate the severity and nature of the immune disorder. A comprehensive T-cell immune workup, including TCR excision circles (TRECs) and TCR repertoire analyses, was performed in three patients with various degrees of severity of T-cell immunodeficiency. All three patients had normal peripheral CD3+ T lymphocytes. TCR repertoire analysis revealed oligoclonal (patient 1), restricted (patient 2), and near-normal (patient 3) patterns. TREC quantification was significantly reduced in patients 1 and 2 but normal in patient 3. Based on clinical features at presentation and at follow-up, and supported by the results of immunologic studies, patients 1 and 2 were diagnosed as having significant T-cell immunodeficiency and patient 3 as having T-cell immunocompetence. Assessment of thymus capabilities by TRECs and TCR repertoire analyses is helpful in diagnosing patients with T-cell immunodeficiency and should be part of the evaluation of every patient suspected of having that condition.

A mutation in the IL-2 receptor gamma chain gene associated with X-linked severe combined immunodeficiency accompanying opisthotonus

Severe combined immunodeficiency (SCID) is an inherited disease with profoundly defective T cells, B cells, and NK cells. X-linked severe combined immunodeficiency (X-SCID) is its most common form. In this report, we describe a 4-month old male with X-SCID who also showed opisthotonic posturing. Opisthotonus represents abnormal motor posturing and is defined as the posturing, in which the neck and back are arched posteriorly. The patient was referred to our hospital with liver dysfunction, respiratory distress, anal abscess, poor feeding and wasting; the patient appeared to suffer from severe and persistent infections. In fact, circulating T cells were not detectable, despite that the number of B cells was maintained in the normal ranges. Diagnosis of X-SCID was established by DNA analysis of the interleukin (IL)-2 receptor gamma chain gene; namely, we detected the novel mutation within exon 2 (221 C-->A), which leads to the substitution of tyrosine codon for stop codon (Y69stop). Computed tomography of the brain revealed mild atrophy, but no hemorrhage and no malformation. There were no pathological findings in the cerebrospinal fluid. Thus, the cause of opisthotonic posturing remains unknown. The patient died due to severe infection at the age of 7 months. It remains to be investigated to clarify the relationship between the mutation and clinical manifestations. In conclusion, we have identified the novel mutation in the IL-2 receptor gamma chain gene, which is associated with X-SCID. Furthermore, this is the first report that describes the patient with X-SCID accompanying opisthotonus.

Skin infiltration of CD56brightCD16-natural killer cells in a case of X-SCID with Omenn syndrome-like manifestations

We observed a patient with X-linked severe combined immunodeficiency (X-SCID) with Omenn syndrome-like manifestations. X-linked inheritance, absence of CD132 expression and impaired response to interleukin-2 (IL-2) indicated that the case is typical of X-SCID due to gamma(c) defect. However, this case was unusual in that circulating natural killer (NK) cells were increased and nearly half of these NK cells exhibited the CD56(bright) CD16(-) phenotype. A missense mutation was found within exon 5 of the IL2RG gene. The identical mutation was detected within NK, CD4(+) T and B cells. Engraftment of maternally derived NK cells or gene reversion was ruled out. The erythroderma-like skin lesion was characterized by infiltration of the dermis by CD56(bright) NK cells admixed with CD1a(+) dendritic cells (DC). Expression of mRNA for inflammatory cytokines was significantly enhanced within the skin. This may be the first human case to demonstrate that close cell-to-cell contact between DC and NK cells provides an effective alternative pathway for NK cell differentiation/activation in vivo.

Application of HSVtk suicide gene to X-SCID gene therapy: ganciclovir treatment offsets gene corrected X-SCID B cells

Recently, a serious adverse effect of uncontrolled clonal T cell proliferation due to insertional mutagenesis of retroviral vector was reported in X-SCID gene therapy clinical trial. To offset the side effect, we have incorporated a suicide gene into therapeutic retroviral vector for selective elimination of transduced cells. In this study, B-cell lines from two X-SCID patients were transduced with bicistronic retroviral vector carrying human gamma c chain cDNA and Herpes simplex virus thymidine kinase gene. After confirmation of functional reconstitution of the gamma c chain, the cells were treated with ganciclovir (GCV). The gamma c chain positive cells were eliminated under low concentration without cytotoxicity on untransduced cells and have not reappeared at least for 5 months. Furthermore, the gamma c chain transduced cells were still sensitive to GCV after five months. These results demonstrated the efficacy of the suicide gene therapy although further in vivo studies are required to assess feasibility of this approach in clinical trial.

Mutation analysis should be performed to rule out gammac deficiency in children with functional severe combined immune deficiency despite apparently normal immunologic tests

To study the correlation between genotype and phenotype in x-linked SCID, we have characterized the presentation of 2 unrelated patients. Both had infections suggestive of immunodeficiency, but their immune function and lymphoid tissues were normal. They were found to have an identical R222C mutation in the gammac gene.

X-linked severe combined immunodeficiency syndrome: the first Korean case with gamma c chain gene mutation and subsequent genetic counseling

X-linked severe combined immunodeficiency (X-SCID) is a rare, life-threatening immune disorder, caused by mutations in the gamma c chain gene, which encodes an essential component of the cytokine receptors for interleukin-2 (IL-2), IL-4, IL-7, IL-9, IL-15, and IL-21. A 13-month-old boy with recurrent infections who had reduced serum immunoglobulin levels and decreased numbers of CD3, CD16/56 cells was evaluated for gamma c chain gene mutation and protein expression. The patient had a C-to-T point mutation at nucleotide position 690, one of the hot spots, resulting in a single amino acid substitution of cysteine for arginine (R226C), as determined by direct sequencing and PCR-RFLP. The patient's mother was a heterozygous carrier. Percutaneous umbilical cord blood sampling was performed at the 6-month of gestation in a subsequent pregnancy. As the immunophenotype of the fetus showed an identical pattern, the pregnancy was terminated and genetic analysis of the abortus confirmed recurrence. This is the first report of the molecular diagnosis of X-SCID in Korea. Genetic analysis of the gamma c chain gene is useful for definite diagnosis and genetic counseling for X-SCID.

The role of common gamma chain in human monocytes in vivo; evaluation from the studies of X-linked severe combined immunodeficiency (X-SCID) carriers and X-SCID patients who underwent cord blood stem cell transplantation

Expression of common gamma chain (gammac) on monocytes was studied in five carriers of X-linked severe combined immunodeficiency (X-SCID) and two X-SCID patients who underwent cord blood stem cell transplantation (CBSCT). Flow cytometric analysis revealed that both gammac-negative and positive monocytes co-existed in X-SCID carriers, whereas no gammac-negative T, B or NK cells were observed in them. Clonal analysis and reverse transcription polymerase chain reaction studies revealed that 13.2-45.0% of monocytes from these carriers expressed the mutant gammac message. X-SCID patients who received CBSCT persistently possessed the majority of gammac-negative monocytes with a good clinical course. These results, together, may indicate that gammac is not essential for monocyte development/function in vivo.