XX T cells and XY B cells in two patients with severe combined immune deficiency

Chimerism in a child with severe combined immunodeficiency: a case report

Severe combined immunodeficiency (SCID) represents a group of rare, sometimes fatal, congenital disorders in which there is a combined absence of T-lymphocyte and B-lymphocyte function. Children with SCID die within two years of age, if untreated. The effective treatment for SCID is a hematopoietic stem cell transplantation (HSCT). It has been repeatedly described that in peripheral blood of infants with SCID maternal T cells can be found. Here we report a case of blood chimerism in a one-year-old boy with SCID.

Chimerism of murine fetal bone marrow by maternal cells occurs in late gestation and persists into adulthood

Studies of murine severe combined immune-deficient (scid/scid) fetuses gestating in transgene-tagged immune competent dams have established high frequencies of transplacental trafficking of nucleated maternal cells. Maternal cells first appeared in thymus at gestation day (gd) 12.5 and were present in more than 90% of late gestation fetuses. Morphologically heterogeneous maternal cells were located predominantly in bone marrow and thymus and also occasionally in liver, spleen, and nonlymphoid organs. We have now evaluated maternal cell chimerism in offspring with normal lymphoid development. Genetically normal blastocysts from random-bred CD1 mice were transferred to C57BL/6J- lacZ transgene-tagged ROSA26 females. Serial sectioning of fetuses followed by histochemistry for lacZ-expressing cells was used to comprehensively define organs containing maternal cells. Fetuses, sectioned in their entirety, had no detectable maternal cells before gd 16.5. Morphologically homogenous, nucleated maternal cells were first present in fetal bone marrow cavities at gd 16.5 and were evident in all offspring in later gestation. Postnatally, maternal cells were also present in bone marrow cavities into adulthood, as determined by lacZ histochemistry and PCR amplification of the maternal transgene. The frequency of maternally derived cells in postnatal bone marrow was increased compared with late gestation, and occasionally, maternal cells were detected in postnatal spleen. The normalcy of maternal cell transfer to genetically immune competent progeny and their long-term engraftment is suggestive of a functional role for maternal cells in offspring.

Transplacentally acquired maternal T lymphocytes in severe combined immunodeficiency: a study of 121 patients

A study in 121 infants with severe combined immunodeficiency (SCID) was performed to determine the prevalence of an engraftment by transplacentally acquired maternal T cells and to explore clinical and immunological findings related to this abnormality. Each newly diagnosed patient with SCID presenting with circulating T cells was evaluated for chimerism by performing selective HLA typing of T cells and non-T cells. In patients with engraftment, maternal T cells were characterized phenotypically and functionally, and results were correlated with clinical findings in the patients. Maternal T cells were detected in the circulation in 48 patients; these cells ranged from fewer than 100/microL in 14 cases to more than 2000/microL in 4 cases (median, 415/microL). Clinical signs of graft-versus-host disease (GVHD) were absent in 29 patients. In the other cases, manifestations of GVHD were present, involving the skin and in 14 cases also the liver. Skin GVHD was mild in 8 patients. In these patients, as well as in patients with no signs of GVHD, maternal T cells were predominantly CD8(+) and, with one exception, failed to respond to mitogen stimulation. In 9 patients, manifestations of skin GVHD were prominent. T cells in these cases were predominantly CD4(+) and responded, with one exception, to mitogen stimulation. In 8 of the cases with prominent skin GVHD, the underlying SCID variant was characterized by the absence of B cells. In this study, further understanding is provided of a phenomenon that is responsible for the significant heterogeneity of clinical and immunological findings in SCID.

Specific immunoglobulin E responses in ZAP-70-deficient patients are mediated by Syk-dependent T-cell receptor signalling

ZAP-70 deficiency is a rare primary immunodeficiency characterized by the absence of peripheral CD8+ T cells and defects in T-cell receptor (TCR) signalling. T cells in ZAP-70-deficient patients are assumed to have no helper functions for B-cell immunoglobulin synthesis, whereas the patients rarely have antigen-specific antibodies. We experienced a ZAP-70-deficient patient, who had immunoglobulin E (IgE) antibodies specific to food allergens, and we investigated the mechanisms of switching to IgE in the patient. Peripheral blood mononuclear cells from the patient did not proliferate upon stimulation with the antigens but produced distinct levels of interleukin-4 (IL-4). Cell sorting analysis indicated that the cells that produced IL-4 in response to the antigens were enriched in CD4+ T cells. Purified CD4+ T cells from the patient produced IL-4 and expressed CD40L upon stimulation with anti-CD3. Moreover, CD4+ T cells pretreated with anti-CD3 induced mature epsilon transcript on naive B cells. Since the results indicated that there remained sufficient T-cell receptor (TCR)-signalling in the patient's T cells to exert antigen-specific IgE switching on B cells, we next investigated the expression of the ZAP-70-homologous kinase Syk. Syk was present in high levels in patient's CD4+ T cells and was tyrosine-phosphorylated after TCR stimulation. Inhibition of Syk by piceatannol resulted in decreased production of IL-4 and expression of CD40L on patient's CD4+ T cells. Moreover, Syk was expressed on all human T-cell leukaemia virus (HTLV-1)-transformed T-cell lines derived from peripheral blood of the patient, whereas it was low or undetectable in control lines. It was therefore concluded that specific IgE responses in the patient were most likely to be mediated by Syk-dependent TCR-signalling.

Acute graft-versus-host disease with unusual cutaneous intracellular vacuolation in an infant with severe combined immunodeficiency

We report an infant with severe combined immunodeficiency (SCID) who had cutaneous manifestations of acute graft-versus-host disease (GVHD) due to maternofetal lymphocyte engraftment. Histologic and ultrastructural examinations of the skin revealed intracellular vacuoles resembling lipid droplets in the epidermis and dermis, which is not a recognized feature of acute GVHD or SCID.

In utero acute graft-versus-host disease in a neonate with severe combined immunodeficiency

We describe a male neonate with severe combined immunodeficiency who at birth had acute graft-versus-host disease (GVHD) as a result of maternal-fetal transfusion during pregnancy. Several clinical signs helped establish this diagnosis. Findings of a skin biopsy specimen confirmed the diagnosis of acute GVHD. Immunologic evaluation disclosed an absence of T and B lymphocytes. Acute GVHD in severe combined immunodeficiency most often occurs during the first weeks of life; intrauterine occurrence is unusual.

X-linked severe combined immunodeficiency

Between a third and half of all males with SCID and no family history of immunodeficiency represent the first manifestation in their family of a new mutation of the gene that causes X-linked SCID. These patients, like boys with a positive family history of X-linked SCID, have markedly reduced numbers of T cells, elevated numbers of B cells, and hypogammaglobulinemia. The hypogammaglobulinemia is due, at least in part, to the expression of the gene defect in B cells as well as in T cells. Patients with X-linked SCID who are treated with bone marrow transplant tend to engraft T cells readily but they do not engraft B cells unless they are treated with cytoreductive therapy prior to transplant. B-cell function after transplant tends to be poor, even in patients who have received transplants from HLA matched siblings. Better transplant strategies are required to achieve optimum long-term results in patients with X-linked SCID.

Combined immunodeficiency due to the selective absence of CD4 inducer T lymphocytes

Selective congenital deficiency of the CD4 inducer T lymphocyte subset is a recently described variant of combined immunodeficiency. To further characterize the cellular and molecular mechanisms which lead to the profound T and B cell immunodeficiency in this condition, we examined in vitro immunoregulatory T lymphocyte activation and effector function, interleukin-2 (IL-2) synthesis, IL-2 receptor generation, and CD4 gene structure. Immunophenotyping of T lymphocytes demonstrated a selective deficiency of CD4+ cells, with normal numbers of CD2+ and CD3+ T cells, nearly all of which expressed the CD8+ determinant. Mitogen- and alloantigen-induced blastogenesis was profoundly decreased. B lymphocytes were present in normal numbers but there was a functional dysgammaglobulinemia (low IgG, normal IgM, low IgA) with no antibody response to in vivo immunization. T cells from the patient did not provide help to normal B cells for in vitro immunoglobulin synthesis; however, the patient's B cells were capable of synthesizing normal amounts of IgG when provided help from normal T cells. Concanavalin A failed to activate suppressor-inducer function in the patient's T cells. However, CD8+ T cell-mediated suppression was expressed if the patients T cells were cocultured with normal CD4+ T cells in a pokeweed mitogen-stimulated IgG secretion assay. IL-2 secretion and IL-2 receptor expression were both markedly reduced. Southern blot analysis of genomic DNA revealed no obvious abnormality in CD4 gene structure. The global defects in T cell activation, effector function, immunoregulation, and lymphokine generation observed in CD4+ inducer lymphocyte deficiency emphasizes the central role that the CD4 T lymphocyte plays in the activation and regulation in vivo immune responses.

X-linked severe combined immunodeficiency. Diagnosis in males with sporadic severe combined immunodeficiency and clarification of clinical findings

Over 80% of infants with severe combined immunodeficiency (SCID) of unknown genetic etiology are males, yet less than a third of these affected males have a family history of X-linked disease. To help identify new mutations of the X-linked SCID gene and to provide genetic counseling, X chromosome inactivation patterns in T cells from 16 women who had sons with sporadic SCID were examined. Between 9 and 35 human/hamster hybrids that selectively retained the active human X chromosome were produced from the T cells of each woman and analyzed with an X-linked restriction fragment length polymorphism for which the woman in question was heterozygous. Exclusive use of a single X as the active X was seen in the T cell hybrids from 7 of the 16 women, identifying these women as carriers of X-linked SCID. Studies on additional family members confirmed the mutant nature of the inactive X and revealed the source of the new mutation in three families. To determine whether there were any laboratory characteristics that might differentiate the boys whose mothers were identified as carriers of X-linked SCID from those whose mothers were not, the clinical records of both groups were compared to each other and to a group of 14 boys with a family history of X-linked SCID. The most consistent finding in the 21 patients with X-linked SCID was an elevated proportion of B cells. These data demonstrate the high incidence of spontaneous mutation for the X-linked SCID gene and help clarify the characteristic presenting features of this disorder.

X-linked severe combined immunodeficiency in the dog

This study documents the occurrence of a form of X-linked severe combined immunodeficiency (SCID) in the dog with clinical, immunologic, and pathologic features similar to those of X-linked SCID with B cells in man. The disease in the dog is characterized by growth retardation and increased susceptibility to bacterial and viral infections in young pups. Affected pups have all died or were euthanatized by 5 months with signs of canine distemper, infectious hepatitis, or bacterial pneumonia. Laboratory findings include normal numbers of circulating B lymphocytes and normal concentrations of serum IgM, but low to absent concentrations of serum IgG and IgA, indicating a defect in the terminal differentiation of IgG and IgA B cells into immunoglobulin-secreting plasma cells. This is supported by the failure of peripheral lymphocytes to produce IgG or IgA plaque-forming cells in response to polyclonal activation. There are low-to-normal numbers of circulating T cells, but a severely depressed blastogenic response to T cell mitogens. Postmortem findings include thymic dysplasia and hypoplasia of lymphoid tissue. Family studies and breeding experiments are consistent with an X-linked recessive mode of inheritance.

Carrier detection in X-linked severe combined immunodeficiency based on patterns of X chromosome inactivation

The X-linked form of severe combined immunodeficiency (XSCID) is underdiagnosed because no methods have been available for detecting carriers. Although boys with XSCID are deficient in T cells, female carriers are immunologically normal. Carriers' normal immune function would be expected if all their T cells were derived from precursors whose X chromosome bearing the XSCID mutation was inactivated early in embryogenesis. Using somatic cell hybridization to separate the active and inactive X chromosomes and restriction fragment length polymorphisms to distinguish them, we have determined the lymphocyte X inactivation pattern in XSCID carriers and their female relatives. In the T cells of three carriers, the X chromosome bearing the XSCID mutation was consistently inactive. Nonrandom X inactivation was also found in the T cells of one at-risk female, while two others had normal, random X inactivation. This method constitutes a generally applicable carrier test for XSCID.

Metabolic defects in severe combined immunodeficiency in man and animals

Severe combined immunodeficiency (SCID) was originally thought to be one disease. Accumulating evidence indicates that SCID is a heterogeneous group of diseases that are clinically similar but are caused by quite different biochemical abnormalities. The best-studied form of SCID is that associated with an autosomal recessive inheritance pattern of adenosine deaminase (ADA) deficiency. Several biochemical mechanisms have been postulated to explain how a deficiency of ADA causes immune dysfunction. In forms of SCID not associated with ADA deficiency, other biochemical abnormalities have been detected. These abnormalities include deficiency in biotin-dependent carboxylases, alteration in lymphocyte surface membranes and irregularities in cytokine production. Two animal models for SCID now exist. Neither of these models is associated with ADA deficiency. Evidence for a possible defect in purine metabolism in one model has been demonstrated.