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

Cooperative Armoring of CAR and TCR T Cells by T Cell-Restricted IL15 and IL21 Universally Enhances Solid Tumor Efficacy

PURPOSE

Chimeric antigen receptor (CAR) and T-cell receptor (TCR) T-cell therapies are effective in a subset of patients with solid tumors, but new approaches are needed to universally improve patient outcomes. Here, we developed a technology to leverage the cooperative effects of IL15 and IL21, two common cytokine-receptor gamma chain family members with distinct, pleiotropic effects on T cells and other lymphocytes, to enhance the efficacy of adoptive T cells.

EXPERIMENTAL DESIGN

We designed vectors that induce the constitutive expression of either membrane-tethered IL15, IL21, or IL15/IL21. We used clinically relevant preclinical models of transgenic CARs and TCRs against pediatric and adult solid tumors to determine the effect of the membrane-tethered cytokines on engineered T cells for human administration.

RESULTS

We found that self-delivery of these cytokines by CAR or TCR T cells prevents functional exhaustion by repeated stimulation and limits the emergence of dysfunctional natural killer (NK)-like T cells. Across different preclinical murine solid tumor models, we observed enhanced regression with each individual cytokine but the greatest antitumor efficacy when T cells were armored with both.

CONCLUSIONS

The coexpression of membrane-tethered IL15 and IL21 represents a technology to enhance the resilience and function of engineered T cells against solid tumors and could be applicable to multiple therapy platforms and diseases. See related commentary by Ruffin et al., p. 1431.

X chromosome inactivation skewing is common in advanced carotid atherosclerotic lesions in females and predicts secondary peripheral artery events

BACKGROUND AND AIM

Sex differences in atherosclerosis have been described with female plaques being mostly perceived as stable and fibrous. Sex-specific mechanisms such as mosaic loss of the Y chromosome in men have been linked to cardiovascular health. In women, X-linked mechanisms such as X chromosome inactivation (XCI) skewing is common in several tissues. Yet, information on the role of XCI in female atherosclerotic plaques is lacking. Here, we investigated the presence of XCI skewing in advanced atherosclerotic lesions and its association with cardiovascular risk factors, histological plaque data, and clinical data.

METHODS

XCI skewing was quantified in 154 atherosclerotic plaque and 55 blood DNA samples of women included in the Athero-Express study. The skewing status was determined performing the HUMARA assay. Then, we studied the relationship of XCI skewing in female plaque and cardiovascular risk factors using regression models. In addition, we studied if plaque XCI predicted plaque composition, and adverse events during 3-years follow-up using Cox proportional hazard models.

RESULTS

XCI skewing was detected in 76 of 154 (49.4%) plaques and in 27 of 55 (67%) blood samples. None of the clinical risk factors were associated with plaque skewing. Plaque skewing was more often detected in plaques with a plaque hemorrhage (OR [95% CI]: 1.44 [1.06-1.98], P = 0.02). Moreover, skewed plaques were not associated with a higher incidence of composite and major events but were specifically associated with peripheral artery events during a 3-year follow-up period in a multivariate model (HR [95%CI]: 1.46 [1.09-1.97]; P = 0.007).

CONCLUSIONS

XCI skewing is common in carotid plaques of females and is predictive for the occurrence of peripheral artery events within 3 years after carotid endarterectomy.

Renal X-inactivation in female individuals with X-linked Alport syndrome primarily determined by age

X-linked Alport syndrome (AS) caused by hemizygous disease-causing variants in COL4A5 primarily affects males. Females with a heterozygous state show a diverse phenotypic spectrum ranging from microscopic hematuria to end-stage kidney disease (ESKD) and extrarenal manifestations. In other X-linked diseases, skewed X-inactivation leads to preferential silencing of one X-chromosome and thus can determine the phenotype in females. We aimed to show a correlation between X-inactivation in blood and urine-derived renal cells and clinical phenotype of females with a heterozygous disease-causing variant in COL4A5 compared to healthy controls. A total of 56 females with a heterozygous disease-causing COL4A5 variant and a mean age of 31.6 ± 18.3 SD years were included in this study. A total of 94% had hematuria, 62% proteinuria >200 mg/day, yet only 7% had decreased eGFR. Using human androgen receptor assay X-inactivation was examined in blood cells of all 56 individuals, in urine-derived cells of 27 of these individuals and in all healthy controls. X-inactivation did not correlate with age of first manifestation, proteinuria or eGFR neither in blood, nor in urine. The degree of X-inactivation showed a moderate association with age, especially in urine-derived cells of the patient cohort (rho = 0.403, p = 0.037). Determination of X-inactivation allelity revealed a shift of X-inactivation toward the COL4A5 variant bearing allele. This is the first study examining X-inactivation of urine-derived cells from female individuals with AS. A correlation between phenotype and X-inactivation could not be observed suspecting other genetic modifiers shaping the phenotype in female individuals with AS. The association of X-inactivation with age in urine-derived cells suggests an escape-mechanism inactivating the COL4A5 variant carrying allele in female individuals with AS.

BEXCIS: Bayesian methods for estimating the degree of the skewness of X chromosome inactivation

Background

X chromosome inactivation (XCI) is an epigenetic phenomenon that one of two X chromosomes in females is transcriptionally silenced during early embryonic development. Skewed XCI has been reported to be associated with some X-linked diseases. There have been several methods measuring the degree of the skewness of XCI. However, these methods may still have several limitations.

Results

We propose a Bayesian method to obtain the point estimate and the credible interval of the degree of XCI skewing by incorporating its prior information of being between 0 and 2. We consider a normal prior and a uniform prior for it (respectively denoted by BN and BU). We also propose a penalized point estimate based on the penalized Fieller’s method and derive the corresponding confidence interval. Simulation results demonstrate that the BN and BU methods can solve the problems of extreme point estimates, noninformative intervals, empty sets and discontinuous intervals. The BN method generally outperforms other methods with the lowest mean squared error in the point estimation, and well controls the coverage probability with the smallest median and the least variation of the interval width in the interval estimation. We apply all the methods to the Graves’ disease data and the Minnesota Center for Twin and Family Research data, and find that SNP rs3827440 in the Graves’ disease data may undergo skewed XCI towards the allele C.

Conclusions

We recommend the BN method for measuring the degree of the skewness of XCI in practice. The R package BEXCIS is publicly available at https://github.com/Wen-YiYu/BEXCIS.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12859-022-04721-y.

Maternal germline factors associated with aneuploid pregnancy loss: a systematic review

BACKGROUND

Miscarriage describes the spontaneous loss of pregnancy before the threshold of viability; the vast majority occur before 12 weeks of gestation. Miscarriage affects one in four couples and is the most common complication of pregnancy. Chromosomal abnormalities of the embryo are identified in ∼50% of first trimester miscarriages; aneuploidy accounts for 86% of these cases. The majority of trisomic miscarriages are of maternal origin with errors occurring during meiotic division of the oocytes. Chromosome segregation errors in oocytes may be sporadic events secondary to advancing maternal age; however, there is increasing evidence to suggest possible maternal germline contributions to this.

OBJECTIVE AND RATIONALE

The objective of this review was to appraise critically the existing evidence relating to maternal germline factors associated with pregnancy loss secondary to embryo aneuploidy, identify limitations in the current evidence base and establish areas requiring further research.

SEARCH METHODS

The initial literature search was performed in September 2019 and updated in January 2021 using the electronic databases OVID MEDLINE, EMBASE and the Cochrane Library. No time or language restrictions were applied to the searches and only primary research was included. Participants were women who had suffered pregnancy loss secondary to numerical chromosomal abnormalities of the embryo. Study identification and subsequent data extraction were performed by two authors independently. The Newcastle-Ottawa Scale was used to judge the quality of the included studies. The results were synthesized narratively.

OUTCOMES

The literature search identified 2198 titles once duplicates were removed, of which 21 were eligible for inclusion in this systematic review. They reported on maternal germline factors having variable degrees of association with pregnancy loss of aneuploid origin. The Online Mendelian Inheritance in Man (OMIM) gene ontology database was used as a reference to establish the functional role currently attributed to the genes reported. The majority of the cases reported and included were secondary to the inheritance of maternal structural factors such as Robertsonian translocations, deletions and insertions. Germline factors with a plausible role in aneuploid pregnancy loss of maternal origin included skewed X-inactivation and CGG repeats in the fragile X mental retardation (FMR1) gene. Studies that reported the association of single gene mutations with aneuploid pregnancy loss were conflicting. Single gene mutations with an uncertain or no role in aneuploid pregnancy loss included mutations in synaptonemal complex protein 3 (SYCP3), mitotic polo-like kinase 4 (PLK4) and meiotic stromal antigen 3 (STAG3) spindle integrity variants and 5,10-methylenetetrahydrofolate reductase (MTHFR).

WIDER IMPLICATIONS

Identifying maternal genetic factors associated with an increased risk of aneuploidy will expand our understanding of cell division, non-disjunction and miscarriage secondary to embryo aneuploidy. The candidate germline factors identified may be incorporated in a screening panel for women suffering miscarriage of aneuploidy aetiology to facilitate counselling for subsequent pregnancies.

Generation of knockout rabbits with X-linked severe combined immunodeficiency (X-SCID) using CRISPR/Cas9

Severe immunodeficient mice are widely used to examine human and animal cells behaviour in vivo. However, mice are short-lived and small in size; while large animals require specific large-scale equipment. Rabbits are also commonly employed as experimental models and are larger than mice or rats, easy to handle, and suitable for long-term observational and pre-clinical studies. Herein, we sought to develop and maintain stable strains of rabbits with X-linked severe combined immunodeficiency (X-SCID) via the CRISPR/Cas9 system targeting Il2rg. Consequently, X-SCID rabbits presented immunodeficient phenotypes including the loss of T and B cells and hypoplasia of the thymus. Further, these rabbits exhibited a higher success rate with engraftments upon allogeneic transplantation of skin tissue than did wild type controls. X-SCID rabbits could be stably maintained for a minimum of four generations. These results indicate that X-SCID rabbits are effective animals for use in a non-rodent model of severe immunodeficiency.

Heritability of skewed X-inactivation in female twins is tissue-specific and associated with age

Female somatic X-chromosome inactivation (XCI) balances the X-linked transcriptional dosages between the sexes. Skewed XCI toward one parental X has been observed in several complex human traits, but the extent to which genetics and environment influence skewed XCI is largely unexplored. To address this, we quantify XCI-skew in multiple tissues and immune cell types in a twin cohort. Within an individual, XCI-skew differs between blood, fat and skin tissue, but is shared across immune cell types. XCI skew increases with age in blood, but not other tissues, and is associated with smoking. XCI-skew is increased in twins with Rheumatoid Arthritis compared to unaffected identical co-twins. XCI-skew is heritable in blood of females >55 years old (h² = 0.34), but not in younger individuals or other tissues. This results in a Gene x Age interaction that shifts the functional dosage of all X-linked heterozygous loci in a tissue-restricted manner.

Skewing of X chromosome inactivation (XCI) occurs when the silencing of one parental X chromosome is non-random. Here, Zito et al. report XCI patterns in lymphoblastoid cell lines, blood, subcutaneous adipose tissue samples and skin samples of monozygotic and dizygotic twins and find XCI skew to associate with tissue and age.

Demonstration of a novel Xp22.2 microdeletion as the cause of familial extreme skewing of X-inactivation utilizing case-parent trio SNP microarray analysis

Background

We report a kindred referred for molecular investigation of severe hemophilia A in a young female in which extremely skewed X‐inactivation was observed in both the proband and her clinically normal mother.

Methods

Bidirectional Sanger sequencing of all F8 gene coding regions and exon/intron boundaries was undertaken. Methylation‐sensitive restriction enzymes were utilized to investigate skewed X‐inactivation using both a classical human androgen receptor (HUMARA) assay, and a novel method targeting differential methylation patterns in multiple informative X‐chromosome SNPs. Illumina Whole‐Genome Infinium microarray analysis was performed in the case‐parent trio (proband and both parents), and the proband's maternal grandmother.

Results

The proband was a cytogenetically normal female with severe hemophilia A resulting from a heterozygous F8 pathogenic variant inherited from her similarly affected father. No F8 mutation was identified in the proband's mother, however, both the proband and her mother both demonstrated completely skewed X‐chromosome inactivation (100%) in association with a previously unreported 2.3 Mb deletion at Xp22.2. At least three disease‐associated genes (FANCB,AP1S2, and PIGA) were contained within the deleted region.

Conclusions

We hypothesize that true “extreme” skewing of X‐inactivation (≥95%) is a rare occurrence, but when defined correctly there is a high probability of finding an X‐chromosome disease‐causing variant or larger deletion resulting in X‐inactivation through a survival disadvantage or cell lethal mechanism. We postulate that the 2.3 Mb Xp22.2 deletion identified in our kindred arose de novo in the proband's mother (on the grandfather's homolog), and produced extreme skewing of X‐inactivation via a “cell lethal” mechanism. We introduce a novel multitarget approach for X‐inactivation analysis using multiple informative differentially methylated SNPs, as an alternative to the classical single locus (HUMARA) method. We propose that for females with unexplained severe phenotypic expression of an X‐linked recessive disorder trio‐SNP microarray should be undertaken in combination with X‐inactivation analysis.

Role of Bruton's tyrosine kinase in B cells and malignancies

Bruton’s tyrosine kinase (BTK) is a non-receptor kinase that plays a crucial role in oncogenic signaling that is critical for proliferation and survival of leukemic cells in many B cell malignancies. BTK was initially shown to be defective in the primary immunodeficiency X-linked agammaglobulinemia (XLA) and is essential both for B cell development and function of mature B cells. Shortly after its discovery, BTK was placed in the signal transduction pathway downstream of the B cell antigen receptor (BCR). More recently, small-molecule inhibitors of this kinase have shown excellent anti-tumor activity, first in animal models and subsequently in clinical studies. In particular, the orally administered irreversible BTK inhibitor ibrutinib is associated with high response rates in patients with relapsed/refractory chronic lymphocytic leukemia (CLL) and mantle-cell lymphoma (MCL), including patients with high-risk genetic lesions. Because ibrutinib is generally well tolerated and shows durable single-agent efficacy, it was rapidly approved for first-line treatment of patients with CLL in 2016. To date, evidence is accumulating for efficacy of ibrutinib in various other B cell malignancies. BTK inhibition has molecular effects beyond its classic role in BCR signaling. These involve B cell-intrinsic signaling pathways central to cellular survival, proliferation or retention in supportive lymphoid niches. Moreover, BTK functions in several myeloid cell populations representing important components of the tumor microenvironment. As a result, there is currently a considerable interest in BTK inhibition as an anti-cancer therapy, not only in B cell malignancies but also in solid tumors. Efficacy of BTK inhibition as a single agent therapy is strong, but resistance may develop, fueling the development of combination therapies that improve clinical responses. In this review, we discuss the role of BTK in B cell differentiation and B cell malignancies and highlight the importance of BTK inhibition in cancer therapy.

Exome sequence identified a c.320A > G ALG13 variant in a female with infantile epileptic encephalopathy with normal glycosylation and random X inactivation: Review of the literature

Congenital Disorders of Glycosylation (CDG) are new and rapidly expanding neurometabolic disorders with multisystem involvements, broad phenotypic manifestations, and variable severity. The majority results from a defect of one of the steps involved with protein or lipid N-glycosylation pathway. Almost all are inherited in autosomal recessive patterns with a few exceptions such as the X-linked ALG13. Mutations of ALG13 are reported, so far in only 10 patients, all were ascertained through exome/genome sequencing. Specifically, the ALG13 c.320A > G (p.Asn107Ser) variant was reported only in females and in all were de novo mutations. These findings may suggest an X-linked dominant inheritance of this mutation with embryonic male lethality. These patients presented with severe infantile epileptic encephalopathy, global developmental delay, and multisystem abnormalities. Only two of these females had glycosylation studies done, and both showed normal pattern of glycosylated serum transferrin isoforms, and none had their X-chromosome inactivation patterns studied. Here, we report on another female patient who is heterozygous for the same ALG13 c.320A > G (p.Asn107Ser) variant. She presented with infantile spasms, epileptic encephalopathy, hypsarrhythmia, hypotonia, developmental delay, intellectual disability, abnormal coagulation profile, feeding problems, hypotonia, and dysmorphic features. The diagnosis of CGD was suspected clinically, but glycosylation studies were done twice and showed normal patterns on both occasions. Her X-inactivation study was also done and, surprisingly, showed a random pattern of X-inactivation, with no evidence of skewness.

The common γ-chain cytokine receptor: tricks-and-treats for T cells

Originally identified as the third subunit of the high-affinity IL-2 receptor complex, the common γ-chain (γc) also acts as a non-redundant receptor subunit for a series of other cytokines, collectively known as γc family cytokines. γc plays essential roles in T cell development and differentiation, so that understanding the molecular basis of its signaling and regulation is a critical issue in T cell immunology. Unlike most other cytokine receptors, γc is thought to be constitutively expressed and limited in its function to the assembly of high-affinity cytokine receptors. Surprisingly, recent studies reported a series of findings that unseat γc as a simple housekeeping gene, and unveiled γc as a new regulatory molecule in T cell activation and differentiation. Cytokine-independent binding of γc to other cytokine receptor subunits suggested a pre-association model of γc with proprietary cytokine receptors. Also, identification of a γc splice isoform revealed expression of soluble γc proteins (sγc). sγc directly interacted with surface IL-2Rβ to suppress IL-2 signaling and to promote pro-inflammatory Th17 cell differentiation. As a result, endogenously produced sγc exacerbated autoimmune inflammatory disease, while the removal of endogenous sγc significantly ameliorated disease outcome. These data provide new insights into the role of both membrane and soluble γc in cytokine signaling, and open new venues to interfere and modulate γc signaling during immune activation. These unexpected discoveries further underscore the perspective that γc biology remains largely uncharted territory that invites further exploration.

Understanding the Complex Circuitry of lncRNAs at the X-inactivation Center and Its Implications in Disease Conditions

Balanced gene expression is a high priority in order to maintain optimal functioning since alterations and variations could result in acute consequences. X chromosome inactivation (X-inactivation) is one such strategy utilized by mammalian species to silence the extra X chromosome in females to uphold a similar level of expression between the two sexes. A functionally versatile class of molecules called long noncoding RNA (lncRNA) has emerged as key regulators of gene expression and plays important roles during development. An lncRNA that is indispensable for X-inactivation is X-inactive specific transcript (Xist), which induces a repressive epigenetic landscape and creates the inactive X chromosome (Xi). With recent advents in the field of X-inactivation, novel positive and negative lncRNA regulators of Xist such as Jpx and Tsix, respectively, have broadened the regulatory network of X-inactivation. Xist expression failure or dysregulation has been implicated in producing developmental anomalies and disease states. Subsequently, reactivation of the Xi at a later stage of development has also been associated with certain tumors. With the recent influx of information about lncRNA biology and advancements in methods to probe lncRNA, we can now attempt to understand this complex network of Xist regulation in development and disease. It has become clear that the presence of an extra set of genes could be fatal for the organism. Only by understanding the precise ways in which lncRNAs function can treatments be developed to bring aberrations under control. This chapter summarizes our current understanding and knowledge with regard to how lncRNAs are orchestrated at the X-inactivation center (Xic), with a special focus on how genetic diseases come about as a consequence of lncRNA dysregulation.

Genetic architecture of skewed X inactivation in the laboratory mouse

X chromosome inactivation (XCI) is the mammalian mechanism of dosage compensation that balances X-linked gene expression between the sexes. Early during female development, each cell of the embryo proper independently inactivates one of its two parental X-chromosomes. In mice, the choice of which X chromosome is inactivated is affected by the genotype of a cis-acting locus, the X-chromosome controlling element (Xce). Xce has been localized to a 1.9 Mb interval within the X-inactivation center (Xic), yet its molecular identity and mechanism of action remain unknown. We combined genotype and sequence data for mouse stocks with detailed phenotyping of ten inbred strains and with the development of a statistical model that incorporates phenotyping data from multiple sources to disentangle sources of XCI phenotypic variance in natural female populations on X inactivation. We have reduced the Xce candidate 10-fold to a 176 kb region located approximately 500 kb proximal to Xist. We propose that structural variation in this interval explains the presence of multiple functional Xce alleles in the genus Mus. We have identified a new allele, Xce^e present in Mus musculus and a possible sixth functional allele in Mus spicilegus. We have also confirmed a parent-of-origin effect on X inactivation choice and provide evidence that maternal inheritance magnifies the skewing associated with strong Xce alleles. Based on the phylogenetic analysis of 155 laboratory strains and wild mice we conclude that Xce^a is either a derived allele that arose concurrently with the domestication of fancy mice but prior the derivation of most classical inbred strains or a rare allele in the wild. Furthermore, we have found that despite the presence of multiple haplotypes in the wild Mus musculus domesticus has only one functional Xce allele, Xce^b. Lastly, we conclude that each mouse taxa examined has a different functional Xce allele.

Although mammalian females have two X chromosomes in each cell, only one is functional, while gene expression from the other is silenced through a process called X chromosome inactivation. Little is known about the early stages of this process including how one parental X chromosome is inactivated over the other on a cell-by-cell basis. It has been shown, however, that certain inbred mouse strains are functionally different at a locus that controls this choice that provides an opportunity to identify the locus and determine its molecular mechanism. This has been the goal of many researchers over the past 40 years with incremental success. Here we took advantage of new mouse genotype and whole genome sequencing data to pinpoint the locus controlling choice. Our results identified a smaller region on the X chromosome that contains large duplicated sequences. We propose an explanation for multiple functional alleles in mouse and provide insight into the possible molecular mechanism of X chromosome inactivation choice. Our evolutionary analysis reveals why functional diversity at this locus appears to be common in laboratory mice and offers an explanation as to why we do not see this level of diversity in humans.

Il2rg gene-targeted severe combined immunodeficiency pigs

A porcine model of severe combined immunodeficiency (SCID) promises to facilitate human cancer studies, the humanization of tissue for xenotransplantation, and the evaluation of stem cells for clinical therapy, but SCID pigs have not been described. We report here the generation and preliminary evaluation of a porcine SCID model. Fibroblasts containing a targeted disruption of the X-linked interleukin-2 receptor gamma chain gene, Il2rg, were used as donors to generate cloned pigs by serial nuclear transfer. Germline transmission of the Il2rg deletion produced healthy Il2rg(+/-) females, while Il2rg(-/Y) males were athymic and exhibited markedly impaired immunoglobulin and T and NK cell production, robustly recapitulating human SCID. Following allogeneic bone marrow transplantation, donor cells stably integrated in Il2rg(-/Y) heterozygotes and reconstituted the Il2rg(-/Y) lymphoid lineage. The SCID pigs described here represent a step toward the comprehensive evaluation of preclinical cellular regenerative strategies.

Expansion of somatically reverted memory CD8+ T cells in patients with X-linked lymphoproliferative disease caused by selective pressure from Epstein-Barr virus

In patients with XLP, a primary immunodeficiency caused by mutations in SH2D1A, EBV infection can lead to somatic reversion of the disease-causing mutation selectively in effector memory CD8 T cells; reverted CD8 cells are better able to respond to and kill EBV-infected cells.

Patients with the primary immunodeficiency X-linked lymphoproliferative disease (XLP), which is caused by mutations in SH2D1A, are highly susceptible to Epstein-Barr virus (EBV) infection. Nonetheless, some XLP patients demonstrate less severe clinical manifestations after primary infection. SH2D1A encodes the adaptor molecule SLAM-associated protein (SAP), which is expressed in T and natural killer cells and is required for cytotoxicity against B cells, the reservoir for EBV. It is not known why the clinical presentation of XLP is so variable. In this study, we report for the first time the occurrence of somatic reversion in XLP. Reverted SAP-expressing cells resided exclusively within the CD8⁺ T cell subset, displayed a CD45RA⁻CCR7⁻ effector memory phenotype, and were maintained at a stable level over time. Importantly, revertant CD8⁺ SAP⁺ T cells, but not SAP⁻ cells, proliferated in response to EBV and killed EBV-infected B cells. As somatic reversion correlated with EBV infection, we propose that the virus exerts a selective pressure on the reverted cells, resulting in their expansion in vivo and host protection against ongoing infection.

Molecular pathogenesis of EBV susceptibility in XLP as revealed by analysis of female carriers with heterozygous expression of SAP

X-linked lymphoproliferative disease (XLP) is a primary immunodeficiency caused by mutations in SH2D1A which encodes SAP. SAP functions in signalling pathways elicited by the SLAM family of leukocyte receptors. A defining feature of XLP is exquisite sensitivity to infection with EBV, a B-lymphotropic virus, but not other viruses. Although previous studies have identified defects in lymphocytes from XLP patients, the unique role of SAP in controlling EBV infection remains unresolved. We describe a novel approach to this question using female XLP carriers who, due to random X-inactivation, contain both SAP(+) and SAP(-) cells. This represents the human equivalent of a mixed bone marrow chimera in mice. While memory CD8(+) T cells specific for CMV and influenza were distributed across SAP(+) and SAP(-) populations, EBV-specific cells were exclusively SAP(+). The preferential recruitment of SAP(+) cells by EBV reflected the tropism of EBV for B cells, and the requirement for SAP expression in CD8(+) T cells for them to respond to Ag-presentation by B cells, but not other cell types. The inability of SAP(-) clones to respond to Ag-presenting B cells was overcome by blocking the SLAM receptors NTB-A and 2B4, while ectopic expression of NTB-A on fibroblasts inhibited cytotoxicity of SAP(-) CD8(+) T cells, thereby demonstrating that SLAM receptors acquire inhibitory function in the absence of SAP. The innovative XLP carrier model allowed us to unravel the mechanisms underlying the unique susceptibility of XLP patients to EBV infection in the absence of a relevant animal model. We found that this reflected the nature of the Ag-presenting cell, rather than EBV itself. Our data also identified a pathological signalling pathway that could be targeted to treat patients with severe EBV infection. This system may allow the study of other human diseases where heterozygous gene expression from random X-chromosome inactivation can be exploited.

Mutations causing severe combined immunodeficiency: detection with a custom resequencing microarray

PURPOSE

Mutation diagnosis of severe combined immunodeficiency is challenging because of the multiplicity of disease genes and large number of disease-causing mutations, including unique ones that continue to be found. A resequencing microarray could facilitate mutation detection, increasing the chance of diagnosing infants early for optimal rescue by hematopoietic stem cell transplantation.

METHODS

After analyzing cumulative mutations, we developed a custom Affymetrix GeneChip microarray including probes representing exons and flanking regions of severe combined immunodeficiency disease genes. DNA samples were analyzed by array versus standard dideoxy genomic sequencing. We tested males and their mothers with X-linked IL2RG variants and patients and carriers with autosomal variants in IL7R, JAK3, and DCLRE1C.

RESULTS

New, unique severe combined immunodeficiency mutations are frequent. Resequencing array call rates of 95-98% exceeded GeneChip product specifications, and all of 47 point mutations in known samples were detected, as were the sites of 12 of 22 disease-causing insertions and deletions. Each gene had particular nucleotides that were often not called correctly and had to be excluded from analysis; exclusion rates ranged from 0.4% (hemizygous IL2RG) to 9.2% (heterozygous JAK3).

CONCLUSION

Microarray resequencing is a promising technology for severe combined immunodeficiency mutation diagnosis that can detect both known and new mutations. Future customization of probe sequences and analysis algorithms could increase the number of accurately called nucleotides.

A skewed view of X chromosome inactivation

X chromosome inactivation involves a random choice to silence either X chromosome early in mammalian female development. Once silenced the inactive X is stably inherited through subsequent somatic cell divisions, and thus, females are generally mosaics, having a mixture of cells with one or the other parental X active. While in most females the number of cells with either X being active is roughly equal, skewing of X chromosome inactivation is observed in a percentage of women. In this issue of the JCI, Bolduc and colleagues address whether skewing of X chromosome inactivation in humans is influenced by an X-linked locus that can alter this initial random inactivation (see the related article beginning on page 333). Their data indicate that most of the skewing observed in humans results from secondary events rather than being due to an inherited tendency to inactivate a particular X chromosome.

Gene therapy for treatment of inherited haematological disorders

Gene therapy, a molecular medicine based on vector-mediated transfer of therapeutic genes, holds promise for a cure of monogenetic inherited diseases. In recent years, tremendous progress has been reported in the treatment of haematological disorders: clinical trials in severe combined immune deficiencies have been successful by using retroviral vectors to express target genes in haematopoietic stem cells, which after transplantation efficiently reconstituted the immune system concomitant with substantial improvement in the clinical status of patients. Conversely, unexpected adverse events were also encountered. In other work, progress towards clinical studies on ex vivo gene transfer for Fanconi anaemia and haemoglobinopathies has been made. Each approach features a unique treatment strategy and also faces various impediments to success. In the case of the X-linked bleeding disorder haemophilia, several Phase I/II clinical trials were conducted, including in vivo administration of viral vectors to skeletal muscle and liver. Adeno-associated viral gene transfer of coagulation Factor IX has been documented in human subjects, reaching therapeutic levels after infusion into a hepatic blood vessel. However, sustained expression of therapeutic levels (as shown in large animal models of haemophilia) has not yet been achieved in humans. In general, long-term follow-up will be important for assessment of the safety of all existing gene therapy strategies.

Severe combined immunodeficiency associated with nephrogenic diabetes insipidus and a deletion in the Xq28 region

We evaluated a baby boy with severe combined immunodeficiency (SCID) and X-linked nephrogenic diabetes insipidus (NDI). This patient had less than 10% CD3+ T cells, almost all of which were positive for CD4 and CD45RO. Genetic studies demonstrated a 34.4 kb deletion at Xq28 which included AVPR2, the gene responsible for NDI; ARHGAP4, a hematopoietic specific gene encoding a GTPase-activating protein; and a highly conserved segment of DNA between ARHGAP4 and ARD1A, a gene involved in the response to hypoxia. Other patients with NDI, but without immunodeficiency, have had deletions that remove all ARHGAP4 except exon 1; however, no other patients have had deletions of the highly conserved intragenic region between ARHGAP4 and ARD1A. X chromosome inactivation studies, done on sorted cells from the mother and grandmother of the patient, carriers of the deletion, demonstrated exclusive use of the non-mutant X chromosome as the active X in CD4 and CD8 T cells. Surprisingly, NK cells, monocytes and neutrophils from these women demonstrated preferential use of the mutant X chromosome as the active X. These results are consistent with an X-linked form of SCID, due to the loss of regulatory elements that control the response to hypoxia in hematopoietic cells.

First among equals: competition between genetically identical cells

Competition between genetically identical organisms is considered insignificant in evolutionary theory because it is presumed to have little selective consequence. We argue that competition between genetically identical cells could improve the fitness of a multicellular organism by directing fitter cells to the germ line or by eliminating unfit cells, and that cell-competition mechanisms have been conserved in multicellular organisms. We propose that competition between genetically identical or highly similar units could have similar selective advantages at higher organizational levels, such as societies.

Successes and risks of gene therapy in primary immunodeficiencies

Several primary immunodeficiencies are under consideration for gene therapy approaches because of limitations of current standard treatment. Many primary immunodeficiencies are caused by defects in single genes expressed in blood cells; thus addition of a correct copy of the gene to hematopoietic stem cells (HSCs) can generate immune cells with restored function. HSCs can be removed from a patient, treated outside the body, and reinfused. In the last decade, significant improvements have been made in transferring genes by means of retroviruses to HSCs in vitro, and gene therapy trials for patients with X-linked severe combined immunodeficiency (XSCID) and adenosine deaminase-deficient severe combined immunodeficiency have restored immune competence. Gene therapy is actively being pursued in other immunodeficiency disorders, including chronic granulomatous disease and Wiskott-Aldrich syndrome. However, enthusiasm for the correction of XSCID by means of gene therapy has been tempered by the occurrence of 2 cases of leukemia in gene therapy recipients caused by insertion of the retroviral vector in or near the oncogene LMO2. The likelihood of retroviral insertional mutagenesis was estimated to be very low in the past on the basis of theoretic calculations and the absence of observed malignancies in animal studies and early clinical trials. Emerging new findings on retroviral integration both in the patients with XSCID and experimental animals now indicate that the insertion of retroviral sequences into the genome carries significant risk. Understanding the magnitude of risk is now a priority so that safety can be improved for future gene therapy clinical trials.

Bruton's tyrosine kinase defect in dendritic cells from X-linked agammaglobulinaemia patients does not influence their differentiation, maturation and antigen-presenting cell function

X-linked agammaglobulinaemia (XLA) is a primary immunodeficiency disease characterized by very low levels or even absence of circulating antibodies. The immunological defect is caused by deletions or mutations of Bruton's tyrosine kinase gene (Btk), whose product is critically involved in the maturation of pre-B lymphocytes into mature B cells. Btk is expressed not only in B lymphocytes but also in cells of the myeloid lineage, including dendritic cells (DC). These cells are professional antigen presenting cells (APC) that play a fundamental role in the induction and regulation of T-cell responses. In this study, we analysed differentiation, maturation, and antigen-presenting function of DC derived from XLA patients (XLA-DC) as compared to DC from age-matched healthy subjects (healthy-DC). We found that XLA-DC normally differentiate from monocyte precursors and mature in response to lipopolysaccharide (LPS) as assessed by de novo expression of CD83, up-regulation of MHC class II, B7.1 and B7.2 molecules as well as interleukin (IL)-12 and IL-10 production. In addition, we demonstrated that LPS stimulated XLA-DC acquire the ability to prime naïve T cells and to polarize them toward a Th1 phenotype, as observed in DC from healthy donors stimulated in the same conditions. In conclusion, these data indicate that Btk defect is not involved in DC differentiation and maturation, and that XLA-DC can act as fully competent antigen presenting cells in T cell-mediated immune responses.

12. Primary immunodeficiency diseases

Although primary immunodeficiency disorders are relatively rare, intensive investigation of these disorders has yielded a great wealth of understanding of basic immunologic mechanisms in host defense, inflammation, and autoimmunity. These advances have led to important developments for the treatment not only of the primary immunodeficiencies but also for patients with secondary immunocompromised states, autoimmune disorders, hypersensitivity, graft rejection, and graft versus host disease. Correction of a form of severe combined immunodeficiency represents the first true success of human gene therapy. This review introduces the major clinical manifestations of primary immunodeficiency disorders, along with descriptions of essential elements of the pathophysiology of those disorders that have been defined at the molecular level. Key concepts in treatment are also presented. It is critical for the practicing primary care provider and allergist to maintain an index of suspicion for immunodeficiency. Early diagnosis offers the best opportunity for reduced morbidity and survival and is critical for accurate genetic counseling.

Immunodeficiency Disorders

Hematological complications occur frequently in patients with both primary and secondary immunodeficiency disorders. Anemia, thrombocytopenia or leukopenias may bring these individuals to the attention of hematologists. Conversely, evidence suggesting a lymphoproliferative disorder may be the cause for referral. This session will provide an update on the diagnosis and treatment of immunodeficiency diseases ranging from isolated defects in antibody production to the severe combined immunodeficiencies (SCID).

Immunodeficiency diseases have traditionally been defined as defects in the development and function of T and B cells, the primary effector cells of specific cellular and humoral immunity. However, it has become increasingly evident that innate immune mechanisms contribute greatly to host defense, either through acting alone or by enhancing specific T and B cell responses.

In Section I, Dr. Lewis Lanier reviews the burgeoning information on the extensive families of activating and inhibitory immunoreceptors that are expressed on NK cells, dendritic cells, T and B cells, and phagocytic cells. He provides an overview on the biological functions of these receptors in host defense.

In Section II, Dr. Mary Ellen Conley defines the spectrum of antibody deficiency disorders, the most frequently occurring types of primary immunodeficiencies. She covers the different defects in B-cell development and function that lead to antibody deficiencies, and includes diagnosis and therapy of these disorders.

In Section III, Dr. Jennifer Puck discusses the diagnosis and treatment of the different types of SCID. She describes the genetic basis for SCID, and the benefits, pitfalls, and complications of gene therapy and bone marrow transplantation in SCID patients.

Retroviral transduction of IL2RG into CD34(+) cells from X-linked severe combined immunodeficiency patients permits human T- and B-cell development in sheep chimeras

X-linked severe combined immunodeficiency (XSCID) is caused by mutations of the common gamma chain of cytokine receptors, gamma(c). Because bone marrow transplantation (BMT) for XSCID does not provide complete immune reconstitution for many patients and because of the natural selective advantage conferred on lymphoid progenitors by the expression of normal gamma(c), XSCID is a good candidate disease for therapeutic retroviral gene transfer to hematopoietic stem cells. We studied XSCID patients who have persistent defects in B-cell and/or combined B- and T-cell function despite having received T cell-depleted haploidentical BMT. We compared transduction of autologous B-cell lines and granulocyte colony-stimulating factor-mobilized peripheral CD34(+) cells from these patients using an MFGS retrovirus vector containing the gamma(c) gene IL2RG pseudotyped with amphotropic, gibbon ape leukemia virus, or RD114 envelopes. Transduced B-cell lines and peripheral CD34(+) cells demonstrated provirus integration and new cell-surface gamma(c) expression. The chimeric sheep model was exploited to test development of XSCID CD34(+) cells into mature myeloid and lymphoid lineages. Transduced and untransduced XSCID CD34(+) cells injected into developing sheep fetuses gave rise to myeloid cells. However, only transduced gamma progenitors from XSCID patients developed into T and B cells. These results suggest that gene transfer to autologous peripheral CD34(+) cells using MFGS-gc retrovirus may benefit XSCID patients with persistent T- and B-cell deficits despite prior BMT.

The role of X-chromosome inactivation in the manifestation of Rett syndrome

X-chromosome inactivation (XCI) is random in the majority of patients with classical Rett syndrome (RTT). Preferential inactivation of the X chromosome with the mutated MECP2 gene is found in mildly symptomatic or asymptomatic carrier females. These findings lead to a hypothesis that random XCI is causally involved in the pathogenesis of RTT in heterozygous females. It is the cluster of functionally defective nerve cells lacking fully functional MeCP2 generated by inactivation of normal MECP2 allele that causes the wide spectrum of RTT symptoms. Thus, RTT is a rare human disease manifestation which is triggered most probably by random XCI.

Bruton's tyrosine kinase is present in normal platelets and its absence identifies patients with X-linked agammaglobulinaemia and carrier females

X-linked agammaglobulinaemia (XLA) is a primary immunodeficiency caused by mutations in the gene coding for Bruton's tyrosine kinase (Btk) and is characterized by an arrest of B-cell development. We analysed Btk protein expression in platelets using flow cytometry and found that normal platelets express large amounts of Btk. Assessment of affected males from 45 unrelated XLA families revealed that platelets of the majority of the patients (37 out of 45 families) had decreased or absent Btk expression, and that platelets from carrier females of these families had both normal and mutated Btk expression, indicating that megakaryocytes in XLA carriers undergo random X-chromosome inactivation. These observations demonstrate that Btk is not crucial for maturation of megakaryocytes and the production of platelets. No correlation between Btk expression in platelets and clinical phenotype was observed in this study. Flow cytometric evaluation using platelets is a simple and rapid method to test Btk expression. It may be used as a screening test for XLA and for carrier detection, followed, if necessary, by more expensive mutation analyses.

The causes and consequences of random and non-random X chromosome inactivation in humans

X chromosome (X) inactivation is a remarkable biological process including the choice and cis-limited inactivation of one X, as well as the stable maintenance of this silencing by epigenetic chromatin alterations. The process results in females generally being mosaic for two populations of cells--one with each parental X active. In this review, we discuss recent advances in our understanding of how inactivation works, as well as the causes and clinical implications of deviations from random inactivation.

Stable and functional lymphoid reconstitution of common cytokine receptor γ chain deficient mice by retroviral-mediated gene transfer

Mutations in the gene encoding the common cytokine receptor gamma chain (γc) are responsible for human X-linked severe combined immunodeficiency disease (SCIDX1). We have used a γc-deficient mouse model to test the feasibility and potential toxicity of γc gene transfer as a therapy for SCIDX1. A retrovirus harboring the murine γc chain was introduced into γc-deficient bone marrow cells, which were then transplanted into alymphoid RAG2/γcdouble-deficient recipient mice. Circulating lymphocytes appeared 4 weeks postgraft and achieved steady-state levels by 8 weeks. The mature lymphocytes present in the grafted mice had integrated the γc transgene, expressed γc transcripts, and were able to proliferate in response to γc-dependent cytokines. The γc-transduced animals demonstrated (1) normal levels of immunoglobulin subclasses, including immunoglobulin G1 (IgG1) and IgG2a (which are severely decreased in γc- mice); (2) the ability to mount an antigen-specific, T-dependent antibody response showing effective in vivo T-B cell cooperation, and (3) the presence of gut-associated cryptopatches and intraepithelial lymphocytes. Importantly, peripheral B and T cells were still present 47 weeks after a primary graft, and animals receiving a secondary graft of γc-transduced bone marrow cells demonstrated peripheral lymphoid reconstitution. That γc gene transfer to hematopoietic precursor cells can correct the immune system abnormalities in γc- mice supports the feasibility of in vivo retroviral gene transfer as a treatment for human SCIDX1.

Stable and functional lymphoid reconstitution of common cytokine receptor γ chain deficient mice by retroviral-mediated gene transfer

Mutations in the gene encoding the common cytokine receptor gamma chain (γc) are responsible for human X-linked severe combined immunodeficiency disease (SCIDX1). We have used a γc-deficient mouse model to test the feasibility and potential toxicity of γc gene transfer as a therapy for SCIDX1. A retrovirus harboring the murine γc chain was introduced into γc-deficient bone marrow cells, which were then transplanted into alymphoid RAG2/γcdouble-deficient recipient mice. Circulating lymphocytes appeared 4 weeks postgraft and achieved steady-state levels by 8 weeks. The mature lymphocytes present in the grafted mice had integrated the γc transgene, expressed γc transcripts, and were able to proliferate in response to γc-dependent cytokines. The γc-transduced animals demonstrated (1) normal levels of immunoglobulin subclasses, including immunoglobulin G1 (IgG1) and IgG2a (which are severely decreased in γc- mice); (2) the ability to mount an antigen-specific, T-dependent antibody response showing effective in vivo T-B cell cooperation, and (3) the presence of gut-associated cryptopatches and intraepithelial lymphocytes. Importantly, peripheral B and T cells were still present 47 weeks after a primary graft, and animals receiving a secondary graft of γc-transduced bone marrow cells demonstrated peripheral lymphoid reconstitution. That γc gene transfer to hematopoietic precursor cells can correct the immune system abnormalities in γc- mice supports the feasibility of in vivo retroviral gene transfer as a treatment for human SCIDX1.

Outcomes analysis of verbal dyspraxia in classic galactosemia

PURPOSE

This study evaluates a genotype/phenotype relationship between developmental verbal dyspraxia (DVD) and the common, missense mutation of the galactose-1-phosphate uridyltransferase gene, Q188R, in patients with classic galactosemia (G/G).

METHODS

As part of this study, we devised a questionnaire for "speech problems" to be completed by the patient\'s clinician. To validate the questionnaire and determine its accuracy in detecting DVD, we analyzed questionnaire responses for 21 patients by testing them independently and directly for DVD through a speech pathologist blinded to the patients' genotype.

RESULTS

We found that the questionnaire had a sensitivity of 0.56 and a specificity of 0.75. We then calculated the prevalence of DVD for a larger set of 113 patients with G/G galactosemia whose biochemical phenotype, molecular genotypes, and clinical status were known. The prevalence of "speech problems" from raw data were 50 of 113 (44.2%). After adjusting for misclassification, 43 (38.1%) were classified as cases of DVD. Using multivariate, logistic, regression analyses we found a significant interaction between genotype and mean red blood cell (RBC) galactose-1-phosphate (Gal-1-P). When corrected, using mean RBC Gal-1-P < h 3.28 mg%, the Q188R/Q188R genotype was the best predictor of DVD. There was a significant risk (odds ratio = 9.6, p = 0.0504) of having DVD associated with homozygosity for Q188R compared with other genotypes.

CONCLUSIONS

We conclude that homozygosity for Q188R mutations in the GALT gene is a significant risk factor for DVD. However, poor metabolic control obviates this relationship as indicated by RBC Gal-1-P greater than 3.28 mg%.

Molecular determination of X inactivation pattern correlates with phenotype in women with a structurally abnormal X chromosome

PURPOSE

To correlate the X inactivation pattern, as determined by one or more molecular assays, with phenotype in individuals with structurally abnormal X chromosomes.

METHODS

We utilized methylation analysis of androgen receptor (AR) and Fragile X (FMR1) genes and expression studies of an XIST polymorphism to assess X inactivation patterns of 28 females with structurally abnormal X chromosomes. Individuals were placed in one of three categories: (1) completely nonrandom inactivation of one X chromosome, (2) preferential or skewed inactivation of one X chromosome, or (3) random inactivation of either X chromosome.

RESULTS

In 19 of 21 cases with complete (>97%) skewing of X inactivation, the phenotype was either normal, consistent with a single gene disorder, or consistent with classical Turner syndrome; two cases with completely nonrandom X inactivation had unexplained mental retardation phenotypes. In contrast, six of seven cases that did not exhibit completely nonrandom X inactivation were phenotypically abnormal. Carriers of two balanced translocations, two duplicated Xs, one deleted X, and one 45,X/46,X,r(X) presented with mental retardation and/or multiple congenital anomalies.

CONCLUSION

In patients with random or skewed X inactivation, the abnormal phenotype was hypothesized to be due to functional nullisomy or disomy of X-linked genes. Based on these results, we propose that X inactivation studies should be performed on all women with structurally abnormal X chromosomes. This should aid in the understanding of abnormal phenotypes in liveborn individuals with abnormal X chromosomes and may help to predict phenotypes for prenatally detected cases in the future.

Immunodeficiency due to a unique protracted developmental delay in the B-cell lineage

A unique immune deficiency in a 24-month-old male characterized by a transient but protracted developmental delay in the B-cell lineage is reported. Significant deficiencies in the number of B cells in the blood, the concentrations of immunoglobulins in the serum, and the titers of antibodies to T-dependent and T-independent antigens resolved spontaneously by the age of 39 months in a sequence that duplicated the normal development of the B-cell lineage: blood B cells followed by immunoglobulin M (IgM), IgG, IgA, and specific IgG antibodies to T-independent antigens (pneumococcal polysaccharides). Because of the sequence of recovery, the disorder could have been confused with other defects in humoral immunity, depending on when in the course of disease immunologic studies were conducted. Investigations of X-chromosome polymorphisms suggested that the disorder was not X linked in that the mother appeared to have identical X chromosomes. An autosomal recessive disorder involving a gene that controls B-cell development and maturation seems more likely. In summary, this case appears to be a novel protracted delay in the development of the B-cell lineage, possibly due to an autosomal recessive genetic defect.

CD40 ligand expression deficiency in a female carrier of the X-linked hyper-IgM syndrome as a result of X chromosome lyonization

We report on the case of a girl with an immune deficiency characterized by recurrent infections of the upper and lower respiratory tract, low IgG and IgA serum levels as well as deficiency of the in vivo antibody response. Since this patient is the sister of a boy affected with a hyper-IgM syndrome due to a defect in CD40 ligand (CD40L) expression, the involvement of CD40L in this phenotypic expression was investigated. A very low fraction of activated T cells (5%) in this female patient expressed CD40L. This resulted from the presence of a heterozygous CD40L nonsense mutation associated with a skewed pattern of X chromosome inactivation as determined by methylation pattern analysis. Although carriers of X-linked hyper-IgM are considered to be asymptomatic, this study indicates that extreme lyonization of the normal X can lead to a mild expression of the hyper-IgM syndrome which is similar to common variable immune deficiency (CVID). Therefore, it is possible that some cases of CVID in females represent partial deficiency of CD40L expression in carriers of the CD40L mutation.

X chromosome inactivation patterns in normal females

Since one of the two X chromosomes is randomly inactivated at an early stage of female embryonic development, X-linked markers have been used to study the origin and development of various neoplastic disorders in affected heterozygous women; clonality assays have provided a useful tool to the understanding of the mechanisms underlying the development of neoplasia. Recently, a technique of clonal analysis has been devised that takes advantage of a highly polymorphic short tandem repeat within the X-linked human androgen receptor (AR) gene, resulting in a heterozygosity rate approaching 90%. The rapid expansion of the number of women now suitable for X inactivation analysis has however given rise to new controversies, one of the more troublesome being the possibility of a modification of the pattern of X- chromosome inactivation pattern in blood cells of elderly women. In the present study we analyze with the AR assay a group of 166 healthy females aged between 8 and 94 years, with no history of genetic or neoplastic familial disorders. We failed to find any correlation between age and X- chromosome inactivation pattern (r = 0.17), even subdividing the subjects in different age groups according to the criteria used by other researchers, and therefore reaffirm that, when tested for with well-standardized and accurate criteria, extremely unbalanced inactivation of the X chromosome is a truly uncommon phenomenon in normal women.

Primary immunodeficiency disorders

The primary immunodeficiency diseases are a relatively rare group of congenital disorders that are linked by the expression of an excessive number, duration, or severity of infections. The clinical features of most of the primary immunodeficiency diseases have been well described by astute physicians over several decades and have provided important clues to our basic understanding of human immunology. In contrast, the genetic basis and potential life-saving therapies for many of these disorders have been established only over the past few years. These recent advances have resulted in the prognosis of many of these disorders being largely dependent on their rapid recognition and treatment. Increased awareness of the differentiating epidemiologic, clinical, laboratory and genetic features of these diseases hold the promise of both furthering our understanding of basic human immunology and providing improved care for this challenging group of patients.

Mosaicism in X-linked severe combined immunodeficiency

We performed gamma c gene analysis of a boy with severe combined immunodeficiency whose brother died of the same condition. A base pair deletion in exon 6 was found, which was absent in his mother, indicating maternal mosaicism with important implications for genetic counseling and demonstrating the importance of mutation analysis in boys with severe combined immunodeficiency.

Retroviral Marking of Canine Bone Marrow: Long-Term, High-Level Expression of Human Interleukin-2 Receptor Common Gamma Chain in Canine Lymphocytes

Optimization of retroviral gene transfer into hematopoietic cells of the dog will facilitate gene therapy of canine X-linked severe combined immunodeficiency (XSCID) and in turn advance similar efforts to treat human XSCID. Both canine and human XSCID are caused by defects in the common γ chain, γc, of receptors for interleukin-2 and other cytokines. In this study, normal dogs were given retrovirally transduced bone marrow cells with and without preharvest mobilization by the canine growth factors granulocyte colony-stimulating factor (G-CSF) and stem cell factor (SCF). Harvey sarcoma virus and Moloney murine leukemia virus constructs were used, both containing cDNA encoding human γc. The Harvey-based vector transduced into cytokine-primed marrow yielded persistent detectable provirus in bone marrow and blood and expression of human γc on peripheral lymphocytes. In three dogs, human γc expression disappeared after 19 to 34 weeks but reappeared and was sustained, in one dog beyond 16 months posttransplantation, upon immunosuppression with cyclosporin A and prednisone, with up to 25% of lymphocytes expressing human γc. The long-term expression of human γc in a high proportion of normal canine lymphocytes predicts that retrovirus-mediated gene correction of hematopoietic cells may prove to be of clinical benefit in humans affected with this XSCID.

This is a US government work. There are no restrictions on its use.

Retroviral Marking of Canine Bone Marrow: Long-Term, High-Level Expression of Human Interleukin-2 Receptor Common Gamma Chain in Canine Lymphocytes

Optimization of retroviral gene transfer into hematopoietic cells of the dog will facilitate gene therapy of canine X-linked severe combined immunodeficiency (XSCID) and in turn advance similar efforts to treat human XSCID. Both canine and human XSCID are caused by defects in the common γ chain, γc, of receptors for interleukin-2 and other cytokines. In this study, normal dogs were given retrovirally transduced bone marrow cells with and without preharvest mobilization by the canine growth factors granulocyte colony-stimulating factor (G-CSF) and stem cell factor (SCF). Harvey sarcoma virus and Moloney murine leukemia virus constructs were used, both containing cDNA encoding human γc. The Harvey-based vector transduced into cytokine-primed marrow yielded persistent detectable provirus in bone marrow and blood and expression of human γc on peripheral lymphocytes. In three dogs, human γc expression disappeared after 19 to 34 weeks but reappeared and was sustained, in one dog beyond 16 months posttransplantation, upon immunosuppression with cyclosporin A and prednisone, with up to 25% of lymphocytes expressing human γc. The long-term expression of human γc in a high proportion of normal canine lymphocytes predicts that retrovirus-mediated gene correction of hematopoietic cells may prove to be of clinical benefit in humans affected with this XSCID.

This is a US government work. There are no restrictions on its use.

Expression of properdin in complete and incomplete deficiency: normal in vitro synthesis by monocytes in two cases with properdin deficiency type II due to distinct mutations

Three properdin deficiency phenotypes have been reported--complete deficiency (type I), incomplete deficiency (type II), and dysfunction of properdin protein (type III)--all associated with increased susceptibility to meningococcal disease. Expression of properdin by monocytes was examined in type I deficiency and in two unrelated cases with type II deficiency, one from a Swedish and one from a Danish family. The properdin gene in the Danish family contained a point mutation in exon 8 causing a Gln316-->Arg substitution, distinct from a point mutation in exon 4 previously found in the Swedish family. Both genes coded for physicochemically abnormal properdin molecules with changed hydrophilicity. Monocytes from all the properdin-deficient individuals produced properdin mRNA in a normal fashion. In type I deficiency no intracellular or secreted properdin was found, indicating rapid intracellular degradation. Monocytes from the males with type II deficiency expressed and secreted properdin normally. Properdin in sera with type II deficiency showed abnormal oligomerization with a relative decrease in properdin trimers and tetramers. Our findings suggest that the low concentration of circulating properdin in type II deficiency is caused by increased extracellular catabolism. Analysis of properdin expression by monocytes in a female carrier in the family with properdin deficiency type I provided direct evidence of lyonization at the cellular level.

The forkhead transcription factor gene FKHL7 is responsible for glaucoma phenotypes which map to 6p25

A number of different eye disorders with the presence of early-onset glaucoma as a component of the phenotype have been mapped to human chromosome 6p25. These disorders have been postulated to be either allelic to each other or associated with a cluster of tightly linked genes. We have identified two primary congenital glaucoma (PCG) patients with chromosomal anomalies involving 6p25. In order to identify a gene involved in PCG, the chromosomal breakpoints in a patient with a balanced translocation between 6p25 and 13q22 were cloned. Cloning of the 6p25 breakpoint led to the identification of two candidate genes based on proximity to the breakpoint. One of these, FKHL7, encoding a forkhead transcription factor, is in close proximity to the breakpoint in the balanced translocation patient and is deleted in a second PCG patient with partial 6p monosomy. Furthermore, FKHL7 was found to harbour mutations in patients diagnosed with Rieger anomaly (RA), Axenfeld anomaly (AA) and iris hypoplasia (IH). This study demonstrates that mutations in FKHL7 cause a spectrum of glaucoma phenotypes.