Bone marrow transplantation in DiGeorge syndrome

Molecular Insights Into the Causes of Human Thymic Hypoplasia With Animal Models

22q11.2 deletion syndrome (DiGeorge), CHARGE syndrome, Nude/SCID and otofaciocervical syndrome type 2 (OTFCS2) are distinct clinical conditions in humans that can result in hypoplasia and occasionally, aplasia of the thymus. Thymic hypoplasia/aplasia is first suggested by absence or significantly reduced numbers of recent thymic emigrants, revealed in standard-of-care newborn screens for T cell receptor excision circles (TRECs). Subsequent clinical assessments will often indicate whether genetic mutations are causal to the low T cell output from the thymus. However, the molecular mechanisms leading to the thymic hypoplasia/aplasia in diverse human syndromes are not fully understood, partly because the problems of the thymus originate during embryogenesis. Rodent and Zebrafish models of these clinical syndromes have been used to better define the underlying basis of the clinical presentations. Results from these animal models are uncovering contributions of different cell types in the specification, differentiation, and expansion of the thymus. Cell populations such as epithelial cells, mesenchymal cells, endothelial cells, and thymocytes are variably affected depending on the human syndrome responsible for the thymic hypoplasia. In the current review, findings from the diverse animal models will be described in relation to the clinical phenotypes. Importantly, these results are suggesting new strategies for regenerating thymic tissue in patients with distinct congenital disorders.

Chromosome 22q11.2 deletion syndrome and DiGeorge syndrome

Chromosome 22q11.2 deletion syndrome is the most common microdeletion syndrome in humans. The effects are protean and highly variable, making a unified approach difficult. Nevertheless, commonalities have been identified and white papers with recommended evaluations and anticipatory guidance have been published. This review will cover the immune system in detail and discuss both the primary features and the secondary features related to thymic hypoplasia. A brief discussion of the other organ system involvement will be provided for context. The immune system, percolating throughout the body can impact the function of other organs through allergy or autoimmune disease affecting organs in deleterious manners. Our work has shown that the primary effect of thymic hypoplasia is to restrict T cell production. Subsequent homeostatic proliferation and perhaps other factors drive a Th2 polarization, most obvious in adulthood. This contributes to atopic risk in this population. Thymic hypoplasia also contributes to low regulatory T cells and this may be part of the overall increased risk of autoimmunity. Collectively, the effects are complex and often age-dependent. Future goals of improving thymic function or augmenting thymic volume may offer a direct intervention to ameliorate infections, atopy, and autoimmunity.

The immune deficiency of chromosome 22q11.2 deletion syndrome

The syndrome originally described by Dr. Angelo DiGeorge had immunodeficiency as a central component. When a 22q11.2 deletion was identified as the cause in the majority of patients with DiGeorge syndrome, the clinical features of 22q11.2 deletion syndrome became so expansive that the immunodeficiency became less prominent in our thinking about the syndrome. This review will focus on the immune system and the changes in our understanding over the past 50 years. Initially characterized as a pure defect in T cell development, we now appreciate that many of the clinical features related to the immunodeficiency are well downstream of the limitation imposed by a small thymus. Dysfunctional B cells presumed to be secondary to compromised T cell help, issues related to T cell exhaustion, and high rates of atopy and autoimmunity are aspects of management that require consideration for optimal clinical care and for designing a cogent monitoring approach. New data on atopy are presented to further demonstrate the association.

Immunodeficiencies Associated with Abnormal Newborn Screening for T Cell and B Cell Lymphopenia

Newborn screening for SCID has revealed the association of low T cells with a number of unexpected syndromes associated with low T cells, some of which were not appreciated to have this feature. This review will discuss diagnostic approaches and the features of some of the syndromes likely to be encountered following newborn screening for immune deficiencies.

Placental transfer of maternally-derived IgA precludes the use of guthrie card eluates as a screening tool for primary immunodeficiency diseases

There is a need for neonatal screening tools to improve the long-term clinical outcome of patients with primary immunodeficiency diseases (PID). Recently, a PCR-based screening method for both TRECs and KRECs using Guthrie card samples has been developed. However, the applicability of these excision circle assays is limited to patients with severe T or B cell lymphopenia (SCID, XLA and A-T), whereas the most common forms of PID are not detected. Absence of serum IgA is seen in a major fraction of patients with immunological defects. As serum IgA in newborns is considered to be of fetal origin, eluates from routinely collected dried blood spot samples might thus be suitable for identification of children with PID. To assess the applicability of such screening assays, stored Guthrie card samples were obtained from 47 patients with various forms of primary immunodeficiency diseases (SCID, XLA, A-T, HIGM and IgAD), 20 individuals with normal serum IgA levels born to IgA-deficient mothers and 51 matched healthy newborns. Surprisingly, normal serum IgA levels were found in all SCID, XLA, A-T and HIGM patients and, additionally, in all those IgAD patients born to IgA-sufficient mothers. Conversely, no serum IgA was found in any of the 16 IgAD patients born by IgA-deficient mothers. Moreover, half of the IgA-sufficient individuals born by IgA-deficient mothers also lacked IgA at birth whereas no IgA-deficient individuals were found among the controls. IgA in neonatal dried blood samples thus appears to be of both maternal and fetal origin and precludes its use as a reliable marker for neonatal screening of primary immunodeficiency diseases.

Tetralogy of Fallot with complete DiGeorge syndrome: report of a case and a review of the literature

Complete DiGeorge syndrome (CDGS) has a severe T-cell immunodeficiency and is fatal without thymus or bone marrow transplantation. Associated congenital heart disease (CHD) further complicates the clinical management. We report an infant with tetralogy of Fallot, confluent and hypoplastic pulmonary arteries, right aortic arch, and aberrant left subclavian artery. He was athymic with no CD3+ T cells. CDGS was diagnosed with 22q11.2 deletion. The patient underwent central aortopulmonary shunt at 12 days of age. The patient died at 5 weeks of age awaiting thymus transplantation. We performed a review of the literature regarding CDGS and CHD. We found 43 cases including conotruncal defects (20) and nonconotruncal defects (23). The overall mortality rate was 67%. Among 30 cases undergoing transplantation (bone marrow 16 and thymus 12, bone marrow + thymus 2), the mortality rate was 53%. The patients with conotruncal defects were more likely to die before transplantation (45% vs. 16%, P =.04). The main cause of death was infection before and after transplantation. We conclude that children with CDGS and CHD have a high mortality. Bone marrow and thymus transplantation can improve the survival, but the overall management of these high risk patients remains challenging.

Multicenter survey on the outcome of transplantation of hematopoietic cells in patients with the complete form of DiGeorge anomaly

Seventeen patients transplanted with hematopoietic cells to correct severe T lymphocyte immunodeficiency resulting from complete DiGeorge anomaly were identified worldwide, and retrospective data were obtained using a questionnaire-based survey. Patients were treated at a median age of 5 months (range, 2-53 months) between 1995 and 2006. Bone marrow was used in 11 procedures in 9 cases: 6 from matched unrelated donors, 4 from human leukocyte antigen (HLA)-identical siblings, and one haploidentical parent with T-cell depletion. Unmobilized peripheral blood was used in 8 cases: 5 from HLA-identical siblings, one from a matched unrelated donor, one from an HLA-identical parent, and one unrelated matched cord blood. Conditioning was used in 5 patients and graft-versus-host disease prophylaxis in 11 patients. Significant graft-versus-host disease occurred in 9 patients, becoming chronic in 3. Median length of follow-up was 13 months, with transplantation from HLA-matched sibling showing the best results. Median survival among deceased patients (10 patients) was 7 months after transplantation (range, 2-18 months). The overall survival rate was 41%, with a median follow-up of 5.8 years (range, 4-11.5 years). Among survivors, median CD3 and CD4 counts were 806 (range, 644-1224) and 348 (range, 225-782) cells/mm(3), respectively, CD4(+)/CD45RA(+) cells remained very low, whereas mitogen responses were normalized.

Immunologic reconstitution in 22q deletion (DiGeorge) syndrome

Adoptive transfer of mature T cells (ATMTC) through bone marrow (BM) transplantation, first attempted over 20 years ago, has recently emerged as a successful therapy for complete 22q deletion syndrome (22qDS). This provides a potential option to thymic transplantation (TT) for immune reconstitution in 22qDS. Compared to thymic transplant, ATMTC is an easier procedure to accomplish and is available at more centers. However, there are differences in the nature of the T-cell reconstitution that results. Predictably, more naïve T cells and recent thymic emigrants are present in patients treated with thymus transplant. There are no significant differences in mortality between the two procedures, but the number of patients is too limited to conclude that the procedures are equally effective. Adoptive transfer should be pursued as a reasonable treatment for 22qDS patients requiring immune reconstitution when thymus transplant is not available.

Chromosome 22q11.2 deletion syndrome: DiGeorge syndrome/velocardiofacial Syndrome

DiGeorge syndrome, or chromosome 22q11.2 deletion syndrome, is a disorder affecting multiple organ systems. The immunologist may be called on to coordinate complex medical care tailored to the specific needs and unique clinical features of each patient. This article focuses on the immune system, but patients require a holistic approach. Attention to cardiac, nutritional, and developmental needs in early infancy is important, and it is critical to identify the rare infants who require either a lymphocyte or thymus transplant. Later, speech and school issues dominate the picture. Allergies and autoimmune disorders also may be troubling for some school-age children.

Immune constitution monitoring after PBMC transplantation in complete DiGeorge syndrome: an eight-year follow-up

A young boy with a confirmed complete DiGeorge Syndrome (cDGS) underwent a peripheral blood mononuclear cell transplantation (PBMCT) from his HLA-identical sister at 4.5 years of age, without a conditioning regimen. Eight years later, he is healthy with good immunological functions in the presence of a stable mixed T-cell chimerism. Absence of recent thymic emigrants is confirmed. We observe an inverted CD4+/CD8+ ratio, related to the CD8 subset expansion, a skewing of the TCR repertoire, especially on the CD8+ subset and a telomere loss on the CD8+ cells compared to the donor. However, these anomalies do not seem to have an impact on functional immunity. PBMCT in cDGS using an HLA-matched sibling donor provides good long-lasting immunity and is an easy alternative to bone marrow transplantation and to thymic transplantation.

Long-term results of bone marrow transplantation in complete DiGeorge syndrome

BACKGROUND

Therapeutic options for DiGeorge syndrome (DGS) with profound T-cell deficiency are very limited. Thymic transplantation has shown promising results but is not easily available. Hematopoietic cell transplantation (HCT) has been successful in restoring immune competence in the short term.

OBJECTIVE

Present the long-term follow-up of 2 patients with complete DGS who received bone marrow transplants in the neonatal period from HLA-matched siblings, and perform a multicenter survey to document the status of other patients with DGS who have undergone HCT.

METHODS

Immune function assessment by immunophenotyping, lymphocyte proliferation, T-cell receptor excision circles, single nucleotide polymorphism mapping arrays, spectratyping, cytogenetics, and fluorescence in situ hybridization were used.

RESULTS

Among reported patients with DGS receiving HCT, survival is greater than 75%. Our patients are in their 20s and in good health. Their hematopoietic compartment shows continuous engraftment with mixed chimerism, normal T-cell function, and humoral immunity. Circulating T cells exhibit a memory phenotype with a restricted repertoire and are devoid of T-cell receptor excision circles.

CONCLUSION

These features suggest that T-cell reconstitution has occurred predominantly through expansion of the donors' mature T-cell pool. Although restricted, their immune systems are capable of providing substantial protection to infection and respond to vaccines. We conclude that bone marrow transplant achieves long-lived reconstitution of immune function in complete DGS and is a good alternative to thymic transplantation in patients with a suitable donor.

CLINICAL IMPLICATIONS

Bone marrow transplant in complete DGS using an HLA-matched sibling donor provides long-lasting immunity and is a suitable and more available alternative to thymic transplantation.

Velocardiofacial syndrome, DiGeorge syndrome: the chromosome 22q11.2 deletion syndromes

Velocardiofacial syndrome, DiGeorge syndrome, and some other clinical syndromes have in common a high frequency of hemizygous deletions of chromosome 22q11.2. This deletion syndrome is very common, affecting nearly one in 3000 children. Here, we focus on recent advances in cardiac assessment, speech, immunology, and pathophysiology of velocardiofacial syndrome. The complex medical care of patients needs a multidisciplinary approach, and every patient has his own unique clinical features that need a tailored approach. Patients with chromosome 22q11.2 deletion syndrome might have high level of functioning, but most often need interventions to improve the function of many organ systems.

Unrelated partially matched lymphocyte infusions in a patient with complete DiGeorge/CHARGE syndrome

We present an infant with cDGS overlapping with CHARGE syndrome, who suffered from T-cell deficiency treated with screened healthy DLI from an unrelated donor (8/10 match). The first dose of DLI (1.1 x 10(6) CD3+/kg) was administered at the age of six months, the second one (0.9 x 10(6) CD3+/kg) 36 days later. No conditioning was employed, GvHD prophylaxis consisting of CsA was used only during the second infusion. Since day+10 after the first DLI, split chimerism showing T-cell engraftment has been documented. Proliferative response to PHA was detected on day+145. The treatment was complicated by severe acute GvHD (grade II-III) after the first DLI and prolonged chronic liver cholestatic GvHD developing after the second DLI. Vigorous EBV proliferation four wk after the second DLI was accompanied by peripheral expansion of CD8+ donor cells. The patient, 26-months old, is clinically well and has slowly started to gain his developmental milestones. We believe that infusions of small doses of DLI from an unrelated donor represent a potentially helpful therapeutic option in patients with cDGS/CHARGE phenotype.

Post-natal ontogenesis of the T-cell receptor CD4 and CD8 Vbeta repertoire and immune function in children with DiGeorge syndrome

DiGeorge syndrome (DGS) is a congenital disorder characterized by typical facial features, hypoparatyroidism, conotruncal cardiac defects and thymic hypoplasia. Although there are some reports addressing lymphocytes counts and function in DGS children over time, few data have been reported on the T-cell receptor V beta (TCRBV) repertoire in relation to disease progression. The aim of this study was to evaluate the degree and nature of immunodeficiency and to investigate a possible correlation to clinical findings. We used third complementary region (CDR3) size spectratyping as a tool for monitoring T-cell repertoire diversity in 7 DGS's children. The rate of thymic output, the phenotype and function of peripheral T-cells and the humoral immunity were also investigated. At baseline a profound alteration of the TCR repertoire was noted, mainly in the CD8+ T-cells, in DGS patients when compared to a control group. Furthermore, analysis of thymic output showed a significant decrease in TCR rearrangement excision circles (TRECs) levels in the patient group. Immunoglobulin abnormalities were also detected. The observed TCR repertoire alterations, although not statistically significant, may suggest an increased susceptibility to infections. A parallel increase in the TCR repertoire diversity and clinical improvement occurred during the follow-up. Our results confirm that the extent of immunodeficiency is highly variable and could improve through childhood, and indicate that TCR repertoire may be a useful marker to clinically monitor thymic function in this primary immunodeficiency.

Complete DiGeorge anomaly in the absence of neonatal hypocalcemia and velofacial and cardiac defects

We report an atypical case of complete DiGeorge (DG) anomaly that presented initially exclusively as severe combined immunodeficiency (SCID). The child had severe infections at diagnosis, in keeping with the SCID phenotype; however, normal lymphocyte counts and immunoglobulin levels were noted at admission, which delayed diagnosis. Importantly, the child presented without neonatal hypocalcemia or velofacial or cardiac abnormalities at the time of diagnosis, which masked underlying DG. This case outlines the difficulties in making the diagnosis of SCID in a timely manner and illustrates the variation in presentation of the 22q11.2 deletion syndrome. There should be a high index of suspicion for primary immunodeficiency among children with severe infections and, because management may vary, DG anomaly should be considered in the differential diagnosis of T- B+ natural killer+ SCID.

Thymic transplantation for complete DiGeorge syndrome: medical and surgical considerations

BACKGROUND/PURPOSE

Complete DiGeorge syndrome results in the absence of functional T cells. Our program supports the transplantation of allogeneic thymic tissue in infants with DiGeorge syndrome to reconstitute immune function. This study reviews the multidisciplinary care of these complex infants.

METHODS

From 1991 to 2001, the authors evaluated 16 infants with complete DiGeorge syndrome. All infants received multidisciplinary medical and surgical support. Clinical records for the group were reviewed.

RESULTS

Four infants died without receiving a thymic transplantation, and 12 children survived to transplantation. The mean age at time of transplantation was 2.7 months (range, 1.1 to 4.4 months). All 16 infants had significant comorbidity including congenital heart disease (16 of 16), hypocalcemia (14 of 16), gastroesophageal reflux disease or aspiration (13 of 16), CHARGE complex (4 of 16), and other organ involvement (14 of 16). Nontransplant surgical procedures included central line placement (15 of 16), fundoplication or gastrostomy (10 of 16), cardiac repair (10 of 16), bronchoscopy or tracheostomy (6 of 16), and other procedures (12 of 16). Complications were substantial, and 5 of the 12 transplanted infants died of nontransplant-related conditions. All surviving infants have immune reconstitution, with follow-up from 2 to 10 years.

CONCLUSIONS

Although the transplantation of thymic tissue can restore immune function in infants with complete DiGeorge syndrome, these children have substantial comorbidity. Care of these children requires coordinated multidisciplinary support.

Otolaryngologic manifestations of immunodeficiency

Otolaryngologists are frequently consulted to manage infectious and noninfectious complications of immune deficiency. Although defects of host defense and recurrent or severe infections are the most obvious manifestations of immune deficiency, patients are often at increased risk for autoimmune and malignant disease as well. Knowledge of primary and acquired immune deficiencies will facilitate appropriate identification, treatment, and referral of patients with these defects. When immunodeficiency is known or suspected, it is particularly important to have a high index of suspicion for unusual or severe manifestations of infection, to have a low threshold for obtaining imaging to aid in diagnosis, and to treat infections for longer periods of time with higher doses of antibiotic. Surgery may be required for definitive treatment of infections that do not respond to medical therapy and for management of complications of infectious disease

Thymus transplantation in complete DiGeorge syndrome: immunologic and safety evaluations in 12 patients

Complete DiGeorge syndrome is a fatal condition in which infants have no detectable thymus function. The optimal treatment for the immune deficiency of complete DiGeorge syndrome has not been determined. Safety and efficacy of thymus transplantation were evaluated in 12 infants with complete DiGeorge syndrome who had less than 20-fold proliferative responses to phytohemagglutinin. All but one had fewer than 50 T cells/mm3. Allogeneic postnatal cultured thymus tissue was transplanted. T-cell development was followed by flow cytometry, lymphocyte proliferation assays, and T-cell receptor Vbeta (TCRBV) repertoire evaluation. Of the 12 patients, 7 are at home 15 months to 8.5 years after transplantation. All 7 survivors developed T-cell proliferative responses to mitogens of more than 100 000 counts per minute (cpm). By one year after transplantation, 6 of 7 patients developed antigen-specific proliferative responses. The TCRBV repertoire showed initial oligoclonality that progressed to polyclonality within a year. B-cell function developed in all 3 patients tested after 2 years. Deaths were associated with underlying congenital problems. Risk factors for death included tracheostomy, long-term mechanical ventilation, and cytomegalovirus infection. Adverse events in the first 3 months after transplantation included eosinophilia, rash, lymphadenopathy, development of CD4-CD8- peripheral T cells, elevated serum immunoglobulin E (IgE), and possible pulmonary inflammation. Adverse events related to the immune system occurring more than 3 months after transplantation included thrombocytopenia in one patient and hypothyroidism and alopecia in one other patient. Thymic transplantation is efficacious, well tolerated, and should be considered as treatment for infants with complete DiGeorge syndrome.

Biased T-cell receptor repertoires in patients with chromosome 22q11.2 deletion syndrome (DiGeorge syndrome/velocardiofacial syndrome)

Chromosome 22q11.2 deletion (del22q11.2) syndrome (DiGeorge syndrome/velocardiofacial syndrome) is a common syndrome typically consisting of congenital heart disease, hypoparathyroidism, developmental delay and immunodeficiency. Although a broad range of immunologic defects have been described in these patients, limited information is currently available on the diversity of the T-cell receptor (TCR) variable beta (BV) chain repertoire. The TCRBV repertoires of nine patients with del22q11.2 syndrome were determined by flow cytometry, fragment size analysis of the third complementarity determining region (CDR3 spectratyping) and sequencing of V(D)J regions. The rate of thymic output and the phenotype and function of peripheral T cells were also studied. Expanded TCRBV families were detected by flow cytometry in both CD4+ and CD8+ T cells. A decreased diversity of TCR repertoires was also demonstrated by CDR3 spectratyping, showing altered CDR3 profiles in the majority of TCRBV families investigated. The oligoclonal nature of abnormal peaks detected by CDR3 spectratyping was confirmed by the sequence analysis of the V(D)J regions. Thymic output, evaluated by measuring TCR rearrangement excision circles (TRECs), was significantly decreased in comparison with age-matched controls. Finally, a significant up-regulation in the percentage, but not in the absolute count, of activated CD4+ T cells (CD95+, CCR5+, HLA-DR+), IFN-gamma - and IL-2-expressing T cells was detected. These findings suggest that the diversity of CD4 and CD8 TCRBV repertoires is decreased in patients with del22q11.2 syndrome, possibly as a result of either impaired thymic function and/or increased T-cell activation.

27. Transplantation immunology: organ and bone marrow

The discovery of the human MHC in 1967 launched the field of organ and tissue transplantation. More than 800,000 such transplants have been performed during this time. Although matching of donor and recipient for MHC antigens was shown to be of great importance and continues to be so, the development of pharmacologic agents and antilymphocyte antibodies that interfere with the process of graft rejection has had a crucial role in the success of organ transplantation during the past 2 decades. Enormous progress has been made in understanding the immunologic mechanisms of graft rejection and of graft-versus-host disease. The roles of antibodies, antigen-presenting cells, helper and cytotoxic T cells, immune cell surface molecules, and signaling mechanisms and the cytokines they release have been clarified. This understanding is leading to the development of newer immunosuppressive agents targeting various components of the rejection process. Combinations of these agents work synergistically, leading to lower doses and reduced toxicity. Similarly, the development of effective T-cell depletion techniques has been of great importance for bone marrow transplantation when an HLA-identical sibling is not available. The major obstacle to the performance of solid organ transplantation currently is the shortage of donor organs.

T-cell immune constitution after peripheral blood mononuclear cell transplantation in complete DiGeorge syndrome

Complete DiGeorge syndrome (cDGS) is a congenital disorder characterized by typical facies, thymic aplasia, susceptibility to infections, hypoparathyroidism and conotruncal cardiac defect. Fetal thymus or post-natal thymus tissue transplantations and human leucocyte antigen (HLA)-genoidentical bone marrow transplantations were followed in a few cases by immune reconstitution. More recently, a peripheral blood mononuclear cell transplantation (PBMCT) was performed with an HLA-genoidentical donor and followed by a partial T-cell engraftment and immune reconstitution. We report a boy with cDGS, without cardiac defect, who suffered recurrent severe infections. At the age of 4 years, he underwent PBMCT from his HLA-genoidentical sister. He received no conditioning regimen, but graft-versus-host disease (GVHD) prophylaxis was with oral cyclosporin A and mycophenolate mofetil. Toxicity was mild, with grade I acute GVHD. The patient is currently 2.5 years post-PBMCT with excellent clinical performances. Mixed chimaerism can only be observed on the T-cell population (50% donor T cells). T-lymphocyte count fluctuated (CD3 more than 400 x 10(6)/l at d 84 and CD4 more than 200 x 10(6)/l at d 46). Exclusive memory phenotype T cells and absence of new thymic emigrants suggest expansion of infused T cells. T-cell mitogen and tetanus antigen responses normalized a few months after transplantation. After immunizations, specific antibodies were produced. PBMCT from an HLA identical sibling could be an efficient treatment of immune deficiency in cDGS.

Primary cellular immunodeficiencies

Genetic defects in T-cell function lead to susceptibility to infections or to other clinical problems that are more grave than those seen in disorders resulting in antibody deficiency alone. Those affected usually present during infancy with either common or opportunistic infections and rarely survive beyond infancy or childhood. The spectrum of T-cell defects ranges from the syndrome of severe combined immunodeficiency, in which T-cell function is absent, to combined immunodeficiency disorders in which there is some, but not adequate, T-cell function for a normal life span. Recent discoveries of the molecular causes of many of these defects have led to a new understanding of the flawed biology underlying the ever-growing number of defects. Most of these conditions could be diagnosed by means of screening for lymphopenia or for T-cell deficiency in cord blood at birth. Early recognition of those so afflicted is essential to the application of the most appropriate treatments for these conditions at a very early age. The latter treatments include both transplantation and gene therapy in addition to immunoglobulin replacement. Fully defining the molecular defects of such patients is also essential for genetic counseling of family members and prenatal diagnosis.

Correction of DiGeorge anomaly with EBV-induced lymphoma by transplantation of organ-cultured thymus and Epstein-Barr-specific cytotoxic T lymphocytes

A young woman with DiGeorge anomaly showed normal immune tests as a child and did not experience the symptoms of profound T cell immunodeficiency. However, she had chronic pulmonary infections which led to bronchiectasis. At age 14, she developed an Epstein-Barr virus-induced lymphoma and her T cell function tests were markedly abnormal. After intensive chemotherapy, she received an organ-cultured thymus transplant but because of an abnormally high EBV DNA titer was also given autologous EBV-specific cytotoxic T cells, prepared prior to transplant. Titers fell from 80,000 genome copies/mg DNA to 2000 within 6 weeks. She was clinically well and her T cell tests improved. Sixteen months after the transplant, however, her tumor returned; EBV DNA levels had risen to 40,000 copies/mg DNA. She again received autologous EBV-specific cytotoxic T lymphocytes and valcyclovir and Cytogam as well. Her tumor resolved on this therapy and she has remained well to this date, 29 months after the recurrence. T cell tests, which had deteriorated with the recurrence of the tumor, now show normal responses. This experience records a number of unique features of thymus transplantation. This is the first recorded successful thymus transplant in a patient with partial T cell immunity and thus expands the potential of this treatment modality to patients other than infants with complete DiGeorge anomaly. The patient demonstrates cytotoxic activity against mouse cells, demonstrating the ability to respond to a new antigen which requires host antigen presenting cells. Measurement of alpha 1 TRECs (T cell receptor excision circles) shows evidence of increasing and sustained thymopoiesis since the transplant at a level consistent with the age of the transplant donor rather than that of the recipient.

The role of the thymus in immune reconstitution in aging, bone marrow transplantation, and HIV-1 infection

The human thymus is a complex chimeric organ comprised of central (thymic epithelial space) and peripheral (perivascular space) components that functions well into adult life to produce naive T lymphocytes. Recent advances in identifying thymic emigrants and development of safe methods to study thymic function in vivo in adults have provided new opportunities to understand the role that the human thymus plays in immune reconstitution in aging, in bone marrow transplantation, and in HIV-1 infection. The emerging concept is that there are age-dependent contributions of thymic emigrants and proliferation of postthymic T cells to maintain the peripheral T cell pool and to contribute to T cell regeneration, with the thymus contributing more at younger ages and peripheral T cell expansion contributing more in older subjects. New studies have revealed a dynamic interplay between postnatal thymus output and peripheral T cell pool proliferation, which play important roles in determining the nature of immune reconstitution in congenital immunodeficiency diseases, in bone marrow transplantation, and in HIV-1 infection. In this paper, we review recent data on human postnatal thymus function that, taken together, support the notion that the human thymus is functional well into the sixth decade and plays a role throughout life to optimize human immune system function.

Transplantation of thymus tissue in complete DiGeorge syndrome

BACKGROUND

The DiGeorge syndrome is a congenital disorder that affects the heart, parathyroid glands, and thymus. In complete DiGeorge syndrome, patients have severely reduced T-cell function.

METHODS

We treated five infants (age, one to four months) with complete DiGeorge syndrome by transplantation of cultured postnatal thymus tissue. Follow-up evaluations included immune phenotyping and proliferative studies of peripheral-blood mononuclear cells plus biopsy of the thymus allograft. Thymic production of new T cells was assessed in peripheral blood by tests for T-cell-receptor recombination excision circles, which are formed from excised DNA during the rearrangement of T-cell-receptor genes.

RESULTS

After the transplantation of thymus tissue, T-cell proliferative responses to mitogens developed in four of the five patients. Two of the patients survived with restoration of immune function; three patients died from infection or abnormalities unrelated to transplantation. Biopsies of grafted thymus in the surviving patients showed normal morphologic features and active T-cell production. In three patients, donor T cells could be detected about four weeks after transplantation, although there was no evidence of graft-versus-host disease on biopsy or at autopsy. In one patient, the T-cell development within the graft was demonstrated to accompany the appearance of recently developed T cells in the periphery and coincided with the onset of normal T-cell function. In one patient, there was evidence of thymus function and CD45RA+CD62L+ T cells more than five years after transplantation.

CONCLUSIONS

In some infants with profound immunodeficiency and complete DiGeorge syndrome, the transplantation of thymus tissue can restore normal immune function. Early thymus transplantation - before the development of infectious complications - may promote successful immune reconstitution.

Chromosomes 22q11 deletion syndrome: an update and review for the primary pediatrician

Chromosome 22q11 deletion syndrome is a relatively newly described syndrome that encompasses the majority of patients previously felt to have velo-cardio-facial syndrome, DiGeorge syndrome, and conotruncal anomaly face syndrome. The disorder is characterized by a deletion of band 11 on the long arm of chromosome 22 most often recognized by fluorescent in situ hybridization (FISH) techniques. Extensive laboratory investigations are currently ongoing to uncover the specific genes involved and their functions. Phenotypically, individuals present with congenital heart disease, palatal abnormalities, facial dysmorphism, and developmental delay, as well as variable degrees of immunodeficiency, hypocalcemia, and endocrine abnormalities. The primary care physician has an important role in caring for these patients and their families. We review the current state of knowledge regarding chromosome 22q11 deletion syndrome, with an emphasis on the clinical presentation and on prevention and treatment of the known complications associated with this multisystem disorder. Chromosome 22q11 deletion syndrome can be inherited in an autosomal dominant fashion or result from a de novo deletion or translocation. Hence, this syndrome may have significant reproductive risks to affected individuals and families.

Humoral immunity in DiGeorge syndrome

OBJECTIVE

To assess humoral immunity after immunization and natural infection in patients with clinical manifestations of the DiGeorge anomalad.

DESIGN

Retrospective review of cases.

SETTING

Ambulatory immunology clinic of a tertiary care teaching hospital.

PATIENTS

The 13 patients had a symptom complex including congenital heart disease, characteristic facies of the DiGeorge anomalad, possible hypocalcemia, and thymic hypoplasia or aplasia. Molecular and cytogenic studies of 12 patients demonstrated that all had 22q11 microdeletions.

METHODS

Serial studies included lymphocyte population enumeration by flow cytometry, lymphocyte proliferation assays with the mitogens phytohemagglutinin and pokeweed mitogen and Staphylococcus aureus, and immunoglobulin quantitation. Specific antibody studies included virus neutralization assays for poliovirus antibodies, and enzyme-linked immunosorbent assay for diphtheria, tetanus, measles, rubella, varicella-zoster virus (VZV), and cytomegalovirus (CMV) antibodies. Avidity of rubella, VZV, and CMV antibodies was tested by enzyme-linked immunosorbent assay modified to include a mild protein denaturant in the first wash after incubation with sera.

RESULTS

All patients had a CD3+ cell count greater than 0.500 x 10(9)/L and a CD4+ cell count greater than 0.350 x 10(9)/L). One patient had low proliferation responses to S. aureus, and one to phytohemagglutinin and pokeweed mitogen. Immunoglobulin levels, compared with those in age-related control subjects, were normal except that two patients had transient, borderline low IgG levels and two had elevated IgA levels. Specific antibody tests showed (No. of patients with positive results/No. tested) the following: diphtheria (13/13); tetanus (13/13); poliomyelitis caused by polio virus type 1 (5/9), type 2 (9/9), and type 3 (8/9); measles (11/13); rubella (11/13); and infection with VZV (5/5) and CMV (7/13). There were no significant differences in antibody avidity results between patients and control subjects for rubella (mean avidity index, 83.5 +/- 8.79 vs 85 +/- 17.6), VZV (81.6 +/- 3.98 vs 65.1 +/- 12.38), or CMV (69.3 +/- 22.31 vs 73.3 +/- 12.46).

CONCLUSIONS

Patients with "partial" DiGeorge anomalad, defined by clinical and immunologic criteria, can be immunized and for the most part can generate good antibody responses.

New perspectives on use of thymic factors in immune deficiency

Current knowledge on the role of thymic factors in the immune response is inadequate and remains relatively primitive when compared with present technical possibilities for assessing lymphocyte subsets or cytokine interaction. New studies support the potential importance of thymic factors as regulators of immune interactions. Indirect evidence supports the concept that thymic factors may work at the level of IL-2. The functional identity of cells responsive to thymic factors and the relation of observed effects to cytokine network interactions need to be established. The use of thymic factors in the future will depend on the development of criteria to identify appropriate settings in which to use such factors and the implementation of appropriate measures of immune functional response.

Human fetal tissue research: practice, prospects, and policy

Tissue from human fetal cadavers has long been used for medical research, experimental therapies, and various other purposes. Research within the last two decades has led to substantial progress in many of these areas, particularly in the application of fetal tissue transplantation to the treatment of human disease. As a result, clinical trials have now been initiated at centers around the world to evaluate the use of human fetal tissue transplantation for the therapy of Parkinson's disease, insulin-dependent diabetes mellitus, and a number of blood, immunological and, metabolic disorders. Laboratory studies suggest a much wider range of disorders may in the future be treatable by transplantation of various types of human fetal tissue. A combination of characteristics renders fetal tissue uniquely valuable for such transplantation, as well as for basic research, the development of vaccines, and a range of other applications. Although substitutes for human fetal tissue are being actively sought, for many of these applications there are at present no satisfactory alternatives. Important issues remain unresolved concerning the procurement, distribution, and use of human fetal cadaver tissue as well as the effects of such use on abortion procedures and incidence. These issues can be addressed by the introduction of appropriate guidelines or legislation, and need not be an impediment to legitimate research and therapeutic use of fetal tissue.

The DiGeorge sequence. II. Immunologic findings in partial and complete forms of the disorder

We present immunological in vitro data on a group of 16 patients with the DiGeorge sequence (DGS). Detailed tests gave evidence that the decrease in number and function of mature T-cells is closely correlated with phenotypic expression and represents a wide immunological spectrum ranging from normal function to severe combined immunodeficiency with B-cells. Careful immunological testing in DGS may help to plan therapeutic procedures (i.e. thymic factor therapy or bone marrow transplantation), may also have prognostic significance and help to gain insight into mechanisms operative in disturbances of T-cell regulation.

Successful bone marrow transplantation with split lymphoid chimerism in DiGeorge syndrome

A female infant with DiGeorge syndrome associated with severe T-cell immunodeficiency underwent a successful bone marrow transplantation from her HLA-identical, mixed leukocyte culture-nonreactive brother at 5 months of age. Mature circulating T cells and mitogen-induced proliferative responses were detectable at 10 days posttransplant, and by 8 months post-transplant functional T- and B-cell reconstitution was documented by normal responses to mitogens and normal levels of serum immunoglobulins as well as in vitro and in vivo T-cell reactivity to specific antigens and production of specific antibody to T cell-dependent antigens in vivo. Phytohemagglutinin-induced interleukin-2 production and cell surface interleukin-2 receptor expression improved posttransplant, with normal production values observed by 8 months posttransplant. Histologic examination of appendix and thoracic lymph node obtained 9 and 17 months posttransplant, respectively, revealed near-normal lymphoid architecture, with germinal center formation providing morphologic confirmation of reconstitution. Stable split lymphoid chimerism with T cells of donor origin and B cells remaining recipient in origin was documented by sex chromosome analysis. Two years posttransplant the subject remains free of serious infections. In conclusion, this case indicates that bone marrow transplantation can produce peripheral immunoreconstitution without need for significant thymic influence, most likely by providing a source of postthymic T cells, and that bone marrow transplantation should be considered a therapeutic option in patients with DiGeorge syndrome associated with severe T-cell deficiency.

Prediction of persistent immunodeficiency in the DiGeorge anomaly

To assess the natural history of the immune defect in DiGeorge anomaly, we reviewed serial immunologic studies in 18 patients. The diagnosis was made with criteria based on the concept of the DiGeorge anomaly as a field defect. Initial or early follow-up laboratory examination suggested moderate to normal T cell function in 14 patients. None of these patients have lost T cell capability; they have never had infections characteristic of T cell deficiency. Four patients had clinical and laboratory evidence of profound immunodeficiency. A decreased number of CD4+ cells (less than 400/microliters) and a decrease in phytohemagglutinin responsiveness (stimulation index less than 10) may be useful in discriminating patients with immunodeficiency; absolute lymphocyte count and immunoglobulin values were not informative. At the time of surgery, the thymus was not found in 11 of 14 patients; however, only two of these patients had immunodeficiency. Patients with a persistently low number of CD4+ cells and decreased phytohemagglutinin response are candidates for immunologic reconstitution.