Foetal thymic transplant in a case of Digeorge's syndrome

Thymus transplantation for DiGeorge Syndrome: a systematic review

BACKGROUND

DiGeorge syndrome (DGS) is a condition typically associated with athymia, parathyroid hypoplasia or aplasia, and congenital heart defects. Athymia in these patients causes severe immunodeficiency, causing high mortality and morbidity, often requiring thymic tissue transplantation. The present systematic review aims to consolidate the present evidence on thymus transplantation in DGS.

METHODS

An electronic literature search of five databases (PubMed, Medline, Scopus, EBSCOhost, and CINAHL) was performed from inception till September 2024. Relevant articles were selected, and data was extracted by two independent reviewers.

RESULTS

A total of 16 articles were included from an initial set of 1227 articles. Patients diagnosed with DGS in the included studies were predominantly male, and the age at which thymus transplantation was done typically varied from 0.8 to 26 months. Several patients had chromosome 22q11 hemizygosity. Thymic tissue was taken from tissues of pediatric patients undergoing cardiothoracic surgery. Pre-transplant medication included immunosuppressants with rabbit anti-thymocyte globulin (RATGAM) being frequently used alongside steroids and tacrolimus. This tissue was cultured and transplanted into the quadriceps muscle of the patients under general anesthesia. Thymopoiesis was well described in most patients with graft failures and rejections occurring rarely. Naive T-cell development was noted in almost all patients with clearance of infections in many cases. Common postoperative complications include sepsis, haemorrhage, gastrointestinal disturbances, among others. Mortality was uncommon but often associated with intracerebral hemorrhages and sepsis.

CONCLUSION

Thymus transplantation is a relatively safe and effective procedure in patients with DGS with athymia. Future research should explore the addition of allogenic parathyroid gland transplantation along with thymic tissue.

Thymic microenvironment's impact on immunosenescence

Age-related thymic involution is characterized by the loss of T cell development and the supporting epithelial network, which are replaced by adipose tissue. We previously showed that aging functionally impairs lymphohematopoietic progenitor cells, including thymic early T cell progenitors (ETPs), contributing to thymic involution. Considering that the thymic microenvironment is essential for thymocyte incubation, we aimed to investigate its role in age-related thymic involution and the mechanisms underlying these changes. The challenge in studying these processes led us to transplant T cell-depleted fetal thymus tissue into the kidney capsule of aged mice. This model allowed us to identify the mechanisms driving age-related changes in the thymic microenvironment and to assess whether these changes could be reversed. Flow cytometry was used to detect naïve T cells (CD62L+CD44-), including CD4 CD8 double-negative, double-positive, and single-positive T cells. Real-time PCR was used to detect and quantify signal-joint T cell receptor excision circles. We rearranged δRec-ΨJα in murine peripheral blood leukocytes to evaluate the thymic output of newly developed naïve T cells in the mice and gene expression in the thymus. Age-related thymic involution decreased naïve T cells and increased memory T cells, while fetal thymus transplantation improved thymic output and T cell production and reversed the impairment of thymopoiesis due to thymic involution in aged mice. Furthermore, the expression of key cytokines was restored and ETPs in the aged mice showed normal thymic T cell development. Our study suggests that degenerative changes in the thymic microenvironment are the primary cause of thymic dysfunction, leading to immunosenescence associated with age-related thymic involution.

Current and Future Therapeutic Approaches for Thymic Stromal Cell Defects

Inborn errors of thymic stromal cell development and function lead to impaired T-cell development resulting in a susceptibility to opportunistic infections and autoimmunity. In their most severe form, congenital athymia, these disorders are life-threatening if left untreated. Athymia is rare and is typically associated with complete DiGeorge syndrome, which has multiple genetic and environmental etiologies. It is also found in rare cases of T-cell lymphopenia due to Nude SCID and Otofaciocervical Syndrome type 2, or in the context of genetically undefined defects. This group of disorders cannot be corrected by hematopoietic stem cell transplantation, but upon timely recognition as thymic defects, can successfully be treated by thymus transplantation using cultured postnatal thymic tissue with the generation of naïve T-cells showing a diverse repertoire. Mortality after this treatment usually occurs before immune reconstitution and is mainly associated with infections most often acquired pre-transplantation. In this review, we will discuss the current approaches to the diagnosis and management of thymic stromal cell defects, in particular those resulting in athymia. We will discuss the impact of the expanding implementation of newborn screening for T-cell lymphopenia, in combination with next generation sequencing, as well as the role of novel diagnostic tools distinguishing between hematopoietic and thymic stromal cell defects in facilitating the early consideration for thymus transplantation of an increasing number of patients and disorders. Immune reconstitution after the current treatment is usually incomplete with relatively common inflammatory and autoimmune complications, emphasizing the importance for improving strategies for thymus replacement therapy by optimizing the current use of postnatal thymus tissue and developing new approaches using engineered thymus tissue.

Replacing defective thymus function

PURPOSE OF REVIEW

Transplantation of cultured postnatal allogeneic thymus has been successful for treating athymia, mostly associated with complete DiGeorge syndrome, for more than 20 years. Advances in molecular genetics provide opportunities for widening the range of athymic conditions that can be treated while advances in cell culture and organ/tissue regeneration may offer the prospect of alternative preparations of thymic tissue. There are potential broader applications of this treatment outside congenital athymia.

RECENT FINDINGS

At the same time as further characterization of the cultured thymus product in terms of thymic epithelial cells and lymphoid composition, preclinical studies have looked at de-novo generation of thymic epithelial cells from stem cells and explored scaffolds for delivering these as three-dimensional structures. In the era of newborn screening for T-cell lymphopaenia, a broadening range of defects leading to athymia is being recognized and new assays should allow differentiation of these from haematopoietic cell defects, pending their genetic/molecular characterization. Evidence suggests that the tolerogenic effect of transplanted thymus could be exploited to improve outcomes after solid organ transplantation.

SUMMARY

Thymus transplantation, the accepted standard treatment for complete DiGeorge syndrome is also appropriate for other genetic defects leading to athymia. Improved strategies for generating thymus may lead to better outcomes and broader application of this treatment.

Sources of Human Hematopoietic Stem Cells for Transplantation–A Review

Transplantation of hematopoietic stem cells provides a means of replacing a defective hematopoietic system in patients with a wide range of malignant and nonmalignant disorders that affect the blood forming tissue. The same procedure has also allowed dose-escalation of standard chemotherapy and radiotherapy in the treatment of malignant disease of nonhematological origin. Until recently, bone marrow has been the sole source of hematopoietic stem cells, but limitations of conventional bone marrow transplantation have stimulated a search for alternative sources and uses of stem cells. Fetal tissues (especially liver) are a recognized source of transplantable stem cells and offer the great advantage of reduced immunogenicity, potentially removing the problems of tissue type matching. Umbilical cord blood is also a rich source of stem cells and, although it contains alloreactive cells, it is readily available without special ethical constraints. Both fetal tissue and cord blood suffer the disadvantages of limited numbers of stem cells per donation, and there is much interest in the development of technologies for the safe and reliable expansion and/or pooling of stem and progenitor cells. The observation that small numbers of stem cells are found in the peripheral blood of adults has led to the exploitation of the blood as a further source of stem cells. The ability to mobilize these cells from the medullary compartment into the periphery by the use of chemotherapy and/or recombinant hematopoietic growth factors has enabled the collection of sufficient numbers of cells for transplantation purposes. All of these advances are increasing the options and the range of choices available to clinicians and patients in the arena of hematopoietic stem cell transplantation.

Clinical course and outcome predictors of critically ill infants with complete DiGeorge anomaly following thymus transplantation

OBJECTIVES

To identify risk factors for PICU admission and mortality of infants with complete DiGeorge anomaly treated with thymus transplantation. We hypothesized that age at transplantation and the presence of congenital heart disease would be risk factors for emergent PICU admission, and these factors plus development of septicemia would increase morbidity and mortality.

DESIGN

Retrospective review.

SETTING

Academic medical-surgical PICU.

PATIENTS

All infants with complete DiGeorge anomaly treated with thymus transplantation between January 1, 1993, and July 1, 2010.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Consent was obtained from 71 infants with complete DiGeorge anomaly for thymus transplantation, and 59 infants were transplanted. Median age at transplantation was 5.0 months (range, 1.1-22.1 mo). After transplantation, 12 of 59 infants (20%) required 25 emergent PICU admissions. Seven of 12 infants (58%) survived to PICU discharge with six surviving 6 months posttransplantation. Forty-two of 59 infants (71%) transplanted had congenital heart disease, and 9 of 12 (75%) who were admitted to the PICU had congenital heart disease. In 15 of 25 admissions (60%), intubation and mechanical ventilation were necessary. There was no difference between median ventilation-free days between infants with and without congenital heart disease (33 d vs 23 d, p = 0.544). There was also no correlation between ventilation-free days and age of transplantation (R, 0.17; p = 0.423). Age at transplantation and the presence of congenital heart disease were not associated with risk for PICU admission (odds ratio, 0.95; 95% CI, 0.78-1.15 and odds ratio, 1.27; 95% CI, 0.30-5.49, respectively) or PICU mortality (odds ratio, 0.98; 95% CI, 0.73-1.31 and odds ratio, 0.40; 95% CI, 0.15-1.07, respectively).

CONCLUSIONS

Most transplanted infants did not require emergent PICU admission. Age at transplantation and the presence of congenital heart disease were not associated with PICU admission or mortality.

Immunodeficiency in DiGeorge Syndrome and Options for Treating Cases with Complete Athymia

The commonest association of thymic stromal deficiency resulting in T-cell immunodeficiency is the DiGeorge syndrome (DGS). This results from abnormal development of the third and fourth pharyngeal arches and is most commonly associated with a microdeletion at chromosome 22q11 though other genetic and non-genetic causes have been described. The immunological competence of affected individuals is highly variable, ranging from normal to a severe combined immunodeficiency when there is complete athymia. In the most severe group, correction of the immunodeficiency can be achieved using thymus allografts which can support thymopoiesis even in the absence of donor-recipient matching at the major histocompatibility loci. This review focuses on the causes of DGS, the immunological features of the disorder, and the approaches to correction of the immunodeficiency including the use of thymus transplantation.

Murine models of Candida gastrointestinal colonization and dissemination

Ninety-five percent of infectious agents enter through exposed mucosal surfaces, such as the respiratory and gastrointestinal (GI) tracts. The human GI tract is colonized with trillions of commensal microbes, including numerous Candida spp. Some commensal microbes in the GI tract can cause serious human infections under specific circumstances, typically involving changes in the gut environment and/or host immune conditions. Therefore, utilizing animal models of fungal GI colonization and dissemination can lead to significant insights into the complex pathophysiology of transformation from a commensal organism to a pathogen and host-pathogen interactions. This paper will review the methodologic approaches used for modeling GI colonization versus dissemination, the insights learned from these models, and finally, possible future directions using these animal modeling systems.

Immunological aspects of 22q11.2 deletion syndrome

Chromosome 22q11 deletion is the most common chromosomal deletion syndrome and is found in the majority of patients with DiGeorge syndrome and velo-cardio-facial syndrome. Patients with CHARGE syndrome may share similar features. Cardiac malformations, speech delay, and immunodeficiency are the most common manifestations. The immunological phenotype may vary widely between patients. Severe T lymphocyte immunodeficiency is rare-thymic transplantation offers a new approach to treatment, as well as insights into thymic physiology and central tolerance. Combined partial immunodeficiency is more common, leading to recurrent sinopulmonary infection in early childhood. Autoimmunity is an increasingly recognized complication. New insights into pathophysiology are reviewed.

Thymus Transplantation

Thymus transplantation was first attempted in the 1960s and 1970s using fetal thymus tissue [1, 2]. The results overall were disappointing [3–6]. In part the poor outcomes related to the lack of reagents needed to characterize and identify the patients into those who were truly athymic (complete DiGeorge anomaly) and those who had bone marrow stem cell problems (severe combined immunodeficiency). It is also possible that the fetal thymus tissue was too small to reconstitute a human infant [7]. The use of fetal thymus carried the risk of fatal graft versus host disease since mature T-cells can be found in the human thymus by the end of the first trimester [3]. By 1986, in a review of 26 infants treated with fetal thymus transplantation, 22 had died; the other 4 patients had achieved a 3-year survival [6].

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.

The fundamental contribution of Robert A. Good to the discovery of the crucial role of thymus in mammalian immunity

Robert Alan Good was a pioneer in the field of immunodeficiency diseases. He and his colleagues defined the cellular basis and functional consequences of many of the inherited immunodeficiency diseases. His was one of the groups that discovered the pivotal role of the thymus in the immune system development and defined the separate development of the thymus-dependent and bursa-dependent lymphoid cell lineages and their responsibilities in cell-mediated and humoral immunity.

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.

Thymopoiesis following allogeneic stem cell transplantation: new possibilities for improvement

Treatment related mortality (TRM) has restricted the application of allogeneic hematopoietic stem cell transplantation (allo-SCT) as a treatment modality for patients with a variety of malignant and non-malignant hematological disorders. TRM is mainly caused by severe opportunistic infections, due to an impaired immune reconstitution. The extreme slow recovery of newly developed, donor stem cell derived naive T-cells is currently considered to be the most important determinant of the impaired immune competence after allo-SCT. Therefore, enhancing naive T-cell recovery following allo-SCT by improving thymopoiesis has recently gained new interest. Possible strategies to improve thymopoiesis may include approaches to protect the nursing stromal compartment and approaches to directly stimulate the differentiation and proliferation of T-cell progenitors intra-thymically. Among the latter is interleukin-7 (IL-7), which has appeared promising in preclinical experimental settings and is expected to enter early clinical studies soon. Keratinocyte growth factor (KGF) is an epithelial growth factor that may protect the thymic epithelium and thereby may preserve it's support of thymopoiesis. KGF has been evaluated clinically in the setting of autologous stem cell transplantation and studies in the setting of allo-SCT are awaited in the near future.

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

Cytokines in the oral mucosa of mice infected with Candida albicans

Oropharyngeal candidiasis is associated with defects in cell-mediated immunity, and is commonly seen in immunocompromised patients. We have previously shown that T-cell-deficient BALB/c nude (nu/nu) mice are extremely susceptible to oropharyngeal candidiasis, and that recovery from a chronic infection is dependent on CD4 T lymphocytes. In this study we describe the local tissue cytokine profile in lymphocyte-reconstituted immunodeficient mice and their euthymic counterparts. Mice were infected orally with 108 cells of the yeast Candida albicans, and oral tissues sampled on days 0, 4, 8, and 14. Nude mice were reconstituted with 3 x 107 naïve lymphocytes following oral inoculation. Interleukin (IL)-6, interferon (IFN)-gamma and tumour necrosis factor (TNF)-alpha were identified in the oral tissues of infected euthymic mice recovering from oral infection, as well as naïve controls. TNF-alpha was identified in nude oral tissue on days 4 and 8, but only after lymphocyte reconstitution. No IL-2, IL-4 or IL-10 was detected in either euthymic or athymic mice at any time-point throughout the experiment. This study confirms the functional activity of T lymphocytes in reconstituted nude mice, and suggests that TNF-alpha may be an important mediator in the recovery from oropharyngeal candidiasis.

Cellular immunology in a historical perspective

Bruton's XLA and DiGeorge syndrome patients show that two basic immune systems are distinct from each other in humans - thymus-dependent cell-mediated immunodeficiencies vs. antibody-based immunodeficiencies. The appendix-sacculus lymphoid organ of rabbits, like the bursa of Fabricius, represents a central lymphoid organ. Chronic granulomatous disease of childhood (CGD) revealed that phagocytosis killing of catalase-positive microorganisms employ oxidative burst. Bone marrow transplantation (BMT) proved life saving in severe combined immunodeficiency (SCID). The first BMT cured XSCID and the second BMT cured a complicating aplastic anemia launching BMT as a treatment of many diseases. Now 75 fatal diseases have been cured by myeloablative BMT. BMT also cured experimental autoimmune diseases. BMT alone did not cure lupus with polyarthritis in MRL/lpr mice or polyarthritis in NZB/KN mice, but BMT plus bone (stromal cell) transplants cured these diseases. Autoimmune diseases and lethal glomerulonephritis were prevented or cured in BXSB mice by mixed allogeneic plus syngeneic BMT. X-linked Hyper IgM syndrome (XHIM) was also cured by BMT from a 2-year-old MHC-matched sibling donor. Nonmyeloablative BMT plus mesenchymal stem cells (stromal cells) was effective treatment for a form of collagen-vascular disease and also a lethal form of hypophosphatasia. Mannan-binding lectin, an opsonin that activates the complement system when mutated and at low levels in blood, opens a door to frequent infections throughout childhood and adult life. This new immunodeficiency is based on genetic mutations that involve a native defense system.

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.

T cells augment monocyte and neutrophil function in host resistance against oropharyngeal candidiasis

The purpose of this study was to identify the cell populations involved in recovery from oral infections with Candida albicans. Monoclonal antibodies specific for CD4+ cells, CD8+ cells, and polymorphonuclear leukocytes were used to deplete BALB/c and CBA/CaH mice of the relevant cell populations in systemic circulation. Monocytes were inactivated with the cytotoxic chemical carrageenan. Mice were infected with 10(8) C. albicans yeast cells and monitored for 21 days. Systemic depletion of CD4+ and CD8+ T lymphocytes alone did not increase the severity of oral infection compared to that of controls. Oral colonization persisted in animals treated with head and neck irradiation and depleted of CD4+ T cells, whereas infections in animals that received head and neck irradiation alone or irradiation and anti-CD8 antibody cleared the infection in a comparable fashion. The depletion of polymorphonuclear cells and the cytotoxic inactivation of mononuclear phagocytes significantly increased the severity of oral infection in both BALB/c and CBA/CaH mice. High levels of interleukin 12 (IL-12) and gamma interferon (IFN-gamma) were produced by lymphocytes from the draining lymph nodes of recovering animals, whereas IL-6, tumor necrosis factor alpha, and IFN-gamma were detected in the oral mucosae of both naïve and infected mice. The results indicate that recovery from oropharyngeal candidiasis in this model is dependent on CD4+-T-cell augmentation of monocyte and neutrophil functions exerted by Th1-type cytokines such as IL-12 and IFN-gamma.

Chronic mucocutaneous candidiasis

Chronic mucocutaneous candidiasis should be viewed as a spectrum of disorders in which the patients have persistent and/or recurrent candidiasis of the skin, nails and mucous membranes. Some of the conditions have genetic predispositions. A common immunologic abnormality is failure of the patient's T lymphocytes to produce cytokines that are essential for expression of cell-mediated immunity to Candida. Antifungal drugs are effective in clearing the infections, and treatments that restore cellular immunity have produced long term remissions.

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.

Analysis and characterization of hematopoietic progenitor cells from fetal bone marrow, adult bone marrow, peripheral blood, and cord blood

Hematopoietic stem cell transplantation has been increasingly used to replace a defective hematopoietic system and to treat various genetic defects as well as malignant diseases. However, the limitations of conventional bone marrow transplantation have stimulated an intense interest in exploring the use of alternative sources of hematopoietic stem cells, including peripheral blood mononuclear cells (PBMC) and cord blood (CB). A major investigative effort of our laboratory has been focused on evaluating fetal bone marrow (FBM) for transplantation. The current study compares and characterizes the functional and phenotypic characteristics of FBM, CB, adult bone marrow (ABM), and PBMC by clonogenicity assays, immunogenicity, and the quantification of progenitor cells. There was a striking difference in the proportion of CD34+ cells in FBM, ABM, PBMC, and CB (24.6%, 2.1%, 0.5%, and 2.0%, respectively). The clonogenic potential, as measured by colony forming unit in culture (CFU-C) assay, was significantly higher in FBM when compared with ABM, PBMC, and CB (202.5, 73.5, 40.8, and 65.5 colonies/10(5) cells, respectively). There was a significant decrease in proliferative responsiveness in mixed lymphocyte reaction (MLR) assay of FBM and CB compared with ABM and PBMC. These observations indicate that each source of hematopoietic stem cells has different intrinsic properties closely correlated with ontogenetic age that is a vital determinant for phenotypic characteristics, lineage commitments, immunogenicity, and proliferative potentials.

Features of DiGeorge syndrome and CHARGE association in five patients

We report on five patients presenting with features of two congenital disorders, DiGeorge syndrome (DGS) and CHARGE association. CHARGE association is usually sporadic and its origin is as yet unknown. Conversely, more than 90% of DGS patients are monosomic for the 22q11.2 chromosomal region. In each of the five patients, both cytogenetic and molecular analysis for the 22q11.2 region were normal. In view of the broad clinical spectrum and the likely genetic heterogeneity of both disorders, these cases are consistent with the extended phenotype of either DGS without 22q11.2 deletion or CHARGE association, especially as several features of CHARGE association have been reported in rare patients with 22q11.2 deletion association phenotypes. On the other hand, these could be novel cases of an independent association involving a complex defect of neural crest cells originating from the pharyngeal pouches.

Normalization of the peripheral blood T cell receptor V beta repertoire after cultured postnatal human thymic transplantation in DiGeorge syndrome

Complete DiGeorge syndrome is an immunodeficiency disease characterized by thymic aplasia and the absence of functioning peripheral T cells. A patient with this syndrome was transplanted with cultured postnatal human thymic tissue. Within 5 weeks of transplantation, flow cytometry, T cell receptor V beta sequence analysis, and cell function studies showed the presence of oligoclonal populations of nonfunctional clonally expanded peripheral T cells that were derived from pretransplantation T cells present in the skin. However, at 3 months posttransplantation, a biopsy of the transplanted thymus showed normal intrathymic T cell maturation of host T cells with normal TCR V beta expression on thymocytes. By 9 months postransplantation, peripheral T cell function was restored and the TCR V beta repertoire became polyclonal, coincident with the appearance of normal T cell function. These data suggest that the transplanted thymus was responsible for the establishment of a new T cell repertoire via thymopoiesis in the chimeric thymic graft.

Organ culture for thymus transplantation

A method is presented for organ culture of postnatal thymus. Such tissue has been used for transplantation for nearly 20 years, but lasting benefit has been observed only in patients with the DiGeorge anomaly. Transplantation in other diseases has produced little or no results. Recently, improved methods for preparing the tissue as well as modifications of the culture media show marked improvement in quality and quantity of tissue suitable for transplant. In addition, using recently available monoclonal antibodies, preservation of vital stromal components can be monitored. The availability of reasonable amounts of high quality thymus tissue for transplantation may stimulate interest in further clinical trials where thymus transplantation may augment or restore T cell immunity.

Upper limb malformations in DiGeorge syndrome

We report on upper limb anomalies in two children with a complete DiGeorge sequence: conotruncal defects, hypocalcemia, thymic aplasia, and facial anomalies. One child had preaxial polydactyly, and the other had club hands with hypoplastic first metacarpal. In both patients, molecular analysis documented a 22q11 deletion. To our knowledge, limb anomalies have rarely been reported in DiGeorge syndrome, and they illustrate the variable clinical expression of chromosome 22q11 deletions.

Chronic mucocutaneous candidiasis

Chronic mucocutaneous candidiasis is a complex disorder in which patients have chronic and recurrent Candida albicans infections of the skin, nails, and mucous membranes. There are several subgroups of patients with chronic mucocutaneous candidiasis, and these can be identified by associated disorders such as autoimmune diseases, endocrinopathies, thymoma, and interstitial keratitis, as well as the distribution and severity of the Candida infections. Several other disorders may coexist in patients with chronic mucocutaneous candidiasis. These include other infectious diseases, endocrinopathies, dental enamel dysplasia, vitiligo, and alopecia totalis. Successful treatment programs should include antifungal drugs and manipulations that correct the immunologic abnormalities that predispose the patient to Candida infections.

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.

Orofacial manifestations in the primary immunodeficiency disorders

Primary immunodeficiencies are increasingly recognized yet there is little data concerning the oral manifestations of such disorders. This article reviews the current literature and details the oral aspects of well-characterized primary immunodeficiencies.

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.

Orofacial manifestations in primary immunodeficiencies: T lymphocyte defects

The orofacial manifestations of 10 non-HIV-infected children with primary defects of cell mediated immunity are reported. Oral candidiasis was observed in 80% of patients, with oral ulceration present in 50%. Other oral manifestations included enamel hypoplasia, angular stomatitis, oral purpura and recurrent herpetic infection.

The calf thymus superoxide dismutase: a protein active on cholesterol metabolism

1. Recent studies on the new aspects of thymus physiology describing the correlation between thymus hormones and pituitary hormone secretion, are illustrated. 2. Subsequently, results of a series of experiments showing the effect of a calf thymus protein on cholesterol synthesis in rat hepatocyte cells are discussed. 3. The last part of this review is focused on the biochemical characteristics of this calf thymus protein that revealed an amino acid sequence that was found to be identical with regions of bovine erythrocyte superoxide dismutase. New perspectives of studies, focused on the isolation of possible superoxide dismutase membrane receptors, are described at the end of this review.

From a historical outline of transplants to the concept of biological ego

A chronology of the biological preliminaries of human transplantation science is proposed together with a chronological listing of the applications which transplants have had in clinical medicine in general and in pediatrics in particular. The most significantly immunological elements which surface from this assortment of experiences (in which those of pediatric interest have a considerable role) contribute easily to a more deeply perceived culture of man's biological individuality.

Chronic mucocutaneous candidiasis

Chronic mucocutaneous candidiasis can be defined as a group of syndromes that have as a common feature infections of the skin, nails and mucous membranes with Candida albicans. A variety of disorders including endocrine dysfunctions, alopecia, vitiligo, malabsorption syndromes, neoplasms and other infections may also occur in patients with chronic mucocutaneous candidiasis, but these vary considerably from patient to patient. In most patients with chronic mucocutaneous candidiasis, there are abnormalities of cell-mediated immunity. These may be limited to antigens of Candida albicans, but in some patients they are more extensive and involve the T-lymphocyte-mediated responses to all antigens. These immunologic defects are the factors that predispose patients to infections with opportunistic organisms such as Candida spp. Fungal infections in patients with chronic mucocutaneous candidiasis usually respond to treatment with conventional antifungal agents, but often relapse shortly after treatment is stopped unless the defects in the cell-mediated immune system have been corrected.

DiGeorge syndrome with hypogammaglobulinaemia: a patient with excess suppressor T cell activity treated with fetal thymus transplantation

A male infant with DiGeorge syndrome had hypogammaglobulinaemia with a normal number of B cells. CD3(+) T cells were reduced and the CD4(+)/CD8(+) ratio was reversed. Proliferative responses of T cells to mitogens and to allogeneic cells were low. The pokeweed mitogen (PWM)-induced B cell differentiation assay revealed a higher than normal suppressor T cell activity. This suggests that some T cells had differentiated into functionally mature cells resulting in an imbalance of regulatory T cell functions and that excess suppressor activity might play a role in hypogammaglobulinaemia. Fetal thymus transplantation improved both cellular and humoral immunity. The patient's susceptibility to viral and bacterial infections, proliferative response of T cells and serum Ig concentration returned to normal. The excess suppressor activity seen before transplantation disappeared. Hypocalcaemia did not improve. These results show that fetal thymus transplantation was effective not only in reconstituting cellular immunity but also in normalizing the imbalance of regulatory T cell functions in this patient with DiGeorge syndrome.

Indications for immunotherapy

Underlying immunodeficiency should be suspected in every patient, irrespective of age, who has recurrent, persistent, severe, or unusual infections. Defects in immunity can be classified into primary or secondary disorders involving specific or nonspecific immune mechanisms. Several forms of primary and secondary immunodeficiency exist for which various immunotherapeutic modalities are available. Significant among these are immunoglobulins commercially available for intravenous infusion. Other therapies include transplantation of tissue such as bone marrow, fetal liver, and fetal thymus. Enzyme replacement therapy is being developed, as is the use of products unique to immunocompetent cells, such as thymus extract, thymosin, interleukins, and transfer factor. Forms of nonspecific immune modulators and stimulators are other possibilities, especially in the context of the immunotherapy of tumors.

Cardiovascular anomalies in DiGeorge syndrome and importance of neural crest as a possible pathogenetic factor

One hundred sixty-one cases of DiGeorge syndrome (111 previously reported in which details concerning individual patients were given and 50 observed) were analyzed for occurrence and type of cardiovascular anomalies. Only 5 patients had a normal heart. Interrupted aortic arch type B was the major anomaly in 48 patients and persistent truncus arteriosus in 37. Therefore, in about half of the patients with DiGeorge syndrome the major anomaly was one that is rare. Conversely, of those patients with interrupted aortic arch, 68% had DiGeorge syndrome, as did 33% of all patients with truncus arteriosus. Although tetralogy of Fallot was also seen often in DiGeorge syndrome (10 patients), these cases represented less than 2% of the total number of cases of tetralogy of Fallot. Similarly, less than 1% of children with isolated ventricular septal defect or transposition of the great arteries had DiGeorge syndrome. The primary cardiovascular anomaly always involved the aortic arch system or the arterial pole of the heart. Recent studies show that neural crest cells play a crucial role in development of pharyngeal (bronchial) pouch derivatives, e.g., thymus and parathyroid glands, as well as the aortic arches and the truncoconal part of the heart. These studies and present observations support the view that DiGeorge syndrome and the associated cardiovascular anomalies are due to an abnormal developmental process involving the neural crest. Curiously, no instances of aortopulmonary septal defect or anomalous origin of a pulmonary artery from the ascending aorta (hemitruncus) have been associated with DiGeorge syndrome.(ABSTRACT TRUNCATED AT 250 WORDS)

Bone marrow transplantation and thymopoietin pentapeptide treatment in two infants with immunodeficiency with predominant T-cell defects

Two infants with immunodeficiency with predominant T-cell defects received transplants of HLA-identical bone marrow cells along with thymopoietin pentapeptide (TP-5) treatment and no prior immunosuppressive therapy. Both patients achieved durable engraftment with early reconstitution of cell-mediated immunity. The study of cell surface antigens with monoclonal antibodies (MoAb) revealed that the early appearance of T-cell subsets defined by OKT4 and OKT8 MoAb occurred. Neither of the patients showed any signs or symptoms of graft versus host disease over a 1-year period. This experience suggests that patients with T-cell deficiency who do not benefit from thymic hormones alone can be successfully treated by bone marrow transplantation. The association of TP-5 with bone marrow transplantation seems to induce an early and stable reconstitution and to protect against fatal post-transplant infection.