The Wiskott-Aldrich Syndrome protein (WASp) controls iNKT cell effector function. (50.39)

The Wiskott-Aldrich Syndrome protein (WASp) is a regulator of actin remodeling in hematopoietic cells. In T cells, WASp is required for a long-lived Immunological Synapse (IS) and TCR-mediated cytokine production. We recently published that WASp is fundamental in the biology of iNKT cells, a peculiar T cell subset activated by glycosphingolipid antigens presented by APC. We showed that murine was-/- iNKT cells were defective in IL-4 and IFN-γ production upon in vivo activation. It remains an open issue whether this functional impairment is caused by a cell autonomous functional defect of was-/- iNKT cells or by an impaired crosstalk between iNKT cells and APC. To address this issue we analyzed cytokine production upon in vitro activation of wt and was-/- iNKT cells by wt and was-/- DC. The data obtained indicate the defective IL-4 production due to a was-/- iNKT cell autonomous defect and the lower IFN-γ production caused by an inefficient crosstalk between was-/- iNKT cells and was-/- DC. However was-/- iNKT cells produced sustained levels of cytokines upon in vitro stimulation with TPA and Ionomycin, suggesting a TCR-mediated functional impairment of these cells. Supporting this hypothesis was-/- iNKT cells presented a decreased TCR avidity. Altogether these results demonstrate the relevance of WASp in TCR-mediated effector function of iNKT cells. Ongoing studies are aimed at evaluating the ability to properly form the IS by was-/- iNKT cell and APC.

Study of peripheral tolerance in ADA SCID patients after different treatments (143.36)

Adenosine deaminase (ADA)-SCID is characterized by increased purine metabolites and severe combined immunodeficiency. Autoimmune manifestations have been observed in milder forms or after enzyme replacement therapy (ERT), and recently in patients following gene therapy (GT). nTregs have a full enzymatic machinery to generate and sustain high concentrations of extracellular adenosine and may be involved in the pathogenesis of autoimmunity. We analyzed the frequency of CD4+CD25+FOXP3+CD127- in the peripheral blood, the methylation profile of the FoxP3 gene and the suppressive function of nTreg in ADA-SCID patients following ERT, GT or bone marrow transplant (BMT) as compared to controls. We found that the proportion and function of nTregs after GT mirrored that of controls, while nTreg from the ERT group showed a reduced frequency and impaired function. We also investigated the maturation state of B cells in the peripheral blood of ADA-SCID patients. After ERT and early after GT, patients displayed an increased proportion of transitional B cells (CD24highCD38high) and of cells with an incomplete BCR (CD21-CD35-) as compared to BMT and healthy controls. At later follow up patients treated with GT showed a tendency to normalize the phenotype in parallel to an increased frequency of gene corrected cells. Collectively, these data provide a first indication of predisposition to autoimmunity in ADA-SCID and the role of different treatments in the maintenance of peripheral tolerance.

Induction of anergic allergen-specific suppressor T cells using tolerogenic dendritic cells derived from children with allergies to house dust mites

BACKGROUND

Dendritic cells (DCs) regulate the immune response to allergens in the lung; they induce either effector or regulatory T cells, which promote or suppress, respectively, the development of allergy. IL-10 is a potent immunosuppressive cytokine that induces type 1 regulatory (Tr1) T cells.

OBJECTIVE

To generate allergen-specific Tr1 cells in vitro from children with allergy.

METHODS

Monocyte-derived DCs from children with allergy to house dust mites (HDM) were generated by incubating the cells with IL-10 and pulsing them with Der p 2, a major HDM allergen, or by pulsing them with Der p 2 and incubating them with IL-10 during their last 2 days of differentiation.

RESULTS

Der p 2-specific T-cell proliferation and T(H)2 cytokine production were significantly reduced when T cells from patients with allergy to HDM were activated with autologous Der p 2-pulsed DCs that had been differentiated or incubated with IL-10. T-cell lines generated with Der p 2-pulsed DCs that were differentiated with IL-10 were hyporesponsive to reactivation with Der p 2 and able to suppress Der p 2-specific T(H)2 effector cells.

CONCLUSION

Dendritic cells differentiated in the presence of IL-10 and pulsed with allergen gave rise to a population of tolerogenic DCs that induced allergen-specific Tr1 cells. This finding represents an important step forward to the prospective clinical application of tolerogenic DCs to modulate allergen-specific T-cell responses.

High incidence of severe cyclosporine neurotoxicity in children affected by haemoglobinopaties undergoing myeloablative haematopoietic stem cell transplantation: early diagnosis and prompt intervention ameliorates neurological outcome

Background

Neurotoxicity is a recognized complication of cyclosporine A (CSA) treatment. The incidence of severe CSA-related neurological complications following hematopoietic stem cell transplantation (HSCT) is 4-11%.

Methods

We describe 6 cases of CSA related neurotoxicity out of 67 matched related HSCT performed in paediatric Middle East patients affected by haemoglobinopaties (5 beta thalassemia major, 1 sickle cell disease-SCD). Conditioning regimen consisted of iv busulphan, cyclophosphamide and graft-versus-host-disease (GvHD) prophylaxis with CSA, methylprednisolone, methotrexate and ATG.

Results

All 6 patients presented prodromes such as arterial hypertension, headache, visual disturbances and vomiting, one to two days before overt CSA neurotoxicity. CSA neurotoxicity consisted of generalized seizures, signs of endocranial hypertension and visual disturbances at a median day of onset of 11 days after HSCT (range +1 to +40). Brain magnetic resonance imaging (MRI) performed in all subjects showed reversible leukoencephalopathy predominantly in the posterior regions of the brain (PRES) in 5/6 patients. EEG performed in 5/6 patients was always abnormal. Neurotoxicity was not explainable by high CSA blood levels, as all patients had CSA in the therapeutic range with a median of 178 ng/ml (range 69-250). CSA was promptly stopped and switched to tacrolimus with disappearance of clinical and radiological findings. All patients are symptoms-free at a median follow up of 882 days (range 60-1065).

Conclusions

Our experience suggests that paediatric patients with haemoglobinopaties have a high incidence of CSA related neurological events with no correlation between serum CSA levels and neurotoxicity. Prognosis is good following CSA removal. Specific prodromes such as arterial hypertension, headache or visual disturbances occurring in the early post-transplant period should be carefully evaluated with electrophysiological and MRI-based imaging in order to intervene promptly and avoid irreversible sequels.

Methods for in vitro generation of human type 1 regulatory T cells

Type 1 regulatory T (Tr1) cells are adaptive regulatory T cells that are induced in the periphery upon chronic exposure to antigen (Ag) in a tolerogenic environment containing interleukin (IL)-10. Tr1 cells are Ag-specific; they produce high levels of IL-10 and TGF-β in the absence of IL-4 and suppress T-cell responses via a cytokine-dependent mechanism. During the last decade, several protocols have been developed to generate Tr1 cell lines in vitro. In this chapter, we outline protocols to generate non-Ag- and Ag-specific Tr1 cell lines and assays used to characterize Tr1 cell phenotype and functions.

Characterization of new arylsulfatase A gene mutations reinforces genotype-phenotype correlation in metachromatic leukodystrophy

Metachromatic Leukodystrophy (MLD) is a rare inherited lysosomal storage disorder caused by the deficiency of Arylsulfatase A (ARSA). The disease manifests itself with a broad spectrum of clinical variants, all characterized by progressive neurodegeneration in the central and peripheral nervous systems. The correlation between mutations in the ARSA gene, residual enzymatic activity associated with the mutated alleles and patients' phenotype, which has been extensively drawn for common ARSA mutations, has recently been expanded to rare ones. In this context, functional studies on the rare allelic variances acquire particular relevance for patients' prognostic evaluation. Here we have characterized eight newly identified ARSA mutations, through lentiviral vector-based expression studies on cell lines and ARSA defective murine fibroblasts. In each case, the residual activity associated with the new mutant allele correlates well with the patient's phenotype. Therefore, our results confirm the importance of functional characterization of mutant alleles for a precise genotype-based classification and definition of prognosis in MLD patients, which is particularly relevant for pre-symptomatic diagnosis.

Loss of mismatched HLA in leukemia after stem-cell transplantation

BACKGROUND

Transplantation of hematopoietic stem cells from partially matched family donors is a promising therapy for patients who have a hematologic cancer and are at high risk for relapse. The donor T-cell infusions associated with such transplantation can promote post-transplantation immune reconstitution and control residual disease.

METHODS

We identified 43 patients who underwent haploidentical transplantation and infusion of donor T cells for acute myeloid leukemia or myelodysplastic syndrome and conducted post-transplantation studies that included morphologic examination of bone marrow, assessment of hematopoietic chimerism with the use of short-tandem-repeat amplification, and HLA typing. The genomic rearrangements in mutant variants of leukemia were studied with the use of genomic HLA typing, microsatellite mapping, and single-nucleotide-polymorphism arrays. The post-transplantation immune responses against the original cells and the mutated leukemic cells were analyzed with the use of mixed lymphocyte cultures.

RESULTS

In 5 of 17 patients with leukemia relapse after haploidentical transplantation and infusion of donor T cells, we identified mutant variants of the original leukemic cells. In the mutant leukemic cells, the HLA haplotype that differed from the donor's haplotype had been lost because of acquired uniparental disomy of chromosome 6p. T cells from the donor and the patient after transplantation did not recognize the mutant leukemic cells, whereas the original leukemic cells taken at the time of diagnosis were efficiently recognized and killed.

CONCLUSIONS

After transplantation of haploidentical hematopoietic stem cells and infusion of donor T cells, leukemic cells can escape from the donor's antileukemic T cells through the loss of the mismatched HLA haplotype. This event leads to relapse.

Type 1 regulatory T cells are associated with persistent split erythroid/lymphoid chimerism after allogeneic hematopoietic stem cell transplantation for thalassemia

BACKGROUND

Thalassemia major can be cured with allogeneic hematopoietic stem cell transplantation. Persistent mixed chimerism develops in around 10% of transplanted thalassemic patients, but the biological mechanisms underlying this phenomenon are poorly understood.

DESIGN AND METHODS

The presence of interleukin-10-producing T cells in the peripheral blood of eight patients with persistent mixed chimerism and five with full donor chimerism was investigated. A detailed characterization was then performed, by T-cell cloning, of the effector and regulatory T-cell repertoire of one patient with persistent mixed chimerism, who developed stable split erythroid/lymphoid chimerism after a hematopoietic stem cell transplant from an HLA-matched unrelated donor.

RESULTS

Higher levels of interleukin-10 were produced by peripheral blood mononuclear cells from patients with persistent mixed chimerism than by the same cells from patients with complete donor chimerism or normal donors. T-cell clones of both host and donor origin could be isolated from the peripheral blood of one, selected patient with persistent mixed chimerism. Together with effector T-cell clones reactive against host or donor alloantigens, regulatory T-cell clones with a cytokine secretion profile typical of type 1 regulatory cells were identified at high frequencies. Type 1 regulatory cell clones, of both donor and host origin, were able to inhibit the function of effector T cells of either donor or host origin in vitro.

CONCLUSIONS

Overall these results suggest that interleukin-10 and type 1 regulatory cells are associated with persistent mixed chimerism and may play an important role in sustaining long-term tolerance in vivo. These data provide new insights into the mechanisms of peripheral tolerance in chimeric patients and support the use of cellular therapy with regulatory T cells following hematopoietic stem cell transplantation.

CD4+ T-regulatory cells: toward therapy for human diseases

SUMMARY

T-regulatory cells (Tregs) have a fundamental role in the establishment and maintenance of peripheral tolerance. There is now compelling evidence that deficits in the numbers and/or function of different types of Tregs can lead to autoimmunity, allergy, and graft rejection, whereas an over-abundance of Tregs can inhibit anti-tumor and anti-pathogen immunity. Experimental models in mice have demonstrated that manipulating the numbers and/or function of Tregs can decrease pathology in a wide range of contexts, including transplantation, autoimmunity, and cancer, and it is widely assumed that similar approaches will be possible in humans. Research into how Tregs can be manipulated therapeutically in humans is most advanced for two main types of CD4(+) Tregs: forkhead box protein 3 (FOXP3)(+) Tregs and interleukin-10-producing type 1 Tregs (Tr1 cells). The aim of this review is to highlight current information on the characteristics of human FOXP3(+) Tregs and Tr1 cells that make them an attractive therapeutic target. We discuss the progress and limitations that must be overcome to develop methods to enhance Tregs in vivo, expand or induce them in vitro for adoptive transfer, and/or inhibit their function in vivo. Although many technical and theoretical challenges remain, the next decade will see the first clinical trials testing whether Treg-based therapies are effective in humans.

The Wiskott-Aldrich syndrome protein is required for iNKT cell maturation and function

The Wiskott-Aldrich syndrome (WAS) protein (WASp) is a regulator of actin cytoskeleton in hematopoietic cells. Mutations of the WASp gene cause WAS. Although WASp is involved in various immune cell functions, its role in invariant natural killer T (iNKT) cells has never been investigated. Defects of iNKT cells could indeed contribute to several WAS features, such as recurrent infections and high tumor incidence. We found a profound reduction of circulating iNKT cells in WAS patients, directly correlating with the severity of clinical phenotype. To better characterize iNKT cell defect in the absence of WASp, we analyzed was(-/-) mice. iNKT cell numbers were significantly reduced in the thymus and periphery of was(-/-) mice as compared with wild-type controls. Moreover analysis of was(-/-) iNKT cell maturation revealed a complete arrest at the CD44(+) NK1.1(-) intermediate stage. Notably, generation of BM chimeras demonstrated a was(-/-) iNKT cell-autonomous developmental defect. was(-/-) iNKT cells were also functionally impaired, as suggested by the reduced secretion of interleukin 4 and interferon gamma upon in vivo activation. Altogether, these results demonstrate the relevance of WASp in integrating signals critical for development and functional differentiation of iNKT cells and suggest that defects in these cells may play a role in WAS pathology.

Evidence for long-term efficacy and safety of gene therapy for Wiskott-Aldrich syndrome in preclinical models

Wiskott-Aldrich Syndrome (WAS) is a life-threatening X-linked disease characterized by immunodeficiency, thrombocytopenia, autoimmunity, and malignancies. Gene therapy could represent a therapeutic option for patients lacking a suitable bone marrow (BM) donor. In this study, we analyzed the long-term outcome of WAS gene therapy mediated by a clinically compatible lentiviral vector (LV) in a large cohort of was(null) mice. We demonstrated stable and full donor engraftment and Wiskott-Aldrich Syndrome protein (WASP) expression in various hematopoietic lineages, up to 12 months after gene therapy. Importantly, we observed a selective advantage for T and B lymphocytes expressing transgenic WASP. T-cell receptor (TCR)-driven T-cell activation, as well as B-cell's ability to migrate in response to CXCL13, was fully restored. Safety was evaluated throughout the long-term follow-up of primary and secondary recipients of WAS gene therapy. WAS gene therapy did not affect the lifespan of treated animals. Both hematopoietic and nonhematopoietic tumors arose, but we excluded the association with gene therapy in all cases. Demonstration of long-term efficacy and safety of WAS gene therapy mediated by a clinically applicable LV is a key step toward the implementation of a gene therapy clinical trial for WAS.

Ten years of gene therapy for primary immune deficiencies

Gene therapy with hematopoietic stem cells (HSC) is an attractive therapeutic strategy for several forms of primary immunodeficiencies. Current approaches are based on ex vivo gene transfer of the therapeutic gene into autologous HSC by vector-mediated gene transfer. In the past decade, substantial progress has been achieved in the treatment of severe combined immundeficiencies (SCID)-X1, adenosine deaminase (ADA)-deficient SCID, and chronic granulomatous disease (CGD). Results of the SCID gene therapy trials have shown long-term restoration of immune competence and clinical benefit in over 30 patients. The inclusion of reduced-dose conditioning in the ADA-SCID has allowed the engraftment of multipotent gene-corrected HSC at substantial level. In the CGD trial significant engraftment and transgene expression were observed, but the therapeutic effect was transient. The occurrence of adverse events related to insertional mutagenesis in the SCID-X1 and CGD trial has highlighted the limitations of current retroviral vector technology. For future applications the risk-benefit evaluation should include the type of vector employed, the disease background and the nature of the transgene. The use of self-inactivating lentiviral vectors will provide significant advantages in terms of natural gene regulation and reduction in the potential for adverse mutagenic events. Following recent advances in preclinical studies, lentiviral vectors are now being translated into new clinical approaches, such as Wiskott-Aldrich Syndrome.

Molecular regulation of cellular immunity by FOXP3

The immune system is responsible for not only eliminating threats to the body, but also for protecting the body from its own immune responses that would cause harm if left unchecked. Forkhead box protein 3 (FOXP3) is a forkhead family member with an important role in the development and function of a type of CD4+ T cell called T regulatory cells that is fundamental for maintaining immune tolerance to self. This chapter reviews the structure of FOXP3 and how its role in the immune system was discovered. Studies of patients with mutations in FOXP3 who suffer from a syndrome known as IPEX (immune dysregulation, polyendocrinopathy, enteropathy, x-linked) are also discussed. Investigation into how expression of FOXP3 is regulated and how it interacts with other proteins have recently provided considerable insight into mechanisms by which the lack of this protein could cause disease. We also discuss how FOXP3 is involved in the reciprocal development ofT regulatory cells and proinflammatory T-cells that produce IL-17. A better understanding of how FOXP3 is regulated and the molecular basis for its function will ultimately contribute to the development ofT regulatory cell-based cellular therapies that could be used to restore dysregulated immune responses.

Metachromatic leukodystrophy - mutation analysis provides further evidence of genotype-phenotype correlation

Metachromatic leukodystrophy (MLD) is a rare lysosomal storage disorder resulting from the inherited deficiency of the arylsulfatase A (ARSA) enzyme. Currently, no valid therapeutic options are available for affected patients. A thorough knowledge of disease progression in its diverse clinical variants, together with the identification of reliable prognostic factors, could be instrumental in accurate patient selection for new upcoming therapeutic opportunities, such as enzyme replacement and gene therapy. The described correlation between genotype and clinical presentation proved helpful in predicting patient's prognosis, only in the minority of MLD patients harboring common mutations. Molecular characterization of a cohort of 26 MLD patients allowed us to identify 18 mutations, excluding the common 0 and R alleles, 10 of which are rare and 8 are novel. By categorizing the rare mutations, we were able to confirm a correlation between ARSA gene mutations, age at onset and patterns of disease progression, not only in those patients bearing common mutations, but also in those carrying rare mutant alleles. Moreover, in the case of absent or delayed molecular diagnosis, or of newly identified mutations, the involvement of peripheral nervous system from disease onset proved to be a sensitive prognostic marker predicting a severe progression.

Clinical improvement and normalized Th1 cytokine profile in early and long-term interferon-alpha treatment in a suspected case of hyper-IgE syndrome

We are reporting on a 7-months-old boy with suspected hyper-IgE syndrome, presenting with a therapy resistant severe eczema and an overall reduction of in vitro cytokine production. Interferon-alpha (IFN-alpha) treatment resulted in a marked and stable clinical improvement and normalization of in vitro T-cell cytokine production, indicating a valid therapeutic potential of IFN-alpha as immunomodulating drug.

Construction of human-SCID chimeric mice

Until recently, testing of new therapeutic agents has relied extensively upon the use of mice and nonhuman primates for in vivo preclinical studies. Unfortunately, these animal models do not always mimic the physiological and pathophysiological processes that occur in humans. The finding that C.B-17 severe combined immunodeficiency (SCID) mice lack a competent immune system, and therefore are unable to mount effective cellular and humoral responses to foreign antigens, has led to their use as recipients for xenografts of human tissues. This unit is focused on the construction of human-SCID chimeric through the surgical implantation of human fetal hematolymphoid tissues into SCID mice (SCID-hu mice). The Basic Protocol describes the surgical implantation of human fetal thymus and liver under the kidney capsules of SCID mice (SCID-hu Thy/Liv model). Subcutaneous transplantation of human fetal bone marrow and thymus (SCID-hu Bm/Thy mice) is described in the Alternate Protocol. Additional support protocols provide procedures to analyze human lymphocyte populations in the peripheral blood and grafted organs of SCID-hu mice. The advantages and disadvantages of each protocol and potential applications are discussed in the Commentary.

Multilineage hematopoietic reconstitution without clonal selection in ADA-SCID patients treated with stem cell gene therapy

Gene transfer into HSCs is an effective treatment for SCID, although potentially limited by the risk of insertional mutagenesis. We performed a genome-wide analysis of retroviral vector integrations in genetically corrected HSCs and their multilineage progeny before and up to 47 months after transplantation into 5 patients with adenosine deaminase-deficient SCID. Gene-dense regions, promoters, and transcriptionally active genes were preferred retroviral integrations sites (RISs) both in preinfusion transduced CD34(+) cells and in vivo after gene therapy. The occurrence of insertion sites proximal to protooncogenes or genes controlling cell growth and self renewal, including LMO2, was not associated with clonal selection or expansion in vivo. Clonal analysis of long-term repopulating cell progeny in vivo revealed highly polyclonal T cell populations and shared RISs among multiple lineages, demonstrating the engraftment of multipotent HSCs. These data have important implications for the biology of retroviral vectors, the dynamics of genetically modified HSCs, and the safety of gene therapy.

Frequency and targeted detection of HLA-DPB1 T cell epitope disparities relevant in unrelated hematopoietic stem cell transplantation

The majority of unrelated donor (UD) hematopoietic stem cell (HSC) transplants are performed across HLA-DP mismatches, which, if involving disparity in a host-versus-graft (HVG) direction for an alloreactive T cell epitope (TCE), have been shown by our group to be associated with poor clinical outcome in 2 cohorts of patients transplanted for hematopoietic malignancies and beta-thalassemia, respectively. Using site-directed mutagenesis of DPB1*0901, we show here that the TCE is abrogated by the presence of amino acids LFQG in positions 8-11 of the DP beta-chain. Based on this and on alloreactive T cell responsiveness, we have determined the presence or absence of the TCE for 72 DPB1 alleles reported in the ethnic groups representative of the worldwide UD registries, and predict that 67%-87% (mean 77%) of UD recipient pairs will not present a DPB1 TCE disparity in the HVG direction. We developed and validated in 112 healthy Italian blood donors an innovative approach of DPB1 epitope-specific typing (EST), based on 2 PCR reactions. Our data show that DPB1 TCE disparities may hamper the clinical success of a considerable number of transplants when DPB1 matching is not included into the donor selection criteria, and that a donor without DPB1 TCE disparities in the HVG direction can be found for the majority of patients. Moreover, the study describes the first protocol of targeted epitope-specific DPB1 donor-recipient matching for unrelated HSC transplantation. This protocol will facilitate large-scale retrospective clinical studies warranted to more precisely determine the clinical relevance of DPB1 TCE disparities in different transplant conditions.

Molecular purging of multiple myeloma cells by ex-vivo culture and retroviral transduction of mobilized-blood CD34+ cells

Background

Tumor cell contamination of the apheresis in multiple myeloma is likely to affect disease-free and overall survival after autografting.

Objective

To purge myeloma aphereses from tumor contaminants with a novel culture-based purging method.

Methods

We cultured myeloma-positive CD34⁺ PB samples in conditions that retained multipotency of hematopoietic stem cells, but were unfavourable to survival of plasma cells. Moreover, we exploited the resistance of myeloma plasma cells to retroviral transduction by targeting the hematopoietic CD34⁺ cell population with a retroviral vector carrying a selectable marker (the truncated form of the human receptor for nerve growth factor, ΔNGFR). We performed therefore a further myeloma purging step by selecting the transduced cells at the end of the culture.

Results

Overall recovery of CD34⁺ cells after culture was 128.5%; ΔNGFR transduction rate was 28.8% for CD34⁺ cells and 0% for CD138-selected primary myeloma cells, respectively. Recovery of CD34⁺ cells after ΔNGFR selection was 22.3%. By patient-specific Ig-gene rearrangements, we assessed a decrease of 0.7–1.4 logs in tumor load after the CD34⁺ cell selection, and up to 2.3 logs after culture and ΔNGFR selection.

Conclusion

We conclude that ex-vivo culture and retroviral-mediated transduction of myeloma leukaphereses provide an efficient tumor cell purging.

A hypomorphic R229Q Rag2 mouse mutant recapitulates human Omenn syndrome

Rag enzymes are the main players in V(D)J recombination, the process responsible for rearrangement of TCR and Ig genes. Hypomorphic Rag mutations in humans, which maintain partial V(D)J activity, cause a peculiar SCID associated with autoimmune-like manifestations, Omenn syndrome (OS). Although a deficient ability to sustain thymopoiesis and to produce a diverse T and B cell repertoire explains the increased susceptibility to severe infections, the molecular and cellular mechanisms underlying the spectrum of clinical and immunological features of OS remain poorly defined. In order to better define the molecular and cellular pathophysiology of OS, we generated a knockin murine model carrying the Rag2 R229Q mutation previously described in several patients with OS and leaky forms of SCID. These Rag2(R229Q/R229Q) mice showed oligoclonal T cells, absence of circulating B cells, and peripheral eosinophilia. In addition, activated T cells infiltrated gut and skin, causing diarrhea, alopecia, and, in some cases, severe erythrodermia. These findings were associated with reduced thymic expression of Aire and markedly reduced numbers of naturally occurring Tregs and NKT lymphocytes. In conclusion, Rag2(R229Q/R229Q) mice mimicked most symptoms of human OS; our findings support the notion that impaired immune tolerance and defective immune regulation are involved in the pathophysiology of OS.

In vivo administration of lentiviral vectors triggers a type I interferon response that restricts hepatocyte gene transfer and promotes vector clearance

Liver gene transfer is a highly sought goal for the treatment of inherited and infectious diseases. Lentiviral vectors (LVs) have many desirable properties for hepatocyte-directed gene delivery, including the ability to integrate into nondividing cells. Unfortunately, upon systemic administration, LV transduces hepatocytes relatively inefficiently compared with nonparenchymal cells, and the duration of transgene expression is often limited by immune responses. Here, we investigated the role of innate antiviral responses in these events. We show that administration of LVs to mice triggers a rapid and transient IFNalphabeta response. This effect was dependent on functional vector particles, and in vitro challenge of antigen-presenting cells suggested that plasmacytoid dendritic cells initiated the response. Remarkably, when LVs were administered to animals that lack the capacity to respond to IFNalphabeta, there was a dramatic increase in hepatocyte transduction, and stable transgene expression was achieved. These findings indicate that, even in the setting of acute delivery of replication-defective vectors, IFNs effectively interfere with transduction in a cell-type-specific manner. Moreover, because disabling a single component of the innate/immune network was sufficient to establish persistent xenoantigen expression, our results raise the hope that the immunologic barriers to gene therapy are less insurmountable than expected.

Current understanding of the Wiskott-Aldrich syndrome and prospects for gene therapy

Gene therapy, based on the transplantation of genetically corrected autologous hematopoietic stem cells (HSCs), has proven to be an effective therapeutic approach as an alternative to allogenic HSC transplantation for the cure of severe combined immunodeficiencies (SCID). In this article, the recent preclinical studies aiming towards gene therapy trials for the Wiskott-Aldrich syndrome (WAS), a life-threatening immunodeficiency characterized by infections, hemorrhages, autoimmune disorders and lymphomas, will be reviewed. An update of the safety and efficacy data obtained in studies performed in murine disease models and in cells from WAS patients will be presented. Based on these data and on the clinical results of the recent trials for SCID, the most critical issues regarding the implementation of a gene therapy approach for WAS will be discussed.

Isolation, expansion, and characterization of human natural and adaptive regulatory T cells

Regulatory T cells play a central role in controlling homeostasis, and in inducing and maintaining tolerance to both foreign and self-antigens. Several types of T cells with regulatory activity have been described both in mice and humans, and those within the CD4+ subset have been extensively studied. Among them, the best characterized are the naturally occurring CD4+CD25+ regulatory T (Treg) cells, and the adaptive type 1 regulatory T (Tr1) cells. Natural Treg cells can arise directly from the thymus, are characterized by the constitutive expression of the transcription factor Foxp3, and suppress T cell responses in a cell-cell contact mediated mechanism. On the contrary, adaptive Tr1 cells arise in the periphery upon encountering antigen in a tolerogenic environment, produce high levels of interleukin (IL)-10 and mediate suppression via IL-10. During the last decade, much effort has been placed on developing protocols to generate regulatory T-cell lines and clones, to further define the similarities and differences between various regulatory T-cell subsets. In this chapter, we will outline protocols to expand naturally occurring Treg cells, to differentiate homogeneous population of Tr1 cells in vitro, and to generate natural Treg and Tr1 cell clones and cell lines.

Ex vivo gene therapy with lentiviral vectors rescues adenosine deaminase (ADA)–deficient mice and corrects their immune and metabolic defects

Adenosine deaminase (ADA) deficiency is caused by a purine metabolic dysfunction, leading to severe combined immunodeficiency (SCID) and multiple organ damage. To investigate the efficacy of ex vivo gene therapy with self-inactivating lentiviral vectors (LVs) in correcting this complex phenotype, we used an ADA–/– mouse model characterized by early postnatal lethality. LV-mediated ADA gene transfer into bone marrow cells combined with low-dose irradiation rescued mice from lethality and restored their growth, as did transplantation of wild-type bone marrow. Mixed chimerism with multilineage engraftment of transduced cells was detected in the long term in animals that underwent transplantation. ADA activity was normalized in lymphocytes and partially corrected in red blood cells (RBCs), resulting in full metabolic detoxification and prevention of severe pulmonary insufficiency. Moreover, gene therapy restored normal lymphoid differentiation and immune functions, including antigen-specific antibody production. Similar degrees of detoxification and immune reconstitution were obtained in mice treated early after birth or after 1 month of enzyme-replacement therapy, mimicking 2 potential applications for ADA-SCID. Overall, this study demonstrates the efficacy of LV gene transfer in correcting both the immunological and metabolic phenotypes of ADA-SCID and supports the future clinical use of this approach.

Interleukin-10-secreting type 1 regulatory T cells in rodents and humans

Interleukin-10 (IL-10)-secreting T regulatory type 1 (Tr1) cells are defined by their specific cytokine production profile, which includes the secretion of high levels of IL-10 and transforming growth factor-beta(TGF-beta), and by their ability to suppress antigen-specific effector T-cell responses via a cytokine-dependent mechanism. In contrast to the naturally occurring CD4+ CD25+ T regulatory cells (Tregs) that emerge directly from the thymus, Tr1 cells are induced by antigen stimulation via an IL-10-dependent process in vitro and in vivo. Specialized IL-10-producing dendritic cells, such as those in an immature state or those modulated by tolerogenic stimuli, play a key role in this process. We propose to use the term Tr1 cells for all IL-10-producing T-cell populations that are induced by IL-10 and have regulatory activity. The full biological characterization of Tr1 cells has been hampered by the difficulty in generating these cells in vitro and by the lack of specific marker molecules. However, it is clear that Tr1 cells play a key role in regulating adaptive immune responses both in mice and in humans. Further work to delineate the specific molecular signature of Tr1 cells, to determine their relationship with CD4+ CD25+ Tregs, and to elucidate their respective role in maintaining peripheral tolerance is crucial to advance our knowledge on this Treg subset. Furthermore, results from clinical protocols using Tr1 cells to modulate immune responses in vivo in autoimmunity, transplantation, and chronic inflammatory diseases will undoubtedly prove the biological relevance of these cells in immunotolerance.

Design and optimization of lentiviral vectors for transfer of GALC expression in Twitcher brain

BACKGROUND

Demyelination in globoid cell leukodystrophy (GLD) is due to a deficiency of galactocerebrosidase (GALC) activity. Up to now, in vivo brain viral gene transfer of GALC showed modest impact on disease development in Twitcher mice, an animal model for GLD. Lentiviral vectors, which are highly efficient to transfer the expression of therapeutic genes in neurons and glial cells, have not been evaluated for direct cerebral therapy in GLD mice.

METHODS

Lentiviral vectors containing the untagged cDNA or the hemagglutinin (HA)-tagged cDNA for the full-length mouse GALC sequence were generated and validated in vitro. In vivo therapeutic efficacy of these vectors was evaluated by histology, biochemistry and electrophysiology after transduction of ependymal or subependymal layers in young Twitcher pups.

RESULTS

Both GALC lentiviral vectors transduced neurons, oligodendrocytes and astrocytes with efficiencies above 75% and conferred high levels of enzyme activity. GALC accumulated in lysosomes of transduced cells and was also secreted to the extracellular medium. Conditioned GALC medium was able to correct the enzyme deficiency when added to non-transduced Twitcher glial cultures. Mice that received intraventricular injections of GALC vector showed accumulation of GALC in ependymal cells but no diffusion of the enzyme from the ependymal ventricular tree into the cerebral parenchyma. Significant expression of GALC-HA was detected in neuroglioblasts when GALC-HA lentiviral vectors were injected in the subventricular zone of Twitcher mice. Life span and motor conduction in both groups of treated Twitcher mice were not significantly ameliorated.

CONCLUSIONS

Lentiviral vectors showed to be efficient for reconstitution of the GALC expression in Twitcher neural cells. GALC was able to accumulate in lysosomes as well as to enter the secretory pathway of lysosomal enzymes, two fundamental aspects for gene therapy of lysosomal storage diseases. Our in vivo results, while showing the capacity of lentiviral vectors to transfer expression of therapeutic GALC in the Twitcher brain, did not limit progression of disease in Twitchers and highlight the need to evaluate other routes of administration.

Induction of Transplantation Tolerance via Regulatory T Cells

In the last two decades, graft survival has been greatly improved by the introduction of efficient immunosuppressive drugs. On the other hand, late graft loss caused by chronic rejection together with the side effects of long-term immunosuppression, remain major obstacles for successful transplantation. Operational tolerance, which is defined by the lack of acute and chronic rejection and indefinite graft survival with normal graft function in the absence of chronic immunosuppression, represents an attractive alternative. Several approaches have been explored to achieve transplantational tolerance, which is considered the "Holy Grail" of transplantation, including induction of central tolerance by establishing mixed chimerism through hematopoietic stem cell transplantation or induction of peripheral tolerance through modulation of allogeneic immune responses. Graft-specific alloreactive T cells, which largely mediate graft rejection, can be silenced through different mechanisms, including deletion, which may occur within the thymus or in the lymphoid organs; anergy, in which alloreactive T cells cannot adequately respond following restimulation with the specific antigen; and suppression, which may be mediated by direct interactions with regulatory T cells (Tregs) or by soluble factors produced by Tregs. This review attempts to summarize the most novel and successful strategies to achieve operational tolerance via induction of Tregs.

Defective regulatory and effector T cell functions in patients with FOXP3 mutations

The autoimmune disease immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) is caused by mutations in the forkhead box protein P3 (FOXP3) gene. In the mouse model of FOXP3 deficiency, the lack of CD4+ CD25+ Tregs is responsible for lethal autoimmunity, indicating that FOXP3 is required for the differentiation of this Treg subset. We show that the number and phenotype of CD4+ CD25+ T cells from IPEX patients are comparable to those of normal donors. CD4+ CD25high T cells from IPEX patients who express FOXP3 protein suppressed the in vitro proliferation of effector T cells from normal donors, when activated by "weak" TCR stimuli. In contrast, the suppressive function of CD4+ CD25high T cells from IPEX patients who do not express FOXP3 protein was profoundly impaired. Importantly, CD4+ CD25high T cells from either FOXP3+ or FOXP3- IPEX patients showed altered suppression toward autologous effector T cells. Interestingly, IL-2 and IFN-gamma production by PBMCs from IPEX patients was significantly decreased. These findings indicate that FOXP3 mutations in IPEX patients result in heterogeneous biological abnormalities, leading not necessarily to a lack of differentiation of CD4+ CD25high Tregs but rather to a dysfunction in these cells and in effector T cells.

Beneficial autoimmunity in Type 1 diabetes mellitus

The trigger that leads to the pathogenesis of type 1 diabetes is currently unknown. It is well established that the pathophysiology of the disease is biphasic. In the first stage, leukocytes infiltrate the pancreatic islets in a response that does not cause damage. In the second phase, which occurs only in diabetes-prone individuals and strains, autoreactive T cells acquire aggressive potential and destroy the majority of the pancreatic islets. Rodents and humans exhibit a physiological ripple of apoptotic beta-cell death shortly after birth, which induces an adaptive autoimmune response towards islet-antigens, both in diabetes-prone non-obese diabetic (NOD) mice and in mice that do not develop diabetes. Here, we propose that the early T cell-mediated autoimmune response towards islet-antigens is physiological, purposeful and beneficial.

The role of 2 FOXP3 isoforms in the generation of human CD4+ Tregs

Little is known about the molecules that control the development and function of CD4+ CD25+ Tregs. Recently, it was shown that the transcription factor FOXP3 is necessary and sufficient for the generation of CD4+ CD25+ Tregs in mice. We investigated the capacity of FOXP3 to drive the generation of suppressive CD4+ CD25+ Tregs in humans. Surprisingly, although ectopic expression of FOXP3 in human CD4+ T cells resulted in induction of hyporesponsiveness and suppression of IL-2 production, it did not lead to acquisition of significant suppressor activity in vitro. Similarly, ectopic expression of FOXP3delta2, an isoform found in human CD4+ CD25+ Tregs that lacks exon 2, also failed to induce the development of suppressor T cells. Moreover, when FOXP3 and FOXP3delta2 were simultaneously overexpressed, although the expression of several Treg-associated cell surface markers was significantly increased, only a modest suppressive activity was induced. These data indicate that in humans, overexpression of FOXP3 alone or together with FOXP3delta2 is not an effective method to generate potent suppressor T cells in vitro and suggest that factors in addition to FOXP3 are required during the process of activation and/or differentiation for the development of bona fide Tregs.

Myelin deterioration in Twitcher mice: motor evoked potentials and magnetic resonance imaging as in vivo monitoring tools

We have used magnetic resonance imaging (MRI) and motor evoked potentials (MEPs) for monitoring disease progression within the CNS of the Twitcher mouse, the murine model for globoid cell leukodystrophy (GLD). GLD is a lysosomal storage disorder, resulting from galactocerebrosidase deficiency, causing central and peripheral myelin impairment, leading to death, usually during early infancy. Neuroradiological, electrophysiological, and pathological parameters of myelin maturation were evaluated in Twitcher mice between postnatal days 20 and 45. Healthy controls showed a gradual-appearance MRI T2-weighted hypointensity of the corpus callosum (CC) starting at about P30 and ending at about P37, whereas MRI of age-matched Twitcher mice showed a complete loss of the CC-related MRI signal. MEPs allowed the functional assessment of myelin maturation within corticospinal motor pathways and showed a progressive deterioration of MEPs in Twitcher mice with increased central conduction time (CCT; 5.12 +/- 0.49 msec at P27 to 6.45 +/- 1.96 msec at P32), whereas physiological CCT shortening was found in healthy controls (3.01 +/- 0.81 msec at P27 to 2.5 +/- 0.27 msec at P32). These findings were not paralleled by traditional histological stainings. Optical observation of Bielchowsky and Luxol fast blue-PAS stainings showed mild axonal/myelin deterioration of the Twitcher brain within this time frame. Our results demonstrate that serial MRI and MEP readings are sensitive evaluation tools for in vivo monitoring of dysmyelination in Twitcher mice and underscore their potential use for longitudinal evaluation of the therapeutic impact of gene and cell therapies on these animals.

Phenotypic and functional differences between human CD4+CD25+ and type 1 regulatory T cells

T regulatory (Tr) cells have an essential role in the induction and maintenance of tolerance to both and foreign self-antigens. Many types of T cells with regulatory activity have been described in mice and humans, and those within the CD4+ subset have been extensively characterized. CD4+ Type-1 regulatory T (Tr1) cells produce high levels of IL-10 and mediate IL-10-dependent suppression, whereas the effects of naturally occurring CD4+CD25+ Tr cells appear to be cell-contact-dependent. Tr1 cells arise in the periphery upon encountering antigen in a tolerogenic environment. In contrast, it appears that CD4+CD25+ Tr cells can either arise directly in the thymus or be induced by antigen in the periphery. We have been interested in defining the phenotype and function of different subsets of CD4+ Tr cells present in human peripheral blood, with the ultimate aim of designing therapeutic strategies to harness their immunoregulatory effects. This review will discuss the similarities and differences between human Tr1 and naturally occurring CD4+CD25+ Tr cells, as well as evidence that indicates that they have nonoverlapping, but synergistic roles in immune homeostasis.

Human CD4+ regulatory T cells and activation-induced tolerance

In the past years growing attention has been given to the role of regulatory T (Tr) cells in inducing and monitoring peripheral tolerance. Various subsets of Tr cells have been described based on their surface phenotype and cytokine production. However, presently there are no specific reliable markers for any of the Tr subsets and their classification is based predominantly upon their mode of suppression. In addition, the molecular mechanisms underlying the induction and mode of action of all Tr cell subsets remain to be elucidated. Here we review recent developments regarding human CD4+ Tr cells, their origin, phenotype, antigen specificity and mode of suppression.

IL-3 or IL-7 increases ex vivo gene transfer efficiency in ADA-SCID BM CD34+ cells while maintaining in vivo lymphoid potential

To improve maintenance and gene transfer of human lymphoid progenitors for clinical use in gene therapy of adenosine deaminase (ADA)-deficient SCID we investigated several gene transfer protocols using various stem cell-enriched sources. The lymphoid differentiation potential was measured by an in vitro clonal assay for B/NK cells and in the in vivo SCID-hu mouse model. Ex vivo culture with the cytokines TPO, FLT3-ligand, and SCF (T/F/S) plus IL-3 or IL-7 substantially increased the yield of transduced bone marrow (BM) CD34(+) cells purified from ADA-SCID patients or healthy donors, compared to T/F/S alone. Moreover, the use of IL-3 or IL-7 significantly improved the maintenance of in vitro B cell progenitors from ADA-SCID BM cells and allowed the efficient transduction of B and NK cell progenitors. Under these optimized conditions transduced CD34(+) cells were efficiently engrafted into SCID-hu mice and gave rise to B and T cell progeny, demonstrating the maintenance of in vivo lymphoid reconstitution capacity. The protocol based on the T/F/S + IL-3 combination was included in a gene therapy clinical trial for ADA-SCID, resulting in long-term engraftment of stem/progenitor cells. Remarkably, gene-corrected BM CD34(+) cells obtained from one patient 4 and 11 months after gene therapy were capable of repopulating the lymphoid compartment of SCID-hu hosts.

Utilizing regulatory T cells to control alloreactivity

Effective resetting of the immune system cannot be achieved by non-specific immunosuppression. Instead, novel strategies aim at harnessing the body's natural tolerance mechanisms to rectify an Ag-specific response without disturbing other immune functions. Fine-tuning of the balance between Ag-specific effector and regulatory T (Tr) cells is a promising strategy that requires detailed understanding of the differentiation and expansion pathways of the relevant Tr cell subsets. Here we review recent developments regarding the control of alloreactivity by induction and expansion of Tr cells. T-cell activation in the presence of tolerogenic APC and cytokines leads to the induction of Tr cells, which can mediate tolerance through cytokine-dependent and/or contact-dependent mechanisms. Better understanding of the mechanisms of immune regulation mediated by Tr cells may enable fine-tuning of specific immune responses and pave the way for novel therapeutic approaches.

A proportion of patients with lymphoma may harbor mutations of the perforin gene

Perforin mutations have been demonstrated in a proportion of patients diagnosed with the familial form of hemophagocytic lymphohistiocytosis (HLH). In the present study, we evaluated whether some patients with lymphoma sharing clinical characteristics with HLH might harbor mutations of the perforin gene. We analyzed 29 patients and found that 4 patients, who developed either Hodgkin or non-Hodgkin lymphoma, had biallelic mutations of the perforin gene. One of these 4 patients, a 19-year-old female with T-cell lymphoma, had a brother carrying the same mutations who developed HLH. In 2 of the 4 patients with biallelic mutations of the perforin gene, we evaluated perforin expression by flow cytometry and natural killer (NK) activity and both were found to be absent. Moreover, we documented the presence of monoallelic mutations of the perforin gene in 4 more patients. One of these 4 latter patients also carried a mutation of the Fas gene. These data indicate that perforin deficiency, either alone or in combination with other mutations of genes involved in lymphocyte survival or functional activity, may be present in patients with lymphoma. These findings suggest that perforin also plays a key role in the mechanisms of immune surveillance that prevent tumor growth and/or development.

Differentiation of Tr1 cells by immature dendritic cells requires IL-10 but not CD25+CD4+ Tr cells

Dendritic cells (DCs) are specialized antigen-presenting cells that monitor the antigenic environment and activate naive T cells. The role of DCs is not only to sense danger but also to tolerize the immune system to antigens encountered in the absence of maturation/inflammatory stimuli. Indeed, if a naive T cell encounters its antigen on immature DCs (iDCs), it may differentiate into a T-regulatory (Tr) rather than a T-effector cell. However, little is known about the mechanisms by which iDCs differentiate Tr cells. We developed a standardized and highly reproducible protocol to differentiate Tr cells by repetitive exposure of naive peripheral blood CD4+ T cells to allogeneic iDCs. The resultant Tr cells are phenotypically and functionally identical to type 1 Tr (Tr1) cells because their generation requires production of IL-10 by iDCs, and they suppress T-cell responses through an interleukin-10 (IL-10)– and a transforming growth factor β (TGF-β)–dependent mechanism. In addition, Tr1 cells induced by iDCs do not require the presence of CD4+CD25+ Tr cells for their generation, nor do they express high constitutive levels of CD25 or the transcription factor FoxP3. Thus, iDCs can drive the differentiation of Tr1 cells and can be used to generate large numbers of alloantigen-specific Tr1 cells for clinical use as a cellular therapy to restore peripheral tolerance.

Mobilized blood CD34+ cells transduced and selected with a clinically applicable protocol reconstitute lymphopoiesis in SCID-Hu mice

We developed a clinically applicable gene transfer procedure into mobilized peripheral blood (MPB) CD34(+) hematopoietic progenitor cells, based on single viral exposure and selection of engineered cells. CD34(+) cells were transduced with a retroviral vector carrying the truncated form of the nerve growth factor receptor (Delta NGFR) marker gene, and immunoselected for Delta NGFR expression. Optimal time and procedure for viral exposure, length of culture, and transgene expression of MPB CD34(+) cells were determined using in vitro assays. The multipotent capacity of MPB CD34(+)-transduced cells was demonstrated in the SCID-hu bone/liver/thymus mouse model. Transduced Delta NGFR(+) cells retained 50% of long-term culture-colony forming cells (LTC-CFC) compared to unmanipulated CD34(+) cells. In SCID-hu mice, 52% of CD45(+) cells, 27% of CD34(+) cells, 49% of B cells, and more than 50% of T cells were derived from transplanted CD34(+)/Delta NGFR(+) cells. Furthermore, transplantation of purified transduced cells greatly reduced the competition with untransduced progenitors occurring in unselected grafts. These data demonstrate that MPB CD34(+) cells, transduced with a single viral exposure and selected by transgene expression, retain multilineage reconstitution capacity and remarkable transgene expression.