Restoration of human B-cell differentiation into NOD-SCID mice engrafted with gene-corrected CD34+ cells isolated from Artemis or RAG1-deficient patients

Severe combined immunodeficiency (SCID) caused by mutation of the recombination-activating gene 1 (RAG1) or Artemis gene lead to the absence of B- and T-cell differentiation. The only curative treatment is allogeneic bone marrow (BM) transplantation, which displays a high survival rate when an HLA compatible donor is available but has a poorer prognosis when the donor is partially compatible. Consequently, gene therapy may be a promising alternative strategy for these diseases. Here, we report that lentiviral gene-corrected BM CD34(+) cells (isolated from Artemis- or RAG1-deficient patients) sustain human B-cell differentiation following injection into non-obese diabetic/SCID (NOD-SCID) mice previously infused with anti-interleukin-2 receptor beta chain monoclonal antibody. In most of the mice BM, engrafted with Artemis-transduced cells, human B-cell differentiation occurred until the mature stage. The B cells were functional as human immunoglobulin M (IgM) was present in the serum. Following injection with RAG1-transduced cells, human engraftment occurred in vivo but B-cell differentiation until the mature stage was less frequent. However, when it occurred, it was always associated with human IgM production. This overall approach represents a useful tool for evaluating gene transfer efficiency in human SCID forms affecting B-cell development (such as Artemis deficiency) and for testing new vectors for improving in vivo RAG1 complementation.

Evaluation of an algorithm based on peripheral blood hematopoietic progenitor cell and CD34+ cell concentrations to optimize peripheral blood progenitor cell collection by apheresis

BACKGROUND

Quantification of peripheral blood (PB) CD34+ cells is commonly used to plan peripheral blood progenitor cell (PBPC) collection but is time-consuming. Sysmex has developed a hematology analyzer that can quickly identify a population of immature hematopoietic cells (HPCs) according to cell size, cell density, and differential lysis resistance, which may indicate the presence of PBPCs in PB. This prospective study has evaluated the potential of such method to predict the PBPC mobilization.

STUDY DESIGN AND METHODS

A total of 141 patients underwent PBPC mobilization. PB HPCs and PB CD34+ cells were simultaneously quantified with a hematology analyzer (SE2100, Sysmex) and flow cytometry, respectively. The number of blood volumes processed was then based on PB CD34+ cell concentration.

RESULTS

The optimal PB HPC level able to predict a minimal level of 10 x 10(6) PB CD34+ cells per L was 5 x 10(6) per L with positive and negative predictive values of 0.93 and 0.36 percent, respectively. For this cutoff point, sensitivity and specificity were 0.81 and 0.65, respectively. The median number of blood volumes processed according to the PB CD34+ cell count allowed us to perform only one apheresis procedure for a majority of patients.

CONCLUSION

PB HPC quantification is very useful to quickly determine the initiation of PBPC apheresis especially for patients with higher concentrations. For patients exhibiting a lower HPC count (<5 x 10(6)/L), other parameters such as a CD34 test may be needed. Such a policy associated with a length of apheresis adapted to the richness in the PB CD34+ cells allows for optimizing the organization of centers with an improvement in patient comfort and economical savings.

Vector integration is nonrandom and clustered and influences the fate of lymphopoiesis in SCID-X1 gene therapy

Recent reports have challenged the notion that retroviruses and retroviral vectors integrate randomly into the host genome. These reports pointed to a strong bias toward integration in and near gene coding regions and, for gammaretroviral vectors, around transcription start sites. Here, we report the results obtained from a large-scale mapping of 572 retroviral integration sites (RISs) isolated from cells of 9 patients with X-linked SCID (SCID-X1) treated with a retrovirus-based gene therapy protocol. Our data showed that two-thirds of insertions occurred in or very near to genes, of which more than half were highly expressed in CD34(+) progenitor cells. Strikingly, one-fourth of all integrations were clustered as common integration sites (CISs). The highly significant incidence of CISs in circulating T cells and the nature of their locations indicate that insertion in many gene loci has an influence on cell engraftment, survival, and proliferation. Beyond the observed cases of insertional mutagenesis in 3 patients, these data help to elucidate the relationship between vector insertion and long-term in vivo selection of transduced cells in human patients with SCID-X1.

Long-term outcome following hematopoietic stem-cell transplantation in Wiskott-Aldrich syndrome: collaborative study of the European Society for Immunodeficiencies and European Group for Blood and Marrow Transplantation

Wiskott-Aldrich syndrome (WAS) is a rare X-linked immunodeficiency with microthrombocytopenia, eczema, recurrent infections, autoimmune disorders, and malignancies that are life-threatening in the majority of patients. In this long-term, retrospective, multicenter study, we analyzed events that occurred in 96 WAS patients who received transplants between 1979 and 2001 who survived at least 2 years following hematopoietic stem-cell transplantation (HSCT). Events included chronic graft-versus-host disease (cGVHD), autoimmunity, infections, and sequelae of before or after HSCT complications. Three patients (3%) died 2.1 to 21 years following HSCT. Overall 7-year event-free survival rate was 75%. It was lower in recipients of mismatched related donors, also in relation with an older age at HSCT and disease severity. The most striking finding was the observation of cGVHD-independent autoimmunity in 20% of patients strongly associated with a mixed/split chimerism status (P < .001), suggesting that residual-host lymphocytes can mediate autoimmune disease despite the coexistence of donor lymphocytes. Infectious complications (6%) related to splenectomy were also significant and may warrant a more restrictive approach to performing splenectomy in WAS patients. Overall, this study provides the basis for a prospective, standardized, and more in-depth detailed analysis of chimerism and events in long-term follow-up of WAS patients who receive transplants to design better-adapted therapeutic strategies.

Gene therapy for severe combined immunodeficiency: are we there yet?

Inherited and acquired diseases of the hematopoietic system can be cured by allogeneic hematopoietic stem cell transplantation. This treatment strategy is highly successful when an HLA-matched sibling donor is available, but if not, few therapeutic options exist. Gene-modified, autologous bone marrow transplantation can circumvent the severe immunological complications that occur when a related HLA-mismatched donor is used and thus represents an attractive alternative. In this review, we summarize the advantages and limitations associated with the use of gene therapy to cure SCID. Insertional mutagenesis and technological improvements aimed at increasing the safety of this strategy are also discussed.

Allogeneic bone marrow transplantation in mevalonic aciduria

Mevalonic aciduria is a rare, inborn error of isoprene biosynthesis characterized by severe, periodic attacks of fever and inflammation, developmental delay, ataxia, and dysmorphic features. This autosomal recessive disease is caused by a mutation in the mevalonate kinase gene that severely reduces mevalonate kinase activity. A 3-year-old boy with mevalonic aciduria whose condition had failed to improve with antiinflammatory treatment underwent allogeneic bone marrow transplantation from an HLA-identical sister who was a heterozygous carrier of the mutant gene. We observed sustained remission of febrile attacks and inflammation during a 15-month follow-up period.

Real-time definition of non-randomness in the distribution of genomic events

Features such as mutations or structural characteristics can be non-randomly or non-uniformly distributed within a genome. So far, computer simulations were required for statistical inferences on the distribution of sequence motifs. Here, we show that these analyses are possible using an analytical, mathematical approach. For the assessment of non-randomness, our calculations only require information including genome size, number of (sampled) sequence motifs and distance parameters. We have developed computer programs evaluating our analytical formulas for the real-time determination of expected values and p-values. This approach permits a flexible cluster definition that can be applied to most effectively identify non-random or non-uniform sequence motif distribution. As an example, we show the effectivity and reliability of our mathematical approach in clinical retroviral vector integration site distribution.

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.

La thérapie cellulaire des maladies héréditaires du système hématopoïétique

Cell therapy was born in 1968 with the first allogeneic transplantation of hematopoietic stem cells for two immune deficiency disorders: the Wiskott-Aldrich syndrome and the Severe Combined ImmunoDeficiency (SCID). From this pioneering experience, thousands of patients affected with inherited or acquired diseases of the hematopoietic system have benefited from this therapeutic approach. Unfortunately, immunologic obstacles, represented by the compatibility in the major histocompatibility HLA system, still dictate today important limitations for a larger therapeutic utilization of hematopoietic stem cells (HSC). In this review, we have summarized the difficulties and the scientific advances leading us to improve the clinical results; the therapeutic research's track for primary immunodeficiencies is also discussed.

Outcomes of hematopoietic stem cell transplantation for Hurler's syndrome in Europe: a risk factor analysis for graft failure

Hurler's syndrome (HS), the most severe form of mucopolysaccharidosis type-I, causes progressive deterioration of the central nervous system and death in childhood. Allogeneic stem cell transplantation (SCT) before the age of 2 years halts disease progression. Graft failure limits the success of SCT. We analyzed data on HS patients transplanted in Europe to identify the risk factors for graft failure. We compared outcomes in 146 HS patients transplanted with various conditioning regimens and grafts. Patients were transplanted between 1994 and 2004 and registered to the European Blood and Marrow Transplantation database. Risk factor analysis was performed using logistic regression. ‘Survival’ and ‘alive and engrafted’-rate after first SCT was 85 and 56%, respectively. In multivariable analysis, T-cell depletion (odds ratio (OR) 0.18; 95% confidence interval (CI) 0.04–0.71; P=0.02) and reduced-intensity conditioning (OR 0.08; 95% CI 0.02–0.39; P=0.002) were the risk factors for graft failure. Busulfan targeting protected against graft failure (OR 5.76; 95% CI 1.20–27.54; P=0.028). No difference was noted between cell sources used (bone marrow, peripheral blood stem cells or cord blood (CB)); however, significantly more patients who received CB transplants had full-donor chimerism (OR 9.31; 95% CI 1.06–82.03; P=0.044). These outcomes may impact the safety/efficacy of SCT for ‘inborn-errors of metabolism’ at large. CB increased the likelihood of sustained engraftment associated with normal enzyme levels and could therefore be considered as a preferential cell source in SCT for ‘inborn errors of metabolism’.

Management options for adenosine deaminase deficiency; proceedings of the EBMT satellite workshop (Hamburg, March 2006)

Adenosine deaminase (ADA) deficiency is a disorder of purine salvage that has its most devastating consequences in the immune system leading to severe combined immunodeficiency (SCID). Management options for ADA SCID include hematopoietic stem cell transplantation, enzyme replacement therapy and gene therapy. Formal data on the outcome following each of the three treatment modalities are limited, and this symposium was held in order to gather together the experience from major centers in Europe and the US. Transplantation for ADA-SCID is highly successful with survival rates of approximately 90% if a matched sibling or matched related donor is available but survival following matched unrelated donor or haploidentical procedures is 63% and 50% respectively with a significant rejection/non-engraftment rate in unconditioned procedures. Successfully transplanted patients demonstrated good immunological recovery with normal cellular and humoral function in the majority of cases. PEG-ADA has been used in over 150 patients worldwide either as an alternative to mismatched transplant or as a stabilizing measure prior to transplant. Overall, approximately two thirds of patients treated with PEG-ADA have survived with the majority of patients showing good clinical improvement. The level of immune recovery long term was less than that seen after transplant and approximately 50% of patients continued to receive immunoglobulin replacement. Gene therapy has been used as an experimental procedure in two centers in Europe. Early results from 9 patients suggest that the treatment is safe and that the majority have shown recovery of cellular immune function. Long-term follow-up of treated patients highlights a significant incidence of non-immunological problems with cognitive, neurological and audiological abnormalities most prominent.

Hématopoïèse humaine : des cellules CD34 aux lymphocytes T

Hematopoietic stem cell (HSC) has two key-properties : the self-renewal and the multipotentiality which guarantee the homeostasis of the hematopoietic system all along the lifespan. Inside this system, T lymphocytes are particular for several reasons. First and foremost, their differentiation takes place in a different organ from the one where the immature progenitors are generated and expanded. This implies the migration of an immature progenitor from the fetal liver and later on from the bone marrow to the thymus. Secondly, T cell differentiation is characterized by thymic selection and generation of T lymphocytes with a diverse repertoire able to answer to all foreign antigens one can meet. These complicated mechanisms underlying the T cell differentiation, completely different from those characterizing the myeloid system, at least partially explain our limited knowledge on human T cell lymphopoiesis. Finally, T cell differentiation pathway shows the particularity of profound ontogenic changes with the huge production of lymphoid progenitors during the fetal and the first years of life which declines during the ageing period. Recently, the discovery of new hematopoietic cytokines, the discovery of genes involved in primary immunodeficiencies and the detailed description of the role of Notch receptors have strongly developed our knowledge on T cell lymphopoiesis. In this review, we will attempt to describe where we stand in the description of this fundamental process and to underline the unresolved questions. The knowledge of this process is crucial, since it will lead us to set up new protocols with the aim to speed up immunological reconstitution after HLA partially compatible HSC and to treat the lymphocytopenia of patients affected by HIV.

Long-term T-cell reconstitution after hematopoietic stem-cell transplantation in primary T-cell-immunodeficient patients is associated with myeloid chimerism and possibly the primary disease phenotype

We studied T-cell reconstitution in 31 primary T-cell-immunodeficient patients who had undergone hematopoietic stem-cell transplantation (HSCT) over 10 years previously. In 19 patients, there was no evidence of myeloid chimerism because little or no myeloablation had been performed. Given this context, we sought factors associated with good long-term T-cell reconstitution. We found that all patients having undergone full myeloablation had donor myeloid cells and persistent thymopoiesis, as evidenced by the presence of naive T cells carrying T-cell receptor excision circles (TRECs). In 9 patients with host myeloid chimerism, sustained thymic output was also observed and appeared to be associated with gammac deficiency. It is therefore possible that the complete absence of thymic progenitors characterizing this condition created a more favorable environment for thymic seeding by a population of early progenitor cells with the potential for self-renewal, thus enabling long-term (> 10 years) T-cell production.

Human leucocyte antigen-identical haematopoietic stem cell transplantation in major histocompatiblity complex class II immunodeficiency: reduced survival correlates with an increased incidence of acute graft-versus-host disease and pre-existing viral infections

Major histocompatibility complex class II deficiency, a rare autosomal recessive primary immunodeficiency, is caused by the defective expression of human leucocyte antigen (HLA) class II molecules due to mutated trans-acting elements of any one of four regulatory genes (CIITA, RFXANK, RFX5, RFXAP). The impaired CD4 T-cell differentiation and antigen presentation in the periphery results in a severe defect of cellular and humoral response consistent with severe recurrent infections, leading to a poor prognosis. Currently, allogeneic haematopoietic stem cell transplantation (HSCT) is the only curative approach, but the overall cure rate is lower than in other immunodeficiencies. We report a single centre experience of 17 HSCTs with 15 HLA-identical donors between 1981 and 2004. Eight patients survived, while the occurrence of acute graft-versus-host disease (GVHD) was 50%. This study aimed to identify potential risk factors for GVHD and outcome within pre-HSCT complications related to the immunodeficiency. Five of seven patients with pre-existing viral infections developed acute GVHD > or = grade II, of whom four died. Two of seven patients without detectable pre-existing viral infection developed GVHD > or = grade II, and one died. The difference was significant (P < 0.05). A plausible link with other factors potentially associated with the development of GVHD could not be found. We suggest that the reduced survival after HLA-identical HSCT may be caused by the high incidence of pre-existing viral infections and associated with the onset of severe acute GVHD.

CD34+stem cell top-ups without conditioning after initial haematopoietic stem cell transplantation for correction of incomplete haematopoietic and immunological recovery in severe congenital immunodeficiencies

Haematopoietic stem cell transplantation can be limited by ineffective haematopoiesis and poor immune recovery. A CD34(+) cell infusion without conditioning has the potential to improve stem cell function with limited toxicity. Eighteen patients with congenital immunodeficiencies received CD34(+) boosts for various defects. When given <1 year after the original graft, six of seven cytopenic patients achieved transfusion independence. A second cohort (n = 11) received boosts >1 year after the original graft; only minimal changes in immune function or chimaerism were noted. Unconditioned stem cell boosts have limited toxicity but should be given early after the original graft to be effective.

X-SCID transgene leukaemogenicity

Gene therapy has been remarkably effective for the immunological reconstitution of patients with severe combined immune deficiency, but the occurrence of leukaemia in a few patients has stimulated debate about the safety of the procedure and the mechanisms of leukaemogenesis. Woods et al. forced high expression of the corrective therapeutic gene IL2RG, which encodes the gamma-chain of the interleukin-2 receptor, in a mouse model of the disease and found that tumours appeared in a proportion of cases. Here we show that transgenic IL2RG does not necessarily have potent intrinsic oncogenic properties, and argue that the interpretation of this observation with respect to human trials is overstated.

Bone marrow transplantation attenuates the myopathic phenotype of a muscular mouse model of spinal muscular atrophy

Bone marrow (BM) transplantation was performed on a muscular mouse model of spinal muscular atrophy that had been created by mutating the survival of motor neuron gene (Smn) in myofibers only. This model is characterized by a severe myopathy and progressive loss of muscle fibers leading to paralysis. Transplantation of wild-type BM cells following irradiation at a low dose (6 Gy) improved motor capacity (+85%). This correlated with a normalization of myofiber number associated with a higher number of regenerating myofibers (1.6-fold increase) and an activation of CD34 and Pax7 satellite cells. However, BM cells had a very limited capacity to replace or fuse to mutant myofibers (2%). These data suggest that BM transplantation was able to attenuate the myopathic phenotype through an improvement of skeletal muscle regeneration of recipient mutant mice, a process likely mediated by a biological activity of BM-derived cells. This hypothesis was further supported by the capacity of muscle protein extracts from transplanted mutant mice to promote myoblast proliferation in vitro (1.6-fold increase). In addition, a tremendous upregulation of hepatocyte growth factor (HGF), which activates quiescent satellite cells, was found in skeletal muscle of transplanted mutants compared with nontransplanted mutants. Eventually, thanks to the Cre-loxP system, we show that BM-derived muscle cells were strong candidates harboring this biological activity. Taken together, our data suggest that a biological activity is likely involved in muscle regeneration improvement mediated by BM transplantation. HGF may represent an attractive paracrine mechanism to support this activity.

Competition within the early B-cell compartment conditions B-cell reconstitution after hematopoietic stem cell transplantation in nonirradiated recipients

Severe combined immunodeficiency (SCID) is characterized by a complete block in T-lymphocyte differentiation. Most SCID also affects B-cell development or function, although a normal pool of pro-B cells is detectable. Treatment of SCID consists of allogeneic hematopoietic stem cell transplantation (HSCT), but in the absence of a myeloablative conditioning regimen, only T cells, and in some cases, natural killer (NK) cells, are of donor origin, while all other leukocytes subsets are of host origin. We hypothesized that donor B-cell development success could be conditioned by the competitive ability of recipient B-cell precursors in the bone marrow. We therefore compared the outcome of unconditioned HSCT in mice that differed with respect to their pro-B-cell compartments. B-cell reconstitution was limited in recipient mice containing a normal pro-B-cell pool, whereas immature and mature B-cell numbers reached wild-type levels in mice with compromised early B-cell precursors. Interestingly, host NK cells did not modify the outcome of unconditioned HSCT as long as the early B-cell compartment was compromised. These observations suggest that recipient B-cell precursors condition the reconstitution of the donor B-cell pool and, if extrapolative to humans, suggest that conditioning regimens targeting host pro-B cells may help improve B-cell reconstitution after allogeneic HSCT.

Allogeneic and autologous transplantation for haematological diseases, solid tumours and immune disorders: definitions and current practice in Europe

The Accreditation Subcommittee of the EBMT regularly publishes special reports on current practice of haemopoietic stem cell transplantation for haematological diseases, solid tumours and immune disorders in Europe. Major changes have occurred since the first report was published in 1996. Haemopoietic stem cell transplantation today includes grafting with allogeneic and autologous stem cells derived from bone marrow, peripheral blood and cord blood. With reduced intensity conditioning regimens in allogeneic transplantation, the age limit has increased, permitting the inclusion of older patients. New indications have emerged such as autoimmune disorders and AL amyloidosis for autologous, and solid tumours for allogeneic transplants. The introduction of alternative therapies has challenged well-established indications such as imatinib for chronic myeloid leukaemia. An updated report with revised tables and operating definitions is presented here.

Gene therapy of metabolic diseases

This review surveys the potential application of gene therapy to metabolic diseases. Proof of principle has been achieved in the treatment of two inherited immunodeficiency conditions. A significant safety issue has also been observed. Several strategies are being experimentally tested for a number of metabolic diseases (more than 20) and may provide a rationale for the future development of clinical trials.

A double-blind low dose-finding phase II study of granulocyte colony-stimulating factor combined with chemotherapy for stem cell mobilization in patients with non-Hodgkin's lymphoma

The aim of the study was to define the minimal effective dose (MED) of granulocyte colony-stimulating factor (G-CSF) among five daily doses following chemotherapy for peripheral blood stem cell (PBSC) collection. Twenty-five patients were included in this double-blind dose-finding phase II study conducted according to a two-stage Bayesian design. The estimated probabilities of success for PBSC collection for the G-CSF doses of 50, 75, 100, 125 and 150 microg/m2/day were 84%, 87.7%, 91%, 93.9 and 96.4%, respectively. Low G-CSF doses may be used with a similar probability of success as conventional doses and could allow significant savings.

Hematopoietic stem cell transplantation in hemophagocytic lymphohistiocytosis: a single-center report of 48 patients

OBJECTIVES

Familial hemophagocytic lymphohistiocytosis (FHLH) is a genetically determined disorder characterized by the early onset of fever, hepatosplenomegaly, central nervous system disease, thrombocytopenia, coagulation disorders, and hemophagocytosis. It is caused by genetic defects that impair T cell-mediated and natural cytotoxicity. Chemotherapy- or immunotherapy-based treatments can achieve remission. Hematopoietic stem cell transplantation (HSCT), however, is the only curative option, but optimal modalities and long-term outcome are not yet well known.

METHODS

We retrospectively analyzed the outcome of HSCT that was performed in 48 consecutive patients who had FHLH and were treated in a single center between 1982 and 2004.

RESULTS

The overall survival was 58.5% with a median follow-up of 5.8 years and extending to 20 years. A combination of active disease and haploidentical HSCT had a poor prognosis because in this situation, HLH disease is more frequently associated with graft failure. Twelve patients received 2 transplants because of graft failure (n = 7) or secondary graft loss that led to HLH relapse (n = 5). Transplant-related toxicity essentially consisted in veno-occlusive disease, which occurred in 28% of transplants and was associated with young age, haploidentical transplantation, and the use of antithymocyte globulin (ATG) in the conditioning regimen. A sustained remission was achieved in all patients with a donor chimerism > or = 20% of leukocytes. Long-term sequelae were limited, because only 2 (7%) of 28 patients experienced a mild neurologic disorder.

CONCLUSIONS

This survey demonstrates the long-term efficacy of HSCT as a cure of FHLH. HSCT preserves quality of life. It shows that HSCT should be performed as early as a complete remission has been achieved. Additional studies are required to improve the procedure and reduce its toxic effects.

The VAD chemotherapy regimen plus a G-CSF dose of 10 μg/kg is as effective and less toxic than high-dose cyclophosphamide plus a G-CSF dose of 5 μg/kg for progenitor cell mobilization: results from a monocentric study of 82 patients

A study was conducted to compare the efficiency and toxicity of two peripheral blood stem cell (PBSC) mobilization procedures for newly diagnosed patients with multiple myeloma. Patients from group 1 (n=51) were treated by high-dose cyclophosphamide (HD-CY) plus G-CSF (5 microg/kg/day), and the second group (n=31) by VAD regimen plus G-CSF administration (10 microg/kg/day). Successful mobilization, defined by a minimal count of 2.5 x 10(6) CD34(+) cells/kg collected, was achieved in 96 and 90% of patients in groups 1 and 2, respectively (P=0.15). The mean peripheral blood CD34(+) cells concentration and the mean CD34(+) cells/kg collected were higher in group 2 than in the group 1 (P=0.05). The mean number of leukaphereses necessary to collect a count of 2.5 x 10(6) CD34(+) cells/kg was reduced in group 2 compared to group 1. Adverse events, blood products consumption and time spent in the hospital were significantly greater after HD-CY. In conclusion, VAD plus a G-CSF dose of 10 microg/kg administration seems preferential to HD-CY plus a G-CSF dose of 5 microg/kg for PBSC collection because of equivalent or better efficiency in stem cell mobilization, strong favorable toxicity profile and reduced cost.

Fragile sites are preferential targets for integrations of MLV vectors in gene therapy

Following gene therapy of SCID-X1 using murine leukemia virus (MLV) derived vector, two patients developed leukemia owing to an activating vector integration near the LMO2 gene. We found that these integrations reside within FRA11E, a common fragile site known to correlate with chromosomal breakpoints in tumors. Further analysis showed that fragile sites attract a nonrandom number of MLV integrations, shedding light on its integration mechanism and risk-to-benefit ratio in gene therapy.

Severe combined immunodeficiency and microcephaly in siblings with hypomorphic mutations in DNA ligase IV

DNA double-strand breaks (dsb) during V(D)J recombination of T and B lymphocyte receptor genes are resolved by the non-homologous DNA end joining pathway (NHEJ) including at least six factors: Ku70, Ku80, DNA-PK(cs), Artemis, Xrcc4, and DNA ligase IV (Lig4). Artemis and Lig4 are the only known V(D)J/NHEJ factors found deficient in human genetic disorders. Null mutations of the Artemis gene result in a complete absence of T and B lymphocytes and increased cellular sensitivity to ionizing radiations, causing radiosensitive-SCID. Mutations of Lig4 are exclusively hypomorphic and have only been described in six patients, four exhibiting mild immunodeficiency associated with microcephaly and developmental delay, while two patient had leukemia. Here we report a SCID associated with microcephaly caused by compound heterozygous hypomorphic mutations in Lig4. Residual activity of Lig4 in these patients is underscored by a normal pattern of TCR-alpha and -beta junctions in the T cells of the patients and a moderate impairment of V(D)J recombination as tested in vitro. These observations contrast with the severity of the clinical immunodeficiency, suggesting that Lig4 may have additional critical roles in lymphocyte survival beyond V(D)J recombination.

Dynamics of Thymus-Colonizing Cells during Human Development

Here, we identify fetal bone marrow (BM)-derived CD34hiCD45RAhiCD7+ hematopoietic progenitors as thymus-colonizing cells. This population, virtually absent from the fetal liver (FL), emerges in the BM by development weeks 8-9, where it accumulates throughout the second trimester, to finally decline around birth. Based on phenotypic, molecular, and functional criteria, we demonstrate that CD34hiCD45RAhiCD7+ cells represent the direct precursors of the most immature CD34hiCD1a- fetal thymocytes that follow a similar dynamics pattern during fetal and early postnatal development. Histological analysis of fetal thymuses further reveals that early immigrants predominantly localize in the perivascular areas of the cortex, where they form a lymphostromal complex with thymic epithelial cells (TECs) driving their rapid specification toward the T lineage. Finally, using an ex vivo xenogeneic thymus-colonization assay, we show that BM-derived CD34hiCD45RAhiCD7+ progenitors are selectively recruited into the thymus parenchyma in the absence of exogenous cytokines, where they adopt a definitive T cell fate.

Long-term immune reconstitution in RAG-1-deficient mice treated by retroviral gene therapy: a balance between efficiency and toxicity

Severe combined immunodeficiency (SCID) caused by mutations in RAG1 or RAG2 genes is characterized by a complete block in T- and B-cell development. The only curative treatment is allogeneic hematopoietic stem cell transplantation, which gives a high survival rate (90%) when an HLA-genoidentical donor exists but unsatisfactory results when only partially compatible donors are available. We have thus been interested in the development of a potential alternative treatment by using retroviral gene transfer of a normal copy of RAG1 cDNA. We show here that this approach applied to RAG-1-deficient mice restores normal B- and T-cell function even in the presence of a reduced number of mature B cells. The reconstitution is stable over time, attesting to a selective advantage of transduced progenitors. Notably, a high transgene copy number was detected in all lymphoid organs, and this was associated with a risk of lymphoproliferation as observed in one mouse. Altogether, these results demonstrate that correction of RAG-1 deficiency can be achieved by gene therapy in immunodeficient mice but that human application would require the use of self-inactivated vector to decrease the risk of lymphoproliferative diseases.

Improving immune reconstitution while preventing GvHD in allogeneic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (HSCT) is the treatment of choice for many hematologic malignancies and inherited disorders of the hematopoietic system. Ex vivo T-cell depletion (TCD) of the graft and post-transplantation immunosuppression efficiently prevents the development of GvHD in no- MHC-identical settings. However, the consequence of these non-specific strategies is a long-lasting immunodeficiency associated with increased incidence of disease relapse, graft rejection and reactivation of viral infections. Donor lymphocyte infusion, which is used for treating leukemic relapse after allogeneic HSCT, can result in severe GvHD. Several strategies are being optimized specifically to inactivate anti-host T cells while preserving anti-leukemic or anti-microbial immunocompetence. Based on the ex vivo or in vivo elimination of anti-host T cells, or on the modulation of their anti-host activity, these approaches, which have been explored extensively in pre-clinical studies and tested in some preliminary clinical trials, are discussed in this paper.

Transient familial haemophagocytic lymphohistiocytosis reactivation post-CD34 haematopoietic stem cell transplantation

Familial haemophagocytic lymphohistiocytosis (FHLH) is a genetic disorder caused by defective lymphocyte cytotoxicity, resulting in impaired lymphocyte homeostasis and macrophage infiltration of solid tissues and bone marrow, with extensive haemophagocytosis. It is invariably fatal unless treated by allogeneic haematopoietic stem cell transplantation (HSCT). In a retrospective analysis of 11 cases of FHLH, transplanted in one centre between January 1999 and December 2003, it was found that host T cell expansion occurred early after HSCT in a setting of a viral infection (cytomegalovirus and Epstein-Barr virus respectively) in two cases who received T cell-depleted HSCT. Transient recurrence of clinical and biological manifestations of FHLH was observed, despite evidence for donor cell engraftment. Secondary development of donor T cells led to stable mixed chimaerism and sustained remission of FHLH. Detection of host-derived T cells soon after HSCT in a patient with FHLH should thus not mistakenly be taken as a manifestation of graft rejection.

Gene therapy for severe combined immunodeficiency

Studies of severe combined immunodeficiency (SCID), a group of rare monogenic disorders, have provided key findings about the physiology of immune system development. The common characteristic of these diseases is the occurrence of a block in T cell differentiation, always associated with a direct or indirect impairment of B cell immunity. The resulting combined immunodeficiency is responsible for the clinical severity of SCID, which, without treatment, leads to death within the first year of life. Eleven distinct SCID phenotypes have been identified to date. Mutations of ten genes have been found to cause SCID. Identifying the pathophysiological basis of most SCID conditions has led to the possibility of molecular therapy as an alternative to allogeneic hematopoietic stem cell transplantation. This review discusses recent developments in SCID identification and treatment.

Severe combined immunodeficiency. A model disease for molecular immunology and therapy

Severe combined immunodeficiencies (SCIDs) consist of genetically determined arrest of T-cell differentiation. Ten different molecular defects have now been identified, which all lead to early death in the absence of therapy. Transplantation of allogeneic hematopoietic stem cells (HSCT) can restore T-cell development, thus saving the lives of SCID patients. In this review, the different characteristics of HSCT are discussed along with the available data regarding the long-term outcome. Transient thymopoiesis caused by an exhaustion of donor progenitor cells and possibly a progressive loss of thymus function can lead to a progressive decline in T-cell functions. The preliminary results of gene therapy show the correction of two SCID conditions. Based on the assumption that long-lasting pluripotent progenitor cells are transduced, these data suggest that gene therapy could overcome the long-term recurrence of the T-cell immunodeficiency. SCID is thus a disease model for experimental therapy in the hematopoietic system.

Failure of SCID-X1 gene therapy in older patients

Gene therapy has been shown to be a highly effective treatment for infants with typical X-linked severe combined immunodeficiency (SCID-X1, γc-deficiency). For patients in whom previous allogeneic transplantation has failed, and others with attenuated disease who may present later in life, the optimal treatment strategy in the absence of human leukocyte antigen (HLA)–matched donors is unclear. Here we report the failure of gene therapy in 2 such patients, despite effective gene transfer to bone marrow CD34+ cells, suggesting that there are intrinsic host-dependent restrictions to efficacy. In particular, there is likely to be a limitation to initiation of normal thymopoiesis, and we therefore suggest that intervention for these patients should be considered as early as possible.

Treatment of an infant with X‐linked severe combined immunodeficiency (SCID‐X1) by gene therapy in Australia

OBJECTIVE

To report the outcome of gene therapy in an infant with X-linked severe combined immunodeficiency (SCID-X1), which typically causes a lack of T and natural killer (NK) cells.

DESIGN AND SETTING

Ex-vivo culture and gene transfer procedures were performed at The Children's Hospital at Westmead, Sydney, NSW, in March 2002. Follow-up to March 2005 (36 months) is available.

PATIENT

A 9-month-old male infant with confirmed SCID-X1 (including complete absence of T cells) with an NK+ phenotype (a less common variant of SCID-X1), and no HLA-identical sibling donor available for conventional bone marrow transplantation.

PROCEDURE

CD34+ haemopoietic progenitor cells were isolated from harvested bone marrow and cultured with cytokines to stimulate cellular replication. Cells were then genetically modified by exposure to a retrovirus vector encoding human gamma c (the common gamma chain of several interleukin receptors; mutations affecting the gamma c gene cause SCID-X1). Gene-modified cells (equivalent to 1.3 x 10(6) CD34+/gamma c+ cells/kg) were returned to the infant via a central line.

RESULTS

T cells were observed in peripheral blood 75 days after treatment, and levels increased rapidly to 0.46 x 10(9) CD3+ cells/L at 5 months. Within 2 weeks of the appearance of T cells, there was a distinct clinical improvement, with early weight gain and clearance of rotavirus from the gut. However, T-cell levels did not reach the reference range, and immune reconstitution remained incomplete. The infant failed to thrive and developed weakness, hypertonia and hyperreflexia in the legs, possibly the result of immune dysregulation. He went on to receive a bone marrow transplant from a matched unrelated donor 26 months after gene therapy.

CONCLUSIONS

This is the first occasion that gene therapy has been used to treat a genetic disease in Australia. Only partial immunological reconstitution was achieved, most likely because of the relatively low dose of gene-corrected CD34+ cells re-infused, although viral infection during the early phase of T-cell reconstitution and the infant's NK+ phenotype may also have exerted an effect.

Integration of retroviruses: a fine balance between efficiency and danger

Since retroviruses can integrate a copy of their DNA into the host cell DNA, they are good vectors for gene therapy. But such vectors also have oncogenic potential

Severe combined immunodeficiency caused by deficiency in either the delta or the epsilon subunit of CD3

We investigated the molecular mechanism underlying a severe combined immunodeficiency characterized by the selective and complete absence of T cells. The condition was found in 5 patients and 2 fetuses from 3 consanguineous families. Linkage analysis performed on the 3 families revealed that the patients were carrying homozygous haplotypes within the 11q23 region, in which the genes encoding the gamma, delta, and epsilon subunits of CD3 are located. Patients and affected fetuses from 2 families were homozygous for a mutation in the CD3D gene, and patients from the third family were homozygous for a mutation in the CD3E gene. The thymus from a CD3delta-deficient fetus was analyzed and revealed that T cell differentiation was blocked at entry into the double positive (CD4+CD8+) stage with the accumulation of intermediate CD4-single positive cells. This indicates that CD3delta plays an essential role in promoting progression of early thymocytes toward double-positive stage. Altogether, these findings extend the known molecular mechanisms underlying severe combined immunodeficiency to a new deficiency, i.e., CD3epsilon deficiency, and emphasize the essential roles played by the CD3epsilon and CD3delta subunits in human thymocyte development, since these subunits associate with both the pre-TCR and the TCR.

Clonal evidence for the transduction of CD34+ cells with lymphomyeloid differentiation potential and self-renewal capacity in the SCID-X1 gene therapy trial

Immune function has been restored in 9 of 10 children with X-linked severe combined immunodeficiency by gamma c gene transfer in CD34+ cells. The distribution of both T-cell receptor (TCR) V beta family usage and TCR V beta complementarity-determining region 3 (CDR3) length revealed a broadly diversified T-cell repertoire. Retroviral integration site analysis in T cells demonstrated a high number of distinct insertion sites, indicating polyclonality of genetically corrected cell clones, in all patients. Detection of gamma c transgene expression on patients' mature myeloid cells has prompted us to investigate the nature of the most immature transduced hematopoietic precursor cells. Insertion sites shared by T and B lymphocytes as well as highly purified granulocytes and monocytes demonstrate the correction of common multipotent progenitor cells. Moreover, our data show that differentiated leukocytes share the same exact insertion sites with CD34+ cells that we obtained 8 months later and that were able to generate long-term culture-initiating cells (LTC-ICs). This finding demonstrates the initial transduction of very primitive multipotent progenitor cells with self-renewal capacity. These results provide a first evidence in the setting of a clinical trial that CD34+ cells maintain both lymphomyeloid potential as well as self-renewal capacity after ex vivo manipulation.

Successful peripheral blood stem cell harvesting with granulocyte colony-stimulating factor alone after previous mobilization failure

A total of 138 patients whose stem cell mobilization failed following chemotherapy and granulocyte colony--stimulating factor (G-CSF) at a dose of 5 microg/kg/d were given a higher dose of G-CSF (10 microg/kg/d) for 5 days after a 7-day resting period. Stem cell mobilization was successful in 90 patients, who yielded a median of 3.5x10(6) CD34(+) cells/kg, partially successful in 17 patients (1-2.4x10(6) CD34+ cells/kg) and failed in the remaining 31 patients.

Does haploidentical transplantation in children with primary immunodeficiencies have the potential to exploit donor NK cell alloreactivity?

Donor potential to exert NK cell alloreactivity has been shown to confer survival advantage in haploidentical hematopoietic cell transplantation for hematological malignancies. We investigated killer immunoglobulin receptor (KIR) ligand incompatibility in 40 children receiving haploidentical transplantation for primary immunodeficiencies. The conditioning regimen consisted of busulfan and cyclophosphamide. T-cell depletion of the graft used complement-dependent lysis or CD34+ selection. Two patients died in the first month. The remaining 38 patients were divided into those with (n=13) and those without (n=25) donor potential to exert NK cell alloreactivity. Engraftment was similar in the two groups (61.5 and 64%, respectively). The incidence of grade II-IV acute graft-versus-host disease (GVHD) tended to be lower in the group with donor potential to exert NK cell alloreactivity, but the difference was not significant. In conclusion, in this series of patients with primary immunodeficiencies, donor potential to exert NK cell alloreactivity was not associated with significant advantages in engraftment and prevention of acute GVHD.

Gene therapy for immunodeficiency diseases

Primary immunodeficiency diseases represent good targets for hematopoietic stem cell-targeted gene therapy. Severe combined immunodeficiencies (SCID) have been the first examples of successful gene therapy based on the ex vivo usage of retroviral vectors. New advances in the technology of gene transfer should further promote gene therapy as a safe and effective therapeutic strategy of immunodeficiency diseases.

IL-7 effect on immunological reconstitution after HSCT depends on MHC incompatibility

Considerable progress has been recently accomplished in the management of patients who have undergone haplo-incompatible haematopoietic stem cell transplantation (HSCT) in terms of intake and prevention of graft-versus-host disease. Nevertheless haplo-incompatible HSCT is a procedure limited to a small number of patients because of the long-lasting immunodeficiency that is responsible for more than 50% of deaths within the first 3 months. Interleukin (IL)-7, which plays a unique and key role in T-cell development both in the mouse and in the human, is particularly attractive for attempting to speed up T-cell reconstitution. However, controversial results have been obtained after bone marrow graft in murine and primate models. To elucidate the impact of IL-7 treatment, we have performed HSCT in irradiated murine recombination activating gene (RAG) immunodeficient recipients, using donors that exhibited increased major histocompatibilty complex (MHC) incompatibility. Although irradiation performed prior to HSCT lead to a profound defect in the thymic stromal cells responsible for IL-7 production, IL-7 treatment had no significant effect on immune reconstitution in the MHC compatible and partially compatible settings. Interestingly, in the MHC fully incompatible setting in which only one-third of the recipients demonstrated active thymopoiesis, probably because of the rejection of donor cells by host natural killer cells, IL-7 treatment had a beneficial effect on T-cell development.

Severe cutaneous papillomavirus disease after haemopoietic stem-cell transplantation in patients with severe combined immune deficiency caused by common gammac cytokine receptor subunit or JAK-3 deficiency

Haemopoietic stem-cell transplantation is a life-saving treatment for severe combined immune deficiency. However, there has been little long-term follow-up of this treatment. There is evidence for the persistance of partial immunodeficiency associated with significant infections, including severe human papillomavirus (HPV) disease. We did a retrospective analysis of severe HPV disease in a group of 41 patients with severe combined immune deficiency from one centre who were alive 10 years or longer after haemopoietic stem-cell transplantation. Nine of the 41 patients had extensive chronic HPV disease limited to the skin, with a median onset at 8 years after transplantation. Four had lesions typical of epidermodysplasia verruciformis, a rare genodermatosis. Transplant characteristics, immune status, and chimerism of these nine patients did not differ significantly from those of the other patients. The nine patients with HPV disease had severe combined immune deficiency associated with either common gammac receptor cytokine subunit or Janus kinase-3 (JAK-3) deficiency. By contrast, patients with other forms of severe combined immune deficiency did not have any signs of HPV disease. That genetic causes are the only predisposing factor to be identified for severe combined immune deficiency, suggests that natural-killer cells or gammac/JAK-3-dependent signalling in keratinocytes could have a role in anti-HPV immunity.