Human leukocyte antigen-DR expression on peripheral blood monocytes and the risk of pneumonia in pediatric lung transplant recipients.

BACKGROUND: Pneumonia is the leading cause of morbidity and mortality after living lobar lung transplantation (LT). Low levels of human leukocyte antigen-DR (HLA-DR) expression on peripheral blood monocytes, have been demonstrated to correlate with risk of infection in surgical, trauma, and adult transplant patients. In addition, interleukin (IL)-10 has been shown to be a negative regulator of HLA-DR expression. This study investigates whether HLA-DR expression and serum IL-10 levels correlate with the development of pneumonia after pediatric LT. METHODS: Thirteen LT recipients were prospectively monitored with blood samples obtained pre-LT (baseline) and post-LT weeks 1-4. Mean fluorescence intensity (MFI) of HLA-DR on CD14+ monocytes was measured by flow cytometry. IL-10 levels were determined by ELISA from frozen serum collected at the same time points as monocyte HLA-DR expression. Correlates of pneumonia were abstracted from the medical record. RESULTS: Monocyte HLA-DR expression declined in 11 of 13 patients in the first week post-LT. Two patients without an initial decline and four others whose HLA-DR expression recovered by week 2 post-LT, did not develop pneumonia or other infection or rejection. Pneumonia was observed in seven patients, six of whom failed to recover their monocyte HLA-DR expression by 2 weeks post-LT. Six of seven patients with pneumonia recovered, and one patient died of aspergillosis. During weeks 1-4, a statistically significant difference was seen in the profile of mean monocyte HLA-DR expression levels, analyzed as percent of baseline, between the patients with and without pneumonia (P=0.002). The greatest difference between groups over time was seen from post-LT weeks 1-2 (P=0.003). In addition, when comparing the values at each week, a significant difference was seen between the two groups at post-LT week 2 (P=0.006) and week 4 (P=0.05). Analysis of IL-10 concentrations revealed that the overall difference between the groups (patients with and without pneumonia) was statistically significant (P=0.014), with a paradoxical positive correlation between HLA-DR expression at post-LT week 4 and IL-10 concentrations. CONCLUSIONS: Persistent low monocyte HLA-DR expression was associated with the risk of post-LT pneumonia in these patients. This measurement may be useful for monitoring risk of infection and stratifying patients into higher and lower risk groups. Increased IL-10 levels may be protective for infection in this group of patients. At present it is unknown whether the predictive power of HLA-DR expression is indicative of a global defect in monocytic function or a specific abnormality.

Expression of CD1d by myelomonocytic leukemias provides a target for cytotoxic NKT cells.

Natural killer T (NKT) cells with an invariant T-cell receptor for alpha-galactosylceramide (alphaGalCer) that is presented by CD1d have been reported to be cytotoxic for myelomonocytic leukemia cells. However, the necessity for leukemia cell CD1d expression, the role of alphaGalCer, and the cytotoxic mechanisms have not been fully elucidated. We evaluated these issues with myeloid leukemia cells from 14 patients and purified NKT cells that were alphaGalCer/CD1d reactive. CD1d was expressed by 80-100% of cells in three of seven acute myeloid leukemias (AMLs) and by 28-77% of cells in five of six juvenile myelomonocytic leukemias (JMML). CD1d+ AML cells were myelomonocytic or monoblastic types, and CD1d+ JMML cells were differentiated and CD34-. Cytotoxicity required leukemia cell CD1d expression and was increased by alphaGalCer (P<0.0001) and inhibited by anti-CD1d mAb (P<0.001). The perforin/granzyme-B pathway of NKT cells caused up to 85% of cytotoxicity, and TNF-alpha, FASL, and TRAIL mediated additional killing. CD56+ NKT cells expressed greater perforin and were more cytotoxic than CD56 NKT cells without alphaGalCer (P<0.0001), but both subpopulations were highly and equally cytotoxic in the presence of alphaGalCer. We conclude that CD1d expression is stage-specific for myelomonocytic leukemias and could provide a target for NKT-cell-mediated immunotherapy.

The combination regimen of idarubicin and taxotere is effective against human drug-resistant leukemic cell lines.

Up-regulation of Bcl-2 protein may contribute to drug resistance, by decreasing apoptosis after treatment, in pre-B and B-cell leukemias in pediatric patients. By contrast, augmented caspase-3 activity, an effector caspase, may be indicative of drug sensitivity due to increased cellular apoptosis. We have reported the development of an in vitro human T-lymphoblastic leukemia model resistant to ara-C and/or native E. coli L-asparaginase (ASNase), mimicking the drug resistance to the Capizzi II regimen. We have investigated the potential drug synergism between Idarubicin (IDA) and Taxotere (TXR) that may be active in the ara-C and ASNase double drug-resistant cell lines. The additive or synergistic activity between IDA and TXR is drug concentration-dependent in inducing caspase-3 activation and cellular apoptosis. We exposed two human drug-resistant cell lines that do not express the MDRI phenotype, one resistant to ASNase alone (CEM/ASNase-1-3) and the other resistant to both ara-C and ASNase (CEM/ara-C/I/ASNase-0.5-2), to physiologically achievable concentrations of IDA, TXR, or their combination. Both lines showed either synergistic drug activity to the combination regimen in comparison to either drug used alone, as determined by MTT assay, or additivity as demonstrated by flow cytometry after Annexin V and propidium iodide (PI) staining. After exposure of the ASNase-resistant line to various concentrations, the intracellular levels of Bcl-2 protein decreased to near zero relative to untreated control cells. The Bcl-2 protein reductions in these cells ranged from 30% to <1%, 49% to <1%, and 27% to 3% when treated with IDA or TXR as a single drug or IDA + TXR combination, respectively. Similarly, intracellular Bcl-2 levels in the double-resistant cell line decreased with reductions ranging from 24% to <1%, 87% to <1%, and 46% to <1% of the untreated control after treatment with IDA, TXR, or their combination, respectively. Conversely, the caspase-3 activity increased in a dose-dependent manner and inversely-correlated with loss of cell viability (r= 0.91) after exposure to IDA + TXR combination in the double drug-resistant line to both ara-C and ASNase. We conclude that the combination of the IDA + TXR regimen is highly synergistic or additive in drug resistant human leukemic cell clones. The molecular mechanism of action is due to the down-regulation of Bcl-2 protein and up-regulation of caspase-3 activity. This drug combination warrants further investigation for use in the treatment of patients with ara-C and/or ASNase refractory leukemias.

Reversal of cytosine arabinoside (ara-C) resistance by the synergistic combination of 6-thioguanine plus ara-C plus PEG-asparaginase (TGAP) in human leukemia lines lacking or expressing p53 protein.

BACKGROUND: Sequence-specific combinations of purine analogs, such as fludarabine or 6-mercaptopurine (6-MP), administered prior to cytosine arabinoside (ara-C) have been shown to abrogate ara-C resistance in human leukemia cells in vitro and in patients with relapsed acute myeloid or lymphoblastic leukemias. The two-drug combination of 6-MP plus ara-C results in greater cytotoxicity than that achieved with either ara-C or 6-MP alone. Further preclinical investigations have shown that the addition of PEG-asparaginase (PEG-ASNase) to the combination of 6-MP plus ara-C (6-MP + ara-C + PEG-ASNase) results in 15.6-fold synergism over that achieved with the two-drug regimen. This is due to increased DNA damage leading to apoptotic cell death. PURPOSE: Since the intravenous preparation of 6-MP is no longer available and since oral 6-thioguanine (6-TG) provides higher levels of intracellular thioguanine nucleotides than an isotoxic dose of oral 6-MP, we investigated the potential drug synergism of 6-TG plus ara-C plus PEG-ASNase (TGAP) in myeloid (HL60/S, HL60/SN3, U937) and lymphoblastic (CEM/0, CEM/ ara-C/B, CEM/ara-C/I, MOLT-4) leukemia cell lines. The CEM clones, MOLT-4 and HL60/SN3 cell lines expressed functional or measurable p53 protein, while the other cell lines did not. METHODS: The MTT and trypan blue dye exclusion assays were used to determine drug cytotoxicity. In addition, cellular apoptosis and cellular p53, p21/waf-1 and bcl-2 protein concentrations were determined by FACS analysis and ELISA assays. RESULTS: Sequential exposure to 6-TG (24 h) plus ara-C (24 h) plus PEG-ASNase (24 h) produced 1.3- to 18.3-fold drug synergism over the two-drug combination of 6-TG plus ara-C. The molecular mechanism of synergism was due to the fact that the three-drug combination was capable of downregulating bcl-2 oncoprotein levels in these cell lines even when p53 was absent. CONCLUSION: These studies strongly demonstrate that the TGAP regimen is highly synergistic in p53-null and p53-expressing leukemia cell lines. We conclude that this combination regimen is collaterally sensitive with ara-C and further evaluation in an investigational phase I trial in relapsed leukemia patients is warranted.

IL-7 is critical for homeostatic proliferation and survival of naive T cells.

In T cell-deficient conditions, naive T cells undergo spontaneous "homeostatic" proliferation in response to contact with self-MHC/peptide ligands. With the aid of an in vitro system, we show here that homeostatic proliferation is also cytokine-dependent. The cytokines IL-4, IL-7, and IL-15 enhanced homeostatic proliferation of naive T cells in vitro. Of these cytokines, only IL-7 was found to be critical; thus, naive T cells underwent homeostatic proliferation in IL-4(-) and IL-15(-) hosts but proliferated minimally in IL-7(-) hosts. In addition to homeostatic proliferation, the prolonged survival of naive T cells requires IL-7. Thus, naïve T cells disappeared gradually over a 1-month period upon adoptive transfer into IL-7(-) hosts. These findings indicate that naive T cells depend on IL-7 for survival and homeostatic proliferation.

Development of a double-drug-resistant human leukemia model to cytosine arabinoside and L-asparaginase: evaluation of cross-resistance to other treatment modalities.

We have developed an in vitro model of 38 T-lymphoblastic leukemia lines resistant to cytosine arabinoside (ara-C) and L-asparaginase (ASNase). Of these, 26 cell lines resistant to both drugs, 6 resistant to ara-C, and 6 resistant to ASNase were isolated. In 18 of these cell lines, all randomly selected, resistance to ara-C, ASNase and gamma radiation was documented by the MTT and trypan blue assays, as well as flow cytometry with Annexin V and propidium iodide (PI) staining. In these lines, p53, p21WAF1, and bcl-2 levels were measured by ELISA. Results show that P21WAF1 upregulation following p53 induction did not occur, suggesting that p53 function may be lost. Moreover, the data imply that upregulation of bcl-2 is critical in the development of resistance to ara-C and ASNase in these leukemic lines. In the CEM/0 parent line, p53 maintained its ability to interact with its DNA binding site as documented by the electrophoretic mobility shift assay (EMSA). But in one single- and one double-resistant leukemic cell line examined, p53 was not shown to maintain this ability. We conclude that double-resistant clones to ara-C and ASNase are refractory to both drugs, providing an excellent leukemic model to investigate the multiple-drug resistance.

MAT1-modulated CAK activity regulates cell cycle G(1) exit.

The cyclin-dependent kinase (CDK)-activating kinase (CAK) is involved in cell cycle control, transcription, and DNA repair (E. A. Nigg, Curr. Opin. Cell. Biol. 8:312-317, 1996). However, the mechanisms of how CAK is integrated into these signaling pathways remain unknown. We previously demonstrated that abrogation of MAT1 (ménage à trois 1), an assembly factor and targeting subunit of CAK, induces G(1) arrest (L. Wu, P. Chen, J. J. Hwang, L. W. Barsky, K. I. Weinberg, A. Jong, and V. A. Starnes, J. Biol. Chem. 274:5564-5572, 1999). This result led us to investigate how deregulation of CAK by MAT1 abrogation affects the cell cycle G(1) exit, a process that is regulated most closely by phosphorylation of retinoblastoma tumor suppressor protein (pRb). Using mammalian cellular models that undergo G(1) arrest evoked by antisense MAT1 abrogation, we found that deregulation of CAK inhibits pRb phosphorylation and cyclin E expression, CAK phosphorylation of pRb is MAT1 dose dependent but cyclin D1/CDK4 independent, and MAT1 interacts with pRb. These results suggest that CAK is involved in the regulation of cell cycle G(1) exit while MAT1-modulated CAK formation and CAK phosphorylation of pRb may determine the cell cycle specificity of CAK in G(1) progression.

Hematopoietic stem cell transplantation for severe combined immune deficiency.

Hematopoietic stem cell transplantation (HSCT) has been the definitive therapy for severe combined immune deficiency (SCID) since the first successful transplant for SCID in 1968. Improvements in the use of HSCT to treat patients with SCID are continuing. For example, during the last 5 years, the first successful in-utero HSCT, and the first success with gene therapy have occurred in patients with SCID. Debate still continues about the role of pretransplantation therapy for SCID patients, and the biology of post-HSCT immune reconstitution is under investigation.

Lentiviral vectors for efficient delivery of CD80 and granulocyte-macrophage- colony-stimulating factor in human acute lymphoblastic leukemia and acute myeloid leukemia cells to induce antileukemic immune responses.

Cell vaccines engineered to express immunomodulators have shown feasibility in eliminating leukemia in murine models. Vectors for efficient gene delivery to primary human leukemia cells are required to translate this approach to clinical trials. In this study, second-generation lentiviral vectors derived from human immunodeficiency virus 1 were evaluated, with the cytomegalovirus (CMV) promoter driving expression of granulocyte-macrophage-colony-stimulating factor (GM-CSF) and CD80 in separate vectors or in a bicistronic vector. The vectors were pseudotyped with vesicular stomatitis virus G glycoprotein and concentrated to high titers (10(8)-10(9) infective particles/mL). Human acute lymphoblastic leukemia (ALL), acute myeloid leukemia (AML), and chronic myeloid leukemia cell lines transduced with the monocistronic pHR-CD80 vector or the bicistronic pHR-GM/CD vector became 75% to 95% CD80 positive (CD80(+)). More important, transduction of primary human ALL and AML blasts with high-titer lentiviral vectors was consistently successful (40%-95% CD80(+)). The average amount of GM-CSF secretion by the leukemia cell lines transduced with the pHR-GM-CSF monocistronic vector was 2182.9 pg/10(6) cells per 24 hours. Secretion was markedly lower with the bicistronic pHR-GM/CD vector (average, 225.7 pg/10(6) cells per 24 hours). Lower amounts of CMV-driven messenger RNA were detected with the bicistronic vector, which may account for its poor expression of GM-CSF. Primary ALL cells transduced to express CD80 stimulated T-cell proliferation in an autologous mixed lymphocyte reaction. This stimulation was specifically blocked with monoclonal antibodies reactive against CD80 or by recombinant cytotoxic T-lymphocyte antigen 4-immunoglobulin fusion protein. These results show the feasibility of efficiently transducing primary leukemia cells with lentiviral vectors to express immunomodulators to elicit antileukemic immune responses. (Blood. 2000;96:1317-1326)

Contact with fibrillar collagen inhibits melanoma cell proliferation by up-regulating p27KIP1.

It is known that the extracellular matrix regulates normal cell proliferation, and it is assumed that anchorage-independent malignant cells escape this regulatory function. Here we demonstrate that human M24met melanoma cells remain responsive to growth regulatory signals that result from contact with type I collagen and that the effect on proliferation depends on the physical structure of the collagen. On polymerized fibrillar collagen, M24met cells are growth arrested at the G(1)/S checkpoint and maintain high levels of p27(KIP1) mRNA and protein. In contrast, on nonfibrillar (denatured) collagen, the cells enter the cell cycle, and p27(KIP1) is down-regulated. These growth regulatory effects involve contact between type I collagen and the collagen-binding integrin alpha(2)beta(1), which appears restricted in the presence of fibrillar collagen. Thus melanoma cells remain sensitive to negative growth regulatory signals originating from fibrillar collagen, and the proteolytic degradation of fibrils is a mechanism allowing tumor cells to escape these restrictive signals.

B-cell function in canine X-linked severe combined immunodeficiency.

Canine X-linked severe combined immunodeficiency (XSCID) is due to mutations in the common gamma (gammac) subunit of the IL-2, IL-4, IL-7, IL-9 and IL-15 receptors and has a similar clinical phenotype to human XSCID. We have previously shown that the block in T-cell development is more profound in XSCID dogs than in genetically engineered gamma c-deficient mice. In this study we evaluated the B-cell function in XSCID dogs. In contrast to the marked decrease in peripheral B-cells in gamma c-deficient mice, XSCID dogs have increased proportions and numbers of peripheral B-cells as observed in XSCID boys. Canine XSCID B-cells do not proliferate following stimulation with the T-cell-dependent B-cell mitogen, pokeweed mitogen (PWM); however, they proliferate normally in response to the T-cell-independent B-cell mitogen, formalin-fixed, heat-killed Staphylococcus aureus. Canine XSCID B-cells are capable of producing IgM but are incapable of normal class-switching to IgG antibody production as demonstrated by in vitro stimulation with PWM and immunization with the T-cell-dependent antigen, bacteriophage PhiX174. Similar results have been reported for XSCID boys. Thus, it appears that gamma c-dependent cytokines have differing roles in human and canine B-cell development than in the mouse making the XSCID dog a valuable model for studying the role of these cytokines in B-cell development and function.

T cell depleted haploidentical bone marrow transplantation for the treatment of children with severe combined immunodeficiency.

Severe combined immunodeficiency (SCID) is fatal in early childhood if unrecognized and if not treated. The aim was to determine the efficacy of T cell depleted bone marrow transplantation (TCD BMT) in the treatment of children with SCID. Eleven children diagnosed with SCID received histocompatible related donor bone marrow transplantation--HRD BMT (group I). Thirty seven children diagnosed with SCID who did not have histocompatible donors were treated with TCD haploidentical parental bone marrow transplantation (BMT) (group II). TCD was performed by in vitro soybean lectin agglutination followed by E-rosette depletion. Patients were longitudinally assessed for the presence and function of T and B lymphocytes. In group I all children survived. The mean age of children in this group at the time of HRD BMT was 15.4 months. All surviving patients normalized their specific T cell function. Two out of 11 require treatment with intravenous immunoglobulin i.v. Ig. In group II 17 out of 37 (46%) children survived. At the time of TCD BMT the mean age of survivors was 7.5 months, vs. 11.4 months in patients who died. Death was caused most commonly by opportunistic infections, Epstein-Barr virus induced lymphoproliferative disease (EBV-LPD), and graft versus host disease (GvHD). Seventeen out of 17 surviving patients recovered normal numbers of CD3+ cells and antigen specific T cell function. Five out of 17 never recovered their B cell function and require i.v. Ig injections. Early diagnosis, prevention or treatment of opportunistic infections, and enhancement of immune recovery will be necessary to improve survival in patients with SCID treated with TCD BMT.

Expression of human Wiskott-Aldrich syndrome protein in patients' cells leads to partial correction of a phenotypic abnormality of cell surface glycoproteins.

The Wiskott-Aldrich syndrome (WAS) is an uncommon X-linked recessive disease characterized by thrombocytopenia, eczema and immunodeficiency. The biochemical defect of this disorder primarily affects cells derived from bone marrow. To understand better the molecular mechanisms underlying this disease and to evaluate the possibility of correcting the genetic defects in hematopoietic cells, a Moloney murine leukemia virus (MoMLV)- based retroviral vector carrying a functional Wiskott-Aldrich syndrome protein (WASp) cDNA driven by an SV40 promoter (LNS-WASp) was constructed. A packaging cell line containing this vector produced a stable level of WAS protein and maintained a high titer of viral output. Epstein-Barr virus (EBV)-transformed B lymphoblastoid cell lines (B-LCL) from WAS patients, which lack expression of the WAS protein, were transduced by the LNS-WASp retroviral vector and showed expression of WASp by Western blot. Analysis of the O-glycan pattern on cell surface glycoproteins from WAS patients' B-LCL showed an altered glycosylation pattern, due to increased activity of beta-1, 6-N-acetylglucosaminyltransferase (C2GnT). Transduction by the retroviral vector carrying the functional WASp cDNA partially restored the abnormal glycosylation pattern, and was accompanied by a decreasing C2GnT activity. These findings imply a functional linkage between the WAS protein and the expression of the glycosyltransferase involved in the O-glycosylation, and also suggest a potential gene therapy via transferring a functional WASp cDNA into hematopoietic cells for Wiskott-Aldrich syndrome. Gene Therapy (2000) 7, 314-320.

Ineffective erythropoiesis in beta-thalassemia major is due to apoptosis at the polychromatophilic normoblast stage.

Beta-thalassemia major is characterized by ineffective erythropoiesis, although it is difficult to define the dynamics of this process from the static information revealed by analysis of bone marrow (BM) aspirates. We aimed to study the kinetics of sequential erythroid differentiation in beta-thalassemia major. We isolated the progenitor cells (CD34(+) and CD34(+)CD38(-) cells) from BM of thalassemia major patients and studied in vitro erythropoiesis. This is the first report of an in vitro study in human beta-thalassemia major from purified BM CD34(+) progenitor cells, using erythroid culture conditions, which allow unilineage differentiation to mature enucleated red blood cells. In contrast to normal donors, a high proportion of BM CD34(+) and CD34(+)CD38(-) progenitors from beta-thalassemia major coexpressed the late erythroid lineage-specific protein glycophorin A and generated a higher proportion of erythroid colonies. However, despite the marked increase in erythroid clonogenicity of the progenitor population, erythroid cultures initiated from beta-thalassemia major BM CD34(+) cells expanded 10- to 20-fold less than from normal BM. There were less viable cells during differentiation, specifically after the polychromatophilic normoblast stage. There was a progressive increase in the apoptotic erythroid progeny with differentiation, and apoptosis occurred predominantly at the polychromatophilic normoblast stage. In thalassemia major, BM progenitor cells show increased erythroid clonogenicity, increased expression of late erythroid lineage-specific proteins, and accelerated erythroid differentiation. However, despite the apparent increased erythroid commitment, ineffective erythropoiesis occurs due to apoptosis at the polychromatophil stage. Identification of the differentiation stage at which apoptosis occurs will permit further studies of the underlying mechanisms and target therapeutic strategies to improve red cell production.

Spontaneous apoptosis in lymphocytes from patients with Wiskott-Aldrich syndrome: correlation of accelerated cell death and attenuated bcl-2 expression.

Wiskott-Aldrich syndrome (WAS) is an X-linked recessive disorder characterized by thrombocytopenia, eczema, and a progressive deterioration of immune function. WAS is caused by mutations in an intracellular protein, WASP, that is involved in signal transduction and regulation of actin cytoskeleton rearrangement. Because immune dysfunction in WAS may be due to an accelerated destruction of lymphocytes, we examined the susceptibility to apoptosis of resting primary lymphocytes isolated from WAS patients in the absence of exogenous apoptogenic stimulation. We found that unstimulated WAS lymphocytes underwent spontaneous apoptosis at a greater frequency than unstimulated normal lymphocytes. Coincident with increased apoptotic susceptibility, WAS lymphocytes had markedly attenuated Bcl-2 expression, whereas Bax expression did not differ. A negative correlation between the frequency of spontaneous apoptosis and the level of Bcl-2 expression was demonstrated. These data indicate that accelerated lymphocyte destruction by spontaneous induction of apoptosis may be one pathogenic mechanism by which the progressive immunodeficiency in WAS patients develops.

Bone marrow transplantation for canine X-linked severe combined immunodeficiency.

Canine X-linked severe combined immunodeficiency (XSCID) is due to mutations in the common gamma chain which is a subunit of the receptors of IL-2, IL-4, IL-7, IL-9 and IL-15. Bone marrow transplantation (BMT) of human XSCID patients without pretransplant conditioning (cytoablation) results in engraftment of donor T-cells and reconstitution of T-cell function but engraftment of few, if any, donor B cells with resultant poor reconstitution of humoral immune function. In this study, we show that XSCID dogs can be transplanted with allogeneic bone marrow cells resulting in engraftment of both donor B and T cells and reconstitution of full systemic immune function including normal humoral immune function without the need for cytoablation.

Defective anticarbohydrate antibody responses to naturally occurring bacteria following bone marrow transplantation.

The long-term recipients of allogeneic bone marrow transplantation (BMT) are at an increased risk of death due to bacterial infections. We evaluated the anticarbohydrate antibody responses of BMT recipients to a naturally occurring bacterial carbohydrate, polyribose phosphate (PRP). The recipients of autologous BMT achieved protective anti-PRP levels (>100 ng/mL) by 3 years after transplantation, with a pattern consistent with a recapitulation of the ontogeny of anticarbohydrate antibody responses. None of the six recipients of unrelated BMT who were off immunosuppressive therapy had protective anti-PRP levels, though their response to a protein antigen (tetanus toxoid) was normal. Of 48 recipients of histocompatible BMT, 22 (46%) had protective anti-PRP antibody levels, whereas 13 (27%) recipients who were >3 years post-BMT did not have protective levels. Therefore, all unrelated recipients and a significant proportion of histocompatible recipients without clinical graft-vs.-host disease had persistent and prolonged defects in their capacity to produce antibodies to naturally occurring bacterial carbohydrate antigens. These results suggest that allogeneic BMT recipients should be longitudinally evaluated for their anticarbohydrate antibody responses and that patients with defective antibody responses should receive prophylactic antibiotics or replacement immunoglobulin therapy or both to reduce their risk of late bacterial infections.

RNA antisense abrogation of MAT1 induces G1 phase arrest and triggers apoptosis in aortic smooth muscle cells.

The human MAT1 gene (ménage à trois 1) is an assembly factor and a targeting subunit of cyclin-dependent kinase (CDK)-activating kinase. The novel mechanisms by which MAT1 forms an active CDK-activating kinase and determines substrate specificity of CDK7-cyclin H are involved in the cell cycle, DNA repair, and transcription. Hyperplasia of vascular smooth muscle cells (SMC) is a fundamental pathologic feature of luminal narrowing in vascular occlusive diseases, and nothing is yet known regarding the cell cycle phase specificity of the MAT1 gene in its involvement in SMC proliferation. To investigate such novel regulatory pathways, MAT1 expression was abrogated by retrovirus-mediated gene transfer of antisense MAT1 RNA in cultured rat aortic SMCs. We show that abrogation of MAT1 expression retards SMC proliferation and inhibits cell activation from a nonproliferative state. Furthermore, we have demonstrated that these effects are due to G1 phase arrest and apoptotic cell death. Our studies indicate a link between cell cycle control and apoptosis and reveal a potential mechanism for coupling the regulation of MAT1 with G1 exit and prevention of apoptosis.

The number and generative capacity of human B lymphocyte progenitors, measured in vitro and in vivo, is higher in umbilical cord blood than in adult or pediatric bone marrow.

The lack of human B lymphocyte development in beige/nude/XID (bnx) mice is in sharp contrast to the robust development observed in another immune deficient strain, the NOD/SCID mouse. The ability to generate human B lymphocytes in the NOD/SCID, but not bnx mouse has been hypothesized to be caused by differences in the microenvironments or systemic cytokine concentrations. In the current studies we report that the differences in development can be primarily attributed to the source of the progenitors transplanted into the mice. The prior studies in bnx mice used cultured pediatric or adult bone marrow (BM) as the source of the CD34+ cells, whereas the NOD/SCID studies have predominantly used fresh or cultured umbilical cord blood (UCB). We have analyzed BM and UCB for the number of human CD34+/CD38- cells capable of in vitro B lymphocyte development, and have found a lower frequency of B lymphocyte generation in BM. The individual B lymphocyte clones that developed from bone marrow produced 100-fold fewer cells than the UCB-derived clones. In agreement with the in vitro studies, human B lymphocytes developed in bnx mice from both CD34+ and CD34+/CD38- cells isolated from human umbilical cord blood, but not from equivalent numbers of CD34+ and CD34+/CD38- progenitors from bone marrow. Therefore, the lower generative capacity, and frequency of B lymphocyte precursors in human marrow may be responsible for the previous results that showed a lack of B lymphocyte development in bnx mice.

X-linked SCID and other defects of cytokine pathways.

Cytokine pathways are essential for the differentiation and function of lymphoid cells. The major T-cell growth factor is IL-2, which is produced by subsets of T lymphocytes in response to antigenic stimulation. The IL-2 receptor is expressed by T cells after antigenic stimulation, and when engaged by IL-2 induces proliferation, differentiation, and protection from apoptosis. Rare patients with severe combined immune deficiency (SCID) have been found to have mature T lymphocytes that do not produce IL-2, although no genetic abnormality has yet been defined for these patients. The fact that these patients and IL-2 knockout mice have the ability to generate mature T lymphocytes indicates that IL-2 is the major growth factor for mature T lymphocytes but not for immature thymocytes. X-linked SCID, the most common form of SCID, has a phenotype of thymic hypoplasia, peripheral T lymphopenia, the presence of B lymphocytes that do not undergo normal class switching, and usually the absence of natural killer (NK) cells. X-SCID is caused by mutations of a receptor subunit, which was originally described as the IL-2Rgamma. The phenotypic differences between X-SCID and IL-2-deficient SCID suggests that the IL-2Rgamma chain might be a component of other receptors needed for thymic development, B cell class-switching, and NK development. The IL-2Rgamma is now known to be a shared subunit between the IL-2, IL-4, IL-7, IL-9, and IL-15 receptors, which explains the complex X-SCID phenotype. Because of this shared usage, the IL-2Rgamma is known as the common gamma chain (gamma c). Each ligand induces dimerization of gamma c with the ligand-specific receptor subunit, eg, the IL-2Rbeta, resulting in signal transduction through the JAK-STAT (signal transducers and activators of transcription) pathway. The JAK3 tyrosine kinase is constitutively associated with the gamma c and is necessary for signaling through the gamma c-containing receptors. Deficiency of JAK3 gives rise to a SCID phenotype that closely resembles that of X-SCID, but is autosomally recessive in inheritance. It is likely that other specific immune deficiencies of the cytokine pathways exist, eg, IL-7Ralpha-deficient SCID. T cells with wild-type gamma c and JAK3 proteins have a profound selective advantage over cells that contain mutant proteins. The selective advantage allows these patients to be treated by bone marrow transplantation (BMT) without ablative chemotherapy, and is the reason that these forms of SCID are potential targets for early gene therapy efforts.