Site-specific DNA methylation by a complex of PU.1 and Dnmt3a/b

The Ets transcription factor PU.1 is a hematopoietic master regulator essential for the development of myeloid and B-cell lineages. As we previously reported, PU.1 sometimes represses transcription on forming a complex with mSin3A-histone deacetyl transferase-MeCP2. Here, we show an interaction between PU.1 and DNA methyltransferases, DNA methyltransferase (Dnmt)3a and Dnmt3b (Dnmt3s). Glutathione-S-transferase pulldown assay revealed that PU.1 directly interacted with the ATRX domain of Dnmt3s through the ETS domain. Dnmt3s repressed the transcriptional activity of PU.1 on a reporter construct with trimerized PU.1-binding sites. The repression was recovered by addition of 5-aza-deoxycitidine, a DNA methyltransferase inhibitor, but not trichostatin A, a histone deacetylase inhibitor. Bisulfite sequence analysis revealed that several CpG sites in the promoter region neighboring the PU.1-binding sites were methylated when Dnmt3s were coexpressed with PU.1. We also showed that the CpG sites in the p16(INK4A) promoter were methylated by overexpression of PU.1 in NIH3T3 cells, accompanied by a downregulation of p16(INK4A) gene expression. These results suggest that PU.1 may downregulate its target genes through an epigenetic modification such as DNA methylation.

Time-frequency analysis for pulse driven ultrasonic microscopy for biological tissue characterization

The authors have proposed a new type of ultrasonic microscopy for biological tissue characterization. The system is driven by a nanosecond pulse voltage, the generated acoustic wave being reflected at the front and rear side of the sliced tissue. In this report, a time-frequency analysis was applied to determine the sound speed thorough the tissue. Frequency dependence of sound speed was obtained with a myocardium of a rat sliced into 10 microm. As the reflected waveform had a significant amount of oscillating component, the waveform was once subjected to the deconvolution process. As the result, two reflections were clearly separated in time domain. Then these two reflections were separately analyzed by time-frequency analysis. Each reflection was extracted by using a proper window function. Phase angles of these reflections at the same frequency were compared. A sound speed micrograph at an arbitrary frequency in between 50 and 150 MHz was successfully obtained. A tendency was found that the sound speed slightly increases with frequency.

Isolation of human single chain antibodies (scFv) against human TNF-alpha from human peripheral blood lymphocyte-SCID mice

By developing an appropriate immunization protocol for SCID (hu-PBL-SCID) mice engrafted with human peripheral blood lymphocytes in combination with scFv phage display library, we were able to establish an efficient strategy to obtain human scFv clones against a human self-antigen, TNF-alpha. The mice pretreated with gamma-radiation (3Gy) and anti-asialo GM1 antibody were immunized with a mixture of human TNF-alpha-keyhole limpet hemocyanin and Freund's adjuvant. Human antibody maturation was suggested to be induced in the mice with the immunization protocol. The scFv clones obtained from the mice were shown to exhibit binding affinities in the range of 10(7)-10(8) M(-1). Together with our previously published work on the isolation of respiratory syncytial virus neutralizing scFvs, the results of this study have implicated that this combined approach is one of the effective alternatives for the cloning of human monoclonal antibodies specific for a wide range of antigens of interest.

IL-4-mediated development of TGF-beta1-producing cells from naïve CD4(+) T cells through a STAT6-independent mechanism

Transforming growth factor-beta1 (TGF-beta1) is an inhibitory cytokine increasingly recognized as a key factor for immuno-regulation. The function of IL-4 in the regulation of TGF-beta1 production from T cells has been reported previously; however, the precise molecular mechanism still remains to be elucidated. For a better understanding of the mechanism involved in regulation, we have investigated a relationship between the STAT6-dependent pathway and TGF-beta1 production from naïve T cells. TCR crosslinking initiates TGF-beta1 production in CD4(+) T cells, and IL-4-mediated signaling enhances the TGF-beta1 production from naïve CD4(+) T cells. The IL-4-mediated up-regulation of TGF-beta1 production from naïve CD4(+) T cells is elicited in STAT6-deficient (STAT6 KO) mice, but not in IL-4 receptor-deficient (IL-4R KO) mice. These results clearly demonstrate that a STAT6-independent pathway is working in IL-4-mediated enhancement of TGF-beta1 production from naïve CD4(+) T cells. Moreover, the addition of IL-4 showed no additive effect on TGF-beta1 promoter-mediated transcription stimulated by TCR. Therefore, we hypothesize that the IL-4-mediated signaling does not work directly on the transcription of the TGF-beta1 gene, but rather regulates the expansion of TGF-beta1-secreting T cells.

Molecular cloning of POEM: a novel adhesion molecule that interacts with alpha8beta1 integrin

Cell adhesion molecules are involved in a number of biological functions, such as cell survival, cell differentiation, tissue repair, and development. A novel molecule, POEM (preosteoblast epidermal growth factor-like repeat protein with meprin, A5 protein, and receptor protein-tyrosine phosphatase mu domain), was isolated by reverse transcription-polymerase chain reaction using a set of degenerate primers designed after other known epidermal growth factor (EGF)-like motifs. From its structure, POEM was suggested to be a novel adhesion molecule with five EGF-like domains, an Arg-Gly-Asp (RGD) cell binding motif, and a meprin, A5 protein, and receptor protein-tyrosine phosphatase mu (MAM) domain. By in situ hybridization using embryonic day 16.5 (E16.5) mouse embryos, strong expression of POEM mRNA was observed in developing kidney renal tubules, parathyroid and thyroid glands, developing bone, tooth germ, and endocrine organs of the brain. The inner ear, skeletal muscle, smooth muscle (except for the vascular system), and skin were also positive for POEM expression. Bacterial recombinant POEM protein containing the RGD sequence and MAM domain showed strong cell adhesion, spreading, and survival-promoting activities. By mutating the RGD sequence to RGE, the cell spreading and survival activities were significantly decreased, but the MAM domain was shown to contribute only to cell adhesion and not to cell spreading and survival-promoting activities. The distribution of POEM in several tissues was close to that of alpha(8)beta(1) integrin. Therefore, we conducted cell adhesion assays using KA8 cells, a K562 leukemia clone stably expressing alpha(8) integrin. Parental K562 cells, which expressed alpha(5)beta(1) integrin, bound to fibronectin but not to POEM. On the other hand, KA8 cells showed strong binding and spreading on both fibronectin and POEM. These results suggest that POEM is a novel ligand for alpha(8)beta(1) integrin and that POEM may be involved in the development and function of various tissues, such as kidney, bone, muscles, and endocrine organs.

A novel differentiation-inducing therapy for acute promyelocytic leukemia with a combination of arsenic trioxide and GM-CSF

Arsenic trioxide (As2O3) effectively induces clinical remission via apoptosis in relapsed acute promyelocytic leukemia (APL). However, because this new anti-leukemic drug is also considered to be a poison, its possible adverse effects are a highly important issue related to its clinical use. We here investigated, both in vitro and in vivo, the effects of a combination of As2O3 and GM-CSF as a novel therapeutic approach for the treatment of APL. Treatment of both retinoic acid (RA)-sensitive and -resistant APL cell lines (NB4 and UF-1 cells, respectively), as well as primary APL cells with a combination of As2O3 and GM-CSF for 4 days resulted in inducing differentiation, but not apoptosis, to mature granulocytes. In addition, a combination of both agents induced degradation of the PML/RARalpha protein. GM-CSF was found to be associated with increased tyrosine phosphorylation of Jak2 kinase in both NB4 and UF-1 cells, and a specific inhibitor of Jak2, AG490, completely blocked the ability of GM-CSF to prevent apoptosis and induce differentiation of As2O3-treated UF-1 cells. In in vivo analysis, As2O3 induced differentiation of APL cells in a RA-resistant APL model of human GM-CSF-producing transgenic SCID mice that had a high level of human GM-CSF in their sera. In contrast, As2O3 alone diminished tumors in UF-1 cells transplanted into NOD/SCID mice via induction of apoptosis. In conclusion, a combination of As2O3 and GM-CSF appears to be a novel differentiation-inducing therapy in patients with APL, including relapsed or RA-resistant cases.

Efficient generation of respiratory syncytial virus (RSV)-neutralizing human MoAbs via human peripheral blood lymphocyte (hu-PBL)-SCID mice and scFv phage display libraries

RSV is one of the major causes of pneumonia and bronchiolitis in infants and young children and is associated with high mortality. RSV neutralizing human antibody (hu-Ab) is known to mediate resistance to viral infection as well as to be an effective treatment for severe lower respiratory tract RSV infection. We have previously demonstrated that human primary and secondary immune responses can be established in severe combined immunodeficient mice engrafted with human peripheral blood lymphocytes (hu-PBL-SCID). By combining this animal model with the single-chain Fv antibody (scFv) phage display library technique, we were able to investigate further its clinical potential by generating a panel of human scFvs that exhibit both high F glycoprotein (RSV-F) binding affinities ( approximately 108 M(-1)) and strong neutralizing activities against RSV infection in vitro. Sequencing analysis of the randomly isolated anti-RSV-F scFv clones revealed that they were derived from different VH families with mutations in the complementarity-determining region 1 (CDR1). The results suggest that: (i) RSV-F-specific human immune responses and affinity maturation can be induced in hu-PBL-SCID mice; and (ii) this approach can be applied to generate large numbers of human scFvs with therapeutic potential. Despite the fact that hu-PBL-SCID mouse and human scFv phage display library have individually been established, our approach contributes a simple and significant step toward the generalization of antigen-specific human monoclonal antibody (hu-MoAb) production and their clinical applications.

BLNK is associated with the CD72/SHP-1/Grb2 complex in the WEHI231 cell line after membrane IgM cross-linking

Tyrosine phosphorylation of CD72 strongly correlates with B cell antigen receptor signals leading to apoptosis. We have previously shown that CD72 carrying two immunoreceptor tyrosine-based inhibition motifs (ITIM) is an in vivo substrate of SHP-1. CD72 forms a complex with SHP-1 and Grb2 via its tyrosine-phosphorylated ITIM when the WEHI231 cell line, which is representative of immature B cells, undergoes apoptosis. The CD72 complex formation was also demonstrated in normal primary B cells, suggesting that the complex formation in apoptotic B cells is a universal mechanism. In this study, we further investigated the molecular components of the CD72 complex in WEHI231 cells in order to understand the molecular mechanism involved in the signaling pathway mediated through the complex. Our experiments demonstrate that BLNK, a recently identified adaptor molecule predominantly expressed in B cells, is associated with the CD72 complex via the Src homology 3 domain(s) of Grb2 in the cell line after membrane IgM (mIgM) engagement. The results suggest that the mIgM-mediated signal strongly correlates with the formation of the CD72 / SHP-1 / Grb2 / BLNK complex.

Effect of interleukin-6 secreted by engineered human stromal cells on osteoclasts in human bone

The effect of elevated human IL-6 (hIL-6) production by human bone marrow (Hu-BM) stromal cells on osteoclasts in human bone was examined. Human bone was implanted into nonobese diabetic mice with severe combined immunodeficiency (Hu-Bone-NOD/SCID mice). Immunohistochemistry of bone implants and mouse spleens (at 20 weeks), showed human CD45+ cells, B cells, and macrophages in both tissues. Thus, Hu-BM cells survive human bone transplantation and infiltrate mouse tissue. Bone implants had 75 +/- 12% (mean +/- SD) human CD45+ cells, and 9 +/- 4% mouse hematopoietic cells. A retrovirus vector containing the human IL-6 gene was used to transduce Hu-BM stromal cells (IL-6/stromal) and the PA317 cell line (IL-6/PA317). IL-6/ stromal cells (secreting, on average, 17 microg of hIL-6/10(6) cells per 24 h) were injected directly into human bone implants in Hu-Bone-NOD/SCID mice. IL-6/PA317 cells (secreting 16 microg/mL of hIL-6/10(6) cells per 24 h) were injected intraperitoneally into Hu-Bone-NOD/SCID mice. Analyses of sera from both groups of animals showed elevated levels of IL-6. However, only bone implants engrafted with IL-6/stromal cells had a statistically significant increase in osteoclast-lined mineralized trabecular bone surface (BS). Thus, a high concentration of serum hIL-6 in Hu-Bone-NOD/SCID mice alone does not increase osteoclast-lined BS in bone implants. Most importantly, it is the type of human BM cell that secretes the high levels of hIL-6 that is most critical.

The function of TGF-beta-mediated innocent bystander suppression associated with physiological self-tolerance in vivo

Innocent bystander suppression has been demonstrated in experimental models of transplantation tolerance and oral tolerance. This phenomenon is associated with expression of cytokines such as TGF-beta or/and type II cytokines (e.g., IL-4, IL-10). However, the mechanism responsible for bystander suppression is poorly understood, as is its role in antigen-specific self-tolerance. Here, we describe a series of investigations using an antigen coimmunization strategy to examine the outcome of bystander suppression in vivo in a well-characterized physiological model, using beef insulin transgenic (BI-Tg) mice, for self-tolerance. Our results demonstrate that: (1) T-cell-mediated peripheral hyporesponsiveness, or CD4(+) regulatory type II Th cell-mediated adoptive transfer of peripheral hyporesponsiveness (defined by an ELISA antibody assay), is antigen-specific at induction but effector-nonspecific (bystander suppression) when the self-antigen (BI) and a control antigen (chicken ovalbumin) are coadministered in BI-Tg mice; (2) bystander suppression is manifest as a local and transient, rather than a systemic and long-term, phenomenon; (3) bystander suppression is both time and antigen dose dependent; and (4) anti-TGF-beta Mab abolishes the effect of bystander suppression in vivo. We suggest that TGF-beta-mediated innocent bystander suppression associated with physiological self-tolerance thus produces no major biological consequence for general immune responsiveness. It may prevent the activation of auto(or cross)-reactive lymphocytes.

The B-cell transmembrane protein CD72 binds to and is an in vivo substrate of the protein tyrosine phosphatase SHP-1

BACKGROUND

Signals from the B-cell antigen receptor (BCR) help to determine B-cell fate, directing either proliferation, differentiation, or growth arrest/apoptosis. The protein tyrosine phosphatase SHP-1 is known to regulate the strength of BCR signaling. Although the B-cell co-receptor CD22 binds SHP-1, B cells in CD22-deficient mice are much less severely affected than those in SHP-1-deficient mice, suggesting that SHP-1 may also regulate B-cell signaling by affecting other signaling molecules. Moreover, direct substrates of SHP-1 have not been identified in any B-cell signaling pathway.

RESULTS

We identified the B-cell transmembrane protein CD72 as a new SHP-1 binding protein and as an in vivo substrate of SHP-1 in B cells. We also defined the binding sites for SHP-1 and the adaptor protein Grb2 on CD72. Tyrosine phosphorylation of CD72 correlated strongly with BCR-induced growth arrest/apoptosis in B-cell lines and in primary B cells. Preligation of CD72 attenuated BCR-induced growth arrest/death signals in immature and mature B cells or B-cell lines, whereas preligation of CD22 enhanced BCR-induced growth arrest/apoptosis.

CONCLUSIONS

We have identified CD72 as the first clear in vivo substrate of SHP-1 in B cells. Our results suggest that tyrosine-phosphorylated CD72 may transmit signals for BCR-induced apoptosis. By dephosphorylation CD72. SHP-1 may have a positive role in B-cell signaling. These results have potentially important implications for the involvement of CD72 and SHP-1 in B-cell development and autoimmunity.

Human gene therapy

Human gene therapy and its application for the treatment of human genetic disorders, such as cystic fibrosis, cancer, and other diseases, are discussed. Gene therapy is a technique in which a functioning gene is inserted into a human cell to correct a genetic error or to introduce a new function to the cell. Many methods, including retroviral vectors and non-viral vectors, have been developed for both ex vivo and in vivo gene transfer into cells. Vectors need to be developed that efficiently transfer genes to target cells, and promoter systems are required that regulate gene expression according to physiologic needs of the host cell. There are several safety and ethical issues related to manipulating the human genome that need to be resolved. Current gene therapy efforts focus on gene insertion into somatic cells only. Gene therapy has potential for the effective treatment of genetic disorders, and gene transfer techniques are being used for basic research, for example, in cancer, to examine the underlying mechanism of disease. There are still many technical obstacles to be overcome before human gene therapy can become a routine procedure. The current human genome project provides the sequences of a vast number of human genes, leading to the identification, characterization, and understanding of genes that are responsible for many human diseases.

Physiologic human T-cell responses to OKT3 in the human peripheral blood lymphocyte-severe combined immunodeficiency mouse model

BACKGROUND

Our goal was to study physiologic responses of human T lymphocytes to OKT3 in the human peripheral blood lymphocyte-severe combined immunodeficiency (hu-PBL-SCID) mouse model.

METHODS

SCID mice were pretreated with anti-asialo-GM1 (alpha-ASGM1) and radiation, then engrafted with human peripheral blood lymphocytes (PBLs). Seven to 14 days after engraftment, when most human T cells in the spleen of these mice are CD3+/CD4+ and CD3+/CD8+, mice were treated with OKT3 or control antibody. Mice were killed for histopathologic examination, for flow cytometric assessment of the engrafted human lymphocytes, and for analysis of human tumor necrosis factor-alpha serum levels.

RESULTS

Intravenous injection of 5 microg of OKT3 resulted in early antigenic modulation of engrafted human T lymphocytes, with the emergence of CD3-/CD4+ and CD3-/CD8+ cells in the spleen of hu-PBL-SCID mice. There was an increase in the serum concentration of human tumor necrosis factor-alpha within 4 hr after OKT3 injection, suggesting early T-cell activation. Antigenic modulation and activation of the human lymphocytes in the spleen was followed by their depletion within 24 hr. This human T-cell response to OKT3 in hu-PBL-SCID mice is analogous to the response in humans treated with OKT3 and in BALB/c mice injected with an anti-murine CD3 monoclonal antibody. Graft-versus-host disease in the mice was abrogated by OKT3 treatment, and OKT3-treated mice lived longer than controls. Histopathologic studies showed clearance of lymphocytic infiltration in the liver and lungs of OKT3-treated mice.

CONCLUSIONS

These findings provide further evidence of functional human immune T cells in the hu-PBL-SCID mouse. This model may have useful applications in the study of transplantation immunology.

Murine antibody responses to the verotoxin 1 B subunit: demonstration of major histocompatibility complex dependence and an immunodominant epitope involving phenylalanine 30

Structurally conserved verotoxin 1 (VT1) mutant derivatives, showing reduced receptor binding and cytotoxicity, may serve as natural toxoids to protect against VT-mediated disease. In this study, the antibody responses to the wild-type VT1 B subunit, a B-subunit mutant (Phe30Ala B), and the corresponding holotoxin (Phe30Ala HT) were examined in three inbred mouse strains. BALB/c (H-2d) and CBA (H-2k) mice produced strong antibody responses to both wild-type and mutant B subunits. VT1 B-raised sera reacted more strongly with VT1 B than with Phe30Ala B in enzyme-linked immunosorbent assays, while Phe30Ala B-raised sera reacted equally with VT1 B and Phe30Ala B. C57BL/6 (H-2b) and congenic BALB/c (BALB x B [H-2b]) mice produced no detectable antibody response to either VT1 B or Phe30Ala B. However, an anti-VT1 B antibody response was detected in H-2b mice immunized with biologically active Phe30Ala HT. Based on these observations, we conclude that the VT1 B subunit possesses a B-cell immunodominant epitope formed partly by phenylalanine 30 and that the B-subunit antibody response is dependent on the H-2 haplotype of the mouse strain. Our results also support a potential role for the A subunit in providing the T-cell help necessary to overcome a deficient B-subunit antibody response in H-2b mice.

Roles of calnexin and Ig-alpha beta interactions with membrane Igs in the surface expression of the B cell antigen receptor of the IgM and IgD classes

Membrane Igs (mIgs) of all five classes are associated with Ig-alpha beta dimers on the B cell surface. While mIgM requires the presence of these two associated molecules for its surface expression, mIgD does not. To study the structural basis for this differential Ig-alpha beta dependence, we created mutant mIgM and mIgD molecules (chimeras and those with reciprocal point mutations in their transmembrane sequences) and identified two amino acid residues in the transmembrane region of the mIg heavy chains responsible for this transport difference. Without Ig-alpha beta, mIgM and mutant mIgD molecules remained endoglycosidase H sensitive, consistent with endoplasmic reticulum (ER) localization. The molecular chaperone calnexin has previously been implicated in retaining unassembled mIgs in the ER. However, we found that inhibition of the association between calnexin and newly synthesized mIgs by castanospermine treatment did not lead to surface expression of normally retained mIgs. Therefore, calnexin cannot be the only retention molecule. Furthermore, for both wildtype and mutant mIgDs, association with calnexin was rather transient, thereby ruling out calnexin being a major ER retention molecule for mIgDs. Our study with castanospermine also showed that calnexin is required for wildtype mIgD surface expression only if Ig-alpha beta is absent, while the latter alone can function to promote mIg folding, assembly, and transport. Further study using our system will help to identify novel molecules and characterize their involvement in the control of mIg transport.

Roles of calnexin and Ig-alpha beta interactions with membrane Igs in the surface expression of the B cell antigen receptor of the IgM and IgD classes

Membrane Igs (mIgs) of all five classes are associated with Ig-alpha beta dimers on the B cell surface. While mIgM requires the presence of these two associated molecules for its surface expression, mIgD does not. To study the structural basis for this differential Ig-alpha beta dependence, we created mutant mIgM and mIgD molecules (chimeras and those with reciprocal point mutations in their transmembrane sequences) and identified two amino acid residues in the transmembrane region of the mIg heavy chains responsible for this transport difference. Without Ig-alpha beta, mIgM and mutant mIgD molecules remained endoglycosidase H sensitive, consistent with endoplasmic reticulum (ER) localization. The molecular chaperone calnexin has previously been implicated in retaining unassembled mIgs in the ER. However, we found that inhibition of the association between calnexin and newly synthesized mIgs by castanospermine treatment did not lead to surface expression of normally retained mIgs. Therefore, calnexin cannot be the only retention molecule. Furthermore, for both wildtype and mutant mIgDs, association with calnexin was rather transient, thereby ruling out calnexin being a major ER retention molecule for mIgDs. Our study with castanospermine also showed that calnexin is required for wildtype mIgD surface expression only if Ig-alpha beta is absent, while the latter alone can function to promote mIg folding, assembly, and transport. Further study using our system will help to identify novel molecules and characterize their involvement in the control of mIg transport.

Effects of glycyrrhizin on immune-mediated cytotoxicity

Intravenous administration of glycyrrhizin is known to decrease elevated plasma transaminase levels in patients with chronic viral hepatitis, in which immune-mediated cytotoxicity by cytotoxic T lymphocytes and tumour necrosis factor (TNF)-alpha is considered to play an important pathogenic role. However, the immunological interpretation of the transaminase-lowering action of glycyrrhizin is not known. Studies were performed to elucidate this action immunologically by assessing the effects of glycyrrhizin on immune-mediated cytotoxicity using an antigen-specific murine CD4+ T hybridoma line, which exhibits cytotoxicity against antigen-presenting cells after stimulation with specific antigen, and a murine TNF-alpha-sensitive fibroblast line. Glycyrrhizin inhibited the cytotoxic activity of the T cells against antigen-presenting cells and also suppressed TNF-alpha-induced cytotoxicity in the TNF-alpha-sensitive cell line in vitro. These results suggest that the decrease of elevated transaminase levels by glycyrrhizin in patients with chronic viral hepatitis is mediated in part by inhibition of immune-mediated cytotoxicity against hepatocytes.

Multiple levels of regulation for self-tolerance in beef insulin transgenic mice

To characterize the mechanism(s) of tolerance toward soluble self-antigens (Ags), beef insulin (BI) transgenic (Tg) mice were generated in which the transgene was expressed in pancreatic beta-cells. Our previous data showed that: (i) Ag-specific tolerance can be induced and/or maintained in peripheral T cells in thymectomized BI-Tg mice and (ii) CD4+ Th2 regulatory T cells are involved in maintaining peripheral tolerance (by anti-BI antibody response). In this paper, we have further characterized the relationship of low levels of BI expression (10(-10)-10(-11) M) in Th1/Th2 activation. In addition, we have explored intrathymic events associated with tolerance to self-Ags not expressed in the thymus and/or to circulating self-Ags. Limiting dilution analysis showed that there was a significantly higher frequency of BI-specific Th2 cells in Tg mice with a corresponding higher frequency of Th1 cells in non-Tg mice. While there was no transgene expression in the thymus (by RT-PCR), independent studies showed that BI can be processed and presented in the Tg thymus, which correlated with the Ag-specific hyporesponsiveness of mature thymocyes detected in vitro. High-dose rIL-2 (150 U/ml) was able to restore in vitro peripheral T cell response of Tg mice to levels comparable to those of the non-Tg control. Collectively, our data suggest that: (i) there is a differential activation of BI-specific Th1/Th2 cells in vivo in the presence of low Ag concentration; (ii) the thymus may play a role in self-tolerance to Ags whose expression in adults is restricted to the periphery; and (iii) multiple levels of regulation such as thymic selection, peripheral anergy, and active suppression may be involved in tolerance to BI in BI-Tg mice.

Human hematopoiesis in SCID mice implanted with human adult cancellous bone

The persistence of hematopoietic cells from human adult cancellous bone fragments implanted subcutaneously into CB-17 scid/scid mice was studied. Recipient mice received either no pretreatment (control group) or pretreatment with 3 Gy total-body irradiation and anti-asialo GM1 sera (ASGM1; pretreated group) before implantation. Pretreated severe combined immunodeficient (SCID) mice implanted with human bone were subsequently given ASGM1 every 7 days for the duration of the experiments. At 12 weeks postimplantation, flow cytometry of cells from pretreated and control animal tissues detected human CD45+ cells in the mouse spleen (mean, 7.8% and 3.4% positive cells, pretreated and control animals, respectively), bone marrow (BM; mean, 16.5% and 4.8% positive cells, respectively), and blood (mean, 5.5% and < 2% positive cells, respectively), and in the implanted human bone (73% and 8.9% positive cells, respectively). At 12 weeks, pretreated mice had human granulocyte-macrophage colony-forming cells (GM-CFC) and burst-forming units-erythrocyte (BFU-E) in the implanted human bone in the murine BM and in some of the spleens. The spleens also had extensive infiltration of human B cells and macrophages. Mean serum levels of human IgG in pretreated animals were 14 micrograms/mL during weeks 6 to 12, compared with trace levels (< 1 microgram/mL) in control mice. Bone from patients with acute myeloblastic leukemia (AML) was also implanted in pretreated SCID mice, and retrieved at 8 weeks for analysis. Comparison of preimplantation and implanted samples showed that the original histology was maintained, and massive infiltration of human CD68+ cells was observed in the mice spleens and BM. Implantation of AML bone in SCID mice facilitates analysis of in situ AML cell interaction with stromal cells in the leukemic state, and therapies against AML can be tested in this system, especially the selective killing of AML cells in the presence of other BM cells. Furthermore, this model requires no exogenous administration of cytokines to maintain human hematopoiesis with both normal or AML bone. Because the structure and function of both normal and diseased human adult bone is maintained, this animal model should facilitate investigation of both normal human hematopoiesis and hematopoietic malignancies.

Endogenous interleukin 6 can function as an in vivo growth- stimulatory factor for advanced-stage human melanoma cells

We have previously shown that a majority of human melanoma cell lines derived from early-stage lesions were growth inhibited by exogenous interleukin 6 (IL-6) in vitro, whereas cell lines from advanced-stage lesions were resistant to such IL-6-induced growth inhibition. Among the resistant melanoma cell lines, 50-60% constitutively produced IL-6, which appeared to function as a growth stimulator in vitro, based on the growth-suppressive effects of antisense oligonucleotides to the IL-6 gene. The present study was primarily aimed at evaluating whether endogenous IL-6 also functions in vivo as a growth modulator for IL-6-producing and -nonproducing melanoma cells. To do so, we first introduced an IL-6 expression vector into IL-6-nonproducing human melanoma cells using WM35, an early-stage (radial growth phase) cell line, the growth of which is normally inhibited by IL-6, and WM983A, an advanced-stage cell line, the growth of which in vitro is not affected by exogenous IL-6. None of the IL-6-producing transfectants showed a significant alteration in tumor growth in nude mice. Next, two IL-6-producing melanoma cell lines, both of which were derived from metastases, MeWo and WM9, and which are growth resistant to exogenously added IL-6, were transfected with an antisense IL-6 expression vector. Several transfectant clones manifested a constitutive decrease in IL-6 gene expression and protein production, and they also gave rise to much smaller tumors with slower growth rates and longer latency periods. However, these IL-6 antisense transfectants were not growth suppressed in in vitro cell cultures, relative to their respective parental controls. Taken together, the results demonstrate that endogenous IL-6 can indeed function as a growth stimulator for human cutaneous melanomas in vivo. This growth-stimulatory or survival mechanism remains to be clarified but may be paracrine rather than autocrine in nature.

Expression of exogenous p59fyn modulates signaling in an immature B cell line, WEHI-231

The WEHI-231 B lymphoma line is representative of immature B cells, which undergo growth arrest/apoptosis following cross-linking of surface immunoglobulin M (sIgM). In B cells, sIgM engagement has been shown to induce immediate (within seconds) activation of src family protein tyrosine kinases (PTKs) such as p53lyn/56lyn, p55blk, p56lck and p59fyn which are associated with B cell antigen receptor (BCR) complex. However, p59fyn expression is very low in both normal immature B cells and apoptosis-prone B cell lines, including WEHI-231. Such a finding prompted us to investigate the effects of ectopic expression of p59fyn in growth regulation of WEHI-231 cells. We have obtained WEHI-231 transfectants expressing the exogenous p59fyn by retroviral mediated gene transfer method. The transfectants demonstrated increased [Ca2+]i level in both the non-stimulated condition and sIgM cross-linking. The expression of ectopic p59fyn also increased the sensitivity of the transfectants to growth arrest signal by sIgM cross-linking. The results suggest that p59fyn can modulate signal transduction and growth regulation when expressed in the immature B cell line.

Human osteoblasts survive and deposit new bone when human bone is implanted in SCID mouse

We describe the first successful engraftment of viable human bone that maintains human osteoblast function and deposits new bone after implantation into pretreated SCID (Hu-bone-SCID) mice. The pretreatment consists of radiation before bone implantation and subsequent administration of antiasialo GM1 antisera every 7 days to deplete mouse macrophage and natural killer (NK) cell activity. The implanted bone samples were analyzed at various times up to 8 weeks. Comparison of pre- and post-implanted human specimens in untreated and pretreated SCID mice showed that while specimens underwent resorption and necrosis in untreated SCID mice, the structure of the implanted bone was preserved in the pretreated Hu-bone-SCID mice. In addition, histochemistry and histomorphometric analysis combined with tetracycline labeling showed that new bone formed in in the implants in the pretreated SCID mice. That the new bone resulted from the activity of the implanted human bone cells rather than from induction of differentiation of host mesenchymal cells into mouse osteoblasts was shown by immunohistochemical analysis with two different monoclonal antibodies (mAb), one mAb recognizing human HLA class II antigens and one recognizing human osteoblasts and osteocytes. Donor variability was observed in the implanted bone; however, bone from the same donor maintained its characteristics in all Hu-bone-SCID mice, and striking quantitative differences were seen in bone implanted from young (4-9 years) vs. adult (67-82 years) individuals. This model will be useful to investigate and compare endogenous osteoblast activity in different bone samples without the variables of isolating cells and examining them in vitro.

Tolerance is overcome in beef insulin-transgenic mice by activation of low-affinity autoreactive T cells

To gain insight into the factors controlling the maintenance or loss of T cell self tolerance we produced beef insulin (BI)-transgenic BALB/c mice. Transgenic mice express BI under control of the human insulin promoter and secrete physiological amounts of beef insulin. Although these mice are tolerant to BI, as evidenced by the lack of insulin-specific IgG antibody production following intraperitoneal immunization, tolerance is not complete. Footpad immunization results in a weak antigen-specific T cell proliferative response, indicating the presence of self-reactive BI-specific T cell in the periphery. These T cells are functional in vivo, providing support for IgG1, IgG2a, and IgG2b BI-specific antibody production, but require higher higher concentrations of antigen than nontransgenic T cells (both in vivo and following recall responses in vitro) to become activated. In vitro, BI-specific T cell proliferation in BI-transgenic mice can be largely restored by addition of interleukin-2, indicating that a significant component of T cell tolerance is mediated by anergy. To characterize the autoreactive T cells that become activated when tolerance is broken, BI-specific T cell hybridomas were generated from transgenic mice and compared to a panel of hybridomas previously derived from nontransgenic BALB/c mice. The majority of BI-transgenic hybridomas recognized the immunodominant A1-14 beef insulin peptide but with lower avidity than BALB/c hybridomas. Consistent with this, none of the dominant T cell receptor rearrangements found in the BALB/c BI-specific T cell receptor repertoire were found in the transgenic hybridomas. These results indicate that, despite evidence for clonal inactivation of many BI-specific T cells in BI-transgenic mice, loss of tolerance results from activation of low-affinity antigen-specific T cells that appear to have escaped this process.

The use of SCID mice in biotechnology and as a model for human disease

The use of SCID (severe combined immunodeficient) mice in medical research and biotechnology has increased tremendously in recent years. This review outlines the major characteristics of these animals and the impediments that they pose to the engraftment of human cells and tissues. The development of our SCID mice pretreatment protocol (anti-asialo GM1 antisera and radiation) is described, and the results of xenotransplantation studies of human cells and tissues in these pretreated animals are outlined. Wherever possible, data from transplantation studies (of human tissues and cells) in pretreated and nonpretreated animals are compared. The potential of our pretreated SCID mice for medical research and biotechnology is discussed.

Interleukin 12 in combination with anti-interleukin 10 reverses graft prolongation after portal venous immunization

Portal venous pretransplantation transfusion augments allogeneic skin graft survival in mice transplanted across multiple minor histocompatibility barriers. We have shown in earlier studies that this is correlated with preferential activation for production of type-2 cytokines (interleukin [IL]-4 and IL-10) and decreased production of type-1 cytokines (IL-2 and interferon-gamma). We show that recombinant IL-12, in association with anti-IL-10 monoclonal antibody, can reverse in vivo the graft prolongation afforded by portal venous immunization and the altered cytokine production that follows. These alterations are in turn associated with increased expression of messenger RNA for interferon-gamma, IL-2, and IL-12 and decreased expression of IL-4, IL-10, and IL-13, as determined by non-quantitative polymerase chain reaction using cells obtained from lymph nodes draining the graft. Recombinant IL-12 in vitro also produces dose-related inhibition of activation for production of type-2 cytokines.

Both MHC and background gene heterozygosity alter T cell receptor repertoire selection in an antigen-specific response

Many autoimmune diseases are associated with specific class II MHC alleles; however, this association is not complete. One explanation for the variable expression of disease in susceptible individuals is that variability in the TCR repertoire may alter the potential to generate pathogenic autoreactive T cells. The current study was undertaken to examine the possibility that MHC and background heterozygosity, which is the norm in the outbred human population, alters the expressed TCR repertoire and, if so, whether this has an impact on peptide recognition and antigenic specificity. We, therefore, systematically analysed the beef insulin-specific TCR repertoire in inbred BALB/c mice before and after introduction of MHC heterozygosity (BALB/c x BALB.K)F1 mice, or MHC and background gene heterozygosity (BALB/c x A/J)F1 mice. We show that T cells from all three repertoires are predominantly Ad-restricted and recognize the same immunodominant peptide. Despite this, the beef insulin-specific TCR repertoires in F1 mice differ from those seen in BALB/c mice with the most dramatic changes seen in (BALB/c x A/J)F1 mice. These changes are accompanied by subtle differences in the antigenic specificity of the T cells. The results demonstrate that both MHC and background gene heterozygosity affect TCR repertoire selection, suggesting that the variable expression of autoimmune disease in individuals with a susceptible MHC allele may result, in part, from variability in the TCR repertoire introduced by this heterozygosity.

Evidence for Th2 cell-mediated suppression of antibody responses in transgenic, beef insulin-tolerant mice

Clonal deletion, anergy and suppression have all been considered mechanisms of immunological tolerance. Although adoptive transfer of immunosuppression has been shown to occur in the periphery, particularly for transplantation tolerance, it has proven difficult to characterize this phenomenon further, due to the lack of suppressor T cell clones. To characterize tolerance towards a physiological soluble antigen, we constructed beef insulin (BI) transgenic (Tg) BALB/c (H-2d) mice, in which the BI transgene is expressed in pancreatic beta cells. These Tg mice were tolerant to BI immunization at the level of both humoral and cell-mediated immune responses. Adoptive transfer of splenocytes from Tg mice into normal syngeneic BALB/c mice demonstrated that the reduction in antibody production is regulated by transferred T cells. The cytokine profile of T cell clones obtained after selection in vitro demonstrated dominant Th1 clones from normal non-Tg mice and dominant Th2 clones from Tg mice. Some Th2 clones (CD4+) from Tg mice produced significant suppression of antibody production after adoptive transfer into normal syngeneic BALB/c mice. These data confirm the existence of Th2 regulatory T cells in vivo in a model of peripheral tolerance to a physiological soluble antigen as a potential mechanism for self tolerance.

Antigen receptor-triggered apoptosis in immature B cell lines is associated with the binding of a 44-kDa phosphoprotein to the PTP1C tyrosine phosphatase

While cross-linking of the membrane IgM (mIgM) molecules expressed on WEHI 231 lymphoma cells induces these cells to undergo apoptosis, we have previously observed that ligation of the mIgD expressed on IgD-transfected WEHI 231 (W delta) cells is not associated with induction of cell death. Thus mIgM+IgD+ W delta cells provide a valuable reagent for delineating the molecular events which modulate the physiologic outcome of B cell antigen receptor (BCR) engagement. In view of recent data implicating the cytosolic phosphotyrosine phosphatase PTP1C in the regulation of BCR signaling capacity, we used W delta cells to investigate the potential role for PTP1C in modulating the cell response to BCR activation. The results of this analysis revealed PTP1C to undergo rapid tyrosine phosphorylation following mIgM or mIgD cross-linking and to associate with a number of other phosphoproteins in stimulated W delta cells. Among these latter phosphoproteins, one prominent species of about 44 kDa (pp44) which co-precipitated with PTP1C in mIgM-ligated cells was not detected in PTP1C immunoprecipitates from mIgD-ligated cells. The association of PTP1C with this 44-kDa phosphoprotein following mIgM cross-linking was also observed in two additional B cell lines representing an immature state of differentiation, but was not detected after BCR engagement in two representative mature B cell lines or in splenic B cells. Initial data concerning the identity of pp44 indicate that this molecule does not represent the Shc, MAPK or Ig-beta proteins and may, therefore, constitute a previously unidentified signaling effector. While the structural and biochemical properties of pp44 require further definition, the findings suggest that BCR-triggered interactions of PTP1C with pp44 occur only in the context of an immature state of cellular differentiation and the induction of apoptosis. These data therefore suggest that PTP1C interactions with pp44 may be relevant to the transduction of BCR signals which evoke cell death.

A human model of xenogeneic graft-versus-host disease in SCID mice engrafted with human peripheral blood lymphocytes

Despite previous attempts there is currently no suitable animal model available for xenogeneic graft versus host disease (XGVHD) mediated via human immunocompetent cells. Recently, we have developed an efficient protocol to engraft SCID mice with human peripheral blood lymphocytes (Hu-PBLs). The engraftment efficiency is extremely high, such that 100% of Hu-PBL-SCID mice die of XGVHD within 4 weeks after engraftment with Hu-PBLs (3-5 x 10(7) cells). A series of experiments was performed to investigate the mechanisms involved in the severe XGVHD. The results suggest that XGVHD was induced by human CD4+ T cells, antixenogeneic (antimouse) antibodies, and lymphokines. The SCID mouse model will be extremely valuable for the evaluation and development of immunosuppressive agents and transplantation protocols for human XGVHD.

Effect of Mycoplasma arthritidis superantigen on enzymatically induced arthritis in mice

The objective of this study was to examine the effect of the stimulation of the immune system with Mycoplasma arthritidis superantigen (MAS) on joint inflammation and cartilage destruction. MAS was administered either alone or combined with a model of degenerative arthritis induced by intraarticular injection of collagenase enzyme. Intraperitoneal injection of MAS resulted in activation of peripheral lymphocytes in BALB/c mice, as shown by a proliferative response of splenocytes isolated from MAS-treated animals to IL-2-containing supernatant. Intraperitoneal or intra-articular administration of MAS alone at concentrations maximally activating lymphocytes had no detectable effect on joints. Intra-articular injection of collagenase resulted in some infiltration of inflammatory cells into the joints, hyperplasia and hypertrophy of synovial lining, pannus formation and surface loss of proteoglycans 7 days following the injection. At 21 days, the animals showed almost total loss of cartilage and minimal or no inflammation. Animals receiving MAS in addition to collagenase treatment showed similar changes in the joints. These data have demonstrated that activation of the immune system with MAS in vivo does not increase joint inflammation or cartilage degradation in enzymatically induced arthritis.

Conserved amino acid residues in the complementarity-determining region 1 of the TCR beta-chain are involved in the recognition of conventional Ag and Mls-1 superantigen

Superantigens activate T cells by interacting primarily with the V beta region of the TCR. This report describes a series of studies performed to elucidate the role of the conserved amino acid motif (Asp-His-Asn) in the complementarity-determining region 1 (CDR1) of the TCR V beta chains that recognize murine endogenous superantigen Mls-1. By using site-directed mutagenesis of the Mls-1-reactive TCR V beta 6 gene, it is shown that the alterations of the conserved CDR1 motif disrupt Mls-1 superantigen and conventional Ag recognition in vitro. The loss of V beta 6 (mutant)+ TCR reactivity to Mls-1 superantigen is apparently dependent on the partner alpha-chain in the V beta 6/V alpha 3 TCR pairing shows some reactivity to Mls-1, whereas other TCR pairings do not. The examination of the developmental fate of the mutated form of the V beta 6 chain in Mls-1+ mice by using retroviral vector-mediated gene transfer confirms the critical role played by the CDR1 residues in Mls-1 recognition in vivo. Collectively, the results indicate that the CDR1 of the TCR V beta 6 chain is involved in interacting with peptide/MHC as well as in Mls-1 recognition. The observation that the conserved residues in selective TCR V beta chains are imparting a significant contribution to Ag recognition suggests a molecular basis for the intrinsic bias of some V beta chains for MHC molecules.

Conserved amino acid residues in the complementarity-determining region 1 of the TCR beta-chain are involved in the recognition of conventional Ag and Mls-1 superantigen

Superantigens activate T cells by interacting primarily with the V beta region of the TCR. This report describes a series of studies performed to elucidate the role of the conserved amino acid motif (Asp-His-Asn) in the complementarity-determining region 1 (CDR1) of the TCR V beta chains that recognize murine endogenous superantigen Mls-1. By using site-directed mutagenesis of the Mls-1-reactive TCR V beta 6 gene, it is shown that the alterations of the conserved CDR1 motif disrupt Mls-1 superantigen and conventional Ag recognition in vitro. The loss of V beta 6 (mutant)+ TCR reactivity to Mls-1 superantigen is apparently dependent on the partner alpha-chain in the V beta 6/V alpha 3 TCR pairing shows some reactivity to Mls-1, whereas other TCR pairings do not. The examination of the developmental fate of the mutated form of the V beta 6 chain in Mls-1+ mice by using retroviral vector-mediated gene transfer confirms the critical role played by the CDR1 residues in Mls-1 recognition in vivo. Collectively, the results indicate that the CDR1 of the TCR V beta 6 chain is involved in interacting with peptide/MHC as well as in Mls-1 recognition. The observation that the conserved residues in selective TCR V beta chains are imparting a significant contribution to Ag recognition suggests a molecular basis for the intrinsic bias of some V beta chains for MHC molecules.

Human primary immune response in SCID mice engrafted with human peripheral blood lymphocytes

Severe combined immune deficient (SCID) mice were engrafted with human peripheral blood lymphocytes (Hu-PBLs) after treatment with anti-asialo GM-1 antiserum and radiation. This pretreatment facilitates high level of Hu-PBL engraftment in the SCID mice spleen. The next day, the Hu-PBL-SCID mice were immunized with either keyhole limpet hemocyanin (KLH), or carbohydrate Ag STn (AcNeu-alpha 2-alpha 6-Gal NAc-0) conjugated to KLH or protein of circumsporozoite malaria parasite (CSP), in a mixture of complete and incomplete Freund's adjuvant (1:10 v/v). The mice were bled 14 to 16 days after immunization, and the sera analyzed for STn-, KLH-, and CSP-specific human IgG and IgM Abs. The results showed that the immunized animals had a significantly higher titer of Ag-specific human IgG and IgM Abs compared to the control Hu-PBL-SCID mice. No significant Ab cross-reactions were detected between sera from KLH-, STn-, and CSP-vaccinated Hu-PBL-SCID mice. Depletion of either human CD4+ or CD8+ cells, in Hu-PBL-SCID mice, showed that CD4+ cells were essential for the primary immune response, but depletion of CD8+ cells had no influence on the titer of Ag-specific human IgG and IgM Abs.

Human primary immune response in SCID mice engrafted with human peripheral blood lymphocytes

Severe combined immune deficient (SCID) mice were engrafted with human peripheral blood lymphocytes (Hu-PBLs) after treatment with anti-asialo GM-1 antiserum and radiation. This pretreatment facilitates high level of Hu-PBL engraftment in the SCID mice spleen. The next day, the Hu-PBL-SCID mice were immunized with either keyhole limpet hemocyanin (KLH), or carbohydrate Ag STn (AcNeu-alpha 2-alpha 6-Gal NAc-0) conjugated to KLH or protein of circumsporozoite malaria parasite (CSP), in a mixture of complete and incomplete Freund's adjuvant (1:10 v/v). The mice were bled 14 to 16 days after immunization, and the sera analyzed for STn-, KLH-, and CSP-specific human IgG and IgM Abs. The results showed that the immunized animals had a significantly higher titer of Ag-specific human IgG and IgM Abs compared to the control Hu-PBL-SCID mice. No significant Ab cross-reactions were detected between sera from KLH-, STn-, and CSP-vaccinated Hu-PBL-SCID mice. Depletion of either human CD4+ or CD8+ cells, in Hu-PBL-SCID mice, showed that CD4+ cells were essential for the primary immune response, but depletion of CD8+ cells had no influence on the titer of Ag-specific human IgG and IgM Abs.

Expression of the NK-TR gene is required for NK-like activity in human T cells

NK cells lyse target cells without previous immune sensitization. A small subset of T cells also exhibits NK-like activity, which is distinct from TCR-mediated, MHC-restricted, and MHC-unrestricted cytotoxicity. We recently cloned a gene, NK-TR, which is postulated to be part of the NK target-recognition/triggering complex. To determine whether the NK-TR gene product is requisite for NK-like killing, stable antisense transfectants were generated by using a human T cell clone with NK-like activity. Two distinct antisense regions of the sequence were used to generate the transfectants alpha NK-TR and alpha Cyclo. Transfectants lost the ability to lyse NK-sensitive targets but did not lose lectin-mediated cytotoxic activity. This effect was not seen with the control vector transfectant cell line. The loss of NK-like activity by the antisense transfectant alpha NK-TR correlated with the specific decrease in endogenous NK-TR mRNA and protein. These results demonstrate the requirement for the NK-TR protein for NK-like killing. Moreover, the results have important implications for examining developmental relationship between T and NK cells and the possible roles for T cells with NK-like activity in vivo.

Expression of the NK-TR gene is required for NK-like activity in human T cells

NK cells lyse target cells without previous immune sensitization. A small subset of T cells also exhibits NK-like activity, which is distinct from TCR-mediated, MHC-restricted, and MHC-unrestricted cytotoxicity. We recently cloned a gene, NK-TR, which is postulated to be part of the NK target-recognition/triggering complex. To determine whether the NK-TR gene product is requisite for NK-like killing, stable antisense transfectants were generated by using a human T cell clone with NK-like activity. Two distinct antisense regions of the sequence were used to generate the transfectants alpha NK-TR and alpha Cyclo. Transfectants lost the ability to lyse NK-sensitive targets but did not lose lectin-mediated cytotoxic activity. This effect was not seen with the control vector transfectant cell line. The loss of NK-like activity by the antisense transfectant alpha NK-TR correlated with the specific decrease in endogenous NK-TR mRNA and protein. These results demonstrate the requirement for the NK-TR protein for NK-like killing. Moreover, the results have important implications for examining developmental relationship between T and NK cells and the possible roles for T cells with NK-like activity in vivo.

High level functional engraftment of severe combined immunodeficient mice with human peripheral blood lymphocytes following pretreatment with radiation and anti-asialo GM1

The severe combined immunodeficient (SCID) mouse engrafted with human peripheral blood lymphocytes (PBLs) is a potentially useful model for the study of cancer immunotherapy. For this application, rapid, consistent, and high level engraftment of SCID mice with functional human cytotoxic effector cells is necessary. To date, short term human lymphoid cell engraftment in SCID mice has generally been low and variable. Further, most of the human cells detected within the first 30 days are found in the peritoneal cavity. The purpose of the present study was to improve short term reconstitution of human PBLs in the SCID mouse. When untreated SCID mice were injected with human PBLs, the mean level of CD3+ cells in the spleens was < 5% on days 6-32 after injection, as determined by flow cytometry (FCM). Depletion of SCID mouse natural killer (NK) cells with anti-asialo GM1 only marginally improved short term reconstitution with human CD3+ cells. Preirradiation of SCID mice with 3 Gy improved reconstitution to over 16% CD3+ cells on days 12-14 following engraftment. However, the combination of pretreatment with anti-asialo GM1 plus radiation, significantly increased the mean percentage of human CD3+ cells in the spleen to 40% within 2 weeks following injection of PBLs. Human T cells positive for CD4, CD8, TcR alpha beta, and TcR gamma delta, and human NK and B cells were detected in the spleens of irradiated plus anti-asialo GM1 pretreated SCID mice. The presence of human lymphoid cells was confirmed by immunohistologic staining. The human immune cells in these mice were shown to be functional by the in vivo demonstration of an appropriate secondary immune response to the injection of tetanus toxoid and by an in vivo proliferative response to phytohemagglutinin. Human NK cells could be found in the spleens and peripheral blood of irradiated plus anti-asialo GM1 pretreated mice. These cells were also shown to be competent by their ability to lyse the human NK sensitive tumor targets K562 and MOLT-4 in 51Cr release assays. Thus, pretreatment of SCID mice with radiation plus anti-asialo GM1 significantly improves short term human PBL engraftment and provides a potentially useful model for the study of cancer immunotherapy.

Expression of Mtv-7 sag gene in vivo using a retroviral vector results in selective inactivation of superantigen reactive T cells

T cells expressing specific TCR V beta chains are intrathymically eliminated in mice expressing the murine Mls (minor lymphocyte stimulating) superantigens. Recently, in vitro studies have shown that the endogenous mouse mammary tumor virus (MMTV)-7 sag gene encodes Mls-1 Ag. The demonstrated ability of MMTV superantigen proteins to react with TCRs has led to the postulate that other infectious retroviruses may use superantigen-like molecules to modify the host's immune system. In this report, successful retrovirus-mediated Mtv-7 sag gene transfer into pluripotent hematopoietic stem cells is described. In two different strains of Mls-1- host mice (CBA/Ca and BALB/c) reconstituted with Mtv-7 sag gene expressing bone marrow cells, low levels of ectopic Mtv-7 sag gene expression on syngeneic donor hematopoietic stem cell-derived population alone can induce partial clonal deletion of Mls-1 reactive V beta 6+ and V beta 8.1+ T cells, and complete clonal inactivation of V beta 8.1+ T cells.

Exogenous Mtv-7 superantigen transgene expression in major histocompatibility complex class II I-E- mice reconstituted with embryonic stem cell-derived hematopoietic stem cells

Direct genetic manipulation of hematopoietic cells is limited by the lack of an established hematopoietic stem cell line. It has been demonstrated that embryonic stem (ES) cell<-->tetraploid embryos are completely ES cell-derived and that fetal liver (FL) cells from these embryos support hematopoiesis in lethally irradiated recipients. In this report, we demonstrate that FL cells from ES cell<-->tetraploid embryos support normal lymphopoiesis and T-cell repertoire development. Moreover, the introduction of the Mtv-7 superantigen transgene coding for minor lymphocyte stimulatory antigen 1 into murine hematopoietic cells via reconstitution with ES cell<-->tetraploid FL cells demonstrates that this method can effectively confer stable genetic changes into the hematopoietic tissues without going through the germ line. Long-term and secondary reconstitution with ES cell<-->tetraploid FL cells expressing the Mtv-7 superantigen transgene clonally deleted minor lymphocyte stimulatory antigen 1-reactive T-cell receptor V beta 6+, -8.1+, and -9+ T cells, but not V beta 7+ T cells, in H-2b (I-E-) mice. This model system will be extremely important for analyzing structure-function relationships of molecules involved in proliferation, differentiation, and selection of hematopoietic cells in vivo and for examining hematopoiesis-specific effects of mutations that are lethal during embryogenesis.

Expression of Mtv-7 sag gene in vivo using a retroviral vector results in selective inactivation of superantigen reactive T cells

T cells expressing specific TCR V beta chains are intrathymically eliminated in mice expressing the murine Mls (minor lymphocyte stimulating) superantigens. Recently, in vitro studies have shown that the endogenous mouse mammary tumor virus (MMTV)-7 sag gene encodes Mls-1 Ag. The demonstrated ability of MMTV superantigen proteins to react with TCRs has led to the postulate that other infectious retroviruses may use superantigen-like molecules to modify the host's immune system. In this report, successful retrovirus-mediated Mtv-7 sag gene transfer into pluripotent hematopoietic stem cells is described. In two different strains of Mls-1- host mice (CBA/Ca and BALB/c) reconstituted with Mtv-7 sag gene expressing bone marrow cells, low levels of ectopic Mtv-7 sag gene expression on syngeneic donor hematopoietic stem cell-derived population alone can induce partial clonal deletion of Mls-1 reactive V beta 6+ and V beta 8.1+ T cells, and complete clonal inactivation of V beta 8.1+ T cells.

Characterization of the insulin A-chain major immunogenic determinant presented by MHC class II I-Ad molecules

Data are presented which demonstrate the minimal insulin peptide required to activate a large group of insulin-specific T hybrids following presentation by either live or fixed APC, is the N-terminal insulin-A(1-13) peptide. Functional activation and competition assays using both live and fixed APC with 19 synthesized variants of the N-terminal bovine insulin A-chain molecule permitted classification of peptide residues into MHC agretope and T cell epitope regions. Our findings indicate insulin A-chain peptide occupies the Ag binding groove of class II MHC in an extended conformation as a result of intracellular reduction of A-loop disulfide bonds. Insulin A-chain Cys7 and Cys11 residues represent two independent T cell epitopes N- and C-terminal to the A-loop region. Data are presented that demonstrate the unique residues associated with several insulin isoform molecules contribute to the peptide agretope region. Our findings may suggest peptide agretopes may subtly modify the peptide/MHC conformation presented to TCR.

Characterization of the insulin A-chain major immunogenic determinant presented by MHC class II I-Ad molecules

Data are presented which demonstrate the minimal insulin peptide required to activate a large group of insulin-specific T hybrids following presentation by either live or fixed APC, is the N-terminal insulin-A(1-13) peptide. Functional activation and competition assays using both live and fixed APC with 19 synthesized variants of the N-terminal bovine insulin A-chain molecule permitted classification of peptide residues into MHC agretope and T cell epitope regions. Our findings indicate insulin A-chain peptide occupies the Ag binding groove of class II MHC in an extended conformation as a result of intracellular reduction of A-loop disulfide bonds. Insulin A-chain Cys7 and Cys11 residues represent two independent T cell epitopes N- and C-terminal to the A-loop region. Data are presented that demonstrate the unique residues associated with several insulin isoform molecules contribute to the peptide agretope region. Our findings may suggest peptide agretopes may subtly modify the peptide/MHC conformation presented to TCR.

Long term expression of IL-4 in vivo using retroviral-mediated gene transfer

Th cell subsets regulate immune responses by cell-cell interaction and secretion of cytokines. IL-4 is one of the cytokines secreted by Th cells important for cellular and humoral, particularly IgG1 and IgE responses. To study the role of IL-4 in T cell development and regulation of immune responses in vivo, low IgE-responder C57BL/6 mice were reconstituted with bone marrow cells that had been infected with recombinant retrovirus expressing a high level of IL-4. The reconstituted mice expressed retroviral IL-4 transcripts (9/10) even 8 mo postreconstitution. Physiologically significant levels of IL-4 were detected in the majority of the provirus-positive animals tested (5/8). Ectopic expression of exogenous IL-4 in hematopoietic cells had dramatic effects on T cell development resulting in changes in CD4:CD8 ratios. Moreover, the levels of serum IgG1 and, with antigenic stimulation, IgE were also increased. These results demonstrate that the retrovirus gene transfer system can be used to study the effects of ectopic cytokine gene expression in vivo on Ig isotype regulation and T helper cell subset differentiation.

Long term expression of IL-4 in vivo using retroviral-mediated gene transfer

Th cell subsets regulate immune responses by cell-cell interaction and secretion of cytokines. IL-4 is one of the cytokines secreted by Th cells important for cellular and humoral, particularly IgG1 and IgE responses. To study the role of IL-4 in T cell development and regulation of immune responses in vivo, low IgE-responder C57BL/6 mice were reconstituted with bone marrow cells that had been infected with recombinant retrovirus expressing a high level of IL-4. The reconstituted mice expressed retroviral IL-4 transcripts (9/10) even 8 mo postreconstitution. Physiologically significant levels of IL-4 were detected in the majority of the provirus-positive animals tested (5/8). Ectopic expression of exogenous IL-4 in hematopoietic cells had dramatic effects on T cell development resulting in changes in CD4:CD8 ratios. Moreover, the levels of serum IgG1 and, with antigenic stimulation, IgE were also increased. These results demonstrate that the retrovirus gene transfer system can be used to study the effects of ectopic cytokine gene expression in vivo on Ig isotype regulation and T helper cell subset differentiation.