Oncogenic role of microRNA-155 in mycosis fungoides: an in vitro and xenograft mouse model study

BACKGROUND

MicroRNA (miR)-155 contributes to the proliferation of mycosis fungoides (MF) in vitro and is upregulated in tumours of MF compared with early MF lesions.

OBJECTIVES

To investigate the contribution of miR-155 to the cancerous phenotype and drug resistance of MF/Sézary cell lines.

METHODS

miR-155 was inhibited in MF cell lines (MyLa and MJ) by transduction of miRZip anti-miR-155, and overexpressed in Hut78 cells by transduction of miRVec-miR-155; empty plasmids served as controls. Cells were analysed for response to inducers of apoptosis and cell-cycle arrest, using fluorescence-activated cell sorting. Transduced MyLa cells were subcutaneously injected into severe combined immunodeficient mice, and tumours were analysed immunohistochemically and for final size.

RESULT

MyLa and MJ cells expressed a high level of miR-155; Hut78 cells expressed a low level. MF cell lines stably expressing miR-155 inhibitor showed increased G2/M arrest in response to N-p-tolyl-2-(3,4,5-trimethoxyphenyl quinazolin-4-amine) (SL111), an inducer of cell-cycle arrest, followed by increased apoptosis. Additionally, they showed increased apoptosis in response to suberoylanilide hydroxamic acid (SAHA). Tumours formed in mice from injected anti-miR-155-expressing MyLa cells had a significantly lower volume and higher occurrence of apoptosis than controls. Stable overexpression of miR-155 in Hut78 cells had no effect.

CONCLUSIONS

Oncogenic miR-155 appears to contribute to the cancerous phenotype of MyLa and MJ cells, but not of Hut78 cells, by interrupting activation of the G2/M checkpoint in response to SL111, and decreasing apoptosis in response to SL111 and SAHA, thereby facilitating tumour growth. These findings have implications for the potential development of novel therapeutic modalities for MF incorporating miR-155 inhibitors.

Preclinical evaluation of two human anti-hepatitis B virus (HBV) monoclonal antibodies in the HBV-trimera mouse model and in HBV chronic carrier chimpanzees

Two human monoclonal antibodies (mAbs) against hepatitis B surface antigen (HBsAg) generated in the Trimera mouse system are described. Both mAbs 17.1.41 and 19.79.5 are of the IgG1 isotype and have high affinity constants for HBsAg binding in the range of 10(-10) mol/L. Monoclonal antibody 17.1.41 recognizes a conformational epitope on the a determinant of HBsAg whereas mAb 19.79.5 recognizes a linear one. The 2 mAbs bind to a panel of hepatitis B virus (HBV) subtypes with distinct patterns. The neutralizing activity of these antibodies was tested in 2 different animal model systems. Administration of each mAb to HBV-Trimera mice, a system that provides a mouse model for human hepatitis B infection, reduced the viral load and the percentage of HBV-DNA-positive mice in a dose-dependent manner. These 2 mAbs were more effective than a polyclonal antibody preparation (Hepatect; Biotest Pharma, Dreieich, Germany) in both inhibition of HBV liver infection and reduction of viral load. A single administration of a mixture of these mAbs into HBV chronic carrier chimpanzees resulted in immediate reduction in HBsAg levels followed by recurrence to initial levels within few days. Thus, these mAbs may be potential candidates for preventive therapy or in combination with other antiviral agents against HBV. Further studies in humans are needed to assess these mAbs in various clinical indications.

The hepatitis B virus-trimera mouse: a model for human HBV infection and evaluation of anti-HBV therapeutic agents

Previous studies have demonstrated the feasibility of implantation of human blood cells or tissues in lethally irradiated mice or rats, radioprotected with SCID mouse bone marrow cells: The Trimera system. In the present study, we describe the development of a mouse Trimera model for human hepatitis B virus (HBV) infection. In this model, viremia is induced by transplantation of ex vivo HBV-infected human liver fragments. Engraftment of the human liver fragments, evaluated by hematoxylin-eosin staining and human serum albumin mRNA expression, was observed in 85% of the transplanted animals 1 month postimplantation. Viremia levels were determined in these mice by measuring serum HBV DNA using polymerase chain reaction (PCR), followed by dot-blot hybridization. HBV DNA is first detected 8 days after liver transplantation. Viremia attains a peak between days 18 and 25 when HBV infection is observed in 85% of the transplanted animals. The HBV-Trimera model was used to evaluate the therapeutic effects of human polyclonal anti-HBs antibodies (Hepatect) and of two reverse-transcriptase inhibitors, lamivudine (3TC) and beta-L-5-fluoro-2',3'-dideoxycytidine (beta-L-5FddC). Treatment of HBV-Trimera mice with these drugs effectively reduced both the percentage of infected animals and the viral load in their sera. Treatment cessation resulted in rebound of viral load, indicating HBV replication upon drug withdrawal. These results show that the HBV-Trimera model represents a novel experimental tool for simulating human HBV infection and evaluating potential anti-HBV therapeutic agents.

Human monoclonal antibodies specific to hepatitis B virus generated in a human/mouse radiation chimera: the Trimera system

An approach to develop fully human monoclonal antibodies in a human/mouse radiation chimera, the Trimera system, is described. In this system, functional human lymphocytes are engrafted in normal strains of mice which are rendered immuno-incompetent by lethal total body irradiation followed by radioprotection with severe combined immunodeficient (SCID) mouse bone marrow. Following transplantation, human lymphocytes colonize murine lymphatic organs and secrete human immunoglobulins. We have established this system as a tool to develop fully human monoclonal antibodies, and applied it for the generation of monoclonal antibodies specific for hepatitis B virus surface antigen. A strong memory response to hepatitis B surface antigen was elicited in Trimera engrafted with lymphocytes from human donors positive for antibodies to hepatitis B surface antigen. The human specific antibody fraction in the Trimera was 10(2)-10(3)-fold higher as compared with that found in the donors. Spleens were harvested from Trimera mice showing high specific-antibody titres and cells were fused to a human-mouse heteromyeloma fusion partner. Several stable hybridoma clones were isolated and characterized. These hybridomas produce high-affinity, IgG, anti-hepatitis B surface antigen antibodies demonstrating the potential of the Trimera system for generating fully human monoclonal antibodies. The biological function and the neutralizing activity of these antibodies are currently being tested.

Human T cells recovered from human/Balb radiation chimeras are hypersensitive to human immunodeficiency virus type 1 infection

Replication of human immunodeficiency virus type 1 (HIV-1) is regulated by virus-encoded regulatory proteins, as well as by a variety of cellular factors. Productive infection of human T lymphocytes by HIV-1 is dependent upon the activation status of the target cells. In general, short-term mitogenic stimulation of CD4 T cells is used to enhance infection of peripheral blood mononuclear cells (PBMC) in vitro. Recently, we demonstrated that adoptive transfer of human PBMC into lethally irradiated BALB/c mice, radioprotected with severe combined immunodeficiency (SCID) mouse bone marrow, leads to marked T-cell activation and proliferation. In the present study, we investigated the effect of such xenoactivation of human T cells on their susceptibility to HIV-1 infection. Human cells that were recovered from human/Balb radiation chimeras supported efficient replication of laboratory strains of HIV-1, as well as of HIV-1 clinical isolates. The multiplicity of infection required to attain effective virus replication in the recovered xenoactivated human cells was 10- to 100-fold lower than that needed for infection of short- or long-term phytohemagglutinin (PHA)-stimulated blasts or of various T-cell lines. Analysis of human cell surface activation markers has indicated that xenoactivation in the mouse, in contrast to in vitro stimulation with PHA, is associated with a marked downregulation of CD25 (interleukin 2 receptor). Our results demonstrate that human cells recovered from human/Balb radiation chimeras, which are hypersensitive to HIV-1 infection, differ from in vitro-stimulated cells in their activation status. Therefore, this system could be used to study host factors that participate in HIV-1 infection and replication in vitro and in vivo.

Engrafted human T and B lymphocytes form mixed follicles in lymphoid organs of human/mouse and human/rat radiation chimera

BACKGROUND

We recently described a new approach that enables the generation of human/mouse chimera by adoptive transfer of human peripheral blood mononuclear cells into lethally irradiated normal strains of mice or rats, radioprotected with bone marrow from donors with severe combined immune deficiency. In such human/mouse chimera, a marked humoral response to recall antigens, as well as a significant primary response to keyhole limpet hemocyanin, has been generated.

METHODS

In the present study, the organ distribution of the engrafted human cells in the human/mouse and human/rat chimera was investigated by immunohistochemistry.

RESULTS

Our results show that the T cells seem to be distributed throughout the reticular endothelial system, almost behaving like particles without any homing specificity. The B cells, however, can barely be found in internal organs, such as the liver or the pancreas, and are concentrated in the secondary lymphoid system (e.g., spleen, lymph node, and nonencapsulated lymphoid tissue). The B cells, together with the engrafted human T cells, form mixed lymphoid follicles.

CONCLUSIONS

The different homing patterns exhibited by the T and B lymphocytes indicate that the homing receptors on human B cells might be cross-reactive with their mouse counterparts, in contrast to the human T cells, which seem to be unable to interact with the mouse homing receptors. The presence of human B and T lymphocytes in close proximity to each other in the lymphoid tissues is in accordance with the ability of human/BALB radiation chimera to mount significant primary human antibody responses.

Generation of primary antigen-specific human cytotoxic T lymphocytes in human/mouse radiation chimera

Severe combined immunodeficient (SCID) mice are increasingly used as hosts for the adoptive transfer of human lymphocytes. Human antibody responses can be obtained in these xenogeneic chimeras, but information about the functionality of the human T cells in SCID mice is limited and controversial. Studies using human peripheral blood lymphocytes (PBL) injected intraperitoneally (IP) into SCID mice (hu-PBL-SCID mice) have shown that human T cells from these chimeras are anergic and have a defective signaling via the T-cell receptor. In addition, their antigenic repertoire is limited to xenoreactive clones. In the present study, we tested the functionality of human T cell in a recently described chimeric model. In this system, BALB/c mice are conditioned by irradiation and then transplanted with SCID bone marrow, followed by IP injection of human PBL. Our experiments demonstrated that human T cells, recovered from these hu-PBL-BALB mice within 1 month posttransplant, proliferated and expressed activation markers upon stimulation with anti-CD3 monoclonal antibody. A vigorous antiallogeneic human cytotoxic T-lymphocyte (CTL) response could be generated in these mice by immunizing them with irradiated allogeneic cells. Moreover, anti-human immunodeficiency virus type 1 (HIV-1) Net-specific human CTLs could be generated in vivo from naive lymphocytes by immunization of mouse-human chimeras with a recombinant vaccinia-nef virus. This model may be used to evaluate potential immunomodulatory drugs or cytokines, and could provide a relevant model for testing HIV vaccines, for production of antiviral T-cell clones for adoptive therapy, and for studying human T-cell responses in vivo.

Human-->mouse radiation chimera do not develop Epstein-Barr virus lymphoma

It has been shown that engraftment of human peripheral blood lymphocytes (PBL) from Epstein-Barr virus (EBV) seropositive donors in C.B-17/SCID mice is associated with a high incidence of human B cell tumors. More recently, we described a new approach enabling engraftment of human PBL in normal strains of mice or rats receiving lethal split-dose radiation and radioprotected with SCID bone marrow. We now demonstrate that, in contrast to SCID recipients of human PBL, Balb/c and C3H/HeJ recipients of 50-100 x 10(6) human PBL did not develop any EBV lymphoma during a 7-month follow-up period, but were successfully engrafted with human B and T cells. On the other hand, lymphoma developed in 90% of the C.B-17/SCID mice infused with 70 x 10(6) human PBL from the same donor. Likewise, 36% of beige/nude/xid (BNX) mice, exposed to 12 Gy TBI, radioprotected with SCID bone marrow and then transplanted with human PBL developed lymphoma. Similar results were obtained when different strains were infused with PBL of the same donor. Immunohistochemical analysis indicated that the tumor cells were of human B cell origin and expressed the EBV-encoded latent membrane protein-1 and nuclear antigen 2. While further studies are required to understand the mechanisms which suppressed outgrowth of EBV lymphoma in human --> mouse radiation chimera, compared to human --> C.B-17/SCID or human --> BNX chimera, this marked resistance offers new possibilities for transplantation of hematopoietic tissues or cells from EBV-positive donors.

Conversion of normal rats into SCID-like animals by means of bone marrow transplantation from SCID donors allows engraftment of human peripheral blood mononuclear cells

We have recently shown that lethally irradiated normal strains of mice, radioprotected with SCID bone marrow, can be engrafted with human peripheral blood mononuclear cells (PBMC). We now demonstrate that lethally irradiated Lewis rats can also be radioprotected with a transplant of SCID bone marrow cells, administered 1 day after total body irradiation. Split chimerism was found in PBMC, 30 days after transplantation, with predominance of SCID donor-type cells. The average percentages of CD4 and CD8 T cells, of mouse or rat origin, were < 1%. This chimerism status could be maintained for over 3 months. When human PBMC (300-1000 x 10(6) cells) were transplanted intraperitoneally 1 day after the administration of SCID bone marrow, prompt engraftment of human CD4 and human CD8 T cells, as well as human CD20 B cells, was found in the peritoneum and in internal organ (such as liver, lung, spleen, thymus, and lymph nodes). T cell activation was high: about 50% of the cells expressed HLA-DR and almost all expressed CD45RO. High titers of human Ig (> 1 mg/ml) were initially found after 2 weeks; these levels were similar to those found in the irradiated mouse model and in the SCID model. Likewise, marked human anti-tetanus response, predominantly of the IgG type, was recorded 2 weeks after the immunization, reaching maximal levels at 4 weeks. The triple-chimeric SCID-like rats, which accept as much as 1000 x 10(6) human PBMC, can potentially be used to elicit both antibody responses and T cell responses against specific antigens, with the advantages of a larger animal.

Human/mouse radiation chimera are capable of mounting a human primary humoral response

Lubin et al recently described a new approach that enables the generation of human/mouse chimera by adoptive transfer of human peripheral blood mononuclear cells (PBMC) into lethally irradiated normal strains of mice, radioprotected with bone marrow (BM) from donors with severe combined immune deficiency (SCID). In the present study, we demonstrate in such human/mouse chimera a marked humoral response to recall antigen, such as tetanus toxoid (TT) or hepatitis B surface antigen (HBsAg), as well as a significant primary response to keyhole limpet hemocyanin (KLH). Maximal anti-KLH response in human/Balb chimera was attained 2 to 4 weeks after the immunization and declined thereafter. One week after transplantation, the predominant anti-KLH subtype was IgM, while after 2 weeks, the dominance had shifted to IgG. Similar primary antibody response was also demonstrated against the human immunodeficiency virus (HIV) Nef protein. Comparison between human/Balb and human/SCID chimera showed a major difference in their ability to mount a primary response against KLH. In Balb/c recipients, more than half of the mice exhibited marked IgM titers against KLH, while there was hardly any anti-KLH IgM response in the SCID recipients. From the earliest time point onwards, when anti-KLH antibodies were found in the latter chimera, they were predominantly of the IgG type. We have previously shown that in human/Balb chimera, unlike in SCID recipients, dissemination of transplanted PBMC into the spleen and other internal organs occurs within 24 hours. Therefore, it is likely that the early seeding in the appropriate microenvironment of the lymphoid tissues, is crucial for the maintenance of virgin human B cells.

Hepatitis C virus viremia in SCID-->BNX mouse chimera

Chimpanzees are currently the only nonhuman animal model for reproducible propagation of hepatitis C virus (HCV). A chimeric mouse model was used for the induction of hepatitis C viremia, using BNX (beige/nude/X-linked immunodeficient) mice preconditioned by total body irradiation and reconstituted with SCID mouse bone marrow cells. HCV-infected liver fragments from patients with HCV RNA-positive sera were transplanted under the kidney capsule of the chimeric mice. HCV-specific RNA sequences were detected by reverse transcriptase nested polymerase chain reaction (RT-PCR) in serum of approximately 50% of grafted animals. In addition, normal liver specimens were incubated with HCV serum and transplanted into chimeric mice, leading to viremia in approximately 25% of animals. Sequential histologic evaluation of the liver implants, from day 2 to week 14 after transplantation, revealed loss of lobular architecture within the implants. However, viremia persisted for 10-50 days after transplantation. These results offer a new HCV model.

Lethally irradiated normal strains of mice radioprotected with SCID bone marrow develop sensitivity to low doses of staphylococcal enterotoxin B

Normal strains of mice are rendered sensitive to small amounts (3-10 micrograms) of staphylococcal enterotoxin B (SEB) by transplanting bone marrow cells of SCID donor mice to lethally irradiated recipients. Four to 12 weeks post-transplantation, SEB induces 56-100% lethality. Transplantation of normal mouse bone marrow cells, either alone or with the SCID mouse selected bone marrow cells, does not confer SEB sensitivity. These data imply that either irradiation ablates certain cell population(s), that confer resistance to SEB in normal mice (populations that are absent in the SCID donor mice) or that the donor cells selectively repopulate recipients with SEB-sensitive cells. This model will help elucidate the cells, cytokines and the SEB peptide fragments responsible for SEB toxicity and will be useful in identifying promising vaccine candidates and in developing preventive medicines to protect against this potent toxin.

Effective graft-versus-leukemia effects independent of graft-versus-host disease after T cell-depleted allogeneic bone marrow transplantation in a murine model of B cell leukemia/lymphoma. Role of cell therapy and recombinant IL-2

After allogeneic bone marrow transplantation (BMT) for leukemia, beneficial graft-vs-leukemia (GVL) effects are usually accompanied by potentially serious graft-vs-host disease (GVHD). Because T cell depletion is the only effective way to prevent GVHD it seems important to understand whether effective GVL can develop after BMT with T cell depletion in GVHD-free recipients. Well-established C57BL/6-->BALB/c chimeras that were free of GVHD, reconstituted with T cell-depleted allogeneic bone marrow cells, and inoculated 3 mo after BMT with a high inoculation of murine B cell leukemia (BCL1) showed no evidence of disease, whereas all control mice developed leukemia and died within 58 days. Results from adoptive transfer experiments in secondary naive BALB/c recipients indicated that all BCL1 cells were eliminated in the chimeras within 14 days. Hence, complete resistance to BCL1 developed in the chimeras despite complete tolerance to host alloantigens. The GVL effects observed in tolerant chimeras were further amplified by administration of immunocompetent allogeneic C57BL/6 spleen cells, low dose rIL-2, or both for 5 days. Our data suggest that GVL effects can develop even after T cell depletion in the absence of clinically overt GVHD and that GVL can be further amplified by rIL-2, either with or without use of additional immunocompetent donor T cells. Our data may provide the basis for new approaches to induce effective GVL after allogeneic BMT with cell therapy and rIL-2 at the stage of minimal residual disease, while avoiding early GVHD induced by the BMT procedure.

Effective graft-versus-leukemia effects independent of graft-versus-host disease after T cell-depleted allogeneic bone marrow transplantation in a murine model of B cell leukemia/lymphoma. Role of cell therapy and recombinant IL-2

After allogeneic bone marrow transplantation (BMT) for leukemia, beneficial graft-vs-leukemia (GVL) effects are usually accompanied by potentially serious graft-vs-host disease (GVHD). Because T cell depletion is the only effective way to prevent GVHD it seems important to understand whether effective GVL can develop after BMT with T cell depletion in GVHD-free recipients. Well-established C57BL/6--&gt;BALB/c chimeras that were free of GVHD, reconstituted with T cell-depleted allogeneic bone marrow cells, and inoculated 3 mo after BMT with a high inoculation of murine B cell leukemia (BCL1) showed no evidence of disease, whereas all control mice developed leukemia and died within 58 days. Results from adoptive transfer experiments in secondary naive BALB/c recipients indicated that all BCL1 cells were eliminated in the chimeras within 14 days. Hence, complete resistance to BCL1 developed in the chimeras despite complete tolerance to host alloantigens. The GVL effects observed in tolerant chimeras were further amplified by administration of immunocompetent allogeneic C57BL/6 spleen cells, low dose rIL-2, or both for 5 days. Our data suggest that GVL effects can develop even after T cell depletion in the absence of clinically overt GVHD and that GVL can be further amplified by rIL-2, either with or without use of additional immunocompetent donor T cells. Our data may provide the basis for new approaches to induce effective GVL after allogeneic BMT with cell therapy and rIL-2 at the stage of minimal residual disease, while avoiding early GVHD induced by the BMT procedure.

Engraftment of human peripheral blood lymphocytes in normal strains of mice

Transplantation of bone marrow from SCID mice into lethally irradiated normal mice can potentially endow the normal recipients with characteristics typical of the immune-deficient SCID mouse. In the present study, we investigated whether intraperitoneal grafting of human peripheral blood lymphocytes (PBLs), which has been documented in the SCID mouse, can also be achieved in irradiated BALB/c mice radioprotected with SCID bone marrow. Evaluation of different radiation protocols suggested that, considering the quality of engraftment and rate of survival, optimal results were obtained with split dose total body irradiation (TBI; 4 Gy followed 3 days later by 10 Gy). Monitoring of mouse T cells in peripheral blood indicated an inverse correlation between the presence of such cells and the engraftment of human CD45+ cells in the peritoneum. Also, engraftment of human PBLs in nude BALB/c mice, conditioned with the same radiation protocol, was significantly higher than that achieved in their normal counterparts. Further improvement of human PBL engraftment was found when the mice were thymectomized 2 weeks before conditioning with split TBI. After transplantation of 80 x 10(6) human PBLs in such recipients, a marked engraftment of human T cells and B cells in the peritoneum cavity could be detected for at least 2 months, whereas significant amounts of human Ig could be detected for more than 3 months. Migration of human PBLs into internal organs such as spleen, liver, kidney, and lungs (and into thymus in nonthymectomized mice) was found within a few days of grafting and also persisted for 2 to 3 months. The majority of the engrafted lymphocytes were single-positive CD4+ and CD8+ T lymphocytes, about 50% of which were activated, as judged by their expression of HLA-DR. Staining with anti-CD25 antibody was lower compared with that found with anti-HLA-DR. CD20+ B cells were detected in all of the above-mentioned internal organs, but were mainly concentrated in the spleen. CD14+ monocytes could be detected only during the first week posttransplant of PBLs. Total human Ig in peripheral blood reached an average of 2.8 mg/mL 14 days posttransplant, and continued to be significant for several months. In vitro transformation by Epstein-Barr virus of human B cells from different tissues could be established 30 days after transplantation and led to outgrowth of two IgG+ cell lines, two IgM+ cell lines, and one IgA+ cell line producing 0.6 to 4.2 micrograms/mL human Ig in the supernatant.(ABSTRACT TRUNCATED AT 400 WORDS)

Enhancement of BM allografting from C57BL/6 'nude' mice into C3H/HeJ recipients by tolerized T cells from (C57BL/6-->C3H/HeJ) and (C3H/HeJ-->C57BL/6) chimeras

The possible participation of T cells in the promotion of hematopoietic engraftment of BM allografts, as opposed to their potential role in overcoming host-versus-graft reactions, was investigated recently by using (host x donor)F1 T cells devoid of graft-versus-host activity. In the present study, we provide further evidence of this effect by using tolerized thymocytes from established allogeneic chimeras. We show that tolerant mature thymocytes from donor type (C57BL/6-->C3H/HeJ) or host type (C3H/HeJ-->C57BL/6) chimeras are as effective as (donor x host)F1 thymocytes in promoting both short-term and long-term engraftment of C57BL/6-Nu/Nu T cell-depleted BM cells in lethally irradiated C3H/HeJ recipients.

Enhancement of T-cell-depleted bone marrow allografts in the absence of graft-versus-host disease is mediated by CD8+ CD4- and not by CD8- CD4+ thymocytes

Transplantation of T-cell-depleted C57BL/6-Nu/Nu ("nude") bone marrow (BM) into C3H/HeJ recipients, conditioned with 8 Gy total body irradiation plus chemotherapy with the myeloablative drug dimethyl myleran, resulted in poor hematopoietic reconstitution 14 days posttransplant, compared with transplantation with T-cell-depleted BM from normal C57BL/6 donors. Hematopoietic reconstitution of "nude" BM could be improved by the addition of (C57BL/6xC3H/HeJ)F1 thymocytes void of graft-versus-host activity. Enhancement of BM allografting by thymocytes is sensitive to low radiation doses (> or = 5.0 Gy) and can be achieved by transplanting the BM 24 hours before the administration of thymocytes. Fractionation of F1 thymocytes by differential agglutination with peanut agglutinin (PNA) and by fluorescence activated cell sorting showed that this hematopoietic enhancing activity is enriched in the unagglutinated (PNA-) thymocyte fraction and is mediated by PNA- CD8+ and not by PNA- CD4+ thymocytes.

Engraftment and development of human T and B cells in mice after bone marrow transplantation

A model for human lymphocyte ontogeny has been developed in a normal mouse. Human bone marrow, depleted of mature T and B lymphocytes, and bone marrow from mice with severe combined immunodeficiency were transplanted into lethally irradiated BALB/c mice. Human B and T cells were first detected 2 to 4 months after transplantation and persisted for at least 6 months. Most human thymocytes (30 to 50 percent of total thymocytes) were CD3+CD4+CD8+. Human immunoglobulin was detected in some chimeras, and a human antibody response to dinitrophenol could be generated after primary and secondary immunization.

Induction of donor-type chimerism in murine recipients of bone marrow allografts by different radiation regimens currently used in treatment of leukemia patients

Three radiation protocols currently used in treatment of leukemia patients before bone marrow transplantation (BMT) were investigated in a murine model (C57BL/6----C3H/HeJ) for BM allograft rejection. These include (a) a single dose of total body irradiation (8.5 Gy TBI delivered at a dose rate of 0.2 Gy/min), (b) fractionated TBI (12 Gy administered in six fractions, 2 Gy twice a day in 3 days, delivered at a dose rate of 0.1 Gy/min, and (c) hyperfractionated TBI (14.4 Gy administered in 12 fractions, 1.2 Gy three times a day in 3 days, delivered at a dose rate of 0.1 Gy/min). Donor-type chimerism 6 to 8 weeks after BMT and hematologic reconstitution on day 12 after BMT found in these groups were compared with results obtained in mice conditioned with 8 Gy TBI delivered at a dose rate of 0.67 Gy/min, routinely used in this murine model. The results in both parameters showed a marked advantage for the single dose 8.5 Gy TBI over all the other treatments. This advantage was found to be equivalent to three- to fourfold increment in the BM inoculum when compared with hyperfractionated radiation, which afforded the least favorable conditions for development of donor-type chimerism. The fractionated radiation protocol was equivalent in its efficacy to results obtained in mice irradiated by single-dose 8 Gy TBI, both of which afforded a smaller but not significant advantage over the hyperfractionated protocol. This model was also used to test the effect of radiation dose rate on the development of donor-type chimerism. A significant enhancement was found after an increase in dose rate from 0.1 to 0.7 Gy/min. Further enhancement could be achieved when the dose rate was increased to 1.3 Gy/min, but survival at this high dose rate was reduced. These results demonstrated indirectly that dose rate affects the expression of host-type pluripotent stem cells, the progeny of which appear 3 to 6 weeks after treatment with 8 Gy TBI delivered at a dose rate of 0.1 Gy/min, but which are eradicated if radiation is delivered at a dose rate of 1.3 Gy/min.

Enhancement of bone marrow allografts from nude mice into mismatched recipients by T cells void of graft-versus-host activity

Transplantation of 8 x 10(6) C57BL/6-Nu+/Nu+ (nude) bone marrow cells into C3H/HeJ recipients after conditioning with 8 Gy of total body irradiation has resulted in a markedly higher rate of graft rejection or graft failure compared to that found in recipients of normal C57BL/6 or C57BL/6-Bg+/Bg+ (beige) T-cell-depleted bone marrow. Mixing experiments using different numbers of nude bone marrow cells with or without mature thymocytes (unagglutinated by peanut agglutinin) revealed that engraftment of allogeneic T-cell-depleted bone marrow is T-cell dependent. To ensure engraftment, a large inoculum of nude bone marrow must be supplemented with a trace number of donor T cells, whereas a small bone marrow dose from nude donors requires a much larger number of T cells for engraftment. Marked enhancement of donor type chimerism was also found when F1 thymocytes were added to nude bone marrow cells, indicating that the enhancement of bone marrow engraftment by T cells is not only mediated by alloreactivity against residual host cells but may rather be generated by growth factors, the release of which may require specific interactions between T cells and stem cells or between T cells and bone marrow stroma cells.

Stoichiometry of large T antigen and pp53 in complexes isolated from simian virus 40-transformed rat cells

Simian virus 40-transformed cells synthesize high-molecular-weight protein complexes (22 to 30S) that consist of the virus-coded large T antigen (81,500 daltons) and the cellular antigen pp53. These complexes were partially purified from lysates of transformed rat cells by sucrose velocity sedimentation. The stoichiometry of the two proteins in the complex was studied by direct enzyme-linked immunosorbent assays, using alkaline phosphatase-conjugated anti-T and anti-pp53 monoclonal antibodies. The results from these experiments indicate that the T antigen-to-pp53 ratio in the complex is 0.87 +/- 0.27. No statistically significant differences were found in this ratio for faster- and slower-sedimenting complexes. These results from enzyme-linked immunosorbent assays and previous molecular weight estimates of the complex suggest that this complex is composed, on the average, of four molecules of T antigen and four or five molecules of pp53.