The CD28 ligand, B7, enhances IL-2 production by providing a costimulatory signal to T cells.

Previous studies demonstrated that a human pre-B acute lymphoblastic leukemia cell line, NALM-6, failed to stimulate a primary MLR, despite expression of class II MHC and adhesion molecules. Here we demonstrate that this is the result of the fact that NALM-6 cells do not express the ligand for CD28, namely B7. NALM-6 transfectants that expressed high levels of B7 gained the capacity to stimulate IL-2 production by class II MHC molecule-specific alloreactive T cells and to costimulate a polyclonal population of purified T cells cultured with immobilized anti-CD3 mAb. In the presence of PMA, NALM-6 cells transfected with B7 polyclonally stimulated T cells in a cyclosporine A-resistant fashion, a property previously attributed only to agonistic anti-CD28 mAb. The gain of these functions could not be explained solely by an increased capacity of the transfectants to form conjugates with T cells, suggesting that the CD28/B7 interaction transduces a costimulatory signal in T cells.     

Use of colony assays and anti-T cell immunotoxins to elucidate the immunobiologic features of leukemic progenitor cells in T-lineage acute lymphoblastic leukemia

The specific binding of radioiodinated rIL-2 to fresh marrow blasts from T-lineage acute lymphoblastic leukemia (ALL) patients was initially investigated. The estimated number of radioiodinated rIL-2 molecules bound per blast ranged from undetectable to 1948. In colony assays, 72% of 32 cases analyzed showed a significant proliferative response to rIL-2, which depended on PHA-stimulated lymphocyte conditioned medium activation. Colony stimulation indices correlated with the number of radioiodinated rIL-2 molecules bound per blast but not with expression of CD25/Tac Ag on fresh marrow blasts or primary colony blasts. These findings provide evidence that in T-lineage ALL functional IL-2R proteins are expressed on leukemic progenitor blasts which may be distinct from Tac Ag. We used the mAb 35.1, T101, and G3.7 to test for expression of CD2, CD5, and CD7 on fresh marrow blasts from 126 T-lineage ALL patients. CD2, CD5, and CD7 were expressed in 84%, 93%, and 99% of cases, respectively. Furthermore, colony blasts that represent the early progeny of leukemic progenitor blasts were also CD2+CD5+CD7+. Ricin conjugates of 35.1, T101, and G3.7 mAb were used as Ag-specific cytotoxic probes to test for expression of CD2, CD5, and CD7 at the level of T-lineage leukemic progenitor blasts. Each immunotoxin was able to selectively eliminate greater than 99% of leukemic progenitor blasts, providing unique and direct evidence that these cells co-express CD2, CD5, and CD7. Neither mixtures of anti-CD5 and anti-CD7 nor anti-CD2, anti-CD5, and anti-CD7 immunotoxins were more effective against blast progenitor cells than the individual immunotoxins alone, confirming that CD2, CD5, and CD7 are not expressed on non-overlapping progenitor cell subpopulations.     

Prevalence of antigen receptor variants in human T cell lines and tumors

Previously, we have shown that a human T acute lymphoblastic leukemia cell line, HPB-ALL, exhibits clonal heterogeneity within its Ag receptor, as revealed by varying reactivity patterns with a panel of anti-idiotype mAb. We now extend these findings to another human T acute lymphoblastic leukemia cell line, SUP-T13, and to two fresh human chronic lymphocytic leukemias, JE and EF. In the two cell lines, two types of Ag receptor variants could be found: those that retained a receptor molecule but lost reactivity with an anti-idiotype mAb (idiotype variants), and those which had lost surface receptor expression completely (receptor-negative variants). The idiotype variants, at least in HPB-ALL, have differentially glycosylated receptor alpha-chains from the parent. The receptor-negative cells, in HPB-ALL as well as in SUP-T13, produce cytoplasmic receptor and CD3 proteins but do not transport them to the surface. Neither idiotype nor receptor-negative variants could be detected in either of the fresh tumors of chronic lymphocytic leukemias. The limit of sensitivity in these analyses was about 0.05%. We conclude that antigen receptor variants can spontaneously occur in cell lines derived from acute lymphoblastic leukemias, but are infrequent in chronic lymphocytic leukemias in vivo, and that therapy with anti-idiotype mAb may be a viable strategy for these malignancies.     

IFN-gamma can promote tumor evasion of the immune system in vivo by down-regulating cellular levels of an endogenous tumor antigen

Although IFN-gamma has been generally thought to enhance antitumor immune responses, we found that IFN-gamma can promote tumor escape in the CT26 colon carcinoma by down-regulating the protein expression of an endogenous tumor Ag. gp70, the env product of the endogenous ecotropic murine leukemia virus, has been reported to be the immunodominant Ag of CT26. We show that IFN-gamma down-regulates intracellular and surface levels of gp70 protein resulting in a reduced lysis by CTL, which is restored by pulsing IFN-gamma-treated CT26 with the L(d)-restricted immunodominant AH1 epitope derived from gp70. To investigate the role of CT26 sensitivity to IFN-gamma in vivo, we constructed two variants of CT26, CT26.mugR and CT26.IFN, that are unresponsive to IFN-gamma or express IFN-gamma, respectively. We demonstrate using these variants that tumor responsiveness to IFN-gamma promotes a reduction in tumor immunogenicity in vivo that is correlated with an increased tumor incidence in immune mice. Analysis of the tumors from mice challenged with CT26 or CT26.mugR revealed infiltration of CD8 T cells secreting IFN-gamma. We conclude that IFN-gamma secreted by tumor-infiltrating T cells promotes tumor escape through the down-regulation of the endogenous tumor Ag gp70. These findings have impact on the design of effective antitumor vaccine strategies.     

IgM monoclonal antibody JD118 recognizes an inducible antigen target for human-complement-mediated cytotoxicity against neoplastic B cells

Cancer therapy using unconjugated monoclonal antibodies (mAb) has been limited by the lack of immune effector function of the mAb and antigenic modulation. JD118 is a cytotoxic murine IgM mAb with reactivity restricted to a subset of normal B cells, some monocytic series cells, and a large percentage of B cell hematopoietic neoplasms including acute and chronic leukemias and lymphomas. Specificity was determined on several hundred normal and neoplastic, hematopoietic and non-hematopoietic cells and tissues, as well as progenitor cells. JD118 was able to kill fresh human leukemias and lymphomas in the presence of human serum as a complement source with an LD₅₀ of 100 ng/ml. At this mAb concentration, fewer than 4% of more than 10⁵ available target sites were bound. Killing was not affected by changes in antigen expression observed during the cell cycle nor by loss of cell-surface targets via antigenic modulation. Cytotoxicity could be achieved with human serum diluted as low as 5%, suggesting that complement depletion in vivo should not limit activity. Autologous human serum could be used effectively as a complement source. The JD118 antigen target has not been identified, but it appears to be a glycoprotein. Up-regulation of antigen expression on normal B cells and chronic lymphocytic leukemia cells in vitro resulted in antigen-negative neoplasms becoming positive and thus targets for JD118 killing. The restricted expression, potent cytotoxic characteristics, and potential for up-regulation of its antigen make JD118 a possible candidate for ex vivo autologous bone marrow purging and in vivo therapeutic trials in patients with B cell neoplasms.This work was supported by ACS grants PRTF-135 and IM-551, the Michael and Ethel Cohen Fellowship Fund, and the Lucille P. Markey Trust. D. A. Scheinberg is a Lucille P. Markey Scholar Correspondence to: Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, New York 10021, USA     

Enhanced modulation of antibodies coating guinea pig leukemic cells in vitro and in vivo. The role of Fc gamma R expressing cells.

We have investigated the antigenic modulation induced by a number of antibody fragments and derivatives directed against the idiotype of the surface Ig of the L2C guinea pig B lymphoblastic leukemia, and studied the effects upon such modulation of the simultaneous presence of cells expressing Fc gamma receptors (FcR). In vitro studies confirmed previous work showing that antibody bivalency is required to induce modulation in vitro in simple systems. However, in the presence of isolated Kupffer cells, Fc-containing univalent antibodies were found to induce significant antigenic modulation, and the modulation induced by intact IgG was also found to be more rapid and extensive. Fragments that did not contain Fc regions behaved similarly in the presence or absence of Kupffer cells. Further investigations demonstrated that all three classes of human FcR can mediate modulation enhancement, and suggest that the mechanism involves indirect cross-linking of cell surface Ag via the antibody and effector cell FcR. In vivo studies showed that univalent antibody derivatives containing Fc regions did induce antigenic modulation, but that this was significantly reduced in comparison with bivalent antibodies, confirming their potential advantage for immunotherapy.     

Establishment and characterization of new B-cell precursor leukemia cell line NALM-35

A novel B-cell precursor (BCP) acute lymphoblastic leukemia (ALL) cell line, NALM-35, was established from the peripheral blood of a 40-year-old woman at diagnosis of ALL. Imunophenotyping showed BCP type III characteristics including expression of TdT, CD10, CD19, CD22, CD79a and HLA class II. T-cell and myeloid-associated antigens tested were negative except CD5 and CD28. The surrogate light chains CD179a and CD179b were positive. NALM-35 cells have the morphological appearance of lymphoblasts. Cytogenetic analysis of NALM-35 revealed an abnormal karyotype with 46, XX, add(9)(p11). Southern blot analysis of the immunoglobulin genes status of NALM-35 at 10 months after establishment showed germ line configuration of the kappa and lambda light chain genes, and rearrangement of the mu heavy chain gene. DNA fingerprinting, chromosomal analysis and immunophenotyping proved that NALM-35 was clonally derived from the primary leukemia cells. The established cell line may provide a useful model system and unprecedented opportunities for analyzing the multitude of biological aspects of normal and neoplastic B-lymphocytes and their precursors.     

Activation of dendritic cells that cross-present tumor-derived antigen licenses CD8+ CTL to cause tumor eradication

The fate of naive CD8(+) T cells is determined by the environment in which they encounter MHC class I presented peptide Ags. The manner in which tumor Ags are presented is a longstanding matter of debate. Ag presentation might be mediated by tumor cells in tumor draining lymph nodes or via cross-presentation by professional APC. Either pathway is insufficient to elicit protective antitumor immunity. We now demonstrate using a syngeneic mouse tumor model, expressing an Ag derived from the early region 1A of human adenovirus type 5, that the inadequate nature of the antitumor CTL response is not due to direct Ag presentation by the tumor cells, but results from presentation of tumor-derived Ag by nonactivated CD11c(+) APC. Although this event results in division of naive CTL in tumor draining lymph nodes, it does not establish a productive immune response. Treatment of tumor-bearing mice with dendritic cell-stimulating agonistic anti-CD40 mAb resulted in systemic efflux of CTL with robust effector function capable to eradicate established tumors. For efficacy of anti-CD40 treatment, CD40 ligation of host APC is required because adoptive transfer of CD40-proficient tumor-specific TCR transgenic CTL into CD40-deficient tumor-bearing mice did not lead to productive antitumor immunity after CD40 triggering in vivo. CpG and detoxified LPS (MPL) acted similarly as agonistic anti-CD40 mAb with respect to CD8(+) CTL efflux and tumor eradication. Together these results indicate that dendritic cells, depending on their activation state, orchestrate the outcome of CTL-mediated immunity against tumors, leading either to an ineffective immune response or potent antitumor immunity.     

Antinucleosome antibody-modified liposomes and lipid-core micelles for tumor-targeted delivery of therapeutic and diagnostic agents

Liposomes and lipid-core micelles prepared of polyethylene glycol-phosphatidylethanolamine (PEG-PE) conjugates have been modified with nucleosome-specific monoclonal antinuclear autoantibody (ANA) 2C5 (mAb 2C5) specifically recognizing a broad variety of cancer cells through the cancer cell surface-bound nucleosomes. mAb 2C5 preserves its specific properties upon the binding with the lipid-based pharmaceutical nanocarriers, and 2C5-modified immunoliposomes and immunomicelles demonstrate an enhanced binding with tumor cells both in vitro and in vivo. We have investigated the delivery of therapeutic and diagnostic agents with such tumor-targeted immunoliposomes and immunomicelles to various tumors in vivo and in vitro. Both lipid-based nanocarriers provided enhanced tumor delivery of imaging agents ((111)In) and antitumor drugs (doxorubicin and photodynamic therapy agents) to tumor cells under different experimental settings. Pharmaceutical lipid-based nanoparticular carriers modified with mAb 2C5 could represent universal systems for tumor-specific delivery of various soluble and insoluble pharmaceuticals.     

Effect of a single amino acid mutation on the activating and immunosuppressive properties of a "humanized" OKT3 monoclonal antibody.

The binding specificity of the murine OKT3 has been transferred into a human antibody framework to reduce its immunogenicity. This "humanized" anti-CD3 mAb (gOKT3-5) was previously shown to retain, in vitro, all the properties of native OKT3, including T cell activation, which has been correlated, in vivo, with the severe side effects observed in transplant recipients after the first administration of the mAb. T cell activation is thought to be triggered by the cross-linking mediated by the antibodies between T cells and Fc receptor-bearing cells. In this study, we introduced a single amino acid mutation from a leucine to a glutamic acid at position 235 in the Fc receptor binding segment of the gOKT3-5 mAb to produce Glu-235 mAb. This mutation generated a 100-fold decrease in the affinity of the antibody for the Fc receptor on U937 cells, without affecting Ag binding. In parallel, we observed a marked reduction in the T cell activation triggered by the mAb (proliferation, cell surface expression of early activation markers including Leu 23 and IL-2R, and release of TNF-alpha, IFN-gamma, and granulocyte macrophage-CSF). In contrast, the mutated mAb retained suppressive properties similar to the gOKT3-5 mAb, as assessed by significant modulation of the T cell receptor complex and suppression of Ag-specific CTL activity. We conclude that this anti-CD3 mAb bearing a single amino acid mutation in its Fc portion retains important immunosuppressive properties, while exhibiting significantly less T cell activation than OKT3 in vitro. This drug might achieve potent immunosuppression while minimizing acute toxicity in vivo and thus be useful in transplantation as well as in autoimmune diseases.     

The role of ricin B chain in the intracellular trafficking of anti-CD5 immunotoxins

The mAb anti-CD5 was linked to purified ricin A chain (RTA) or intact ricin (Rc) containing B chain to determine the role of ricin B chain in the intracellular trafficking of anti-CD5 immunotoxins (IT). IT were radiolabeled with iodine-125 and then studied for their subcellular compartmentalization in an acute lymphoblastic leukemia T cell line, CEM. Ricin A chain IT was not as toxic to CEM cells as Rc-IT in protein synthesis inhibition assays. This difference was not attributed to differential binding or modulation of the CD5 determinant from the cell surface as measured by FACS analysis. However, we found a relationship between the toxicity of anti-CD5-Rc and anti-CD5-RTA and their ability to traffic to CEM lysosomes. Kinetic analysis of the transfer of radioimmunotoxin to the lysosomes showed that anti-CD5-Rc was trafficked significantly more slowly than anti-CD5-RTA, perhaps due to an extended period of time in the Golgi compartment. The possibility of a Golgi interaction was tested by adding monensin, a carboxylic ionophore that interrupts trafficking through the Golgi, to cells treated with anti-CD5-RTA. The addition of monensin caused anti-CD5-RTA to traffic in a manner identical to anti-CD5-Rc. We conclude that 1) B chain slows trafficking of anti-CD5-Rc to the lysosomes; 2) the rate-limiting step in the toxicity difference between anti-CD5-Rc and anti-CD5-RTA is the rate of transfer to the lysosomes; and 3) trafficking through the Golgi may be important for anti-CD5-IT toxicity.     

Antigen distribution drives programmed antitumor CD8 cell migration and determines its efficiency

Understanding both the role of tumor Ag in CD8 cell differentiation and the reasons that CD8 cells may work inefficiently is crucial for therapeutic approaches in cancer. We studied OT-1 CD8 cell responses in vivo in a differential Ag-distribution model that used EG-7, the EL-4 thymoma transfected with OVA. On their initial Ag encounter, OT-1 CD8 cells underwent programmed expansion in the lymph nodes, where they acquired the ability to migrate to the encapsulated tumor site after > or =4 divisions, without continuous antigenic stimulation. This short antigenic stimulation was sufficient to induce the migration differentiation program, which included modulation of chemokine receptor mRNA expression and down-regulation of CD62L. Moreover, Ag quantity determined the behavior of the OT-1 CD8 cells, including their effector functions and sensitivity to apoptosis. Thus, the initial Ag encounter drives the programmed cell migration potencies, but neither effector functions nor cell death can occur without continuous TCR triggering.     

Activated T cells and monocytes have characteristic patterns of class II antigen expression

The expression of human histocompatibility class II Ag was measured on activated T cells and monocytes by quantitative mAb binding in direct two-color immunofluorescence. Monocytes activated by IFN-gamma bound an average of 2 x 10(6) DR-specific mAb, 3 x 10(5) DQ-specific mAb, and 7 x 10(5) DP-specific mAb per cell. For T cells activated by anti-CD3, a subpopulation bound 1 x 10(5) DR-specific mAb, 5 x 10(4) DQ-specific mAb and 5 x 10(4) DP-specific mAb per cell. These measurements were obtained after establishing a base line of class II Ag expression on resting B cells and monocytes. Resting B cells and those monocytes that were positive for class II Ag bound identical amounts of mAb; 3 x 10(4) DR-specific mAb, 3 x 10(3) DQ-specific mAb and 2 x 10(4) DP-specific mAb. However, most resting monocytes (75%) expressed only DR Ag. In the process of studying the expression of class II Ag on T cells, it was necessary to define and analyze the activated T cell state. Cell cultures activated with 0.3 ng/ml anti-CD3 had the highest expression of class II Ag on T cells, whereas those activated with 3.0 ng/ml anti-CD3 had the highest expression of IL-2R on T cells. Addition of IL-2 had no further effect on DR Ag expression on T cells but did up-regulate IL-2R expression. Reducing the initial monocyte concentration before activating T cells increased class II Ag expression on T cells without affecting IL-2R expression. The results obtained on T cell activation suggest that perhaps a lymphokine may be made by CD3-activated T cells which induces class II Ag expression on T cells.     

Hairy cell leukemia-associated antigen (HC2) is an activation antigen of several hemopoietic cell lineages, inducible on monocytes by IFN-gamma

The HC2 Ag is defined by a mAb raised against leukemic B lymphocytes from a patient with hairy cell leukemia (HCL). This 60 to 70-kDa Ag was immunoprecipitated from EBV-transformed B lymphoblastoid cell lines, from HCL-B cells, from the HUT-102 T cell line infected with HTLVI, and from activated monocytes. A binding assay with radioiodinated Fab' anti-HC2 confirmed this cellular distribution of the Ag and demonstrated 500 to 3000 binding sites on resting T cells, 300 to 11,000 binding sites on non-T cells, less than 3000 binding sites on chronic lymphocytic leukemia B cells, and 29,000 to 223,000 binding sites on HCL-B cells. PMA plus anti-CD3 up-regulated HC2 expression on T cells and IFN-gamma up-regulated expression on monocytes. On B cells, EBV transformation may result in HC2 expression, and antibody to HC2 has been found to inhibit B cell differentiation and proliferation. The combined results suggest an important role for the HC2 membrane-associated Ag on cells responsible for the immune response.     

Mouse complement receptor-related gene y/p65-neutralized tumor vaccine induces antitumor activity in vivo

Two mouse tumor cell lines, Meth A (BALB/c mouse-derived fibrosarcoma) and MM46 (C3H/He mouse-derived mammary tumor), were shown to express high levels of complement receptor-related gene y/p65 (Crry/p65), a membrane-bound complement-regulatory protein. Inhibiting the complement-regulatory activity of Crry/p65 with mAb 5D5 induced high levels of C3 deposition on in vivo tumor-derived Meth A and MM46 cells. To determine the effect of Crry/p65 blockade and increased C3 deposition on in vivo tumor growth, Meth A and MM46 cells were treated with 5D5 mAb and injected into BALB/c and C3H/He mice, respectively. Pretreating MM46 cells with 5D5 mAb significantly suppressed their tumorigenicity when injected s.c. Pretreatment with 5D5 mAb had a modest effect on Meth A s.c. tumor growth. Because complement is involved in the induction of an immune response, we investigated the effect of Crry/p65 blockade and increased C3 deposition on the immunogenicity of the tumor cells in a vaccination protocol. Vaccination of mice with irradiated Meth A cells pretreated with 5D5 mAb protected mice from subsequent challenge. In contrast, vaccination with irradiated Meth A cells without pretreatment was not protective. Survival was correlated with a high titer IgM response and specific CTL activity. These data demonstrate that the functional inhibition of Crry/p65 on tumor cells affects tumor growth and immunogenicity, and that the complement deposition resulting from this inhibition can act in concert with antitumor effector mechanisms to elicit potent antitumor immunity in vivo.     

Regression of extensive pulmonary metastases in mice by adoptive transfer of antigen-specific CD8(+) CTL reactive against tumor cells expressing a naturally occurring rejection epitope

In this study, we developed a mouse model of adoptive immunotherapy reflecting immune recognition of syngeneic tumor cells naturally expressing an endogenous rejection Ag. Specifically, in a pulmonary metastases model, we examined the potency and maintenance of an antitumor CD8(+) CTL response in vivo, as well as its effectiveness against an "extensive" tumor burden. The approach taken was to first generate tumor-specific CTL from mice challenged with the CMS4 sarcoma coadministered with anti-CTLA4 mAb, which has been shown to facilitate the induction of Ag-specific T cell responses in vivo. An H-2L(d)-restricted nonamer peptide, derived from an endogenous murine leukemia provirus was identified as a CMS4-reactive CTL epitope based upon the following: CTL cross-recognition of another syngeneic tumor cell line (CT26 colon carcinoma) previously characterized to express that gene product; sensitization of Ag-negative lymphoblasts or P815 targets with the peptide; and by cold target inhibition assays. In vivo, the adoptive transfer of CMS4-reactive CTL (> or =1 x 10(6)) resulted in nearly the complete regression of 3-day established lung metastases. Furthermore, mice that rejected CMS4 following a single adoptive transfer of CTL displayed antitumor activity to a rechallenge 45 days later, not only in the lung, but also at a s.c. distal site. Lastly, the adoptive transfer of CTL to mice harboring extensive pulmonary metastases (> 150 nodules) led to a substantial reduction in tumor burden. Overall, these data suggest that the adoptive transfer of tumor-specific CTL may have therapeutic potential for malignancies that proliferate in or metastasize to the lung.     

AMG-232, a New Inhibitor of MDM-2, Enhance Doxorubicin Efficiency in Pre-B Acute Lymphoblastic Leukemia Cells

Background:Doxorubicin (DOX)-induced cardiotoxicity appears to be a growing concern for extensive use in acute lymphoblastic leukemia (ALL). The new combination treatment strategies, therefore might be an effective way of decreasing its side effects as well as improving efficacy. AMG232 (KRT-232) is a potential MDM-2 inhibitor, increasing available p53 through disturbing p53-MDM-2 interaction. In this study, we examined the effects of AMG232 on DOX-induced apoptosis of NALM-6 cells.Methods:The anti-leukemic effects of Doxorubicin on NALM-6 cells, either alone or in combination with AMG232, were confirmed by MTT assay, Annexin/PI apoptosis assay, and cell cycle analysis. Expression of apoptosis and autophagy-related genes were further evaluated by Real time-PCR method. To investigate the effect of AMG232 on NALM-6 cells, the activation of p53, p21, MDM-2, cleaved Caspase-3 proteins was evaluated using western blot analysis.Results:The results showed that AMG232 inhibition of MDM-2 enhances Doxorubicin-induced apoptosis in NALM-6 cells through caspase-3 activation in a time and dose-dependent manner. Furthermore, co-treatment of AMG232 with Doxorubicin hampered the transition of NALM-6 cells from G1 phase through increasing p21 protein. In addition, this combination treatment led to enhanced expression of apoptosis and autophagy-related genes in ALL cell lines.Conclusion:The results declared that AMG232 as an MDM-2 inhibitor could be an effective approach to enhance antitumor effects of Doxorubicin on NALM-6 cells as well as an effective future treatment for ALL patients.Key Words: Acute Lymphoblastic Leukemia, AMG 232, Autophagy, Doxorubicin, p53     

Influence of avidity and idiotope recognition on the modulation of surface immunoglobulin on malignant human B cells by rat monoclonal anti-idiotype antibodies

Immunoglobulin (Ig) was obtained from the tumor cells of patients with B cell malignancies by somatic cell hybridization to mouse-human heteromyeloma cells. The human Ig secreted by one of these hybridomas was used as an immunogen for the production of rat monoclonal antibodies (mAb). A panel of mAb specific for the idiotype (Id) was produced and characterized. Competitive binding studies that made use of [Se]-labeled anti-Id mAb (MAID) demonstrated several distinct yet topographically related Id on the Id-bearing Ig. These antibodies were shown to have avidities ranging from 0.38 to 45.3 X 10(8) l/mol. Additional studies demonstrated varying degrees of antigenic modulation of surface Id in vitro by MAID. The degree of modulation correlates with antibody avidity.     

An anti-double-stranded DNA monoclonal antibody induced by tumor cell-derived DNA inhibits the growth of tumor in vitro and in vivo via triggering apoptosis

Serological presence of anti-double-stranded DNA (anti-dsDNA) antibodies is a common phenomenon in cancer patients. Some patients with relatively high levels of anti-dsDNA antibodies may have a better prognosis, indicating the potential antitumor roles of anti-dsDNA antibodies. To delineate the role and mechanisms of anti-dsDNA antibodies in delaying tumor development, here we prepared a panel of anti-dsDNA monoclonal antibodies (mAbs) and assessed their antitumor effects both in vitro and in vivo. After immunization of BALB/c mice with DNA from SP2/0 tumor cells, 12 anti-dsDNA mAbs were obtained. Among these mAbs, mAb 2G8 exhibited the strongest cytotoxicity to Wehi164 cells in vitro and significantly inhibited the growth of tumor in vivo. This mAb 2G8-mediated antitumor effect was mainly exerted by triggering apoptosis, as evidenced by Annexin V staining and DNA fragmentation. Further, the expression of antiapoptotic genes Bcl-2 and Bcl-xL was downregulated while that of pro-apoptotic gene Bax was upregulated, suggesting the involvement of mitochondrial apoptotic pathway. Taken together, dsDNA-specific mAb 2G8 revealed promising tumor-suppressive activity by inducing apoptosis, which provides a possible new strategy for the development of tumor intervening methods.