Fas-induced in vivo apoptosis in bone marrow: anti-Fas mAb-induced elimination and successive proliferation of Fas-expressing cells especially those of myeloid lineage

Highly frequent anti-idiotype antibody in cynomolgus monkeys developed against mouse-derived regions of anti-Fas antibody humanized by complementarity determining region grafting

BACKGROUND AND PURPOSE

We investigated the immunogenicity of a humanized anti-human Fas monoclonal antibody, R-125224, in cynomolgus monkeys to estimate its efficacy, as well as its toxicity in clinical situations.

EXPERIMENTAL APPROACH

R-125224 was intravenously administered to cynomolgus monkeys at single doses of 0.4, 1.2, 6 and 30 mg kg(-1), and the plasma concentrations of R-125224 and anti-R-125224 antibody (ARA) were measured. We conducted a competitive enzyme-linked immunosorbent assay to determine which part of R-125224 was recognized by ARA. We also examined the retention of radioactivity in mononuclear cells and granulocytes after the injection of [(125)I]-R-125224 to a collagen-induced arthritis monkey model.

KEY RESULTS

After i.v. administration of R-125224, the elimination of the plasma R-125224 concentrations was accelerated at around 10 days post-dose, and 10 of 12 monkeys were ARA positive. From an epitope analysis of ARA, the ARA produced in monkeys recognized the mouse-derived regions located in complementarity determining regions, but could not recognize the human IgG. After the injection of [(125)I]-R-125224 to a collagen-induced arthritis monkey model, a significantly longer retention of the radioactivity in mononuclear cells compared to granulocytes was observed.

CONCLUSIONS AND IMPLICATIONS

In monkeys, the development of antibodies against R-125224 is rapid and highly frequent. Our hypothesis is that this highly frequent development of ARA might be due to the binding of R-125224 to immune cells, and its circulation in monkey blood might contribute to an increase in its chances of being recognized as an immunogen.

Tissue distribution of humanized anti-human Fas monoclonal antibody (R-125224) based on fas antigen–antibody reaction in collagen-induced arthritis monkeys

R-125224 is a novel humanized anti-human Fas monoclonal antibody prepared from HFE7A, which is a monoclonal mouse IgG anti-Fas antibody, by grafting the mouse complementarity-determining regions to human IgG, presently being developed as a drug for treatment of rheumatoid arthritis. In the present study, we investigated the tissue distribution of radioactivity in cynomolgus monkeys with collagen-induced arthritis at the arm joint (CIA monkeys) after intravenous administration of (125)I-labeled R-125224 ((125)I-R-125224). At 168 h after administration, we observed a high radioactivity in the bone marrow, thymus, lungs, liver, adrenals, spleen, ovaries, axillary lymph node and mesenteric lymph node compared to the radioactivity in the plasma. These tissues and organs in human are reported to express Fas antigen, strongly suggesting a specific binding of (125)I-R-125224 to Fas antigen in cynomolgus monkeys. Semi-micro autoradioluminograms of arm joint showed that radioactivity is detected in pharmacological site, such as the bone marrow and articular cavity at 168 h. The kinetics in binding of R-125224 to activated monkey lymphocytes and hepatocytes was also investigated. K(d) values of activated lymphocytes and hepatocytes were 1.51+/-0.08 and 0.60+/-0.11 nM, respectively, which were similar to those values in human lymphocytes and hepatocytes, demonstrating that R-125224 cross-reacts with the monkey Fas antigen.

In SCID mice with transplanted joint tissues from rheumatism patients, a model mice of human rheumatoid arthritis, anti-human fas antibody (R-125224) distributes specifically to human synovium

PURPOSE

We investigated the tissue distribution of a humanized anti-human Fas monoclonal antibody, R-125224, in SCID mice transplanted with synovial tissues from patients with rheumatoid arthritis (SCID-HuRAg mice). The binding kinetics of R-125224 was also determined, using isolated human synovial cells.

MATERIALS AND METHODS

Tissue distribution was assessed at 1, 24 and 168 h after intravenous administration of (125)I-R-125224 to SCID-HuRAg mice (0.4 mg/kg). The in vitro binding of (125)I-R-125224 to isolated human synovial cells was investigated.

RESULTS

After intravenous administration of (125)I-R-125224 to SCID-HuRAg mice, the radioactivity distributed to various tissues at 1 h. Thereafter, the radioactivity in the tissues gradually decreased except for the transplanted synovial tissues, in which the radioactivity increased in a time-dependent manner, and at 168 h, the tissue/plasma concentration ratio was about 1. The in vitro binding affinity of (125)I-R-125224 to human synovial cells was high with a dissociation constant of 1.32 +/- 0.62 nM and the binding was inhibited by non-labeled R-125224 in a concentration-dependent manner.

CONCLUSION

R-125224, a candidate compound for treating rheumatoid arthritis, specifically distributed to the pharmacological target site, human synovium transplanted in SCID mice, with high affinity.

Tumor necrosis factor receptor regulation of bone marrow cell apoptosis during endotoxin-induced systemic inflammation

Although inflammation-induced release of cells from the bone marrow (BM) is well established, less is known regarding inflammation-induced modulation of bone marrow cell numbers by apoptosis. The purpose of this study is to assess apoptosis of BM immature and mature myeloid cells and peripheral granulocytes, and to elucidate the role(s) of TNFR-p55 and TNFR-p75 as modulators of apoptosis in these cellular compartments in a mouse model of endotoxin-induced systemic inflammation. Gene knockout (p55(-/-), p75(-/-), and p55(-/-)/p75(-/-)), or wild-type (WT) mice were injected i.p. with saline (Sal) or LPS (4 microg/g) followed by collection of BM cells and peripheral blood after 24 h. Apoptosis was assessed by propidium iodide staining using two-color flow cytometry with differentiated granulocyte-specific Gr1-fluorescein isothiocyanate. Repeated-measures analysis of variance and Neuman-Keuls post hoc test were used for statistical analyses. After i.p. LPS, apoptosis was induced to the higher level in BM Gr1(-) cells than in BM Gr1(+) cells and was not induced in peripheral Gr1(+) cells. Depletion of cell numbers in both BM Gr1(-) and Gr1(+) subpopulations after LPS treatment was consistent with increase of the apoptotic cell percentages in the groups. LPS-induced apoptosis was significantly lower in Gr1(-) cells from the -p55(-/-)/LPS and p55(-/-)/p75(-/-)/LPS mice but not from p75(-/-)/LPS mice as compared with WT/LPS mice, whereas there was no difference in apoptosis of BM Gr1(+) and peripheral Gr1(+) cells among WT groups and knockout groups. Thus, apoptosis of myeloid cells during endotoxemia is minimized because these cells undergo differentiation, which in turn may be because of the attenuation of the proapoptotic effect of TNFR-p55 shown herein to occur with myeloid differentiation. In contrast, TNFR-p75 seems to play a minimal role in apoptosis induction in Gr1(-) myeloid cells during endotoxemia. One explanation for a decrease in BM cell numbers during endotoxemia may be via induction of apoptosis in immature myeloid cells.

Bone marrow cell transfer of autoimmune diseases in a MRL strain of mice with a deficit in functional Fas ligand: dissociation of arteritis from glomerulonephritis

MRL/MpTn-gld/gld (MRL/gld) mice, which are deficient in a functional Fas ligand (FasL), spontaneously develop autoimmune diseases involving both lethal glomerulonephritis and systemic arteritis, while MRL/Mp-+/+ (MRL/+) and C3H/HeJ-gld/gld (C3H/gld) do not. To determine the cells responsible for the development of glomerulonephritis and arteritis, we transferred bone marrow cells from MRL/gld mice to undiseased MHC-compatible gld/gld or +/+ mice. In bone marrow irradiation chimeras, MRL/gld bone marrow cells were transferred to lethally irradiated MRL/+ or C3H/HeJ-+/+ (C3H/+) mice, and both recipients developed glomerulonephritis associated with hypergammaglobulinemia without causing graft-versus-host (GVH)-like diseases. However, a striking difference between them was that MRL/+ recipients developed arteritis, but C3H/+ recipients did not. In bone marrow mixed chimeras formed by transferring MRL/gld bone marrow cells to unirradiated mice, the MRL/gld bone marrow cells induced glomerulonephritis in C3H/gld mice, but not in C3H/+ and MRL/+ mice. These results indicate that bone marrow cells from MRL/gld mice can cause glomerulonephritis in mice, even in those with a C3H background, possibly if they survive longer by escaping from Fas-mediated apoptosis, while the development of arteritis requires the MRL genetic background in the recipients. This is the first report of the transfer of arteritis in lupus mice to undiseased recipients.

Involvement of death receptor Fas in germ cell degeneration in gonads of Kit-deficient Wv/Wv mutant mice

Kit and its ligand stem cell factor (SCF) play a fundamental role in hematopoiesis, melanogenesis and gametogenesis. Homozygous W(v) mutant mice with a mutation in kit show abnormalities in these cell lineages. Fas is a member of the death receptor family inducing apoptosis. In this study, we generated double-mutant mice (W(v)/W(v):Fas(-/-)) and analyzed histologically their reproductive organs. In testes and ovaries of the double-mutant mice, testicular germ cells and oocytes were detected, respectively, whereas the same-aged W(v)/W(v) mice contained neither cells. In addition, inhibition of Kit signals by administration of anti-Kit mAb, which induces degeneration of testicular germ cells in vivo in wild-type mice, did not cause degeneration in Fas-deficient mice. In testicular germ cells of W(v)/W(v) mutant mice, an increase of Fas expression was observed in spermatogonia. Further, in vitro treatment with SCF was shown to downregulate Fas on fibroblasts expressing exogenous Kit through activation of PI3-kinase/Akt. All the results clearly indicate that Fas-mediated apoptosis is involved in germ cell degeneration accompanied by defects in Kit-mediated signals, and Kit signaling negatively regulates Fas-mediated apoptosis in vivo.

Differentiation, apoptosis, and function of human immature and mature myeloid cells: intracellular signaling mechanism

Human myeloid cells include hematopoietic cells at various stages of differentiation, from immature myeloid cells to mature phagocytes. Normal immature myeloid cells undergo differentiation concomitantly with proliferation in response to hematopoietic growth factors, and terminally differentiated cells, ie, mature phagocytes, exert their effector functions and then die a natural death via apoptosis. However, leukemic myeloid cells are induced to differentiate with growth suppression by several inducers, such as retinoic acid. This review describes differentiation, apoptosis, and functionality of human myeloid cells. mainly focusing on the intracellular signaling mechanism. The signal transduction system for these biological events of the life cycle of myeloid cells has recently been studied, and several characteristics have been elucidated. First, the signaling pathway for myeloid differentiation is mainly focused in the mitogen-activated protein kinases, such as extracellular signal-regulated kinase and p38, and transcriptional factors such as the signal transducers and activators of transcription PU.1 and CCAAT enhancer binding protein. Second, the signaling mechanism for myeloid cell apoptosis is fundamentally identical to that found in other cells. Caspases, caspase-activated DNase, and mitochondrial molecules such as apoptosis-inducing factor have been reported to be important, and mitogen-activated protein kinases such as p38 appear to be less important. Finally, p38 and phosphatidylinositol 3-kinase play critical roles in the signaling cascade for functional activation of mature phagocytes. The reasons why the same signaling molecules play distinct roles according to the differentiation stage and biological event await future clarification.

Natural killer cell-dependent apoptosis of peripheral murine hematopoietic progenitor cells in response to Fas cross-linking: involvement of tumor necrosis factor-alpha

Recently, a marked extramedullary myelopoiesis in Fas/CD95- or FasL/CD95L-deficient mice has been reported. In the present in vitro study, the mechanisms underlying Fas-induced apoptosis of normal peripheral colony-forming unit-C (CFU-C) progenitors in the spleen were analyzed. Surprisingly, it was found that clonogenic progenitors were protected from gammaIFN plus Fas-induced programmed cell death when Lin(+) cells were removed from cultured splenocytes. The cells that rendered CFU-C sensitive to the activation of the Fas pathway did not belong to the T or the myelocytic-monocytic lineage but comprised a non-B-cell subset expressing the activation marker B220. Among CD19(-) B220(+) splenocytes, nearly half were natural killer (NK) 1.1(+) cells whose in vivo depletion or deficiency in RAG2-gamma(c)(-/-) mice abrogated the effect of Fas cross-linking. NK cells exerted their accessory function, at least in part, through tumor necrosis factor-alpha (TNF-alpha), which they readily produced during pretreatment with the anti-Fas/CD95 monoclonal antibody and IFN-gamma and whose addition could compensate for the loss of sensitivity. In conclusion, this study provides evidence that peripheral clonogenic progenitors are not directly responsive to Fas cross-linking, even in the presence of IFN-gamma, but require NK cells as a source of TNF-alpha to make them susceptible to this death pathway.

A novel murine anti-human Fas mAb which mitigates lymphadenopathy without hepatotoxicity

Defects in Fas-mediated apoptosis are implicated in autoimmune diseases including rheumatoid arthritis (RA). Although induction of Fas-mediated apoptosis could have therapeutic effects on these diseases, it might cause deleterious effects in liver as Fas ligand or an agonistic anti-murine Fas antibody Jo2 causes severe hepatic injury in mice. We report here on the interesting characteristics of the newly obtained anti-Fas mAb, HFE7A, which cross-reacts with the Fas molecules of various species ranging from human to mouse and mitigates autoimmune symptoms without hepatotoxicity in mice. The administration of HFE7A to mice induced apoptosis in the thymocytes, although administration of HFE7A to mice or to marmosets did not induce any sign of hepatitis. The effect of HFE7A on liver is different from that of anti-murine Fas antibody Jo2, which causes acute and lethal hepatic injury to mice. Administration of HFE7A reduced lymphadenopathy and abnormal T cells in MRL-gld/gld mice. HFE7A induced apoptosis in synovial cells prepared from RA patients. Surprisingly, HFE7A protected mice from fulminant hepatitis induced by Jo2. Therefore, HFE7A is a potential therapeutic antibody not only for autoimmune diseases including RA but also for fulminant hepatitis.