Transplantable myeloproliferative disease induced in mice by an interleukin 6 retrovirus

Enhanced immunogenicity of B cell lymphoma genetically engineered to express both B7-1 and interleukin-12

The A20 murine B cell lymphoma was transfected with B7-1 and subsequently these variants and vector control variants were retrovirally infected to express murine interleukin-12 (mIL-12). In vitro data showed that the B7-1 variants enhanced secretion of IL-2 and IL-4 by allogeneic T cells in mixed lymphocyte tumor cultures. While IL-12 variants stimulated IFN-gamma, variants expressing both B7-1 and IL-12 stimulated IFN-gamma, IL-2, and IL-4 secretion. Tumorigenicity experiments showed that whereas B7-1 delayed tumor onset, only the mIL-12 variants with or without B7-1 were completely rejected in syngeneic hosts. In addition, tumor-free mice were protected against subsequent challenge with the parental unmodified cells and had enhanced cytotoxic T lymphocyte (CTL) lysis activity. Results from minimal disease mixing experiments demonstrated that only the A20/B7-1/mIL-12 variant was able to reject A20 unmodified cells inoculated at the same site, whereas prolonged survival was observed when the A20 parental cells were inoculated at different sites. Depletion studies and injections into nu-/nu- mice demonstrated that both CD4+ and CD8+ T cells may mediate immunity. These data suggest that vaccinations with tumor cells genetically modified to express both B7-1 and IL-12 may alter cytokine profiles and generate CTL activity and, thus, the mechanisms of enhanced antitumor immunity may be multifactorial.

PLAB, a novel placental bone morphogenetic protein

Bone morphogenetic proteins (BMP) constitute a sub-group of the large transforming growth factor-beta (TGF-beta) family. They play important roles in the embryonic development of multiple structures and in adult bone modeling. We have recently isolated a novel member of the BMP family from placenta, termed PLAB. PLAB is expressed highly in placenta, but can be found upon stringent analysis in low levels in most other tissues. At the amino acid level, PLAB is most closely related to BMP-8/OP-2, another member of the BMP family. Like TGF-beta, PLAB inhibits the proliferation of primitive hematopoietic progenitors. The high expression of PLAB by placenta raises the possibility that it may be a mediator of placental control of embryonic development.

Chronic Expression of Murine flt3 Ligand in Mice Results in Increased Circulating White Blood Cell Levels and Abnormal Cellular Infiltrates Associated With Splenic Fibrosis

The effect of chronic expression of flt3 ligand (FL) on in vivo hematopoiesis was studied. Retroviral vector-mediated gene transfer was used in a mouse model of bone marrow transplantation to enforce expression of mouse FL cDNA in hematopoietic tissues. As early as 2 weeks posttransplantation, peripheral blood white blood cell counts in FL-overexpressing recipients were significantly elevated compared with controls. With the exception of eosinophils, all nucleated cell lineages studied were similarly affected in these animals. Experimental animals also exhibited severe anemia and progressive loss of marrow-derived erythropoiesis. All of the FL-overexpressing animals, but none of the controls, died between 10 and 13 weeks posttransplantation. Upon histological examination, severe splenomegaly was noted, with progressive fibrosis and infiltration by abnormal lymphoreticular cells. Abnormal cell infiltration also occurred in other organ systems, including bone marrow and liver. In situ immunocytochemistry on liver sections showed that the cellular infiltrate was CD3+/NLDC145+/CD11c+, but B220− and F4/80−, suggestive of a mixed infiltrate of dendritic cells and activated T lymphocytes. Infiltration of splenic blood vessel perivascular spaces resulted in vascular compression and eventual occlusion, leading to splenic necrosis consistent with infarction. These results show that FL can affect both myeloid and lymphoid cell lineages in vivo and further demonstrate the potential toxicity of in vivo treatment with FL.

Chronic Expression of Murine flt3 Ligand in Mice Results in Increased Circulating White Blood Cell Levels and Abnormal Cellular Infiltrates Associated With Splenic Fibrosis

The effect of chronic expression of flt3 ligand (FL) on in vivo hematopoiesis was studied. Retroviral vector-mediated gene transfer was used in a mouse model of bone marrow transplantation to enforce expression of mouse FL cDNA in hematopoietic tissues. As early as 2 weeks posttransplantation, peripheral blood white blood cell counts in FL-overexpressing recipients were significantly elevated compared with controls. With the exception of eosinophils, all nucleated cell lineages studied were similarly affected in these animals. Experimental animals also exhibited severe anemia and progressive loss of marrow-derived erythropoiesis. All of the FL-overexpressing animals, but none of the controls, died between 10 and 13 weeks posttransplantation. Upon histological examination, severe splenomegaly was noted, with progressive fibrosis and infiltration by abnormal lymphoreticular cells. Abnormal cell infiltration also occurred in other organ systems, including bone marrow and liver. In situ immunocytochemistry on liver sections showed that the cellular infiltrate was CD3+/NLDC145+/CD11c+, but B220− and F4/80−, suggestive of a mixed infiltrate of dendritic cells and activated T lymphocytes. Infiltration of splenic blood vessel perivascular spaces resulted in vascular compression and eventual occlusion, leading to splenic necrosis consistent with infarction. These results show that FL can affect both myeloid and lymphoid cell lineages in vivo and further demonstrate the potential toxicity of in vivo treatment with FL.

Selective block in erythropoietin-induced differentiation of growth factor-independent retrovirally-infected TF-1 cells

The erythroleukaemic cell line TF-1, infected with either the pBabe neo retrovirus or the retrovirus bearing the human erythropoietin (hEpo) gene, developed three growth factor-independent clones. Erythropoietin (Epo), interleukin-3 (IL-3) and granulocyte-macrophage colony stimulating factor (GM-CSF) accelerated the proliferation of these clones. Autonomous growth of the clones was independent of Epo because it was not altered by Epo anti-sense oligonucleotides, nor was Epo detectable in culture supernatants. Cells from the mutant clones could not be induced by Epo to express glycophorin A and haemoglobin synthesis was markedly reduced. Haemin reversed the block in Epo-induced haemoglobin synthesis. Acquisition of growth factor-independence appears to be linked with the selective loss of differentiation capacity. These cells may provide a useful model for the study of the mechanisms involved in leukaemic transformation.

Isolation and analysis of different subpopulations of normal human breast epithelial cells after their infection with a retroviral vector encoding a cell surface marker

The use of gene transfer procedures has greatly facilitated the investigation of cell lineage relationships and other developmental processes in a variety of primary tissues. In this report we described the infection and selection of primary human breast epithelial cells using retroviral vectors (Jzen-HSA-NEO and MSCV-HSA.NEO) containing the complete 228 bp coding sequence of a murine cell surface marker (Heat Stable Antigen, HSA) as well as the neomycin resistance (neo(r)) gene. Expression of the transduced HSA gene was detectable using either flow cytometry or immunohistochemistry after staining cells with an anti-murine HSA-specific antibody (M1/69). Expression of the transduced neo(r) gene conferred resistance to G418. In initial experiments with the MCF-7 breast cancer cell line, continued expression of both markers was demonstrated in a high proportion of cells for at least 4 weeks after their infection by positive M1/69 staining of cells that had been selected by prior incubation in G418. Evidence of gene transfer to early stage (< 9 days old) primary cultures of normal human breast epithelial cells (15 experiments with cells from 12 normal individuals) was also obtained using an infection protocol in which these calls were exposed to helper-free viral supernatants (2 incubations, 4 to 6 hr each) after being subcultured for 12 to 18 hr to increase their rate of proliferation. The presence of 5-50% (mean = 26%) HSA+ cells was demonstrated in these experiments within 5 days after their infection and the HSA+ populations included both myoepithelial and luminal phenotypes. The transduced (HSA+) cells within both of these subpopulations could also be separately isolated by FACS and subcultured. These results should provide an important starting point for future studies of genetically modified or marked primary human breast epithelial cell populations.

Overexpression of HOXA10 in murine hematopoietic cells perturbs both myeloid and lymphoid differentiation and leads to acute myeloid leukemia

Multiple members of the A, B, and C clusters of Hox genes are expressed in hematopoietic cells. Several of these Hox genes have been found to display distinctive expression patterns, with genes located at the 3' side of the clusters being expressed at their highest levels in the most primitive subpopulation of human CD34+ bone marrow cells and genes located at the 5' end having a broader range of expression, with downregulation at later stages of hematopoietic differentiation. To explore if these patterns reflect different functional activities, we have retrovirally engineered the overexpression of a 5'-located gene, HOXA10, in murine bone marrow cells and demonstrate effects strikingly different from those induced by overexpression of a 3'-located gene, HOXB4. In contrast to HOXB4, which causes selective expansion of primitive hematopoietic cells without altering their differentiation, overexpression of HOXA10 profoundly perturbed myeloid and B-lymphoid differentiation. The bone marrow of mice reconstituted with HOXA10-transduced bone marrow cells contained in high frequency a unique progenitor cell with megakaryocytic colony-forming ability and was virtually devoid of unilineage macrophage and pre-B-lymphoid progenitor cells derived from the transduced cells. Moreover, and again in contrast to HOXB4, a significant proportion of HOXA10 mice developed a transplantable acute myeloid leukemia with a latency of 19 to 50 weeks. These results thus add to recognition of Hox genes as important regulators of hematopoiesis and provide important new evidence of Hox gene-specific functions that may correlate with their normal expression pattern.

Immunodeficiency and chronic myelogenous leukemia-like syndrome in mice with a targeted mutation of the ICSBP gene

Interferon consensus sequence binding protein (ICSBP) is a transcription factor of the interferon (IFN) regulatory factor (IRF) family. Mice with a null mutation of ICSBP exhibit two prominent phenotypes related to previously described activities of the IRF family. The first is enhanced susceptibility to virus infections associated with impaired production of IFN(gamma). The second is deregulated hematopoiesis in both ICSBP-/- and ICSBP+/- mice that manifests as a syndrome similar to human chronic myelogenous leukemia. The chronic period of the disease progresses to a fatal blast crisis characterized by a clonal expansion of undifferentiated cells. Normal mice injected with cells from mice in blast crisis developed acute leukemia within 6 weeks of transfer. These results suggest a novel role for ICSBP in regulating the proliferation and differentiation of hematopoietic progenitor cells.

Thrombopoietic potential and serial repopulating ability of murine hematopoietic stem cells constitutively expressing interleukin 11

Based on transplantation studies with bone marrow cultured under various conditions, a role of interleukin 11 (IL-11) in the self-renewal and/or the differentiation commitment of hematopoietic stem cells has been indicated. To better evaluate the in vivo effects of IL-11 on stem/progenitor cell biology, lethally irradiated mice were serially transplanted with bone marrow cells transduced with a defective retrovirus, termed MSCV-mIL-11, carrying the murine IL-11 (mIL-11) cDNA and the bacterial neomycin phosphotransferase (neo) gene. High serum levels (i.e., > 1 ng/ml) of mIL-11 in all (20/20) primary and 86% (12/14) of secondary long-term reconstituted mice, as well as 86% (12/14) of tertiary recipients examined at 6 weeks posttransplant, demonstrated persistence of vector expression subsequent to transduction of bone marrow precursors functionally definable as totipotent hematopoietic stem cells. In agreement with results obtained with human IL-11 in other myeloablation models, ectopic mIL-11 expression accelerated recovery of platelets, neutrophils, and, to some extent, total leukocytes while preferentially increasing peripheral platelet counts in fully reconstituted mice. When analyzed 5 months posttransplant, tertiary MSCV-mIL-11 recipients had a significantly greater percentage of G418-resistant colony-forming cells in their bone marrow compared with control MSCV animals. Collectively, these data show that persistent stimulation of platelet production by IL-11 is not detrimental to stem cell repopulating ability; rather, they suggest that IL-11 expression in vivo may have resulted in enhanced maintenance of the most primitive hematopoietic stem cell compartment. The prolonged expression achieved by the MSCV retroviral vector, despite the presence of a selectable marker, contrasts with the frequent transcriptional extinction observed with other retroviral vectors carrying two genes. These findings have potentially important implications for clinical bone marrow transplantation and gene therapy of the hematopoietic system.

Adhesion molecules involved in the binding of murine myeloma cells to bone marrow stromal elements

In previous work, we reported the development of the B9/BMI syngeneic murine bone marrow metastasis model. Interleukin (IL)-6-dependent, IL-I-producing B9/BMI cells, which preferentially home to and colonise the vertebral and femoral marrow after i.v. injection, exhibit striking similarity in cell surface phenotype to human myeloma cells, especially the expression of 3 adhesion molecules, CD44, VLA-4 and ICAM-I. Because the haematopoietic microenvironment consists of different cell types, such as endothelial cells, fibroblasts, adipocytes and macrophages, we investigated the functional significance of these adhesion molecules in heterotypic binding assays between B9/BMI cells and a newly established bone marrow-derived endothelial cell line (BMEC), a fibroblastoid pre-adipocyte cell line (BMS2.2) and primary bone marrow-derived macrophages. B9/BMI cells adhered well to all stromal elements: a combination of monoclonal antibodies (MAbs) against CD44 and VLA-4 significantly inhibited the adherence of B9/BMI cells to BMEC and BMS2.2 cells, whereas binding of B9/BMI cells to macrophages was partially blocked with an anti-ICAM-I MAb. Our results implicate multiple recognition mechanisms, including those involving CD44, VLA-4 and ICAM-I, in the retention of B9/BMI cells in the bone marrow.

Novel retroviral vectors for efficient expression of the multidrug resistance (mdr-1) gene in early hematopoietic cells

We present data that retroviral gene expression in early hematopoietic cells is subjected to transcriptional controls similar to those previously described for embryonic stem cells. Transient transfection experiments revealed that both the viral enhancer region in the U3 region of the long terminal repeat as well as a repressor element coincident with the primer binding site of Moloney leukemia viruses are limiting for expression in hematopoietic cells in a differentiation-dependent manner. Within the group of Moloney leukemia virus-related viruses, only the myeloproliferative sarcoma virus showed high enhancer activity in myeloid (including erythroid) cells. In contrast, enhancer regions related to the Friend mink cell focus-forming viruses mediate much higher gene expression levels in both multipotent and lineage-committed myeloid cells. In addition, transcriptional repression related to sequences in the primer binding site of Moloney leukemia virus-derived vectors is also found in early hematopoietic cells and can be overcome by using the corresponding sequences of the murine embryonic stem cell virus. On the basis of these results, two types of novel retroviral hybrid vectors were developed; they combine the U3 regions of either the Friend mink cell focus-forming virus family or the myeloproliferative sarcoma virus with the primer binding site of the murine embryonic stem cell virus. When used to express the human multiple drug resistance gene, these vectors substantially improve protection to cytostatic drugs in transduced hematopoietic cell lines FDC-Pmix, TF-1, and K-562 in comparison with Moloney leukemia virus-derived vectors presently used for the stem cell protection approach in somatic gene therapy.

Adenovirus vectors for cytokine gene expression

Recombinant Adenovirus type 5 constructs containing IL-6 cDNA can be used to infect cells in vitro and obtain a high level of IL-6 expression and secretion into culture media. Furthermore, Ad5-IL-6 viruses can also be used to infect Balb/c mice or Sprague-Dawley rats and obtain a high level of IL-6 expression that is sustained over a period of 3-5 days. Intratracheal infection was accompanied by dramatic increases in virus-encoded IL-6 mRNA levels in rat lung tissue, raised levels of IL-6 detected in bronchoalveolar lavage fluids and in serum, and IL-6-dependent sequelae such as liver acute phase responses. This occurs in a tissue-specific manner, depending on routes of infection by the virus. Rat lungs showed a prominent expansion (10 fold in numbers) of all classes of lymphocytes, including B cells, T helper cells (CD4+) and CTL (CD8+) at day 7 after infection which resolved significantly by day 12. Thus the associated biological effects of viral vector mediated IL-6 over-expression was also transient in nature. Other tissues can be infected with Ad5 and thus can also be induced to express selected genes in a transient fashion. We are currently examining the potential for Ad recombinant cytokine vectors in therapy for cancer and for bone marrow reconstitution after transplantation. Thus the use of recombinant Ad5 vectors may have a broad application in the study of cytokine function and possibly in future therapy as a transient gene transfer approach.

Overexpression of HOXB4 in hematopoietic cells causes the selective expansion of more primitive populations in vitro and in vivo

Hox genes were first recognized for their role in embryonic development and may also play important lineage-specific functions in a variety of somatic tissues including the hematopoietic system. We have recently shown that certain members of the Hox A and B clusters, such as HOXB3 and HOXB4, are preferentially expressed in subpopulations of human bone marrow that are highly enriched for the most primitive hematopoietic cell types. To assess the role these genes may play in regulating the proliferation and/or differentiation of such cells, we engineered the overexpression of HOXB4 in murine bone marrow cells by retroviral gene transfer and analyzed subsequent effects on the behavior of various hematopoietic stem and progenitor cell populations both in vitro and in vivo. Serial transplantation studies revealed a greatly enhanced ability of HOXB4-transduced bone marrow cells to regenerate the most primitive hematopoietic stem cell compartment resulting in 50-fold higher numbers of transplantable totipotent hematopoietic stem cells in primary and secondary recipients, compared with serially passaged neo-infected control cells. This heightened expansion in vivo of HOXB4-transduced hematopoietic stem cells was not accompanied by identifiable anomalies in the peripheral blood of these mice. Enhanced proliferation in vitro of day-12 CFU-S and clonogenic progenitors was also documented. These results indicate HOXB4 to be an important regulator of very early but not late hematopoietic cell proliferation and suggest a new approach to the controlled amplification of genetically modified hematopoietic stem cell populations.

Isolation of new oncogenic forms of the murine c-fms gene

The c-fms gene encodes the receptor for the macrophage colony-stimulating factor, which plays a key role in the proliferation and differentiation of cells of the myelomonocytic lineage. In order to study the effects of overexpression of the macrophage colony-stimulating factor receptor in hematopoietic cells, a Harvey sarcoma virus-derived retroviral vector containing the murine c-fms cDNA was pseudotyped with Friend murine leukemia virus and inoculated into newborn DBA/2 mice. This viral complex induced monoclonal or oligoclonal leukemias with a shorter latency than that for Friend murine leukemia virus alone. Unexpectedly, 60% of the integrated fms proviruses had deletions at the 5' end of the c-fms gene. Sequence analysis of seven mutant proviruses indicated that the deletions always included the c-fms ligand binding domain and either occurred within the c-fms sequences, leaving the fms open reading frame unchanged, or joined VL30 sequences located at the 5' end of the parental retroviral vector to internal c-fms sequences, resulting in truncated fms proteins devoid of the canonical signal peptide. In contrast to all tyrosine kinase receptors transduced in retroviruses, no helper gag- or env-derived sequences were fused to the rearranged fms sequences. Viral supernatants isolated from hematopoietic tumors with viruses with deletions were able to transform NIH 3T3 cells as efficiently as parental fms virus, indicating that deletions resulted in constitutive activation of the c-fms gene. These oncogenic variants differ from those transduced in the Suzan McDonough strain of feline sarcoma viruses (L. Donner, L. A. Fedele, C. F. Garon, S. J. Anderson, and C. J. Sherr, J. Virol. 41:489-500, 1982). The high rate of c-fms rearrangement and its relevance in the occurrence of hematopoietic tumors are discussed.

Interleukin-6 is required in vivo for the regulation of stem cells and committed progenitors of the hematopoietic system

The development of blood cells from hematopoietic stem cells is controlled by multiple cytokines. These growth factors influence survival, cell cycle status, differentiation into lineage-committed progenitors, final maturation into blood cells, and perhaps self-renewal of stem cells. The specific contribution of IL-6 to these processes in vivo was evaluated in mice with a targeted disruption of the IL-6 gene. Decreases in the absolute numbers of CFU-Sd12 and preCFU-S, as well as in the functionality of LTRSC in these mutant mice, suggests a role for IL-6 in the survival, self-renewal, or both of hematopoietic stem cells and early progenitors. In addition, as a result of the IL-6 deficiency, the control between proliferation and differentiation of the progenitor cells of the granulocytic-monocytic, megakaryocytic, and erythroid lineages into mature blood cells is altered, leading to abnormal levels of committed progenitors of these lineages and to a slow recovery from hematopoietic ablation.

Retroviral integration within the Fli-2 locus results in inactivation of the erythroid transcription factor NF-E2 in Friend erythroleukemias: evidence that NF-E2 is essential for globin expression

Activation of either Fli-1 or Spi-1 members of the ets family of transcription factors as a result of retroviral insertion and mutational inactivation of the p53 tumor suppressor gene play essential roles in the multistage erythroleukemias induced in mice by various strains of Friend virus. We have previously identified another common site for provirus integration, designated Fli-2 (Friend leukemia integration 2), in some erythroleukemia clones induced either by Friend murine leukemia virus (F-MuLV) or by the polycythemia-inducing strain of Friend virus complex (FV-P). Here we show that genomic sequences adjacent to Fli-2 correspond to the coding region of the erythroid-specific DNA binding protein NF-E2 p45. In one erythroleukemia cell line the expression of NF-E2 p45 is undetectable due to proviral integration in one allele and loss of the other allele. The complete loss of NF-E2 p45 in this cell line is associated with a drastic reduction in expression of the alpha- and beta-globin genes that were partially restored by reintroduction of the NF-E2 p45 gene. Taken together, these results provide direct evidence that NF-E2 gene is essential for globin transcription and suggest that perturbation in expression of this transcription factor may contribute to erythroleukemia progression.

Interleukin-6 enhances hepatic transferrin uptake and ferritin expression in rats

To explore a mechanism of interleukin (IL)-6-induced hypoferremia in rats, iron metabolism was investigated both in vivo and in vitro. Recombinant IL-6 was intraperitoneally administered to male Wistar rats and the serial change of parameters related to iron metabolism was examined. After administration of IL-6, plasma IL-6 concentration increased rapidly, reached its maximum in 1 hr and thereafter decreased quickly. Plasma IL-6 3 hr after IL-6 injection (50 micrograms/kg) was 3 units/ml, which is a concentration capable of inducing hepatic 125I-labeled transferrin uptake in vitro using isolated hepatocytes. Plasma iron concentration and transferrin saturation had decreased to approximately one third of the initial level within 3 hr and then recovered. Total iron binding capacity remained unchanged for 6 hr, then began to decrease. Red blood cell count and hemoglobin concentration showed no remarkable changes during this period. By ferrokinetic study with plasma that contained iron 59-labeled transferrin, the plasma iron disappearance half time, calculated from the disappearance curve, was significantly shortened from 55 min to 22 min by IL-6 treatment (p < 0.01). The ferritin concentration in the liver was increased significantly after the administration of IL-6 (p < 0.001), but transiently decreased in the spleen. The plasma ferritin showed a gradual increase during the 6-hr period after IL-6 injection. The uptake of 125I-labeled diferric transferrin by isolated hepatocytes was increased by IL-6 treatment and this increment was inhibited by addition of 100-fold excess unlabeled transferrin. On the other hand, no significant increment of 125I-labeled diferric transferrin uptake was observed in Kupffer cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Progenitor cell hyperplasia with rare development of myeloid leukemia in interleukin 11 bone marrow chimeras

Post 5-fluorouracil-treated murine bone marrow cells infected with a recombinant retrovirus (murine stem cell virus-interleukin 11 [MSCV-IL-11]) bearing a human IL-11 gene were transplanted into lethally irradiated syngeneic mice. Analysis of proviral integration sites in DNA prepared from hematopoietic tissues and purified cell populations of long-term reconstituted primary and secondary recipients demonstrated polyclonal engraftment by multipotential stem cells. High levels (100-1,500 U/ml) of IL-11 were detected in the plasma of the MSCV-IL-11 mice. Systemic effects of chronic IL-11 exposure included loss of body fat, thymus atrophy, some alterations in plasma protein levels, frequent inflammation of the eyelids, and often a hyperactive state. A sustained rise in peripheral platelet levels (approximately 1.5-fold) was seen throughout the observation period (4-17 wk). No changes were observed in the total number of circulating leukocytes in the majority of the transplanted animals (including 10 primary and 18 secondary recipients) despite a > 20-fold elevation in myeloid progenitor cell content in the spleen. The exceptions were members of one transplant pedigree which presented with myeloid leukemia during the secondary transplant phase. A clonal origin of the disease was determined, with significant expansion of the MSCV-IL-11-marked clone having occurred in the spleen of the primary host. Culturing of leukemic spleen cells from a quaternary recipient led to the establishment of a permanent cell line (denoted PGMD1). IL-11-producing PGMD1 myeloid leukemic cells are dependent on IL-3 for continuous growth in vitro and they differentiate into granulocytes and macrophages in response to granulocyte/macrophage colony-stimulating factor. The inability of autogenously produced IL-11 to support autonomous growth of PGMD1 cells argues against a mechanism of transformation involving a classical autocrine loop.