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Journal of Virology, December 2007, p. 13259-13264, Vol. 81, No. 23
0022-538X/07/$08.00+0 doi:10.1128/JVI.01353-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.
null Mice Transplanted with Hematopoietic Stem Cells under Nonmyeloablative Conditions Show Prolonged Life Spans and Allow Detailed Analysis of Human Immunodeficiency Virus Type 1 Pathogenesis
Department of Virology, Division of Medical Science, Medical Research Institute, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8519, Japan,1 Open Research Center for Genome and Infectious Disease Control, Nihon University School of Medicine, 30-1 Oyaguchikami-chou, Itabashi-ku, Tokyo 173-8610, Japan,2 AIDS Research Center, National Institute of Infectious Diseases, 1-23-1 Toyama, Shinjuku-ku, Tokyo 162-8640, Japan,3 Department of Infectious Diseases, National Research Institute for Child Health and Development, 2-10-1 Okura, Setagaya-ku, Tokyo 154-8567, Japan,4 Department of Molecular Virology, Graduate School of Medicine, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8519, Japan,5 Central Institute for Experimental Animals, 1430 Nogawa, Miyamae-ku, Kawasaki, Kanagawa 216-0001, Japan,6 Department of Pediatrics and Child Health, Nihon University School of Medicine, 30-1 Oyaguchikami-chou, Itabashi-ku, Tokyo 173-8610, Japan7
Received 21 June 2007/ Accepted 3 September 2007
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null (hNOG) mice constructed with human hematopoietic stem cells (HSCs) allow efficient human immunodeficiency virus type 1 (HIV-1) infection. However, HIV-1 infection could be monitored for only 43 days in the animals due to their short life spans. By transplanting HSCs without any myeloablation methods, the mice successfully survived longer than 300 days with stable engraftment of human cells. The mice showed high viremia state for more than the 3 months examined, with systemic HIV-1 infection and gradual decrease of CD4+ T cells analogous to that in humans. These capacities of the hNOG mice are very attractive for modeling mechanisms of AIDS progression and therapeutic strategy. |
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Considering the significant advantages of developing a mouse model for HIV-1 infection, we previously introduced a novel HIV-1 mouse model using nonobese diabetic (NOD)/SCID/interleukin-2 receptor (IL-2R) gamma chain-knocked-out (NOG) mice (22). Multilineage human cells, including T, B, NK cells, monocytes/macrophages, and dendritic cells (DCs) differentiate in the mice when transplanted with human CD34+ hematopoietic stem cells (HSCs) (6, 9, 22). These mice show high levels of susceptibility to both CCR5 (R5)- and CXCR4 (X4)-tropic HIVs with intense plasma viral loads lasting for over 40 days (22). Thus, this mouse model may be valuable for the study of HIV-1 infection. However, a serious problem remains. The mice showed symptoms of a wasting condition and a hunched back 5 to 7 months after HSC transplantation, following which most of them died. This life span is not sufficient if we are to better understand HIV pathogenesis and to develop novel anti-HIV countermeasures, because more than 4 months posttransplantation is required for the development of human T cells before HIV-1 can be studied in mice.
In past studies for the construction of humanized mouse models using NOD/SCID, ß2 microglobulin-deficient NOD/SCID (NOD/SCID/B2mnull) or NOG mice, the mice were subjected to total body irradiation or given drugs for HSC transplantation (6, 9, 11, 14, 21, 23). Since NOG mice do not develop any thymic lymphomas in contrast to NOD/SCID or NOD/SCID/B2mnull mice (3, 19), the irradiation might influence the reduction of their life spans. In this study, we therefore searched for optimal conditions for HSC transplantation and consequently found that in NOG mice, myeloablation procedures were not required for human cell generation. Importantly, these mice stably survived longer than 300 days after the HSC transplantation, which allowed further investigation of HIV-1 pathogenesis and progression to disease state in the animals.
NOG mice constructed with HSCs without myeloablation showed prolonged survival time and stable human cell generation. Six- to eight-week-old female NOG mice were obtained from the Central Institute for Experimental Animals (Kawasaki, Japan), and human cord blood-derived CD34+ HSCs (2 x 104 to 12 x 104 cells) were injected intravenously with or without irradiation. As shown in Fig. 1A, most of the mice that received 300 cGy irradiation were dead within 250 days posttransplantation (mean survival time, 188 days). In contrast, more than 80% of the mice with transplanted HSCs without irradiation survived over 300 days (mean survival time, 387 days). These mice were successfully engrafted with HSCs, resulting first in the generation of human CD19+ B cells and subsequently in the generation of human CD3+ T cells (Fig. 1B). Figure 1C and D show the percentages of human CD45+ leukocytes and human CD3+ T cells in peripheral blood at 40 to 413 days after HSC transplantation. Up to 74% of leukocytes in peripheral blood samples were reconstituted with human cells in nonirradiated mice (mean ± standard deviation, 22.8% ± 14.0%; n = 222), and this was maintained over 400 days after transplantation (Fig. 1C). Although higher levels of human cell reconstitution were observed in the irradiated mice (45.2% ± 23.9%; n = 65) (Fig. 1C), which may be due to reduction of absolute numbers of murine cells by destruction of their progenitor cells in bone marrow (BM), human CD3+ T cells developed with similar kinetics between the two groups (Fig. 1D). Figure 1E shows the engraftment efficiency of NOG mice transplanted with different numbers of HSCs without irradiation. More than 2 x 104 HSCs could be stably engrafted, and the levels of human cell reconstitution increased relative to the number of transplanted cells.
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FIG. 1. Human cell generation in hematopoietic stem cell-engrafted hNOG mice with or without myeloablation. (A) Life spans of NOG mice transplanted with human stem cells after receiving 300 cGy irradiation (n = 25) or not receiving irradiation (n = 25). (B) Representative flow cytometric profiles of the mice from 2 to 6 months after transplantation without irradiation. The ratio of human to murine CD45+ cells and that of human CD3+ cells to CD19+ cells are shown. Note that the mice generated human CD45+ leukocytes that eventually developed human CD19+ B cells first and then CD3+ T cells. (C and D) Percentages of human CD45+ cells (C) and CD3+ T cells in human CD45+ cells (D) in peripheral blood from 65 mice that received 300 cGy irradiation and 222 nonirradiated mice 40 to 413 days after transplantation. (E) Summary of engraftment levels in nonirradiated mice transplanted with 2 x 104 to 5 x 104 cells (n = 11), 5 x 104 to 7 x 104 cells (n = 53), or 7 x 104 to 12 x 104 (n = 30) human stem cells. Percentages of human CD45+ leukocytes in peripheral blood during 4 to 5 months after transplantation were shown. The horizontal black bars indicate the averages of the groups. (F to I) Flow cytometric analysis and immunohistochemical analysis of the expression of myelomonocytic markers in nonirradiated mice 4 months after transplantation. Human CD14+ monocytes/macrophages were recognized in peripheral blood and BM (F). A gate was set on the human CD45+ population. Human CD68+ macrophages and CD205+ DCs were also detected in spleen (G) and uterus (H and I). Visualization was performed with 5-bromo-4-chloro-3-indolylphosphate (BCIP). The original magnifications were x100 (G and H) and x200 (I).
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hNOG mice induced systemic and long-lasting HIV-1 infection with CD4+ T-cell depletion. We prepared 29 stem cell-transplanted hNOG mice and inoculated them intravenously with a high dose of R5-tropic HIV-1JRCSF (65,000 50% tissue culture infective doses [TCID50]), X4-tropic HIV-1MNp (20,000 TCID50), or X4-tropic HIV-1NL4-3 (60,000 TCID50) at 122 to 150 days posttransplantation. Then, plasma viral RNA copy numbers were measured at successive time points. The mice showed marked, long-lasting viremia state for more than 3 months, reaching the highest levels of 3.0 x 105 copies/ml from HIV-1JRCSF-infected mice, 3.7 x 106 copies/ml from HIV-1MNp-infected mice, and 7.8 x 106 copies/ml from HIV-1NL4-3-infected mice (Fig. 2A). None of the mice weakened or died as a result of HIV-1 infection throughout the entire follow-up period.
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FIG. 2. Long-lasting viremia and CD4+ T-cell depletion in R5- and X4-tropic HIV-1-infected hNOG mice. (A) Viral copy numbers in plasma from 29 mice intravenously inoculated with R5-tropic HIV-1JRCSF (65,000 TCID50; n = 11), X4-tropic HIV-1MNp (20,000 TCID50; n = 10), and X4-tropic HIV-1NL4-3 (60,000 TCID50; n = 8). RNA viral copy numbers were measured using a real-time PCR quantification assay as previously described (22). (B) The percentages of CD4– CD8+ (top left), CD4+ CD8+ (top right), and CD4+ CD8– (bottom right) cells in blood, spleen, and thymus from a uninfected control mouse and a V-1NL4-3-infected mouse (32 days postinfection). These two mice were constructed with HSCs from the same cord blood donor, and sacrificed 181 and 169 days after transplantation, respectively. A gate was set on the human CD45+ population. (C) Comparison of the apparent size of mesenteric LN from uninfected mice or mice infected with HIV-1JRCSF (109 days postinfection), HIV-1MNp (109 days postinfection), or HIV-1NL4-3 (112 days postinfection). A uninfected control mouse was sacrificed 249 days after transplantation, and three HIV-1-infected mice were sacrificed 246, 246, and 249 days after transplantation. (D) Comparison of CD4/CD8 T-cell ratios and absolute CD4+ T-cell numbers in peripheral blood from uninfected control mice (n = 7), R5-tropic HIV-1JRCSF-infected mice (n = 7), X4-tropic HIV-1MNp-infected mice (n = 5), and X4-tropic HIV-1NL4-3-infected mice (n = 6). Results are expressed as means ± standard deviations (error bars).
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TABLE 1. CD4/CD8 ratios in peripheral blood and spleen and CD4+ CD8+ cells in thymus of groups of uninfected and HIV-1-infected micea
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TABLE 2. Comparison of DNA proviral copies in various organs from HIV-1-infected micea
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In this study, we successfully prolonged the life span of hNOG mice by improving the HSC transplantation method and further clarified characteristics of HIV-1 infection in the mice including the following: (i) high levels of viremia lasting over 3 months, (ii) CD4+ T-cell depletion in peripheral blood and spleen regardless of thymic T-cell loss, (iii) systemic HIV-1 infection not only in lymphoid tissues but also in various other organs, and (iv) a different rate of CD4+ T-cell depletion for R5- versus X4-tropic HIV-1 strains. Recently, several studies on HIV-1 infection in Rag2–/–
c–/– mice, transplanted with HSCs at birth, have also been reported (1, 2, 5, 24). The mice showed high susceptibility to both R5- and X4-tropic HIVs and long-term viremia with CD4+ T-cell depletion, which is partly similar to our present results. However, the efficiency of human cell generation in Rag2–/–
c–/– mice strongly depends on the dose of irradiation, and levels of chimerism in mice are not stable even receiving 550 to 750 cGy irradiation, which does eventually induces reduction of their life spans (5). In contrast, very stable engraftment of HSCs and subsequent human cell generation were noted in our hNOG mice even without any myeloablation procedures. Their long life spans and long-term human cell reconstitution allowed persistent HIV-1 infections mirroring HIV-1 infections in humans. Thus, this hNOG mouse system is a very useful tool as an advanced mouse model for the study of AIDS progression and long-term evaluation of new anti-HIV-1 drugs.
This work was supported by a grant from the Ministry of Education, Culture, Sports, Science, and Technology to promote open research for young academics and specialists.
Published ahead of print on 19 September 2007. ![]()
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cnull mouse: an excellent recipient mouse model for engraftment of human cells. Blood 100:3175-3182.
cnull (NOG) mice transplanted either with human umbilical cord blood, bone marrow, or mobilized peripheral blood CD34+ cells. Exp. Hematol. 31:789-797.[CrossRef][Medline]
null mice develop human lymphoid systems and induce long-lasting HIV-1 infection with specific humoral immune responses. Blood 109:212-218.
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