Mouse lymphoma cell line and animal model of human high grade B-cell lymphoma
11617356 · 2023-04-04
Assignee
Inventors
Cpc classification
A01K2207/12
HUMAN NECESSITIES
A01K67/0271
HUMAN NECESSITIES
C12N5/0694
CHEMISTRY; METALLURGY
International classification
Abstract
The invention relates to a new, spontaneous mouse lymphoma cell line displaying CD19, B220, MHC II, surface IgG2a/kappa chain and MAC-1, which is negative for CD5, animal models of B-cell lymphoma based on said cell line and methods for assessing lymphoma propagation and lymphoma expansion based on said cell line.
Claims
1. A method for assessment of an effect of an agent on lymphoma cells, said method comprising administering to a mouse lymphoma cells, said lymphoma cells being of the mouse lymphoma cell line deposited at the Deutsche Sammlung von Mikroorganismen and Zellkulturen (DSMZ) on Sep. 24, 2015 under the number DSMZ ACC3278 or derived therefrom, wherein said lymphoma cells are positive for CD19, B220, MHC II, surface IgG2a/kappa chain and MAC-1, and negative for CD5, and an agent of interest, and evaluating the effect of the agent on the propagation or migration of the lymphoma cells.
2. The method according to claim 1 wherein said lymphoma cells comprise a chromosomal translocation selected from the group consisting of the following translocations: t(10:6), t(6:10), t(11:19) and t(10:11).
3. The method according to claim 1, wherein said lymphoma cells, when administered intraperitoneally to the mouse in a dose of 10.sup.4 to 5×10.sup.6 cells/recipient, expand to one or more site(s) selected from the omentum and the fat associated lymphoid clusters (FALC) along the blood vessels in the mesentery within 7 days after the administration.
4. The method according to claim 3, wherein said lymphoma cells, upon said administration, expand to said expansion site(s) within 5 days after the administration.
5. The method according to claim 1, wherein said lymphoma cells, when administered intraperitoneally to the mouse in a dose of 10.sup.4 to 5×10.sup.6 cells/recipient, are substantially absent from a tissue or organ selected from: spleen, peripheral lymph nodes and liver up to 8 days after the administration.
6. The method according to claim 5, wherein the lymphoma cells are substantially absent from a tissue or organ selected from: spleen, peripheral lymph nodes and liver up to 3 days after the administration.
7. The method according to claim 1, wherein said lymphoma cells, when administered intraperitoneally to the mouse the mouse in a dose of 10.sup.4 to 5×10.sup.6 cells/recipient, are absent from a tissue or organ selected from: bone marrow, thymus, brain, kidney, muscle, Peyer's patches and lung up to 8 days after the administration.
8. The method according to claim 1, wherein the lymphoma cells, when administered intraperitoneally to the mouse in a dose of 10.sup.6 to 5×10.sup.6 cells/recipient, expand to one or more site(s) selected from the omentum and the fat associated lymphoid clusters (FALC) along the blood vessels in the mesentery within 3 days after the administration.
9. The method according to claim 1, wherein the lymphoma cells, when administered intraperitoneally to the mouse in a dose of 10.sup.6 to 5×10.sup.6 cells/recipient, are substantially absent from a tissue or organ selected from: spleen, peripheral lymph nodes and liver up to 5 days after the administration.
10. The method according to claim 1, wherein said lymphoma cells, when administered intraperitoneally to the mouse in a dose of 10.sup.4 to 5×10.sup.6 cells/recipient, are absent from a tissue or organ selected from: bone marrow, thymus, brain, kidney, muscle, Peyer's patches and lung up to 12 days after the administration.
11. The method according to claim 1, wherein said lymphoma cells, when administered intraperitoneally to the mouse in a dose of 10.sup.6 to 5×10.sup.6 cells/recipient, are absent from a tissue or organ selected from: bone marrow, thymus, brain, kidney, muscle, Peyer's patches and lung up to 8 days after the administration.
12. The method according to claim 1, wherein the lymphoma cells, when administered intraperitoneally to the mouse in a dose of 10.sup.4 to 5×10.sup.6 cells/recipient, expand to abdominal lymphatic tissue showing adhesion to the lymphoma cells mediated by PNAd and MAdCAM within 7 days from the administration.
13. The method according to claim 12, wherein the lymphoma cells, when administered intraperitoneally to the mouse in a dose of 10.sup.4 to 5×10.sup.6 cells/recipient, expand to abdominal lymphatic tissue showing adhesion to the lymphoma cells mediated by PNAd and MAdCAM within 2 days from the administration.
14. The method according to claim 12, wherein the lymphoma cells, when administered intraperitoneally to the mouse in a dose of 10.sup.6 to 5×10.sup.6 cells/recipient, expand to abdominal lymphatic tissue showing adhesion to the lymphoma cells mediated by PNAd and MAdCAM within 5 days from the administration.
15. A method for assessment of B-cell lymphoma expansion, the method comprising administering lymphoma cells to a mouse intraperitoneally in a dose of 10.sup.4 to 5×10.sup.6 cells/recipient, said lymphoma cells being of the mouse lymphoma cell line deposited at the Deutsche Sammlung von Mikroorganismen and Zellkulturen (DSMZ) on Sep. 24, 2015 under the accession number DSMZ ACC3278 or derived therefrom, wherein the lymphoma cells are positive for CD19, B220, MHC II, surface IgG2a/kappa chain and MAC-1, and negative for CD5, and detecting the localization of the lymphoma cells, which are positive for CD19, B220, MHC II, surface IgG2a/kappa chain and MAC-1 and negative for CD5.
16. The method according to claim 15, wherein the lymphoma cells comprise a chromosomal translocation selected from the group consisting of the following translocations: t(10:6), t(6:10), t(11:19) and t(10:11).
17. The method according to claim 15, wherein the lymphoma cells are administered in a dose of 10.sup.6 to 5×10.sup.6 cells/recipient.
18. The method according to claim 15, wherein the detection is performed within 7 days after the administration.
19. The method according to claim 15, wherein the detection is performed within 5 days after the administration.
20. The method according to claim 15, wherein the lymphoma cells are detected in tissues showing adhesion mediated by PNAd and MAdCAM.
21. The method according to claim 15, wherein the lymphoma cells are detected in the omentum and/or the fat associated lymphoid clusters (FALC) along the blood vessels in the mesentery.
22. An in vitro method for assessment of an effect of an agent on lymphoma cells or on interaction of lymphoma cells and tumor microenvironment, said method comprising providing lymphoma cells, said lymphoma cells being of the cell line deposited at the Deutsche Sammlung von Mikroorganismen and Zellkulturen (DSMZ) on Sep. 24, 2015 under the accession number DSMZ ACC3278 or derived therefrom, wherein said lymphoma cells are positive for CD19, B220, MHC II, surface IgG2a/kappa chain and MAC-1, and negative for CD5, culturing the lymphoma cells in the presence and/or absence of tumor stroma, administering the agent to the culture, evaluating, optionally while considering the presence and/or absence of tumor stroma, the effect of the agent on the propagation of the lymphoma cells.
23. The in vitro method according to claim 22, wherein the lymphoma cells comprise a chromosomal translocation selected from the group consisting of the following translocations: t(10:6), t(6:10), t(11:19) and t(10:11).
24. A method for propagation of a population of lymphoma cells, said lymphoma cells being of the cell line deposited at the Deutsche Sammlung von Mikroorganismen and Zellkulturen (DSMZ) on Sep. 24, 2015 under accession number DSMZ ACC3278 or derived therefrom, wherein said lymphoma cells are positive for CD19, B220, MHC II, surface IgG2a/kappa chain and MAC-1, and negative for CD5, comprising injecting the lymphoma cells into a recipient mouse, obtaining further lymphoma cells positive for CD19, B220, MHC II, surface IgG2a/kappa, and MAC-1, and negative for CD5 and tumor stroma from the mouse, co-culturing the further lymphoma cells positive for CD19, B220, MHC II, surface IgG2a/kappa, and MAC-1, and negative for CD5 and the tumor stroma obtained from the mouse in a culture medium suitable for B-lineage cells.
Description
SHORT DESCRIPTION OF THE DRAWINGS
(1)
(2) Macroscopic pathology (a) reveals significant splenomegaly (arrow) and enlarged mesenteric lymph nodes (mLNs) (arrowhead), with the dotted lines outlining the borders of organs in control mice. Hematoxylin and eosin (H&E) staining of mLN (b; scale bar=200 μm) and spleen (c; scale bar=200 μm) shows lymphoma infiltrate composed of centroblasts intermingled with centrocytes in a representative spleen sample from a BALB/c recipient injected with lymphoma cells (d; scale bar=20 μm).
(3)
(4) Survival of a cohort of BALB/c mice (n=10 recipients/group) following intraperitoneal injection of lymphoma cells at various doses.
(5)
(6) Anti-B220 staining of a spleen (A) and mLN (B) section from a lymphoma-injected BALB/c mouse reveals a homogenous infiltrate composed of B220.sup.+ cells, where in the spleen both the remnants of follicles with more intense B220 expression (arrowhead) and lymphoma (arrow) with a weaker B220 display can be identified (a representative sample from a group of n=8; scale bar=200 μm). (C/1-C/2) A representative flow cytometric staining of lymphoma cells from the mLN a Rag1.sup.−/− recipient indicates the expression of B-lineage associated markers and lack of CD3 (n=7). Numbers in the histograms correspond to the cumulative percentage of positive cells in the fluorescence channel range indicated by the horizontal line.
(7)
(8) (a) B220-positive cells in Rag1.sup.−/− recipient mLN sample were stained for cell surface Ig isotypes as indicated, with the mean fluorescence intensities (MFI) shown (n=5), where only IgG2a Ig subclass expression is detectable. (b) PCR analysis of IgH V-region rearrangement demonstrates identical VDJ-rearrangement of V.sub.H7183 family in lymphoma-injected BALB/c or Rag1.sup.−/− recipient (indicated at the top), with using control BALB/c mLN (NFW, nuclease-free water; n=5).
(9)
(10) Lymphoma cells from Rag1.sup.−/− recipients' mLN were labeled for various adhesion molecules (indicated at the vertical axis) and surface Ig κ-chain together with B220 staining. Density plots depict the expression of adhesion molecule plotted against surface Ig κ-chain of B220.sup.+ lymphocytes (n=7).
(11)
(12) (a) Perivascular spreading in the mesentery (arrow) draining towards the mLN (arrowhead) of Bc-DLFL.1 lymphoma cells in BALB/c recipient following ip. injection involves (b) a compact accumulation of B220-positive lymphoma cells (brown with blue hematoxyline counterstain), also visible in dilated lymphatic vessels (arrow in c; H&E stain). (d) Dual immunofluorescent staining of mesentery for LYVE-1 (green) and B220 (red) shows tight clustering both inside and outside the lymphatic capillaries. (e) mLN section stained for B220 (red) and LYVE-1 also demonstrates numerous lymphoma cells both in the subcapsular sinus (arrowhead) and the corticomedullary lymphatic sinuses (arrow), whereas (f) the PNAd-positive HEVs labeled with MECA-79 mAb (green, arrowhead) are devoid of lymphoma cells (n=5; scale bars=100 μm).
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DETAILED DESCRIPTION OF THE INVENTION
(20) The present inventors have unexpectedly found, isolated and successfully propagated a lymphoma cell line, denoted Bc-DLFL.1, displaying CD19, B220, MHC II, surface IgG2a/kappa chain and MAC-1, indicating B-cell origin. The cells, however, do not express CD5, ruling out B-1a origin. The cells are further characterized by a number of translocation involving chromosomes 6, 10, 11 and 19 as t(10:6), t(6:10), t(11:19) and t(10:11) chromosomal translocation. Although the lymphoma showed characteristics of a malignancy that may be correlated to human indolent diffuse large B-cell lymphomas, further studies revealed very unusual properties, such as restricted and time dependent tissue distribution, marker pattern and propagation conditions. As used herein, the term “lymphoma cell” refers to a B-lineage cell arising after malignant transformation.
(21) Based on the results, a new lymphoma cell line and a laboratory tool for the assessment of B-cell lymphoma expansion and normal B-cell migration, for the assessment of in vivo tumor microenvironment in an in vitro method are provided. For example the role of FALC (fat associated lymphoid clusters) located along the blood vessels in the mesentery and/or of milky spots in the omentum in lymphoma/B-cell homing may be assessed using the cells according to the invention, because these cells show an extensive accumulation of lymphoma within short time after administration without a significant amount of cells outside these regions within the same time frame. Bc-DLFL.1 cells expand rapidly in a recipient mouse, but the migration is highly specific as described herein and due to the specific marker pattern, the cells may be identified reliably. Assessment of agents affecting the lymphoma-tumor microenvironment cooperation will also benefit from the use of Bc-DLFL.1. Agents of interest may be e.g. agents produced by the tumor microenvironment (i.e. stroma), e.g. cytokines, growth factors and the like or compounds to be tested for their anti-tumor or pro-tumor activities. Studies may be performed either in vivo or in vitro, as animal models of B-cell lymphoma are also provided. According to the studies of the inventors, histologic and cytopathological features of the lymphoma are preserved even after serial propagation.
(22) A BALB/c mouse-derived novel spontaneous B-cell lymphoma has been isolated and characterized. The intraperitoneal injection of this lymphoma has resulted in a selective tumor seeding of the omentum and the fat associated lymphoid clusters located along the blood vessels in the mesentery, followed by a delayed colonization of the spleen and mesenteric lymph nodes in the moribund state. The metastasis has been formed via the lymphatic vasculature of mesentery. Thus this novel B-cell lymphoma offers a unique model for studying the in vivo lymphatic propagation of B-cell tumors. Additionally, unlike the majority of other mouse lymphoma models, this tumor arose without any previous induction, such as viral or other microbial infection, exposure to chemical carcinogens, or employing genetic manipulation by introducing mutated proto-oncogenes or other regulatory elements, therefore its origin is closer to the human conditions.
(23) Serial intraperitoneal injection of the primary tumor into both BALB/c and RAG-1-deficient hosts led to the successful propagation of lymphoma. Despite the cytological characteristics of high-grade follicular B-cell lymphoma, the tumor cells showed significantly lesser spreading to extraabdominal locations upon intraperitoneal passage compared to expansion into the omentum and the FALC located along the blood vessels in the mesentery, and later, splenic and mesenteric lymph node expansion. In mesenteric lymph nodes the high endothelial venules contained only few tumor cells, while the lymphatic vessels were almost completely filled with lymphoma cells. Similarly, the LYVE-1-positive lymphatic capillaries within the mesentery were packed with lymphoma cells. Accordingly, the lymphoma shows restricted tissue distribution and metastasis, depending on tissue type and time.
(24) Culturing the tumor cells in vitro and in vivo. A population of cells according to the invention may be provided by in vivo propagation, in vitro culturing and/or the combination of steps of propagation in vitro and in vivo. For in vitro propagation, culture media suitable for B-lineage cells is required. Media for B-lineage cells are numerous and are commercialized by well-known suppliers, such as Sigma, Biological Industries, ATCC, etc. The different culture media may require different supplementation or conditions, which may be determined by the manufacturer. Cell culture techniques are within the skills of the skilled person. Such methods can be found in various textbooks, see e.g. [27]. General purpose culture media, such as different types of Dulbecco's modified Eagle's media (DMEM) may be used. Typically, DMEM has almost twice the concentration of amino acids and four times the amount of vitamins as Eagle's Minimum Essential Medium, as well as ferric nitrate, sodium pyruvate, and some supplementary amino acids. A variation with 4500 mg/L of glucose has been proved to be optimal for culture of various types of cells. DMEM is a basal medium and contains no proteins or growth promoting agents. Therefore, it requires supplementation to be a “complete” medium. It is most commonly supplemented with 5-10% Fetal Bovine Serum (FBS). DMEM utilizes a sodium bicarbonate buffer system (3.7 g/L) and therefore requires artificial levels of CO.sub.2 to maintain the required pH. Typical composition of the culture medium for the cells according to the invention may be 10% DMSO, 20% fetal bovine serum (FBS), 70% DMEM. Growth conditions may include 37° C. and 5% CO.sub.2. Antibiotics such as penicillin (e.g. 100 IU/ml) or streptomycin (e.g. 0.1 mg/ml) may be added.
(25) RPMI and its variations are general purpose media with a broad range of applications for mammalian cells, especially hematopoietic cells. RPMI-1640, for example, was developed for the long-term culture of peripheral blood lymphocytes. RPMI-1640 uses a bicarbonate buffering system and differs from the most mammalian cell culture media in its typical pH 8 formulation. RPMI-1640 supports the growth of a wide variety of cells in suspension and grown as monolayers. For culturing B-lineage cells, RPMI-type media, e.g. RPMI-1640 are usually supplemented with 10% fetal bovine serum or autologous serum. The cells of the invention may be propagated in RPMI, such as RPMI-1640, supplemented with 10% FBS, and antibiotics, such as penicillin (e.g. 100 IU/ml) or streptomycin (e.g. 0.1 mg/ml). The culture medium may be supplemented and prepared differently, according to the manufacturer's instructions.
(26) A cell culture of the cells according to the invention may be prepared as follows: inoculating mice with the cells according to the invention, isolating and dissecting the removed organ affected by the lymphoma (e.g. mesenteric lymph node), mechanically releasing the lymphoma cells using a cell strainer, initiating cultures from the washed/stroma-containing fraction retrieved from the strainer (e.g. in RPMI supplemented by 10% fetal bovine serum) and adding the washed lymphoma cells. Although inoculation with Bc-DLFL.1 cells results in high and rapid mortality (within 12-14 days when an amount of 2.5×10.sup.6-2.5×10.sup.7 cell/recipient mouse is administered intraperitoneally) the tumor cells can only transiently be propagated in vitro. The growth of the tumor cells is dependent on the parallel expansion of stromal cells. Growth can be promoted on cell culture trays covered with a layer of tumor stroma. If the lymphoma cells are separated after the early phase of stromal cells sedimenting and adhering, thus reducing the stromal components, then they mostly die in 2-3 days. Hence the stromal elements are necessary for keeping the cells survivable until they are ready to be reinjected into recipient mice. However, lymphoma cells maintaining contact keep growing and form grapelike agglomerates.
(27) “Tumor stroma”, “stroma cells”, “stromal elements”. By stroma the supportive framework of a tissue is meant, which can be transformed by tumor cells. Both normal and tissue stroma contain different types of cells and extracellular elements. “Tumor stroma” as used herein refers to the stromal elements of the tumor environment in vivo. Tumor stroma may be derived from the lymphoma bearing animal together with the lymphoma. In the culture methods according to the invention, preferably the original, from the animal derived stromal microenvironment of the lymphoma is used as tumor stroma.
(28) Transient propagation is possible in RPMI (e.g. RPMI-1640)+10% fetal bovine serum. Growth conditions include 37° C., 5% CO.sub.2 and humidity (standard cell culture conditions). The medium can be changed at 1/3 ratio (1/3 remaining, 2/3 new medium added). Typical composition of the culture medium may be 10% DMSO, 20% fetal bovine serum, 70% DMEM (Dulbecco's modified Eagle's medium). Antibiotics such as penicillin (e.g. 100 IU/ml) or streptomycin (e.g. 0.1 mg/ml) may be added.
(29) Thawed cells after overnight culture can be propagated by intraperitoneal injection where the injected mice will develop the original lymphoma in their mesenteric lymph nodes and spleen in 14-18 days.
(30) Symptoms of the developed lymphoma are usually evident even without dissecting the animal. The enlargement of the spleen is apparent in moribund mice.
(31) Bc-DLFL.1 lymphoma cells cultured by the method described above have been deposited at the Deutsche Sammlung von Mikroorganismen and Zellkulturen (DSMZ) on Sep. 24, 2015 under the number DSMZ ACC3278.
(32) The specific conditions needed for in vitro growth indicate that the Bc-DLFL.1 cell line is a suitable tool to study stroma-tumor cell relationship in vitro and in vivo.
(33) Characterization of the tumor and the tumor cells. The original tumor was found in a BALB/c mouse as a robust splenomegaly and a soft tissue mass surrounding the terminal segment of the ileum. Macroscopic gross pathology could not have been detected in the abdominal organs, lungs and brain and also peripheral lymph nodes (inguinal, cervical and brachial) and Peyer's patches. Single cell suspensions of the original enlarged spleen injected ip. in BALB/c recipients caused similar phenomena to the original tumor-bearing mouse, i.e. enlarged mesenteric lymph nodes (mLN) and spleen (
(34) Further studies identified chromosomal translocations (t(10:6), t(6:10), t(11:19) and t(10:11)), the presence of CD19, B220, MHC II, surface IgG2a/kappa chain and MAC-1, the lack of CD3 expression and CD5 production. The presence of BAFF-R, BCMA and TACI has been confirmed. Cytometric analysis has shown the presence of Bcl-6, later indirect immunohistochemistry found no detectable Bcl6 expression at a level displayed by normal splenic centroblasts. Expression of Bcl7A was detectable by the same method. The cells are mostly negative or only weakly positive for CXCR5.
(35) It was found, that the Day 7:Day 3 ratio of MAC-1/B220 double positive cells in the total lymphocyte population was highest in the mesenteric lymph nodes and mesenterium followed by the spleen (5.9×) and least in the peripheral lymph nodes.
(36) Due to the specific pattern of cell surface markers on the lymphoma cells according to the invention, it is possible to identify the different cells (e.g. in a lymph node or other affected organ) by incubating the cells with a cocktail of labeled anti-CD19, anti-CD5, anti-MAC-1 and anti-B220 antibodies. Cell populations will be stained as shown in Table 1.
(37) TABLE-US-00001 TABLE 1 Cell population CD5 CD19 MAC-1 B220 T cells + − − − Normal B1a cells − + − + Lymphoma B cells − + + +
(38) For example, lymphoma cells may be incubated with a cocktail of FITC-labeled anti-CD19 (clone 1D3), PE-labeled anti-CD5 (clone 53_7.3), biotinylated anti-MAC-1 (clone M1/70), and Alexa-647 labeled anti-B220 (clone RA3-6B2), followed by incubation with Streptavidin-PE-Cy5 conjugate. After washing the cells are fixed with formaldehyde and analyzed by flow cytometry.
(39) Identification of a cell displaying CD19, B220, MHC II, surface IgG2a/kappa chain and MAC-1, which is negative for CD5. Methods for the identification of cell surface markers are well known in the art Immunohistochemical staining with antibodies against MAC-1, CD19, B220, MHC II molecules, IgG2a/kappa chain and other markers are commercially available (e.g. from Abcam, Sigma Aldrich, etc.) or may be produced in-house. Detection of bound antibodies may be performed by e.g. flow citometry. A non-limiting description of the detection and identification of said markers can be found in the Examples section. Textbooks on immunohistochemistry are e.g. [28].
(40) Animal models according to the invention. It is possible to use the cells according to the invention to generate animal models of human (high-grade) diffuse large B-cell lymphoma (DLBCL), activated B-cell (ABC) subtype. Such an animal model is useful for the in vivo evaluation of an agent or a therapeutic treatment for the treatment of lymphoma and/or prevention of proliferation of lymphoma cells. Due to the specific cell surface marker pattern of the cells according to the invention, it is possible to investigate tumor cell migration (tumor expansion) in vivo in an animal model according to the invention. To generate a mouse model, lymphoma cells according to the invention may be administered to a mouse, preferably a BALB/c or an immunocompromised mouse intraperitoneally in a dose of 10.sup.4 to 2×10.sup.5 cells/recipient, preferably 10.sup.6 to 5×10.sup.6 cells/recipient.
(41) In vitro models according to the invention. The cells according to the invention are useful models for the in vitro evaluation of an agent or a therapeutic treatment for the treatment of lymphoma and/or prevention of proliferation of lymphoma cells. The specific conditions necessary for in vitro growth indicate that the Bc-DLFL.1 cell line is a suitable tool to study stroma-tumor cell relationship in vitro and to test whether an agent affects this relationship. Agents affecting lymphoma and/or normal B-cell expansion/migration may also be studied in an in vitro model using the population of lymphoma cells of the invention.
EXAMPLES
Materials and Methods
Mice
(42) Inbred BALB/c and Rag1−/− [10] mice were originally purchased from Jackson Laboratory, and were maintained under SPF conditions at the Department of Immunology and Biotechnology under permits BAI/01/1390-003/2013 (issued by the Baranya County Government Office) and SF/688-18/2013 and SF/27-1/2014 (issued by the Ministry of Agriculture). After their retrieval from the SPF unit the mice were kept under clean conditions with 12 hours of light/dark cycles and were provided with water and pelleted food ad libitum.
Lymphoma Cell Isolation and Passage
(43) The original tumor was mechanically dispersed using a 70 μm cell strainer (BD Biosciences, Soft Flow Ltd, Pécs, Hungary) and resuspended in DMEM medium (Sigma-Aldrich, Budapest). The tumor cells at the dose of 10.sup.7 cells/recipients in 0.2 ml medium were injected intraperitoneally. For tumorigenicity testing various doses of lymphoma cells were injected intraperitoneally and the mice were observed daily up to 30 days. Mice with terminal stage tumor were sacrificed by cervical dislocation, and their lymphoid and other organs were collected under aseptic conditions in a laminar flow. For further passage mesenteric lymph node (mLN) and spleen were collected and processed by mechanical dispersion through 70 μm mesh size cell strainer (BD Biosciences (Soft Flow Hungary, Pecs).
Antibodies and Reagents
(44) Rat mAb against MHC Class II (IBL-5/22) was produced in our lab [11] and was used as hybridoma supernatant. mAb against peripheral lymph node addressin (PNAd, clone MECA-79) was purchased from BD Biosciences (Soft Flow Hungary, Pécs), anti-LYVE-1 (clone 223322) and goat anti-mouse Bcl-6 antibodies from R&D Systems (Biomedica Hungária Kft, Budapest). Anti-mouse VEGF-R2/flk-1 mAb (clone Avas12α1) was purchased from BD Biosciences. Anti-mouse CD19 (clone B3B4), anti-mouse CD3 (clone KT-3), anti-mouse LFA-1 (clone M14.4) and anti-mouse L-selectin/CD62L (clone MEL-14) and anti-mouse ICAM-1/CD54 (clone YN1/1) and anti-MAC-1 (clone M1/70) hybridoma lines were obtained from ATCC, anti-α4 integrin mAb (from clone PS/2) was kindly provided by Dr. Eugene C. Butcher. Anti-B220 IgG (clone RA3-6B2 from ATCC) was purified by Protein G chromatography and labeled with FITC or Alexa Fluor 568 dye (Life Technologies Magyarorszag Kft, Budapest) using standard labeling conditions or used as hybridoma supernatant. FITC-conjugated anti-mouse IgM, IgG1, IgG2a, IgG2b and IgA rabbit antibodies were purchased from Sigma-Aldrich. Control rat IgG was purified from Wistar rat serum using Protein G affinity chromatography. The unlabeled rat mAbs and the goat polyclonal antibodies were detected with goat anti-rat IgG or donkey anti-goat IgG respectively, conjugated with FITC or PE (BD Biosciences). For immunohistochemical staining the anti-B220 mAb was detected by Histols polymeric anti-rat IgG HRPO-conjugate (Hisztopatologia Kft, Pécs, Hungary).
Flow Cytometry
(45) Single cell suspension prepared from mLN, peripheral lymph nodes (pLN) or spleen of Rag1−/− or BALB/c recipients were incubated with monoclonal antibodies against MHC Class II, CD3, CD19, B220 or normal rat IgG and various anti-mouse immunoglobulin isotype antibodies at 10 μg/ml in PBS containing 0.1% Na-azide and BSA for 30 minutes followed by two washing steps. The bound antibodies were detected using FITC-conjugated goat anti-rat IgG, followed by washing. The cells were fixed in 1% buffered paraformaldehyde and the samples were analyzed using a Becton-Dickinson FACSCalibur and the CellQuest Pro software. Typically ten thousand single lymphocyte events as defined by their FSC/SSC characteristics were collected.
Histology and Immunohistology
(46) Formol-fixed and paraffin embedded tissues (spleen, mesenteric lymph nodes and mesenterium, thymus, peripheral lymph nodes, liver, kidney, lungs and brain) were processed according to standard histological procedures using hematoxylin-eosin and periodic acid-Schiff staining. For immunohistochemical or immune-fluorescent labeling tissues were placed in Killik embedding medium and snap-frozen in plastic molds. Frozen sections at 8 μm thickness were cut with a Leica cryostat and placed onto microscopic slides, and were allowed to dry. After fixing in cold acetone the sections were allowed to dry. The endogenous peroxidase activity was quenched with 0.1% phenyl-hydrazine hydrochloride in PBS for 20 minutes followed by washing. After blocking with 5% BSA in PBS for 20 minutes anti-B220 antibody was added and incubated for 4 minutes. After washing polymeric Histols anti-rat IgG-HRPO conjugate was added and incubated for 45 minutes. After repeated washing the enzymatic reaction was developed using DAKO acetate buffer and diamino-benzidine solution, and mounted using Permount medium.
(47) For dual immunofluorescence after fixation in acetone the slides were allowed to dry, and then rehydrated in 5% BSA-PBS. Next the sections were incubated either with anti-LYVE-1 or anti-PNAd mAbs, followed by FITC-conjugated goat anti-rat IgG. After washing the residual binding sites of the secondary antibody were saturated with normal rat serum at 1:50 dilution for 20 minutes, followed by adding Cy3-conjugated anti-B220 mAb. After incubation the sections were repeatedly washed in PBS and covered in 1:1 PBS-glycerol, and viewed under Olympus BX61 fluorescent microscope.
(48) The mesenteric location of tumor cells was determined by labeling the cells with either XenoLight DiR lipophilic dye or CFSE (5(6)-Carboxyfluorescein N-hydroxysuccinimidyl ester). DiR fluorescence was detected by FMT 4000 In Vivo Imaging System with 710(ex)/760(em) filter set, CFSE-labeled cells were revealed by immunohistochemistry of whole-mount mesenteric samples using HRP-conjugated anti-FITC or multifluorescent labeling for LYVE-1 lymphatic endothelium and fibronectin 24 to 72 hours following intraperitoneal injection of 2×10.sup.5 labeled lymphoma cells.
(49) The in vivo tissue distribution of Bc-DLFL.1 lymphoma cells was monitored by dual staining for MAC-1 and B220 followed by the flow cytometric evaluation of various lymphoid tissues (inguinal lymph nodes, mesenteric lymph nodes, mesenterium and spleen) at days 3 and 7 after the cell transfer.
(50) The expression of Bcl6 and Bcl7A was determined by indirect immunohistochemistry using 4B2 anti-mouse Bcl6 and 15C anti-Bcl7A monoclonal antibodies on formaldehyde-fixed and paraffin-embedded tissue sections from mesenteric lymph nodes and spleen from control and lymphoma-bearing mice.
Cytogenetic Alterations
(51) The cytogenetic characterization for modal chromosome number and translocation pattern was performed by SKY spectratypic analysis and Giemsa chromosomal staining at the Department of Genetics, University of Texas M. D. Anderson Cancer Center, Houston, USA.
Analysis of IgH Rearrangement
(52) DNA from 2×10.sup.5 lymphoma cells was extracted using Qiagen QIAamp DNA Micro Kit according to the user's instructions. The rearrangement status of Ig heavy chain gene was determined by PCR reaction using degenerate primers for various murine VH families as described [12]. The amplified products were electrophoresed and visualized using Biotium GelRed. The images were recorded using Bio-Rad Gel Doc XR instrument and Image Lab 5.0.0 software.
Expression of BAFF Receptors Variants (BAFF-R, TACI and BCMA) and CXCR5
(53) The expression of BAFF receptors variants (BAFF-R, TACI and BCMA) and CXCR5 was determined by flow cytometric analysis.
Statistical Analysis
(54) Survival data for Kaplan-Meier evaluation were statistically analyzed by logrank (Mantel-Cox) test using GraphPad Prism software.
Identification of the Spontaneous High-Grade B-cell Lymphoma
(55) As an incidental finding during the dissection of an aged BALB/c female mouse a soft tissue mass was found surrounding the terminal segment of ileum, accompanied with a robust splenomegaly. Macroscopic observation of the abdominal organs, lungs and brain and also peripheral lymph nodes (inguinal, cervical and brachial) and Peyer's patches did not reveal any gross pathology. To test whether the splenic enlargement may be caused by lymphohematopoietic malignancy the enlarged spleen was removed and single cell suspension was injected intraperitoneally into a cohort of BALB/c recipients. The injected mice showed a sharp decline of physical activities at around 15-18 days after the injection, and after sacrificing the moribund mice we observed enlarged mesenteric lymph nodes (mLN) and spleen, similar to the original tumor-bearing mouse (
(56) In both syngeneic BALB/c and allogeneic Rag1.sup.−/− recipients the tumor cells could efficiently be propagated. We found that injecting large number of cells (2.5×10.sup.7 and 2.5×10.sup.6 cells in each recipient) could uniformly lead to death within 15 days (p<0.001), and even 2.5×10.sup.5 cells/recipient were sufficient to induce 50% mortality in BALB/c recipients (
(57) Given the relative frequent appearance of B-cell derived malignancies in aged BALB/c mice [13], to define the hematopoietic lineage affiliation of the tumor we performed immunohistochemistry using B220 as a B-cell antigen. We found that both the splenic white pulp and the mLN contained homogenously B220-positive lymphoma cells, although at some locations within the splenic white pulp some remnants of the original follicles could be found, based on their more intense B220 expression (
Cytogenetic Alterations
(58) Chromosome staining of Bc-DLFL.1 cells revealed 39-41 chromosomes, typically 40/XX. SKY analyses revealed a number of translocation involving chromosomes 6, 10, 11 and 19 as t(10:6), t(6:10), t(11:19) and t(10:11) [
Expression of BAFF Receptors Variants
(59) The specific conditions needed to propagate Bc-DLFL.1 raised the dependence of this lymphoma for tissue-derived factors for survival. The most likely candidates are the different receptors for BAFF. Exploiting the co-expression of MAC-1 and B220 by the lymphoma cells, thus separating them from the MAC-1 negative normal B cells we found that Bc-DLFL.1 cells co-expressed all three receptors (BAFF-R, BCMA and TACI) with BAFF-R showing the most intense labeling, while normal B cells expressed only BAFF-R at detectable levels [
Immunoglobulin Gene Expression and Production in the Bc-DLFL.1 Lymphoma
(60) Most B-cell lymphomas in both humans and mice express productively rearranged immunoglobulin genes. To test whether such a rearrangement results in detectable cell surface immunoglobulin, we stained the lymphoma cells for IgM, IgD, IgG subclasses and IgA, in addition to kappa light chain. We found positive reactivity for kappa chain and IgG2a without the appearance of IgM, IgD, other IgG classes or IgA (
(61) Flow cytometric analyses established that the lymphoma cells express MAC-1, CD19, MHC Class II, B220, supporting that the malignant transformation affected B cells. Furthermore, the expression of surface BcR of IgG2a/κ light chain isotype also indicates mature B-cell origin, unlike the frequent B-cell progenitor tumors observed in mice with conditional Pax5-deletion [12]. The combined phenotypic characterization and IgH V-region rearrangement analysis revealed that, within the B-lineage, the lymphoma cells most likely have originated from a germinal center stage subset, although its Bcl-6 protein expression is below the normal germinal center intensity, rendering this cell unclassifiable between germinal center (GCB) or activated B cell (ABC) regarding cell of origin.
(62) To determine the rearrangement pattern of the Ig heavy chain gene variable region of the Bc-DLFL.1 lymphoma we amplified the genomic DNA using VH-family specific primer pairs. We found rearrangement of IgH genes within the VH7183 region in lymphoma cells isolated from both BALB/c and Rag1−/− recipients using normal BALB/c mLN as reference sample for successful IgH V-region amplification (
(63) The presence of IgG2a/κ surface immunoglobulin indicated isotype switch, usually associated with B cells having undergone germinal center (GC) reaction coupled with Ig affinity maturation, in which process Bcl-6 transcriptional repressor plays a crucial role [14, 15]. As GC-derived B-cell lymphomas in humans overwhelmingly express of Bcl-6, next we investigated the presence of Bcl-6 in Bc-DLFL.1 by flow cytometry. Early studies found Bcl-6 expression in lymphoma cells. However, a later study using indirect immunohistochemistry using 4B2 anti-mouse Bcl6 and 15C anti-Bcl7A monoclonal antibodies on formaldehyde-fixed and paraffin-embedded tissue sections from mesenteric lymph nodes and spleen from control and lymphoma-bearing mice found no detectable Bcl6 expression at a level displayed by normal splenic centroblasts. On the other hand, while normal germinal center cells and follicles are devoid of Bcl7A labeling, we found a readily detectable expression both by marginal zone B cells and Bc-DLFL.1 cells. [
Mesenterial Accumulation of Bc-DLFL.1 Cells
(64) We found that fluorescence-labeled lymphoma cells rapidly accumulate in the mesenterium in the perivascular fat tissue, forming small lymphoma clusters arranged in a discrete bead-like pattern. Both in vivo bioimaging of lipophilic DiR dye-labeled lymphoma cells or CFSE-loaded cells detected by anti-fluorescein immunohistochemistry revealed identical pattern as condensed patches along the mesenterial fat, thus excluding labeling artifacts. The omental fat pads also showed an extensive accumulation of lymphoma cells, in agreement with previous reports on the involvement of this structure in the peritoneal homing of lymphocytes [
Tissue Location of Bc-DLFL.1 Cells Independent from CXCR5
(65) The lack of Bcl6 and the presence of Bcl7A raised that the propagation of the high-grade B-cell lymphoma cells occurs outside follicular location, thus bypassing the need for the recognition of CXCL13 chemokine by its cognate receptor CXCR5. Labeling of mesenteric lymph node from tumor-bearing mice revealed that while the residual small-sized lymphocytes preserve their CXCR5 display, the blast-sized B220-positive lymphoma cells are mostly negative or only weakly positive for this chemokine receptor [
Preferential Expansion of Bc-DLFL.1 Cells in the Mesenterium and Mesenteric Lymph Nodes
(66) To monitor which organs can provide suitable microenvironment for the expansion of Bc-DLFL.1 cells we compared frequency of MAC-1/B220 double positive cells in the total lymphocyte population in various lymphoid organs, and calculated the fold increase as a measure of expansion. We found that the Day 7:Day 3 ratio was highest in the mesenteric lymph nodes and mesenterium (17× and 15.6×, respectively) followed by the spleen (5.9×) and least in the peripheral lymph nodes (4.4×) [
Analysis of Homing Receptor Expression in Bc-DLFL.1 Lymphoma
(67) Efficient homing to peripheral lymphoid tissues is initiated by specific interaction between recirculating leukocytes and endothelial cell surface adhesion molecules. We labeled freshly removed lymphoma cell suspension from mLN of Rag1.sup.−/− recipients with rat mAbs against LFA-1 (CD11α/CD18), ICAM-1 (CD54), L-selectin (CD62L) and α4 integrin. Bc-DLFL.1 lymphoma cells express ICAM-1 (CD54), L-selectin (CD62L) and α4 integrin. Expression of ICAM-1 and LFA-1 molecules is higher than that of L-selectin and α4 integrin (
(68) The combined level of ICAM-1 and LFA-1 seems sufficient to promote mLN-directed migration, as the high endothelial venules in mLN co-express PNAd and MAdCAM-1 addressins as docking molecules for L-selectin and α4 integrin, respectively, whereas the lower level of L-selectin reduces the degree of lymphoma homing to pLN where only PNAd acts as homing addressin [20].
Metastasis of Bc-DLFL.1 Lymphoma Cells to Mesenteric Lymph Nodes Involves Afferent Lymphatic Vessels of the Mesentery
(69) In addition to the enlarged spleen and mLN in lymphoma-bearing mice, we also noticed a substantial swelling of perivascular adipose cuffs surrounding the arterioles in the mesentery, a bi-layered sheet of mesothelium. HE staining combined with immunohistochemical labeling for B220 revealed that lymphoma cells accumulate both in the reticular perivascular connective tissue and in tight compact clusters in luminal arrangement (
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