Three-dimensional in vitro lung model, process for preparing said model, and its use for determining and /or predicting the sensitizing effects of inhalable products

Abstract

The invention relates to a three-dimensional in vitro alveolar lung model comprising essentially the four cells types as follows: alveolar type II epithelial cells able to secrete (lung laying) surfactant, endothelial cells which forms the inner lining of capillaries providing a permeable barrier, dendritic-like cells, such as non-differentiated THP-1, linking innate and adaptive immunity and macrophage-like cells, able to participate to defense mechanisms by ingesting foreign materials by phagocytosis. The invention also relates to a process for preparing said model, and its use for assessing the irritation potential or toxicity of inhalable products such as particles or molecules on the alveolar barrier of lungs, and also for determining and/or predicting the sensitizing effects of inhalable products such as particles or molecules on the alveolar barrier of lungs.

Claims

1. A three-dimensional in vitro alveolar lung model comprising: without mast cells, the four cells types as follows: a) alveolar type II epithelial cells able to secrete surfactant, b) endothelial cells which form the inner lining of capillaries providing a permeable barrier c) dendritic-like cells, d) macrophage-like cells, able to participate to defense mechanisms by ingesting foreign materials by phagocytosis, wherein: said three-dimensional in vitro lung model is in the form of a culture well equipped with a porous membrane separating the well into an apical compartment exposed to an air-liquid interface, and a basolateral compartment submerged in a culture medium, said epithelial cells and said macrophages being present in the apical compartment, and said endothelial cells and said dendritic-like cells being present at the basolateral compartment and immerged in the culture medium, said porous membrane has pores comprised between 2 and 10 μm, dimensioned to allow migration of the dendritic-like cells from the basolateral compartment to the apical compartment.

2. The model according to claim 1 wherein said macrophage-like cells are THP-1 cells, differentiated with either one of PMA (Phorbol-12-myristate-13-acetate) or with 1,25-dihydroxyvitamin D3.

3. The model according to claim 1, wherein all cells are immortalized human cell lines.

4. The model according to claim 1, wherein said alveolar type II epithelial cells are A549 cells.

5. The model according to claim 1, wherein said endothelial cells are EA.hy926 cells.

6. The model according to claim 1, wherein said dendritic-like cells are non-differentiated THP-1 cells.

7. The model according to claim 1, wherein the porous membrane has pores comprised between 3 and 8 μm.

8. A process for preparing the three-dimensional in vitro alveolar lung model as defined in claim 1, comprising: co-culturing of cells a)-d) in a culture well equipped with an insert having a porous membrane that separates the apical and the basolateral compartments of said culture well, in the following step sequence: i) seeding the lower face of a membrane insert having pores between 2 and 10 μm, with 0.24×10.sup.5 to 0.6×10.sup.5 endothelial cells/cm.sup.2, said lower face corresponding to the basolateral side, ii) at least four hours later, seeding the other side of the membrane insert with the alveolar type II epithelial cells, said other side of the membrane insert corresponding to the apical side, iii) about 4 days later, adding a cell suspension containing between 0.1 and one million dendritic-like cells/mL to the lower basolateral side of the membrane insert, and then iv) adding macrophage-like cells on top of the alveolar type II epithelial cells seed, and finally, v) introducing the membrane insert into a co-culture medium in order that said endothelial cells and said dendritic-like cells are present at the basolateral compartment and immerged in the co-culture medium; and said epithelial cells and said macrophages-like cells are present in the apical compartment, at the air-liquid interface.

9. The process according to claim 8, wherein at least one of said macrophage-like cells are THP-1 cells differentiated with PMA (Phorbol-12-myristate-13-acetate), said alveolar type II epithelial cells are A549 cells, said endothelial cells are EA.hy926 cells, or said dendritic-like cells are non-differentiated THP-1 cells.

10. The process according to claim 8, wherein, in the step ii) the other side of the membrane insert is seeded with the alveolar type II epithelial cells at a seeding density of 0.12×10.sup.5 to 1.2×10.sup.5/cm.sup.2 cells.

11. The process according to claim 8, wherein, in the step ii) the other side of the membrane insert is seeded with the alveolar type II epithelial cells at a seeding density of 0.5×10.sup.5 to 1.0×10.sup.5/cm.sup.2 cells.

12. The process according to claim 8, wherein, in the step iv) 0.12×10.sup.5 to 1.2×10.sup.5 macrophage-like cells/cm.sup.2 are added on top of the alveolar type II epithelial cells.

13. A process for determining and/or predicting the sensitizing effects, and/or the irritation potential or toxicity of an inhalable product on the alveolar barrier of lungs, comprising: A) a step of exposing by pulverizing and nebulizing the inhalable product over the apical compartment of a three-dimensional in vitro alveolar lung model as defined in claim 1, wherein the porous membrane having pores comprised between 2 and 10 μm, and wherein exposing leads to activation of the dendritic-like cells, and B) a step of co-culturing said activated dendritic-like cells with a T lymphoblast cell line.

14. The process according to claim 13, wherein T-cells present a Helper type 2 (TH2) profile if the product to be tested is a suspected respiratory sensitizer.

15. The process according to claim 13, wherein markers for the respiratory sensitization potential are measured by FACS and/or by ELISA.

16. The process according to claim 15, wherein said markers for the respiratory sensitization measured by FACS are at least one of the following: CD40, CD54, CD86, TSLPr, IL-1ra, OX40L.

17. The process according to claim 15, wherein markers for the respiratory sensitization measured by ELISA are at least one of the following: TSLP, IL-33, IL-25, RANTES, MCP-1, MIP-3a, IL-6, IL-7, IL-10, GM-CSF.

18. The process according to claim 13, wherein further biological endpoints comprising release of interleukins, genotoxicity, biomarkers of sensitization, proteomics, transcriptomics and metabolic activation are measured.

Description

FIGURES

(1) Further advantages and aspects of the lung model of the invention could be deducted from the description of the embodiments presented in the example part below, with reference to the accompanying drawings, in which:

(2) FIG. 1: is a schematic drawing of the Transwell® insert with the tetraculture of the present invention representing the lung model;

(3) FIGS. 2A to 2E are histograms showing the expression of the respective cell surface markers CD86, CD40, IL7ra, CD54 and OX40L on the cell surface of THP-1 cells in the tetraculture lung model after 24 h exposure to HDM;

(4) FIGS. 3A and 3B are diagrams presenting the viability % after 24 h and 48 h exposure to different concentrations of chemical respiratory sensitizers, respectively Trimellitic Anhydride (TMA) and Phthalic Anhydrid (PA);

(5) FIGS. 4A, 4B and 4C are diagrams showing the viability % after 24 h and 48 h exposure to different concentrations of chemical respiratory irritants, respectively Sodium Dodecyl Sulfate (SDS), Acrolein (Acr) and Methyl Salicylate (MeSa);

(6) FIGS. 5A and 5B are diagrams showing the cell surface marker expression of CD54 on THP-1 cells in the tetraculture in vitro lung model according to the invention (A), and in monoculture model not forming part of the invention (B) after exposure to sensitizers and irritants for 24 h (mean+/−standard error);

(7) FIGS. 6A and 6B are diagrams showing the cell surface marker expression of CD86 on THP-1 cells in the tetraculture in vitro lung model according to the invention (A), and in a monoculture model not forming part of the invention (B) after exposure to sensitizers and irritants for 24 h (mean+/−standard error);

(8) FIG. 7 is a diagram showing the cell surface marker expression of ILra on THP-1 cells in the tetraculture in vitro lung model according to the invention after exposure to sensitizers and irritants for 24 h (mean+/−standard error);

(9) FIG. 8 is a diagram showing the cell surface marker expression of OX40L on THP-1 cells in the tetraculture in vitro lung model according to the invention after exposure to sensitizers and irritants for 24 h (mean+/−standard error);

(10) FIG. 9 is a diagram showing the cell surface marker expression of TSLPr on THP-1 cells in the tetraculture in vitro lung model according to the invention after exposure to sensitizers and irritants for 24 h (mean+/−standard error);

(11) FIGS. 10A and 10B are diagrams showing cytokines released in the tetraculture in vitro lung model according to the invention after exposure to chemical sensitizers and irritants for 24 h and 48 h (A): IL-7 basal levels: DMSO basal level for 24 h: 18.2±0.0 pg/mL; for 48 h: 19.5±1.2 pg/mL; Water for 24 h: 18.6±0.3 pg/mL; for 48 h: 18.2±0.0 pg/mL (B) GM-CSF basal levels: DMSO basal level: DMSO: for 24 h: 32.4±6.0 pg/mL; for 48 h: 31.0±3.7 pg/mL; water: for 24 h: 47.0±9.2 pg/mL; for 48 h: 43.1±5.4 pg/mL (Mean+/−SE) (Letters illustrate significant differences (Factorial ANOVA+Fisher LSD post hoc test at P<0.05 level of significance, n=6).

(12) FIGS. 11A and 11B are diagrams showing viability of THP-1 cells after 24 h exposure to PA (FIG. 11A) and TMA (FIG. 11B) in monoculture in submerged conditions. In this figure, the highest tested concentrations represent the maximum of solubility of the compounds in medium containing 0.2% of DMSO.

EXAMPLES

Example 1

(13) In this example are used the following cell lines: A549, EA.hy926, THP-1 and Mϕ-THP-1. Their respective characteristics are as follows:

(14) Cell line A549 corresponds to Human bronchial epithelial cells with ability to produce surfactant;

(15) EA.hy926 cell line is a somatic cell hybrid with endothelial characteristics;

(16) THP-1 is a human monocytic leukemic cell line; and

(17) Mϕ-THP-1 are macrophages derived from THP-1 cells, differentiated with PMA (Phorbol-12-myristate-13-acetate) or with 1,25-dihydroxyvitamin D3.

(18) Preparation of the Different Media:

(19) The protocols used are as follows:

(20) EA.hy926 medium: Remove 60 mL of DMEM (Dulbecco's Modified Eagle's medium) medium from a new bottle (500 mL) and add 50 mL of FBS (10%), then 5 mL of HEPES stock solution (250 mM; sterile, filtered) to get a HEPES buffered medium (25 mM), Preservation with 5 mL Pen/Strep (penicillin/streptomycin).

(21) Coculture 10% medium: Remove 5 mL of DMEM media from a new bottle (500 mL) and add 5 mL of HEPES stock solution (250 mM; sterile, filtered) to get a HEPES buffered medium (25 mM), Mix and remove 125 mL, Add 50 mL of IMDM, then add 75 mL of RPMI medium, Mix and remove 55 mL, Then add 50 mL of FBS (10%) into the medium and 5 mL of Pen/Strep.

(22) Coculture 1% Medium: Remove 5 mL of DMEM medium from a new bottle and add 5 mL of HEPES stock solution (250 mM; sterile, filtered) to get a HEPES buffered medium (25 mM), Mix and remove 125 mL, Add 50 mL of IMDM then add 75 mL of RPMI, Mix and remove 10 mL, Add 5 mL of FBS (1%) into the medium and 5 mL of Pen/Strep.

(23) THP-1 Complete Medium: Remove 57.5 mL of RPMI medium from a new bottle (500 mL). From those 52.5 mL, transfer 10 mL in a falcon tube and throw away the remaining medium, Prepare the working solution of 10 mM 3-mercapto ethanol in RPMI medium by adding 7 μL of commercial solution into 10 mL RPMI, mix, transfer 2.5 mL into the bottle of medium, Add 50 mL of FBS (10%) into the medium, then 5 mL of Pen/Strep.

(24) Preparation of the Three-Dimensional In Vitro Alveolar Lung Model:

(25) In this example, the chronology of the different steps was the following:

(26) 1. Day −2

(27) Differentiating macrophage cells (overnight): THP-1 cells are differentiated with PMA (Phorbol-12-myristate-13-acetate) or with 1,25-dihydroxyvitamin D3 (80 μLPMA+40 mL medium+16 million cells per flask T125) overnight and then kept in the flask for 1-5 days, medium being renewed overnight.

(28) 2. Day 0: Seeding of the Insert

(29) Preparation of the EA.Hy926 Cells: Add 0.11 million to 0.54 million cells per insert (0.24 10.sup.5 to 0.6 10.sup.5 cells/cm.sup.2, preferentially 0.24 10.sup.5 cells/cm.sup.2), The volume needed for the seeding in the insert is here 700 μL, Prepare first the cell suspension for all inserts (+2 extra inserts for pipetting mistakes), mix in order to well homogenate the cell suspension, Properly put the inserts inside the well of the plate, Return the plate and gently put the 700 μL of EA.hy926 under the insert, Then place the plate into incubator.

(30) At least 4 hours later:

(31) Preparation of the A549 Cells: The volume needed for the seeding in the insert is here 2 mL, The pellet of A549 cells is re-suspended in the EA.hy926 medium: 0.27 million to 0.54 million cells per insert (0.12 10.sup.5 to 1.2 10.sup.5 cells/cm.sup.2, preferentially 0.6 10.sup.5 cells/cm.sup.2), Prepare first the cell suspension of A549 cells for all inserts (into EA.hy926 medium, count 2 extra inserts for pipetting errors). Mix/homogenate well the cell suspension.

(32) Prepare the plate with inserts for the seeding and homogenate the cell suspension from time to time when seeding cells on inserts, to avoid the cells settling down in the tube): Return plate and add 1.5 mL of EA.hy926 medium into the well, Check the endothelial cellular layer under microscope, Add the 2 mL of A549 cells in the insert.

(33) 3. Day 3:

(34) Changing the medium of the plate of inserts: Remove old medium of the insert and add 2 mL of Coculture 10% medium, Remove old medium of the well and add 2 mL of Coculture 10% medium,

(35) 4. Day 4:

(36) Prepare DC-THP-1 in a 6-Well Plate: Prepare cell suspension at 1 million of DC-THP-1 cells/mL in the present example (from 0.1 million cells to 1 million cells per mL). Take a new plate and add 1 mL (i.e. a volume sufficient to recover the EA.hy926 cells) of DC-THP-1 cell suspension in the 6 wells of the new plate and move inserts from the old plate to the new one.

(37) Differentiated THP-1 Cells (Mϕ-THP-1): Wash cells with PBS, Add accutase on differentiated THP-1 cells to detach cells, and put the flask into incubator for 15 minutes, Centrifuge 5 minutes at 300 g, discard supernatant, Dissolve the pellet in Coculture 1%, Count the cells and add into the insert 0.27 to 0.54 million of MD-THP-1 cells per insert in the present example (0.12 to 1.2 10.sup.5 cells/cm.sup.2, preferentially 0.6 10.sup.5 cells/cm.sup.2) in 700 μL of Coculture 1% medium.

(38) At least 4 hours later: discard the medium from the insert to switch to the ALI. Overnight incubation.

(39) Exposure of the insert to the inhalable product (particles or molecules) to be tested on the three-dimensional model of the invention, prepared under the above protocol, can be performed after 10 to 12 hours (time required for the cells to produce the surfactant) with the in vitro lung model as presented on FIG. 1.

(40) 5. Day 5:

(41) Example of exposure of the inserts is performed in a Vitrocell® Cloud device (Waldkirch, Germany), previously cleaned under sterile conditions, and maintained at 37° C. The inserts are placed into the device. A cloud, from 200 to 500 μL of the product to be tested) is then distributed homogenously inside the chamber and starts to settle on the surface. After about 10 to 30 minutes (depending on the injected product), the cloud is settled by single droplet sedimentation. The concentration which is deposited on the insert can be calculated in g/cm.sup.2.

(42) After exposure, the inserts are moved back to their plate and, after incubation (usually 24 h or 48 h depending of the compound to test, the following measurements can be performed.

(43) 6. Day 5, 6 or 7: Measurements

(44) The biological endpoints from 0 to 48 h after exposure depending on the expected time- and end-points can be performed.

(45) The possible biological endpoints to be measured are for instance: Cell viability or cytotoxicity, Cytokines secretion, DC migration, DC activation, Macrophages phagocytosis, EC activation, Macrophages phagocytosis, Staining for immune-cytochemistry or immune-fluorescence, or RNA extraction. This list is not limitative.

(46) 7. Day 5: Example of DC Isolation and Coculture with T-Cells

(47) DC Isolation Using:

(48) Cell sorting using FACS (e.g. BD FACS Aria) by using different markers required for T cells activation such as MHCII, CD86, CD54 (to recover activated THP-1 cells) and CD11a (to isolate cells from EA.hy.926 cells). It could be necessary to pool different wells in order to have enough cells for the coculture with T-cells. Magnetic beads (e.g. Dynabeads) with positive or negative isolation with different surface markers such as MHCII, CD86, CD54 and CD11a.

(49) Activated DC Coculture with T-Cells: T-cells should present surface markers allowing the cell activation (TCR and CD4), survival (CD28 binding B7.1 or CD80 and B7.2 or CD86) and differentiation, Coculture cells in media: Coculture with 1% FBS (used for exposure of the tetraculture-DC) or RPMI 1640 with 10% FBS (used for both THP-1 and T-cell line) The addition of several compounds (such as cytokines needed for T cells differentiation . . . ) to mimic the complex tissue environment of the Secondary Lymphoid Organ has to be considered. Cell ratio: several cellular ratios have been tested as only a few naïve T cells are able to recognize any given epitope (1 in 10.sup.6). DC should interact with many T cells in the hope of being found by a T cell that recognize in the antigen on its surface: 0.01 million DC for 0.1 million T cells (1/10) 0.01 million DC for 1 million T cells (1/100) 0.01 million DC for 10 million T cells (1/1000) Depending on the selected T cell line, medium should be either renewed or complemented by adding fresh medium (20% to 30% of volume every 2 or 3 days) following ATCC/supplier subculturing recommendations.

(50) Endpoints Measurements:

(51) Cytokines secretion (IL-4, IL-5 and IL-13) and surface marker expression should be measured every 24 h, from 24 h (1 day) coculture to 120 h (5 days) coculture. T-cells should present a Helper type 2 (TH2) profile if the compounds are a respiratory sensitizer.

Example 2

(52) Inserts prepared according to example 1 were exposed to chemical compounds and to positive controls using the Vitrocell® Cloud system (Vitrocell, Waldkirch, Germany). All compounds were diluted in a 1/1(v/v) solution of sterile saline solution and PBS.

(53) Exposure to HDM (House Dust Mite):

(54) House dust mite is a very common allergen which is associated with asthma and allergic rhinitis. As no data were found for in vitro exposure, concentration to which cells of the lung model of the present invention were to be exposed was determined on the basis of in vivo studies. In vivo, mice are generally exposed intra-nasally to 1 pg of Der p1 (major protein allergen of HDM). Knowing that the alveolar surface of mice is 82.2 cm.sup.2, a concentration of 0.01 μg/cm2 was calculated to expose to the insert (being 45 pg/insert).

(55) Exposure to Chemicals:

(56) Inserts were exposed to a range of concentrations to chemical respiratory irritants and sensitizers in order to determine first the viability of the tissue using the Alamar Blue assay. Resazurin, the active ingredient of Alamar Blue assay, is a cell permeable blue non-fluorescent compound. Upon entering cells, resazurin is reduced to pink highly fluorescent resorufin. Viable cells continuously convert resazurin to resorufin. The fluorescence is proportional to cell viability.

(57) Following 24 h and 48 h exposure to the compounds through the Vitrocell cloud, cells were incubated for 1 hour to 400 μM of Alamar Blue diluted in Coculture 1% medium.

(58) Once cell viability was determined for each compound, a concentration around 75% of viability was selected for the measurement of the expression of cell surface markers on THP-1 DC.

(59) The tetraculture lung model was exposed to several concentrations of two known chemical respiratory sensitizers: Phthalic Anhydrid (PA) or Trimellitic Anhydride (TMA) and two known respiratory irritants: Acrolein (Acr), Methyl Salicylate (MeSa), or Sodium Dodecyl Sulfate (SDS).

(60) Flow Cytometry Measurements:

(61) 24 h and 48 h after exposure to the Vitrocell Cloud, THP-1 DC were recovered in the medium in the well. After centrifugation for 5 minutes at 300 g, cells were washed with PBS and staining was performed using antibodies listed in table 1 below (following the manufacturer's recommended dilutions) and the corresponding isotype control to determine the unspecific binding of the antibody and ensure the observed staining is due to specific binding rather than an artifact.

(62) TABLE-US-00001 TABLE 1 Sensitization Surface Excitation Emission Marker Antibody (nm) (nm) TSLPr APC mouse IgG1 645 660 (Biolegend) OX40L PE mouse IgG1 k anti- 496 578 human OX40L (BD) IL-7Ra Alexa Fluor 647 mouse 650 668 IgG1 (Biolegend) CD86 PE mouse IgG1 (BD) 496 578 CD54 APC mouse IgG1 (BD) 645 660 CD40 FITC mouse IgG1 (BD) 493 525

(63) For Cytotoxicity:

(64) With SYTOX Blue the excitation wavelength is 444 nm, and the emission wavelength is 480.

(65) Relative Fluorescence Intensity (RFI) was used as an indicator of OX40L, IL7ra, CD40 and CD86 and CD54 expression and was calculated by the following formula I:

(66) $\mathrm{RFI}\left(\%\right)=\frac{\mathrm{MFI}\mathrm{of}\mathrm{treated}\mathrm{cells}-\mathrm{MFI}\mathrm{of}\mathrm{treated}\mathrm{isotype}\mathrm{control}\mathrm{cells}}{\begin{array}{c}\mathrm{MFI}\mathrm{of}\mathrm{vehicle}\mathrm{control}\mathrm{cells}-\\ \mathrm{MFI}\mathrm{of}\mathrm{vehicle}\mathrm{isotype}\mathrm{control}\mathrm{cells}\end{array}}\times 100$

(67) FIGS. 2A to 2E show respectively the expression of the cell surface markers CD86, CD40, IL7ra, CD54 and OX40L on the cell surface of THP-1 cells in the tetraculture lung model after 24 h exposure to HDM. Expression of the cell surface markers on the viable cells was measured via flow cytometry.

(68) It is observed that all markers are upregulated after 24 h exposure to HDM compared to the control. Therefore, the markers IL7ra, OX40L, CD86, CD40, and CD54 on the cell surface of THP-1 cells in the tetraculture lung model could be used to determine the respiratory sensitization potential of chemical compounds.

(69) The diagrams of FIGS. 3A and 3B show the viability after 24 h and 48 h exposure to different concentrations of chemical respiratory sensitizers, respectively Trimellitic Anhydride (TMA) and Phthalic Anhydrid (PA).

(70) A dose response is observed for cell viability of the alveolar tissue model.

(71) The diagrams of FIGS. 4A, 4B and 4C show the viability after 24 h and 48 h exposure to different concentrations of chemical respiratory irritants, respectively Sodium Dodecyl Sulfate (SDS) and Acrolein (Acr) and Methyl Salicylate (MeSa).

(72) A dose response is also observed for cell viability of the alveolar tissue model.

Example 3

(73) The Vitrocell® Cloud system (Vitrocell, Waldkirch, Germany) was used for the delivery and exposure of cells to nebulize the compounds diluted in PBS and depending on the vehicle control, in sterile water or sterile water plus DMSO.

(74) House Dust Mites (HDM), protein Bet v1 (an additional known protein sensitizer) and Acrolein (Acr) were diluted in sterile water. Phthalic anhydride (PA), Trimellitic anhydride (TMA) and Methyl salicylate (MeSa) were diluted in DMSO.

(75) Viability was assessed using the Alamar Blue assay 24 h and 48 h after exposure according to the protocol detailed in example 2 above.

(76) The concentration leading to 25% of cytotoxicity (meaning 75% of viability: CV75) relatively compared to the vehicle control was determined using the graphs presented in example 2.

(77) To measure the expression of cell surface markers and the release of different cytokines, the cells of inserts prepared according to example 1 above were exposed to the CV75 or, when it was not possible to reach 75% of viability, cells were exposed to the maximum of solubility of the compounds.

(78) Bet v1 Exposure:

(79) As no data were found for in vitro exposure, concentration to which cells of the lung model of the present invention were to be exposed was determined on the basis of in vivo studies. In vivo, mice were exposed to 2 pg of bet v1 (important protein allergen of pollen). Knowing that the alveolar surface of mice is 82.2 cm.sup.2, a concentration of 0.024 pg/cm2 was calculated.

(80) After 24 h and 48 h, THP-1 cells were recovered, stained and analysed using a flow cytometer according to the protocol detailed in example 2 above. Supernatants were recovered for cytokines measurements.

(81) No effect on viability was observed after exposure to HDM and Bet v1.

(82) Exposure to Bet v1 led to a viability relatively compared to control of 100.7%+/−1.2% at 24 h and 89.5%+/−4.2% at 48 h. Exposure to HDM led to a viability relatively compared to control of 100.0%+/−0.03% at 24 h and 95.7%+/−0.03% at 48 h.

(83) In parallel, THP-1 cells were exposed in submerged conditions in monoculture in order to reproduce the data obtained using the h-CLAT (human cell line activation test) assay. The h-CLAT assay is based on the property of chemicals to activate dendritic cells, property which is common to both skin and respiratory sensitizers. The h-CLAT is an in vitro model validated at the European level (ECVAM validation).

(84) On a comparative purpose, the expression of CD86 and CD54 cell surface markers were also evaluated in the h-CLAT. It is currently recommended to use the h-CLAT to assess the skin sensitizing potential of chemicals. As skin and lung share the DC activation property, h-CLAT may be considered to be used to assess also the respiratory sensitizing potential of chemicals. To remind, there is no validated models to assess respiratory sensitization available on the market yet.

(85) As different antibodies, fluorochromes and equipment were used to measure the CDs expression, threshold level obtained in literature on the h-CLAT could not be compared to those measured in this example.

(86) However, FIG. 5 shows the expression of CD54 on THP-1 cells in tetraculture (A) and in monoculture (B). Increases were observed after the exposure to chemical respiratory irritants (PA and TMA) whereas no increase was observed for vehicle controls (water and DMSO) and the chemical irritant (acrolein) (FIG. 5A). On the contrary in FIG. 5B, no increase was observed in monoculture after exposure to respiratory sensitizers and increase of CD54 expression was measured after exposure to the irritant which misclassifying the irritant chemical acrolein as sensitizer.

(87) FIG. 6 shows the expression of CD86 on THP-1 cells in tetraculture (A) and in monoculture (B). Increases were observed after the exposure to chemical respiratory irritants (PA and TMA) whereas no increase was observed for vehicle controls (water and DMSO) and the chemical irritant (acrolein) (FIG. 6A). On the contrary, no increase was observed in monoculture after exposure to respiratory sensitizers and the CD86 expression after TMA exposure is even lower than the vehicle control (FIG. 6B).

(88) The three-dimensional in vitro alveolar lung model according to the present invention (tetraculture) shows then an improvement for the discrimination of chemical respiratory sensitizers and irritants. To reinforce the discriminating property of the system, additional markers were used and respiratory protein sensitizers were also added to the set of tested compounds.

(89) FIG. 7 shows the cell surface marker expression of IL7ra on THP-1 cells in the tetraculture after exposure to sensitizers and irritants for 24 h. The decrease of IL7ra expression after acrolein exposure could be used as a discriminating marker between irritants and sensitizers (regardless of types, chemical or protein).

(90) FIG. 8 shows the cell surface marker expression of OX40L on THP-1 cells in the tetraculture after exposure to sensitizers and irritants for 24 h. The increase of OX40L expression after protein sensitizers exposure could be used as a discriminating marker between protein sensitizers and the chemical irritants/sensitizers.

(91) FIG. 9 shows the cell surface marker expression of TSLPr on THP-1 cells in the tetraculture after exposure to sensitizers and irritants for 24 h. The increase of TSLPr expression after chemical sensitizers exposure could be used as a discriminating marker between chemical sensitizers and the chemical irritants/protein sensitizers.

(92) Other parameters were evaluated in the system after the exposure of acrolein and both chemical respiratory sensitizers PA and TMA.

(93) Table 2 below gives a summary of the results obtained for all cytokines measured, wherein, indicates a decrease of cytokine release compared to the vehicle control, indicates an increase of cytokine release compared to the vehicle control and =indicates no change observed between exposure and the vehicle control:

(94) TABLE-US-00002 TABLE 2 Acrolein PA TMA 24 h 48 h 24 h 48 h 24 h 48 h MCP-1 = = = = MIP-3a IL-6 IL-7 = = = = RANTES = GM-CSF IL-10 =

(95) These results are also illustrated in FIG. 10 which gives more insights of IL-7 (FIG. 10A) and GM-CSF (FIG. 10B) concentrations relatively compared to vehicle controls. Increase of MCP-1, MIP-3a, IL-6 RANTES, GM-CSF and IL-10 release could be used as markers for respiratory sensitizers. The decrease of MCP-1, MIP-3a, IL-6, GM-CSF and IL-10 release could be used as markers for respiratory irritants along with the increase of IL-7 cytokine release.

(96) Finally, and as shown on FIG. 11, it has to be noted that due to the low solubility of TMA and PA, it is not possible to reach any cytotoxity of THP-1 cells in monoculture in submerged conditions (FIGS. 11A and 11B) while decrease in viability is observed in the tetraculture system after exposure to these compounds (FIGS. 3A and 3B).

(97) While only certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes or equivalents will now occur to those skilled in the art. It is therefore, to be understood that this application is intended to cover all such modifications and changes that fall within the true spirit of the invention.