In Vitro Granuloma Models of Tuberculosis: Potential and Challenges

Abstract

Despite intensive research efforts, several fundamental disease processes for tuberculosis (TB) remain poorly understood. A central enigma is that host immunity is necessary to control disease yet promotes transmission by causing lung immunopathology. Our inability to distinguish these processes makes it challenging to design rational novel interventions. Elucidating basic immune mechanisms likely requires both in vivo and in vitro analyses, since Mycobacterium tuberculosis is a highly specialized human pathogen. The classic immune response is the TB granuloma organized in three dimensions within extracellular matrix. Several groups are developing cell culture granuloma models. In January 2018, NIAID convened a workshop, entitled "3-D Human in vitro TB Granuloma Model" to advance the field. Here, we summarize the arguments for developing advanced TB cell culture models and critically review those currently available. We discuss how integrating complementary approaches, specifically organoids and mathematical modeling, can maximize progress, and conclude by discussing future challenges and opportunities.

Keywords: granuloma; tissue culture models; tuberculosis.

Figure 1.

The collagen matrix model: (A) infected peripheral blood mononuclear cells (PBMCs); (B) uninfected PBMCs; (C) H & E staining showing multinucleated giant cells (arrows); (D) fluorescent staining of granulomas sections with 4′,6-diamidino-2-phenylindole (DAPI, nuclear stain), CD68 (macrophage marker, red), and CD3 (T cells, green) monoclonal antibodies. Reproduced from [17]. Permission to reprint this figure provided by ©2013 Kapoor et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License.

Figure 2.

The human in vitro lung tissue model. Cells are sequentially layered onto a collagen matrix and then infected macrophages are added to model the early events of human lung infection.

Figure 3.

The host immune response impact on granulomas. Human peripheral blood mononuclear cells from either naive or latent tuberculosis-infected individuals are incubated with autologous serum and Mycobacterium tuberculosis. The model has shown that host immune status has significant impacts on granuloma formation and function, and bacterial responses. Abbreviations: IFN-γ, interferon gamma; IL, interleukin; LAM, lipoarabinomannan; TNF, tumor necrosis factor.

Figure 4.

The bioelectrospray microsphere model: immunoaugmentation with Mycobacterium tuberculosis-specific T cells. A, Cellular aggregates within microspheres after 14 days. Scale bar 20 μm. B, Microspheres imaged after 4 days show early granuloma formation (orange). C, Addition of either ESAT-6 responsive T cells (red) or CFP-10 responsive T cells (blue) increases M. tuberculosis (Mtb) growth compared to infected peripheral blood mononuclear cells without supplemented T cells (black). Reproduced from [12] . Permission to reprint this figure by 2017 Tezera et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License. *P < .05; ***P < .001. Abbreviation: Con, control; RLU, relative light unit.

Figure 5.

A human breathing lung-on-a-chip. A, The alveolar system is modeled in a microfluidic device consisting of 2 overlapping parallel microchannels separated by a thin porous membrane. B, The alveolar-capillary interface is created in this system by culturing human alveolar epithelial cells and lung microvascular endothelial cells on either side of the membrane. To mimic breathing, cyclic vacuum is applied to the hollow chambers adjacent to the cell culture channels to stretch the membrane in the lateral direction. C, Introduction of Escherichia coli into the alveolar compartment of this model induces adhesion (top row) and transmigration (middle row) of neutrophils flowing in the lower vascular chamber. The recruited neutrophils then phagocytose the bacteria (bottom row). Portions of figure from [43] Huh D, Matthews BD, Mammoto A, Montoya-Zavala M, Hsin HY, Ingber DE. Reconstituting organ-level lung functions on a chip. Science 2010; 328:1662–8. Reprinted with permission from AAAS.