Targeting myeloid cells in the tumor microenvironment in BRGSF-HIS mice

The emergence of immunotherapies has revolutionized oncology as, in addition to targeting tumor cells, treatments are now largely targeting immune cells. While many compounds have been developed, and proved efficient, to target effector T cells through immune checkpoint blockade, tumor-associated myeloid cells, present in the tumor microenvironment (TME), are now the focus of a lot of interest, especially to overcome and/or avoid a potential resistance to ICP therapies.

Relevant preclinical models to study myeloid cells in immuno-oncology

Immunodeficient mice reconstituted with a human immune system have proved their relevance and efficiency to test immunotherapies, and are now largely used.¹ One of these models, the BRGSF-HIS, displays stable engraftment for over a year, ² does not develop graft versus host disease, and develops functional human lymphoid and myeloid compartments. In addition, BRGSF-HIS mice’s human myeloid compartment can be boosted with exogenous human Flt3L injections, without side effects. ³ Among other features, BRGSF-HIS mice are permissive to mouse and human cancer cell line engraftment, ^4-6 and represent a valuable preclinical model to study cancer development and evaluate novel therapeutics.

Optimized non-small-cell lung cancer model with Flt3L-induced boost of myeloid compartment in BRGSF-HIS mice

The A549 cell line is commonly used in oncology to study non-small-cell lung cancer (NSCLC). These cells develop tumors when inoculated in BRGSF-HIS mice, and a single Flt3 boost prior to tumor cell inoculation does not impact tumor growth (Figure 1A). Interestingly, this single Flt3 boost does not significantly change the percentage of infiltrating human immune cells (Figure 1B), but associates with increased tumor-infiltrating T cells (mainly CD8⁺ T cells; not shown) and myeloid cells, and reduced tumor-infiltrating NK cells in the TME (Figure 1C). Notably, the immune infiltrate profile of Flt3-boosted BRGSF-HIS mice appears closer to the one observed in NSCLC patients, ⁷ with a majority of T cells (36% in FLt3-BRGSF-HIS mice vs. 46.5% in NSCLC patients).

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Figure 1. Effects of Flt3L-induced boost of myeloid compartment in BRGSF-HIS non-small-cell lung cancer (A549) tumor model. 25-week-old BRGSF-HIS mice were injected with hFlt3/Fc or vehicle prior to A549 inoculation (D0). Tumor growth was followed over 40 days (A), and tumors (400–500 mm³) were collected and analyzed by flow cytometry. Percentage of human CD45⁺ cells was determined (B), and immune infiltrate composition was identified (C). T cells = hCD3⁺; NK cells = hCD3^-/hCD19^-/hCD56⁺; Myeloid cells = hCD3^-/hCD19^-/hCD56^-. B cells (hCD19⁺) were absent from the tumors. Data from 26 mice, 3 donors.

BRGSF-HIS triple-negative breast cancer model mimics patients’ TME

Human triple-negative cancer (TNBC) MDA-MB-231 cell line is widely used in cancer research and drug development.

Figure 2. TNBC BRGSF-HIS model is donor independent and recapitulates TNBC patients’ TME. 22-week-old BRGSF-HIS mice were injected with hFlt3/Fc prior to MDA-MB-231 inoculation (D0). Tumor growth was followed over 30 days (A), and tumors (400-500 mm³) were collected and analyzed by flow cytometry. Percentage of human CD45⁺ cells in live cells (B), human monocytes in myeloid cells (C), hCD206⁺ M2 macrophages in monocytes (D), and hCD80⁺ and/or hCD86⁺ activated M2 macrophages (E) were determined. T cells = hCD3⁺/hCD56^-; NK cells = hCD3^-/hCD56⁺; Myeloid cells = hCD3^-/hCD56^-/hCD11b⁺/hCD33⁺; B cells = hCD19⁺/hCD3^-; Monocytes = hCD19^-/hCD3^-/hCD14⁺. Data from 25 mice, 5 donors.

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Upon implantation in FLt3-boosted BRGSF-HIS mice, in vivo growth of MDA-MB-231 cells is CD34⁺ donor independent (Figure 2A). As seen in TNBC patients, 8 TME of MDA-MB-231-bearing BRGSF-HIS mice is enriched in myeloid cells, representing around 60% of human infiltrating immune cells (Figure 2B). In addition, 70% of these infiltrating myeloid cells are monocytes (Figure 2C), and almost all are actually CD206⁺ M2 macrophages (Figure 2D). Thus, CD206-expressing M2 macrophages represent the main tumor-associated macrophages. Interestingly, M2 macrophages are known to promote breast cancer initiation, angiogenesis, invasion, and metastasis by generating an immunosuppressive TME. ⁹Finally, these M2 macrophages are mostly activated, as shown by hCD80 and hCD86 co-expression (Figure 2E).

These data demonstrate the relevancy and reliability of BRGSF-HIS mice to model human cancers and their TME, making BRGSF-HIS mice a good model to investigate potential immunotherapies, in particular therapies targeting tumor-associated myeloid cells.

Of note, the BRGSF-HIS model is available at genOway, designer and provider of multiple preclinical models in several research areas, including immuno-oncology, metabolism, cardiovascular diseases, and neuroscience.

References:

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3. Lopez-Lastra, S. et al. A functional DC cross talk promotes human ILC homeostasis in humanized mice. Blood Adv 1, 601-614 (2017). https://doi.org:10.1182/bloodadvances.2017004358
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