Challenging the predictability of preclinical models for assessment of T-cell engagers

(Excerpt from Kader Thiam's talk at the Cell Engager Summit)

The 4th Annual Cell Engager Summit was held May 24–26 in Boston. It was an in-person opportunity for scientific experts to meet around themes to advance the development of new, safe and effective multi-specific immune cell engagers for solid and liquid tumors in the clinic. As expertise partner, it was also an opportunity for genOway, and for Kader Thiam, our Senior VP, to present its preclinical BRGSF-HIS mouse model and demonstrate how this physiologically relevant model could best meet the needs of researchers.

As a preamble, Kader Thiam emphasized the increasing need for translational preclinical models to assess efficacy and immune-related adverse events (irAE). T-cell engagers have been shown to be effective in B-cell malignancies, and the development of new strategies is essential to improve the efficacy in solid tumors. In humans, a high risk of immune-related adverse events has been reported in clinical settings.

So, the first question was to understand if preclinical models could be predictive of irAE induced by T-cell engagers.

In 2020, Matas-Cespedes et al.¹ evaluated the human cytokines secreted into mouse plasma in PBS and OKT3 (anti-CD3 antibody)-treated NSG mice at sacrifice. The revealed that PBMC-reconstituted NSG mice enable OKT3-induced hIL-2, hIL-10, hTNF & hIFN-ᵧ cytokine release, but hCD45⁺ cells circulating in the blood were predominantly hCD3⁺ cells (>90%) with minimal hCD19⁺ and hCD14⁺ cells. This study, conducted by AstraZeneca and Medimmune, thereby demonstrates that CD34⁺ reconstituted NSG mice enable limited OKT3-induced cytokine release syndrome (CRS).

The trigger for CRS appears to be T-cell activation and massive release of interferon γ from either activated killer T cells or the tumor cells themselves. In a second step, the secreted interferon induces macrophage activation, producing excessive amounts of additional cytokines such as interleukin-6, tumor necrosis factor-α, or interleukin-1020. Thus, presence of the human myeloid compartment should amplify the inflammatory response and be more translatable to Humans.

Our BRGSF-HIS model exhibits both human lymphoid and myeloid compartments and has a wide therapeutic window. Compared to 12 weeks, the 28-week-old BRGSF-HIS mice show a relatively stable reconstitution rate, a slight variation in myeloid populations (pDCs, cDCs) and NK, and an 8% increase in monocytes. Moreover, injection of exogenous Flt3 ligand boosts human cDC & pDC in blood and spleen and enhances the frequency and number of human monocytes and NK cells.

And compared to the NOG-EXL6HIS mouse, induction of the myeloid compartment in BRGSF-HIS has no effect on body weight and no obvious phenotype reported up to 55 weeks post reconstitution.

How to ensure that the myeloid compartment is functional in the BRGSF-HIS mouse?

Experiments conducted by Lightchain Bioscience with fluorescence have shown that human macrophages from the BRGSF-HIS incubated anti-CD47-TAA bispecific display phagocytosis of target cells. Moreover, Anti-CD303 Ab injection induces 90% depletion of hpDCs in blood and spleen from the first day of treatment to 7 days after treatment. Fournier et al.², mAbs, 2018, showed that this depletion was mediated by antibody-dependent cell-mediated cytotoxicity (and ADCP) in vivo, suggesting that the myeloid compartment is functional.

Could the BRGSF-HIS mice be used to investigate immune-related adverse events?

Administration of OKT3 induces human cytokine release in blood of BRGSF-HIS mice in a time-dependent manner. This secretion is increased in the case of treatment with FLT3 ligand. IL-6, TNF-alpha and IFN-gamma are notably detected, unlike what happens in NSG-HIS mice confronted with a CRS¹. In the BRGSF-HIS mouse, cytokines IL-10, IL-12p70, IL-13 and IL-8 are also induced. This CRS could be mitigated upon tocilizumab (α-IL6-R mAb) pre-treatment. This confirms the fact that the myeloid compartment of BRGSF-HIS mice enhances the predictability of CRS in preclinical models. Boosting the myeloid compartment increases mouse serum amyloid A (SAA) levels induced by OKT3, clinical signs that are also mitigated by tocilizumab.

Evidence of CRS induction and modulation in BRGSF-HIS mice

Using the clinical compound blinatumomab, or BLINCYTO^®, (which is an anti-CD3/anti-CD19 antibody) 24 hours after boosting the myeloid compartment with the Flt3 ligand causes a release of cytokines and an important decrease in the body temperature of the mouse.

However, no change appears in the concentration of these other interleukines: hIL-1RA, hIL-7, hIFN-α, hRANTES, and hIL-8. Analysis of the immune cell population after injection of the myeloid-targeted compound shows that these injected mice tend to have less cDC and more pDC than OKT3-injected mice.

Conclusion and Take-Home Messages

The BRGSF-HIS mouse seems to be a highly relevant preclinical model to study CRS because:

• Cytokine profile is modified when myeloid compartment is present
• The clinical signs (loss in body weight and temperature) are observed 24h post OKT3 and BLINCYTO^® administration
• The model responds to standard rescue protocol; CRS, SAA, and loss in body weight and temperature drop are mitigated upon tocilizumab administration

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References:

1. Matas-Céspedes et al., Clinical & Translational Immunology, 2020 Nov 4;9(11):e1202. doi: 10.1002/cti2.1202. eCollection 2020. https://pubmed.ncbi.nlm.nih.gov/33173582/
2. Fournier et al., mAbs, 2018 May/Jun 2018;10(4):651-663. doi: 10.1080/19420862.2018.1451283. Epub 2018 Apr 10. https://pubmed.ncbi.nlm.nih.gov/29553870/

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