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BackgroundAlthough Immune checkpoint inhibitors (ICI)-targeting therapies have revolutionized the treatment of cancer, several tumors do not respond to those therapies. Preclinical and clinical evidences suggest that STING is a promising target to improve the immunogenicity of tumors, turning them responsive to ICI, and enhancing anti-tumor response. DMXAA failed to show efficacy in clinical trials, despite its encouraging anti-tumor response in preclinical phase, highlighting the need of accurate translational preclinical models. On top of the specificity barrier reported for STING-targeting agents, the heterogeneity of STING variants and their variability in the response to STING-targeting therapies, brings another level of complexity in preclinical evaluation of anti-STING therapies. Here, we report the generation of STING humanized (hSTING) mouse models enabling the in vivo assessment of STING-targeting agents.MethodsHuman STING variants show a high heterogenicity and population stratification. Different variants, and isoforms, respond differently to STING agonists. We developed mouse models expressing the main human STING variants and isoforms found in the population to recapitulate this complexity. Human STING was inserted by knock-in at the endogenous locus to enable a physiological expression pattern of STING while invalidating the mouse gene. Herein, we will focus on the human STING full length H323 model.ResultsT and B lymphocytes, NK, DCs and monocytes frequence in the spleen, bone marrow and blood were found to be similar in hSTING and WT mice, suggesting that the humanization of STING did not alter the immune cell distribution in these compartments. These cells express human STING, while no expression of mouse STING was observed. Splenocytes isolated from hSTING and WT mice produced IL-6 and IFN-γ upon activation with 2'3'-cGAMP, a cyclic dinucleotide with activity towards both mouse and human STING. Similarly, a mouse and human STING agonist induced the activation of DCs in both hSTING and WT mice, as observed by the increased expression of CD80/CD86 on DCs ex vivo and in vivo. Moreover, systemic production of IL-6, IFN-γ and TNF-α in response to this STING agonist was observed and suggest that human STING is functional in hSTING mice. As expected, hSTING mice did not respond to activation with DMXAA in vivo, whereas this agonist induced the systemic production of cytokines and activation of DCs in WT mice.ConclusionsThe novel hSTING model described here supports the assessment of human STING-targeting agents in immuno-oncology and inflammation. Intercrosses of this model with ICI humanized models could support the assessment of combination therapies

BackgroundThe breakthrough of immunotherapies has unleashed new hope and new success for cancer therapy. However, the choice of a preclinical model is one of the main challenges as they are important for evaluation of translatability to help support testing in clinical studies, including potential efficacy and tolerability of immunotherapies during preclinical development.The development of mouse models featuring a human immune system (HIS) provides new paths for the investigation of the efficacy of immunotherapies in preclinical models engrafted with human tumors. Although these models provided a breakthrough in the assessment of immune targeting agents, they also come with a few significant caveats. These include: a lack of a mature human myeloid compartment in the mouse, and a short life span of the model when this compartment is promoted at non-physiological levels via the over-expression of human cytokines. Here, we report a novel mouse model (BRGSF-HIS), featuring functional human lymphoid and myeloid compartments. The human immune response of this model was assessed through examination of the immune cells composition in the tumor microenvironment (TME), and its ability to respond to biologics known to trigger cytokine release syndrome (CRS).MethodsBRGSF (balb/C Rag2-/-, IL2Rg-/-, SIRPaNOD and Flt3-/-) is a highly immunodeficient mouse, with reduced murine myeloid cells, which allows long term CD34+ HSC-engraftment and development of human lymphoid and myeloid compartments (human CD141+ and CD1c+ DC subsets, CD123+ pDC, CD14+ monocytes), in blood, spleen and bone marrow. The engraftment is stable for over twelve months with no side effects. The effect of exogenous human Flt3 ligand (Flt3L) on the composition of TME in A549 model, and an anti-CD3 antibody (OKT3)-induced CRS, were assessed.ResultsExogenous human Flt3L significantly and transiently increased the proportion of human myeloid cells. This can be recalled by continuous dosing of Flt3L. Assessment of tumor immunobiology in A549 model, showed increased tumor-infiltrating T-cells (mainly CD8+ T-cells) and myeloid cells, while tumor-infiltrating NK cells were decreased. The presence of myeloid cells provides a new opportunity for assessment of myeloid targeted therapies, as proven using pDC-depleting antibodies. OKT3 administration resulted in CRS symptoms including a temperature drop, body weight loss and a change in serum cytokine levels. Symptoms were mitigated upon administration of tocilizumab, suggesting the contribution of the myeloid compartment in the response observed.ConclusionsThese data demonstrate that BRGSF-HIS mice support development of functional human myeloid cells and that this mouse model enables preclinical evaluation of cancer immunotherapy in vivo.