Enhancing CAR T Cell Efficacy in Breast Cancer with STING Agonist
Summary
The tumor microenvironment's poor infiltration and persistent cell viability make it difficult to treat solid tumors using CAR T cells (TME). The STING agonists DMXAA or cGAMP were utilized in a recent study to enhance CAR T cell function in an orthotopic model of breast cancer. Improvements in tumor control and a rise in CAR T cell persistence in the TME were seen in the data. Single-cell RNA sequencing revealed that the use of STING agonists increased the recruitment of CAR T cells and changed the ratio of immune-stimulating to suppressive myeloid cells in the TME. The combination of anti-PD-1 and anti-GR-1 mAbs to the CAR T cell and STING agonist therapy was necessary for complete tumor regression.
Fig.1 Graphical abstract. (Xu, 2021)
Research Criteria
They have put into practice a combinatorial immunotherapy strategy based on CAR T cells polarized to a Th/Tc17 phenotype, anti-PD-1 mAb, STING agonists DMXAA or c-GAMP, and anti-GR-1 mAb that eradicates tumors in an immunocompetent syngeneic model of breast cancer by following a logical and sequential approach. The capacity of the STING agonists, DMXAA and c-GAMP, given at a site distant from the tumor, to boost CAR T cell recruitment and persistence at the tumor site was the most striking discovery. These studies, to our knowledge, are the first to show how a STING agonist affects the trafficking characteristics of adoptive T cell products. Additionally, no intratumoral injection of the STING agonist was necessary for this action.
Sample Type
Cells from mouse solid tumor tissues.
Result—The Stimulator of IFN Genes (STING) Agonist DMXAA Greatly Enhances CAR T Efficacy
They evaluated the effect of STING agonist DMXAA on the efficacy of Th/Tc17 CAR T cells in treating NT2 tumors in mice. DMXAA improved the persistence of Th/Tc17 CAR T cells and significantly enhanced antitumor efficacy and survival compared to mock-transduced T cells or Th/Tc17 CAR T cells alone. Single-cell transcriptome sequencing showed three immune cell populations in the TME with different gene expression profiles in the presence or absence of DMXAA. On day 7 after therapy, T cells and macrophages increased and regulatory T cells and a subcluster of myeloid cells decreased in the TME.
Fig.2 Tumor control by Th/Tc17 CAR T cells is enhanced by DMXAA injection owing to the altered composition of tumor-infiltrating immune cells. (Xu, 2021)
Result—CAR T Cell Exhaustion Limits In Vivo Efficacy
Combining DMXAA with LH28z Th/Tc17 CAR T cell treatment effectively slowed the growth of tumors for around 10 days, but it was unable to entirely remove them. On days 7 and 10 following the LH28z Tc/Th17 CAR T cell therapy, single-cell transcriptome sequencing of the tumor microenvironment was carried out to ascertain the reason for the loss of efficacy. The research showed that early expression of PD-1, lag3, cd160, and tox by possible CAR T cells increased along with a decrease in tcf7 expression. Through flow analysis of CAR T cells in the tumor microenvironment, which revealed a significantly higher expression of PD-1 in CD4+ and CD8+ T cells on day 7 following treatment compared to mock-transduced CAR T cells, the single-cell results were confirmed. Increased expression of the proteins S100A8, S100A9, and cxcl2, which are responsible for the production of the hormone's calprotectin and suppressive myeloid cells, respectively, was also noticed. Overall, the results show distinct variations in the expression of genes involved with fatigue and function in T cells 7 to 10 days following DMXAA therapy.
Fig.3 DMXAA treatment enhances the number and cytotoxicity of Tc17 CAR T cells in the TME, although they eventually become exhausted. (Xu, 2021)
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Reference
- Xu, N.; et al. STING agonist promotes CAR T cell trafficking and persistence in breast cancer. Journal of Experimental Medicine. 2021, 218(2): e202000844.
