Abstract 568: Activation of the RXR nuclear receptor regulates CD4 T cell activity in a murine model of HER2+ breast cancer
Authors: Leal Ana Sofia , Liby Karen T. 
Published: June 2023

Abstract
The role of CD4 T cells for anti-tumor responses is less recognized than CD8 cells. Evidence suggests that CD4 T cells can act directly as antitumor cells or direct the maturation and activation of dendritic cells (DCs). The retinoid X receptor (RXR) is a member of the nuclear receptor superfamily of ligand-dependent transcription factors. RXR and its heterodimers have profound effects on the function of myeloid cells, but effects on T cells are less known. Treatment with the RXR agonist MSU42011 (100 mg/Kg diet) reduced tumor burden in a HER2+ model of breast cancer (p=0.0068) and in a KRAS-driven model of lung cancer (p=0.0015). However, when human lung cancer cells were implanted into immunodeficient mice, MSU42011 failed to reduce tumor burden, suggesting that the anti-tumor properties of MSU42011 are dependent on a functional immune system. After 10 days of treatment, the percentage of CD4, CD62L+ T cells in HER2+ mammary tumors treated with MSU42011 was significantly higher compared to the control group (2.41 vs 3.78, p=0.05), as analysed by flow cytometry. Additionally, tumor antigen presenting cells (CD11c+, CD11b+, IA-IE+) and DCs (CD11c+, IA-IE+) had increased expression of PDL1 in the MSU42011 group when compared with controls (MFI=4016 vs 5225, p=0.069; 5484 vs 7140, p=0.045, respectively). RT-PCR analysis of whole tumors showed a significant increase in mRNA expression of interferon (IFN; p=0.0026) and IL12a (p=0.0011) in treated mice. Similar increases in IFN and IL12a were found in the murine model of lung cancer. Next, T cells were depleted to determine if required for the anti-tumor effects of MSU42011. CD8 cells depletion did not reverse the anti-tumor efficacy of MSU42011. CD4 depletion in mice treated with MSU42011 rescued tumor growth (p=0.016 MSU42011 vs MSU42011+anti-CD4), as tumors of mice treated with MSU42011 and anti-CD4 antibodies for 10 days grew at the same rate as tumors treated with control plus or minus anti-CD4 antibodies. Tumors treated with MSU42011 and anti-CD4 antibodies also showed reduced levels of IL12a compared with MSU42011 alone (2.28 vs 0.87, p&gt;0.05), as determined by RT-PCR.To dissect the effects of RXR activation on CD4 and DC cells, primary DCs, alone or co-cultured with T cells and conditioned media from cancer cells, were treated with MSU42011 (100 nM). This treatment increased PDL1 and IL12 mRNA expression in DCs. T cells, co-cultured with DC and conditioned media and treated with MSU42011, expressed higher IL2 mRNA levels. MSU42011 also increased expression of IFN in CD3 T cells. In conclusion, MSU42011 increased recruitment and activation of CD4 T cells in vitro and in HER2+ mammary tumors. These data, in combination with our previous work showing that RXR agonists reduce expression of tumor-promoting FOXP3 T cells in vitro and in vivo, confirm a strong correlation between RXR pharmacologic activation and CD4 T cell activation within the tumor microenvironment.
Citation Format: Ana Sofia Leal, Karen T. Liby. Activation of the RXR nuclear receptor regulates CD4 T cell activity in a murine model of HER2+ breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 568.