STAT5 and STAT3 balance shapes dendritic cell function and tumor immunity

Immune checkpoint blockade (ICB) has transformed cancer therapy. Therapeutic efficacy of ICB depends on dendritic cell (DC)-mediated tumor antigen presentation, T-cell priming and activation. However, the relationship between the key transcription factors in DCs and ICB efficacy remains unknown. Here, we discover that ICB reprogramed the interplay between the STAT3 and STAT5 transcriptional pathways in DCs, thereby activating T-cell immunity, and enabling ICB efficacy in cancer patients and tumor bearing mice. Mechanistically, STAT3 competed with STAT5 for JAK interaction, determining the fate of DC function. As STAT3 is often activated in the tumor microenvironment (TME), we designed specific PROTAC degraders of STAT3, SD-36 and SD-2301. Low doses of SD-36 selectively and preferentially degraded STAT3 in DCs and reprogramed the DC transcriptional network toward immunogenicity. Furthermore, SD-36 monotherapy efficiently treated mice bearing large, advanced tumors and ICB resistant tumors without any signs of toxicity. Notably, SD2301 exhibits superior therapeutic efficacy compared to SD-36. Thus, the crosstalk between STAT3 and STAT5 determines DC phenotype in the TME and STAT3-degradation holds promise for cancer immunotherapy. Overall design: BMDC derivation protocol: Bone marrow was collected from the femurs and tibias of mice, and red blood cells were lysed using ACK lysis buffer. Dendritic cells were generated with bone marrow cells cultured with GM-CSF (20 ng/ml) and Flt3L (100 ng/ml) in IMDM (Gibco, 12440-053) supplemented with 10% FBS, 1% penicillin-streptomycin and 55 µ? ß-meraptoethanol for 7-10 days. BMDCs were either sorted as DC1 (CD11c+ Xcr1+) using a FACSAria flow cytometry sorter (BD Biosciences) or purified using biotin anti-mouse XCR1 antibody (BioLegend,148212) and anti-biotin microbeads (Miltenyi Biotec, 130-090-485) following the manufacturer's protocols for subsequent experiments. Primary cell cultures were tested to be mycoplasma-free by MycoAlert Mycoplasma Detection kit. The RNA was isolated using the miRNeasy Micro Kit (Qiagen, 217084). 150PE RNA-seq was conducted by BGI Genomics via the DNBSEQ platform with a target of 30 million reads per sample.