Genomic binding of wild-type and mutant Trp53 in mouse breast cancer cell lines

TP53 is one of the most frequently mutated gene in breast cancer. While p53 mutations often lead to loss of wild-type p53 activity, they can have a wide variety of gain-of-function (GOF) consequences. The impact of these GOF mutations in p53 on the anti-tumor immune response in breast cancer remains elusive. To address this, we have generated mouse mammary tumor models based on orthotopic injection of isogenic cell lines harboring the p53 mutations that most frequently occur in human breast cancer. By comparing the tumor immune landscape of these models and human breast tumors, we have uncovered that specific p53 point mutants consistently induce an immunologically ‘hot’ tumor phenotype, characterized by high infiltration of cytotoxic T cells, while other p53 mutations induce a non-T cell inflamed (‘cold’) microenvironment. In accordance with these high T cell levels, the hotp53 mutant tumors respond better to anti-PD-1immune checkpoint blockade than cold p53 mutant tumors. By comparing the different p53 mutants in terms of proteome profile, chromatin bindingproperties and protein complex formation, we have uncovered that T cell-enriched p53 mutants activate autophagy. Disruption of autophagy in an immunologically hot p53 mutant tumor abrogated the response to anti-PD-1 therapy. This work demonstrates that not all p53 mutations shape the immune microenvironment of mammary tumors in a similar fashion, and that response to immune checkpoint blockade depends on specific mutations in p53. This argues that screening for specific p53 aberrations in breast cancer may help guide immunotherapeutic strategies. The binding of Trp53 to the genome was examined in nine cell lines either harbouring differential Trp53 mutations or not (wild-type) . Cells were grown in DMEM + 10% FBS + 1% P/S. As a control, a TP53-KO cell line was used. Two biological replicates were performed.