MPPE1 and neoplasm: We therefore propose that CLEC9A should be used for assessing cDC1 content in tumors, either as a single marker or in combination with other strictly cDC1-specific genes such as XCR1. However, XCR1 expression on intratumoral cDC1 has to be carefully evaluated, given our observation that tumor-derived PGE2 can induce its downregulation.