A novel HDAC inhibitor, OBP-801, upregulated LMP2, an immunoproteasome subunit, in clear cell renal cell carcinoma (ccRCC) cells, resulting in enhanced MHC class I expression, and a combined treatment of OBP-801 and anti-PD-1 antibody effectively alleviated ccRCC in mice. Here, HDAC9 is linked to clear cell renal carcinoma.