Monosodium urate (MSU) crystals are known to induce
gouty arthritis, but also evoke specific cell immunity and work as an adjuvant by delivering several kinds of
binding proteins, including idiotypic
cancer vaccine peptides into dendritic cells. To investigate the potency of MSU crystals as a
cancer vaccine carrier in vivo, this preclinical study examined whether
intradermal injection of MSU crystals was safe for healthy adults. Subjects comprised 12 volunteers. Four different dose levels of MSU crystals were injected as follows: 2 μg (n = 3), 20 μg (n = 3), 200 μg (n = 3), or 2000 μg (n = 3). At 24 hours after administration, documented
erythema was seen around the injection site in a dose-dependent manner, particularly in all adults with MSU dose ≥200 μg. However, redness was limited to the grade I level of the National Cancer Institute toxicity criteria. Serum
uric acid levels did not show any change before and after injection. Moreover, neither
gouty arthritis nor tophi developed in any volunteers, indicating that
intradermal injection of MSU crystals did not induce systemic
inflammation at the doses that evoked significant local
inflammation. These findings suggest that
intradermal injection of MSU crystals is fundamentally safe and should be made available for clinical trials using MSU-crystal-conjugated
cancer vaccines.