An increased content of free cystine has been found in phagocytic blood cells, the polymorphonuclear leukocytes and monocytes, but not in lymphocytes of patients with cystinosis. Electron micrographs showed no intracellular crystals, suggesting that cystine may be primarily in noncrystalline form in these cells. A primary derangement of cystine metabolism or transport within the lysosomes of cells carrying out active endocytosis could account for these observations.
Schulman JD, Wong VG, Kuwabara T, Bradley KH, Seegmiller JE. Intracellular Cystine Content of Leukocyte Populations in Cystinosis. Arch Intern Med. 1970;125(4):660-664. doi:10.1001/archinte.1970.00310040084009