In regulatory CD4+ T cells, RGCC was a common target of HAM/TSP and ATLL donors’ IgG, while ATLL IgG also strongly recognized cell division cycle-associated 3 (CDCA3), oncomodulin (OCM), and signal transducing adaptor molecule (STAM). This evidence concerns the gene CDCA3 and adult T-cell leukemia/lymphoma.