Acute myeloid leukemia (AML) is a heterogeneous disease classified into 9 FAB subtypes according to the origin and/or maturity of the malignant cells: M0 undifferentiated, M1 minimally mature myeloblastic, M2 mature myeloblastic, M3 promyelocytic, M4 myelomonocytic, M4eos eosinophilic, M5 monocytic, M6 erythrocytic and M7 megakaryocytic. Overcoming this heterogeneity by the induction of a common surface antigen which would already be the target of an existing immunotherapy would be of great potential therapeutic interest to standardize a common immunotherapy approach to AML. Inecalcitol, a vitamin D receptor agonist characterized by a high anti-proliferative effect and a low calcemic potential, has been shown to stimulate CD38 expression at the surface of the M3 subtype HL-60 cell line and of the M5 subtype U-937, MOLM-13 and THP-1 cell lines (ASH 2016, AACR 2017). We now report the effect of inecalcitol on AML cell lines representative of the 7 other FAB subtypes: KG-1 (M0), UOC-M1 (M1), Kasumi-1 (M2), OCI-AML2 (M4), EOL-1 (M4eos), HEL-92.1.7 (M6) and CMK (M7). Inecalcitol induced CD38 at the surface of CD38- cell lines (HL-60, U-937 and EOL-1) and strongly increased CD38 density at the surface of already CD38+ cell lines (KG-1, UOC-M1, Kasumi-1, OCI-AML2, MOLM-13, THP-1 and CMK) in a concentration-dependent manner, but remained without effect on CD38- HEL-92.1.7 cells. We have quantified the number of CD38 molecules at the surface of all cell lines (except HEL-92.1.7 which was unresponsive to inecalcitol) using the CellQuant calibrator (Biocytex) analysis by flow cytometry. In basal vehicle-treated condition, the number (in thousands, mean ± sem, n=2 or 3) of CD38 molecules per CD38+ cell were: Kasumi-1, 1.5 ± 1.0; MOLM-13, 2.5 ± 0.6; KG-1, 2.7 ± 0.9; THP-1, 7.0 ± 0.2; CMK, 12.1 ± 1.5; OCI-AML2, 16.1 ± 1.2. With 10nM inecalcitol, a maximal increase in CD38 density was usually obtained within 3 days, or after 7 days for KG-1 and CMK: Kasumi-1, 16.1 ± 3.3 (x11); MOLM-13, 43.3 ± 0.3 (x17); KG-1, 15.4 ± 3.7 (x5.7); THP-1, 17.9 ± 0.6 (x2.3); CMK, 15.4 ± 3.3 (x1.3); OCI-AML2, 73.5 ± 3.5 (x4.6). After 3 days of exposure to 10 nM inecalcitol, CD38 molecules appeared at the surface of initially CD38- cells and became quantifiable: U-937, 7.5 ± 0.4 (n=3); HL-60, 24.4 ± 4.9 (n=3) and EOL-1 ranged from 5.5 to 72.7 (n=2). In conclusion, after exposure to inecalcitol, CD38 appeared at the surface of CD38- AML cell lines and the density of CD38 increased at the surface of CD38+ AML cell lines, altogether representative of all 9 FAB classification subtypes M0 to M7, except M6 (erythrocytic) which represents 5% of all AML cases. These results suggest that treatment by inecalcitol may render 95% of AML patients sensitive to highly sensitive to anti-CD38 immunotherapy such as daratumumab. Citation Format: Enguerran Mouly, Cécile Planquette, Emilie Rousseau, Rémi Delansorne. Inecalcitol respectively induces or increases CD38 expression at the surface of CD38- or CD38+ AML cell lines representative of all 9 FAB subtypes except M6 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1890.