CD44-Induced differentiation of HL60, NB4, THP1 and KG1a myeloid leukemia cell lines

CD44-ligation with the anti-CD44 antibodies A3D8 and H90 triggers terminal differentiation in AML1/2 to AML5 blasts (Charrad et al, Nat Med, 5:669, 1999). Here we show that A3D8 and H90 inhibits the proliferation of myeloid leukemia cell lines HL60, NB4, THP1 and KG1a (by a factor 2 - 5 at day 2). Using three specific criteria: NBT assay, expression of differentiation antigens CD11b, CD14 and/or CD15, and cytological modifications we presently show that H90 is as efficient as retinoic acid to trigger terminal granulocytic differentiation of HL60 (myeloblastic) and NB4 (promyelocytic) cells. Moreover, like RA, H90 provokes the degradation of PML-RARα oncoprotein in NB4 cells. This differentiation is maximum at days 3 to 4. H90 is unable to induce any significant differentiation of either THP1 (monoblastic) or KG1a (most immature myeloblast) cells. The differentiation-inducing activity of A3D8 is similar to that of H90 in HL60 cells but not in the other cell lines. Indeed, unlike H90, A3D8 induces an important apoptotic cell death in NB4 cells (about 50% apoptotic cells at day 3, as shown by acridine orange assay) and it induces terminal differentiation of the monoblast-like THP1 leukemia cells. KG1a cells, which are most immature, cannot be significantly differentiated by either H90 or A3D8. However, simulataneous treatment with on one hand H90 or A3D8, on the other hand RA (which is inactive when used alone), induces full monocytic differentiation of KG1a cells. These data show for the first time that 1) CD44-ligation inhibits the proliferation of leukemia cells, 2) its differentiation and apoptosis-inducing ability depends on the antibody and the myeloid cell type, and 3) the differentiative effect is greatly improved by RA in most immature KG1a cells.