Effects of GSI inhibition with crenigacestat in the context of anti-BCMA CAR T cells. Although crenigacestat increased surface expression of BCMA on myeloma cells and decreased levels of soluble BCMA, expression of genes targeted by NF-κB family members was altered. Coculture of myeloma cells with monocytes in the presence of GSI inhibited myeloma cell growth. Changes in the microenvironment included decreased numbers and cell-cell interaction of nonclassical monocytes. Importantly, CAR T-cell function was not impaired by GSI.