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CD38 CAR-NK cells targeting AML
through a retinoic acid response element within the CD38 gene.25 The vitamin D receptor agonist inecalcitol represents another investigational approach to CD38 modulation which could enhance the efficacy of CD38- directed therapies in AML through a similar principle.26 The timing of a clinically applied combination therapy using ATRA and a CD38 CAR-NK cell would require
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careful planning. Evidence suggests that NK cell exposure to ATRA may have a net inhibitory effect on NK cell function, suggesting that the preferred approach may be ATRA prior to adoptive cell transfer.27
CD38 targeted therapies are complicated by NK cell CD38 expression, observed clinically with the NK cell- depleting effects of daratumumab seen during the treat-
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Figure 4. CD38 KD - CD38 CAR-NK cells show enhanced cytotoxicity against primary acute myeloid leukemia samples. (A) CD38 knockdown (KD) expanded natural killer (NK) cells were electroporated with CD38 CAR mRNA or ‘dummy’ mRNA (CD16) prior to co-culture with bone marrow mononuclear cells from acute myeloid leukemia (AML) patients. Blast cell cytotoxicity was measured by percentage of propidium iodide (PI)-positive cells (representative dot-plots are shown). (B) Summary data of co-culture assays as described in (A), for seven AML patients compared using unpaired t-tests for each effector to target (E:T) cell ratio. (C) The CD38 expres- sion level of the blast population was correlated with the cytotoxic effect observed at an E:T ratio of 5:1 for experiments conducted in (B), and a linear regression model fitted using GraphPad Prism. (D) Bone marrow mononuclear cells from n=4 donors were treated with 10 nM all-trans retinoic acid (ATRA) or dimethyl sulfoxide (DMSO) for 48 h prior to anti-CD38 staining. A representative histogram is displayed and summary data of four pooled donors were compared using an unpaired t- test. (E) ATRA or DMSO pretreated cells were co-cultured with CD38 KD-CD38 CAR-NK cells. Summary data from three experiments. Analysis by unpaired t-test for each E:T ratio. Statistical significance is defined as *P≤0.05, **P≤0.01, ***P≤0.001.
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