Page 99 - 2022_02-Haematologica-web

CD38 CAR-NK cells targeting AML
cytotoxicity after irradiation and could be applied clinical- ly in a similar manner to the NK-92 cell line.21 However, irradiation limits the potential for in vivo expansion and persistence - important variables in determining the clini- cal efficacy of cellular therapies. This requirement for irradiation may be avoided by using donor-derived, eNK cells, although this approach is further complicated by robust CD38 upregulation encountered during ex vivo expansion. Our CRISPR/Cas9 CD38 KD eNK cells reduce effector cell fratricide, representing an approach that could be explored clinically.
CD38 was a breakthrough immunotherapeutic target in multiple myeloma. While there is greater variability in CD38 expression in AML, CD38 is a potential target anti- gen in this disease. Daratumumab was shown to be active in an in vivo model of AML, while isatuximab has recently been examined in a large-scale, in vitro study.10,22
The expression pattern of CD38 in AML, in which there is often overlap with normal cell populations including myeloid and monocytic populations, raises concerns about considerable ‘on-target, off-tumor’ toxicity when a potent effector cell is directed toward CD38. High-affini- ty CD38 CAR strategies may maximize the proportion of patients for whom a CD38-directed therapy is likely to have activity, at the expense of considerable myelosup- pressive effects. It is important to consider that not all off- tumor effects are undesirable: in the case of CD38, elimi- nation of CD38-positive immunoregulatory cell subsets may lead to a beneficial therapeutic effect.23,24 The effica- cy of lower-affinity CD38 CAR strategies is likely to be limited to cases with strong expression or pharmacologi- cal upregulation of CD38. Herein we investigated an approach to CD38 CAR targeting in AML which aims to strike the balance of efficacy, applicability, and off-tumor
A
B
C
Figure 2. CD38 CAR-KHYG-1 activity against primary acute myeloid leukemia samples. (A) Histograms depict unstained controls (blue) and anti-CD38 stained blast cells (red), from a range of acute myeloid leukemia (AML) patients chosen to represent a spectrum of CD38 expression. Relative mean fluorescence intensity (MFI) figures for stained samples are reported. (B) Graphs represent specific blast cytotoxicity after co-culture assays with CD38 CAR transduced KHYG-1 (blue) and mock- transduced KHYG-1 (black) at specified effector to target (E:T) ratios for each corresponding patient’s sample in Figure 2A. (C) The correlation plot and linear regres- sion line depicts specific blast cell cytotoxicity at the E:T ratio of 3:1, versus CD38 expression (relative MFI) of primary AML samples from all co-culture experiments carried out in 2A, (n=8 experiments).
haematologica | 2022; 107(2)
441