TIGIT Expression Positively Associates with NK Cell Function in AML Patients

Abstract

Natural killer (NK) cells are essential innate immune effectors with promising anti-leukemia activity in acute myeloid leukemia (AML). However, clinical success of applying NK cells in AML treatment has not been achieved. A better understanding of the regulatory mechanisms for NK cell function is important to optimize this therapeutic strategy. T cell immunoglobulin and ITIM domain (TIGIT) is a recently identified inhibitory receptor expressed on T cells and NK cells. Multiple studies including ours have demonstrated its suppressive effect in anti-tumor CD8 T cell response. However whether and how TIGIT impacts NK cells in AML is unknown. Here we performed phenotypic and functional studies on NK cells derived from patients with newly diagnosed AML (n=30). Cells collected from healthy individuals (n=18) were used as controls. TIGIT expression and their contributions to NK cell function in AML were assessed. Peripheral blood samples were first examined by flow cytometry for the frequency of NK cells (defined as CD56+CD3-). The percentage of NK cells among peripheral blood mononuclear cells (PBMCs) in AML patients is comparable with that of healthy controls. In contrast, when we performed functional analysis to assess NK cells for cytokine release upon in vitro stimulation with a human leukemia cell line K562, we observed significantly lower intracellular production of IFN-γ in cells from AML patients compared with that of healthy controls. Consistently NK cells from AML patients expressed less Perforin, indicating a compromised killing capacity. We next evaluated the expression of TIGIT on CD56+CD3- NK cells. As some AML blasts and monocytes also express CD56, we performed multichannel flow cytometry and carefully gated out other cell components when assessing TIGIT expression. To our surprise, we observed a significantly lower frequency of TIGIT-expressing NK cells in AML compared with that of healthy controls (36.82 ±4.543% vs. 48.9±3.818%, P=0.0463). This data indicated that low-TIGIT expression associates with impaired NK cell function and AML progression. We further examined the phenotype and functional status of TIGIT+ NK cells. Expression of activating receptors (CD16 and CD160) and inhibiting receptors (KIR and NKG2A) on TIGIT+ vs. TIGIT- NK cells were analyzed. We observed a significant higher expression of CD16 (51.27±9.009% vs. 20.63±5.334%, P=0.0001) and CD160 (39.84±6.447% vs. 21.24±4.287%, P=0.0103) on TIGIT+ NK cells compared with that of TIGIT- NK cells. By contrast, TIGIT+ NK cells expressed lower KIR (24.06±3.796% vs. 43.59±6.96%, P=0.0046) and NKG2A (7.658±1.717% vs. 18.68±4.256%, P=0.0167) than TIGIT- NK cells. Importantly, functional studies demonstrated an elevated expression of Granzyme B and increased cytokine (IFN-γ and TNF-α) production by TIGIT+ NK cells compared with TIGIT- NK cells (IFN-γ, P=0.0283; TNF-α P=0.0347; Granzyme B, P=0.0493). These data suggest that TIGIT expression on NK cells associated with activated and high functional status. Collectively, our study demonstrates that 1) in line with lower capacity to produce IFN-γ, NK cells from AML patients express less frequency of TIGIT compared with healthy individuals; 2) TIGIT+ NK cells from AML patients express high levels of activating receptors and are highly functional manifested by more cytokine production and enhanced expression of Granzyme B compared with TIGIT- NK cells. These results indicate that in AML patient, TIGIT may contribute to the upregulation of NK cell function. This is in contrast to the observations of CD8 T cells in which TIGIT plays a suppressive role. Targeting TIGIT for cancer treatment is currently under active development. Our findings bring a call for caution on the TIGIT-targeted therapeutic strategy in AML as TIGIT might be a double-edged sword in anti-leukemia immune regulation. Disclosures No relevant conflicts of interest to declare.

Realizing Innate Potential: CAR-NK Cell Therapies for Acute Myeloid Leukemia

“…NK-cells and blast cells do express PD-1 and PD-L1, respectively and blockade using a PD-1 monoclonal antibody or scFv enhanced NK cell cytotoxicity against AML targets in vitro, although appears to be most relevant for resting rather than cytokine activated NK cells [ 181 ]. Inhibition of TIGIT in AML is intuitive, however conflicting reports regarding its effect in experimental systems in vitro suggest caution is warranted [ 92 , 182 ]. An antibody recognizing CD200 positive blast cells enhances the activity of cytokine induced killer cells, and the expression of CD200 on AML LSCs suggests this may be a useful pathway to target [ 183 , 184 ].…”

Targeting NK Cell Inhibitory Receptors for Precision Multiple Myeloma Immunotherapy

“…In one study, Jia et al. ( 190 ) found that, although the number of TIGIT +ve NK cells in AML patients were significantly lower in comparison to the healthy controls, these TIGIT +ve NK cells also express high levels of ARs CD16 and CD160. Importantly, functional experiments showed an elevated expression of granzyme B and increased IFN-γ and TNF-α production by TIGIT +ve NK cells compared with TIGIT −ve NK cells.…”

“…Importantly, functional experiments showed an elevated expression of granzyme B and increased IFN-γ and TNF-α production by TIGIT +ve NK cells compared with TIGIT −ve NK cells. Therefore, the authors suggest that TIGIT expression on NK cells could be associated with activated and functional status of NK cell in AML and may impede tumor progression ( 190 ). The role of TIGIT is also complicated by the duality of the TIGIT ligand PVR.…”

γδ T cells mediate robust anti‐HIV functions during antiretroviral therapy regardless of immune checkpoint expression

“…Engagement of CD160 on NK cells induces potent effector functions, even in the context of HIV infection, [40][41][42][43] while there are contradictory reports of the inhibitory or activating nature of signalling through Tim-3 and TIGIT. [44][45][46][47][48][49][50][51][52][53] Currently, the impact of ICM expression on cd T cells remains poorly defined, both at steady-state and in the context of HIV infection. 54,55 In addition to CD8 + T cells and NK cells, cd T cells are intriguing candidates for targeting HIV-infected cells in HIV cure strategies.…”

“…While expression of these markers can reflect a state of immune exhaustion, the functional impact of ICM expression can vary across cellular subsets. Engagement of CD160 on NK cells induces potent effector functions, even in the context of HIV infection, 40–43 while there are contradictory reports of the inhibitory or activating nature of signalling through Tim‐3 and TIGIT 44–53 . Currently, the impact of ICM expression on γδ T cells remains poorly defined, both at steady‐state and in the context of HIV infection 54,55 …”