A novel model of controlling PD-L1 expression in ALK+ anaplastic large cell lymphoma revealed by CRISPR screening

Abstract

The success of programmed cell death protein 1 (PD-1)/PD-L1-based immunotherapy highlights the critical role played by PD-L1 in cancer progression and reveals an urgent need to develop new approaches to attenuate PD-L1 function by gaining insight into how its expression is controlled. Anaplastic lymphoma kinase (ALK)-positive anaplastic large-cell lymphoma (ALK+ ALCL) expresses a high level of PD-L1 as a result of the constitutive activation of multiple oncogenic signaling pathways downstream of ALK activity, making it an excellent model in which to define the signaling processes responsible for PD-L1 upregulation in tumor cells. Here, using clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 library screening, we sought a comprehensive understanding of the molecular effectors required for PD-L1 regulation in ALK+ ALCL. Indeed, we determined that PD-L1 induction is dependent on the nucleophosmin-ALK oncoprotein activation of STAT3, as well as a signalosome containing GRB2/SOS1, which activates the MEK-ERK and PI3K-AKT signaling pathways. These signaling networks, through STAT3 and the GRB2/SOS1, ultimately induce PD-L1 expression through the action of transcription factors IRF4 and BATF3 on the enhancer region of the PD-L1 gene. IRF4 and BATF3 are essential for PD-L1 upregulation, and IRF4 expression is correlated with PD-L1 levels in primary ALK+ ALCL tissues. Targeting this oncogenic signaling pathway in ALK+ ALCL largely inhibited the ability of PD-L1-mediated tumor immune escape when cocultured with PD-1-positive T cells and natural killer cells. Thus, our identification of this previously unrecognized regulatory hub not only accelerates our understanding of the molecular circuitry that drives tumor immune escape but also provides novel opportunities to improve immunotherapeutic intervention strategies.

Expanded and activated allogeneic NK cells are cytotoxic against B-chronic lymphocytic leukemia (B-CLL) cells with sporadic cases of resistance

“…These data indicate that PD-L1 expression is dependent on PI3Kδ activity in B-CLL cells. Remarkably, a recent study has shown a dependence of PD-L1 expression on the PI3K/Akt signaling pathway in anaplastic large cell lymphoma 47 .…”

The NKL-code for innate lymphoid cells reveals deregulated expression of NKL homeobox genes HHEX and HLX in anaplastic large cell lymphoma (ALCL)

“…Aberrant activities of AP1 TFs including JUN, JUNB and BATF3 are an additional ALCL hallmark [26]. Moreover, BATF3 is a target gene of STAT3 [27], demonstrating close regulatory relationships between these oncogenes in ALCL. Expression profiling analysis indicated that primary ALCL cells express several TH17 signature genes [28].…”

Current Clinical Applications and Future Perspectives of Immune Checkpoint Inhibitors in Non-Hodgkin Lymphoma

“…Signaling pathways that are intrinsically activated and responsible for the expression of PD-L1 are ill defined in this subtype and include SVs of PD-L1 in 15% of EBV positive cases, caused by a truncation of the 3′-untranslated region [ 93 ]. PD-L1 is upregulated in anaplastic large cell lymphoma (ALCL), and novel mechanisms of PD-L1 regulation and expression have been discovered in anaplastic lymphoma kinase- (ALK-) positive and ALK-negative subtypes of the disease [ 134 , 135 ]. Natural killer/T-cell lymphomas (NKTCL) are invariably infected with EBV, and EBV-infected lymphoma cells upregulate PD-L1 expression [ 37 ].…”