Immune checkpoints PVR and PVRL2 are prognostic markers in AML and their blockade represents a new therapeutic option

Abstract

Immune checkpoints are promising targets in cancer therapy. Recently, poliovirus receptor (PVR) and poliovirus receptor-related 2 (PVRL2) have been identified as novel immune checkpoints. In this investigation we show that acute myeloid leukemia (AML) cell lines and AML patient samples highly express the T-cell immunoreceptor with Ig and ITIM domains (TIGIT) ligands PVR and PVRL2. Using two independent patient cohorts, we could demonstrate that high PVR and PVRL2 expression correlates with poor outcome in AML. We show for the first time that antibody blockade of PVR or PVRL2 on AML cell lines or primary AML cells or TIGIT blockade on immune cells increases the anti-leukemic effects mediated by PBMCs or purified CD3+ cells in vitro. The cytolytic activity of the BiTE® antibody construct AMG 330 against leukemic cells could be further enhanced by blockade of the TIGIT-PVR/PVRL2 axis. This increased immune reactivity is paralleled by augmented secretion of Granzyme B by immune cells. Employing CRISPR/Cas9-mediated knockout of PVR and PVRL2 in MV4-11 cells, the cytotoxic effects of antibody blockade could be recapitulated in vitro. In NSG mice reconstituted with human T cells and transplanted with either MV4-11 PVR/PVRL2 knockout or wildtype cells, prolonged survival was observed for the knockout cells. This survival benefit could be further extended by treating the mice with AMG 330. Therefore, targeting the TIGIT-PVR/PVRL2 axis with blocking antibodies might represent a promising future therapeutic option in AML.

Targeting PVR (CD155) and its receptors in anti-tumor therapy

“…Consistent with these findings, in vitro antibody-mediated blockade of PVR on acute myeloid leukemia cells was recently shown to increase the anti-leukemic effects of immune cells. 184 Similar findings were observed when melanoma cell lines were treated with anti-PVR antibody, leading to increased production of IFNγ by antigen-specific CTLs. 55 In addition, the first study using an anti-PVR mAb in in vivo tumor model also reported the anti-tumor properties of this treatment, with the Ab-inhibiting cancer metastasis.…”

“…185 According to another recent study, NSG mice that were reconstituted with human T cells and engrafted with tumor cells lacking both PVR and Nectin-2 exhibit prolonged survival compared to mice engrafted with WT (ligand expressing) tumor cells. 184 Although the indicated studies attributed the observed anti-tumor effects to immune cells, i.e., to the immune cell-dependent role of PVR, strategies targeting PVR might also rely on additional mechanisms. For example, given the role of PVR in cellular proliferation and its association with growth factor receptors, 34,35 researchers have hypothesized that the disruption of these complexes with antibodies might exert an anti-tumor effect.…”

Targeting the TIGIT-PVR immune checkpoint axis as novel therapeutic option in breast cancer

“…Expression of PVR in the AML cell line MV4-11 was used as a reference and set to 100%. 32 In the PVR-specific Western blot of the breast cancer samples, we detected a band of varying intensity with a mean expression level after densitometry of 23.6% and a range from 0% to 128.4% (Figure 2(a)). A positive correlation between PVR mRNA level and protein expression was found, with a Spearman correlation coefficient of 0.488 (p = .006) for probeset 32699_s_at.…”

“…The protein lysate from the cell line MV4-11 was used as a reference and internal control in all blots. 18 After electrophoresis and blotting to PVDF membranes, PVR was detected using the monoclonal anti-PVR antibody L95. 63 Equal loading was verified by immunoblotting with anti-β-actin antibody (sc-47778, Santa Cruz Biotechnology).…”

“…16 High expression of PVR could be associated with a poor survival in several cancer entities and the blockade of the TIGIT/PVR axis resulted in antitumor activity in a number of preclinical models. [17][18][19][20][21][22][23] Based on those promising observations, the clinical evaluation of blocking TIGIT was initiated (NCT02794571, NCT03119428, NCT02913313).…”