PD-L1 expression on malignant cells is no prerequisite for checkpoint therapy

Abstract

Immunotherapy with PD-1/PD-L1-blocking antibodies is clinically effective for several tumor types, but the mechanism is not fully understood. PD-L1 expression on tumor biopsies is generally regarded as an inclusion criterion for this cancer therapy. Here, we describe the PD-L1-blocking therapeutic responses of preclinical tumors in which PD-L1 expression was removed from cancer cells, but not from immune infiltrate. Lack of PD-L1 expression on malignant cells delayed tumor outgrowth in a CD8+ T cell-mediated fashion, showing the importance of this molecule in immune suppression. PD-L1 expression was evident on myeloid-infiltrating cells in the microenvironment of these tumors and targeting stromal PD-L1 with blocking antibody therapy had additional antitumor effect, demonstrating that PD-L1 on both malignant cells and immune cells is involved in the mechanism of immunotherapeutic antibodies. Importantly, comparable results were obtained with PD-1-blocking therapy. These findings have implications for inclusion of cancer patients in PD-1/PD-L1 blockade immunotherapies.

PD-L1 on host cells is essential for PD-L1 blockade–mediated tumor regression

“…However, the essential or sufficient role of PD-L1 on tumor versus nontumor cells for immune evasion is still unclear (1,22,23). Recently, the importance of PD-L1 on tumor versus host cells during tumor growth has been intensively debated (24)(25)(26)(27). In one study, the role of PD-L1 during tumor formation was studied (25).…”

FcγR interaction is not required for effective anti‐PD‐L1 immunotherapy but can add additional benefit depending on the tumor model

“…As FcγR were dispensable for the therapeutic efficacy of anti‐PD‐L1 antibody in MC38 tumor model, we aimed to test if this is a general feature of this treatment modality, by verifying this in another tumor model. For this, we selected the CT26 colon adenocarcinoma syngeneic model on BALB/c background which is also known to be immunogenic and hence highly responsive to anti‐PD‐L1 mAb monotherapy . When CT26 tumor bearing BALB/c mice were treated with murinized anti‐PD‐L1 mAb, all mIgG subclasses including D265A mIgG2a again effectively delayed tumor outgrowth resulting in prolonged survival (Figs.…”

“…PD‐L1 deficient MC38 and CT26 cell lines were generated using CRISPR/Cas9 technology as described in Kleinovink et al . 2017 . Two hundred micrograms of therapeutic antibody was injected intraperitoneally at day 6, 9 and 12 after tumor inoculation.…”

“…Several lines of evidence suggest that the main effect of anti‐PD‐L1 mAb is abolishing suppression of on‐going antitumor T cell responses through blocking PD‐L1 on the tumor or tumor infiltrating myeloid cells from interacting with PD‐1 on T cells . Theoretically, this mechanism should be FcγR independent.…”

Transgenic mice that accept Luciferase‐ or GFP‐expressing syngeneic tumor cells at high efficiencies

“…The Tg-mLuc2 mice were injected with C26-Luc2 cells at 1 × 10 3 (n = 6), 1 × 10 4 (n = 6), or 1 × 10 5 (n = 8) per mouse. To evaluate immunemodulatory drugs in mouse models, many studies have used subcutaneous transplantation of syngeneic cancer cells for the ease of tumor size determination (Chamoto et al, 2017;van Elsas, Hurwitz, & Allison, 1999;Kleinovink et al, 2017). (b) Photon count quantification of the data in (a).…”