PD-1 Specific ‘Blocking’ Antibodies That Deplete PD-1+ T Cells Present An Inconvenient Variable In Pre-clinical Immunotherapy Experiments

Abstract

Therapeutic antibodies blocking PD-1-/PD-L1 interaction have achieved remarkable clinical success in cancer. In addition to blocking a target molecule, some isotypes of antibodies can activate complement, NK cells or phagocytes, resulting in death of the cell expressing the antibody's target. Human anti-PD-1 therapeutics use antibody isotypes designed to minimize such antibody-dependent lysis. In contrast, anti-PD-1 reagents used in mice are derived from multiple species, with different isotypes, and are not engineered to reduce target cell death: few studies analyze or discuss how antibody species and isotype may impact data interpretation. We demonstrate here that anti-PD-1 therapy to promote activation and proliferation of PD-1-expressing CD8 T cells sometimes led instead to a loss of antigen specific cells. This phenomenon was seen in two tumor models and a model of virus infection, and was varied with the clone of anti-PD-1 antibody. Additionally, we compared competition among anti-PD-1 clones to find a combination that allows detection of PD-1-expressing cells despite the presence of blocking anti-PD1 antibodies in vivo. These data bring attention to the possibility of unintended target cell depletion with some commonly used anti-mouse PD-1 clones, and should provide a valuable resource for the design and interpretation of anti-PD-1 studies in mice. (200)

PD‐1 blocking antibodies moonlighting as killers

“…Moreover, unlike the majority of therapeutic PD‐1 blockers, which are characterized by a low capacity to interact with Fcγ receptors (FcγRs), such considerations are often not prioritized when designing experiments in mouse models. In this issue of the European Journal of Immunology , Polesso and colleagues report that the use of the PD‐1‐specific antibody (clone) G4 did not show a protective effect in the MCA‐205 mouse sarcoma model, whereas 60% of the animals that were treated with a PD‐L1 antibody rejected the tumor [9]. PD‐1 expression was much higher on tumor‐specific CD8 T cells that resided in the tumor than those in the spleen.…”

“…Indeed, Polesso et al. found that RMP1‐14 interacted weakly with PD‐1 + EL4 cells, whereas other PD‐1 antibodies gave much stronger binding signals [9].…”

“…Several of these counteract the beneficial effects of PD‐1 inhibition. They can outweigh the immune‐promoting effects of PD‐1 blockade, such as in the study by Polleso et al., or they can merely act to reduce the antitumor effects of PD‐1 blockers [9, 13]. As shown for PD‐L1 antibodies, FcγR‐mediated effects can also add to the antitumor effects of PD‐1 blockade by inhibiting immunosuppressive myeloid cell populations or by directly attacking PD‐L1‐ expressing tumor cells [13, 15].…”