LAUSR

Background With the increased use of immune checkpoint inhibitors (ICIs), side effects and toxicity are a great concern. Anaphylaxis has been identified as a potential adverse event induced by ICIs. Anaphylaxis is a life-threatening medical emergency. However, the mechanisms and factors that can potentially influence the incidence and severity of anaphylaxis in patients with cancer remain unclear. Methods Healthy, murine colon 26, CT26, breast 4T1, EMT6, and renal RENCA tumor-bearing mice were treated with an anti-PD-L1 antibody (clone 10F.9G2). Symptoms of anaphylaxis were evaluated along with body temperature and mortality. The amounts of antidrug antibody and platelet-activating factor (PAF) in the blood were quantified via ELISA and liquid chromatography-mass spectrometry (LC-MS/MS). Immune cells were analyzed and isolated using a flow cytometer and magnetic-activated cell sorting, respectively. Results Repeated administration of the anti-PD-L1 antibody 10F.9G2 to tumor-bearing mice caused fatal anaphylaxis, depending on the type of tumor model. After administration, antidrug immunoglobulin G (IgG), but not IgE antibodies, were produced, and PAF was released as a chemical mediator during anaphylaxis, indicating that anaphylaxis was caused by an IgG-dependent pathway. Anaphylaxis induced by 10F.9G2 was treated with a PAF receptor antagonist. We identified that neutrophils and macrophages were PAF-producing effector cells during anaphylaxis, and the tumor-bearing models with increased numbers of neutrophils and macrophages showed lethal anaphylaxis after treatment with 10F.9G2. Depletion of both neutrophils and macrophages using clodronate liposomes prevented anaphylaxis in tumor-bearing mice. Conclusions Thus, increased numbers of neutrophils and macrophages associated with cancer progression may be risk factors for anaphylaxis. These findings may provide useful insights into the mechanism of anaphylaxis following the administration of immune checkpoint inhibitors in human subjects.