LMB-100 is an
immunotoxin targeting the
cell surface protein mesothelin, which is highly expressed in many
cancers including
mesothelioma. Having observed that patients receiving
pembrolizumab off protocol after
LMB-100 treatment had increased
tumor responses; we characterized these responses and developed animal models to study whether
LMB-100 made
tumors more responsive to
antibodies blocking programmed cell death protein 1 (PD-1). The overall objective
tumor response in the 10 patients who received
PD-1 inhibitor (
pembrolizumab, 9;
nivolumab, 1) after progression on
LMB-100 was 40%, and the median overall survival was 11.9 months. Of the seven evaluable patients, four had objective
tumor responses, including one complete response and three partial responses, and the overall survival for these patients was 39.0+, 27.7, 32.6+, and 13.8 months. When stratified with regard to
programmed death ligand 1 (PD-L1) expression, four of five patients with
tumor PD-L1 expression had objective
tumor response. Patients with positive
tumor PD-L1 expression also had increased progression-free survival (11.3 versus 2.1 months, P = 0.0018) compared with those lacking PD-L1 expression. There was no statistically significant difference in overall survival (27.7 versus 6.8 months, P = 0.1).
LMB-100 caused a systemic inflammatory response and recruitment of CD8+ T cells in patients'
tumors. The enhanced antitumor effects with
LMB-100 plus anti-PD-1 antibody were also observed in a human peripheral blood mononuclear cell-engrafted
mesothelioma mouse model and a human
mesothelin-expressing syngeneic
lung adenocarcinoma mouse model.
LMB-100 plus
pembrolizumab is now being evaluated in a prospective clinical trial for patients with
mesothelioma.