Biomarkers of activity from a phase I study of cergutuzumab amunaleukin in patients with advanced solid tumors

Background Cergutuzumab amunaleukin (CA) is an immunocytokine comprising an anticarcinoembryonic antigen (CEA) linked to an interleukin-2 (IL-2) variant. CA does not bind to CD25 (IL-2 receptor α) and was designed to maintain the T and natural killer (NK) cell stimulatory effect, while avoiding stimulating effects on regulatory T cells (Tregs). In mouse models, CA previously demonstrated superior tumor targeting to CEA surface expression-positive (CEA+) tumors and increased CD8+ Tcells and NK cell numbers in peripheral blood and tumor tissue when compared with wild-type IL-2. We present biomarker data from the first-in-human, open-label, multicenter, phase I, dose-escalation study investigating CA in patients with metastatic/unresectable CEA+ solid tumors (NCT02004106). Methods Patients received ascending doses of CA intravenously weekly (qw: 6/10/20mg) or every 2weeks (q2w: 10/20/30/40mg). Flow cytometry determined absolute numbers/mL of CD4+ andCD8+ Tcells, NK cells, macrophages/monocytes, Tregs, and B cells and their expression of activation and proliferation markers in circulation. Sequential pretreatment and on-treatment paired tumor biopsies were studied by flow cytometry, multicolor immunohistochemistry, and bulk RNA sequencing. Antitumor activity was used for correlative studies. Results Biomarker data were collected from 55patients. After treatment, peripheral blood samples showed increased proliferating NK cells, CD8+ Tcells, and CD4+ Tcells, without an apparent dose effect. Levels of circulating soluble CD25 increased in patients with intermediate/high CA doses on-treatment; levels of cytokines, such as tumor necrosis factor, also increased with high CA dose levels. On-treatment tumor samples showed increases in total and proliferating CD8+ Tcells as well as CD3+ perforin+ T cells but, importantly, not in Tregs. Notably, increases in the ratio of CD8+/CD4+ Tcells were more pronounced for qw than for q2w dosing, while programmed death ligand-1-positive CD14+ cells increased, particularly for the q2w schedule. Higher on-treatment circulating levels of cytokines correlated with longer progression-free survival (PFS). Apart from the positive correlation with NK cell density, no other correlations between PFS and infiltrating immune cell populations in the tumor were observed. Conclusions CA-induced immune pharmacodynamic effects in peripheral blood and in the tumor microenvironment without preferential Treg cell activation in patients with metastatic/unresectable CEA+ solid tumors.