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+ T cells 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: 6/10/20 mg) or every 2 weeks (q2w: 10/20/30/40 mg). Flow cytometry determined absolute numbers/mL of CD4+ and CD8+ T cells, 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 55 patients. After treatment, peripheral blood samples showed increased proliferating NK cells, CD8+ T cells, and CD4+ T cells, 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+ T cells as well as CD3+ perforin+ T cells but, importantly, not in Tregs. Notably, increases in the ratio of CD8+/CD4+ T cells 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.

TRIAL REGISTRATION NUMBER: NCT02004106; BP28920.