Targeted T-cell Therapy in Stage IV Breast Cancer: A Phase I Clinical Trial

This study reports a phase I immunotherapy trial in 23 women with metastatic breast cancer consisting of eight infusions of anti-CD3 × anti-HER2 bispecific antibody (HER2Bi) armed anti-CD3-activated T cells (ATC) in combination with low-dose IL-2 and granulocyte-macrophage colony-stimulating factor to determine safety, maximum tolerated dose (MTD), technical feasibility, T-cell trafficking, immune responses, time to progression, and overall survival (OS).

ATC were expanded from leukapheresis product using IL2 and anti-CD3 monoclonal antibody and armed with HER2Bi. In 3+3 dose escalation design, groups of 3 patients received 5, 10, 20, or 40 × 10(9) armed ATC (aATC) per infusion.

There were no dose-limiting toxicities and the MTD was not defined. It was technically feasible to grow 160 × 10(9) ATC from a single leukapheresis. aATC persisted in the blood for weeks and trafficked to tumors. Infusions of aATC induced anti-breast cancer responses and increases in immunokines. At 14.5 weeks after enrollment, 13 of 22 (59.1%) evaluable patients had stable disease and 9 of 22 (40.9%) had progressive disease. The median OS was 36.2 months for all patients, 57.4 months for HER2 3+ patients, and 27.4 months for HER2 0-2+ patients.

Targeting HER2(+) and HER2(-) tumors with aATC infusions induced antitumor responses, increases in Th1 cytokines, and IL12 serum levels that suggest that aATC infusions vaccinated patients against their own tumors. These results provide a strong rationale for conducting phase II trials.