Granulocyte-macrophage colony-stimulating factor (GM-CSF)-secreting tumor vaccines are bioactive, but limited by disease burden and immune tolerance. Cyclophosphamide (CY) augments vaccine activity in tolerant neu mice and metastatic breast cancer (MBC) patients. HER-2-specific monoclonal antibodies (MAb) enhance vaccine activity in neu mice. We hypothesized that CY-modulated vaccination with HER-2-specific MAb safely induces relevant HER-2-specific immunity in neu mice and HER-2+ MBC patients. Adding both CY and the HER-2-specific MAb 7.16.4 to vaccination maximized HER-2-specific CD8+ T cell immunity and tumor-free survival in neu transgenic mice. We therefore conducted a single arm feasibility study of CY, an allogeneic HER-2+ GM-CSF-secreting breast tumor vaccine, and weekly trastuzumab in 20 HER-2+ MBC patients. Primary clinical trial objectives were safety and clinical benefit (CB), where CB represents complete response+partial response+stable disease. Secondary study objectives were to assess HER-2-specific T cell responses by delayed type hypersensitivity (DTH) and intracellular cytokine staining. Subjects received three monthly vaccinations, with a boost 6-8 months from trial entry. This combination immunotherapy was safe, with CB rates at 6 months and 1 year of 55% (95% CI:32-77%, p=0.013)) and 40% (95% CI:19-64%) respectively. Median progression-free survival (PFS) and overall survival (OS) were 7 (95% CI:4-16) and 42 months (95% CI:22-70) respectively. Increased HER-2-specific DTH developed in 7/20 subjects (of whom 4 had CB (95% CI:18-90)), with a trend toward longer PFS and OS in DTH responders. Polyfunctional HER-2-specific CD8+ T cells progressively expanded across vaccination cycles. Further investigation of CY-modulated vaccination with trastuzumab is warranted. Clinicaltrials.gov identifier: NCT00399529
- Received April 1, 2014.
- Revision received July 25, 2014.
- Accepted July 30, 2014.
- Copyright © 2014, American Association for Cancer Research.