Concurrent HER2 vaccination and inhibition of kinase activity: safety and immunogenicity

Passive immunotherapy with the monoclonal antibody trastuzumab and tyrosine kinase activity inhibition with lapatinib are HER2-targeted therapies used in the clinic for the treatment of HER2-overexpressing breast cancers. Unfortunately, the therapeutic efficacy of both these therapies is abolished by primary and acquired tumor resistance. Active immunotherapy against HER2, which, thanks to trastuzumab, is a clinically validated tumor-associated antigen, might provide an alternative therapeutic strategy for HER2-overexpressing breast cancers. This Phase I study of HER2 immunotherapy with concomitant lapatinib treatment in 12 patients with metastatic breast cancer resistant to trastuzumab demonstrates the feasibility and safety of concurrent vaccination against HER2 and inhibition of HER1 and HER2 kinases. However, it is inconclusive regarding the effect of lapatinib on the immune responses induced by dHER2/AS15; vaccination triggered variable levels of anti-HER2 antibodies in all the patients, but a HER2-specific T-cell response was detected in one patient only. Since the presence of Tregs in these patients was not assessed, it remains unclear whether lapatinib and/or Tregs account for the near absence of a T-cell response.