BACKGROUND:
The authors are conducting clinical trials of the HER‐2/neu E75‐peptide vaccine in clinically disease‐free breast cancer (BC) patients. Their phase 1‐2 trials revealed that the E75 + granulocyte‐macrophage colony‐stimulating factor (GM‐CSF) vaccine is safe and effective in stimulating clonal expansion of E75‐specific CD8+ T cells. They assessed the need for and response to a booster after completion of primary vaccination series.
METHODS:
BC patients enrolled in the E75 vaccine trials who were ≥6 months from completion of their primary vaccination series were offered boosters with E75 + GM‐CSF. Patients were monitored for toxicity. E75‐specific CD8+ T cells were quantified using the human leukocyte antigen‐A2:immunoglobulin G dimer before and after boosting.
RESULTS:
Fifty‐three patients received the vaccine booster. Median time from primary vaccination series was 9 months (range, 6‐35 months), and median residual E75‐specific immunity was 0.70% (range, 0‐3.49%) CD8+ lymphocytes. Elevated residual immunity (ERI) (CD8+ E75‐specific T cells >0.5%) was seen in 94.4% of patients at 6 months from primary vaccination series versus 48% of patients at >6 months (P = .002). The booster was well tolerated, with only grade 1 and 2 toxicity observed. Local reactions were more robust in patients receiving the booster at 6 months from primary vaccination series compared with those at >6 months (99.4 ± 6.1 mm vs 81.8 ± 4.1 mm, P = .01). In patients lacking ERI, 85% had increased ERI after vaccination (P = .0014).
CONCLUSIONS:
The HER‐2/neu E75 peptide vaccine E75 stimulates specific immunity in disease‐free BC patients. However, immunity wanes with time. A vaccine booster is safe and effective in stimulating E75‐specific immunity in those patients without ERI. These results suggest that the booster may be most effective at 6 months after completion of the primary vaccination series. Cancer 2011. Published 2010 by the American Cancer Society.