Nelipepimut-S

Summary

Nelipepimut‑S (also called E75 or NeuVax) is a synthetic peptide derived from the HER2/neu protein, formulated with the immune‑stimulating cytokine GM‑CSF. It is being investigated as a cancer vaccine intended to provoke HER2‑specific cytotoxic T‑cell responses that could prevent recurrence of breast cancer, particularly in patients whose tumours express low levels of HER2 or in the pre‑operative setting, or as an adjuvant after standard therapy.

Mechanism of Action

Nelipepimut‑S is a nine‑amino‑acid peptide (KIFGSLAFL) that corresponds to an HLA‑A2/A24‑restricted epitope of HER2. After intradermal or subcutaneous injection together with GM‑CSF, the peptide is taken up by dendritic cells, which present it on MHC class I molecules to CD8⁺ T cells. This stimulates expansion of HER2‑specific cytotoxic T‑lymphocytes that can recognise and kill HER2‑expressing tumour cells. When combined with trastuzumab, antibody‑mediated HER2 blockade may increase antigen release, potentially enhancing the vaccine‑induced T‑cell response.

What the Research Shows

Clinical investigation of nelipepimut‑S began with phase I/II studies that demonstrated safety and the ability to generate HER2‑specific CTL responses. A randomized phase II trial in HLA‑A2‑positive ductal carcinoma in situ patients (n = 13 receiving vaccine) showed a numerically higher increase in CTLs compared with GM‑CSF alone, though the difference was not statistically significant. In HER2‑low (IHC 1+/2+) disease‑free patients, a phase II safety interim analysis of nelipepimut‑S + GM‑CSF combined with trastuzumab reported no excess toxicity versus trastuzumab alone. A subsequent phase IIb trial identified a subgroup benefit: triple‑negative breast cancer patients, especially those expressing HLA‑A24 or HER2 1+, experienced markedly improved 36‑month disease‑free survival (hazard ratios 0.25–0.41). However, a large phase III adjuvant trial in HER2‑low, node‑positive breast cancer showed no significant difference in disease‑free survival at interim analysis, leading to early termination. Across studies, injection‑site reactions were the most common adverse events.

Reported Benefits

Nelipepimut‑S is consistently reported as well tolerated, with mostly mild injection‑site reactions. Immunologically, it can elicit HER2‑specific cytotoxic T‑cell responses detectable by dextramer or tetramer assays. In exploratory analyses, certain patient subsets—triple‑negative tumours, HLA‑A24 carriers, or those receiving concurrent trastuzumab—have shown improved disease‑free survival, suggesting a potential preventive benefit in high‑risk groups. The vaccine’s peptide nature allows targeted immune activation without the systemic toxicities typical of conventional chemotherapy.

Limitations of the Evidence

Evidence for clinical efficacy remains limited. The phase III trial did not meet its primary endpoint, and benefits have only been observed in post‑hoc subgroup analyses, which require prospective confirmation. Sample sizes in early trials were small, and the lack of a statistically significant CTL increase in the DCIS study leaves immunogenicity uncertain. Moreover, the vaccine is applicable only to patients expressing specific HLA alleles (e.g., HLA‑A2 or A24) and to tumours with some HER2 expression, restricting its broader use. Long‑term outcomes and overall survival data are still lacking.

Safety Considerations

Across phase I‑III studies, nelipepimut‑S combined with GM‑CSF was associated primarily with grade 1‑2 local reactions such as erythema, induration and pruritus at the injection site. Systemic adverse events were rare and comparable to GM‑CSF alone. No increase in cardiac toxicity was observed when the vaccine was given with trastuzumab. Overall, the safety profile is considered favorable, but monitoring for injection‑site inflammation and rare hypersensitivity reactions is advised.

How It Is Administered

Nelipepimut‑S is administered by intradermal or subcutaneous injection, typically together with 250 µg of GM‑CSF. In the phase III protocol the vaccine dose was 1 000 µg given monthly for six months and then every six months up to three years. Earlier studies used two pre‑operative doses before surgery. The formulation is a sterile peptide solution mixed with the cytokine adjuvant.

Routes of Administration

Goals & Uses

• Prevention of breast cancer recurrenceOncology / Cancer PreventionModerate
• Adjuvant therapy in node-positive breast cancerOncologyLow
• Combination with trastuzumab for HER2-low breast cancerCombination ImmunotherapyModerate
• HER2-specific immune activationImmunotherapyModerate
• Adjuvant therapy for HER2‑positive breast cancerOncologyModerate

Contraindications

• HLA-A2 or HLA-A3 negativityGenetic/ImmunologicHigh
• Immunosuppressive therapyPharmacologicalModerate
• Known hypersensitivity to GM-CSF or vaccine componentsAllergicHigh
• Active autoimmune diseaseAutoimmunityModerate

Adverse Effects

• Flu-like symptomsSystemic/ImmunologicalUncommon
• Flu‑like symptomsSystemicUncommon
• Local Injection Site ReactionsDermatologicalCommon
• FatigueGeneralCommonLow energy or tiredness
• Allergic/hypersensitivity reactionsImmunologicalRare
• Injection‑site erythemaLocalCommon
• LymphadenopathyLymphoreticularUncommon

Drug Interactions

• Chemotherapy agentsModerate
• TrastuzumabLow
• CorticosteroidsModerate

Population Constraints

• PregnancyReproductive SafetyRelative
• Pregnant or breastfeeding womenReproductiveRelative
• Severely immunocompromised patientsImmunologicalRelative
• HER2-overexpressing (3+) breast cancerOncologicRelative
• HLA-A2 or HLA-A3 negative patientsGeneticAbsolute

Regulatory Status

• European UnionInvestigationalClinical trials conducted under EU Clinical Trial Regulation; no marketing authorization.
• United StatesInvestigationalInvestigational New Drug (IND) application filed; not FDA‑approved.
• United KingdomInvestigationalNo MHRA approval; investigational only.

Investigational vaccine studied in phase I/II trials; not approved in any jurisdiction.

Evidence & Sources

• Phase II Trial of Nelipepimut-S Peptide Vaccine in Women with Ductal Carcinoma In Situ
  Journal ArticleModerateO'Shea AE, et al.2023-01-01T00:00:00.000000Z
• Evaluating Nelipepimut-S in the Treatment of Breast Cancer: A Short Report on the Emerging Data
  Journal ArticleModerateDillon PM, Brenin CM, Slingluff CL Jr2020-01-01T00:00:00.000000Z
• Initial safety analysis of a randomized phase II trial of nelipepimut-S + GM-CSF and trastuzumab compared to trastuzumab alone to prevent recurrence in breast cancer patients with HER2 low-expressing tumors
  Journal ArticleModerateClifton GT, et al.2019-01-01T00:00:00.000000Z
• Subgroup analysis of nelipepimut-S plus GM-CSF combined with trastuzumab versus trastuzumab alone to prevent recurrences in patients with high-risk, HER2 low-expressing breast cancer
  Journal ArticleModerateChick RC, et al.2021-01-01T00:00:00.000000Z
• The HER2 peptide nelipepimut-S (E75) vaccine (NeuVax™) in breast cancer patients at risk for recurrence: correlation of immunologic data with clinical response
  Journal ArticleModerateSchneble EJ, et al.2014-01-01T00:00:00.000000Z
• Efficacy and Safety Analysis of Nelipepimut-S Vaccine to Prevent Breast Cancer Recurrence: A Randomized, Multicenter, Phase III Clinical Trial
  Journal ArticleModerateMittendorf EA, et al.2019-01-01T00:00:00.000000Z

Frequently Asked Questions