Abstract OT2-10-02: Phase I trial of an alpha-lactalbumin vaccine in patients with operable triple-negative breast cancer (TNBC)

Abstract Background: Triple-negative breast cancer (TNBC) is the subtype of breast cancer with the worst prognosis and is the subtype most often associated with germline mutations of BRCA1 as well as other genes. Alpha-lactalbumin (aLA) is a milk protein expressed in lactating breasts but not at other times or in other normal tissues. Expression of aLA is found in approximately 70% of TNBC (Cancers PMID: 27322324) so is an attractive immunologic target for TNBC based on the “retired protein hypothesis” (Semin Immunol PMID: 31926646). Pre-clinical studies have shown that vaccination with aLA inhibits the growth of established breast tumors and provides potent protection from development of autochthonous tumors in transgenic murine models of breast cancer and against 4T1 transplantable breast cancer in BALB/c mice (Nat Med PMID: 20512124). Specific Aims: We are conducting a Phase I trial of vaccination with an aLA vaccine in patients with early stage TNBC to demonstrate the safety of this approach and to document the ability to produce a relevant immunologic response to aLA. Trial Design: Patients are being entered into a Phase I trial of alpha-lactalbumin with GMP-grade zymosan adjuvant in Montanide ISA 51 VG vehicle. Subjects receive a total of 3 vaccinations administered once every 2 weeks. Toxic events of Common Terminology Criteria for Adverse Events (CTCAE) grade 2 or greater are considered dose-limiting. Dose levels being tested in the current protocol are alpha-lactalbumin/zymosan 0.01/0.01, 0.1/0.01, 0.5/0.01, 0.5/0.03, and 0.5 mg/0.06 mg. Patients are being monitored for toxicity until 84 days after the first vaccination or resolution of toxicity, whichever is later. Blood is being drawn prior to therapy and 14, 28, and 56 days after the first vaccination to assess cellular response using enzyme-linked immunosorbent spot (ELISpot) assays of interferon-gamma and interleukin-17 production in response to aLA. Humoral response to aLA vaccination is being assessed by enzyme-linked immunosorbent assay (ELISA). Eligibility Criteria: Patients with ER-negative, PR-negative, HER2-negative breast cancer of pathologic stage II-III or who had residual disease after standard pre-operative systemic therapy. Participants must be within 3 years of initiation of treatment and have no evidence of recurrence. Dose Selection: Doses are being escalated using a 3+3 trial design to determine the maximum tolerated dose, the lowest immunologic dose and the optimal immunologic dose Present Accrual and Target Accrual: Dependent on toxicity, 18-30 patients will be treated. Future Plans and Contact Information: After identification of the maximum tolerated dose and expansion of the dose levels associated with effective tumor immunity we plan to enroll 2 additional cohorts of patients: 1) patients who have completed pre-operative chemo-immunotherapy and are receiving pembrolizumab as standard of care therapy, and 2) patients without cancer planning to undergo prophylactic bilateral mastectomy. Interested parties may contact Dr. Budd at buddg@ccf.org. Funding Source: Department of Defense (W81XWH-17-1-0592 and W81XWH-17-1-0593) Citation Format: George Budd, Justin M. Johnson, Emily Rhoades, Halle Moore, Megan L. Kruse, Erin Roesch, Jame Abraham, Brenna Elliott, Elena Haury, Vincent K. Tuohy. Phase I trial of an alpha-lactalbumin vaccine in patients with operable triple-negative breast cancer (TNBC) [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr OT2-10-02.