Abstract LB-203: VXL100, a MUC1 signal peptide based immunotherapy, acts through a neoantigen-like mechanism, and shows promising effects in hematological cancers

Abstract

Abstract VXL100 (ImMucin®), a 21mer peptide, pan-HLA vaccine derived from the MUC1 signal peptide (SP) domain, has been shown to be safe and to elicit a robust and specific T and B-cell responses in stable and progressive multiple myeloma patients in a phase I/II clinical trial. It is now becoming recognized that the advantages of using the signal peptide domain for immunization stem from its unique B and T cells epitope restriction density and TAP independent presentation. Additionally, the low avidity of signal peptides as antigens, is believed to result in escaping negative selection in the thymus during development, and preservation of active clones in the peripheral blood. This may allow signal peptides to be presented as true neoantigens during tumor development and generate a robust immune response. To prove the neoantigenic properties of MUC1 SP, we have recently tested endogenous levels of specific anti-VXL100 T-cells by staining for VXL100-specific or control multimers. We also performed proliferation assays for patient TIL and normal donors PBMCs using cells stimulated with VXL100 or other MUC1 antigenic control peptides. VXL100 specific T-cell were found in 100% of patients (1.3-6%), VS. 0% in normal donors. We have found a direct correlation between the MUC1 signal peptide expression levels on tumor cells and levels of endogenous VXL100 specific T-cells. Positive signals were observed for multimers of other MUC1 peptides as well, but these were also seen in normal donors, suggesting a non-specific binding. Moreover, we were able to show that VXL100 specific exhausted CD8 cells exist at a non-significant levels as compared to the total exhausted CD8. When stimulated in-vitro with VXL100, PBMCs from 70% of naive normal donors and 94% of cancer patients showed a strong proliferative response (average of 8.9% and 16.5% proliferating cells, respectively). When stimulated with control peptides 0.5% - 5.2% of patients and 0 - 13% of donors showed positive proliferation response. Conclusions: VXL100, a novel immunotherapy agent shows the capacity to elicit a specific and robust T-cell response in healthy individuals and hematological cancer patients. These features suggest that MUC1 SP is a native sequence functioning as a cancer neoantigen and preserved through normal and tumor development. It presents an attractive opportunity for the development of an effective cancer immunotherapy. Citation Format: Limor Chen, Riva Kovjazin, Michael Shapira. VXL100, a MUC1 signal peptide based immunotherapy, acts through a neoantigen-like mechanism, and shows promising effects in hematological cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-203. doi:10.1158/1538-7445.AM2017-LB-203