Abstract P3-06-08: Turning tumor cells into antigen-presenting cells for cancer immunotherapy
Authors: Lopez-Lago Miguel , Williams William , Wiseman Charles 
Published: March 2023

Miguel Lopez-Lago1, Sagarika pachhal1, Charles L. Wiseman1, William V. Williams1. 1BriaCell Therapeutics Corporation, Philadelphia, PA Turning tumor cells into antigen-presenting cells for cancer immunotherapy Background: Therapeutic cancer vaccines are based on specific stimulation of the immune system using tumor antigens to elicit an antitumor response. We have been conducting clinical trials using the breast cancer cell line SV-BR-1-GM as a therapeutic vaccine. SV-BR-1-GM is a GM-CSF expressing breast cancer cell line with features of an antigen presenting cell (APC) owning to the expression of several immunomodulatory molecules, including MHC-I (HLA-A, B & C) and MHC-II (HLA-DRB3 & -DRA). Initial results in patients treated with irradiated SV-BR-1-GM cells, low dose cyclophosphamide and local IFNα suggest that patients that match SV-BR-1-GM at least at 1 HLA allele are more likely to derive clinical benefit. This clinical observation, together with the fact that SV-BR-1-GM cells can directly activate CD4+ T-cells in an antigen-specific HLA-restricted manner, as demonstrated by an in vitro antigen presentation assay (1), lead us to hypothesize that SV-BR-1 (the parent cell line) can function as APC. To further enhance direct antigen presentation to T-cells, SV-BR-1 cells have been genetically modified to express co-stimulatory molecules, immunomodulatory cytokines, and an extended repertoire of HLA alleles. Methods: To generate an off-the-shelf semi-allogeneic cell therapy covering most of the population, SV-BR-1 was genetically modified to express an extended repertoire of HLA alleles. Based on population analysis, four cell lines, each carrying two (2) HLA-A and two (2) HLA-DRB3/4/5 alleles, should produce at least a single match in 99% of the population, with a 92% match at Class I HLA-A alleles and a 98% match at Class II HLA-DRB3/4/5 alleles. SV-BR-1 was genetically modified using CRISPR/cas9 deletion of the endogenous HLA-A and HLA-DRB3 alleles and subsequent lentiviral mediated expression of alternative HLA-A and DRB3 alleles. To generate tumor cell lines with enhanced direct antigen presentation to T-cells, SV-BR-1 cells were genetically modified to express co-stimulatory molecules and immunomodulatory cytokines by using a lentiviral mediated expression system. Results: Following sequential CRISPR/Cas9 editing, the SV-BR-1 cells were cloned, and one clone selected (clone 17) for further engineering. Lack of expression of HLA-A and HLA-DRB3 was confirmed using flow cytometry and DNA sequencing. Clone 17 was subsequently transduced with 6 lentiviral vectors each expressing 2 genes under the control of separate promoters:CD86-IL12, CD80-HLA-DRA, 4-1BBL-IL7, GM-CSF-IFN, HLA-allele-1-HLA-allele-2 and HLA-DR-allele-1-HLA-DR-allele-2. Four cell lines were generated with different combinations of HLA alleles. Following selection, cells were evaluated by ELISA, flow cytometry and RT-PCR to confirm gene expression. Cell lines that secreted GM-CSF, IFN IL12, IL7 and expressed CD80, CD86, 4-1BBL, and both Class I and Class II HLA alleles are then transferred to GMP manufacturing. These modified breast cancer cell lines will be used in clinical studies designed to first evaluate the safety of intradermal inoculation with the irradiated cells and later combined with other agents to augment the immune response. Each patient will be treated with the cell line(s) that match them at least at one HLA allele. 1. Lacher M. D. et al, Front Immunol. 2018 May 15;9:776

Citation Format: Miguel Lopez-Lago, William Williams, Charles Wiseman. Turning tumor cells into antigen-presenting cells for cancer immunotherapy [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 P3-06-08.