Abstract 3557: Toward a personalized off-the-shelf cellular immunotherapy for cancer

Abstract

Abstract Objectives: We have been developing SV-BR-1-GM, a breast cancer cell line with features of an antigen presenting cell which has been stably transfected with the CSF2 gene encoding GM-CSF. SV-BR-1-GM has been in clinical trials in a regimen including low-dose pre-dose cyclophosphamide to reduce immune suppression, and post-dose local interferon alpha to boost the immune response. The SV-BR-1-GM regimen has been administered alone or in combination with PD-1 inhibitors in patients with advanced breast cancer. We have noted that patients that match the SV-BR-1-GM cell line at least at 1 HLA allele are more likely to derive clinical benefit. Therefore, steps were taken to genetically modify the SV-BR-1 cell line to match more patients. Methodology: We focused on the least polymorphic HLA types in the population: HLA-A (Class I) and HLA-DRB3/4/5 (Class II). The published allele frequencies (Gragert 2013) for HLA-A and HLA-DRB3/4/5 were evaluated for the major demographic groups in the US. The following HLA alleles were selected: A*02:01, A*01:01, A*03:01, A*24:02, A*11:01, A*68:01, A*23:01, A*33:03 for Class I and DRB4*01:01, DRB3*02:02, DRB3*01:01, DRB5*01:01, DRB3*03:01, DRB5*01:02, DRB5*02:02 for HLA-DRB3/4/5. Based on population analysis, this combination of 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 modified using CRISPR technology deleting expression of the endogenous HLA-A and HLA-DRB3 alleles. Four lentiviral vectors were constructed to express the HLA alleles, along with the CSF2 gene (which encodes GM-CSF), using a 2A self-cleaving multi-gene expression system. Each lentiviral vector expressed 4 HLA types: 2 HLA-A and 2 HLA-DRB3/4/5 types. Preliminary Data: Following sequential CRISPR treatment, 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 separately with the four lentiviral vectors each expressing four HLA genes as well as the CSF2 gene. Following selection and cloning, clones were evaluated by ELISA, flow cytometry and RT-PCR to confirm gene expression. Several clones that secreted GM-CSF and expressed both Class I and Class II HLA alleles have subsequently been 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 that matches them at least at one HLA allele. Gragert L, et. al. Hum Immunol. 2013;74(10):1313-1320. Citation Format: William V. Williams, Markus D. Lacher, Vivek G. Sunkari, Charles Wiseman, Miguel Lopez-Lago. Toward a personalized off-the-shelf cellular immunotherapy for cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3557.