419 Development and mechanism of action of a novel cellular immunotherapeutic platform for the treatment of cancer

BackgroundTherapeutic cancer vaccines are designed to program a patient‘s immune system to recognize and eliminate tumor cells. We sought to harness gene-modified tumor cells as a vaccine platform and developed cancer vaccines composed of breast cancer cells expressing GM-CSF (SV-BR-1-GM). We have recently reported favorable clinical outcomes in patient populations that match SV-BR-1-GM at one or more HLA alleles. Mechanistically, 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. Building upon these observations, we hypothesized that tumor cells could function as antigen-presenting cells, and that direct CD4+ T-cell allorecognition may provide T-cell help for the generation of self-HLA restricted T-cell responses to tumor antigens.Our rationale was to genetically modify tumor cells to express a semi-allogeneic range of HLA molecules and T-cell co-stimulatory molecules & cytokines. The goal is to develop an off-the-shelf cell-based vaccine that enhances existing tumor-specific T-cell responses and expand the T-cell repertoire by inducing new responses from naïve T-cells.MethodsSV-BR-1 (Breast cancer), PC-3 (prostate cancer), SK-MEL-24 (Melanoma), and NCI-H2228 (Lung cancer) were chosen for vaccine development based on their expression of an immune signature. To create semi-allogeneic cell lines that closely match over 99% of the population in terms of at least one HLA allele, four cell lines were generated for each parental tumor cell line. Each of these cell lines carries two HLA-A alleles and two HLA-DRB3/4/5 alleles. Subsequently, the tumor cells were genetically modified using a lentiviral-mediated expression system to express co-stimulatory molecules and immunomodulatory cytokines. To monitor the immune responses elicited by the newly generated cell lines, we established a modified mixed lymphocyte reaction assay (mMLRA). This assay involved co-culturing tumor cells with peripheral blood mononuclear cells. Additionally, we performed T-cell activation assays using transgenic Jurkat cells that expressed HLA-restricted T-cell receptorsResultsFour cell lines (for each tumor type) that secreted GM-CSF, IFNα, IL-12, IL-7 and expressed CD80, CD86, 4–1BBL, and different combinations of both Class I and Class II HLA alleles were generated. By using the mMLRA and T-cell activation assays we successfully demonstrated that these novel cell lines can effective