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Objectives: CAR‐T cells are being investigated as a novel immunotherapy for glioblastoma, but clinical success has been limited. We recently described fibroblast activation protein (FAP) as an ideal target antigen for glioblastoma immunotherapy, with expression on both tumor cells and tumor blood vessels. However, CAR‐T cells targeting FAP have never been investigated as a therapy for glioblastoma. Methods: We generated a novel FAP targeting CAR with CD3ζ and CD28 signalling domains and tested the resulting CAR‐T cells for their lytic activity and cytokine secretion function in vitro (using real‐time impedance, flow cytometry, imaging and bead‐based cytokine assays), and in vivo (using a xenograft mimicking the natural heterogeneity of human glioblastoma). Results: FAP‐CAR‐T cells exhibited target specificity against model cell lines and potent cytotoxicity against patient‐derived glioma neural stem cells, even when only a subpopulation expressed FAP, indicating a bystander killing mechanism. Using co‐culture assays, we confirmed FAP‐CAR‐T cells mediate bystander killing of antigen‐negative tumor cells, but only after activation by FAP‐positive target cells. This bystander killing was at least partially mediated by soluble factors and amplified by IL‐2 which activated the non‐transduced fraction of the CAR‐T product. Finally, a low dose of intravenously administered FAP‐CAR‐T cells controlled, without overt toxicity, the growth of subcutaneous tumors created using a mixture of antigen‐negative and antigen‐positive glioblastoma cells. Conclusions: Our findings advance FAP as a leading candidate for clinical CAR‐T therapy of glioblastoma and highlight under‐recognised antigen nonspecific mechanisms that may contribute meaningfully to the antitumor activity of CAR‐T cells. [ABSTRACT FROM AUTHOR]

Summary: While bortezomib has significant benefits in multiple myeloma (MM) therapy, the disease remains incurable due to the invariable development of bortezomib resistance. This emphasises the need for advanced models for preclinical evaluation of new therapeutic approaches for bortezomib‐resistant MM. Here, we describe the development of an orthotopic syngeneic bortezomib‐resistant MM mouse model based on the most well‐characterised syngeneic MM mouse model derived from spontaneous MM‐forming C57BL/KaLwRij mice. Using bortezomib‐resistant 5TGM1 cells, we report and characterise a robust syngeneic mouse model of bortezomib‐resistant MM that is well suited to the evaluation of new therapeutic approaches for proteasome inhibitor‐resistant MM. [ABSTRACT FROM AUTHOR]

Objectives: Targeted immunotherapies such as chimeric antigen receptor (CAR)‐T cells are emerging as attractive treatment options for glioblastoma, but rely on identification of a suitable tumor antigen. We validated a new target antigen for glioblastoma, fibroblast activation protein (FAP), by undertaking a detailed expression study of human samples. Methods: Glioblastoma and normal tissues were assessed using immunostaining, supported by analyses of published transcriptomic datasets. Short‐term cultures of glioma neural stem (GNS) cells were compared to cultures of healthy astrocytes and neurons using flow cytometry. Glioblastoma tissues were dissociated and analysed by high‐parameter flow cytometry and single‐cell transcriptomics (scRNAseq). Results: Compared to normal brain, FAP was overexpressed at the gene and protein level in a large percentage of glioblastoma tissues, with highest levels of expression associated with poorer prognosis. FAP was also overexpressed in several paediatric brain cancers. FAP was commonly expressed by cultured GNS cells but absent from normal neurons and astrocytes. Within glioblastoma tissues, the strongest expression of FAP was around blood vessels. In fact, almost every tumor vessel was highlighted by FAP expression, whereas normal tissue vessels and cultured endothelial cells (ECs) lacked expression. Single‐cell analyses of dissociated tumors facilitated a detailed characterisation of the main cellular components of the glioblastoma microenvironment and revealed that vessel‐localised FAP is because of expression on both ECs and pericytes. Conclusion: Fibroblast activation protein is expressed by multiple cell types within glioblastoma, highlighting it as an ideal immunotherapy antigen to target destruction of both tumor cells and their supporting vascular network. [ABSTRACT FROM AUTHOR]