Anti-FAP CAR-T cell therapy ( Tmunity Therapeutics)

Despite the success of chimeric antigen receptor (CAR) T-cell therapy against hematologic malignancies, successful targeting of solid tumors with CAR T cells has been limited by a lack of durable responses and reports of toxicities. Our understanding of the limited therapeutic efficacy in solid tumors could be improved with quantitative tools that allow characterization of CAR T–targeted antigens in tumors and accurate monitoring of response.

We used a radiolabeled FAP inhibitor (FAPI) [18F]AlF-FAPI-74 probe to complement ongoing efforts to develop and optimize FAP CAR T cells. The selectivity of the radiotracer for FAP was characterized in vitro, and its ability to monitor changes in FAP expression was evaluated using rodent models of lung cancer.

[18F]AlF-FAPI-74 showed selective retention in FAP+ cells in vitro, with effective blocking of the uptake in presence of unlabeled FAPI. In vivo, [18F]AlF-FAPI-74 was able to detect FAP expression on tumor cells as well as FAP+ stromal cells in the tumor microenvironment with a high target-to-background ratio. We further demonstrated the utility of the tracer to monitor changes in FAP expression following FAP CAR T-cell therapy, and the PET imaging findings showed a robust correlation with ex vivo analyses.

This noninvasive imaging approach to interrogate the tumor microenvironment represents an innovative pairing of a diagnostic PET probe with solid tumor CAR T-cell therapy and has the potential to serve as a predictive and pharmacodynamic response biomarker for FAP as well as other stroma-targeted therapies. A PET imaging approach targeting FAP expressed on activated fibroblasts of the tumor stroma has the potential to predict and monitor therapeutic response to FAP-targeted CAR T-cell therapy.See related commentary by Weber et al., p. 5241

Fibroblast activation protein (FAP) is a marker of activated fibroblasts in various human cardiovascular diseases. FAP is of special interest because it is expressed exclusively in activated, pathogenic fibroblasts and has been proposed as a target for chimeric antigen receptor (CAR) T cell ablation therapy. It has been shown previously that fibroblasts from patients with hypertrophic and dilated cardiomyopathy express FAP, while fibroblasts from non‐failing hearts did not. The aim of the project was to examine FAP expression in other human cardiac diseases by obtaining heart samples from patients who suffered diseases characterized by cardiac fibrosis so that we could determine which cardiac diseases might be amenable to FAP CAR T therapy. In addition, we sought to characterize an in vitro model of FAP expression to aid in the ability to assess the effectiveness of engineered T cells to kill FAP‐expressing cells. Heart tissue from patients diagnosed with various cardiac disorders, including idiopathic giant cell myocarditis, COVID‐19, and sarcoidosis were stained for FAP expression and compared to non‐failing, control hearts. The results showed significant FAP expression in all cardiac specimens with interstitial fibrosis compared to non‐failing hearts. Notably, samples from patients who died from COVID‐19 exhibited significant fibrosis and FAP expression. This suggests that there may be a large and growing population that may be amenable to anti‐fibrotic therapy. In order to develop an in vitro model of FAP expression to assay anti‐FAP CAR T cell activity, we treated IMR‐90 human fibroblasts with TGF‐B, a known activator of fibrosis, and assayed for FAP expression. TGF‐B exposure resulted in an increase in FAP expression 24‐hours after treatment. Our observation of fibroblast restricted FAP expression in multiple different cardiovascular diseases supports the potential use of FAP CAR T cell therapy as an anti‐fibrotic treatment in multiple heart diseases.