Preprint Club
A cross-institutional Journal Club Initiative

Keywords

• CAR T Cells

• Metastasis

• Circulating Tumor Cells

Main Findings

CAR T cells are an effective treatment for haematological malignancies, but currently lack efficacy in solid tumors. In primary tumors, cells are shed, termed circulating tumor cells (CTC) that can circulate and cause metastasis. Creating a CAR T cell to target CTCs could potentially prevent or inhibit tumor metastasis in a similar fashion as the CAR T cell targeting of haematological malignancies in circulation. This is a proof of concept study to show CARs can target CTC in solid tumors. In this preprint, the authors created a GrB-based CAR T cell targeting tumor-specific antigen HSP70 and evaluated specificity, cytotoxicity, and off target effects in in vitro and in vivo xenograft spontaneous tumor models. The authors show:

• GrB-CAR T cells kill cancer cells that express HSP70 on their cell membrane (mHSP70)

• GrB-CAR T cells suppress tumor growth in vivo.

• GrB-CAR T cells target CTCs, which prevents tumor metastasis in spontaneous tumor models

• Potential (additional) treatment for solid tumors in multiple different cancers.

• Limited toxicities and good safety profiles in healthy macaques.

Limitations

• While the study uses a mouse xenograft model in NCG mice, the study could improve by use of a mouse tumor model with an intact immune system to better mimic patients.

• In addition to using cancer cell lines with limited heterogeneity, it would be interesting to see the effectiveness of this CAR T cell in a primary human tumor engrafted in the mouse model (PDX).

• Providing data of tumor-infiltrating CAR T cell function with flow cytometry would be useful to provide data on exhaustion and other markers.

• While the membrane expression of HSP70 is shown, the study could improve by investigating the mechanism.

• It is not sufficiently clear in immunostaining figures whether the commercial HSP70 antibody was used for staining or the antibody produced in their lab.

• It would be interesting if the authors could explain further on the strong differences in CAR T cell effect on the primary tumor when cells are administered on day 5 vs day 14 after tumor cell injection (best time point for CAR administration in clinical setting?)

• Testing cell lysis of human PBMC or tissue samples in vitro could be used to assess off target effects.

• Assessing the safety and effectiveness of CAR T cell infusion in tumor-bearing macaques could provide further information and validation to start a Phase 1 clinical trial in patients using this GrB-CAR T cell system.

Significance/Novelty

• Use of CAR T cells in solid tumor context which has previously had limited success.

• Identifying and providing data that mHSP70 can be targeted as a tumor-specific antigen with limited side effects.

• mHSP70 could be a “universal” target for multiple different solid tumors.

• The results provide data to support novel clinical trials for mHSP70-specific CAR T cells in addition to already showing non-human primate safety evaluation data with no side effects/ toxicities.

Credit

Reviewed by KayLee Steiner and Julia Hitschfel as part of a cross-institutional journal club between the Vanderbilt University Medical Center (VUMC), the Max-Delbrück Center Berlin, the Ragon Institute Boston (Mass General, MIT, Harvard), the Medical University of Vienna and other life science institutes in Vienna.

The author declares no conflict of interests in relation to their involvement in the review.