Abstract
Recent clinical advances with chimeric antigen receptor (CAR) T cells have led to the accelerated clinical approval of CD19-CARs to treat acute lymphoblastic leukemia. The CAR T cell therapy is nevertheless associated with toxicities, especially if the CARs are not entirely tumor-specific. Therefore, strategies for controlling the CAR T cell activity are required to improve their safety profile. Here, by using the multiple myeloma (MM)-associated CD38 molecule as target molecule, we tested the feasibility and utility of a doxycycline (DOX) inducible Tet-on CD38-CAR design to control the off-target toxicities of CAR T cells. Using CARs with high affinity to CD38, we demonstrate that this strategy allows the proper induction of CD38-CARs and CAR-mediated T cell cytotoxicity in a DOX-dose dependent manner. Especially when the DOX dose was limited to 10ng/ml, its removal resulted in a relatively rapid decay of CAR- related off-tumor effects within 24 hours, indicating the active controllability of undesired CAR activity. This Tet-on CAR design also allowed us to induce the maximal anti-MM cytotoxic activity of affinity-optimized CD38-CAR T cells, which already display a low toxicity profile, hereby adding a second level of safety to these cells. Collectively, these results indicate the possibility to utilize this DOX inducible CAR-design to actively regulate the CAR-mediated activities of therapeutic T cells. We therefore conclude that the Tet-on system may be more advantageous above suicide-genes to control the potential toxicities of CAR T cells without the need to destroy them permanently.
Highlights
Over the past years, the clinical successes of chimeric antigen receptor (CAR) engineered T (CAR T) cells have evoked a tremendous enthusiasm for this new mode of immunotherapy in the battle against cancer [1,2,3,4,5,6,7]
We evaluated whether the level of CD38-CAR expression and the CD38-dependent cytotoxic activity of tetracycline responses elements (TRE)-CD38-CAR T cells could be regulated by the dose of DOX, by incubation with serial concentrations of DOX ranging from 1–1000 ng/ml for 48 hours (Fig 2B)[32,33]
In this study we evaluated the feasibility of controlling the on-target, off- tumor effects of CD38-CAR T cells using a DOX inducible Tet-on CAR design
Summary
The clinical successes of chimeric antigen receptor (CAR) engineered T (CAR T) cells have evoked a tremendous enthusiasm for this new mode of immunotherapy in the battle against cancer [1,2,3,4,5,6,7]. Several currently known toxicities of CAR T cells are associated with their in vivo uncontrolled growth and excess cytokine release soon after infusion in the patients, most probably—though not entirely- due to the on-target off-tumor activities of CAR T cells. This is considered an important concern since virtually all CAR T cells developed to date, including the most successful CD19 CAR T cells, are directed against tumor-associated, but not entirely tumor specific antigens [11,12].
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