Micromolar affinity CAR T cells to ICAM-1 achieves rapid tumor elimination while avoiding systemic toxicity

Spencer Park,Susan Park,Marjan Zaman,Moonsoo M. Jin,Yogindra Vedvyas,Yen-Michael S. Hsu,Irene M. Min,Enda Shevlin

doi:10.1038/s41598-017-14749-3

Spencer Park, Susan Park + Show 6 more

Open Access

https://doi.org/10.1038/s41598-017-14749-3

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Abstract

Adoptive transfer of high-affinity chimeric antigen receptor (CAR) T cells targeting hematological cancers has yielded impressive clinical results. However, safety concerns regarding target expression on healthy tissue and poor efficacy have hampered application to solid tumors. Here, a panel of affinity-variant CARs were constructed targeting overexpressed ICAM-1, a broad tumor biomarker, using its physiological ligand, LFA-1. Anti-tumor T cell potency in vitro was directly proportional to CAR affinity and ICAM-1 density. In a solid tumor mouse model allowing simultaneous monitoring of anti-tumor potency and systemic off-tumor toxicity, micromolar affinity CAR T cells demonstrated superior anti-tumor efficacy and safety compared to their nanomolar counterparts. Longitudinal T cell tracking by PET/CT and concurrent cytokine measurement revealed superior expansion and contraction kinetics of micromolar affinity CAR T cells. Therefore, we developed an ICAM-1 specific CAR with broad anti-tumor applicability that utilized a reduced affinity targeting strategy to significantly boost efficacy and safety.

Highlights

chimeric antigen receptor (CAR) molecules are composed of synthetic binding moieties, typically an antibody-derived single chain fragment variable or any native antigen-sensing element, fused to intracellular signaling domains composed of the T cell receptor (TCR) zeta chain and costimulatory molecules such as CD28 and/or 4-1BB1,2
We found that I domain CARs exhibiting affinities in the micromolar range (~10 μM) exhibited a significantly higher therapeutic index in vivo compared to CARs with higher affinity (1–100 nM) which tended to cause unbiased reactivity against normal cells with basal intercellular adhesion molecule (ICAM)-1 expression and led to less efficient tumor regression
The paucity of native, surface-expressed, and tumor-specific antigens presents a significant hurdle to developing CAR T cell therapy against solid cancers[38,39]

Summary

Results

ICAM-1 specific CAR T cells with 106-fold, step-wise variation in affinity. CAR constructs specific to ICAM-1 were built using the I domain derived from LFA-1 (Fig. 1a,b). Specific tracer uptake was observed in mice treated with SSTR2-F292A CAR T cells, demonstrating the expansion and contraction phases in the lungs, with peak CAR T cell signal occurring approximately 4 days following peak tumor burden and gradually decreasing to background levels (Fig. 6c,d). This biphasic T cell expansion and contraction phenomenon was reminiscent of our previous study using SSTR2-R6.5 CAR T cells in the same mouse tumor model[29].

Discussion

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