Abstract 3501: Binary control of CAR-CTL by transgenic IL-7 and IL-7R expression

Abstract

While adoptive transfer of cytotoxic T lymphocytes (CTLs) engrafted with chimeric antigen receptors (CAR) has produced objective clinical responses in vivo, the infused cells usually fail to persist long-term, limiting benefit. We have recently demonstrated that CTL persistence can be improved by engineering cells to express the IL-7 receptor alpha chain (IL-7R) which is physiologically absent on CTLs. However, this approach requires access to clinical grade cytokine and biodistribution to T lymphocytes at tumor sites may be insufficient. To circumvent these problems we have prepared two CTL products: one expressing a tumor-specific CAR in combination with IL-7R (product #1), and the second engineered to co-express the same CAR and produce IL-7 cytokine (product #2). In this way, both products have anti-tumor activity mediated through the CAR, while cytokine produced from CTL#2 should support the survival and persistence of the IL-7R-expressing CTL#1. A binary system such as this should be intrinsically safer than incorporating a positive feedback loop of both cytokine and receptor in a single cell. As a proof of this principle, we used the SFG-CAR that targets the ≤ light chain expressed on B cell malignancies: SFG-CAR/IL-7R-GFP(#1) and SFG-CAR/IL-7cyto-mOrange(#2). EBV-CTLs from 3 donors were transduced with each vector. FACS analysis of transgene expression indicated that all were expressed at approximately equivalent levels: CTL#1 (CAR, IL-7Rα, and GFP; 58%±15, 53%±18, 57.8%±12) and CTL#2 (CAR and mOrange; 54%±18 and 52%±20). The modified CTL were functional, and cells transduced with either vector were able to kill the α+ B cell tumors Daudi as evaluated by Cr51 assay (72%±13 and 69%±25, respectively) at an R:S of 40:1. Preliminary data indicates that CTLs#1 were able to proliferate in response to exogenous IL-7 administration, and IL-7 cytokine production from CTLs#2 was directly proportional to the antigenic stimulation provided to the cells. In addition, when CTLs#1 and #2 were cultured together we observed that CTLs#2 were capable of promoting the expansion of their CTL counterpart in a more efficient way than that compared to exogenous administration of IL-7 or IL-2. These results indicate that binary control of CAR modified CTLs is possible through transgenic expression of IL-7R and IL-7 cytokine in two different CTL populations. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3501. doi:1538-7445.AM2012-3501