Immunotherapy of human cancers using gene modified T lymphocytes

Abstract

Adoptive T cell therapies can produce objective clinical responses in patients with hematologic and solid malignancies. Genetic manipulation of T lymphocytes has been proposed as a means of increasing the potency and range of this anti-tumor activity. We now review how coupling expression of transgenic receptors with countermeasures against potent tumor immune evasion strategies is proving highly effective in pre-clinical models and describe how these approaches are being evaluated in human subjects.

Fig. 1. Tumor immune evasion strategies

Tumors have evolved complex mechanisms to subvert the cellular immune response, including expression of FasL or PD-L1 which induce apoptosis or anergy in effector T cells, recruitment of Tregs, secretion of TGF-β and other immunosuppressive cytokines which inhibit T cell proliferation, constitutive expression of IDO by tumors and regulatory DCs, which depletes tryptophan resulting in T cell anergy and downregulation or modulation of MHC and co-stimulatory molecules.

Fig. 2. Generation and function of CARs

Panel A) illustrates the structure of a chimeric antigen receptor, and expression by T cells after gene transfer. After modification T cells can be redirected against tumor antigens and elicit a cytotoxic effect. Panel B) shows the expression of a CAR on T cells after retroviral transduction, by using a monoclonal antibody that recognizes the CH₂CH₃ extracellular component of the protein. Panel C) Cytolysis by gene modified T cells: a B cell tumor (Daudi) expressing green fluorescent protein (GFP) was cultured with non-modified T cells or T cells transduced with a CAR targeting the κ-light chain of human immunoglobulins at a of ratio 5:1 (tumor cells to T cells). After 12 hours in culture, T cells modified with the CAR-κ have destroyed the tumor.

Fig. 3. Enhancing the anti-tumor effect of gene modified T cells

Several genetic modifications have been used to improve the antitumor efficacy and longevity of T cells in vivo. These include transgenic expression of IL-2, IL-15, or IL-7Rα to improve proliferation, over-expression of hTERT, Bcl-2, Bcl-XL to increase survival, expression of CD80, 41BBL or modification of antigen-specific T cells to enhance co-stimulation, overexpression of CCR4 to improve migration to tumor sites, expression of a dominant-negative TGF-β receptor as well as downregulation of GCN2 or Fas on T cells to neutralize the inhibitory tumor microenvironment.

Fig. 4. Improving T cell manufacture

The figure shows the manipulations required for the expansion of antigen-specific CTLs using conventional 24 well plates versus the G-Rex bioreactor. The G-Rex manufacturing increases cell output with minimal manipulation and shortens the required CTL production time.