Adoptive cell therapy: genetic modification to redirect effector cell specificity

Abstract

Building on the principals that the adoptive transfer of T cells can lead to the regression of established tumors in humans, investigators are now further manipulating these cells using genetic engineering. Two decades of human gene transfer experiments have resulted in the translation of laboratory technology into robust clinical applications. The purpose of this review is to give the reader an introduction to the 2 major approaches being developed to redirect effector T-cell specificity. Primary human T cells can be engineered to express exogenous T-cell receptors or chimeric antigen receptors directed against multiple human tumor antigens. Initial clinical trial results have demonstrated that both T-cell receptor- and chimeric antigen receptor-engineered T cells can be administered to cancer patients and mediate tumor regression.

FIGURE 1.

Preparative regimens for cell transfer. To facilitate engraftment and persistence of adoptively transferred T cells, patients received 3 separate conditionings treatments. Nonmyeloblative chemotherapy consisted of 2 days of cyclophosphamide (Cy, 60 mg/kg) then fludarabine (Flu, 25mg/m2) for 5 days. For additional ablation, total body irradiation (TBI) of 200 cGy and 1200 cGy was added at the days indicated. All patients received high-dose IL-2 (720,000 U/kg) every 8 hours to tolerance. Patients receiving TBI where administered autologous CD34⁺ mobilized peripheral blood cells (previously harvested and cryopreserved) on day 1 after cell infusion.

FIGURE 2.

Gammaretroviral vector designs. Shown are examples of gammaretroviral vector designs that have been used in the Surgery Branch, National Cancer Institute, to treat cancer patients with genetically modified T cells. TCR vectors (top) require expression of 2 proteins (the alpha and beta chains of the TCR), which can be done by the use of an internal promoter (such as PGK), an internal ribosome entry site (IRES), or a picornavirus ribosomal skip peptide (2A). CAR vectors (bottom) express an antitumor antigen single chain antibody (scFv) linked to T-cell signaling domains. Second-generation CAR vectors generally use a combinations of CD28 plus CD3zeta signaling domains, whereas third-generation CAR vectors include additional elements such as a hinge and transmembrane domain from CD8 and the second costimulatory elements, eg, derived from the 4–1BB gene. The specific proteins that have been targeted in Surgery Branch clinical trials using these vector designs is as indicated on the right of the figure. LTR indicates long terminal repeat; sd, RNA splice donor; sa, RNA splice acceptor; ψ, packaging signal; CEA, carcinoembryonic antigen; and arrows, direction of transcription.