Genetic approaches for antigen-selective cell therapy.

Attempts to improve the efficacy of adoptive T-cell therapies have led to the development of innovative strategies that combine the high specificity of antibody molecules with the efficient trafficking properties and effector functions of immune cells. These antigen-selective cell therapies are designed to convert therapeutically important native antigens expressed on the cell surface (tumor associated antigens, viral envelope proteins) into recruitment points of effector functions, and address the goal of major histocompatibility complex- and exogenous cytokine-independent activation of mature effector T-cells. The most promising and best characterized antigen-selective strategy is based on the genetic manipulation of the recognition specificity of T-cells by grafting the recognition specificity of a monoclonal antibody onto a lymphocyte triggering molecule (TCR-associated polypeptides, Fc epsilon RI-gamma chain). Upon encountering specific antigen, cells harboring chimeric immune receptors (CIRs) are able to undergo specific stimulation and kill antigen bearing cells in both in vitro and in vivo model systems. Initial studies have focused on terminally differentiated effector cell-based protocols. However, recent data indicate that progenitor cell-based therapies allow the permanent generation of stable populations of CIR-expressing cells of multiple lineages, leading to long-term persistent systemic immunity. Emerging gene therapy strategies are based on the use of biespecic antibody fragments. The advantages of these biespecic antibody-mediated immune recruitment (BIR) approaches (trans-recruitment and multieffector activation) could complement conventional CIR-based immunotherapies. Although further scientific progress is required regarding the selection of the ideal effector cell/s and the definition of the optimal targeting and recruitment systems, clinical trials recently initiated in patients with advanced cancer and human immunodeficiency virus infection should help us to determine the real efficacy of these approaches. The relevance of these and other emerging concepts to cell-mediated immunotherapy is discussed.