Functional analysis of the co-stimulatory molecules CD27 and CD137 (4-1BB) during T cell-mediated immune responses

Rowley, Tania Francesca (2004) Functional analysis of the co-stimulatory molecules CD27 and CD137 (4-1BB) during T cell-mediated immune responses. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

Identification of the signals required for optimal differentiation of naive T cells into effector and memory cells is critical for the design of effective vaccines for use in immunotherapy. This thesis describes the generation and characterisation of soluble recombinant ligands for two members of the TNFR superfamily of cell surface receptors, CD27 and CD137 (4-1BB). These receptors provide co-stimulatory signals, which act in concert with antigen-driven T cell receptor signals to promote optimal T cell activation. The recombinant fusion proteins, which encompassed the extracellular domains of murine CD27 ligand (CD70) or 4-1BB ligand (4-1BBL) and the Fc domain of human IgG1, formed large multimeric complexes that proved to have potent signalling capacity. Stimulation of CD27 by soluble recombinant CD70 was found to enhance both the magnitude and quality of CD8⁺ T cell responses. Triggering CD27 in the presence of antigen significantly enhanced the division and survival of CD8⁺ T cells in vitro, as well as their ability to produce interleukin-2 and interferon-γ and up regulate expression of 4-1BB and CD25 (interleukin-2 receptor α-chain). In an in vivo model of T cell activation, administration of peptide antigen and soluble CD70 resulted in a massive (> 300-fold) expansion of antigen-specific CD8⁺ T cells, due to the enhanced division and survival promoted by CD27 co-stimulation. In mice that received antigen and soluble CD70, CD8⁺ T cells developed into effectors with direct ex vivo cytotoxicity and the capacity to eradicate syngeneic tumour cells expressing antigen in vivo. Furthermore, unlike immunization with peptide antigen alone, which resulted in a diminished secondary response after rechallenge, CD27 co-stimulation during primary T cell activation led to a strong secondary response being evoked upon rechallenge with the antigenic peptide. Thus, in addition to increasing the frequency of primed antigen-specific T cells, CD27 signalling during the primary response instils a programme of differentiation that allows CD8⁺ T cells to maintain their responsiveness. Ligation of 4-1BB using soluble 4-1BBL exhibited similar co-stimulatory effects to those of CD27 when administered with a peptide antigen, causing enhanced primary CD8⁺ T cell expansion and affecting the quality of the T cell response so that a population of reactive T cells was maintained after the primary response. However, closer comparison of the effects of CD27 versus 4-1BB co-stimulation using their soluble ligands demonstrated that while CD27 predominantly enhanced the initial burst of T cell expansion, 4-1BB altered the kinetics of the primary response so that the activated T cells survived for longer and the contraction phase was slowed.