Cancer Immunity 1:10 (2001)

Minimal costimulatory requirements for T cell priming and TH1 differentiation: Activation of naive human T lymphocytes by tumor cells armed with bifunctional antibody constructs

Peter Kufer^1,2*, Florian Zettl¹*, Katrin Borschert^1,2, Ralf Lutterbüse^1,2, Roman Kischel^1,2, and Gert Riethmüller¹

¹Institute of Immunology, Goethestrasse 31, 80336 Munich, Germany
²Micromet AG, Am Klopferspitz 19, 82152 Martinsried, Germany
*These authors contributed equally to this work

Keywords: human, naive T lymphocytes, bispecific antibodies, T cell priming, TH1/TH2 differentiation, tumor immunity

Abstract

Direct priming of naive human CD8+ and CD4+ T cells by tumor cells devoid of any intrinsic antigen presentation properties, but passively armed with recombinant proteins mediating primary and costimulatory T cell signals, was investigated. Bifunctional antibody constructs were used to specifically target costimulatory molecules such as B7-1, B7-2 and LFA-3 to the epithelial cell adhesion molecule (EpCAM), a surface antigen successfully used as target for antibody therapy of minimal residual colorectal cancer. T cell priming was monitored by flow cytometric analysis of CD45 isoform expression and confirmed by measuring typical effector functions of primed T cells known to be absent from naive T lymphocytes. Accordingly, CD8+ T cells were tested for cytotoxic activity and secretion of TNF-alpha, while secretion of IFN-gamma, IL-5 and IL-4 was determined for CD4+ T cells. B7, known to be required for the initial activation of naive T cells, also proved to be sufficient for T cell priming when present as the only costimulatory molecule together with an appropriate primary signal. The requirement of dendritic and other antigen presenting cells (APCs) for T cell priming through non-APCs such as tumor cells could be ruled out. Under minimal priming conditions, naive CD4+ T cells were found to exclusively enter the TH1 developmental pathway, while several factors thought to favor TH2 polarization, like weak primary signals and B7-2 versus B7-1 costimulation, could be excluded as dominant TH2 promoters.