Complementary Costimulation of Human T Cell Subpopulations by CD28 and CD81

Abstract 1124

CD81 is a widely expressed tetraspanin molecule that physically associates with CD4 and CD8 on the surface of human T cells. Coengagement of CD81 and CD3 results in the activation and proliferation of T cells. CD81 also costimulated mouse T cells that lack CD28, suggesting either a redundant or a different mechanism of action. Here we show that CD81 and CD28 have a preference for different subsets of T cells - primary human naïve T cells are better costimulated by CD81, while the memory T cell subsets and Tregs are better costimulated by CD28. The more efficient activation of naïve T cells by CD81 was due to prolonged signal transduction compared to that by CD28. We found that IL-6 played a role in the activation of the naïve T cell subset by CD81. Combined costimulation through both CD28 and CD81 resulted in an additive effect on T cell activation. Thus, these two costimulatory molecules complement each other both in the strength of signal transduction and in T cell subset inclusions. Costimulation via CD81 might be useful for expansion of T cells for adoptive immunotherapy to allow the inclusion of naïve T cells with their broad repertoire.