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CD63 as an activation-linked T cell costimulatory element
Katharina Pfistershammer1, Otto Majdic, Johannes Stöckl
1Institute of Immunology, Medical University of Vienna, Borschkegasse 8A, A-1090 Vienna, Austria.
Insights
Researchers identified CD63 as a key molecule in T cell activation. This lysosomal-associated membrane protein (LAMP-3) on activated T cells, not dendritic cells, enhances T cell proliferation and IL-2 production.
Area of Science:
- Immunology
- Cell Biology
Background:
- Dendritic cells (DC) and T cells interact via receptor/ligand pairs to regulate immune responses.
- An anti-DC monoclonal antibody (mAb), 11C9, initially thought to target DC, was studied for its functional effects.
Purpose of the Study:
- To identify the target of mAb 11C9 and elucidate its role in T cell activation.
- To investigate the function of CD63 as a costimulatory molecule on T cells.
Main Methods:
- Monoclonal antibody (mAb) 11C9 characterization and functional assays in mixed lymphocyte reactions (MLR).
- Retroviral expression cloning to identify the 11C9 antigen.
- Analysis of CD63 expression on T cells upon stimulation.
- Assessment of T cell proliferation, IL-2 production, and restimulation responsiveness.
Main Results:
- mAb 11C9 inhibited DC-induced T cell activation, but preincubation of DC with mAb 11C9 did not affect T cell responses.
- The 11C9 antigen was identified as CD63 (LAMP-3), a molecule minimally expressed on resting T cells but rapidly upregulated upon activation.
- Cross-linking CD63 on activated T cells, along with T cell receptor (TCR) triggering, strongly enhanced T cell activation, proliferation, and IL-2 production.
- CD63 costimulation demonstrated superior enhancement of T cell responsiveness to restimulation compared to CD28 and other CD28-independent pathways.
Conclusions:
- CD63 on activated T cells, not on dendritic cells, is the primary target of mAb 11C9, mediating potent T cell costimulation.
- CD63 acts as an activation-induced reinforcing element, promoting sustained and efficient T cell activation and expansion.
- CD63 represents a significant pathway for enhancing T cell responses, surpassing other known costimulatory mechanisms.
Abstract:
Dendritic cells (DC) are unique in their capacity to either stimulate or regulate T cells, and receptor/ligand pairs on DC and T cells are critically involved in this process. In this study we present such a molecule, which was discovered by us when analyzing the functional effects of an anti-DC mAb. This mAb, 11C9, reacted strongly with DC, but only minimally with lymphocytes. In MLR it constantly reduced DC-induced T cell activation. Therefore, we assumed that mAb 11C9 primarily exerts its functions by binding to a DC-structure. This does not seem to be the case, however. Preincubation of DC with mAb 11C9 before adding T cells had no inhibitory effect on T cell responses. Retroviral expression cloning identified the 11C9 Ag as CD63. This lysosomal-associated membrane protein (LAMP-3), is only minimally expressed on resting T cells but can, as we show, quickly shift to the surface upon stimulation. Cross-linkage of that structure together with TCR-triggering induces strong T cell activation. CD63 on T cells thus represents an alternative target for mAb 11C9 with its binding to activated T cells rather than DC being responsible for the observed functional effects. This efficient CD63-mediated costimulation of T cells is characterized by pronounced induction of proliferation, strong IL-2 production and compared with CD28 enhanced T cell responsiveness to restimulation. Particularly in this latter quality CD63 clearly surpasses several other CD28-independent costimulatory pathways previously described. CD63 thus represents an activation-induced reinforcing element, whose triggering promotes sustained and efficient T cell activation and expansion.
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