Changes in lymphocytes' telomerase activity by 4-1BB costimulation

Lymphocytes are exceptional among somatic cells as these cells can induce telomerase enzyme after antigen stimulation to compensate chromosomal loss during rapid cell division. Activation of telomerase in lymphocytes needs CD28 signal, which simultaneously costimulates T cells during activation. 4-1BB of tumor necrosis factor superfamily also has been shown to costimulate T cells. Herein, we investigated changes in telomerase activity of lymphocytes during longitudinal cultures when T cells costimulated by CD80 or 4-1BB ligand or both molecules in conjunction with anti-CD3 stimulation. Artificial antigen presenting cells (aAPCs) were produced by transduction of CD80, 4-1BB ligand or green fluorescent protein genes into A549 carcinoma cells using recombinant adenoviral vectors. Peripheral blood mononuclear cells were stimulated with anti-CD3 and co-cultured with the aAPCs. Cellular growth, expression of telomerase and production of interferon gamma (IFN-γ) were assessed at different time points and followed up to day 35. 4-1BBL provided effective costimulation for lymphocytes' activation, cytokine production or long-lasting growth where its effects exceeded over CD80 after the first week. 4-1BBL also promoted the telomerase activity and more importantly was able to re-induce the enzyme in the cells that stopped to grow with CD80 costimulation. Although combination of CD80 and 4-1BBL has additional effect on cellular growth or initial telomerase activity, it could not support telomerase activity in later time points. Our results underscored unique features of 4-1BB over CD28 for prolonged support of lymphocytes' costimulation, which can be recruited for in vitro or ex vivo propagation of T cells for cancer immunotherapy purposes.