Modifying interleukin-2 concentrations during culture improves function of T cells for adoptive immunotherapy

Adoptive immunotherapy with cytotoxic T cells has shown promising clinical results in patients with metastatic melanoma and post-transplant-associated viral infections. Cell transfer therapies often require the ex vivo expansion of large numbers of reactive lymphocytes. Therefore interleukin-2 (IL-2), a potent T-cell mitogenic cytokine that critically affects the features and effectiveness of T cells, is frequently added to cell culture media.

We examined the influence of various IL-2 concentrations on cell growth, cytotoxicity, cytokine release and surface marker expression of tumor-infiltrating lymphocytes (TIL) during a standard 14-day rapid expansion phase. The study was conducted under good manufacturing practice (GMP) conditions, using approved reagents in a class 10000 laboratory.

T-cell cultures grown in very high IL-2 concentrations (600-6000 IU/mL) expanded massively and maximally secreted interferon (IFN)-gamma in response to antigenic stimulation, but exhibited only low direct cytotoxicity. On the other hand, TIL cultures grown in low concentrations of IL-2 throughout the rapid expansion phase expanded to a lower extent and barely secreted IFN-gamma but displayed high cytotoxic activity. A combined approach of starting with 10-120 IU/mL IL-2 during the first week, followed by increasing the IL-2 concentration to 6000 IU/mL during the second week, results in T cells that expand well, maximally produce IFN-gamma and are highly cytotoxic against tumor cells.

Fine tuning of the IL-2 concentration during ex vivo expansion of T cells can yield high numbers of T cells with optimal features for clinical use.