Results

The current CTL019 process targets 450e9 total nucleated cells (TNC) at seeding of the static culture bags prior to activation and transduction (Kalos M et al. 2011; Maude et al. 2014). However, less is known on the impact of a range of T cell numbers within the TNC population on, transduction efficiency and expansion. Healthy donor T cells cultures were evaluated in the range of the starting T cell percentages between 1.7% and 97.7%. T cells expanded in all tested conditions with the population doubling range between 3.7 and 8.5, and the percentages of T cells at the end of the culture period were 94.9 ± 5.0%. The major non-target cell population at the end of culture was NK cell population (4.8 % ± 2.9%).

The feasibility of expanding T cells from leukemic donors with very low T cell content was assessed on three ALL patient samples with original T cell contents of 1.4%, 1.2% and 2.0%. After polyclonal stimulation and growth in culture T cell percentages were respectively the following: 78.1%, 95.9% and 1.1% (non-expander), supporting the potential of some ALL patients with low T cell counts to meet cell number requirements after 9 day expansion for cell therapy in the absence of T cell enrichment steps.