IL-7 along with Optimized CD3/CD28 Artificial APC Beads Promotes Ex Vivo Expansion of Cord Blood T Cells towards Adoptive Immunotherapy.

Background: Viral infections are the leading cause of non-relapse mortality after unrelated umbilical cord blood transplants (UCBT). Post-transplant lymphopenia, lack of established antiviral memory, and lack of cytotoxic function among infused UCB lymphocytes are jointly responsible for ineffective immunity. We have previously demonstrated ex vivo T cell expansion and maturation starting from a very small fraction (<5%) of the graft that could be employed post transplant as donor leukocyte infusion (DLI). Naïve UCB T cells proliferate when stimulated with IL-2 + CD3/CD28 co-stimulatory beads that function as artificial antigen presenting cells (APCs). However, high rate of apoptosis (>10%) has hindered T cell expansion. We hypothesized

1. that the presence of cytokines essential for T cell homeostasis, in particular IL-7 may aid expansion and survival,

2. beads with different densities of CD3/CD28 antibodies may impact UCB T cell expansion.

Research Design: From frozen/thawed specimens we tested 2 different sources of CD3/CD28 artificial beads (historical control beads vs ClinExVivo®, (Invitrogen Corporation), ± IL-7.

Methods: Thawed UCB samples were centrifuged over Ficoll gradient. T cells were positively selected with EasySep®, (StemCell Technologies) and were incubated in gas permeable bags with CD3/CD28 beads in 5% serum replete media + 100u/ml IL-2 ± 10ng/ml of IL7. Media & cytokines were replenished to maintain a concentration of ∼0.75 ×10⁶ cells/ ml. Automated cell count, trypan blue viability assessed overall cell growth and viability at each feeding . ‘Lyse no wash’ FACS staining with Trucount® beads quantified viable CD3+ T cells. 4-color FACS was employed to characterize the evolution of surface and intracellular immunophenotype. Cytotoxicity profile of the day 0 and D12-14 progeny was tested by Europium release assay (Delfia® assay) against a Burkitt’s lymphoma cell line (IM9). Two-tailed paired Student t-tests analyzed the impact of the experimental variables.

Results: At the end of 12–14 day expansion periods, analyzing all cytokine conditions, we could demonstrate an average of 43-fold viable CD3+ T cell expansion using control APC beads (n=8), while T cells on ClinExVivo® beads expanded on average 94-fold (p=0.11, n=11). Addition of IL7 to the culture media afforded significantly better expansion with the control bead condition (mean 43 vs 26 fold, p=0.02). IL7 also enhanced T cell expansion with ClinExVivo® beads (mean 147 fold vs 49 fold, though statistically NS). There were significantly more viable T cells generated with ClinExVivo® beads when all timepoints were analyzed, irrespective of the absence (p=0.017) or presence (p=0.05) of IL7. We also analyzed the mechanism how IL7 may potentiate overall T cell expansion. T cells entering cell cycle was enhanced (though not significantly) as demonstrated with intracellular Ki-67 staining (65% T cells in cycle with IL7 versus 52% without, p=0.2). IL7’s overall salutary effect on total expansion may be best explained by simultaneously reduced T cell apoptosis as quantified by activated ic Caspase-3 detection (9.3% versus 7.6% without vs with IL7, respectively, p=0.08) regardless of the source of beads. Granzyme A, B, perforin expression was enhanced comparably, while cytotoxicity was absent against IM9 cells regardless of ± IL-7.

Conclusions: These results demonstrate significant expansion of UCB T cell that is further improved by utilizing ClinExVivo® clinical grade APC beads and IL7. These results pave the way to donor-derived UCB T cell expansion suitable for DLI to boost immunity.