Antitumor Activity of Human CD34+ Cells Expressing Membrane-Bound Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand (mTRAIL).

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is expected to play a key role in anti-cancer therapy due to its high cancer cell-specificity and potent antitumor activity. The clinical development of soluble (s)TRAIL is however hampered by several limitations, including

• short plasma half-life;

• liver toxicity;

• tumor cell resistance.

To overcome these limitations, we used CD34+ cells transduced with an adenovirus encoding the full-length human TRAIL gene (CD34−TRAIL+) as vehicles for intra-tumor delivery of membrane-bound (m)TRAIL. The mean (±SD) transduction efficiency of CD34+ cells exposed to a multiplicity of infection (MOI) of 500 was 83 ± 8% (range 70 – 95%) with a cell viability ≥85%. In vitro, exposure of the sTRAIL-sensitive KMS-11 cell line to CD34−TRAIL+, but not mock-transduced CD34+ cells consistently resulted in caspase-3, -8, and -9 activation and in PARP cleavage, as well as in potent induction of apoptosis (up to 80% after a 48-hour co-culture). Exposure of the sTRAIL-resistant JVM-2 cell line to CD34−TRAIL+ cells resulted in significant levels of tumor cell death (up to 50% after a 48-hour co-culture). Studies in nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice xenografted with KMS-11 cell line showed that CD34−TRAIL+ cells significantly increased the median survival of mice bearing early-stage (92 vs 55 days, P ≤ 0.0001) and advanced-stage (83 vs 55 days, P ≤ 0.0001) disease, as compared with controls. Additionally, CD34−TRAIL+ cells significantly prolonged the median survival of mice xenografted with the sTRAIL-resistant JVM-2 (40 vs 31 days, P ≤ 0.0001) and SU-DHL-4V (38 vs 30 days, P ≤ 0.0001) cell lines. No obvious toxicity was observed upon administration of CD34−TRAIL+ cells. Histological analysis of subcutaneous lymphoma revealed an efficient tumor homing of transduced cells and high level expression of the agonistic TRAIL-R2 receptor by tumor endothelial cells. Following injection of CD34−TRAIL+ cells, but not mock-transduced CD34+ cells, TUNEL staining revealed increasing amounts of apoptotic cells with a 21-fold increase of the apoptotic index at 120 hour post-injection. Additionally, CD34−TRAIL+ cells induced signs of vascular damage leading to a progressive disintegration of the vascular bed, suggesting that tumor endothelial cells represent an early target of CD34−TRAIL+ cells. Our experiments show that:

• in vitro, the co-culture of tumor cells and CD34−TRAIL+ cells resulted in a marked apoptosis of both sTRAIL-sensitive and sTRAIL-resistant tumor cells;

• in vivo, injection of CD34−TRAIL+ cells in mice bearing advanced-stage tumors as well as sTRAIL-resistant tumors was associated with a significant prolongation of survival.

These results show that CD34−TRAIL+ cells might be an efficient vehicle for mTRAIL delivery to tumors, where they exert a potent antitumor effect possibly mediated by both direct tumor cell killing and indirect vascular-disrupting mechanisms.