Dramatic Reduction of Chronic Lymphocytic Leukemia (CLL) Cells Following Adoptive Transfer of Cord Blood (CB) Natural Killer (NK) Cells Using CB-Engrafted NOD-SCID IL2Rγ^null (NSG) Mice as a Model.

Abstract 2370

Poster Board II-347

Adoptive transfer of NK cells in human B-CLL has been limited by the lack of suitable animal models to test the clinical efficacy of this immune therapy strategy. Primary patient B-CLL cells are difficult to engraft in NOD-SCID mice as these mice lack an immune microenvironment that provides essential accessory cells for tumor development. In the current study, we utilize a novel 2-step engraftment protocol using NOD-SCID γnull mice (NSG). Firstly, human cord blood (CB) derived CD34+ stem cells were engrafted to generate humanized chimeric mice capable of supporting B-CLL cells. By week 12, the human engraftment level reached 30% to 60% as detected in peripheral blood. Secondly, these mice were infused with human primary B-CLL cells labeled with CFSE. Our results show that following tail vein injection of 5E7 primary patient CLL cells, chimeric mice exhibited proliferation of CFSE+CD5+ B cells in the spleen and bone marrow, with disease development resembling human CLL. This allowed us to investigate the efficacy of ex vivo IL-2 expanded CB NK cell therapy using this novel mouse model system. As early as 24 hours post-infusion of IL-2 expanded human CD56+CD3- CB NK cells (10E7 per mouse) there was a detectable reduction of CD5+ leukemia cells in the peripheral circulation of CLL-engrafted mice by flow cytometry analysis. Moreover, by day 7 there was a dramatic 99.5 % reduction of CD5+ B-CLL cells in the blood, bone marrow, and spleen of experimental animals compared to the non-treated control group (P<0.001). Of note, expanded CB-NK cells exhibited high anti-leukemic specificity as healthy B cells from the original CB transplant were spared post-infusion. Overall, our studies suggest that the chimeric NSG mouse has utility as an in vivo model for testing immunotherapeutic strategies in aggressive B-CLL. Here, our results highlight the strong anti-leukemic response of infused ex vivo expanded CB-NK cells.