Natural killer (NK) cells mediate natural cytotoxicity against virus-infected or transformed cells. Alloreactive NK cells derived from haplotype mismatched hematopoietic stem cell (HSC) transplantation donors are used to successfully treat patients with high-risk acute myeloid leukemia (AML) without causing graft versus host disease (GVHD). However, equal benefit is not afforded to patients with B-cell acute lymphoblastic leukemia (B-ALL), suggesting that alloreactive NK cells fail to control B-ALL.
This failure may be due to inhibitory signal-mediated resistance caused by B-ALL. To address this problem, mature NK cells can be genetically modified to express chimeric antigen receptors (CARs) specific for tumor antigen, thus harnessing their ability to kill B-ALL blasts. To date, adoptive transfer of ex vivo expanded mature NK cells has not shown therapeutic benefit in hematological malignancies, in part from the lack of target specificity and the short period of persistence after infusion.
We hypothesize that CAR modified NK progenitors/precursors derived from CD34+ HSCs combined with HSC transplantation may provide enhanced anti-B-ALL-specific NK effectors with long-term persistence, thus likely increasing the efficacy of NK cell therapy for B-ALL. To test this hypothesis, two specific aims are proposed.
Aim 1: To evaluate specific and enhanced killing of B-ALL in vitro and in immunodeficient mice by genetically modified NK progenitors/precursors. We will use the non-viral Sleeping Beauty (SB) transposon system to achieve integration and stable expression of CAR for CD19 antigen in cord blood-derived CD34+ cells. Transfected CD34+ cells will subsequently be differentiated into NK cells using the feeder free Glycostem clinical grade bioreactor system. As controls, we will use stromal cell co-culture derived NK progenitors and peripheral blood NK cells that are similarly modified by SB. Ex vivo generated NK cells will be evaluated for transgene expression, surface phenotype, cytotoxicity and cytokine production against B-ALL cells and patient blasts. NK cell expansion, persistence and anti-B-ALL activity in mice will be determined.
Aim 2: To establish conditions for the production of genetically modified NK progenitors/precursors in a good manufacturing practice (GMP) facility. GMP grade NK cells will be evaluated for in vitro function and in vivo anti-leukemia efficacy. We are well positioned to complete these studies considering the extensive experience of our team in SB-mediated HSC gene transfer and NK cell therapeutics. Our strong preliminary data also support the likelihood of accomplishing the proposed aims.
Our study is significant and innovative because our work can rapidly lead to a clinical trial for high-risk B-ALL using SB modified NK progenitors/precursors as universal “off-the-shelf” immunotherapy and can potentially be applied to the treatment of other hematological malignancies, solid tumors and viral infections.
