Successful Remission of Poor Prognosis AML after Adoptive Transfer and In Vivo Expansion of Human Haploidentical NK Cells.
Authors: Miller Jeffrey S. , Soignier Yvette , Panosskaltsis-Mortari Angela , McKenna David , Le Chap , Defor Todd E. , Burns Linda J. , Orchard Paul J. , Blazar Bruce R. , Wagner John E. , Slungaard Arne , Weisdorf Daniel J. , Okazaki Ian J. , McGlave Philip B. 
Published: April 2020

Abstract
We previously demonstrated that although autologous NK cell therapy after hematopoietic cell transplantation (HCT) is safe, it does not provide an anti-tumor effect. We hypothesize that the lack of NK cell inhibitory receptor (KIR) mismatching with autologous tumor cells limits anti-tumor efficacy. Allogeneic NK cell infusions may overcome this restriction. Here we tested haploidentical, related donor NK cell infusions in a non-transplant setting to establish safety with a goal of in vivo NK cell expansion. A low intensity outpatient immune suppressive regimen of fludarabine (Flu) alone was tested in 8 renal cell carcinoma patients. A higher intensity inpatient regimen of high-dose cyclophosphamide and Flu (Hi-Cy/Flu) was tested in 12 patients with poor prognosis AML, all with active leukemia and most who failed 1 or more standard theries. NK cells were enriched from donor apheresis products using CD3 depletion by the CliniMacs system. All patients received subcutaneous IL-2 after infusions. Patients who received the lower intensity Flu regimen showed transient persistence of donor cells, but no in vivo expansion (&lt;0.1%) using a PCR based chimerism assay of unique MHC class I alleles in the donor but not present in the recipient. There were no objective responses in renal cell carcinoma patients. In marked contrast, 6 of 7 AML patients who were evaluable for engraftment receiving Hi-Cy/Flu showed engraftment of donor cells, some for &gt; 28 days. Three of 6 patients had peak engraftment levels of 10%, 100% and 100% of PBMC in the first 2 weeks after the haploidentical infusion. The remaining three patients had lower levels of approximately 1%. Five of 12 patients have achieved a remission with this therapy. Compared to patients who failed to clear their leukemia, the remission patients had significantly higher proportions of circulating NK cells (35±8% vs. 1.5±0.4%, p=.001) and cytotoxicity against K562 targets (50±10% vs. 10±5% at E:T 20:1, p=0.01) suggesting that in vivo expansion was required to achieve efficacy. We next tested whether endogenous cytokines play a role in the in vivo expansion. Based on its established role in NK cell differentiation and on recent mouse studies, IL-15 was a likely candidate to drive homeostatic NK cell expansion. Flu patients showed only a slight increase in IL-15 after several days compared to pre-treatment levels. In marked contrast, AML patients had significant increases in plasma IL-15 after Hi-Cy/Flu therapy, which appeared before haploidentical cell infusions and was sustained for several weeks. There was an inverse correlation between the absolute lymphocyte count and the IL-15 concentration (r = −.62, p-value &lt; .0001). We conclude that Hi-Cy/Flu therapy allows for expansion of allogeneic NK cells in vivo in part through increased endogenous IL-15 concentrations, which can induce remissions in poor prognosis AML patients. For the first time, these findings suggest that haploidentical NK cells can persist and expand in vivo and may have a role in the treatment of AML used alone or as an adjunct to HCT. Future studies will address NK cell donor-recipient mismatch at KIR ligands, patient selection and other variables that impact on response.