Phase II Clinical Trial of “Off-the-Shelf” NK Cells with Allogeneic Stem Cell Transplantation in Patients with High-Risk Myeloid Malignancies
Authors: Ramdial Jeremy , Clemente Lorlyn , Banerjee Pinaki , Dabaja Bouthaina S. , Al-Atrash Gheath , Alousi Amin M. , Oran Betul , Popat Uday , Im Jin S. , Srour Samer A. , Chen George , Kebriaei Partow , Hosing Chitra , Marin David , Rezvani Katayoun , Shpall Elizabeth J. , Champlin Richard E. 
Published: December 2024

Background
Acute myeloid leukemia, myelodysplastic syndrome, and TKI resistant CML continue to be the most aggressive forms of blood cancer. Allogeneic hematopoietic stem cell transplantation (alloSCT) remains one of the most effective treatments available due to the immune-mediated graft-versus-leukemia effect to prevent relapse. Nevertheless, disease relapse remains the most important cause of treatment failure.
A potential solution to reduce relapse may be found in Natural Killer (NK) cells, a unique class of lymphocytes known for their cytotoxic and potent anti-leukemia effects. NK cell function is regulated by germ-line encoded receptors including killer-cell Immunoglobulin-like Receptors (KIR), which mediate their cytotoxic functions through receptor-ligand interactions. Alloreactive NK cells have been reported to enhance engraftment, reduce GVHD and prevent relapse of leukemia post transplant in both preclinical and clinical studies.
Study Design and Methods
This is a single-arm Phase II trial of ex vivo expanded 3rd party peripheral blood-derived natural killer (NK) cells at a fixed dose added to an allogeneic stem cell transplant to reduce relapse and to improve relapse free survival. The primary endpoint is the reduction in adverse event (graft failure, grade 3-4 GVHD, relapse or non-relapse death within 100 days post-transplant).
Patients with high risk AML, MDS, or TKI-resistant/intolerant CML who have either an HLA matched related donor, HLA matched unrelated donor, a haploidentical related donor, or a one antigen mismatched unrelated donor were enrolled. Patients with AML relapsing after a prior allogeneic transplant were also eligible. HLA matching included HLA A, B, C, and DR-B1. Inclusion criteria also included ages 18 to 70 years old, weighing at least 42 kg, with adequate organ function (Clinical trial registered as NCT05115630).
KDS-1001 is composed of NK cells from an allogeneic third party donor, expanded ex vivo using PM21 membrane particles, which are formed from the plasma membranes of K562.mbIL21.41BBL.
Results
Our trial began enrollment in June, 2022 and we have treated 16 patients beyond day 100. The median age was 42.5 (27-67), 5 patients received MSD and 11 patients received MUD alloSCT. 14 patients had a diagnosis of AML and 2 patients had MDS. This was the second transplant for 9 patients. 3 patients had MLFS as disease response and 13 had a CR/CRi with 4 being MRD positive by multicolor flow cytometry.
Starting on day -7 patients received melphalan 100 or 140 mg/m2, fludarabine, and on day -3, total body radiation (2Gy) as the preparative regimen, with bone marrow or peripheral blood progenitor cells on day 0. Cyclophosphamide, tacrolimus and mycophenolate was given as GVHD prophylaxis. Patients received KDS-1001 cells 3 x107/kg on day -2, +7 and +28.
All patients achieved engraftment and hematologic recovery; the average time to neutrophil engraftment was 17.3 days with 2 patients dying from bacterial sepsis before engraftment. 1 patient had a transient secondary graft failure that spontaneously resolved after 1 week. No patient had graft rejection. The NK cell infusions were generally well tolerated. Two patients had a Grade 1 infusion reaction with their first NK cell infusion but tolerated subsequent infusions. No episodes of CRS were reported.
As correlative analysis, NK cell levels were monitored throughout the first 60 days. A sequential gating strategy identified 3rd party donor NK population and could be detected in all patients up to 7 days post each infusion.
3 patients relapsed within 6 months post transplant. 5 patients have died; 3 from sepsis and 2 from relapsed disease. 5 patients had acute GVHD with max grade 2; four UGI and one skin. No cases of grade 3/4 acute GVHD occurred and none have developed chronic GVHD.
Since the collection of this data 4 more patients have been enrolled and treated and have not yet reached their 90-100 day time point; they all engrafted and received the planned NK infusions.
Conclusions
Administration of 3rd party, expanded NK cells after matched allogeneic stem cell transplantation was safe, well tolerated, and importantly, did not increase the risk of graft failure or GVHD. The post stem cell transplant course for those treated thus far seems to be similar to the reported literature. Longer follow up is needed to assess the impact on disease relapse and relapse free survival.