Early Clinical Experience of aAPC Activated NK-DLI Following Allogeneic PBSCT in Pediatric Solid Tumor Patients.
Authors: Baird Kristin , Fry Terry J , Merchant Melinda , Richards Kelly , Delbrook Cynthia , Wayne Alan S , Mackall Crystal L 
Published: October 2019

Abstract
Abstract 3013

Background:
Allogeneic Hematopoietic Stem Cell Transplant (alloHSCT) is effective in some hematologic malignancies and studies of alloHSCT for ultra high-risk pediatric solid tumors have shown some promise. Preclinical data demonstrates that activated NK cells readily kill pediatric solid tumors and leukemias, large numbers of activated NK cells can be generated ex vivo using artificial APCs (aAPCs) and the post-transplant period may be favorable for expansion and survival of adoptively transferred NK cells.

Methods:
We initiated a Phase I trial to assess feasibility and toxicity of escalating doses of donor-derived activated NK cell donor lymphocyte infusions (NK-DLI) on days 7 and 35 days following HLA-matched T cell depleted PBSCT in children and young adults with ultra-high risk solid tumors and leukemias. Donors underwent a single apheresis for filgrastim mobilized PBSC. The product was T cell depleted and CD34 and CD56 selected prior to cryopreservation, and the CD56+ fraction was cultured for 9–11 days with a K562 based aAPC expressing 4-1BBL and IL-15Ra plus rhIL-15 to generate the NK-DLI. NK-DLI consistently expressed high levels of natural cytotoxicity receptors NKp44 and NKp46 and mediated potent cytotoxicity ex vivo. T cell addback to the CD34 selected graft was performed to administer a T cell dose of 0.8–1.4 × 10e4 T cells/kg. Except for two pilot patients where NK-DLI was infused following engraftment, NK-DLI were administered ∼Day 7 and 35 post-transplant. Patients received a reduced intensity preparative regimen (fludarabine 30 mg/m2 and cyclophosphamide, 1200 mg/m2 on days –6 to -3; and melphalan 100 mg/m2 on day -2), and no prophylactic immunosuppression.

Results:
Seven patients with sarcomas were transplanted with NK-DLI infusion (1×10e5 CD56+ cells/kg/dose). Engraftment was brisk (median platelet recovery at 8d and neutrophil recovery at 9d). Patients had full donor myeloid chimerism by day 14 and all but one had >80% lymphoid chimerism by day 28. Patient #1 received NK-DLI on day +24 following alloHSCT and experienced aGVHD within 24 hours of NK-DLI with bullous skin rash and voluminous diarrhea. Prior to infusion the patient had what appeared to be a viral rash and fevers (skin biopsy negative for GVHD), but in retrospect likely GVHD, which was exacerbated by NK-DLI. Patient #2 received NK-DLI on Day +15 with no adverse effects. Subsequent patients enrolled onto cohort 1 with planned NK-DLI at days 7 and 35 (+7). Two patients developed aGVHD (rash and diarrhea), one with a cytokine-type reaction (fevers, hypotension) within 48 hours of NK-DLI infusion and one with aGVHD starting 21 days post NK-DLI. All 3 patients with matched unrelated donors experienced aGVHD after NK-DLI, whereas the 5 patients with matched sibling donors had no apparent adverse reactions nor GVHD. Persistence/engraftment of infused NK-DLI cannot be definitively determined, however, mean NK cell counts measured pre-alloHSCT and day +28 are 165/mm3 and 668/mm3 in the present cohort (n=6) compared to 149/mm3 and 395/mm3 in a historical alloHSCT population that did not receive NK-DLI (n=24). Antitumor effects via PET imaging were observed in patients with measurable disease and those without disease at the time of transplant have remained NED.

Conclusions:
Ex-vivo, aAPC expanded NK-DLIs do not interfere with stem cell engraftment but may contribute to or induce aGVHD, particularly in patients with matched, unrelated donors. Preliminary results suggest that aAPC NK-DLI expand in vivo and mediate antitumor effects following allogeneic PBSCT.

Disclosures:
No relevant conflicts of interest to declare.