Ex Vivo IL-2 Expansion of CB-NK Cells Promotes Synergistic LFA-1 and CD2 Engagement at the NK Cell Lytic Immune Synapse; Implications for Adoptive CB-NK Cell Therapy in Acute Myeloid Leukemia.
Authors: Xing Dongxia , Ramsay Alan G. , Decker William , Li Sufang , Robinson Simon , Yang Hong , Bollard Catherine M. , Gribben John G. , Shpall Elizabeth J. 
Published: October 2019

Abstract
Abstract 3029
Poster Board II-1005
Donor peripheral blood (PB) natural killer (NK) cell have shown clinical promise in cancer immunotherapy. Tightly regulated receptor signaling between NK cells and susceptible tumor cells is essential for NK cell-mediated cytotoxicity. Umbilical cord blood (CB) represents an important alternative source of NK cells for adoptive immune therapy. We first demonstrated that cord blood (CB) derived NK cells have poor cytolytic activity and deficiency in the formation of the F-actin immunological synapse with HLA class I deficient target K562 cells and primary AML blasts compared to PB-NK cells. In this study, we explored the cellular mechanism of these dysfunctions. We hypothesized that adhesion and signaling molecules may be defective in unmanipulated CB NK cells. Activating receptor Both CD2 and the integrin lymphocyte function-associated antigen (LFA-1) play important roles in both T lymphocyte and NK cell immune synapse formation and their trafficking to the immune synapse regulates both T and NK cell function. We now show that unmanipulated CB NK cells exhibit reduced LFA-1 mediated adhesion to mobilized ICAM-1 compared to IL-2 expanded CB NK cells (CB NK 29.7+/- 3.2 %, vs expanded CB NK 78.5+/- 6.1%, n=6). Moreover, unmanipulated CB-NK cells demonstrated reduced surface expression of CD2, and high affintyLFA-1 detected by the specific antibody (MHM24). There was decreased recruitment of CD2 and LFA-1 to the NK cell immune synapse site as quantified by confocal microscope analysis (RRI CD2 CB NK 2.02 vs PB NK 4.98, n=3). Furthermore, defective LFA-1 trafficking lead to a decrease in downstream cytotoxic granules that traffic to the immunological synapse as demonstrated by decreased perforin trafficking to the CB-NK synapse site (> 60% reduction).We next wanted to confirm that CD2 or LFA-1 play a role in restoring the immune synapseformation for IL-2 expanded CB NK cells. We incubated expanded CB NK cells with blocking antibodies specific for LFA-1 or CD2 prior to conjugation to the K562 target cells. After CD2 or LFA-1 blocking there was decreased synapse formation, with a resultant decrease in cytotoxic function. When monoclonal antibodies against both CD2 and LFA-1 were used there was significant blockade of the formation of the immune synapse, and a marked reduction of CB NK cell cytolytic activity (Mean specific lysis of K562 targets at E:T ratio 20:1 was 81% IgG control vs 22% with anti-CD2; and 29% with anti-LFA-1, n=6, P<0.001). This data shows that CD2 and LFA-1 are defective in unmanipulated CB NK cells resulting in impaired immune synapse formation. In contrast, ex vivo IL-2 expansion of CB-NK cells enhanced lytic synapse formation with the synergistic repair of CD2 and LFA-1 localization and activity. We believe our results provide important mechanistic insights for the potential use of IL-2 expanded CB-derived NK cells for adoptive immune therapy in leukemia.

Disclosures
No relevant conflicts of interest to declare.