Impact of NK Cell Reconstitution and Recipient HLA-C Typing on Clinical Outcome after Reduced Intensity Cord Blood Transplant: Results of a Prospective Phase II Multicentric Trial on Behalf of Societe Francaise De Greffe De Moelle Osseuse Et Therapie Cellulaire (SFGM-TC) and Eurocord

Background:

Unrelated cord blood transplantation (UCBT) after reduced intensity conditioning regimen (RIC) has extended the use of UCB in elderly and unfit patients without an HLA identical donor. KIR ligand incompatibility between donor and recipient might favor Natural Killer (NK) cell alloreactivity after UCBT in AML patients (Wilhemze et al, 2009), although contradictory results were reported (Brunstein et al, 2009). We previously reported the results of the biological NK cell reconstitution after RIC-UCBT in a French prospective phase II multicentric trial (Rio et al, 2015). We showed that NK cells generated from RIC-UCBT exhibited features of transient immaturity and stable activation, correlating with a high ability to produce IFN-γ and a quick restoration of the ability both to produce TNF-α and degranulate (Souchet et al, ASH 2013). The aim of the present study is to analyze the impact of KIR ligand incompatibilities and NK cell reconstitution on OS, DFS and TRM after RIC-UCBT in a prospective trial.

Materials and methods:

Seventy-six patients with a de novo or secondary AML in complete remission were enrolled in 23 centers from Oct. 2007 to Sept. 2009. Peripheral blood samples were collected during the first year following UCBT in order to realize an extensive prospective phenotypic and functional study of NK cells. DNA samples were also collected in recipient and cords blood to perform KIROTYPE and HLA-C allelic typing. NK biological data were available at M1 for 54 patients. The inhibitory Killer-Immunoglobin Receptors (KIR) KIR2DL1, and KIR2DL2/3 bind KIR ligand C2 and C1 respectively, resulting in inhibition of NK-cell mediated lysis. Recipients and UCB were classified into C1 or C2 family depending on their HLA-C typing (C1-C1, C1-C2 or C2-C2).

Results:

Among the 54 patients, 35 events occurred (relapse or TRM). Median EFS and OS were 13.2 and 18.3 months, respectively. Recipients C2-C2 had a significant worse EFS and OS than C1-C1 or C1-C2 (median EFS C2-C2=3.8 month vs 15.1 month for C1-x; p=0.002); median OS C2-C2 3.8 months vs 29.9 months for C1-x; HR=6.12, IC95% [2.069; 18.113], p=0.001). High intracellular staining of CD107a, reflecting the capacity of NK degranulation with HLA negative K562 target, correlated with better OS. CD107a expression was divided in 2 groups at median (=51%). Median OS of CD107 (0-50%) was 12.8 months vs 20.9 months for CD107a (51-66); p=0.029. Relapse risk was highly increased in recipients C2-C2 (HR=5.04 (IC 95% [1.23; 20.56], p=0.02). Low expression of CD16 (HR=0.97, IC95% [0.937; 0.999], p=0.043), high expression of HLA-DR (HR=1.08, IC95% [1.031; 1.123], p=8e-04) on NK cells, and recipients C2-C2 (HR=9.44, IC95% [1.311; 67.882], p=0.026) significantly increased the risk of TRM. The inhibitory KIR2DL1 receptor binds to C2 ligands. Of interest, KIR2DL1 was significantly decreased on C2-C2 recipients NK cells at M1, as compared to C1-x recipients NK cells. On the contrary, KIR2DL2/3 and KIR3DL1 restored promptly, suggesting a sequential expression of KIRs. As interaction between inhibitory KIRs and their ligands are essential for NK cells to become functional ("licensing" process), we can hypothesize that the weaker expression of KIR2DL1 on C2-C2 NK cells alters the licensing process, rendering the NK cells hypo-responsiveness.

Conclusion:

Recipient C2-C2 is correlated with a worse outcome (EFS, OS, relapse, TRM) after RIC-UCBT in a prospective trial for AML patients. Weak capacity of degranulation and low expression of CD16 are associated with worse OS and increased TRM, respectively. These features can reflect an alteration of the NK licensing process and might have impact on clinical outcome after UCBT.