NK-Cell Alloreactivity Is Associated with Acute Gvhd and Decreased Relapse Incidence after T-Replete Haplo-Identical Allotransplant with High-Dose Post-Transplant Cyclophosphamide

Background: NK cells express activating (act) and inhibitory (inh) receptors, which recognize MHC class-I alleles, termed "Killer cell Immunoglobulin-like Receptors" (KIRs). Previous clinical data from haplo-identical T-cell-depleted allotransplant have demonstrated that donor vs recipient NK cell alloreactivity (or KIR/HLA incompatibility, KIR/HLA inc) plays a major role as effectors against acute myeloid leukemia (AML). Recently, T-replete haplo-transplant using high-dose post-transplant cyclophosphamide (PTCY) has been a revolution in the field as it is associated with good rate of engraftment and very low incidence of severe acute and chronic GVHD.

Methods: The main objective of this prospective study was to study the impact of NK alloreactivity after T-replete haplo-transplant using PTCY. The Baltimore conditioning regimen (Luznik, 2008) was used for lymphoid malignancies while fludarabine as part of this regimen was replaced by clofarabine (Clo-Baltimore) for patients with myeloid malignancies.

KIR/HLA inc were studied between donor and recipient considering various act and inh KIR receptors. We then studied the correlation between the presence of KIR/HLA inc and inh KIR/HLA inc and the occurrence of GVHD and relapse post-transplant. Finally, we compared reconstitution of various NK cell subsets (KIR2DL3, KIR2DL1, NKp46+2B4-, NKp46-2B4+, NKG2A+) between cases with or without acute GVHD, KIR/HLA inc, and between Baltimore vs Clo-Baltimore patients. For this purpose, peripheral blood samples were collected at days+10, +20, +30, +60 and +90/100 post-transplant. All patients gave informed consent.

Results: Between August 2014 and March 2017, 34 patients (males n=23, median age: 62.5 years) were included in the study. Twelve cases received a Baltimore regimen vs 22 a Clo-Baltimore regimen. All patients except one received peripheral blood stem cell as source of graft. 56% and 14.7% of patients developed grade 2-4 and 3-4 acute GVHD, respectively, at a median of 35 days post-transplant. In July 2017, 9 patients had relapsed and 10 are dead. No differences were observed in terms of acute GVHD incidence, relapse or deaths between Baltimore and Clo-Baltimore sub-groups.

KIR/HLA inc was documented in 17 cases of whom 13 presented with acute grade 2-4 while it was only 6/17 cases among patients with no KIR/HLA inc (p=0.001). The same was observed when considering only inhKIR/HLA inc (n=11/13 vs n=8/21, p=0.006). Conversely, relapse was less frequent in patients with KIR/HLA inc (n=2/17 vs n=7/17, p=0.05). However, incidence of relapse was similar between patients developing GvHD (n 5/19) vs no (n=4/15), suggesting that decreased incidence of relapse was not due to GVHD but was related to KIR/HLA inc.

The proportions of NK cells at each kinetic point considered after transplant were similar regardless of GVHD, KIR/HLA inc, or conditioning. Phenotypic analyses of NK cell subsets showed that patients developing GVHD had higher mature/activated NKp46+2B4- and NKG2A+NK cells at day +20 post-transplant. The proportion of KIR2DL3+ NK cells was also significantly higher in absence of KIR/HLA inc at day+30, in contrast to KIR2DL1+ NK cells that were similar between each sub-groups at any time considered.

Conclusion: KIR/HLA inc are associated with acute GVHD and decreased relapse incidence after T-repleted haplo-identical allotransplantation using PTCY. NKp46+2B4- and NKG2A+NK cells were significantly higher in cases developing GVHD at day+20, suggesting a role of these activated NK cells in the occurrence of GVHD. Also, KIR/HLA inc impact the phenotypic NK cell reconstitution and may favor NK cell expansion with better leukemic effect. These results may be of crucial importance regarding the selection of haplo-donor.