ILT-2 and ILT-4 expression and donor genotype as factors associated with HSCT outcome.

Background: NK cell activity after allogeneic haematopoietic stem cell transplantation (HSCT) is still not fully understood. Their cytotoxic activity is modulated by a range of inhibitory and activating surface receptors. Among these, the inhibitory receptors ILT-2 and ILT-4 have yet to be explored in relation to HSCT and its outcomes.

Methods: Genotyping for ILT-2 and ILT-4 was performed using TaqMan assays. ILT-2 and ILT-4 surface expression on NK cells was assessed by flow cytometry. Levels of sHLA-F and sHLA-G were determined using ELISA. mRNA expression of ILT-2, ILT-4 and IFN-γ was measured with quantitative real-time PCR with TaqMan Gene Expression probes.

Results: Presence of donor ILT-2 rs1061681 T allele was associated with increased risk of chronic graft-versus-host disease (cGVHD) (p = 0.0239). Donor ILT-4 rs1128646 T allele was related with decreased risk of overall survival after HSCT (p = 0.0506) and with higher risk of acute GvHD (aGvHD) (p = 0.0834). Serum levels of sHLA-F and sHLA-G were significantly higher at day +30 than day +90 after HSCT (p = 0.0002 and p < 0.0001, respectively). Expression of ILT2 at mRNA level was significantly decreased among recipients with aGvHD (p = 0.0266). ILT-4 expression correlated negatively with expression of interferon gamma (p = 0.0280, R = -0.532). The percentages of LILRB1/ILT-2+ and LILRB2/ILT4+ NK cells were the highest at day +21 after HSCT (p = 0.0014 and p < 0.0001 for ILT-2 and ILT-4, respectively).

Conclusions: Both ILT-2 and ILT-4 inhibitory receptors were found to be associated with allogeneic HSCT outcome. This suggests that ILT receptor expression on NK cells may potentially play a role in post-transplant complications.