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

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.

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.

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).

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.