Polymorphisms Of Human Leukocyte Antigen-G Gene and Clinical Outcome Of Patients With Chronic Lymphocytic Leukemia

The human leucocyte antigen-G (HLA-G) is a nonclassical class Ib molecule that suppresses various immune cell functions and may contribute to immune escape and cancer development. HLA-G polymorphisms, especially HLA-G-725(C/G/T) 5’URR and HLA-G 14bp del/ins 3’UTR, might influence the expression of HLA-G transcript and protein, and in consequence, affect the biological features of HLA-G. Therefore, we investigated whether these two polymorphisms, which seem to be functionally relevant, may play a role in susceptibility to chronic lymphocytic leukemia (CLL) and a clinical course of the disease. So far, no studies have reported any potentially impact of HLA-G polymorphisms on lymphoid neoplasms.

HLA-G725(C/G/T) 5’URR and HLA-G 14bp del/ins 3’UTR polymorphisms were genotyped in 167 previously untreated patients with CLL. The control group consisted of 98 randomly selected blood donors.

Strong linkage disequilibrium between HLA-G-725(C/G/T) and HLA-G 14 bp del/ins was observed (D’=1.0 and r²=0.2). Six distinct haplotypes, including G/del, C/del, T/del, G/ins, C/ins, T/ins were found in the CLL patients. Among the controls only five haplotypes were found due to the T/ins haplotype not being observed. The probability of the occurrence of G/ins and T/ins haplotypes was higher in the CLL than in the controls (p= 0.01).

The analysis of the prognostic significance of diplotypes, as well as the previously reported correlations between HLA-G genotypes and HLA-G expression in vitro and in vivo, allowed us to identify the HLA-G diplotype-based risk groups. The low-risk (LR) group comprised CC/del-del, CC/del-ins and CC/ins-ins diplotypes, and the high risk (HR) group included GG/del-del, GG/del-ins, GG/ins-ins, GC/del-del, GC/del-ins, GC/ins-ins, TT/del-del, TT/del-ins, TT/ins-ins and CT/del-ins diplotypes.

The patients carrying LR diplotypes presented a higher 3-year treatment-free survival (TFS) (56.7%, 95% CI 47-66) than those with HR diplotypes (38.6%, 95% CI 27-52; p= 0.005). Additionally in the group of mutated IGHV patients, subjects carrying LR diplotypes presented a higher probability of 3-year TFS than those with HR diplotypes (68.5% vs 43.2%; p= 0.04). In regard to overall survival (OS), the estimated 5-year OS rates were 95.6% (95% CI 89-98) and 74.2% (95% CI 57-86) in the LR and HR group respectively (p= 0.005). Moreover, among the unmutated IGHV patients, those carrying LR diplotypes had a better 5-year OS compared to the patients with HR diplotypes (87.1% vs 71%; p= 0.02). Multivariate analysis demonstrated the IGHV mutation status (p= 0.005) and HLA-G diplotype-based risk groups (p= 0.01) to be independent factors predicting OS.

The results suggest the potential role of HLA-G and its polymorphisms in CLL. The inherited ability of the host to increase expression of the HLA-G antigen might contribute to the escape of CLL cells of the immuno-surveillance of the host and in turn to disease progression and the worse outcome for patients with CLL.

No relevant conflicts of interest to declare.