Immunomodulatory Role of HLA-G in Hematopoietic Stem Cell Transplantation Outcome

Abstract

Introduction: HLA-G, the non-classical HLA class I molecule, is encoded by the human MHC complex at chromosome 6. Limited polymorphism, restricted expression and presence as isoforms are unique features of this immunomodulatory molecule that interacts with receptors ILT-2/ILT-4/KIR2DL4 on immune cells and creates a tolerogenic microenvironment. HLA-G expression and function is influenced by the polymorphism in 3’UTR region where different miRNA interact and impact mRNA stability. Objectives: The present study aimed to evaluate the clinical relevance of HLA-G in Hematopoietic Stem Cell Transplantation (HSCT). Material and Methods: We enrolled 50 North Indian patients (diagnosed with acute leukemia or aplastic anemia) who underwent HSCT and 202 healthy controls belonging to same ethnicity. We investigated HLA-G 3’UTR exon8 polymorphism, 14 bp insertion/deletion (ins/del) and SNPs. Exon8-14 bp ins/del was detected using sequence specific primers and SNPs were identified by sequencing. The soluble HLA-G levels and Treg cell frequency were estimated at pre and post transplant days 15,30,60,90,GvHD. Results: In this cohort, although the 14 bp ins/del genotype was predominant among controls, the sHLA-G levels were highest in those carrying14bp ins/ins genotype. Based on SNP linkage, 8 UTR haplotypes were identified. The sHLA-G levels were higher in individuals with 14 bp-INS linked haplotypes UTR2 and UTR4, in comparison to those with UTR 1, 6 and 7 (intermediate levels) and with 14 bp-DEL linked haplotypes UTR3 and UTR5 (low level). 40% of HSCT recipients experienced graft versus host disease (GvHD). Recipients with 14 bp ins/ins genotype had lower incidence of GvHD compared to those with del/del or ins/del genotype. Higher percentage of recipients carrying HLA-G 3’UTR SNPs +3027 CC vs CA/AA, +3035 CC vs TT/TC experienced GvHD. Majority of recipients carrying UTR1 and UTR3 developed GvHD. Further, sHLA-G levels were significantly lower at the time of GvHD, compared to the pre and post-transplant time points. The Treg cell frequency also correlated with sHLA-G levels. Discussion: GvHD is the major cause of morbidity and mortality post HSCT. Investigating HLA-G 3’UTR polymorphism, sHLA-G levels and Treg cell frequency may be beneficial for transplant monitoring. HLA-G molecule could be proposed as possible biomarker for predicting GvHD and HSCT outcome. All India Institute of Medical Sciences, New Delhi. Indian Council of Medical Research, India.