Immunogenetic Factors Determining Evolution of T-Cell Large Granular Lymphocyte Leukemia and Associated Cytopenias.

Abstract

T cell large granular lymphocyte leukemia (T-LGL) is a chronic clonal lymphoproliferation of cytotoxic T cells (CTL). T-LGL presents with cytopenias, implying a relationship to other immune-mediated bone marrow failure states. T-LGL is often accompanied by autoimmune diseases, suggesting a clonal transformation in the context of an initially polyclonal autoimmune response. Immunogenetic predisposition factors have been described for both immune-mediated bone marrow failure as well as other autoimmune conditions and it is possible that some of these factors can promote evolution of T-LGL and/or the development of cytopenias. Here, we analyzed the association of T-LGL (and clinical variants) with a number of immunogenetic factors, including HLA and KIR genotype, KIR-L/KIR mismatch, CTLA4 (−658T/C, −318C/T, +49A/G) and cytokine single nucleotide polymorphisms (SNP) including: TNF-a (−308G/A), TGF-b 1 (codons 10 C/T, 25 G/C), IL-10 (−1082 G/A, −819 T/C, −592 C/A), IL-6 (−174 C/G), and IFN-g (+874 T/A). We studied a large cohort of patients with T-LGL (N=79) systematically followed at our institution. Using molecular analysis of TCR utilization as previously described (Wlodarski et al, Blood 2005) we have determined the relative and absolute size of the clonal LGL population for each case. We performed HLA typing as certain alleles serve as KIR ligands and can determine quality of immune response. HLA-B37 and Cw-7 were over expressed in LGL patients (13 vs 2%, p<.001; 60 vs 45%, p=.039); no other alleles correlated with the disease. No HLA association was found in patients presenting with neutropenia or splenomegaly, however HLA-Cw7 was found in 100% of patients with an increased number of clonal CTL (>1900/uL; N=13 vs 45% in controls and 33% in patients with low LGL count; p<.001). HLA-Cw alleles can be divided into C1 and C2 groups based on recognition by KIR; in the above 13 patients, C1/C1 phenotype was significantly increased compared to normal controls while C2/C2 was absent (p<.001, p=.04, respectively). This finding suggests a protective function for the C2/C2 phenotype in T-LGL patients. Subsequently, we analyzed KIR genotype by SSP PCR; no association between a specific KIR genotype and disease was found. LGL patients did not vary from controls in the ratio of inhibitory to stimulatory KIR. As KIR genotype may exert pathogenic influence in the context of KIR/KIR-L interactions, we hypothesized that a KIR/KIR-L mismatch would result in less regulation of CTL response and thus more severe cytopenias. According to the subdivision of HLA-Cw alleles into group C1 (ligands KIR2DL2 and 2DL3) and C2 (ligands 2DL1), genetic mismatch between KIR-L and KIR was found in 50% of patients, but proved statistically insignificant compared to normal controls. The severity of cytopenias and other hematologic manifestations was greater in patients without KIR-L/KIR mismatch. This finding may be due to an overshooting CTL response resulting from silencing NK-cells. SNP in cytokines and their promoters may play a pathogenic role in autoimmune conditions, as such we also analyzed the frequency of multiple cytokine polymorphisms in T-LGL to determine a potential secretion/stimulation phenotype. Among cytokine SNP studied in T-LGL, overrepresentation of TNF-a -308G/A polymorphism (for A/A: 14 vs 1% in controls, p=.009), and CTLA4 +49 SNP A/A genotype was found (50 vs 27%, p=.013), suggesting that the presence of G allele is protective.