Characterization of in Vivo Mutated T Cell Clones from Patients with Systemic Lupus Erythematosus

Abstract

Patients with systemic lupus erythematosus (SLE) have increased percentages of activated T cells and increased numbers of cells with mutations in their hypoxanthine-guanine phosphoribosyltransferase (hprt) gene, as judged by growth in the presence of 6-thioguanine. To study the relevance of these mutant T cells to disease pathogenesis, we have assessed the phenotype and functional capabilities of such cells from 21 patients with SLE who never had received cytotoxic drugs. The frequency of T cells with mutations in hprt in the blood of these patients ranged from normal to 25 times normal (mean ± SEM [21.1 ± 6.1] × 10 -6 versus [4.8 ± 0.8] × 10 -6, in 15 age-matched normal individuals, P < 0.001) and correlated significantly with disease duration. CD4 + and CD8 + phenotypes were comparable among mutated and nonmutated clones from both patients and normals. Although the frequency of CD3 +CD4 -CD8 - cells was low, it was increased among SLE-derived T cells (mutated and wild-type) compared with clones derived from normals (5% for SLE vs 1% for normals). A substantial percentage of all clones were able to help autologous B cells to produce anti-ssDNA, 11 of 68 (16%) selected clones and 3 of 28 (11%) nonselected clones. Help for autoantibody production was confined to CD4 + SLE-derived T cell clones. It could be blocked using an anti-HLA-DR mAb, suggesting that classical cognate help was operative. This represents the first estimate of the frequency of T cells able to drive autoantibody production in SLE.