Association of the autoimmune disease scleroderma with an immunologic response to cancer

Abstract

Autoimmune diseases are thought to be initiated by exposures to foreign antigens that cross-react with endogenous molecules. Scleroderma is an autoimmune connective tissue disease in which patients make antibodies to a limited group of autoantigens, including RPC1, encoded by the POLR3A gene. As patients with scleroderma and antibodies against RPC1 are at increased risk for cancer, we hypothesized that the "foreign" antigens in this autoimmune disease are encoded by somatically mutated genes in the patients' incipient cancers. Studying cancers from scleroderma patients, we found genetic alterations of the POLR3A locus in six of eight patients with antibodies to RPC1 but not in eight patients without antibodies to RPC1. Analyses of peripheral blood lymphocytes and serum suggested that POLR3A mutations triggered cellular immunity and cross-reactive humoral immune responses. These results offer insight into the pathogenesis of scleroderma and provide support for the idea that acquired immunity helps to control naturally occurring cancers.

Fig. 1. Mutant and WT peptide-specific CD4⁺ T cells in patients SCL-4 and SCL-42

CD154 expression on CD4⁺ T cells was assayed after stimulation (18 hours) with patient-specific WT or mutant RPC1 peptides, PAD4 peptide (negative control), or a pool of peptides from infectious agent antigens (CEFT, positive control). Healthy donors matched for one HLA-DR allele were used as controls. Experiments on SCL-4 (A) and SCL-42 (B) were repeated on separate blood draws, three and two times, respectively, with similar results. Gate frequencies are expressed as percentage of CD4⁺ T cells. (C) Frequency of peptide-reactive CD4 T cells expressed as fold change over CD154⁺ CD4 T cells in the unstimulated negative control.

Fig. 2. Vβ-family usage and CDR3 length in patient SCL-42 PBMCs stimulated with WT or mutant peptides

SCL-42 PBMCs were stimulated for 6 days with patient-specific mutant (gray bars) and corresponding WT (black bars) RPC1 peptides. No appreciable differences in TCR diversity were observed in Vβ8 (A), Vβ17 (B), and Vβ20 (C) TCR families. Skewing of the CDR3 length distribution in Vβ7 (D), Vβ12 (E), and Vβ24 (F) TCR families was observed, and CDR3 lengths that differed by >15% between WT and mutant stimulated PBMCs are indicated (*). CDR3 length is expressed in amino acids (a.a).