Myeloablative autologous haematopoietic stem cell transplantation resets the B cell repertoire to a more naïve state in patients with systemic sclerosis

Abstract

Objectives: Myeloablative autologous haematopoietic stem cell transplant (HSCT) was recently demonstrated to provide significant benefit over cyclophosphamide (CYC) in the treatment of diffuse cutaneous systemic sclerosis (dcSSc) in the Scleroderma: Cyclophosphamide or Transplantation (SCOT) trial. As dysregulation of the B cell compartment has previously been described in dcSSc, we sought to gain insight into the effects of myeloablative autologous HSCT as compared with CYC.

Methods: We sequenced the peripheral blood immunoglobulin heavy chain (IGH) repertoires in patients with dcSSc enrolled in the SCOT trial.

Results: Myeloablative autologous HSCT was associated with a sustained increase in IgM isotype antibodies bearing a low mutation rate. Clonal expression was reduced in IGH repertoires following myeloablative autologous HSCT. Additionally, we identified a underusage of immunoglobulin heavy chain V gene 5-51 in patients with dcSSc, and usage normalised following myeloablative autologous HSCT but not CYC treatment.

Conclusions: Together, these findings suggest that myeloablative autologous HSCT resets the IGH repertoire to a more naïve state characterised by IgM-expressing B cells, providing a possible mechanism for the elimination of pathogenic B cells that may contribute to the benefit of HSCT over CYC in the treatment of dcSSc.

Keywords: B-Lymphocytes; Immune System Diseases; Systemic Sclerosis.

Figure 1

IgM-encoded decreases in somatic hypermutation levels following HSCT. (A, B) Per cent of repertoire comprised of IgM in individuals with dcSSc at baseline (M0) and 26, 38 and 48 months following either HSCT (A) or CYC treatment (B). (C, D) Quantification of mean somatic hypermutation rates in individuals with dcSSc at baseline and at 26, 38 and 48 months following either HSCT (C) or CYC treatment (D). (E) Quantification of mean somatic hypermutation rates for the fraction of each repertoire comprised of IgM in healthy individuals at baseline and in individuals with dcSSc at baseline and at 26, 38 and 48 months following either HSCT or CYC treatment. Data represent mean±SD, by paired t-test. CYC, cyclophosphamide; dcSSc, diffuse cutaneous systemic sclerosis; HSCT, haematopoietic stem cell transplant.

Figure 2

IGH repertoires exhibit decreases in clonality following HSCT. (A, B) Quantification of the per cent clonal expressions for repertoires from individuals with dcSSc at baseline (M0) and 26, 38 and 48 months following treatment with either HSCT (A) or CYC (B). (C) and (D) Changes in clonal expressions were assessed by normalising repertoire clonality at 26, 38 or 48 months following either HSCT (C) or CYC treatment (D) to clonality at baseline in five dcSSc individuals for which baseline and at least one additional consecutive timepoint sample was available. Lines connect data points from the same individual. (E) and (F) Clonal expression sizes were calculated as percentages of total repertoire size. Represented as quantification of mean clonal expression size in the repertoires of individuals with dcSSc at baseline (M0) and 26, 38 and 48 months following either HSCT (E) or CYC treatment (F). (A), (B), (E) and (F) Data represent mean±SD, by paired t-test. CYC, cyclophosphamide; dcSSc, diffuse cutaneous systemic sclerosis; HSCT, haematopoietic stem cell transplant; IGH, immunoglobulin heavy chain.

Figure 3

Differences in IGHV gene usage in patients with dcSSc. (A) Heatmap depicting the z-scores of the fraction of usage within each repertoire for the seven genes identified to have significant differences in usage between healthy individuals and individuals with dcSSc at baseline through SAM (q<0.1). (B) Quantification of the per cent of each repertoire using IGHV5-51 in healthy individuals at baseline and in individuals with dcSSc at baseline (M0) and 26, 38 and 48 months following either HSCT or CYC treatment. Data represent mean±SD, by paired t-test. CYC, cyclophosphamide; dcSSc, diffuse cutaneous systemic sclerosis; HSCT, haematopoietic stem cell transplant; IGHV, immunoglobulin heavy chain V gene; SAM, significance analysis of microarrays.