Autoantibody Production during Chronic Graft-Versus-Host Disease Does Not Associate with Long-Term Persistence of Host B Cells in Humans

Background. Chronic graft-versus-host disease (cGvHD) is a common complication of allogeneic hemopoietic cell transplantation (allo-HCT). The pathogenesis of cGvHD is poorly understood. In cGvHD, the homeostasis of B lymphocytes is perturbed, as demonstrated by the production of autoantibodies. B-cell depletion with monoclonal antibodies (mAb) interferes with autoantibody production and ameliorates signs and symptoms of cGvHD. In mouse models, cGvHD and autoantibodies associate with the long-term persistence of host B cells after allo-HCT (Sylvain Perruche et al., Transplantation 2006). It has been postulated that host B cells may present alloantigens to donor T cells and, in turn, receive help for autoantibody production. This could be crucial to the pathogenesis of cGvHD. Aim. To investigate whether the long-term persistence of host B lymphocytes is associated with cGvHD and autoantibodies in humans.

Patients and methods. We recruited 13 consecutive patients with active cGvHD (4 mild, 5 moderate, 4 severe according to NIH classification) with a median time of onset of 6 months (range 3–36) from HLA-identical sibling (9 patients) and HLA-matched unrelated (4) allo-HCT. As controls, we chose 10 patients that underwent HLAidentical sibling (2), HLA-matched unrelated (5) or haploidentical (3) allo-HCT and never experienced cGvHD. In the two groups, we studied:

• circulating autoantibodies, including anti-nuclear (ANA), anti-DNA, anti-extractable nuclear antigen, anti-beta2 glycoprotein, anti-neutrophil cytoplasm, anti-thyroid, anti-mytocondria antibodies, rheumatoid factor,

• absolute numbers of T (CD3+, CD4+, CD8+), conventional B (CD19+), B1 (CD5+/CD19+) and NK cells (CD16+/CD56+) in the graft and in the peripheral blood,

• microchimerism by short-tandem repeats (STR) on B, T and myeloid cells purified by immunomagnetic cell sorting (sensitivity 0,01%).

Results. Patients with cGvHD had high-titer circulating ANA (>1:160) more frequently than controls (54% versus 10%, P<0,05). All other autoantibodies were negative. Peripheral T-cell counts were lower in patients with cGvHD than in controls (for CD8+ cells P<0,05). This was not due to a difference in the absolute numbers of T lymphocytes within the graft between the two groups. Peripheral counts of conventional B and B1 cells in patients with cGvHD were similar to controls. Autoantibodies and cGvHD were not associated with the persistence of host B lymphocytes, since the analysis of STR on purified B cells revealed that they were all of donor origin. T and myeloid cells were also of donor origin. Of interest, in univariate analysis, in vivo B-cell depletion with mAb for the prophylaxis against Epstein-Barr virus-related lymphoproliferative disease showed a trend towards a lower risk of cGvHD (P=0,06).

Conclusions. This study indicates that autoantibody production during cGvHD does not associate with long-term persistence of host B cells in humans. Moreover, it suggests that the early depletion of donor B lymphocytes in vivo may be effective for GvHD prophylaxis