Lymphocyte Subsets In Chronic Gvhd – a Key Role for B Cells?

Chronic graft-versus host disease (cGVHD) features certain similarities with autoimmune diseases. The pathogenesis of cGVHD after allogeneic hematopoietic stem cell transplantation (alloHSCT), however, is poorly understood.

Peripheral blood samples from 52 pts with active (median day 976, range 177–2773) (group 1), 28 pts with resolved (median day 1207, range 147–2849) (group 2) and 18 pts without cGVHD (median day 1015, range 124–2655) (group 3) were analysed for T and B cell subsets by FACS. 47 pts were transplanted from matched related donors, 40 pts from matched and 11 from mismatched unrelated donors. In addition, blood samples from 20 patients with and 10 patients without history of cGVHD were tested for: antinuclear antibody (ANA), anti-neutrophil cytoplasmatic antibody (ANCA), antimitochondrial antibody (AMA), anti-smooth-muscle antibody (ASMA) and double stranded DNA (dsDNA). Chronic GVHD was evaluated using criteria and guidelines of the National Institute of Health (mild n=16, moderate=18, severe n=18).

The absolute CD19⁺ B cell counts (median in 10⁹/l) in pts with active chronic GVHD (0.03; range 0–2.59) were subnormal and lower than in pts of group 2 (0.140; range 0.001–0.856; p 0.019) and group 3 (0.175; range 0.20–0.553; p 0.002). Significant differences in absolute numbers of the CD27⁻ B cell compartment, including immature (CD19⁺ CD27⁻ CD38⁺⁺CD20⁺IgM⁺) and transitional B cells (CD19⁺ CD27⁻ CD38⁺⁺CD10⁺CD20⁺IgM⁺), (median in 10⁹/l: group1: 0.015; range 0–0.499 vs. group 2: 0.090; range 0–0.667 or vs. group 3: 0.158; range 0.02–0.52; both p<0.001) as well as class switched memory B cells (median in 10⁶/l: 0.045; range 0–96.00 vs. 3.40; range 0–69.35; p 0.032 or vs. 7.40; range 0–56.83; p 0.003) were observed between the groups. Of interest, the CD 27⁺IgD⁺IgM⁺ B cell subpopulation (median in 10⁶/l) is lacking in pts with active cGVHD (0; range 0–1.35) in contrast to patients with resolved (0.43, range 0–17.47; p<0.001) or pts who never experienced cGVHD (1.69; range 0–10.00; p<0.001).

The counts of CD8⁺ T cells (median in 10⁹/l) were significantly lower in pts of group 1 (0.257, range 0.01–1.76) compared to pts of group 2 (0.373; range 0 –1.96; p 0.010) or group 3 (0.545; range 0.06–1.61; p 0.027). No significant differences in CD4⁺ T cell counts (median in 10⁹/l: 0.274 vs. 0.355 vs. 0.293) including naïve and memory CD4⁺ T cells as well as regulatory CD25⁺CD4⁺ FoxP3⁺ T cell counts (median in 10⁶/l: 8.11 vs. 6.55 vs. 9.72) were observed between the three groups.

In patients with cGVHD ANA was positive in 35% (7/20), ASMA in 20% (4/20) and AMA in 5% (1/20). ANA was positive in 36% (4/11) and ASMA in 27% (3/11) of patients without cGVHD. AMA and dsDNA were negative in all patients without cGVHD and ANCA was negative in all tested patients. 10% (3/31) of patients showed more than one autoantibody.

Our data confirm a close association of diminished B cell counts with cGVHD while no difference of the tested autoantibodies was observed between pts with and without cGVHD. The lack of CD 27⁺IgD⁺IgM⁺ B cells in pts with cGVHD indicates functional asplenia in these pts, because IgM⁺ memory B cells are dependent upon a functional spleen for their generation and/or survival. Analysis of B cell subsets can provide a diagnostic tool for monitoring cGVHD activity but requires prospective evaluation.

No relevant conflicts of interest to declare.