Deficit of circulating CD19 + CD24 hi CD38 hi regulatory B cells in severe aplastic anaemia.

Immune aplastic anaemia (AA) is caused by cytotoxic T lymphocytes (CTLs) that destroy haematopoietic stem and progenitor cells. Enhanced type 1 T helper (Th1) responses and reduced regulatory T cells (Tregs) are involved in the immune pathophysiology. CD24 ^hi CD38 ^hi regulatory B cells (Bregs) suppress CTLs and Th1 responses, and induce Tregs via interleukin 10 (IL-10). We investigated circulating B-cell subpopulations, including CD24 ^hi CD38 ^hi Bregs, as well as total B cells, CD4 ⁺ T cells, CD8 ⁺ T cells and natural killer cells in 104 untreated patients with severe and very severe AA, aged ≥18 years. All patients were treated with standard immunosuppressive therapy (IST) plus eltrombopag. CD24 ^hi CD38 ^hi Bregs were markedly reduced in patients with AA compared to healthy individuals, especially in very severe AA, but residual Bregs remained functional, capable of producing IL-10; total B-cell counts and the other B-cell subpopulations were similar to those of healthy individuals. CD24 ^hi CD38 ^hi Bregs did not correlate with responses to IST, and they recovered to levels present in healthy individuals after therapy. Mature naïve B-cell counts were unexpectedly associated with IST response. Markedly reduced CD24 ^hi CD38 ^hi Bregs, especially in very severe AA, with recovery after IST suggest Breg deficits may contribute to the pathophysiology of immune AA.
(Published 2020. This article is a U.S. Government work and is in the public domain in the USA. British Journal of Haematology published by British Society of Haematology and John Wiley & Sons Ltd.)