Increases in IgA levels were associated with a reduced risk of infections in 84 chronic lymphocytic leukemia (CLL) patients participating in a trial of ibrutinib 420 mg once daily.
After 28 months of ibrutinib treatment, 69 (82%) patients had developed 177 infections. Lower rates of infections were found in those who experienced an IgA increase of at least 50% from their baseline values (P = .03), reported Dr. Clare Sun of the hematology branch of the National Heart, Lung and Blood Institute in Bethesda, Md., and her associates.
At baseline, the patients’ median IgA value was 0.47 g/L; after 6 months of treatment with ibrutinib, the median IgA value was 0.74 g/L. The levels of IgA continued to rise in the next 12 months (n = 43, median increase of 45%, P less than 0001), and patients’ IgA levels at 24 months also were greater than their baseline levels (n = 28, median increase of 64%, P less than .0001).
Using serum-free light chain measures to distinguish clonal and normal B cells, researchers also found recovery of normal B cells and increases in B-cell precursors in bone marrow and in normal B cells in the peripheral blood. This growth, however, was not large enough to raise the majority of patients’ normal B cells to normal levels.
The findings suggest “ibrutinib allows for a clinically meaningful recovery of humoral immune function in patients with CLL,” Dr. Sun and her associates wrote. “The rapidity of increase in IgA suggests that pre-existing antibody-producing cells may be secreting more immunoglobulins, whilst CLL cells, which impair immunoglobulin production, are removed by ibrutinib.”
The patients also had a decline in IgG levels, however, which did not appear to have an adverse impact. The patients’ IgG levels remained stable during the first 6 months of treatment, but by 12 months they had decreased (n = 35, median reduction of 4%, P < .0006), falling further at 24 months (n = 21, median reduction of 23%, P < .0001).
Because ibrutinib may be given indefinitely, extended follow-up is needed to determine the immunologic consequences of prolonged Bruton’s tyrosine kinase inhibition, the researchers wrote.
Read the full study in Blood (2015. doi: 10.1182/blood-2015-04-639203).