Monoclonal IgA gammopathy due to maternal B cells in an infant with severe combined immunodeficiency (SCID) prior to hematopoietic stem cell transplantation.

Monoclonal gammopathies result in hypergammaglobulinemia due to uncontrolled immunoglobulin production by a B-cell clonal population. They have been reported in patients with severe combined immune deficiency (SCID) after hematopoietic cell transplant, and also in normal children and in adults over 50 years of age. Generally they are benign, but malignant transformation does occur. The authors report an unusual case of a monoclonal IgA gammopathy occurring in an infant with SCID, prior to transplantation, due to engraftment of maternal B cells. Transplacental passage of maternal cells may occur more frequently than previously estimated. Persistence of activated B cells occurred even after treatment with rituximab and could pose a risk for the development of malignancies such as multiple myeloma.