Blnk deficiency is an autosomal recessive immune disorder characterized by the absence of B cells in periphery and the absence of any seric immunoglobulins due to an early blocage at the pro-B cell stage in the bone marrow. The very rare patients affected by blnk deficiency develop severe infections. In the murine model of the disease, a similar blocage in B cell development is described as well as susceptibility to infections and to pre-B lymphomas.
A homozygote stop mutation in blnk gene was identified in a 8-yr old boy. Bone marrow cells analysis revealed that CD34+CD10+CD24-CD19- lymphoid progenitors were present as well as CD34+CD10+CD24+CD19- early B cells and CD34+CD19+ pro B cells. However, no surface IgM or seric Ig were detected in this patient.
To demonstrate the implication of Blnk in the B-cell differentiation process, we transduced CD34+ sorted bone marrow cells from this patient with a lentiviral construct containing human wild type Blnk cDNA. The transduced cells were intravenously injected into irradiated NOD/SCID/IL2rg knock-out mice. Twelve weeks after transplantation, recipients were analysed. Human engraftment was detected in bone marrow and spleen. Among bone marrow human CD45+ cells, more than 80% were CD19+ and 6 to 8% express surface IgM. In the spleen, between 14 and 30% of CD19+ cells were detected. Eight to 42% of CD19+ cells expressed surface IgM.
This is the first demonstration that Blnk is absolutely required for the differentiation of pro-B cells toward mature B cells.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.