STUDIES OF PRIMARY IMMUNODEFICIENCY DISEASES

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Studies in our laboratory have focused on defining the nature of the B cell and T cell defects in Common Variable Immunodeficiency (CVI), a primary acquired human immunodeficiency state characterized by hypogammaglobulinemia and impaired functional antibody responses. Previous studies of purified B cells of patients with CVI show that although the cells have a normal capacity to proliferate, they manifest differentiation defects at multiple levels. Thus, as compared with normal B cells, circulating CVI B cells contain reduced numbers of sIgG+ and sIgA+ cells with a commensurate increase in sIgM+ B cells, suggesting an in vivo defect in isotype switch. In addition, they fail to undergo differentiation into immunoglobulin-producing cells. We now have shown that these defects are associated with the ability of CVI B cells to upregulate and sustain high level surface expression of a critical T cell ligand, B7-2. We have found that CVI B cells, under a variety of stimulatory conditions manifest premature upregulation of B7-1, a surface molecule now thought to inhibit B cell-T cell interaction. These abnormalities of cell surface B7 expression area a likely explanation of the fact that CVI B cells are relativiely poor antigen presenting cells (APC). Thus, purified CVI B cells are less efficient APC when compared to normal B cell of PHA-stimulated T cells using IL-2 as a read-out of T cell stimulation. Moreover, this deficiency is corrected by the addition of anti-CD28 antibody, i.e., an antibody that replicates the function of B7. Overall, these data provide evidence that B cell function in CVI is abnormal in a way that is quite separate from the known immunoglobulin production deficit. A second area of focus in immunodeficiency concerns X-linked agammaglobulinemia (XLA), another major humoral immunodeficiency syndrome. In this disease, B cell development is arrested at the pre-B cell stage and there is an absence of mature B cells. This abnormality results from mutation in a gene, the btk gene whose product is a key tyrosine kinase in B cell activation. In the present study we have prepared a retroviral vector containing a btk cassette and have used this vector to transfer btk into NIH 3T3 fibroblasts. If this vector is producing btk protein, as determined by tyrosine kinase activity, we will be in a position to transfect patient CD34+ cells with the retroviral vector.