Correction of the molecular defect in B lymphocytes from X-linked agammaglobulinemia by cell fusion

Transcription of germline VH gene elements by normal human fetal liver

Transcription of the gene elements that form the variable region of immunoglobulin heavy chains has been proposed to represent the process that controls access for the recombination enzymes in their sequential steps of catalysis. Evidence for germline transcription of VH gene elements, as part of VH to DJH recombination, has been limited to transcripts of only a few gene elements. We have examined normal fetal liver mRNA by Northern blotting and present evidence for germline transcripts from six human VH gene families. The candidate VH4 transcripts have been confirmed as germline transcripts by hybridization with 3' flanking sequences that would have been removed by recombination from mature VHDJH genes. The candidate transcripts for VH1, VH3, VH4 and VH6 have been confirmed by polymerase chain reaction amplification with primers from the 3' flanking sequences of these gene families and determination of the sequence of these products. Determination of sequence from two clones of VH1, VH3 and VH4 indicates that more than one gene from each of these families is transcribed. PCR amplification of VH4 and VH6 with primers specific for the leader sequence (exon 1) and 3' flanking sequence indicate that these transcripts are spliced, representing RNA processing. Germline transcripts from these families are also present in normal human bone marrow. These results indicate that transcriptional activation of germline VH gene elements is a general phenomenon in tissues undergoing V to DJ recombination.

Expression from leukocyte integrin promoters in retroviral vectors

Human gene therapy for diseases involving leukocytes would be facilitated by the identification of specific promoter/enhancer sequences capable of directing high levels of tissue and stage-specific expression of the requisite cDNA when used in a retroviral vector. We tested the promoter sequences from the leukocyte integrin CD11a (LFA-1), CD11b (Mac-1), and CD18 subunits in retroviral vectors to express a reporter gene, adenosine deaminase, in the human leukocyte cell lines K562 and HL-60. The leukocyte integrins are expressed in leukocytes, and they are inducible in HL-60 cells, a model system for myeloid differentiation. Although the leukocyte integrin promoter/enhancer sequences direct the expression of reporter genes in myeloid lineage cell lines in transient transfection assays, in these studies, the leukocyte integrin promoters direct low levels of reporter gene expression following retroviral-mediated transduction in K562 and HL-60 cells and selection of stable integrants. Treatment of HL-60 cells transduced with retroviral vectors containing the leukocyte integrin promoters with retinoic acid or phorbol myristate acetate results in less than a two-fold increase in reporter gene expression. These studies indicate that: (i) expression from the leukocyte integrin promoters from stable integrants in retroviral vectors does not parallel the results observed in transient transfection assays, and (ii) additional promoter/enhancer sequences will likely be required for these promoters to direct high levels of tissue and stage-specific expression in retroviral vectors.

X-linked immunodeficiencies: clues to genes involved in T- and B-cell differentiation

There are five major human X-linked immunodeficiencies, each with a characteristic impairment of T-and/or B-cell differentiation. The molecular bases of these diseases remain unknown but, as Geneviève de Saint Basile and Alain Fischer report, major steps towards that goal have been taken: the location of the defective genes has been precisely defined and the cell lineages and stages of differentiation in which the genes are expressed have been partly identified.

Expression of immunoglobulin genes in common variable immunodeficiency

Five common variable immunodeficiency (CVI) patients were analyzed for expression of immunoglobulin (Ig) genes. In the pokeweed mitogen (PWM)-induced Ig-production assay, the combination of T and B cells showed that all patients' T cells had normal helper functions and all patients' B cells had profound defects. The defective B-cell maturation stages based on their Ig gene expression patterns were variable. One of five patients showed normal mu-chain gene expression and nearly normal IgM production, but neither IgG nor IgA production, which suggested that this patient's B-cell defects might lie on a mu- to gamma or mu- to alpha class-switch stage. B cells in another patient showed low mu-chain gene expression and low IgM production, but an Ig enhancer region, which is an important region for expression of Ig genes, was intact. Thus, this patient might have a transacting factor defect which interacts with the Ig enhancer region. The other three patients showed no mu-chain gene expression and no IgM production. Thus, their B-cell defects lay on the B-cell maturation stage, similar to X-linked agammaglobulinemia. These results showed that primary B-cell defects in CVI occurred at several B-cell differentiation stages, which could be recognized by expression of Ig genes.