Christopher E. Walsh

Engraftment of Hematopoietic Progenitor Cells Transduced with the Fanconi Anemia Group C Gene (FANCC)

Fanconi anemia (FA) is an autosomal recessive disorder that leads to aplastic anemia. Mutations in the FANCC gene account for 10-15% of cases. FA cells are abnormally sensitive to DNA-damaging agents such as mitomycin C (MMC). Transfection of normal FANCC into mutant cells corrects this hypersensitivity and improves their viability in vitro. Four FA patients, representing the three major FANCC mutation subgroups, were entered into a clinical trial of gene transduction aimed at correction of the hematopoietic defect. Three patients received three or four cycles of gene transfer, each consisting of one or two infusions of autologous hematopoietic progenitor cells that had been transduced ex vivo with a retroviral vector carrying the normal FANCC gene. Prior to infusion, the FANCC transgene was demonstrated in transduced CD34-enriched progenitor cells. After infusion, FANCC was also present transiently in peripheral blood (PB) and bone marrow (BM) cells. Function of the normal FANCC transgene was suggested by a marked increase in hematopoietic colonies measured by in vitro cultures, including colonies grown in the presence of MMC, after successive gene therapy cycles in all patients. Transient improvement in BM cellularity coincided with this expansion of hematopoietic progenitors. A fourth patient, who received a single infusion of transduced CD34-enriched BM cells, was given radiation therapy for a concurrent gynecologic malignancy. The FANCC transgene was detected in her PB and BM cells only after recovery from radiation-induced aplasia, suggesting that FANCC gene transduction confers a selective engraftment advantage. These experiments highlight both the potential and difficulties in applying gene therapy to FA.

Gene Therapy for Human Hemoglobinopathies

Summary Gene transfer of human globin genes into human pluripotent stem cells via viral vectors may soon be realized. The high level of globin gene expression believed to be required for the treatment of severe hemoglobinopathies necessitated the inclusion of cisacting sequences (LCR). Retroviral vectors containing the LCR elements are prone to rearrangement, low titer, and poor expression. Inclusion of a “minilocus” containing four HS sites linked to a globin gene resulted in higher expression in transplanted mice, but rearrangement of the provirus still occurs, and it is unclear what significance these experiments have with regard to human marrow stem cell transduction. Recombinant AAV is among the newest of genetic transfer vectors. This once obscure virus possesses unique properties that distinguish it from all other vectors. Its major advantage is the lack of pathogenicity in humans. Wild-type AAV has the unusual ability to selectively integrate into the mammalian genome at a specific region, thus reducing the concern for genomic disruption and insertional mutagenesis. The ability of AAV to carry regulatory elements without interference from the viral template may enable greater control of transferred gene expression. Disadvantages currently include the inferior packaging systems which yield low numbers of recombinant virions which are contaminated with wild-type adenovirus. The small AAV genome that can be packaged (~5 kb) rules out its use for transfer of larger genes. Recombinant AAV viruses do not appear to demonstrate the same site-specific genomic integration as wild-type viruses. Elucidation of the mechanism of site-specific integration should prove useful in the development of safe vectors for gene transfer as well as provide insight into the nature of DNA recombination in humans.

A trial of recombinant human interleukin‐1 in patients with severe refractory aplastic anaemia

Summary. We report here the effects of in vivo administration of recombinant interleukin‐1 alpha (rIL‐1α) to patients with severe, idiopathic aplastic anaemia. Four patients who were refractory to immunosuppressive therapy and were not bone marrow transplantation candidates received daily doses of 0.03 μg/kg and 0.10 μg/kg intravenously as 5 d courses. No significant changes in either peripheral blood counts or bone marrow cellularity were observed at either dose during or following therapy. Two patients showed increased numbers of bone marrow progenitor colonies. Lymphocyte pheno typing demonstrated an elevated percentage of CD8 +/DR+ activated suppressor T lymphocytes prior to therapy. After rIL‐1α administration, the percentage of CD8 +/DR+ cells was reduced or returned to normal in all patients. Significant side‐effects included fever, rigours, fatigue, headache and nausea. Transient hypotension was observed at both doses in all patients. These results suggest that while rIL‐1α can be safely administered, no significant haematologic improvement was observed in patients with severe aplastic anaemia.