Publications

One of the most powerful techniques for studying the function of a gene is to disrupt the expression of that gene using genetic engineering strategies such as targeted recombination or viral integration of gene trap cassettes. The tremendous utility of these tools was recognized this year with the awarding of the Nobel Prize in Physiology or Medicine to Capecchi, Evans, and Smithies for their pioneering work in targeted recombination mutagenesis in mammals. Another noteworthy discovery made nearly a decade ago was the identification of a novel class of non-coding genes called microRNAs. MicroRNAs are among the largest known classes of regulatory elements with more than 1000 predicted to exist in the mouse genome. Over 50% of known microRNAs are located within introns of coding genes. Given that currently about half of the genes in mouse have been knocked out, we investigated the possibility that intronic microRNAs may have been coincidentally deleted or disrupted in some of these mouse models. We searched published murine knockout studies and gene trap embryonic stem cell line databases for cases where a microRNA was located within or near the manipulated genomic loci, finding almost 200 cases where microRNA expression may have been disrupted along with another gene. Our results draw attention to the need for careful planning in future knockout studies to minimize the unintentional disruption of microRNAs. These data also raise the possibility that many knockout studies may need to be reexamined to determine if loss of a microRNA contributes to the phenotypic consequences attributed to loss of a protein-encoding gene.

During development and repair of bone, two distinct yet complementary mechanisms, intramembranous and endochondral, mediate new bone formation via osteoblasts. Because mechanical bone marrow ablation leads to the rapid and transient formation of new bone in the marrow cavity, we postulated that parathyroid hormone (PTH), which is a bone anabolic hormone, enhances the formation of new bone that forms after marrow ablation. We subjected the left femur of rats to mechanical marrow ablation, or sham operation, and injected the animals daily with PTH or vehicle for 1, 2, or 3 weeks in a first experiment, then with PTH, parathyroid hormone-related peptide (PTHrP), or vehicle for 3 weeks in a second experiment. We subjected both femurs from each rat to soft X-ray, peripheral quantitative computed tomography, computed tomography on a microscale, and histological analysis, and determined the concentration of serum osteocalcin. In addition, in the second experiment, we determined the serum concentration of calcium, tartrate-resistant acid phosphatase (TRAP), and receptor activator of NF-kappaB ligand (RANKL) at 3 weeks, and subjected femurs to biomechanical testing. Following treatment with PTH or PTHrP for 3 weeks, bone filled the marrow cavity of the shafts whose marrow had been ablated. PTH increased trabecular density in the right femur, but failed to induce bone formation in the medullary region of the right unoperated femoral shafts. The newly formed bone endowed left femoral shafts with improved biomechanical properties when compared to those of right femurs and left femurs from control, sham-operated, and vehicle-treated rats. PTHrP, like PTH, increased serum osteocalcin, but neither increased serum calcium, TRAP, or RANKL at 3 weeks. Our results reveal that the newly formed bone that follows marrow ablation is responsive to PTH, expand the role of PTH in bone, and might open new avenues of investigations to the field of regenerative medicine and tissue engineering. Local bone marrow removal in conjunction with pharmacologic intervention with an anabolic agent might provide a technique for rapid preferential site-directed bone growth in areas of high bone loss.

BACKGROUND

The recombinant humanized anti-IgE antibody omalizumab rapidly reduces serum free IgE concentrations and alleviates allergic airway disease. It is not known whether stopping or reducing the dose of omalizumab maintains adequate suppression of free IgE levels and IgE-mediated mast cell activation.

OBJECTIVE

To determine the effects of omalizumab on serum free IgE and immediate allergen skin test reactivity during initial therapy followed by treatment reduction and cessation.

METHODS

Forty patients with perennial allergic rhinitis were randomized to receive 0.015 or 0.030 mg/kg/IU/mL open-label intravenous omalizumab every 2 weeks for 28 weeks, followed by 0.0015 or 0.0050 mg/kg/IU/mL every 2 weeks for 18 weeks. Serum free IgE levels were measured and titrated dust mite allergen skin tests conducted throughout.

RESULTS

At day 98, serum free IgE concentrations were decreased by 96% to 99%, and wheal-and-flare reactions to skin tests were markedly suppressed. After reduced omalizumab doses (day 322), serum free IgE and allergen skin test reactivity increased significantly. On complete discontinuation of therapy (day 378), serum free IgE levels and skin test reactivity returned to baseline levels. Patients with lower initial levels of IgE had significantly less suppression of skin test reactivity.

CONCLUSION

Omalizumab reduced serum free IgE and immediate skin test reactivity to allergen during initial, high-dose administration. These effects were not fully maintained during dose reduction and returned to baseline after cessation of chronic treatment.