FROM MEDICAL MYCOLOGY
Elevated Aspergillus RNA blood levels after 4-6 weeks of antifungal treatment predict poor response at week 12 in patients with proven or probable invasive aspergillosis, according to results of a small observational study of 41 evaluable patients.
The investigators are working to address the need for reliable biomarkers of early invasive aspergillosis (IA) treatment response. Standard clinical and radiological criteria are somewhat subjective, and serial biopsies and bronchoalveolar lavage are often impractical, reported Yanan Zhao, PhD, of the New Jersey Medical School–Rutgers Biomedical and Health Sciences, Newark, and her associates.
Study participants’ blood was checked for serum galactomannan (GM), 1, 3-beta-D-glucan (BG), and Aspergillus RNA within 24 hours of starting antifungal therapy, then twice per week during the first 2 weeks, then once during weeks 4, 6, and 12, the investigators reported ( Med Mycol. 2016 Jun 22. pii: myw043 ).
Ribosomal Aspergillus RNA – like GM and BG, a marker of fungal load – was measured by nucleic acid sequence-based amplification (NASBA), a robust isothermal amplification technique more sensitive than polymerase chain reaction due largely “to increased starting target numbers (RNA versus DNA) and more robust amplification.” Although NASBA has been used before to diagnose IA, using it to monitor treatment “is still in its infancy,” the authors noted.
Eleven of 14 patients who did not respond to treatment at 12 weeks (79%) had Aspergillus RNA in their blood after 4 weeks of treatment, and 12 (86%) were positive at 6 weeks.
Among patients who did respond at 12 weeks, 11 of 27 (41%) had RNA in their blood at 4 weeks, and 14 (52%) at 6 weeks. The findings were statistically significant.
There was no correlation between Aspergillus RNA and serum GM levels in terms of outcomes, but the kinetics of circulating Aspergillus RNA correlated with BG in some patients, with an excellent match in three.
Serum GM responds fairly soon if treatment is working. Aspergillus RNA, however, responds more slowly, like BG. “This may explain … the correlation between Aspergillus RNA and BG … Therefore, the combination of Aspergillus RNA and BG might be useful to assess therapeutic response, particularly in GM negative cases,” the investigators said.
This work was funded by Merck. Four investigators are current or former employees.