Drug Sensitivity of Vaccine-Derived Rubella Viruses and Quasispecies Evolution in Granulomatous Lesions of Two Ataxia-Telangiectasia Patients Treated with Nitazoxanide

A strong association between rubella virus (RuV) and chronic granulomas, in individuals with inborn errors of immunity, has been recently established. Both the RA27/3 vaccine and wild-type RuV strains were highly sensitive to a broad-spectrum antiviral drug, nitazoxanide (NTZ), in vitro. However, NTZ treatment, used as a salvage therapy, resulted in little or no improvements of RuV-associated cutaneous granulomas in patients. Here, we report investigations of possible causes of treatment failures in two ataxia-telangiectasia patients. Although a reduction in RuV RNA in skin lesions was detected by real-time RT-PCR, live immunodeficiency-related vaccine-derived rubella viruses (iVDRV) were recovered from granulomas, before and after the treatments. Tizoxanide, an active NTZ metabolite, inhibited replications of all iVDRVs in cultured A549 cells, but the 50% and 90% inhibitory concentrations were 10-40 times higher than those for the RA27/3 strain. There were no substantial differences in iVDRV sensitivities, neither before nor after treatments. Analysis of quasispecies in the El gene, a suspected NTZ target, showed no effect of NTZ treatments on quasispecies' complexity in lesions. Thus, failures of NTZ therapies were likely due to low sensitivities of iVDRVs to the drug, and not related to the emergence of resistance, following long-term NTZ treatments.

Automated summary

A strong association between rubella virus and chronic granulomas in individuals with inborn errors of immunity has been confirmed. The antiviral drug nitazoxanide (NTZ) was highly effective against both the RA27/3 vaccine and wild-type RuV strains in vitro. However, NTZ treatment as a salvage therapy did not improve cutaneous granulomas associated with RuV in patients. Investigation of treatment failures in two ataxia-telangiectasia patients revealed that live immunodeficiency-related vaccine-derived rubella viruses (iVDRVs) were still present in granulomas before and after treatment, despite a reduction in RuV RNA. The low sensitivities of iVDRVs to NTZ were likely the cause of treatment failures, rather than the emergence of resistance.