Author(s): Yang CF, Wang CK, Malkin E, Schickli JH, Shambaugh C,
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Abstract MEDI-534 is the first live vectored RSV vaccine candidate to be evaluated in seronegative children. It consists of the bovine parainfluenza virus type 3 (PIV3) genome with substituted human PIV3 F and HN glycoproteins engineered to express RSV F protein. A Phase 1 study of 49 healthy RSV and PIV3 seronegative children 6 to <24 months of age demonstrated an acceptable safety profile at the following doses: 10(4), 10(5) and 10(6)TCID50. After 3 doses of MEDI-534 at 10(6)TCID50, administered at 0, 2 and 4 month intervals, 100\% of subjects seroresponded to PIV3, whereas only 50\% seroresponded to RSV. To investigate the discordance in seroresponse rates, the RSV F transgene and its flanking non-coding nucleotides were sequenced from shed virus recovered from the nasal washes of 24 MEDI-534-vaccinated children. Eleven out of 24 samples contained no nucleotide changes in the analyzed region. The other 13 samples contained mixtures of variant subpopulations. Fifty-five percent exhibited changes in the transcription termination poly A gene sequences of the upstream bPIV3N gene while 21\% had variant subpopulations in the RSV F open reading frame that resulted in pre-mature stop codons. Both types of changes are expected to reduce RSV F expression. Evaluation of the administered vaccine by dual immunofluorescence staining showed ~2.5\% variants with low or no RSV F expression while single nucleotide primer extension detected ~1\% variation at nucleotide 2045 that resulted in a pre-mature translational termination at codon 85. An association between shedding of variants and lower RSV F serological response was observed but it was not possible to establish a definitive clinical significance due to the small number of subjects in this study. TRIAL REGISTRATION: ClinicalTrials.gov NCT00686075. Copyright © 2013 Elsevier Ltd. All rights reserved.
This article was published in Vaccine
and referenced in Journal of Antivirals & Antiretrovirals