Arbutus Biopharma Corporation and Barinthus Biotherapeutics plc announced preliminary data from the Phase 2a clinical trial (AB-729-202) combining Arbutus' RNAi therapeutic, imdusiran (AB-729), with Barinthus Bio's T-cell stimulating immunotherapeutic, VTP-300, and standard-of-care nucleos(t)ide analogue (NA) therapy. Clinical trial AB-729-202 enrolled 40 non-cirrhotic, virally suppressed cHBV patients that were on stable NA therapy. The patients initially received imdusiran (60mg every 8 weeks) for 24 weeks and were then randomized to receive either VTP-300 or placebo at week 26 and 30 (and conditionally at week 38 if they experienced a >0.5 log10 decline in HBsAg between weeks 26 and 34), in addition to ongoing NA therapy.

The preliminary data include a subset of patients that received the two dose VTP- 300 regimen (28/40 patients) and available follow-up data to week 48 (12/40 patients) and showed the following: · Robust reductions of HBsAg were seen during the imdusiran treatment period (-1.86 log10 mean reduction from baseline after 24 weeks of treatment). This decline in HBsAg is comparable to the declines seen with imdusiran in other clinical trials conducted to date. 97% of the imdusiran treated patients (33/34) had HBsAg <100 IU/mL at the time of the first VTP-300/placebo dose.

VTP-300 treatment appears to contribute to the maintenance of low HBsAg levels in the early post-treatment period, as the mean HBsAg levels in the placebo group begin to increase starting ~12 weeks after the last dose of imdusiran. All VTP-300 treated patients have maintained HBsAg <100 IU/mL through week 48, 60% have maintained HBsAg <10 IU/mL, and all have qualified to stop NA therapy. Preliminary immunology data suggests HBV-specific T cell IFN- production is enhanced in patients receiving imdusiran plus VTP-300 compared to placebo.

The preliminary safety data from this trial demonstrate that imdusiran and VTP-300 were both safe and well-tolerated. There were no serious adverse events, Grade 3 or 4 adverse events or treatment discontinuations.