Ibalizumab phase 3 results and susceptibility to drug-resistant HIV
Simon Collins, HIV i-Base
CROI 2018 included a poster on the most recent HIV drug, ibalizumab, which was given FDA approval in the US during the conference week.
Ibalizumab is a monoclonal antibody that post-attachment, blocks HIV entry into cells while preserving normal CD4 functions. After an initial loading dose, it is given by infusion every two weeks.
Baseline susceptibility data was presented for 38/40 highly treatment-experienced participants in the 24-week, single arm, phase 3 TBM-301 study. At baseline, 50% of participants had resistance to at least three classes, with major mutations to NRTIs, NNRTIs, PIs and INIs on 93%, 85%, 83% and 61%, respectively.
Results from the main study were previously reported in HTB last year, but in summary, include 83% of participants meeting the primary endpoint of >0.5 log reduction in viral load seven days after adding a single dose as virtual monotherapy to the background failing combination and mean viral load reduction of 1.1 log copies/mL. Background ART was then optimised with 24-week follow-up. 
At week 24, viral load was <50 copies/mL in 43% (50% < 200 c/mL) with median viral load reductions of 1.6 log at week 24.
The poster at CROI presented results of in vitro analysis showing that ibalizumab retained sensitivity irrespective of baseline resistance to NRTIs, NNRTIs, PIs and INSTIs.
Although ibalizumab is not currently approved in the EU, the company are actively pursuing the regulatory pathway in Europe.
- Weinheimer S et al. Ibalizumab susceptibility in patient HIV isolates resistant to antiretrovirals. 25th CROI, 4 – 7 March 2018, Boston. Poster abstract 561.
www.croiconference.org/sessions/ibalizumab-susceptibility-patient-hiv-isolates-resistant-antiretrovirals (abstract and poster)
- HTB. FDA approves ibalizumab in the US to treat multidrug HIV resistance. (06 March 2018).
- HTB. Ibalizumab infusion reduces viral load in people with HIV multi-drug resistance. HTB (29 November 2017).