He was an ingenious organic chemist, developed first adefovir, then, together with de Clerq in Belgium Tenofovir a compound which has only one Methyl group additional attached to Adefovir, which was surprisingly reducing its toxicity by at least 50fold.
Due to the extremely low susceptibility to resistance and very low toxicity this drug became the cornerstone of antiviral treatment for HIV and HBV. It made Gilead Billions, of which Holy has seen a million a year grant for his Institute in Prague.
At the day he died, the FDA had approved Truvada, a combo of tenofovir and emtricitabine (FTC) (300/200mg) for use as a preventative in healthy individuals exposed to risk of infection. This is at least some indication, that the toxicity analysis that the FDA had conducted has at least not shown a strong toxicity signal assoociated with its use. The trial has shown a 96% reduction in infection events compared to placebo.
The dramatic suppression of the HBV virion production/output reduces the signal of infection to the immune system, which causes in turn a reduction in the damage done to the liver by the chronic unsucsessful attack of immune activation. it reduces chronic active hepatitis into very mild or no hepatitis, leading to reduction or reversal of fibrosis and even cirrhosis ( in not too advanced cases) in the vast majority of cases.
Unfortunately, as a side effect of the critical benefit of liver disease reduction, the turnover oof cccDNA infected cells also slows down, since the immune elimination becomes a very slow event. Eventually a very slow daily elimination is balanced by a slow but still existing reinfection spreading, an equilibrium state of fairly low level HBV presence in the liver. Thus the surface antigen, produced by the remnannt cccDNA, will not be eliminated in the majority of patients. And a low level, but long term toxicity, ill defined at the moment, will also persist.
But it is time for a moment of thoughtful gratitude to Antonin Holy, who saved countless millions.