War in the Body身体的战争

War in the Body

Preface
It has often been said that nothing in biology is comprehensible except in
the light of evolution.1 HIV/AIDS provides the latest—and most sobering—
proof of this adage.
Evolution in the microbial world burst into scientific and public-health
consciousness 60 years ago, with the appearance of antibiotic-resistant bacteria.
In this well-known episode, the bugs developed resistance to penicillin
in a matter of months after it was introduced (around 1947) in the clinic;
some bacterial strains are now resistant to every antibiotic we possess. If you
become infected by one, you might as well be living in the 19th century. HIV
is presumably second only to bacteria in the rate it evolves: roughly a million
times faster than mammalian evolution. Only a half-dozen decades after the
probable introduction of HIV into the human population (most likely from
chimps in Western Africa), variants of HIV have diverged to such an extent
that if we were discussing something other than viruses we would call them
separate species. But HIV evolution is not just of interest to biologists; it
matters profoundly to doctors and their patients. In 1987, the first drug with
an impact on HIV was tested in a clinical trial. At first, it appeared that a
treatment, if not a cure, was at hand; but, 6 months later, the treated patients
were found to be progressing to AIDS as fast as untreated. The virus
had acquired mutations, negating the drug’s benefit in every subject. It required
a combination of three drugs to (partially) overcome the resistance
problem.
The immune system fares better than a single drug, suppressing the infection
for a decade on average; but the virus eventually learns to evade specific
responses and escapes control. The implications of this evolutionary battle
for vaccine design cannot be overstated. (After 25 years of research, we still
have no licensed vaccine for HIV/AIDS.)

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