You're in: AIDS at 25 Coverage / 25 Years Later: The Vaccine
—New York
By far, the biggest challenge in HIV vaccine development stems from the virus' structural and functional complexity. The vaccines we have today—against measles, polio, rabies, etc.—were far easier to develop because their targets are simpler and more predictable.
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Many different strains of HIV exist worldwide. Viruses within a single strain can differ significantly—this is what gives the virus its complexity. HIV's coat, or envelope, is covered in "sugars" and can rapidly mutate within an indiv-idual and throughout a population. Finding a way to prime immune systems against such an elusive and diverse target is extremely difficult.
For these reasons, at least in the near term, we know that an effective HIV vaccine is going to be very different from any other vaccine we have today. Aside from the fact that the most common historical approaches to vaccine design (i.e., live attenuated or whole killed virus) are not used due to safety concerns, most licensed vaccines initiate an antibody-mediated immune response, priming cells to produce antibodies to effectively attack the target.
Grandmother and Granddaughter
Both of this girl's parents and one of her siblings died from AIDS. Her grandmother struggles to care for her and her seven brothers and sisters. In Papua New Guinea, children orphaned by AIDS place an increasing strain on the economy; new awareness and training efforts have been initiated to combat the disease.
But HIV forces us to take a novel approach because we have not found a way to elicit a broadly neutralizing antibody against it. So until we do, we will focus on priming the body for another type of immune response, a cell-mediated response, which involves the activation of different kinds of immune cells.
We already know that cell-mediated responses are important in controlling viral load in HIV-infected individuals, and we have seen subtle cell-mediated responses in people who have been able to remain uninfected after HIV exposure. We believe that key segments of the virus must remain the same between different worldwide strains in order for it to reproduce efficiently, and that certain cell-mediated responses should be able to detect and attack these segments. As a result, a cell-mediated approach may be helpful in getting past the challenge of the diversity of HIV.
That said, most scientists believe that a fully effective vaccine will require both types of immune responses, antibody-mediated and cell-mediated. Gary J. Nabel, director of the Vaccine Research Center (VRC) at the NIH, calls the broadly neutralizing antibody-approach the "Holy Grail" for HIV vaccine research—and I agree that it would be highly desirable to achieve this in combination with a strong cell-mediated response. But for the time being, we're making do by pursuing the "slightly less holy" grail, a solely cell-mediated vaccine, because of our difficulties in inducing broadly neutralizing antibodies.