Regarding HIV vaccine (AIPG 2009)
Assertion: vaccine is still in development phase
Reason: HIV is not attacked by immune system
|A||Both Assertion and Reason are true, and Reason is the correct explanation for Assertion|
|B||Both Assertion and Reason are true but Reason is not the correct explanation for Assertion|
|C||Assertion is true but Reason is false|
|D||Reason is true but Assertion is false|
(Ref: S. Fauci, 2010, An HIV vaccine: breaking the paradigms, Proc. Am. Assoc. Phys. 108:6.)
a. There are a number of factors that cause development of an HIV vaccine to differ from the development of other classic vaccines:
i. First, HIV is highly mutable. Because of the virus' ability to rapidly respond to selective pressures imposed by the immune system, the population of virus in an infected individual typically evolves so that it can evade the two major arms of the adaptive immune system; humoral (antibody-mediated) and cellular (mediated by T cells) immunity.
ii. Classic vaccines mimic natural immunity against reinfection generally seen in individuals recovered from infection; there are almost no recovered AIDS patients.
iii. Most vaccines protect against disease, not against infection; HIV infection may remain latent for long periods before causing AIDS.
iv. Most effective vaccines are whole-killed or live-attenuated organisms; killed HIV-1 does not retain antigenicity and the use of a live retrovirus vaccine raises safety issues.
v. Most vaccines protect against infections that are infrequently encountered; HIV may be encountered daily by individuals at high risk.
vi. Most vaccines protect against infections through mucosal surfaces of the respiratory or gastrointestinal tract; the great majority of HIV infection is through the genital tract.