Download AIDS and Immunodeficiency

Biol 430
Question Bank
AIDS and HIV
1. Would each one of the following situation be associated with a primary (P) or secondary (S)
immunodeficiency?
a. ____ A man with leukemia.
b. ____ People in underdeveloped nations suffering severe food shortage
c. ____ A child born with a congenital defect in MHC-II production
d. ____ Students worrying about the Immunology course final exam
e. ____ A young man having just recovered from acute infectious mononucleosis
f. ____ A recent recipient of a kidney transplant receiving anti-rejection drugs
g. ____ An AIDS patient
2. Match each of these disorders with the site of the associated immune defect
Disorder
Immune deficiency
___ SCID
A. thymus
___ Bare lymphocyte
B. B-cells and T-cells
___ DiGeorges
C. neutrophils, basophils and eosinophils
___ Agranulocytosis
D. MHC-II
3. Sequence (1 to 9) the following events of the HIV infection cycle:
___ synthesis of HIV RNA and proteins
___ integration of the viral DNA into a host cell chromosome
___ binding to CD4 and a chemokime receptor
___ onset of a latency period
___ self assembly and budding of HIV
___ fusion with the target cell membrane
___ HIV protease cleavage of the HIV precursor protein
___ release of viral RNA and enzymes into the cells cytoplasm
___ reverse transcription of the viral RNA
4. The immune response to HIV diminishes overtime for several reasons. For each one of the
processes listed below, indicate if it applies to B-cells, TH cells and/or Tc-cells.
Process
Mutation of target epitopes
Loss of TH cell stimulation
CTL-mediated cytotoxicity
Viral-mediated clonal exhaustion
Viral-mediated apoptosis
Viral-mediated anergy
Weak response to viral antigens
Viral mediated cell lysis
Biol 430
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Question Bank
AIDS & HIV
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5. Using the diagram of HIV to the right
identify:
Enzymes carried into the cell:
A: _____________
B: _____________
C: _____________
Surface proteins:
D: _____________
E: _____________
Core proteins:
F: _____________
G: _____________
Outer layer of virus:
H: _____________
Genetic material:
I: ______________
6. The HIV genome has several important characteristics.
A. What are the functions of the proteins encoded by the HIV gag, pol, env, and nef genes?
B. Which enzymes are carried into the virus during the infection?
C. Proteins from which genes require processing by the HIV protease?
D. How does the nef protein promote immune evasion by ingfected host cells?
7. There have been many challenges and failures in the effort to develop an HIV vaccine. Suppose that
you were given the opportunity to lead an HIV vaccine development project. Describe your reasoning
for making the following decisions.
A. Given the proteins from the gag, pol and env genes, which would you target first as potential
vaccines (hint: Which proteins are the best targets for an acquired immune response?) Would
you do so using proteins purified from the HIV virus or using a recombinant expression
system?
B. If instead you chose to develop a whole virus vaccine, would your preference be an attenuated
or inactivated form?
Biol 430
Question Bank
AIDS & HIV
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8. Discuss the biological characteristics of HIV and the disease it causes that make AIDS very difficult
to control.
9. Discuss the social issues that hinder efforts to control the spread of AIDS in developing nations.
10. In the diagram to the right:
A. Identify the three stages (A, B, and C) of the
clinical course of an HIV infection.
B. Which line represents viral load and which
represents TH cells? Why does each line trend as
shown?
C. Draw into the diagram the expected trend for
changes in anti-HIV antibodies.
Biol 430
Question Bank
AIDS & HIV
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11. Little et al studied changes in drug resistance among AIDS patients. For this investigation, drug
resistance was determined by inserting protease and reverse transcriptase genes from the patient’s
serum into a recombinant virus system (PhenoSense HIV). The concentration each drug required for
50 percent inhibition [IC50] of the recombinant virus was then compared to the IC50 for a drugsensitive reference strain (NL4-3), to yield a relative susceptibility ratio (i.e., susceptibility
recombinant viruses / susceptibility reference strain). The susceptibility of the recombinant strains
were categorized into three ratio groups: >2.5x, >5x and >10x. These values were determined for
patients from 1995 to 2000, and results are shown in Chart A.
A. Why would the researchers insert the protease and reverse transcriptase genes from the
patient’s serum into a recombinant virus
system, rather than simply study drug
resistance in the original HIV isolates?
B. Evaluate the following statement by the
authors about the chart A. “The proportion
of subjects with an IC50 more than 2.5 times
that for the drug-susceptible reference virus
did not change significantly during the study
period (P=0.65). In contrast, the proportion
of subjects with an IC50 more than 5 times
that for the reference virus or more than 10
times that for the reference virus increased,
primarily between 1998 and 1999.”
Chart B shows the shows the percentages of
subjects identified each year with an IC50 ratio >10
one or more HIV drugs.
C. What are nucleoside-analog RT and nonnucleoside RT inhibitors?
D. Describe the general trends shown in chart
B.
Chart C shows the response of patients with
susceptibility threshold of <2.5 and >10 to drug
therapy. Results show the fraction of the patients
had detectible levels of HIV-RNA at different times
treatment was started.
E. What do these data show about the
effectiveness of the drug regimens for the
different patients?
F. Do you see any weaknesses in the data?
for
who
after
Little SJ, Holte S, Routy JP, Daar ES, Markowitz M, Collier AC, Koup RA, Mellors JW, Connick E, Conway B, Kilby M,
Wang L, Whitcomb JM, Hellmann NS, Richman DD. 2002. Antiretroviral-drug resistance among patients Recently
infected with HIV. N Engl J Med 347:385-394.
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AIDS & HIV
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12. In recent studies Wu et al (Science 329:856, 2010 & Science 333:1593, 2011) studied the formation of HIV
broadly-neutralizing antibodies from human donors. Broadly neutralizing antibodies (bnAb) are capable of
blocking the infectivity of HIV from a wide-range of human patients, and of particular interest are bnAbs that
bind to a highly conserved region of GP120 which binds to the CD4 coreceptor. For this study, they used a
modified form of GP120 (called RSC3) for which the only remaining naturally-antigenic region was the CD4
binding site. (As explained in different article, to generate a GP120 that preserved the antigenic structure of the
CD4 binding site but eliminated other antigenic regions, the other exposed surface regions were substituted with
amino acid sequences from simian immunodeficiency virus (SIV) other non–HIV-1 sequences.) They also
produced another GP120 (called ΔRSC3) that was identical to RSC3 except that the conserved CD4 binding site
was also modified.
A. What are the function and properties of GP120?
B. Would bnAbs against the CD4 binding site be expected to bind to RSC3 or ΔRSC3? Explain.
To test for the ability of antibodies to neutralize HIV (i.e., block HIV infectivity), HIV is mixed with serum
from a patient and then the HIV is tested for ability to infect TZM-bl cells –HeLa cells that express CD4 and
CCR5 and genetically engineered to express the firefly luciferase gene– which fluoresce when infected by HIV.
C. Explain why TMZ-bl cells were used as targets for HIV infection; why is expression of CD4,
CCR5 and luciferase important?
In one experiment, the researchers looked for
the presence of bnAb capable of blocking the
infectivity (neutralize) of different strains of
HIV in sera from different patients. Serum
containing bnAbs should be able to neutralize
HIV. However, the serum was mixed with
HIV + RSC3, or HIV + ΔRSC3, and the bars
show the mean serum reduction in
neutralization of the virus strains resulting
from RSC3 versus ΔRSC3 competition.
D. Why would RSC3 block the HIVneutralizing ability of some
patients’ sera but not others? Which patients appear to produce bnAbs against the conserved
CD4 binding region? Explain.
Cont. on next page
Biol 430
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AIDS & HIV
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To study the properties of the antibodies, it was necessary to isolate B-cells producing bnAbs. To do
so, B- memory cells from patients were mixed with fluorescently
labeled RSC3 or ΔRSC3. The results are shown in the second figure
to the right, and using FACS, the researchers were able to recover 29
B-cells that produced an antibody against the CD4 binding site
E. In the chart, circle the region of the plot in which the 29
selected B-cells would be found. Explain.
From those 29 cells, the heavy and light chain genes were isolated and used to produce IgG
Monoclonal Abs. Three antibodies (VRC01, VRC02, and VRC03) bound strongly to RSC3 and
weakly or not at all to ΔRSC3. The HC variable region for these antibodies were sequenced and
compared to the gene sequences of the original V, D, and J genes; the results for one comparison is
shown below:
Bases and AAs in blue or crossed out are additions and deletions, respectively to junctional regions,
those in red are due to mutations. Similar results for found for the other bnAbs.
F. Which antibody diversification processes, specifically, would lead to these changes?
G. Based upon the sequencing results, would you expect that antibodies that are broadly
neutralizing against many different strains of HIV would be part of the normal repertoire of
antibodies produced in the body? Explain.
Biol 430
Question Bank
AIDS & HIV
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