Download 12mb ppt - UCLA.edu

HIV
Cellular Pathogenesis III
Benhur Lee, M.D.
Adult v. infant (IgG v. IgA)
CTL response (MHC tetramers)
p24 antigenimia
Ab response
Viral load
Viral load “set-point” is a major determinant
of disease progression
“Set-point” determined by a balance between
the virulence of the viral strain and the
quality/strength of host immune response
Control of HIV replication and
disease progression by
balance of host factors
Viral load “set-point” is a major determinant
of disease progression
“Set-point” determined by a balance between
the virulence of the viral strain and the
quality/strength of host immune response
Viral Load is a stronger and more independent predictor of
disease progression than CD4 count
Viral Load Tests

Quantitative (Viral Load determination)

Quantitative RT-PCR (<2x102-1x106)



Branched chain DNA (<5x102-1x106)




Most sensitive for low levels of viral RNA
Requires ~200 ml of blood
Most accurate for high levels of viral RNA
Requires ~2 ml of blood
NASBA (Nucleic Acid Based Sequence Amplification)
(<4x103-1x106)
Clinical interpretation of Viral Load must take into
account the type of assay used. Inter-assay
differences can differ by as much a 0.5 log.
Combination anti-viral Rx can reduced viral loads down to
undetectable levels (<50 copies /ml)
RT
Pr
Protease Inhibitors
Synergism
Entry
Inhibitors
(Fuzeon™)
RT Inhibitors
Log Viral Load
Phase 1: Exponential Decay
Phase 2: Linear Decay
Phase 3: t1/2 of this phase can
be used to approximate
treatment time for
eradication
}
Latently Infected Cells
--turnover is very slow
--relatively resistant to anti-viral Rx
CCR5CCR5++
CCR5+
CCR5++
Activation Step
Is critical for
recovery of virus
from latent reservoir
Viral Eradication may require repeated “flush and kill” regimens
How do we determine the number of latently infected cells if
(1) Latently infected cells are so rare, and
(2) Virus is not replicating in latently infected cells
Isolate highly purified CD4+ Naïve T-cells
<0.01% of resting T-cells are latently infected
(Activation Markers)
CD4+, CD3+, CD25-. CD69-, HLA-DRLimiting Dilution
5 x 106
1 x 106
2 x 105
4 x 104
8 x 103
Activation
add PHA, add CD4+ T cells from HIV-negative donor to rescue virus
Detect viral replication on day 7-9, back-calculate IUPM based on
lowest dilution from which virus can be rescued
5 x 106
1 x 106
2 x 105
4 x 104
IUPM
8 x 103
+
+
+
+
-
25
+
+
-
-
-
1
+
+
+
+
+
>100
Time on HAART
+
+
+
+
+
+
+
-
+
+
-
+
-
+
-
-
-
-
-
-
-
-
-
Key: (+) = virus replication detected
(- ) = no virus replication detected
Increasing time
+
+
+
+
Is Eradication Possible?
Rx period>67 years
Mechanism for persistance of
latent reservoir

Stability reflects basic biology of memory T cells

Long lived immunity (resting T cells)
HepC and Measles specificT cells can be detected >20
years after primary infection
 Half life of memory T cells (>6 months)
Viremia is NOT completely eliminated




Undetectable viral load = No viral replication
Continual low-level infection of T cells, replenishment of
latent reservoir
How does one determine low level of viral
replication below limits of detection?
Eradication of Viral Reservoirs

Treatment Intensification--5-drug HAART

“Flushing out” latent virus


T cell activation
Structured Treatment Interruptions

“Autoimmunization” (no longer recommended)
North America
Challenges for an AIDS Vaccine

Antibody response



Elicitation of Abs towards neutralizing
epitopes (conserved)
Oligomeric vs monomeric Env response
CTL response



Conserved CTL epitopes
Neutralization Escape mutants
Sustaining the response (live viral vectors)