Myeloid Cells as Active
Reservoir of HIV
Prof. Guido Poli
Vita-Salute San Raffaele University & Scientific Institute
Milano, Italy
[email protected]
HIV Latency vs. HIV Persistence
Hypothesis 1:
❖ Viral Persistence = Proviral Latency
Hypothesis 2:
❖ Viral Persistence includes Proviral Latency, but
also additional forms of HIV-host interaction.
HIV Reservoir. The Dominant View.
❖HIV persistence in the presence of effective cART is mostly, if
not exclusively accounted for by a small pool of long-lived
CD4+ T cells with a “resting memory” phenotype infected
with replication-competent proviruses.
❖Clonal expansion of CD4+ T cells carrying integrated
proviruses (in some case proven to be infectious) is an
additional component of this “CD4 T cell centric” view of the
HIV reservoir.
The contribution of non-T cells to the HIV Reservoir and HIV
persistence is considered marginal, poorly defined,
barely relevant
The CD4 T Cell Centric Model: A
“Fractal” View of the HIV Reservoir
Main Implication
❖ If the problem is exclusively
linked to resting memory T
cells (or related T cell subsets)
all the efforts should be
focusing on strategies aimed
at either eliminating or
curtailing/silencing
this
infected cell type.
A fractal is a mathematical set that
exhibits a repeating pattern displayed
at every scale.
March 2017
A Different View of the HIV Reservoir
❖The HIV Reservoir of a single individual is the results of multiple
forms of HIV-host interaction involving CD4+ T cells, but also
other cell types such as:
❖ Mucosal Myeloid Dendritic Cells
❖ Follicular Dendritic Cells in lymph nodes
❖ Astrocytes (CNS)
❖ Self-renewing, BM-independent tissue resident
macrophages, including microglia, and BM-dependent
monocyte-derived macrophages
Main Distinctive Features of HIV-1 Infection of
CD4+ T Cells and Macrophages
CD4+ T lymphocytes
❖
Productive infection (mostly) in
activated, proliferating cells
❖ Acute, cytopathic (in vitro and in
Macrophages
❖
Productive infection occurs in
non-proliferating cells
❖
Low-absent cytopathicity (in vitro
and in vivo)  prolonged virus
production (weeks in vitro)
❖
Infectious virions accumulate in
subcellular vacuolar
compartments (VCC)
❖
Organ pathology: HIV
Encephalitis  Death
vivo)
❖ Proviral latency establishes
in
vitro and in vivo in a minority of
“resting memory” T cells
❖ Profound cell depletion 
immunodeficiency  AIDS
phase  Death
Main Distinctive Features of HIV-1 Infection of
CD4+ T Cells and Macrophages
CD4+ T lymphocytes
❖
Productive infection (mostly) in
activated, proliferating cells
❖ Acute, cytopathic (in vitro and in
Macrophages
❖
Productive infection occurs in
non-proliferating cells
❖
Low-absent cytopathicity (in vitro
and in vivo)  prolonged virus
production (weeks in vitro)
❖
Infectious virions accumulate in
subcellular vacuolar
compartments (VCC)
❖
Organ pathology: HIV
Encephalitis  Death
vivo)
❖ Proviral latency establishes
in
vitro and in vivo in a minority of
“resting memory” T cells
❖ Profound cell depletion 
immunodeficiency  AIDS
phase  Death
Main Distinctive Features of HIV-1 Infection of
CD4+ T Cells and Macrophages
CD4+ T lymphocytes
Productive infection (mostly) in
activated, proliferating cells
❖ Acute, cytopathic*
❖
Productive infection occurs in
non-proliferating cells
❖
Low-absent cytopathicity*
 prolonged virus production
*both in vitro and in vivo
❖
Macrophages
Main Distinctive Features of HIV-1 Infection of
CD4+ T Cells and Macrophages
CD4+ T lymphocytes
❖
Productive infection occurs in
non-proliferating cells
❖
Low-absent cytopathicity*
 prolonged virus production
❖
Phagocytosis of infected T
lymphocytes:
Productive infection (mostly) in
activated, proliferating cells
❖ Acute, cytopathic*

degradation? Infection?
*both in vitro and in vivo
❖
Macrophages
Main Distinctive Features of HIV-1 Infection of
CD4+ T Cells and Macrophages
CD4+ T lymphocytes
Productive infection (mostly) in
activated, proliferating cells
❖ Acute, cytopathic*
❖ In vivo, proviral latency
establishes in a minority of
“resting memory” T cells
❖
Productive infection occurs in
non-proliferating cells
❖
Low-absent cytopathicity*
 prolonged virus production
❖
Phagocytosis of infected T
lymphocytes
*both in vitro and in vivo
❖
Macrophages
Main Distinctive Features of HIV-1 Infection of
CD4+ T Cells and Macrophages
CD4+ T lymphocytes
Productive infection (mostly) in
activated, proliferating cells
❖ Acute, cytopathic*
❖ In vivo, proviral latency
establishes in a minority of
“resting memory” T cells
❖
Productive infection occurs in
non-proliferating cells
❖
Low-absent cytopathicity*
 prolonged virus production
❖
Phagocytosis of infected T
lymphocytes
❖
Infectious virions accumulation in
vacuolar compartments (VCC)*
 “Trojan Horse” hypothesis
*both in vitro and in vivo
❖
Macrophages
The Journal of Experimental Medicine, 176: 739-750, 1992
1992
❖ Is HIV virion release from VCC regulated by specific
signals?
❖ Is the release only consequent to cell death with loss
of membrane integrity?
2016
2015
ICAR Award 2015
Imipramine Prevents eATP-Induced Virion
Release in MDM
Imipramine (G 22355),
Tofranil®, is a tricyclic
dibenzazepine anti-depressant
used in major depression,
enuresis and panic disorders.
• Imipramine is a potent inhibitor of
microvesicle release by interfering
with membrane-associated acid
sphingo-myelinase (aSMase)
(Bianco et al., EMBO J, 2009)
shedding
vesicles
Our current goal is to identify other potential pharmacologic
agents that could be tested in relevant animal models and
eventually in infected individuals on cART to either purge or
“seal” the macrophage-associated HIV reservoir
2016
Main Distinctive Features of HIV-1 Infection of
CD4+ T Cells and Macrophages
CD4+ T lymphocytes
Productive infection (mostly) in
activated, proliferating cells
❖ Acute,
cytopathic*
❖ In
vivo, proviral latency
establishes in a minority of
“resting memory” T cells
cell depletion 
immunodeficiency  AIDS
 Death
❖
Productive infection occurs in nonproliferating cells
❖
Low-absent cytopathicity* 
prolonged virus production
❖
Phagocytosis of infected T
lymphocytes
❖
Infectious virions accumulation in
VCC*  “Trojan Horse” hypothesis
❖
Organ pathology:
Encephalitis  Death
❖ Profound
HIV
*both in vitro and in vivo
❖
Macrophages
1986
❖“Up to 50% of (cART-treated) HIV pts. still report cognitive problems.”
❖146 HIV pts with cognitive problems (2011-2015)  evidence of HIV
expression/replication in 22 (15%).
❖Pts. with diffuse white matter alterations were 10 times more likely to
have active HIV in the brain, or HIV-related inflammation, than those with
normal white matter appearance.
Conclusions
❖ HIV, as a lentivirus, has a natural propensity to infect
myeloid cells.
❖ The acquisition of CD4 as its primary entry receptor
has extended its tropism to T lymphocytes causing
profound immunodeficiency and AIDS.
❖ Strategies aiming at achieving a “functional cure”
should take into account both latently infected CD4 T
cells and the more elusive non-CD4 T cell reservoir.
Grazie!
A Copernican Revolution in
Mononuclear Phagocyte Biology
❖In adult life, tissue-resident macrophages undergo a slow,
homeostatic proliferation and are responsible for tissue
homeostasis without requiring supply of blood monocytes.
Evolution of IAS Vision on HIV Cure
2012
ATP
Adenosine triphosphate (ATP) is a nucleoside triphosphate used in cells as
coenzyme, that can be released via Pannexin-1, a large TM channel .
Extra-cellular ATP (eATP), ADP, and adenosine are recognized by
Purinergic R, P2Y and P2X, the most abundant R in mammalian tissues.
After: F. Jacob et al., Purinergic Signalling, 2013;
S. Velasquez & E. Eugenin, Frontiers in Physiology, 2014
eATP. A “Danger Signal” for Macrophages
Primary Human MDM Infection & ATP Stimulation
Remove
Supernatant  ATP
Days of
culture
0
7
8
9
12
15