Download Current subjects of research:

Current subjects of research:
HIV-host interactions: HIV is a particularly interesting virus to explore CD4 T cell
immunity to infection as it both infects the CD4 T- cell, and is known to alter it's
function. Elucidating HIV interaction pathways in a CD4 T cell may be (a) directly
relevant to antiviral immunity and therefore be exploited as novel antiviral targets, (b)
serve as novel correlates of protective immunity, and/or (c) contribute to
pathogenicity or viral subversion, that could be blocked as part of novel therapeutic
strategies in the treatment of infectious diseases.
My laboratory initially
demonstrated using clonal populations, that CD4 T cells in the peripheral blood of
healthy volunteers exhibit significant diversity in their susceptibility to HIV infection,
despite expressing equivalent levels of the HIV receptor and coreceptors [16]. To
probe the underlying mechanisms that account for this variation, we proceeded to
examine the transcriptome of a HIV permissive and a non-permissive cell. One of the
differentially expressed proteins identified, which rendered cells more permissive to
HIV infection, belonged to the ancient Whey Acidic Protein (WAP) family [7]. WAP
proteins are defined by a highly conserved 4-dilsuphide core domain and identified as
pleiotropic soluble factors. Functionally, they are implicated in mucosal immunity
through the multifaceted innate effector functions of protease inhibition, attenuation
of inflammatory responses and microbial clearance. Recently, three of these proteins
have been ascribed significant roles in regulating HIV-1 infection. Secretory
leukocyte protease inhibitor (SLPI) and Elafin block early steps of HIV infection and
increased levels of these factors have been shown to correlate with reduced HIV
transmission [see 6,8]. On the other hand, the WAP protein ps20, encoded by the
WFDC1 gene identified in our laboratory as the only member to be expressed in CD4
T-cells, enhances HIV infection by promoting intercellular adhesion specifically
through CD54/ICAM-1 up-regulation, thereby promoting entry of cell-free virus and
cell-cell virus transfer through the virological synapse [3,7]. Apart from their ability
to regulate HIV infection, this class of proteins can significantly impact immune
responses through their ability to negatively regulate the inflammatory response
following TLR activation of macrophages or CD3/28 activation of CD4 T-cells.
Indeed, one member Elafin, has been shown to have beneficial effects in the treatment
of chronic inflammatory lung disorders [see 1, 6,8]. The significant
immunomodulatory effects of these ancient, innate immune soluble factors that are
expressed in tissue sites of relevance to HIV transmission and spread, has prompted
us to systematically explore their mode of function, which is currently very poorly
understood. Understanding WAP protein function in terms of their expression
pattern, regulation, binding partners, signaling properties, structure /function and
interaction specifically with Type 1 and Type II interferons has the potential to shed
vital light on HIV pathogenesis.
Figure 5!
Uninfected
target
Productively infected ps20 secreting CD4 T-cell
1. CD54 on
HIV virion binds cell-surface
LFA-1 & promotes
entry of cell-free virus
LFA-1
HIV receptor
complex
CD54hi
ps20hi CD4 T-cell
CD54
(ICAM-1)
LFA-1
4. CD54 on
HIV virion binds cell-surface
LFA-1 & promotes
cell-cell HIV transmission
3. ?signalling to
up-regulateCD54
?signalling to
up-regulateCD54
Cell surface ps20
binding partner?
autocrine
2. Secreted ps20
Binds cell surface binding partner
paracrine
Figure 1: The proposed HIV enhancing effects of ps20 (taken from Bingle CD &
Vyakarnam A, Trends in Immunology, 2008)
ps20 has both autocrine and paracrine effects. Thus, a ps20+ cell can be made less
permissive to infection by adding neutralizing anti-ps20 antibody and, conversely, a
ps20- cell can be made more permissive to infection by exogenous addition of factor.
It is hypothesized that this effect may be mediated through a cognate receptor–ligand
interaction. ps20 can enhance HIV infection by up-regulating cell-surface CD54
integrin, which is known to promote both cell-free and cell–cell spread of HIV. HIV
can pick up a number of host factors, including adhesion antigens during egress from
a productively infected cell, which are then used to promote infection of a
neighboring cell.
Correlates of protective immunity to HIV:
The objective is to elucidate the antiviral and immune regulatory properties of CD4 Tcells from patients who do exceptionally well clinically following HIV infection (so
called controllers) or following multiple exposures to HIV (so called highly-exposed
persistently seronegative individuals {HEPS}). My group has extensively
characterised CD4 T-cells from these cohorts, being one of the first to demonstrate
that IFNg+IL-2+ polyfunctional CD4 T-cells to be a marker of slow HIV-1
progression [15]. In addition, we have demonstrated that HEPS subjects can generate
HIV Gag-specific CD4 T cells that secrete high levels of MIP1β, which renders these
cells selectively resistant to HIV-1 infection [13]. We plan to extend these studies to
include Indian HIV+ cohorts through a new collaboration with the Indian Institute of
Science and the St John’s Research Institute, both in Bangalore, India. Bangalore is in
the South Indian state of Karnataka, which borders the states of Maharashtra and
Tamil Nadu, where there is not only a recurrent incidence of HIV Clade C infections
but high proportion of HIV-infected subjects are co-infected with Mycobacterium
tuberculosis (Mtb). Studies on HIV-TB are therefore planned. A major current
interest is to elucidate the complex role that CD4 T regulatory cells (Treg) play in
HIV infection.
Altered balance in the quality and quantity of Th17 versus Regulatory CD4 T cell
populations in the gut and blood contribute to HIV-1 disease progression: Two CD4 T
cell subsets that orchestrate immune homeostasis under reciprocal patterns of
differentiation include Th17 cells, producing proinflammatory cytokines and
regulatory T (Treg) cells, whose function is immunosuppressive. The unequal loss of
these cell types in HIV infection is hypothesized to favor virus persistence and disease
progression. There is evidence from both our laboratory and others to show that HIV
can selectively infect and replicate in CD4 Treg cells. How HIV achieves this and
replicates in a cell type that is otherwise largely anergic is poorly understood. Our
observations lead us to focus on two aspects of Treg function.
(i)
(ii)
Frequency, Function: Recently, we demonstrated blood CD25+ FOXP3+
Treg cell number to be significantly reduced in all chronic HIV+ subjects
tested irrespective of their disease stage, although the suppressive function
of these cells was maintained. In addition, we provided novel evidence that
CD4+ CD25 negative effector T-cells from chronic, asymptomatic HIV+
subjects become more sensitive to Treg-mediated suppression than those
isolated from healthy volunteers and this phenomenon was associated with
good clinical outcome [2,5]. This increased sensitivity was not associated
with reduced IL-17 expression. Our objective is to understand this
phenomenon. As HIV resides largely in gut tissue, our observations will be
extended by comparing the gut- versus blood-derived CD4 T cells from
chronic asymptomatic versus those of HIV+ progressors and control HIVsubjects to identify candidate genes/pathways that might account for
increased sensitivity of CD25- cells to Treg-mediated suppression that can
be subsequently functionally validated. To probe the balance between
Th17 and Tregs we will use new markers of gut homing CD4 T cells, e.g.
CD161. Specifically, changes in CD161, Th17 and Treg subsets during
untreated and treated HIV infection will be monitored. In addition, how
CD161 identifies follicular T helper cells and gut homing Treg cells will
be explored. Collaboration with Prof. P Klenerman (Oxford).
HIV compartmentalization: Understanding how HIV compartmentalizes
to and thereby contributes to loss of Treg cells [5] could improve our
understanding of the mechanisms that drive chronic T-cell activation,
which is associated with poor clinical outcome following HIV infection.
Antibodies specific for emerging Treg cell markers that capture the
plasticity of this population and viral DNA PCR is being used to define
more precisely what types of CD4 subsets harbor virus in vivo in blood
versus gut and to establish if the resultant virus is integrated and
replication competent (Collaboration: J Spencer, KCL). Together, our
studies should provide a fresh perspective of the role of Treg cells in HIV
infection.