Following viral infection or vaccination dendritic cells (DC) perform an intricate series
of roles at the interface of innate and adaptive immunity. Peripheral DC recognition of
pathogen associated molecular patterns initiates signaling cascades leading to
morphological and phenotypic maturation. The differentiation to a mature phenotype
licenses DCs to efficiently prime T- and B-lymphocytes. Thus, DCs shape early innate
immune responses that limit viral replication and initiate the generation of protective
and adaptive immunological memory.
In this thesis, we began by studying the interaction of human primary DCs with human
adenovirus (AdV). While the causative agent of a variety of human diseases, AdVs are
also a valuable research tool for probing virological, immunological, and cellular
mechanisms of nature. Recombinant human AdVs (rAdV), rendered replication
incompetent and thus unable to cause disease, have gained prominence as gene delivery
vehicles in multiple vaccine trials. In light of the clinical importance of AdV vectors,
we employed a reductionist approach to study mechanisms of virus-mediated
regulation of human DC function. Since DCs activate adaptive immunity, we extended
our investigations to the impact of rAdV on the activation of T-lymphocytes. These
studies are particularly relevant since the induction of potent T-cell responses is one
objective of rAdV based vaccine vectors.
In assessing the interaction of rAdV with primary human blood myeloid and
plasmacytoid DC subsets, we found that activation of these cells was dependent on
rAdV type. rAdV-35 more efficiently infected DCs than rAdV-5, and matured blood
DCs and strongly induced interferon-! in plasmacytoid DCs. Infection by rAdV-35
was dependent on the receptor CD46, whereas the receptor for rAdV-5 was less clear.
We then showed that lactoferrin facilitated rAdV-5 infection of multiple DC subsets in
a similar manner to epithelial cells. rAdV-exposed DCs were able to process and
present rAdV encoded transgenes and activate polyfunctional memory T cells, which
indicated that rAdV infected DCs retained their antigen presentation capacity.
However, it remained unclear from these studies whether rAdV affected the activation
of naive T cells, which is an important step for vaccination. To this end, rAdV-35 was
found to strongly inhibit activation of naive CD4+ T cells through binding of its
cellular attachment receptor, CD46. Attenuated activation was characterized by lower
proliferation and IL-2 production, as well as deficient NF-!B nuclear translocation.
Further studies showed that cross-linking with CD46 monoclonal antibodies and
recombinant trimeric rAdV-35 knob proteins was sufficient to cause similar
suppression as the whole virus, substantiating the role of CD46 in regulating CD4+ T cell function.
Our findings provide insights into the mechanisms by which host immune cells respond
to rAdV and also how the virus may act to modulate host cell function. These findings
may also guide the development of rAdVs as vaccine vector
