Biology Reference
In-Depth Information
Chapter 9
Oncolytic Adenovirus Characterization: Activity
and Immune Responses
Raul Gil-Hoyos , Juan Miguel-Camacho , and Ramon Alemany
Abstract
Virotherapy in one of the main current applications of recombinant adenoviruses. Oncolytic adenovirus
are designed to target tumors, replicate selectively in tumor cells, and elicit immune responses against
tumor antigens. Transgene expression in replication-competent oncolytic vectors allows to explore multi-
ple strategies to enhance the potential of virotherapy. In this chapter we describe common in vivo and in
vitro techniques used to evaluate the potency and biodistribution of oncolytic viruses. Monitoring immune
responses against viral and tumor antigens is crucial as the immune system determines the outcome of
virotherapy.
Key words
Adenovirus, Oncolytic, Virotherapy, Cancer, Immune responses
1
Introduction
During recent years, many strategies have been used to increase the
potency of oncolytic adenoviruses. Arming adenoviruses with
exogenous genes encoding suicide or prodrug-activating proteins,
cytotoxic proteins, proteases, or immunomudulatory cytokines has
improved the prospects of oncolytic adenoviruses [
1
,
2
]. There are
different strategies for the expression of the exogenous genes from
the viral genome. The transgene can be expressed using the endog-
enous E1a, E3, or major late promoters, linked to these expression
units with internal ribosome entry sites (IRES) or splicing accep-
tors. This strategy is advantageous compared to the use of exoge-
nous promoters (CMV and other promoters) because adenovirus
(commonly used serotype 5) can package up to 38 kb of DNA,
which is only 2 kb over the genome size. This packaging limitation
is important if we consider that most oncolytic adenoviruses also
contain tumor-selective promoters that regulate viral genes, com-
monly the E1a transcription unit. The deletion of some E3 genes
(those associated to immune-inhibitory functions but not the
