16
serotypes used in clinical gene therapy applications (AAV5, AAV8, and AAV9)
[ 162 ]. Table 1.1 summarizes some of the important features of each viral vector
discussed previously.
1.6 Ex Vivo CRISPR Therapies
1.6.1 CAR T-Cell Therapy
Adoptive cell immunotherapy, or the transfer of lymphocytes to mediate effector
function, is not a novel concept; in 1992, it was shown that a single infusion for
CMV-specified CD8 CTLs could be used to treat disseminated CMV infection in
post-allogeneic transplant patients [ 163 ]. In 2002, CD4 effector cells were shown to
be efficiently transferred in HIV and elevated CD4 cell counts, and in 2005 it was
shown that vaccine responses could be augmented in patients with myeloma using
autologous T cells [ 164 , 165 ]. It is generally believed that the beginnings of modern
human immunooncology began with the approval of ‘1st Generation’ Sipuleucel-T
in 2010 and Ipilimumab, a CTLA-4 checkpoint inhibitor, in 2011 for treatment of
castrase-resistance prostate cancer. ‘2nd Generation’ agents included programmed
cell death protein 1 (PD1) and PD1 ligand 1 (PD-L1) blocking antibodies as well as
blinatumomab, a bi-specific antibody, an oncolytic GM-CSF-encoding herpes sim-
plex virus known as talimogene laherparepvec or T-vec for metastatic melanoma,
and CAR-T cells in 2014–2015 [ 166 ].
As previously mentioned, one of the most promising emerging uses of retroviral
vectors to treat human disease, specifically cancer, is known as chimeric antigen
receptor or CAR T-cell therapy. It involves the modification of patient T-cells to
target malignant cell populations by employing antigen receptors that bind to cancer
cell-specific antigens. CARs are fusion proteins that incorporate antigen recognition
Table 1.1 A summary of viral vector genome size and notable applications
Viral vector
Approximate genome
size (kilobase pairs) Notable applications
Adenovirus 36 In vitro gene delivery (highly immunogenic)
[ 90 , 126 ]
Vaccination against pathogens and addictive
compounds [ 87 , 113 , 116 ]
Destruction of malignant cells [ 119 , 121 ]
Adeno-associated
virus
4.7 In vitro and in vivo gene delivery [ 140 , 155 ]
Relatively lower immunogenicity [ 145 ]
Broad cell type specificity, depending on
serotype [ 152 ]
Retrovirus (including
lentivirus)
7–12 In vitro and in vivo gene delivery [ 57 , 62 ,
68 , 79 ]
Modification of cells for ex vivo therapy [ 82 ]
J.E. DiCarlo et al.