64 times less self-amplifying VEE RNA (1.25 μg) was required
compared to synthetic mRNA (80 μg) [12]. In the context of
plasmid DNA-based delivery, a single intramuscular immunization
of a SIN DNA vector expressing the herpes simplex virus type I
glycoprotein B (HSV-1-gB) protected mice from lethal HSV-1
challenges [13]. Moreover, SIN DNA-based expression of the
p85 antigen generated long-term protection against Mycobacterium tuberculosis in mice [14]. One aspect of utilizing alphavirus
DNA replicons instead of conventional DNA plasmids for immunization relates to the much lower dose needed for reaching the same
level of response [15, 16]. For example, 100- to 1000-fold lower
doses of SIN-HSV-1-gB elicited strong immune responses and
protection against lethal HSV-1 challenges in mice [13].
Related to cancer vaccines, reduction in tumor volume (87%)
and significantly prolonged survival were observed after administration of SFV particles expressing interleukin-12 (IL-12) in a
syngeneic RG2 rat glioma model [17]. Moreover, tumor cell replication was targeted by intraperitoneal administration of SFV particles carrying six micro-RNAs (miRNAs), which resulted in glioma
targeting, limited spread in the central nervous system, and significantly prolonged survival in BALB/c mice with tumor xenografts
[18]. In another study, the naturally oncolytic M1 alphavirus was
evaluated in a liver tumor model resulting in selective killing of
zinc-finger antiviral protein (ZAP)-deficient cancer cells and potent
oncolytic activity [19]. Related to RNA-based delivery, a single
injection of SFV-LacZ RNA provided complete protection of
mice against colon tumor challenges [20]. Moreover, vaccination
2 days after tumor cell administration prolonged the survival of
mice by 10–20 days. In the context of alphavirus-based DNA
vectors, intradermal administration of SFV vectors expressing the
human papilloma virus (HPV) E6 and E7 antigens generated effective therapeutic antitumor activity with 85% tumor-free mice
[21]. In comparison to conventional DNA plasmids, a 200-fold
lower equimolar dose of 0.05 μg of SFV replicon DNA was sufficient to achieve therapeutic efficacy. In the context of melanoma,
immunization with SIN DNA-based vectors expressing the melanoma cell adhesion molecule (MCAM/MUC18) provided protection against lethal challenges with tumor cells in both primary and
metastatic mouse tumor models [22].
So far, alphaviruses have been subjected to a limited number of
clinical trials. In this context, VEE particles carrying a CMV gB or a
PP65/IE1 fusion protein were subjected to a randomized doubleblind, phase I clinical trial in CMV seronegative volunteers
[23]. Intramuscular or subcutaneous administration proved safe
and elicited neutralizing antibody and multifunctional T cell
responses. Moreover, subcutaneous administration of VEE-Gag
in healthy HIV-negative volunteers in a randomized, doubleblind, placebo-controlled phase I study in the USA and
Alphavirus-Based Antigen Preparation
65
compared to synthetic mRNA (80 μg) [12]. In the context of
plasmid DNA-based delivery, a single intramuscular immunization
of a SIN DNA vector expressing the herpes simplex virus type I
glycoprotein B (HSV-1-gB) protected mice from lethal HSV-1
challenges [13]. Moreover, SIN DNA-based expression of the
p85 antigen generated long-term protection against Mycobacterium tuberculosis in mice [14]. One aspect of utilizing alphavirus
DNA replicons instead of conventional DNA plasmids for immunization relates to the much lower dose needed for reaching the same
level of response [15, 16]. For example, 100- to 1000-fold lower
doses of SIN-HSV-1-gB elicited strong immune responses and
protection against lethal HSV-1 challenges in mice [13].
Related to cancer vaccines, reduction in tumor volume (87%)
and significantly prolonged survival were observed after administration of SFV particles expressing interleukin-12 (IL-12) in a
syngeneic RG2 rat glioma model [17]. Moreover, tumor cell replication was targeted by intraperitoneal administration of SFV particles carrying six micro-RNAs (miRNAs), which resulted in glioma
targeting, limited spread in the central nervous system, and significantly prolonged survival in BALB/c mice with tumor xenografts
[18]. In another study, the naturally oncolytic M1 alphavirus was
evaluated in a liver tumor model resulting in selective killing of
zinc-finger antiviral protein (ZAP)-deficient cancer cells and potent
oncolytic activity [19]. Related to RNA-based delivery, a single
injection of SFV-LacZ RNA provided complete protection of
mice against colon tumor challenges [20]. Moreover, vaccination
2 days after tumor cell administration prolonged the survival of
mice by 10–20 days. In the context of alphavirus-based DNA
vectors, intradermal administration of SFV vectors expressing the
human papilloma virus (HPV) E6 and E7 antigens generated effective therapeutic antitumor activity with 85% tumor-free mice
[21]. In comparison to conventional DNA plasmids, a 200-fold
lower equimolar dose of 0.05 μg of SFV replicon DNA was sufficient to achieve therapeutic efficacy. In the context of melanoma,
immunization with SIN DNA-based vectors expressing the melanoma cell adhesion molecule (MCAM/MUC18) provided protection against lethal challenges with tumor cells in both primary and
metastatic mouse tumor models [22].
So far, alphaviruses have been subjected to a limited number of
clinical trials. In this context, VEE particles carrying a CMV gB or a
PP65/IE1 fusion protein were subjected to a randomized doubleblind, phase I clinical trial in CMV seronegative volunteers
[23]. Intramuscular or subcutaneous administration proved safe
and elicited neutralizing antibody and multifunctional T cell
responses. Moreover, subcutaneous administration of VEE-Gag
in healthy HIV-negative volunteers in a randomized, doubleblind, placebo-controlled phase I study in the USA and
Alphavirus-Based Antigen Preparation
65