Recent Advances and Current Status of GM-CSF as an Adjuvant in DNA Vaccines for Viral Diseases

Here, I update the recent advances and current status of Granulocyte macrophage colony-stimulating factor (GM-CSF), since we have reported for the first time that porcine GM-CSF gene in a DNA vaccine formulation exerted immuno-adjuvant and protective effects against Aujeszky’s (Pseudorabies)viral disease to the natural host pigs with a single vaccination. GM-CSF has been broadly used as an adjuvant in preclinical DNA vaccine studies for cancer and viral diseases. Currently, GeoVax Labs, Inc. reported a recombinant HIV vaccine (GEO-D03) that co-expresses the human GM-CSF and non-infectious HIV-1 virus-like particles (VLPs) is being evaluated in HIV infected young adults in several Phase I studies (NCT01571960). In addition, I summarized here the outcomes of the use of GM-CSF in DNA vaccine for other viral diseases. Further, phase 3 clinical studies reported that GM-CSF showed an improvement in patient outcome when applied in combination with suitable anti-tumor vaccines. However, GM-CSF in excessive levels was reported to expand myeloid suppressor cells that were shown to dampen adaptive immune responses.


Introduction
Here, I update the recent advances and current status of Granulocyte macrophage colony-stimulating factor (GM-CSF), since we have reported for the first time [1,2] that a DNA vaccine formulation with porcine GM-CSF gene exerted immuno-adjuvant effects and protected the natural host pigs against Aujeszky's (Pseudorabies) viral disease with single vaccination. The hematopoietic cytokine GM-CSF has been shown as an efficient adjuvant in DNA vaccine preclinical studies for cancer and viral diseases. Xiang Z et al. [3] first reported that GM-CSF is a genetic adjuvant for DNA vaccine.

GM-CSF as a genetic adjuvant for HIV DNA vaccine in human clinical trials
A recombinant HIV vaccine (GEO-D03) that co-expresses the human GM-CSF and non-infectious HIV-1 virus-like particles (VLPs) is being currently evaluated in HIV infected young adults in several Phase I studies (NCT01571960) [4,5]. This trial will determine whether this vaccine will provide excellent protection in humans as in macaques by simian immunodeficiency virus (SIV)-prototype [6] (NCT01909414).
Lai et al. [7] reported that the SIV vaccine co-expressing GM-CSF achieved significantly higher reduction in risk of infection and protected more SIV challenged macaques in preclinical studies. In addition, this vaccine elicited both anti-viral T cells and antibody. The vaccine-induced prevention of infection was shown to increase from 25% to 71% in the presence of GM-CSF [7]. The outcomes of the use of GM-CSF as genetic adjuvant in DNA vaccine for other viral diseases is given in Table 1.

Use of GM-CSF in Cancer
GM-CSF was found as the most efficient adjuvant for cancer cell vaccines in early preclinical screens of retroviral-expressed cytokines [27]. Further, the ability of the fused GM-CSF to elicit anti-tumor immune responses and boost vaccine efficiency is found in the first licensed cancer vaccine, Provenge [28].
Despite, a number of studies demonstrating cytokines can act as adjuvants in tumor vaccines, the cost prevent their widespread use, except for the GM-CSF. More recently, GM-CSF has shown improved patient outcome in phase 3 studies when applied in combination with suitable anti-tumor vaccines [29].
In addition, GM-CSF is licensed to use as an adjuvant in a fusion protein for a dendritic cell therapy for prostate cancer and for recovery and replacement of white blood cells following bone marrow transplantation and chemotherapy [30]. However, GM-CSF in excessive levels may expand myeloid suppressor cells that were shown to dampen adaptive immune responses [31][32][33]. Table 1: Efficacy and outcomes of GM-CSF as genetic adjuvant in DNA vaccines for viral diseases.

Efficacy/Outcome of GM-CSF Reference
Porcine Circovirus Type-2 Pigs immunized with Cap-GM-CSF subunit vaccine showed significantly higher levels of PCV2specific antibodies and neutralizing antibodies and higher average daily weight gain than pigs receiving immunized with the Cap subunit vaccine and a commercial vaccine (Ingelvac CircoFLEX; P<0.05) after wild-type PCV2 challenge. [8] Flaviviridae Virus Reported as complex and diverse, ranging from enhancement to suppression, depending on the immunogen of Flaviviridae virus DNA vaccine candidates. [9] Simian ImmunoDeficiency Virus The co-expressed GM-CSF increased vaccine-induced prevention of infection from 25% to 71% in simian immunodeficiency virus in macaques. [7] GEO-D03, a DNA vaccine that expresses human GM-CSF and non-infectious HIV-1 virus-like particles .entered into human trials. [4] HIV/AIDS A phase 1 study of the safety and immunogenicity of DNA/MVA immunizations with co-expressed GM-CSF in HIV-1 infected young adults with suppressed viremia on HAART. [5,6]

Foot and Mouth Disease
Efficacy of the DNA vaccine with GM-CSF was improved further in reducing the clinical disease and virus excretions by electroporation. [10] Japanese Encephalitis Virus Reported no protection [11] HIV Induced long-lived humoral and cell mediated immune memory responses. [12] Dengue Virus DV1 challenged mice showed long-term IgG response, strong cytotoxic T lymphocyte activity, produced high levels of splenocyte-secreted interferon-γ and interleukin-2 and sufficient protection after immunization with pCAG-DV1-GM-CSF immunization than pCAG-DV1/E alone [13] Induced stronger immunogenicity and protection from virus challenge in Aotus monkeys. [14] Influenza Virus GM-CSF gene enhanced systemic and mucosal immunogenicity of the HA DNA vaccine in Rhesus macaque [15] Hepatitis B Virus HBV-S gene fused with GM-CSF strengthened the immune effects of the HBV DNA vaccine in HBV-transgenic mice [16] Bronchitis Virus pVAX-chGM-CSF and pVAX-S1 provided more protection against IBV challenge in chickens than pVAX-S1 vaccination alone. [17] Feline Immuno Deficiency Virus Preserved global CD4 T lymphocyte function after the challenge.. [18] Porcine Reproductive and Respiratory Syndrome Virus Significantly enhanced the humoral and cellular immune responses and protection against PRRSV challenge in pigs [19] Hepatitis C Virus Reported no change in the Th1/Th2 balance as compared with simultaneous IL-23 administration. [20] Co-immunization with Flt3-L and GM-CSF shown promise in the development of an effective antiviral HCV vaccine [21] Simian-Human Immuno Deficiency Virus Enhanced IgA response was associated with the best protection, but did not achieve significance. [22] HIV-1 Gag Demonstrated strong antibody and CTL responses and a protective response against infection with recombinant vaccinia virus expressing HIV-1 Gag. [23] Equine Herpes Virus DNA vaccine with GM-CSF, formulated in DMRIE-DOPE significantly improved virus neutralizing antibody responses to EHV-1. [24]
We demonstrated that the Porcine GM-CSF gene in a DNA vaccine formulation exerted immuno-adjuvant and protective effects with single vaccination in the natural host pigs against Aujeszky's disease. [1]