NDV-3: The First Cross-Kingdom Vaccine for Candida albicans and Staphylococcus aureus

By: Jenny Vitcak

Figure 1. Image of a patient afflicted
with oral candidiasis. 

             Fungal pathogens are an increasing problem in healthcare due to a rising number of immunocompromised individuals as well as an increasing resistance to antifungal drugs (1).  One of these opportunistic fungal pathogens is Candida albicans. In the United States alone, 60,000 cases of bloodstream Candida infections are reported yearly, which is a 15 to 20-fold increase compared to the 1990s (2). This fungus is able to cause superficial oral and vaginal infections in healthy individuals as well as systemic infections in immunocompromised patients (3). To demonstrate the scope of these infections, 70% of all women will experience at least one episode of vaginitis caused by Candida within their lifetime while 70% of patients with AIDS will experience oropharyngeal candidiasis (4).

Figure 2. Yeast (round) and hyphal
(filamentous) forms of C. albicans.    

             Despite this high occurrence of infection, C. albicans is generally non-pathogenic. It is a normal microbe found at many different tissue sites, including the oral cavity, vagina, and on the skin. However, it is capable of causing disease in both healthy patients and those with a compromised immune system when it turns from its yeast form into filamentous hyphal cells. In addition to this morphogenesis, the fungus also requires adhesion to the host tissue for infection (4). The genome for C. albicans contains an eight-member family of proteins called ALS. The proteins made from these genes function as adhesins, which allows the cell that expresses them to adhere to a variety of surfaces. Als3 is a member of the ALS family and this specific protein is expressed on the cell surface during hyphal development, which helps the fungus adhere to epithelial cells (3, 5). Once the pathogen is stuck to host tissue, Als3 functions as an invasion. This function causes the host cell to produce protrusions around the hyphal cell and subsequently engulfs it, resulting in infection (6).
             Researchers have been trying to develop a vaccine that combats Candida infections since it is the third-leading cause of hospital-acquired infections in the United States (7). The ALS family seemed like a good place to start, considering that ALS1 and ALS3 are highly expressed in clinical specimens (8). In 2005, a preclinical trial was performed using a vaccine for Als1 that showed significant improvement in survival for both healthy and immunocompromised mice after infection with C. albicans (9).  Despite these promising results, more work went into developing a vaccine that targeted Als3 since this protein shows greater adherence to cells compared to Als1 (10).
             In 2005, another preclinical trial was performed on mice that compared the Als3 vaccine to the Als1 vaccine. Both of these developmental vaccines were made using the N-terminal portion of the protein (7). This is the part of the protein that is furthest away from the cell membrane of C. albicans and comes in contact with immune cells. This contact allows the immune cell to become primed to a specific protein (known as an antigen) on the pathogen, which allows the cell to remember it for future infections. Mice were given either the Als1 or the Als3 vaccine and infected with C. albicans directly in the bloodstream, orally, or vaginally.  Overall, mice who received either vaccination had a 40% higher survival rate compared to mice who did not receive any treatment. Orally or vaginally infected mice showed a lower number of lesions caused by C. albicans when they were given the Als3 vaccine compared to the Als1 vaccine (7). These results suggest that the Als3 vaccine offers more protection against oropharyngeal and vaginal candidiasis; therefore, research continued with Als3 as a vaccine candidate.

Figure 3. Patient afflicted with a MRSA
infection caused by S. aureus in a burn wound.    

             In 2008, the Als3 vaccine demonstrated cross-kingdom protection against both fungal and bacterial pathogens (11). The idea that this vaccine could provide protection against two different types of organisms came through the discovery that both Als1 and Als3 have structural similarity to clumping factor (ClfA) in Staphylococcus aureus. ClfA is a protein that is expressed on the bacterium’s surface and helps the organism with adherence (10), which is a similar function of the Als family in C. albicans. Based upon this finding, mice were immunized with the N-terminal portion of Als3 and exposed to S. aureus two weeks later. 60% of the mice that received the vaccine were alive after 28 days compared with 5% of the mice who did not receive the drug (11).
             This study also determined that T cells are the portion of the immune system that are primed to recognize Als3 (11). Once a T cell is able to recognize a specific antigen, it will remember what that antigen looks like to help destroy it when another infection occurs. B cells also play a similar role in immunity, except they produce antibodies that recognize and kill the pathogen. The researchers determined which immune cell type was responsible for protection by infecting mice that were deficient in either T cells or B cells with S. aureus. Mice that lacked T cells perished quickly after infection with S. aureus, while mice without B cells had similar survival rates compared to mice with a fully functional immune system (11).
             The promising results from the preclinical trials using Als3 led to the first in-human trial in 2012 that used a vaccine called NDV-3.  The vaccine was developed using the N terminal portion of Als3. The Phase I clinical trial was a double-blind, placebo-controlled study performed on healthy individuals age 19-47 from a single study site.  The study looked at the safety and ability to produce an immune response for both a low dose and high dose of the vaccine.  Volunteers were given the low dose vaccine, high dose vaccine or saline control.  Participants who were receiveing the vaccine were also given a booster shot after three months and were followed for a total of nine months (2).
             After vaccination, all participants had a rapid rise in antibody levels, which suggests that only one dose would need to be administered rather than a vaccine with a booster (2). This rise in antibody levels, which come from B cell activity, is a different result than was seen in the preclinical trials with mice. The mice did not have any benefit from B cell activity (11) whereas humans do (2). With regards to T cell activation, robust activity was seen in both treatment groups with the higher dose having a more rapid response. Since this is a Phase I clinical trial, safety of the drug was monitored. NDV-3 was shown to be well tolerated in healthy adults with only mild or moderate adverse events at both doses. The most common adverse event was pain at the injection site that resolved within one to two days (2). A second Phase I trial was conducted in May 2012 using three different vaccine formulations and two routes of administration. Once again, NDV-3 was safe, well-tolerated and produced a robust immune response (Results not published) (12).
             Based upon the experiments performed in mice using an Als3 vaccine as well as the Phase I clinical trial, NDV-3 looks promising. The results have shown a highly immunogenic response as well as increased survival in mice after infection with either C. albicans or S. aureus. It has also proved to be safe in humans with little side effects. As of September 2013, NovaDigm Therapeutics announced the beginning of a Phase Ib/IIa clinical trial for NDV-3. This trial will specifically look at preventing vaginal candidiasis in patients with recurrent vaginal infections (13). Hopefully, this trial will have successful results and research can continue with this vaccine to help the ever growing number of people who are afflicted with either candidiasis or MRSA skin infections.

References

1.     Morschhauser, J. (2010). Regulation of multidrug resistance in pathogenic fungi. Fungal Genetics and Biology 47, 94-106.

2.     Schmidt, C.S., White, C.J., Ibrahim, A.S., Filler, S.G., Fu, Y.,  Yeaman, M.R., Edwards, J.E. Jr., & Hennessey, J.P. Jr. (2012). NDV-3, a recombinant alum-adjuvanted vaccine for Candida and Staphylococcus aureus, is safe and immunogenic in healthy adults. Vaccine 30(52), 7594-7600.

3.     Argimόn, S., Wishart, J.A., Leng, R., Macaskill, S., Mavor, A., Alexandris, T., Nicholls, S., Knight, A.W., Enjalbert, B., Walmsley, R., Odds, F.C., Gow, N.A.R., & Brown, A.J.P. (2007). Developmental regulation of an adhesion gene during cellular morphogenesis in the fungal pathogen Candida albicans. Eukaryotic Cell 6(4), 682-692.

4.     Calderone, R.A., & Fonzi, W.A. (2001). Virulence factors of Candida albicans. TRENDS in Microbiology 9(7), 327-335.

5.     Liu, Y. & Filler, S.G. (2011). Candida albicans Als3, a multifunctional adhesion and invasion. Eukaryotic Cell 10(2), 168-173.

6.     Rotrosen, D., Edwards, J.E. Jr., Gibson, T.R., Moore, J.C., Cohen, A.H., & Green, I. (1985). Adherence of Candida to cultured vascular endothelial cells: mechanisms of attachment and endothelial cell penetration. J. Infect Dis. 152(6), 1264-1274.

7.     Spellberg, B.J., Ibrahim, A.S., Avanesian, V., Fu, Y., Myers, C., Phan, Q.T., Filler, S.G., Yeaman, M.R., & Edwards, J.E. Jr. (2006). Efficacy of the anti-Candida rAls3p-N or rAls1p-N vaccines against disseminated and mucosal candidiasis. JID 194, 256-260.

8.     Cheng, G., Wozniak, K., Wallig, M.A., Fidel, P.L., Trupin, S.R., & Hoyer, L.L. (2005). Comparison between Candida albicans agglutinin-like sequence gene expression patterns in human clinical specimens and models of vaginal candidiasis. Infect. Immun. 73, 1656-1663.

9.     Ibrahim, A.S., Spellberg, B.J., Avenissian, V., Fu, Y., Filler, S.G., & Edwards, J.E. Jr. (2005). Vaccination with recombinant N-terminal domain of Als1p improves survival during murine disseminated candidiasis by enhancing cell-mediated, not humoral, immunity. Infect Immun 73, 999-1005.

10.  Sheppard, D.C., Yeaman, M.R., Welch, W.H., Phan, Q.T., Fu, Y., Ibrahim, A.S., Filler, S.G., Zhang, M., Waring, A.J., & Edwards, J.E. Jr. (2004). Functional and structural diversity in the Als protein family of Candida albicans. J Biol Chem 279, 30480-30489.

11. Spellberg, B., Ibrahim, A.S., Yeaman, M.R., Lin, L., Fu, Y., Avanesian, V., Bayer, A.S., Filler, S.G., Lipke, P., Otoo, H., & Edwards J.E. Jr. (2008). The antifungal vaccine derived from the recombinant N terminus of Als3p protects mice against the bacterium Staphylococcus aureus. Infection and Immunity 76(10), 4574-4580.

12. Business Wire (2012). Results from positive Phase I study of NovaDigm Therapeutics’ NDV-3 vaccine for Candida and Staph infections published in Vaccine. Business Wire. Retrieved from http://www.businesswire.com/news/home/20121213005244/en/Results-Positive-Phase-1-Study-NovaDigm-Therapeutics%E2%80%99.

13. Business Wire (2013). NovaDigm Therapeutics initiates Phase 1b/2a clinical trial with NDV-3 vaccine in recurrent vulvovaginal candidiasis (RVVC). Business Wire. Retrieved from http://www.businesswire.com/news/home/20130926005382/en/NovaDigm-Therapeutics-Initiates-Phase-1b2a-Clinical-Trial.