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Silvestri: Independent Confirmation of Inactivated AT-2 Treated SIV mac239 and Lactobacillus


The search for a safe and effective vaccine for HIV infection and AIDS remains a major priority in contemporary biomedical research. A recent study performed by the group of Dr. Jean Marie Andrieu has shown that intra-gastric immunization of Chinese rhesus macaques (RMs) with AT-2 inactivated Simian Immunodeficiency Virus of the strain mac239 (SIVmac239) and Lactobacillus plantarum (iSIV+LP) completely protected from high-dose intra-rectal SIVmac239 challenge in 8/8 (100%) of animals challenged at three months post-immunization, and 7/8 animals re-challenged at 14 months post-immunization. In addition, the iSIV+LP immunized macaques showed a marked decrease in peak and set-point viremia when challenged intravenously.

The goal of this project is to determine if the results published by Dr Andrieu and his colleagues can be independently repeated, thereby providing compelling evidence in favor of moving this highly innovative HIV vaccine platform into clinical trials. To this end, we propose to perform an independent immunization and​ challenge experiment in a cohort of 54 Indian origin rhesus macaques (RM) divided in four groups: (i) seventeen animals that will be immunized intra-gastrically with iSIV+LP; (ii) ten animals that will be immunized intra-gastrically with iSIV only; (iii) ten animals that will be immunized intra-gastrically with LP only; and (iv) seventeen animals that will undergo a sham intra-gastric immunization. All RMs included in this study will be challenged intra-rectally with a high-dose of SIVmac239 at 6 months post-immunization, and then followed for ~12 months after challenge with monitoring of the main virological and immunological markers of SIV disease progression. We anticipate that this study will define the potential of LP-based candidate AIDS vaccines. The studies proposed in this project will not involve the use of genetically modified animals, plants, or insects, or recombinant DNA.


1. To test in the preclinical model of immunization and SIV challenge of rhesus macaques the efficacy of a novel regimen composed of inactivated SIV and Lactobacillum plantarum.

2. To define the correlates of immune protection following iSIV-LP vaccination.


In this project we tested an innovative vaccine concept based on immune modulation that was originally developed by the laboratory of Dr. Jean-Marie Andrieu (Wei Lu, et al. Induction of CD8+ Regulatory T Cells Protects Macaques against SIV Challenge. 2012. Cell Reports 2: 1736-46.) Rationale for this approach is provided by the long-standing notion that vaccination may result in immune activation and unwarranted expansion of CD4+ cells that are target for HIV/SIV. In this context, immunizing with an approach that favors immune tolerance may confer protective immunity. In the original study intragastric vaccination of Chinese origin rhesus macaques was performed with a combination of Lactobacillus plantarum (a commensal bacterium that favors immune tolerance) plus inactivated SIV. The hypothesis was that LP would promote immune tolerance to SIV thus preventing the establishment of SIV infection by lowering the number of activated CD4+ target cells. In the Lu et al., study, the vaccine induced CD8+ regulatory T cells that suppressed SIV harboring CD4+ T cell activation and ex vivo SIV replication in 15 of 16 animals without inducing SIV-specific antibodies or robust CTL responses. Of 16 macaques that were intra-rectally challenged with SIVmac239 or heterologous strain SIVB670, 15 showed sterile protection, and in 4 macaques that were re-challenged intravenously, plasma SIV levels peaked slightly and then dropped to undetectable levels, with the animals harboring SIV-DNA in cells. These findings suggested that a new avenue of research toward developing an HIV-1 vaccine—based on these results BMGF funded a confirmatory study to be conducted in our laboratory.

In our study we conducted intra-gastric immunization with 25 mls of preparation (LP + iSIV) every thirty minutes for 3 hours for 5 consecutive days. The study included four experimental groups (total of 54 animals): inactivated SIV+LP=17 animals; inactivated SIV= 10 animals; LP=10 animals; Controls=17 animals (received mock i.g. immunization with water alone). There are two differences between studies: (i) Intrarectal challenge was done with a different stock of SIVmac239 (in our case provided by K. VanRompay at UC Davis); (ii) Chinese vs Indian origin of the rhesus macaques. Prior to the study we conducted a detailed reagent characterization (the reagents were provided by Dr. Andrieu). The characterization was conducted by Dr. Todd Klaenhammer at North Carolina State University for LP and Dr. Jeff Lifson at NCI Fredrick for iSIV. The immunization phase of the study was completed successfully per protocol and the animals were subsequently moved to the challenge phase of the project. Challenge with 10,000 TCID-50 of SIVmac239 resulted in rapid infection in all groups of vaccinated Indian rhesus macaques as well as controls; as such, no significant protective effect as conferred by the tested candidate AIDS vaccine was detected. In addition, challenge with SIVmac239 resulted in similar viral loads in vaccinated vs. control animals. Based on these results we concluded that, in our hands, intra-gastric immunization of Indian rhesus macaques with L. plantarum + iSIV did not induce any protection from intra-rectal challenge with SIVmac239. SIV-infected animals that were vaccinated with LP+iSIV showed similar peak and post-peak viral loads than unvaccinated controls, thus indicating that the tested immunization regimen did not induce any significant post-transmission immune-mediated control of the virus. Based on these results, we concluded that the rationale for moving the combination of LP and iSIV as a candidate HIV vaccine in human trials remains unclear.


Grant at a Glance

Principal Investigator

Guido Silvestri, PhD

Grantee Institution

Emory University, GA, USA

Project Title

Independent Confirmation of Inactivated AT-2 Treated SIV mac239 and Lactobacillus

Grant Award

Up to $2.1 million, awarded November,​ 2013

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