Intragastric Administration of Lactobacillus plantarum and 2,2'-Dithiodipyridine-Inactivated Simian Immunodeficiency Virus (SIV) Does Not Protect Indian Rhesus Macaques from Intrarectal SIV Challenge or Reduce Virus Replication after Transmission

The Immunomodulatory Effects and Applications of Probiotic Lactiplantibacillus plantarum in Vaccine Development

Lactiplantibacillus plantarum (previously known as Lactobacillus plantarum) is a lactic acid bacterium that exists in various niches. L. plantarum is a food-grade microorganism that is commonly considered a safe and beneficial microorganism. It is widely used in food fermentation, agricultural enhancement, and environmental protection. L. plantarum is also part of the normal flora that can regulate the intestinal microflora and promote intestinal health. Some strains of L. plantarum are powerful probiotics that induce and modulate the innate and adaptive immune responses. Due to its outstanding immunoregulatory capacities, an increasing number of studies have examined the use of probiotic L. plantarum strains as natural immune adjuvants or alternative live vaccine carriers. The present review summarizes the main immunomodulatory characteristics of L. plantarum and discusses the preliminary immunological effects of L. plantarum as a vaccine adjuvant and delivery carrier. Different methods for improving the immune capacities of recombinant vector vaccines are also discussed.

Complement Potentiates Immune Sensing of HIV-1 and Early Type I Interferon Responses

Complement-opsonized HIV-1 triggers efficient antiviral type I interferon (IFN) responses in dendritic cells (DCs), which play an important role in protective responses at the earliest stages in retroviral infection. In contrast, HIV-1 suppresses or escapes sensing by STING- and MAVS-associated sensors. Here, we identified a complement receptor-mediated sensing pathway, where DCs are activated in CCR5/RLR (RIG-I/MDA5)/MAVS/TBK1-dependent fashion. Increased fusion of complement-opsonized HIV-1 via complement receptor 4 and CCR5 leads to increased incoming HIV-1 RNA in the cytoplasm, sensed by a nonredundant cooperative effect of RIG-I and MDA5. Moreover, complement-opsonized HIV-1 down-modulated the MAVS-suppressive Raf-1/PLK1 pathway, thereby opening the antiviral recognition pathway via MAVS. This in turn was followed by MAVS aggregation and subsequent TBK1/IRF3/NF-κB activation in DCs exposed to complement- but not non-opsonized HIV-1. Our data strongly suggest that complement is important in the induction of efficient antiviral immune responses by preventing HIV-1 suppressive mechanisms as well as inducing specific cytosolic sensors.

Evidence of a tolerogenic vaccine against AIDS in the Chinese macaque prefigures a potential human vaccine

In 2006 we discovered a new type of mucosal vaccine against simian immunodeficiency virus (SIV) in Chinese macaques. Here, we review 15 years of our published work on this vaccine, which consists of inactivated SIVmac239 particles adjuvanted with Bacillus Calmette-Guérin, Lactobacillus plantarum, or Lactobacillus rhamnosus. Without adjuvant, the vaccine administered by the intragastric route induced the usual SIV-specific humoral and cellular immune responses but provided no protection against intrarectal challenge with SIVmac239. In contrast, out of 24 macaques immunized with the adjuvanted vaccine and challenged intrarectally with SIVmac239 or SIVB670, 23 were sterilely protected for up to five years, while all control macaques were infected. This protection was confirmed by an independent group from the Pasteur Institute. During the past 15 years, we have identified the mechanism of action of the vaccine and discovered that the vaccinated macaques produced a previously unrecognized class of MHC-Ib/E-restricted CD8⁺ T cells (which we refer to as tolerogenic CD8⁺ T cells) that suppressed the activation of SIV-RNA-infected CD4⁺ T cells and thereby inhibited the (activation-dependent) reverse transcription of the virus, which in turn prevented the establishment of SIV infection. Importantly, we discovered also that the tolerogenic CD8⁺ T cell subset observed in vaccinated Chinese macaques could also be found in human elite controllers, a small group of HIV-infected patients in whom these tolerogenic CD8⁺ T cells were shown to naturally suppress viral replication. Given that SIV and HIV require activated immune cells in which to replicate, the specific prevention of activation of SIV-RNA-containing CD4⁺ T cells by a tolerogenic vaccine approach offers an exciting new avenue in HIV vaccine research.

A 30-year journey of trial and error towards a tolerogenic AIDS vaccine

Since 1985, we have tested several immunological approaches to suppressing HIV replication in HIV-infected patients and to prevent HIV acquisition in uninfected people. Here, after briefly reviewing our studies on immunosuppressive treatments and therapeutic dendritic cell-based therapies, we examine in more detail our work on the tolerogenic vaccines we developed against AIDS in Chinese macaques. The vaccine consisted of inactivated SIVmac239 particles adjuvanted with the Bacillus of Calmette and Guerin (BCG), Lactobacillus plantarum (LP), or Lactobacillus rhamnosus (LR). Without adjuvant, the vaccine administered by the intragastric route induced the usual simian immunodeficiency virus (SIV)-specific humoral immune responses but no post-challenge protection. In contrast, out of 24 macaques that were immunized with the adjuvanted vaccine and challenged intrarectally with SIVmac239 or SIVB670, 23 were sterilely protected for up to 5 years, while all control macaques were infected. On the other hand, all macaques of Indian origin that were immunized with the same adjuvanted vaccine were not protected. We then discovered that vaccinated Chinese macaques developed a previously unrecognized class of non-cytolytic MHC-Ib/E-restricted CD8⁺ T cells (or CD8⁺ T-Regs) that suppressed the activation of SIV RNA-infected CD4⁺ T cells and thereby inhibited the (activation-dependent) reverse transcription of the virus and prevented the establishment of SIV infection. Finally, we found a similar population of HLA-E-restricted CD8⁺ T-Regs in human elite controllers (a small group of HIV-infected patients whose viral replication is naturally inhibited). Ex vivo, their CD8⁺ T-Regs suppressed viral replication in the same manner as those of vaccinated Chinese macaques. It is noteworthy that all of these elite controllers had a homo- or heterozygous HLA-Bw4-80I genotype. Taking into account the longevity and the high percentage of vaccine-protected Chinese macaques together with the concomitant identification of a robust ex vivo correlate of protection and the discovery of similar CD8⁺ T-Regs in human elite controllers, preventive and therapeutic HIV vaccines should be envisaged in humans.