A Single Dose SARS-CoV-2 Replicon RNA Vaccine Induces Cellular and Humoral Immune Responses in Simian Immunodeficiency Virus Infected and Uninfected Pigtail Macaques

The ongoing COVID-19 vaccine rollout is critical for reducing SARS-CoV-2 infections, hospitalizations, and deaths worldwide. Unfortunately, massive disparities exist in getting vaccines to vulnerable populations, including people living with HIV. Preliminary studies indicate that COVID-19 mRNA vaccines are safe and immunogenic in people living with HIV that are virally suppressed with potent antiretroviral therapy but may be less efficacious in immunocompromised individuals. This raises the concern that COVID-19 vaccines may be less effective in resource poor settings with limited access to antiretroviral therapy. Here, we evaluated the immunogenicity of a single dose COVID-19 replicon RNA vaccine expressing Spike protein (A.1) from SARS-CoV-2 (repRNA-CoV2S) in immunocompromised, SIV infected and immune competent, naïve pigtail macaques. Moderate vaccine-specific cellular Th1 T-cell responses and binding and neutralizing antibodies were induced by repRNA-CoV2S in SIV infected animals and naïve animals. Furthermore, vaccine immunogenicity was elicited even among the animals with the highest SIV viral burden or lowest peripheral CD4 counts prior to immunization. This study provides evidence that a SARS-CoV-2 repRNA vaccine could be employed to induce strong immunity against COVID-19 in HIV infected and other immunocompromised individuals.

Simultaneous in vivo Pharmacokinetics and Pharmacodynamics of TDF Intravaginal Ring during High-dose Vaginal SHIV Challenge in Pigtail Macaques

The demonstration of complete protection of macaques in a repeated low dose virus challenge by a tenofovir disoproxil fumarate (TDF) intravaginal ring (IVR) and the success of the dapivirine IVR in clinical trials highlighted the potential of IVRs as pre-exposure prophylaxis against HIV. Efficacy of TDF ring was not investigated in sexually active women. Our understanding of the mechanisms of protection is limited. To address this knowledge gap, we performed simultaneous pharmacokinetic and pharmacodynamic analysis of a TDF-IVR at the site of SIV challenge in pigtail macaques at the anatomical and cellular level. Specifically, we challenged TDF-IVR administered pigtail macaques with a single high dose of a non-replicative SIV-based vector containing a dual reporter system that helped us to identify the earliest targets of SIV infection within the mucosa. Two and three days after challenge, the macaques were euthanized and tenofovir (TFV) concentrations were measured in the female reproductive tract (FRT) by HPLC-MS/MS to correlate drug concentrations and SIV-vector transduction efficiency. TFV formed a gradient through the mucosal tissue, with the highest concentrations near the ring, in the upper vagina and endocervix. Despite this, several transduction events were identified with the most common sites being in the ovaries. Moreover, proviral DNA was detected in the cervix and vagina. Thus, our studies demonstrate an uneven distribution of TFV in the FRT of macaques after release from a TDF-IVR that leads to incomplete FRT protection from high viral dose challenge.

Differentiation of Cardiomyocytes and Identification of Cardiac Conduction System Connexins Derived from Bone Marrow Mesenchymal Stem Cells of Macaca nemestrina

Bone marrow mesenchymal stem cells have been widely used, because plasticity, specific surface markers, self-renewal to transform into various lineages including cardiomyocytes. Information about the connexin (Cx) cardiac conduction systems of the pigtail macaque (Macaca nemestrina) is limited. This study aimed to evaluate cardiomyocyte differentiation from bone marrow mesenchymal stem cells of pigtail macaques and to clarify the Cx cardiac conduction system. Bone marrow aspirates were obtained from the proximal humerus of four adult male pigtail macaques, collected into heparinized tubes, then centrifuged to obtain mononuclear cells that were isolated and cultured in an incubator. After these cells reached 70–80% monolayer confluency as homogeneous fibroblast-like cells, they were subcultured. On the second subculture passage, the cells were pelleted to extract the mRNA, which was analysed by reverse transcription–polymerase chain reaction, and then cultured for a third passage. Cells were positive for CD73 and CD105 and the reference gene glyceraldehyde-3-phosphate dehydrogenase, and negative for CD34 and CD45. Osteogenic, chondrogenic, adipogenic, and cardiomyocyte differentiation was confirmed based on specific staining. The pigtail macaque bone marrow mesenchymal stem cells can be isolated and subcultured. The transcription of genes and translation of proteins of the connexin cardiac conduction systems was successfully identified.

Derivation of simian tropic HIV-1 infectious clone reveals virus adaptation to a new host

To replicate in a new host, lentiviruses must adapt to exploit required host factors and evade species-specific antiviral proteins. Understanding how host protein variation drives lentivirus adaptation allowed us to expand the host range of HIV-1 to pigtail macaques. We have previously derived a viral swarm (in the blood of infected animals) that can cause AIDS in this new host. To further exploit this reagent, we generated infectious molecular clones (IMCs) from the viral swarm. We identified clones with high replicative capacity in pigtail peripheral blood mononuclear cells (PBMC) in vitro and used in vivo replication to select an individual IMC, named stHIV-A19 (for simian tropic HIV-1 clone A19), which recapitulated the phenotype obtained with the viral swarm. Adaptation of HIV-1 in macaques led to the acquisition of amino acid changes in viral proteins, such as capsid (CA), that are rarely seen in HIV-1–infected humans. Using stHIV-A19, we show that these CA changes confer a partial resistance to the host cell inhibitor Mx2 from pigtail macaques, but that complete resistance is associated with a fitness defect. Adaptation of HIV-1 to a new host will lead to a more accurate animal model and a better understanding of virus–host interactions.