Caspase cleavage of gasdermin E causes neuronal pyroptosis in HIV-associated neurocognitive disorder.

Despite effective antiretroviral therapies, 20-30% of persons with treated HIV infection develop a neurodegenerative syndrome termed HIV-associated neurocognitive disorder (HAND). HAND is driven by HIV expression coupled with inflammation in the brain but the mechanisms underlying neuronal damage and death are uncertain. The inflammasome-pyroptosis axis coordinates an inflammatory type of regulated lytic cell death that is underpinned by the caspase-activated pore-forming gasdermin proteins. The mechanisms driving neuronal pyroptosis were investigated herein in models of HAND, using multi-platform molecular and morphological approaches that included brain tissues from persons with HAND and simian immunodeficiency virus (SIV)-infected non-human primates as well as cultured human neurons. Neurons in the frontal cortices from persons with HAND showed increased cleaved gasdermin E (GSDME), which was associated with ß-III tubulin degradation and increased HIV levels. Exposure of cultured human neurons to the HIV-encoded viral protein R (Vpr) elicited time-dependent cleavage of GSDME and Ninjurin-1 (NINJ1) induction with associated cell lysis that was inhibited by siRNA suppression of both proteins. Upstream of GSDME cleavage, Vpr exposure resulted in activation of caspases-1 and 3. Pretreatment of Vpr-exposed neurons with the caspase-1 inhibitor, VX-765, reduced cleavage of both caspase-3 and GSDME, resulting in diminished cell death. To validate these findings, we examined frontal cortical tissues from SIV-infected macaques, disclosing increased expression of GSDME and NINJ1 in cortical neurons, which was co-localized with caspase-3 detection in animals with neurological disease. Thus, HIV infection of the brain triggers the convergent activation of caspases-1 and -3, which results in GSDME-mediated neuronal pyroptosis in persons with HAND. These findings demonstrate a novel mechanism by which a viral infection causes pyroptotic death in neurons while also offering new diagnostic and therapeutic strategies for HAND and other neurodegenerative disorders.

Microbial molecule ingress promotes neuroinflammation and brain CCR5 expression in persons with HIV-associated neurocognitive disorders.

BACKGROUND: Systemic inflammation accompanies HIV-1 infection, resulting in microbial translocation from different tissues. We investigated interactions between lentivirus infections, neuroinflammation and microbial molecule presence in the brain. METHODS: Brain tissues from adult humans with (n = 22) and without HIV-1 (n = 11) infection as well as adult nonhuman primates (NHPs) with (n = 11) and without (n = 4) SIVmac251 infection were investigated by RT-PCR/ddPCR, immunofluorescence and western blotting. Studies of viral infectivity, host immune gene expression and viability were performed in primary human neural cells. FINDINGS: Among NHPs, SIV DNA quantitation in brain showed increased levels among animals with SIV encephalitis (n = 5) that was associated with bacterial genomic copy number as well as CCR5 and CASP1 expression in brain. Microbial DnaK and peptidoglycan were immunodetected in brains from uninfected and SIV-infected animals, chiefly in glial cells. Human microglia infected by HIV-1 showed increased p24 production after exposure to peptidoglycan that was associated CCR5 induction. HIV-1 Vpr application to human neurons followed by peptidoglycan exposure resulted in reduced mitochondrial function and diminished beta-III tubulin expression. In human brains, bacterial genome copies (250-550 copies/gm of tissue), were correlated with increased bacterial rRNA and GroEL transcript levels in patients with HIV-associated neurocognitive disorders (HAND). Glial cells displayed microbial GroEL and peptidoglycan immunoreactivity accompanied by CCR5 induction in brains from patients with HAND. INTERPRETATION: Increased microbial genomes and proteins were evident in brain tissues from lentivirus-infected humans and animals and associated with neurological disease. Microbial molecule translocation into the brain might exacerbate neuroinflammatory disease severity and represent a driver of lentivirus-associated brain disease.

Immunogenicity and efficacy of one and two doses of Ad26.COV2.S COVID vaccine in adult and aged NHP.

Safe and effective coronavirus disease-19 (COVID-19) vaccines are urgently needed to control the ongoing pandemic. While single-dose vaccine regimens would provide multiple advantages, two doses may improve the magnitude and durability of immunity and protective efficacy. We assessed one- and two-dose regimens of the Ad26.COV2.S vaccine candidate in adult and aged nonhuman primates (NHPs). A two-dose Ad26.COV2.S regimen induced higher peak binding and neutralizing antibody responses compared with a single dose. In one-dose regimens, neutralizing antibody responses were stable for at least 14 wk, providing an early indication of durability. Ad26.COV2.S induced humoral immunity and T helper cell (Th cell) 1-skewed cellular responses in aged NHPs that were comparable to those in adult animals. Aged Ad26.COV2.S-vaccinated animals challenged 3 mo after dose 1 with a SARS-CoV-2 spike G614 variant showed near complete lower and substantial upper respiratory tract protection for both regimens. Neutralization of variants of concern by NHP sera was reduced for B.1.351 lineages while maintained for the B.1.1.7 lineage independent of Ad26.COV2.S vaccine regimen.

Needle-free delivery of DNA: Targeting of hemagglutinin to MHC class II molecules protects rhesus macaques against H1N1 influenza.

Conventional influenza vaccines are hampered by slow and limited production capabilities, whereas DNA vaccines can be rapidly produced for global coverage in the event of an emerging pandemic. However, a drawback of DNA vaccines is their generally low immunogenicity in non-human primates and humans. We have previously demonstrated that targeting of influenza hemagglutinin to human HLA class II molecules can increase antibody responses in larger animals such as ferrets and pigs. Here, we extend these observations by immunizing non-human primates (rhesus macaques) with a DNA vaccine encoding a bivalent fusion protein that targets influenza virus hemagglutinin (HA) to Mamu class II molecules. Such immunization induced neutralizing antibodies and antigen-specific T cells. The DNA was delivered by pain- and needle-free jet injections intradermally. No adverse effects were observed. Most importantly, the immunized rhesus macaques were protected against a challenge with influenza virus.

Strong vaccine-induced CD8 T-cell responses have cytolytic function in a chimpanzee clearing HCV infection.

A single correlate of effective vaccine protection against chronic HCV infection has yet to be defined. In this study, we analyzed T-cell responses in four chimpanzees, immunized with core-E1-E2-NS3 and subsequently infected with HCV1b. Viral clearance was observed in one animal, while the other three became chronically infected. In the animal that cleared infection, NS3-specific CD8 T-cell responses were observed to be more potent in terms of frequency and polyfunctionality of cytokine producing cells. Unique to this animal was the presence of killing-competent CD8 T-cells, specific for NS3 1258-1272, being presented by the chimpanzee MHC class I molecule Patr-A*03∶01, and a high affinity recognition of this epitope. In the animals that became chronically infected, T-cells were able to produce cytokines against the same peptide but no cytolysis could be detected. In conclusion, in the animal that was able to clear HCV infection not only cytokine production was observed but also cytolytic potential against specific MHC class I/peptide-combinations.

DNA/long peptide vaccination against conserved regions of SIV induces partial protection against SIVmac251 challenge.

OBJECTIVES: We recently developed a HIVconsv vaccine strategy, consisting of combined conserved regions of HIV-1, to adequately cover viral diversity. To evaluate efficacy in nonhuman primates, an equivalent SIV-derived immunogen SIVconsv was designed and delivered as plasmid DNA or synthetic long peptides. DESIGN: Rhesus macaques lacking protective MHC class I alleles Mamu-A*001 : 01, B*008 : 01, B*017 : 01 were immunized with either SIVconsv synthetic long peptides (S) alone or in combination with plasmid DNA encoding the same conserved regions (D) using SSS or DDSS regimens. METHODS: The SIVconsv synthetic long peptide vaccine consisted of 46 approximately 30-amino acid-long peptides emulsified in Montanide ISA-720 and adjuvanted with pegylated type I interferon and imiquimod. RESULTS: Both SSS and DDSS regimens generated high frequencies of SIV-specific IFN-γ-producing cells comparable with reported adenoviral vector systems. Strong polyfunctional CD4⁺ T-cell and modest CD8⁺ T-cell responses were generated, which were of central memory T-cell phenotype. Furthermore, SIVconsv-specific antibody responses were induced capable of recognizing the Env glycoprotein. Eight weeks after the last immunization, control and SIVconsv-vaccinated animals were challenged intrarectally with 10 MID50 of pathogenic SIVmac251. Two out of six animals in the DDSS group were protected against infection, while all 14 animals in the SSS and two control groups were infected. Vaccine induced SIV-specific IgG responses in mucosal washes prechallenge were highest in the two protected animals. CONCLUSION: This study demonstrates that vaccine-elicited responses towards conserved regions can afford partial protection against a high-dose intrarectal SIVmac251 challenge.

Immunization with apoptotic pseudovirus transduced cells induces both cellular and humoral responses: a proof of concept study in macaques.

Dendritic cells are able to present viral antigens to T-cells after uptake of apoptotic bodies derived from virus-infected cells. Immunization with virus-infected apoptotic cells was previously shown to induce HIV-specific immune responses in mice. Here we evaluate the safety and immunogenicity of immunization with activated apoptotic cells in non-human primates using autologous T-cells infected with replication defective VSV pseudotyped SIV(mac239)Δenv. Animals were immunized with γ-irradiated activated T-cells carrying the VSVenvSIV(mac239)Δenv pseudovirus. SIV Gag-specific cellular immune responses were induced as early as two weeks after the first immunization eliciting a biased IFN-γ and IL-2 response. In addition, induction of SIV Gag-specific antibody responses and high titer neutralizing activity against the SIV pseudovirus harboring a VSV-env were detected after two immunizations. The vaccinated group and a control group of Chinese rhesus macaques were intravenously challenged with pathogenic SIV(mac251.) All animals became infected, but SIV-replication was effectively suppressed (below 100 copies/ml) in several animals in both groups. However the group immunized with apoptotic cells revealed better preservation of the gut CD4(+) T-cell compartment. Viral control was inversely correlated with an early (4 weeks) but transient increase in the percentage of Ki67(+)CD4(+) peripheral blood T-cells (Spearman -0.73). We here show that immunizations with activated apoptotic lymphocytes expressing transduced SIV genes result in induction of both cellular and humoral immune responses. This study provides evidence for an immunological principle demonstrating that certain apoptotic cells can be considered as carriers of antigens directing immune responses in macaques.

Herpesvirus saimiri infection of rhesus macaques: a model for acute rhadinovirus-induced t-cell transformation and oncogenesis.

Herpesvirus saimiri (HVS) causes acute lymphoma and leukemia upon experimental infection of various monkey species. HVS strain C488 is also capable of transforming human T-lymphocytes to stable growth in culture. The most susceptible species for oncogenesis are New World primates, in particular the cottontop tamarin (Saguinus oedipus). However, Old World monkeys such as macaques are the most used animal model for the close-to-human situation. The limited data on HVS infection in Old World monkeys prompted us to investigate susceptibility to infection and disease induction by HVS in macaques. After having established that rhesus macaques can be infected productively, and that rhesus T-cells can be transformed in vivo by HVS, we observed induction of lymphoma in all inoculated animals. Pre-existing humoral immunity in part of the rhesus colony capable of blocking HVS infection could be overcome by preselecting rhesus macaques for lack of this immunity of unknown origin. HVS infection of rhesus macaques as compared to that of New World monkeys has the advantages that disease progression is more prolonged, and larger blood volumes can be collected, which allows more extended analyses. Also, rhesus monkeys are the best immunologically and immunogenetically characterized primate species next to humans. This model could be useful for the evaluation of candidate tumor vaccines and to test novel approaches for cancer immunotherapy. In addition, HVS infection of macaques could eventually be useful as a surrogate model to address certain questions in rhadinovirus-induced human cancer such as effusion lymphoma or Kaposi's sarcoma.

Clearance of genotype 1b hepatitis C virus in chimpanzees in the presence of vaccine-induced E1-neutralizing antibodies.

Accumulating evidence indicates that neutralizing antibodies play an important role in protection from chronic hepatitis C virus (HCV) infection. Efforts to elicit such responses by immunization with intact heterodimeric E1E2 envelope proteins have met with limited success. To determine whether antigenic sites, which are not exposed by the combined E1E2 heterodimer structure, are capable of eliciting neutralizing antibody responses, we expressed and purified each as separate recombinant proteins E1 and E2, from which the immunodominant hypervariable region (HVR-1) was deleted. Immunization of chimpanzees with either E1 or E2 alone induced antigen-specific T-helper cytokines of similar magnitude. Unexpectedly, the capacity to neutralize HCV was observed in E1 but not in animals immunized with E2 devoid of HVR-1. Furthermore, in vivo only E1-vaccinated animals exposed to the heterologous HCV-1b inoculum cleared HCV infection.

No difference in Gag and Env immune-response profiles between vaccinated and non-vaccinated rhesus macaques that control immunodeficiency virus replication.

Recent advances in human immunodeficiency virus (HIV) vaccine design have resulted in induction of strong CD4 T-cell proliferative and polyfunctional cytokine responses, which are also characteristic for long-term non-progressing (LTNP) HIV-infected individuals. However, limited information is available on the persistence of these responses after infection. Results from studies in non-human primates indicate that vaccine-induced immune responses are partially maintained upon viral infection and differ from the responses seen in non-vaccinated animals that typically progress to disease. However, it is unclear how these partially preserved responses compare to immune responses that are acquired naturally by LTNP animals. In this study, immune-response profiles were compared between vaccinated animals that, upon SHIV89.6 challenge, became infected but were able to control virus replication, and a group of animals having spontaneous control of this viral infection. Both groups were found to develop very similar immune responses with regard to induction of CD4 and CD8 T-cell polyfunctional cytokine responses, proliferative capacity and cytotoxic capacity, as measured by a standard 51Cr release assay and more direct ex vivo and in vivo CTL assays. Hence, vaccinated animals that become infected, but control infection, appear to establish immune responses that are similar to those elicited by long-term non-progressors.

CD8+ NK cells are predominant in chimpanzees, characterized by high NCR expression and cytokine production, and preserved in chronic HIV-1 infection.

HIV-1 infection in humans results in an early and progressive NK cell dysfunction and an accumulation of an "anergic" CD56- CD16+ NK subset, which is characterised by low natural cytotoxicity receptor expression and low cytokine producing capacity. In contrast to humans, chimpanzee NK cells do not display a distinguishable CD56(bright) and CD56(dim) subset but, as shown here, could be subdivided into functionally different CD8+ and CD8- subsets. The CD8+ NK cells expressed significantly higher levels of triggering receptors including NKp46 and, upon in vitro activation, produced more IFN-gamma, TNF-alpha and CD107 than their CD8- counterparts. In addition, chimpanzee CD8- NK cells had relatively high levels of HLA-DR expression, suggestive of an activated state. Killing inhibitory receptors were expressed only at low levels; however, upon in vitro stimulation, they were up-regulated in CD8+ but not in CD8- NK cells and were functionally capable of inhibiting NKp30-triggered killing. In contrast to HIV-1-infected humans, infected chimpanzees maintained their dominant CD8+ NK cell population, with high expression of natural cytotoxicity receptors.

Acute-phase CD4+ T-cell proliferation and CD152 upregulation predict set-point virus replication in vaccinated simian-human immunodeficiency virus strain 89.6p-infected macaques.

Human immunodeficiency virus (HIV) infection in humans and simian immunodeficiency virus (SIV) infection in macaques are accompanied by a combined early loss of CCR5 (CD195)-expressing CD4(+) memory T cells, loss of T-helper function and T-cell hyperactivation, which have all been associated with development of high virus load and disease progression. Here, a cohort of vaccinated simian-human immunodeficiency virus strain 89.6p (SHIV(89.6p))-infected rhesus macaques, where preferential depletion of these memory T-cell subsets does not take place and CD4(+) T cells are relatively well maintained, was used to study the role of hyperactivation as an independent factor in the establishment of set-point virus load. In the acute phase of the infection, a transient loss of CD4(+) T cells, as well as strong increases in expression of proliferation and activation markers on CD4(+) and CD8(+) T cells, together with CD152 expression on CD4(+) T cells, were observed. Peak expression levels of these markers on CD4(+) T cells, but not on CD8(+) T cells, were correlated with high virus replication in the chronic phase of the infection. In addition, the peak expression level of these markers was correlated inversely with acute-phase, but not chronic-phase, HIV/SIV-specific gamma interferon responses. These data highlight a central role for an acute but transient CD4 decrease, as well as CD4(+) T-cell activation, as independent factors for prediction of set-point levels of virus replication.

Systemic neutralizing antibodies induced by long interval mucosally primed systemically boosted immunization correlate with protection from mucosal SHIV challenge.

Immune correlates of vaccine protection from HIV-1 infection would provide important milestones to guide HIV-1 vaccine development. In a proof of concept study using mucosal priming and systemic boosting, the titer of neutralizing antibodies in sera was found to correlate with protection of mucosally exposed rhesus macaques from SHIV infection. Mucosal priming consisted of two sequential immunizations at 12-week intervals with replicating host range mutants of adenovirus type 5 (Ad5hr) expressing the HIV-1(89.6p) env gene. Following boosting with either heterologous recombinant protein or alphavirus replicons at 12-week intervals animals were intrarectally exposed to infectious doses of the CCR5 tropic SHIV(SF162p4). Heterologous mucosal prime systemic boost immunization elicited neutralizing antibodies (Nabs), antibody-dependent cytotoxicity (ADCC), and specific patterns of antibody binding to envelope peptides. Vaccine induced protection did not correlate with the type of boost nor T-cell responses, but rather with the Nab titer prior to exposure.

Chimpanzee CD4+ T cells are relatively insensitive to HIV-1 envelope-mediated inhibition of CD154 up-regulation.

CD40-CD154 interaction forms a key event in regulation of crosstalk between dendritic cells and CD4 T cells. In human immunodeficiency virus (HIV)-1 infected patients CD154 expression is impaired, and the resulting loss of immune responsiveness by CD4+ T cells contributes to a progressive state of immunodeficiency in humans. Although chimpanzees are susceptible to chronic HIV-1/SIVcpz infection, they are relatively resistant to the onset of AIDS. This relative resistance is characterized by maintenance of CD4+ T cell populations and function, which is highly compromised in human patients. In our cohort of chronically HIV-1- and SIVcpz-infected chimpanzees, we demonstrated the capacity to produce IL-2, following CD3/CD28 stimulation, as well as preserved CD154 up-regulation. Cross-linking of CD4 with mAb was found to inhibit CD3/CD28-induced up-regulation of CD154 equally in chimpanzees and humans. However, specific cross-linking with trimeric recombinant HIV-1 gp140 revealed reduced sensitivity for inhibition of CD154 up-regulation in chimpanzees, requiring fourfold higher concentrations of viral protein. Chimpanzee CD4+ T cells are thus less sensitive to the immune-suppressive effect of low-dose HIV-1 envelope protein than human CD4+ T cells.

Aerosol immunization with NYVAC and MVA vectored vaccines is safe, simple, and immunogenic.

Each year, approximately five million people die worldwide from putatively vaccine-preventable mucosally transmitted diseases. With respect to mass vaccination campaigns, one strategy to cope with this formidable challenge is aerosol vaccine delivery, which offers potential safety, logistical, and cost-saving advantages over traditional vaccination routes. Additionally, aerosol vaccination may elicit pivotal mucosal immune responses that could contain or eliminate mucosally transmitted pathogens in a preventative or therapeutic vaccine context. In this current preclinical non-human primate investigation, we demonstrate the feasibility of aerosol vaccination with the recombinant poxvirus-based vaccine vectors NYVAC and MVA. Real-time in vivo scintigraphy experiments with radiolabeled, aerosol-administered NYVAC-C (Clade C, HIV-1 vaccine) and MVA-HPV vaccines revealed consistent mucosal delivery to the respiratory tract. Furthermore, aerosol delivery of the vaccines was safe, inducing no vaccine-associated pathology, in particular in the brain and lungs, and was immunogenic. Administration of a DNA-C/NYVAC-C prime/boost regime resulted in both systemic and anal-genital HIV-specific immune responses that were still detectable 5 months after immunization. Thus, aerosol vaccination with NYVAC and MVA vectored vaccines constitutes a tool for large-scale vaccine efforts against mucosally transmitted pathogens.

Immune-response profiles induced by human immunodeficiency virus type 1 vaccine DNA, protein or mixed-modality immunization: increased protection from pathogenic simian-human immunodeficiency virus viraemia with protein/DNA combination.

Current data suggest that prophylactic human immunodeficiency virus type 1 (HIV) vaccines will be most efficacious if they elicit a combination of adaptive humoral and T-cell responses. Here, we explored the use of different vaccine strategies in heterologous prime-boost regimes and evaluated the breadth and nature of immune responses in rhesus monkeys induced by epidermally delivered plasmid DNA or recombinant HIV proteins formulated in the AS02A adjuvant system. These immunogens were administered alone or as either prime or boost in mixed-modality regimes. DNA immunization alone induced cell-mediated immune (CMI) responses, with a strong bias towards Th1-type cytokines, and no detectable antibodies to the vaccine antigens. Whenever adjuvanted protein was used as a vaccine, either alone or in a regime combined with DNA, high-titre antibody responses to all vaccine antigens were detected in addition to strong Th1- and Th2-type CMI responses. As the vaccine antigens included HIV-1 Env, Nef and Tat, as well as simian immunodeficiency virus (SIV)mac239 Nef, the animals were subsequently exposed to a heterologous, pathogenic simian-human immunodeficiency virus (SHIV)89.6p challenge. Protection against sustained high virus load was observed to some degree in all vaccinated groups. Suppression of virus replication to levels below detection was observed most frequently in the group immunized with protein followed by DNA immunization, and similarly in the group immunized with DNA alone. Interestingly, control of virus replication was associated with increased SIV Nef- and Gag-specific gamma interferon responses observed immediately following challenge.

Systemic mobilization of antigen presenting cells, with a chimeric Flt-3 and G-CSF receptor agonist, during immunization of Macaca mulatta with HIV-1 antigens is insufficient to modulate immune responses or vaccine efficacy.

In order to improve the efficacy of current vaccine candidates against HIV/AIDS, we sought to strengthen the induction of immune responses via simultaneous in vivo mobilization of dendritic cells using a chimeric Flt-3 and G-CSF receptor agonists (ProGP). We investigated ProGP treatment in combination with two DNA immunizations encoding HIV-Env89.6, SIV-Gag proteins to increase the priming of immune responses. Administration of this Flt-3/G-CSF chimera elicited marked increases in numbers of both plasmacytoid and myeloid dendritic cells. However, there was no increase seen in T-cell responses either directly following the DNA immunization or after further boosting with MVA vectors expressing HIV-Env89.6p, SIV-Gag. After challenge with SHIV89.6p all animals became infected and no differences were seen between the ProGP treated versus the control group with regard to plasma virus load or CD4 T-cell count. We conclude that besides mobilization of dendritic cells additional stimuli to induce dendritic cell maturation may be needed for avid boosting of antigen specific immune activation.

Molecular and functional characterization of NKG2D, NKp80, and NKG2C triggering NK cell receptors in rhesus and cynomolgus macaques: monitoring of NK cell function during simian HIV infection.

An involvement of innate immunity and of NK cells during the priming of adaptive immune responses has been recently suggested in normal and disease conditions such as HIV infection and acute myelogenous leukemia. The analysis of NK cell-triggering receptor expression has been so far restricted to only NKp46 and NKp30 in Macaca fascicularis. In this study, we extended the molecular and functional characterization to the various NK cell-triggering receptors using PBMC and to the in vitro-derived NK cell populations by cytofluorometry and by cytolytic activity assays. In addition, RT-PCR strategy, cDNA cloning/sequencing, and transient transfections were used to identify and characterize NKp80, NKG2D, CD94/NKG2C, and CD94/NKG2A in M. fascicularis and Macaca mulatta as well as in the signal transducing polypeptide DNAX-activating protein DAP-10. Both M. fascicularis and M. mulatta NK cells express NKp80, NKG2D, and NKG2C molecules, which displayed a high degree of sequence homology with their human counterpart. Analysis of NK cells in simian HIV-infected M. fascicularis revealed reduced surface expression of selected NK cell-triggering receptors associated with a decreased NK cell function only in some animals. Overall surface density of NK cell-triggering receptors on peripheral blood cells and their triggering function on NK cell populations derived in vitro was not decreased compared with uninfected animals. Thus, triggering NK cell receptor monitoring on macaque NK cells is possible and could provide a valuable tool for assessing NK cell function during experimental infections and for exploring possible differences in immune correlates of protection in humans compared with cynomolgus and rhesus macaques undergoing different vaccination strategies.

Increase in plasmacytoid and myeloid dendritic cells by progenipoietin-1, a chimeric Flt-3 and G-CSF receptor agonist, in SIV-Infected rhesus macaques.

As in HIV-1 infection in humans, SIVsm infection of rhesus macaques causes a slow progressive loss of CD4 T-cells followed by the onset of AIDS. In addition, there is a loss of dendritic cells (DC) in peripheral blood, peripheral lymphoid tissues, and the skin. Increasing the number of CD4 T cells and DC may be an important step in restoring immune competence and thus delay disease progression. Recently, progenipoietins (ProGP), a new family of chimeric Flt3 and G-CSF receptor agonists, were demonstrated to possess the capacity to mobilize hematopoietic progenitor cells in normal rhesus monkeys. In addition, these molecules induced increased numbers of myeloid cells, including dendritic cells, in the blood. Here we demonstrate that SIVsm-infected macaques, treated with ProGP-1, developed increased numbers of both plasmacytoid (CD123+, CD11c-) and myeloid (both CD11b+, CD11c+, and CD123-, CD11c+ subsets) DC and CD4 and CD8 T cells in peripheral blood. Importantly, during treatment, no changes in plasma virus load were observed. After 14 to 20 days of treatment, antibodies were formed against ProGP in all animals. As a consequence, white blood cell levels returned to baseline in several animals. In other animals values only returned to baseline after termination of ProGP treatment. In conclusion, ProGP-1 may be used to generate a transient increase in DC as well as CD4 T-cell numbers, thereby creating a window of opportunity for immunotherapeutic intervention.