Shuttle peptide delivers base editor RNPs to rhesus monkey airway epithelial cells in vivo

Gene editing strategies for cystic fibrosis are challenged by the complex barrier properties of airway epithelia. We previously reported that the amphiphilic S10 shuttle peptide non-covalently combined with CRISPR-associated (Cas) ribonucleoprotein (RNP) enabled editing of human and mouse airway epithelial cells. Here, we derive the S315 peptide as an improvement over S10 in delivering base editor RNP. Following intratracheal aerosol delivery of Cy5-labeled peptide in rhesus macaques, we confirm delivery throughout the respiratory tract. Subsequently, we target CCR5 with co-administration of ABE8e-Cas9 RNP and S315. We achieve editing efficiencies of up-to 5.3% in rhesus airway epithelia. Moreover, we document persistence of edited epithelia for up to 12 months in mice. Finally, delivery of ABE8e-Cas9 targeting the CFTR R553X mutation restores anion channel function in cultured human airway epithelia. These results demonstrate the therapeutic potential of base editor delivery with S315 to functionally correct the CFTR R553X mutation in respiratory epithelia.

Dynamics of temporal immune responses in nonhuman primates and humans immunized with COVID-19 vaccines

We assessed the humoral immune responses to a COVID-19 vaccine in a well-controlled rhesus macaque model compared to humans immunized with two mRNA vaccines over several months post-second dose. The plasma IgG levels against seven coronaviruses (including SARS-CoV-2) and antibody subtypes (IgG 1-4 and IgM) against SARS-CoV-2 were evaluated using multiplex assays. The neutralization capacity of plasma antibodies against the original SAR-CoV-2 isolate and nine variants was evaluated in vaccinated humans and non-human primates. Immunization of macaques and humans with SARS-CoV-2 vaccines induced a robust neutralizing antibody response. In non-SIV-infected adult macaques immunized with an adenoviral vector expressing S-RBD (n = 7) or N protein (n = 3), elevated levels of IgG and neutralizing antibodies were detected 2 weeks post-second dose. Immune responses to the S-RBD vaccine in SIV-infected adult macaques (n = 2) were similar to the non-SIV-infected animals. Adult humans immunized with Pfizer (n = 35) or Moderna (n = 18) vaccines developed IgG and neutralizing antibodies at 4 weeks post-second dose. In both vaccine groups, IgG 1 was the predominant subtype, followed by IgG 3. The IgG levels, including total and IgG 1,2,3 elicited by the Moderna vaccine, were significantly higher than the corresponding levels elicited by the Pfizer vaccine at 4 weeks post-second dose. A significant correlation was observed between the plasma total IgG antibody levels and neutralization titers in both macaques and humans. Furthermore, broad-spectrum neutralization antibodies against several variants of SARS-CoV-2 were detected in the plasma of both macaques and humans after two vaccinations.

FcRγ- NK Cell Induction by Specific Cytomegalovirus and Expansion by Subclinical Viral Infections in Rhesus Macaques

"Adaptive" NK cells, characterized by FcRγ deficiency and enhanced responsiveness to Ab-bound, virus-infected cells, have been found in certain hCMV-seropositive individuals. Because humans are exposed to numerous microbes and environmental agents, specific relationships between hCMV and FcRγ-deficient NK cells (also known as g-NK cells) have been challenging to define. Here, we show that a subgroup of rhesus CMV (RhCMV)-seropositive macaques possesses FcRγ-deficient NK cells that stably persist and display a phenotype resembling human FcRγ-deficient NK cells. Moreover, these macaque NK cells resembled human FcRγ-deficient NK cells with respect to functional characteristics, including enhanced responsiveness to RhCMV-infected target in an Ab-dependent manner and hyporesponsiveness to tumor and cytokine stimulation. These cells were not detected in specific pathogen-free (SPF) macaques free of RhCMV and six other viruses; however, experimental infection of SPF animals with RhCMV strain UCD59, but not RhCMV strain 68-1 or SIV, led to induction of FcRγ-deficient NK cells. In non-SPF macaques, coinfection by RhCMV with other common viruses was associated with higher frequencies of FcRγ-deficient NK cells. These results support a causal role for specific CMV strain(s) in the induction of FcRγ-deficient NK cells and suggest that coinfection by other viruses further expands this memory-like NK cell pool.

Encapsulated Allografts Preclude Host Sensitization and Promote Ovarian Endocrine Function in Ovariectomized Young Rhesus Monkeys and Sensitized Mice

Transplantation of allogeneic donor ovarian tissue holds great potential for female cancer survivors who often experience premature ovarian insufficiency. To avoid complications associated with immune suppression and to protect transplanted ovarian allografts from immune-mediated injury, we have developed an immunoisolating hydrogel-based capsule that supports the function of ovarian allografts without triggering an immune response. Encapsulated ovarian allografts implanted in naïve ovariectomized BALB/c mice responded to the circulating gonadotropins and maintained function for 4 months, as evident by regular estrous cycles and the presence of antral follicles in the retrieved grafts. In contrast to non-encapsulated controls, repeated implantations of encapsulated mouse ovarian allografts did not sensitize naïve BALB/c mice, which was confirmed with undetectable levels of alloantibodies. Further, encapsulated allografts implanted in hosts previously sensitized by the implantation of non-encapsulated allografts restored estrous cycles similarly to our results in naïve recipients. Next, we tested the translational potential and efficiency of the immune-isolating capsule in a rhesus monkey model by implanting encapsulated ovarian auto- and allografts in young ovariectomized animals. The encapsulated ovarian grafts survived and restored basal levels of urinary estrone conjugate and pregnanediol 3-glucuronide during the 4- and 5-month observation periods. We demonstrate, for the first time, that encapsulated ovarian allografts functioned for months in young rhesus monkeys and sensitized mice, while the immunoisolating capsule prevented sensitization and protected the allograft from rejection.

SIV clearance from neonatal macaques following transient CCR5 depletion

Treatment of people with HIV (PWH) with antiretroviral therapy (ART) results in sustained suppression of viremia, but HIV persists indefinitely as integrated provirus in CD4-expressing cells. Intact persistent provirus, the "rebound competent viral reservoir" (RCVR), is the primary obstacle to achieving a cure. Most variants of HIV enter CD4 + T cells by binding to the chemokine receptor, CCR5. The RCVR has been successfully depleted only in a handful of PWH following cytotoxic chemotherapy and bone marrow transplantation from donors with a mutation in CCR5 . Here we show that long-term SIV remission and apparent cure can be achieved for infant macaques via targeted depletion of potential reservoir cells that express CCR5. Neonatal rhesus macaques were infected with virulent SIVmac251, then treated with ART beginning one week after infection, followed by treatment with either a CCR5/CD3-bispecific or a CD4-specific antibody, both of which depleted target cells and increased the rate of plasma viremia decrease. Upon subsequent cessation of ART, three of seven animals treated with CCR5/CD3-bispecific antibody rebounded quickly and two rebounded 3 or 6 months later. Remarkably, the other two animals remained aviremic and efforts to detect replication-competent virus were unsuccessful. Our results show that bispecific antibody treatment can achieve meaningful SIV reservoir depletion and suggest that functional HIV cure might be achievable for recently infected individuals having a restricted reservoir.

Cytomegalovirus infection disrupts the influence of short-chain fatty acid producers on Treg/Th17 balance

BACKGROUND

Both the gut microbiota and chronic viral infections have profound effects on host immunity, but interactions between these influences have been only superficially explored. Cytomegalovirus (CMV), for example, infects approximately 80% of people globally and drives significant changes in immune cells. Similarly, certain gut-resident bacteria affect T-cell development in mice and nonhuman primates. It is unknown if changes imposed by CMV on the intestinal microbiome contribute to immunologic effects of the infection.

RESULTS

We show that rhesus cytomegalovirus (RhCMV) infection is associated with specific differences in gut microbiota composition, including decreased abundance of Firmicutes, and that the extent of microbial change was associated with immunologic changes including the proliferation, differentiation, and cytokine production of CD8+ T cells. Furthermore, RhCMV infection disrupted the relationship between short-chain fatty acid producers and Treg/Th17 balance observed in seronegative animals, showing that some immunologic effects of CMV are due to disruption of previously existing host-microbe relationships.

CONCLUSIONS

Gut microbes have an important influence on health and disease. Diet is known to shape the microbiota, but the influence of concomitant chronic viral infections is unclear. We found that CMV influences gut microbiota composition to an extent that is correlated with immunologic changes in the host. Additionally, pre-existing correlations between immunophenotypes and gut microbes can be subverted by CMV infection. Immunologic effects of CMV infection on the host may therefore be mediated by two different mechanisms involving gut microbiota. Video Abstract.

Translational Utility of the Nonhuman Primate Model

Nonhuman primates are essential for the study of human disease and to explore the safety of new diagnostics and therapies proposed for human use. They share similar genetic, physiologic, immunologic, reproductive, and developmental features with humans and thus have proven crucial for the study of embryonic/fetal development, organ system ontogeny, and the role of the maternal-placental-fetal interface in health and disease. The fetus may be exposed to a variety of inflammatory stimuli including infectious microbes as well as maternal inflammation, which can result from infections, obesity, or environmental exposures. Growing evidence supports that inflammation is a mediator of fetal programming and that the maternal immune system is tightly integrated with fetal-placental immune responses that may set a postnatal path for future health or disease. This review addresses some of the unique features of the nonhuman primate model system, specifically the rhesus monkey (Macaca mulatta), and importance of the species for studies focused on organ system ontogeny and the impact of viral teratogens in relation to development and congenital disorders.

Nonhuman Primates in Translational Research

Nonhuman primates are critically important animal models in which to study complex human diseases, understand biological functions, and address the safety of new diagnostics and therapies proposed for human use. They have genetic, physiologic, immunologic, and developmental similarities when compared to humans and therefore provide important preclinical models of human health and disease. This review highlights select research areas that demonstrate the importance of nonhuman primates in translational research. These include pregnancy and developmental disorders, infectious diseases, gene therapy, somatic cell genome editing, and applications of in vivo imaging. The power of the immune system and our increasing understanding of the role it plays in acute and chronic illnesses are being leveraged to produce new treatments for a range of medical conditions. Given the importance of the human immune system in health and disease, detailed study of the immune system of nonhuman primates is essential to advance preclinical translational research. The need for nonhuman primates continues to remain a high priority, which has been acutely evident during the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) global pandemic. Nonhuman primates will continue to address key questions and provide predictive models to identify the safety and efficiency of new diagnostics and therapies for human use across the lifespan.

Human Immunodeficiency Virus-1 Latency Reversal via the Induction of Early Growth Response Protein 1 to Bypass Protein Kinase C Agonist-Associated Immune Activation

Human Immunodeficiency Virus-1 (HIV) remains a global health challenge due to the latent HIV reservoirs in people living with HIV (PLWH). Dormant yet replication competent HIV harbored in the resting CD4+ T cells cannot be purged by antiretroviral therapy (ART) alone. One approach of HIV cure is the "Kick and Kill" strategy where latency reversal agents (LRAs) have been implemented to disrupt latent HIV, expecting to eradicate HIV reservoirs by viral cytopathic effect or immune-mediated clearance. Protein Kinase C agonists (PKCa), a family of LRAs, have demonstrated the ability to disrupt latent HIV to an extent. However, the toxicity of PKCa remains a concern in vivo. Early growth response protein 1 (EGR1) is a downstream target of PKCa during latency reversal. Here, we show that PKCa induces EGR1 which directly drives Tat-dependent HIV transcription. Resveratrol, a natural phytoalexin found in grapes and various plants, induces Egr1 expression and disrupts latent HIV in several HIV latency models in vitro and in CD4+ T cells isolated from ART-suppressed PLWH ex vivo. In the primary CD4+ T cells, resveratrol does not induce immune activation at the dosage that it reverses latency, indicating that targeting EGR1 may be able to reverse latency and bypass PKCa-induced immune activation.

Monoclonal antibodies protect aged rhesus macaques from SARS-CoV-2-induced immune activation and neuroinflammation

Anti-viral monoclonal antibody (mAb) treatments may provide immediate but short-term immunity from coronavirus disease 2019 (COVID-19) in high-risk populations, such as people with diabetes and the elderly; however, data on their efficacy in these populations are limited. We demonstrate that prophylactic mAb treatment blocks viral replication in both the upper and lower respiratory tracts in aged, type 2 diabetic rhesus macaques. mAb infusion dramatically curtails severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-mediated stimulation of interferon-induced chemokines and T cell activation, significantly reducing development of interstitial pneumonia. Furthermore, mAb infusion significantly dampens the greater than 3-fold increase in SARS-CoV-2-induced effector CD4 T cell influx into the cerebrospinal fluid. Our data show that neutralizing mAbs administered preventatively to high-risk populations may mitigate the adverse inflammatory consequences of SARS-CoV-2 exposure.

Early post-infection treatment of SARS-CoV-2 infected macaques with human convalescent plasma with high neutralizing activity reduces lung inflammation

Early in the SARS-CoV-2 pandemic, there was a high level of optimism based on observational studies and small controlled trials that treating hospitalized patients with convalescent plasma from COVID-19 survivors (CCP) would be an important immunotherapy. However, as more data from controlled trials became available, the results became disappointing, with at best moderate evidence of efficacy when CCP with high titers of neutralizing antibodies was used early in infection. To better understand the potential therapeutic efficacy of CCP, and to further validate SARS-CoV-2 infection of macaques as a reliable animal model for testing such strategies, we inoculated 12 adult rhesus macaques with SARS-CoV-2 by intratracheal and intranasal routes. One day later, 8 animals were infused with pooled human CCP with a high titer of neutralizing antibodies (RVPN NT ₅₀ value of 3,003), while 4 control animals received normal human plasma. Animals were monitored for 7 days. Animals treated with CCP had detectable levels of antiviral antibodies after infusion. In comparison to the control animals, they had similar levels of virus replication in the upper and lower respiratory tract, but had significantly reduced interstitial pneumonia, as measured by comprehensive lung histology. By highlighting strengths and weaknesses, data of this study can help to further optimize nonhuman primate models to provide proof-of-concept of intervention strategies, and guide the future use of convalescent plasma against SARS-CoV-2 and potentially other newly emerging respiratory viruses.

AUTHOR SUMMARY

The results of treating SARS-CoV-2 infected hospitalized patients with COVID-19 convalescent plasma (CCP), collected from survivors of natural infection, have been disappointing. The available data from various studies indicate at best moderate clinical benefits only when CCP with high titer of neutralizing antibodies was infused early in infection. The macaque model of SARS-CoV-2 infection can be useful to gain further insights in the value of CCP therapy. In this study, animals were infected with SARS-CoV-2 and the next day, were infused with pooled human convalescent plasma, selected to have a very high titer of neutralizing antibodies. While administration of CCP did not result in a detectable reduction in virus replication in the respiratory tract, it significantly reduced lung inflammation. These data, combined with the results of monoclonal antibody studies, emphasize the need to use products with high titers of neutralizing antibodies, and guide the future development of CCP-based therapies.

Cytomegalovirus mediates expansion of IL-15-responsive innate-memory cells with SIV killing function

Interindividual immune variability is driven predominantly by environmental factors, including exposure to chronic infectious agents such as cytomegalovirus (CMV). We investigated the effects of rhesus CMV (RhCMV) on composition and function of the immune system in young macaques. Within months of infection, RhCMV was associated with impressive changes in antigen presenting cells, T cells, and NK cells-and marked expansion of innate-memory CD8+ T cells. These cells express high levels of NKG2A/C and the IL-2 and IL-15 receptor beta chain, CD122. IL-15 was sufficient to drive differentiation of the cells in vitro and in vivo. Expanded NKG2A/C+CD122+CD8+ T cells in RhCMV-infected macaques, but not their NKG2-negative counterparts, were endowed with cytotoxicity against class I-deficient K562 targets and prompt IFN-γ production in response to stimulation with IL-12 and IL-18. Because RhCMV clone 68-1 forms the viral backbone of RhCMV-vectored SIV vaccines, we also investigated immune changes following administration of RhCMV 68-1-vectored SIV vaccines. These vaccines led to impressive expansion of NKG2A/C+CD8+ T cells with capacity to inhibit SIV replication ex vivo. Thus, CMV infection and CMV-vectored vaccination drive expansion of functional innate-like CD8 cells via host IL-15 production, suggesting that innate-memory expansion could be achieved by other vaccine platforms expressing IL-15.

Disruption of latent HIV in vivo during the clearance of actinic keratosis by ingenol mebutate

Actinic keratosis (AK) is a precancerous skin lesion that is common in HIV-positive patients. Without effective treatment, AKs can progress to squamous cell carcinoma. Ingenol mebutate, a PKC agonist, is a US Food and Drug Administration-approved (FDA-approved) topical treatment for AKs. It can induce reactivation of latent HIV transcription in CD4+ T cells both in vitro and ex vivo. Although PKC agonists are known to be potent inducers of HIV expression from latency, their effects in vivo are not known because of the concerns of toxicity. Therefore, we sought to determine the effects of topical ingenol mebutate gel on the HIV transcription profile in HIV-infected individuals with AKs, specifically in the setting of suppressive antiretroviral therapy (ART). We found that AKs cleared following topical application of ingenol mebutate and detected marginal changes in immune activation in the peripheral blood and in skin biopsies. An overall increase in the level of HIV transcription initiation, elongation, and complete transcription was detected only in skin biopsies after the treatment. Our data demonstrate that application of ingenol mebutate to AKs in ART-suppressed HIV-positive patients can effectively cure AKs as well as disrupt HIV latency in the skin tissue microenvironment in vivo without causing massive immune activation.

Idiopathic Colitis in Rhesus Macaques Is Associated With Dysbiosis, Abundant Enterochromaffin Cells and Altered T-Cell Cytokine Expression

Idiopathic chronic diarrhea (ICD) is a common ailment affecting captive rhesus macaques ( Macaca mulatta). ICD cases are characterized by diarrhea in the absence of commonly identified diarrheal pathogens and multiple recurrences even after supportive therapy. Histologically, the disease is characterized by lymphoplasmacytic colitis. We identified 35 rhesus macaques euthanized for ICD during a 7-month period and described demographic, clinical, histologic, and immunologic commonalities. We found a trend of historic Campylobacter spp. and trichomonad infections. Furthermore, rhesus macaques with ICD demonstrated loss of normal colonic adherent bacterium, identified in this study as Helicobacter macacae; increased abundance of Pentatrichomonas hominis; and increased frequency of colonic serotonin-positive enterochromaffin cells. Interestingly, colonic and ileal T-helper cells of animals with ICD manifested decreased capacity for expression of certain cytokines, in particular interleukin (IL)-4 and IL-13. These data further describe a common ailment and suggest new avenues to identify complex interactions involved in the etiology of recurring diarrhea in young rhesus macaques.

HIV latency is reversed by ACSS2-driven histone crotonylation

Eradication of HIV-1 (HIV) is hindered by stable viral reservoirs. Viral latency is epigenetically regulated. While the effects of histone acetylation and methylation at the HIV long-terminal repeat (LTR) have been described, our knowledge of the proviral epigenetic landscape is incomplete. We report that a previously unrecognized epigenetic modification of the HIV LTR, histone crotonylation, is a regulator of HIV latency. Reactivation of latent HIV was achieved following the induction of histone crotonylation through increased expression of the crotonyl-CoA-producing enzyme acyl-CoA synthetase short-chain family member 2 (ACSS2). This reprogrammed the local chromatin at the HIV LTR through increased histone acetylation and reduced histone methylation. Pharmacologic inhibition or siRNA knockdown of ACSS2 diminished histone crotonylation-induced HIV replication and reactivation. ACSS2 induction was highly synergistic in combination with either a protein kinase C agonist (PEP005) or a histone deacetylase inhibitor (vorinostat) in reactivating latent HIV. In the SIV-infected nonhuman primate model of AIDS, the expression of ACSS2 was significantly induced in intestinal mucosa in vivo, which correlated with altered fatty acid metabolism. Our study links the HIV/SIV infection-induced fatty acid enzyme ACSS2 to HIV latency and identifies histone lysine crotonylation as a novel epigenetic regulator for HIV transcription that can be targeted for HIV eradication.

Memory T Cell Proliferation before Hepatitis C Virus Therapy Predicts Antiviral Immune Responses and Treatment Success

The contribution of the host immune system to the efficacy of new anti-hepatitis C virus (HCV) drugs is unclear. We undertook a longitudinal prospective study of 33 individuals with chronic HCV treated with combination pegylated IFN-α, ribavirin, and telaprevir/boceprevir. We characterized innate and adaptive immune cells to determine whether kinetics of the host response could predict sustained virologic response (SVR). We show that characteristics of the host immune system present before treatment were correlated with successful therapy. Augmentation of adaptive immune responses during therapy was more impressive among those achieving SVR. Most importantly, active memory T cell proliferation before therapy predicted SVR and was associated with the magnitude of the HCV-specific responses at week 12 after treatment start. After therapy initiation, the most important correlate of success was minimal monocyte activation, as predicted by previous in vitro work. In addition, subjects achieving SVR had increasing expression of the transcription factor T-bet, a driver of Th1 differentiation and cytotoxic effector cell maturation. These results show that host immune features present before treatment initiation predict SVR and eventual development of a higher frequency of functional virus-specific cells in blood. Such host characteristics may also be required for successful vaccine-mediated protection.

Depletion of Gut-Resident CCR5+ Cells for HIV Cure Strategies

The HIV reservoir forming at the earliest stages of infection is likely composed of CCR5+ cells, because these cells are the targets of transmissible virus. Restriction of the CCR5+ reservoir, particularly in the gut, may be needed for subsequent cure attempts. Strategies for killing or depleting CCR5+ cells have been described, but none have been tested in vivo in nonhuman primates, and the extent of achievable depletion from tissues is not known. In this study we investigate the efficacy of two novel cytotoxic treatments for targeting and eliminating CCR5+ cells in young rhesus macaques. The first, an immunotoxin consisting of the endogenous CCR5 ligand RANTES fused with Pseudomonas exotoxin (RANTES-PE38), killed CCR5+ lamina propria lymphocytes (LPLs) ex vivo, but had no detectable effect on CCR5+ LPLs in vivo. The second, a primatized bispecific antibody for CCR5 and CD3, depleted all CCR5+ cells from blood and the vast majority of such cells from the colonic mucosa (up to 96% of CD4+CCR5+). Absence of CCR5-expressing cells from blood endured for at least 1 week, while CCR5+ cells in colon were substantially replenished over the same time span. These data open an avenue to investigation of combined early ART treatment and CCR5+ reservoir depletion for cure of HIV-infected infants.

IL-21 Therapy Controls Immune Activation and Maintains Antiviral CD8+ T Cell Responses in Acute Simian Immunodeficiency Virus Infection

Human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) replicate during acute infection in lymphocytes of the gastrointestinal tract, before disseminating systemically. Localized replication and associated loss of gut-resident CD4⁺ T cells occur regardless of the portal of entry of the virus (e.g., intravenous vs. rectal). Thus, HIV and SIV are tropic for gut tissue, and their pathogenesis requires the special environment of the intestine. T helper 17 (Th17) cells are important contributors to microbial defense in the gut that are vulnerable to HIV infection and whose loss is associated with translocation of microbial products to the systemic circulation, leading to chronic immune activation and disease progression. Interleukin (IL)-21 promotes differentiation and survival of Th17 cells and stimulates CD8⁺ T cell function. By promoting Th17 cell survival, IL-21 could limit bacterial translocation and immune activation in the setting of acute or rebounding HIV/SIV disease. In this study, we tested the effect of recombinant IL-21-IgFc treatment, given at the time of infection, on SIV_mac251 infection. We found that rIL-21-IgFc decreases immune activation and maintains effective antiviral responses by CD8⁺ T cells in blood, but this maintenance is not associated with lower viral loads. rIL-21-IgFc treatment also did not generally support Th17 cell populations, but Th17 cells remained strongly and independently associated with control of plasma viremia. For example, the single animal exhibiting greatest control over viremia in our study also manifested the highest levels of IL-21 in plasma, Th17 cell maintenance in blood, and Th17 cells in intestinal tissue. These findings provide rationale for further exploration of IL-21 treatment as a support for host CD8⁺ T cell responses in HIV cure strategies.

Exposure to SIV in utero results in reduced viral loads and altered responsiveness to postnatal challenge

HIV disease progression appears to be driven by increased immune activation. Given observations that fetal exposure to infectious pathogens in utero can result in reduced immune responses, or tolerance, to those pathogens postnatally, we hypothesized that fetal exposure to HIV may render the fetus tolerant to the virus, thus reducing damage caused by immune activation during infection later in life. To test this hypothesis, fetal rhesus macaques (Macaca mulatta) were injected with the attenuated virus SIVmac1A11 in utero and challenged with pathogenic SIVmac239 1 year after birth. SIVmac1A11-injected animals had significantly reduced plasma RNA viral loads (P < 0.02) up to 35 weeks after infection. Generalized estimating equations analysis was performed to identify immunologic and clinical measurements associated with plasma RNA viral load. A positive association with plasma RNA viral load was observed with the proportion of CD8(+) T cells expressing the transcription factor, FoxP3, and the proportion of CD4(+) T cells producing the lymphoproliferative cytokine, IL-2. In contrast, an inverse relationship was found with the frequencies of circulating CD4(+) and CD8(+) T cells displaying intermediate expression of the proliferation marker, Ki-67. Animals exposed to simian immunodeficiency virus (SIV) in utero appeared to have enhanced SIV-specific immune responses, a lower proportion of CD8(+) T cells expressing the exhaustion marker PD-1, and more circulating TH17 cells than controls. Although the development of tolerance was not demonstrated, these data suggest that rhesus monkeys exposed to SIVmac1A11 in utero had distinct immune responses associated with the control of viral replication after postnatal challenge.

Persistent effects of early infant diet and associated microbiota on the juvenile immune system

Early infant diet has significant impacts on the gut microbiota and developing immune system. We previously showed that breast-fed and formula-fed rhesus macaques develop significantly different gut microbial communities, which in turn are associated with different immune systems in infancy. Breast-fed animals manifested greater T cell activation and proliferation and harbored robust pools of T helper 17 (TH17) cells. These differences were sustained throughout the first year of life. Here we examine groups of juvenile macaques (approximately 3 to 5 y old), which were breast-fed or formula-fed in infancy. We demonstrate that juveniles breast-fed in infancy maintain immunologic differences into the fifth year of life, principally in CD8(+) memory T cell activation. Additionally, long-term correlation networks show that breast-fed animals maintain persistent relationships between immune subsets that are not seen in formula-fed animals. These findings demonstrate that infant feeding practices have continued influence on immunity for up to 3 to 5 y after birth and also reveal mechanisms for microbial modulation of the immune system.

Breast-fed and bottle-fed infant rhesus macaques develop distinct gut microbiotas and immune systems

Diet has a strong influence on the intestinal microbiota in both humans and animal models. It is well established that microbial colonization is required for normal development of the immune system and that specific microbial constituents prompt the differentiation or expansion of certain immune cell subsets. Nonetheless, it has been unclear how profoundly diet might shape the primate immune system or how durable the influence might be. We show that breast-fed and bottle-fed infant rhesus macaques develop markedly different immune systems, which remain different 6 months after weaning when the animals begin receiving identical diets. In particular, breast-fed infants develop robust populations of memory T cells as well as T helper 17 (TH17) cells within the memory pool, whereas bottle-fed infants do not. These findings may partly explain the variation in human susceptibility to conditions with an immune basis, as well as the variable protection against certain infectious diseases.

Monocyte activation by interferon α is associated with failure to achieve a sustained virologic response after treatment for hepatitis C virus infection

BACKGROUND

Interferon α (IFN-α) and ribavirin can induce a sustained virologic response (SVR) in some but not all hepatitis C virus (HCV)-infected patients. The mechanism of effective treatment is unclear. One possibility is that IFN-α differentially improves the functional capacity of classic myeloid dendritic cells (mDCs) by altering expression of surface molecules or cytokines. Others have proposed that antigen-presenting cell activation could be paradoxically detrimental during HCV infection because of the production by monocytes of substances inhibitory or toxic to plasmacytoid dendritic cells.

METHODS

We examined responses to in vitro IFN-α treatment of peripheral blood leukocyte samples from a retrospective treatment cohort of nearly 200 HCV-seropositive patients who had undergone antiviral therapy with ribavirin and pegylated IFN. We analyzed the variable responses of antigen-presenting cell subsets to drug.

RESULTS

We found that patients achieving SVR were no more likely to have robust mDC activation in response to IFN-α than those who did not achieve SVR. Rather, patients achieving SVR were distinguished by restrained monocyte activation in the presence of IFN-α, a factor that was second in importance only to IL28B genotype in its association with SVR.

CONCLUSIONS

These results suggest that interindividual variability in the response of monocytes to IFN-α is an important determinant of treatment success with IFN-α-based regimens.

IL-7 production in murine lymphatic endothelial cells and induction in the setting of peripheral lymphopenia

IL-7 is a required factor for T-cell homeostasis. Because of low expression levels and poor reagent availability, the cellular sources of IL-7 have proven challenging to characterize. In this study, we describe a reporter mouse in which enhanced GFP is expressed from the endogenous Il7 locus. We show that IL-7 is produced by lymphatic endothelial cells (LECs) distributed throughout the systemic lymphatic vasculature as well as by fibroblastic reticular cells, and that phosphorylation of STAT5 in lymphocytes is higher in lymphatics than in blood. Furthermore, in nodes depleted of lymphocytes, Il7 transcription is increased in stromal but not in myeloid subsets. These data support recent findings that lymphocyte homeostasis is influenced by access to secondary lymphoid organs and point to LECs as an important in vivo source of IL-7, bathing trafficking immune cells under both resting and lymphopenic conditions.

SIV replication in the infected rhesus macaque is limited by the size of the preexisting TH17 cell compartment

The mechanisms by which some HIV-infected subjects resist disease progression, whereas others progress rapidly, are incompletely understood. Viral and host genetic factors, such as nef deletions and major histocompatibility complex alleles, explain a portion of the observed variability. However, it has been difficult to identify host immune functions that may be present before infection and that allow resistance to lentiviral disease progression. Here, we show that simian immunodeficiency virus replication in the infected rhesus macaque is limited by the size of the preexisting T helper 17 (T(H)17) cell compartment: Animals with a high representation of such cells in blood and intestinal tissue before infection experienced peak and set-point viral loads about one log unit lower than those with a lower representation of T(H)17 cells. Reciprocally, treatment of macaques with interleukin-2 and granulocyte colony-stimulating factor before infection led to depletion of T(H)17 cells, reduction of the ratio between T(H)17 cells and CD3(+)CD4(+)CD25(+)CD127(low) regulatory T cells, and higher viral loads for 6 months after infection. These results demonstrate that the composition of the host immune system before infection has an influence on the course of disease after infection. Furthermore, to the extent that this influence shapes and interacts with T cell-mediated responses to virus, our findings provide a new framework for understanding interindividual variation in responses to therapies and vaccines against HIV.

Th17 cells and regulatory T cells in elite control over HIV and SIV

PURPOSE OF REVIEW

We present current findings about two subsets of CD4+ T cells that play an important part in the initial host response to infection with the HIV type 1: those producing IL-17 (Th17 cells) and those with immunosuppressive function (CD25+FoxP3+ regulatory T cells or T-reg). The role of these cells in the control of viral infection and immune activation as well as in the prevention of immune deficiency in HIV-infected elite controllers will be examined. We will also discuss the use of the simian immunodeficiency virus (SIV)-infected macaque model of AIDS to study the interplay between these cells and lentiviral infection in vivo.

RECENT FINDINGS

Study of Th17 cells in humans and nonhuman primates (NHPs) has shown that depletion of these cells is associated with the dissemination of microbial products from the infected gut, increased systemic immune activation, and disease progression. Most impressively, having a smaller Th17-cell compartment has been found to predict these outcomes. T-reg have been associated with the reduced antiviral T-cell responses but not with the suppression of generalized T cell activation. Both cell subsets influence innate immune responses and, in doing so, may shape the inflammatory milieu of the host at infection.

SUMMARY

Interactions between Th17 cells, T-reg, and cells of the innate immune system influence the course of HIV and SIV infection from its earliest stages, even before the appearance of adaptive immunity. Such interactions may be pivotal for elite control over disease progression.

The human fetal immune response to hepatitis C virus exposure in utero

BACKGROUND

Although the rate of mother-to-child transmission of hepatitis C virus (HCV) is low, the effect of HCV exposure in utero on the fetal immune system is unknown.

METHODS

Umbilical cord blood was obtained from 7 neonates born to HCV-seropositive, HCV RNA-positive women and 8 neonates born to HCV-seronegative women. Cord blood mononuclear cells were analyzed by immunophenotyping and by intracellular cytokine staining after HCV-specific and polyclonal stimulation. Plasma was analyzed for anti-HCV immunoglobulin M (IgM), cytokine/granzyme concentrations, and indoleamine 2,3-dioxygenase (IDO) activity.

RESULTS

HCV-exposed neonates had significantly lower levels of regulatory T cells expressing HLA-DR, lower CD4(+) and CD8(+) T cell activation, and lower plasma levels of pro-inflammatory markers than did controls. However, CD4(+) and CD8(+) T cells from HCV-exposed neonates had higher IFN-γ production in response to polyclonal stimulation than did T cells from controls. IDO activity was similar between groups. No HCV-specific T cell responses or anti-HCV IgM were detected in any neonates.

CONCLUSIONS

HCV-exposed neonates showed a relative suppression of immune activation and pro-inflammatory markers, which was counterbalanced by an increased production capacity for IFN-γ. These results suggest that HCV encounters the fetal immune system in utero, and alters the balance between suppressive and pro-inflammatory responses.

Development of cytomegalovirus (CMV) immune recovery uveitis is associated with Th17 cell depletion and poor systemic CMV-specific T cell responses

We tested whether impaired systemic immunoregulation and hyperactive immune responses are associated with an immune reconstitution inflammatory syndrome, CMV IRU. We found instead that T-regs in CMV IRU patients are functionally intact, while virus-specific immune responses and Th17 cells are compromised

Background. The immune reconstitution inflammatory syndromes (IRIS) are a spectrum of inflammatory conditions associated with opportunistic infections and occurring in ∼16% of human immunodeficiency type 1 (HIV-1)–infected patients given antiretroviral therapy. It has been proposed that these conditions are linked by a dysregulated immune system that is prone to exaggerated responses. However, immunologic studies have been limited by the availability of longitudinal samples from patients with IRIS and appropriate matched control subjects. Cytomegalovirus (CMV) immune recovery uveitis (IRU) is an IRIS occurring in up to 38% of patients with CMV retinitis. Although the pathologic immune responses occur in the eye, immune dysregulation that allows for development of pathologic responses is presumably caused by faulty systemic immune cell reconstitution.

Methods. We examined CMV-specific T cell responses, regulatory T (T_reg) cell function and polyclonal T cell responses, including IL-17 production, in 25 patients with CMV IRU and 49 immunorestored control subjects with CMV retinitis who did not develop IRU.

Results. Patients with CMV IRU had poor CMV-specific CD4⁺ T cell responses, as compared with control subjects, whereas CD8⁺ T cell responses were comparable. Patients with CMV IRU were characterized by smaller numbers of circulating Th17 cells. Deficiency in anti-CMV responses was not associated with differences in T_reg cell function.

Conclusions. The T_reg cell compartment is intact in patients with CMV IRU, and these patients do not develop exaggerated systemic CMV-specific or polyclonal immune responses. Cases are instead characterized by more profound depletion of Th17 cells and poor antiviral immune responses. CMV IRU may be most likely to develop in persons experiencing the greatest degree of immune dysfunction before initiating highly active antiretroviral therapy.

Suppression of SIV-specific CD4+ T cells by infant but not adult macaque regulatory T cells: implications for SIV disease progression

The impact of regulatory T cells (T reg cells) on the course of HIV and SIV disease is unknown. T reg cells could suppress protective antiviral responses and accelerate disease progression. Alternatively, these cells might block T cell activation and thereby limit viral replication as well as activation-associated immunopathology. Given the higher frequency of T reg cells known to be present during human fetal ontogeny, such influences may be most important in the context of perinatal infection. We found that infant macaques had higher fractions of CD4⁺CD25⁺CD127^lowFoxP3⁺ T reg cells in the peripheral blood and in lymphoid tissues, and that these T reg cells showed greater in vitro suppressive activity on a per cell basis. Infant and adult macaques were infected with SIVmac251 to test the influence of the T reg cell compartment on SIV-specific immune responses. After infection with SIV, most (three out of four) infant macaques had persistently high viral loads, weak and transient SIV-specific CD4⁺ and CD8⁺ T cell responses, and rapid disease progression. T reg cells in the infant but not in the adult directly suppressed SIV-specific CD4⁺ T cell responses, which were detectable only after depletion of T reg cells. In the case of both the infant and the adult macaque, T reg cells were not able to directly suppress SIV-specific CD8⁺ T cell responses and had no apparent effect on T cell activation. In aggregate, these observations suggest that the T reg cell compartment of the infant macaque facilitates rapid disease progression, at least in part by incapacitating SIV-specific CD4⁺ T cell responses.

Human CD4+ regulatory T cells express lower levels of the IL-7 receptor alpha chain (CD127), allowing consistent identification and sorting of live cells

Although quantitative identification and viable enrichment of natural regulatory T cells (T-regs) in humans are problematic, such steps would greatly facilitate the analysis of these cells in disease states. In an attempt to identify markers that are sensitive and specific for human T-regs, we analyzed the expression of fourteen intracellular and cell surface markers on human CD4(+) cells. Many markers were partially selective for CD25(hi) T-regs, but consistent and specific discrimination of functional T-regs was only made possible by focus on CD127, the alpha chain of the IL-7 receptor. Although most CD4(+) human T cells express CD127, T-regs exhibiting suppressive activity in vitro display distinctly lower surface expression of this marker, irrespective of their level of CD25 expression. Sorted cells with the surface phenotype CD4(+)CD25(+)CD127(low) had higher levels of intracellular FOXP3 and CTLA-4 and, as determined by functional assays, were suppressive, hypoproliferative, and poorly responsive to TCR signaling. The CD4(+)CD25(+)CD127(low) phenotype was also found to be characteristic of T-regs found in mice and in rhesus macaques. This surface phenotype should allow for quantitative studies of regulatory T cells in disease states as well as for enrichment of live regulatory T cells for functional analyses and/or expansion in vitro.

Mice lacking the homeodomain transcription factor Nkx2.2 have diabetes due to arrested differentiation of pancreatic beta cells

The endocrine pancreas is organized into clusters of cells called islets of Langerhans comprising four well-defined cell types: alpha beta, delta and PP cells. While recent genetic studies indicate that islet development depends on the function of an integrated network of transcription factors, the specific roles of these factors in early cell-type specification and differentiation remain elusive. Nkx2.2 is a member of the mammalian NK2 homeobox transcription factor family that is expressed in the ventral CNS and the pancreas. Within the pancreas, we demonstrate that Nkx2.2 is expressed in alpha, beta and PP cells, but not in delta cells. In addition, we show that mice homozygous for a null mutation of Nkx2.2 develop severe hyperglycemia and die shortly after birth. Immunohistochemical analysis reveals that the mutant embryos lack insulin-producing beta cells and have fewer glucagon-producing alpha cells and PP cells. Remarkably, in the mutants there remains a large population of islet cells that do not produce any of the four endocrine hormones. These cells express some beta cell markers, such as islet amyloid polypeptide and Pdx1, but lack other definitive beta cell markers including glucose transporter 2 and Nkx6.1. We propose that Nkx2.2 is required for the final differentiation of pancreatic beta cells, and in its absence, beta cells are trapped in an incompletely differentiated state.