Immunotoxin-mediated depletion of Gag-specific CD8+ T cells undermines natural control of SIV.

Antibody-mediated depletion studies have demonstrated that CD8+ T cells are required for effective immune control of SIV. However, this approach is potentially confounded by several factors, including reactive CD4+ T cell proliferation, and provides no information on epitope specificity, a likely determinant of CD8+ T cell efficacy. We circumvented these limitations by selectively depleting CD8+ T cells specific for the Gag epitope CTPYDINQM (CM9) via the administration of immunotoxin-conjugated tetrameric complexes of CM9/Mamu-A*01. Immunotoxin administration effectively depleted circulating but not tissue-localized CM9-specific CD8+ T cells, akin to the bulk depletion pattern observed with antibodies directed against CD8. However, we found no evidence to indicate that circulating CM9-specific CD8+ T cells suppressed viral replication in Mamu-A*01+ rhesus macaques during acute or chronic progressive infection with a pathogenic strain of SIV. This observation extended to macaques with established infection during and after continuous antiretroviral therapy. In contrast, natural controller macaques experienced dramatic increases in plasma viremia after immunotoxin administration, highlighting the importance of CD8+ T cell-mediated immunity against CM9. Collectively, these data showed that CM9-specific CD8+ T cells were necessary but not sufficient for robust immune control of SIV in a nonhuman primate model and, more generally, validated an approach that could inform the design of next-generation vaccines against HIV-1.

Multiple modes of antigen exposure induce clonotypically diverse epitope-specific CD8+ T cells across multiple tissues in nonhuman primates.

Antigen-specific CD8+ T cells play a key role in the host's antiviral response. T cells recognize viral epitopes via the T cell receptor (TCR), which contains the complementarity-determining region-3 (CDR3), comprising the variable, diversity and joining regions of the TCRß gene. During chronic simian immunodeficiency virus (SIV) infection of Asian macaque nonhuman primates, tissue-specific clonotypes are identifiable among SIV-specific CD8+ T cells. Here, we sought to determine level of antigen exposure responsible for the tissue-specific clonotypic structure. We examined whether the priming event and/or chronic antigen exposure is response for tissue-specific TCR repertoires. We evaluated the TCR repertoire of SIV-specific CD8+ T cells after acute antigen exposure following inoculation with a SIV DNA vaccine, longitudinally during the acute and chronic phases of SIV, and after administration of antiretrovirals (ARVs). Finally, we assessed the TCR repertoire of cytomegalovirus (CMV)-specific CD8+ T cells to establish if TCR tissue-specificity is shared among viruses that chronically replicate. TCR sequences unique to anatomical sites were identified after acute antigen exposure via vaccination and upon acute SIV infection. Tissue-specific clones also persisted into chronic infection and the clonotypic structure continued to evolve after ARV administration. Finally, tissue-specific clones were also observed in CMV-specific CD8+ T cells. Together, these data suggest that acute antigen priming is sufficient to induce tissue-specific clones and that this clonal hierarchy can persist when antigen loads are naturally or therapeutically reduced, providing mechanistic insight into tissue-residency.

Translocated microbiome composition determines immunological outcome in treated HIV infection.

The impact of the microbiome on HIV disease is widely acknowledged although the mechanisms downstream of fluctuations in microbial composition remain speculative. We detected rapid, dynamic changes in translocated microbial constituents during two years after cART initiation. An unbiased systems biology approach revealed two distinct pathways driven by changes in the abundance ratio of Serratia to other bacterial genera. Increased CD4 T cell numbers over the first year were associated with high Serratia abundance, pro-inflammatory innate cytokines, and metabolites that drive Th17 gene expression signatures and restoration of mucosal integrity. Subsequently, decreased Serratia abundance and downregulation of innate cytokines allowed re-establishment of systemic T cell homeostasis promoting restoration of Th1 and Th2 gene expression signatures. Analyses of three other geographically distinct cohorts of treated HIV infection established a more generalized principle that changes in diversity and composition of translocated microbial species influence systemic inflammation and consequently CD4 T cell recovery.

Epigenetic silencing of CD4 expression in nonpathogenic SIV infection in African green monkeys.

African green monkeys (AGMs) are natural hosts of SIV that postthymically downregulate CD4 to maintain a large population of CD4-CD8aa+ virus-resistant cells with Th functionality, which can result in AGMs becoming apparently cured of SIVagm infection. To understand the mechanisms of this process, we performed genome-wide transcriptional analysis on T cells induced to downregulate CD4 in vitro from AGMs and closely related patas monkeys and T cells that maintain CD4 expression from rhesus macaques. In T cells that downregulated CD4, pathway analysis revealed an atypical regulation of the DNA methylation machinery, which was reversible when pharmacologically targeted with 5-aza-2 deoxycytidine. This signature was driven largely by the dioxygenase TET3, which became downregulated with loss of CD4 expression. CpG motifs within the AGM CD4 promoter region became methylated during CD4 downregulation in vitro and were stably imprinted in AGM CD4-CD8aa+ T cells sorted directly ex vivo. These results suggest that AGMs use epigenetic mechanisms to durably silence the CD4 gene. Manipulation of these mechanisms could provide avenues for modulating SIV and HIV-1 entry receptor expression in hosts that become progressively infected with SIV, which could lead to novel therapeutic interventions aimed to reduce HIV viremia in vivo.

Immunotherapy of Relapsed and Refractory Solid Tumors With Ex Vivo Expanded Multi-Tumor Associated Antigen Specific Cytotoxic T Lymphocytes: A Phase I Study.

PURPOSE: Tumor-associated antigen cytotoxic T cells (TAA-Ts) represent a new, potentially effective and nontoxic therapeutic approach for patients with relapsed or refractory solid tumors. In this first-in-human trial, we investigated the safety of administering TAA-Ts that target Wilms tumor gene 1, preferentially expressed antigen of melanoma, and survivin to patients with relapsed/refractory solid tumors. MATERIALS AND METHODS: TAA-T products were generated from autologous peripheral blood and infused over three dose levels: 1, 2, and 4 × 107 cells/m2. Patients were eligible for up to eight infusions administered 4 to 7 weeks apart. We assessed dose limiting toxicity during the first 45 days after infusion. Disease response was determined within the context of a phase I trial. RESULTS: There were no dose-limiting toxicities. Of 15 evaluable patients, 11 (73%) with stable disease or better at day 45 postinfusion were defined as responders. Six responders remain without progression at a median of 13.9 months (range, 4.1 to 19.9 months) after initial TAA-Ts. Patients who were treated at the highest dose level showed the best clinical outcomes, with a 6-month progression-free survival of 73% after TAA-T infusion compared with a 38% 6-month progression-free survival with prior therapy. Antigen spreading and a reduction in circulating tumor-associated antigens using digital droplet polymerase chain reaction was observed in patients after TAA-T infusion. CONCLUSION: TAA-Ts safely induced disease stabilization, prolonged time to progression, and were associated with antigen spreading and a reduction in circulating tumor-associated antigen DNA levels in patients with relapsed/refractory solid tumors without lymphodepleting chemotherapy before infusion. TAA-Ts are a promising new treatment approach for patients with solid tumors.

Altered differentiation is central to HIV-specific CD4+ T cell dysfunction in progressive disease.

Dysfunction of virus-specific CD4+ T cells in chronic human infections is poorly understood. We performed genome-wide transcriptional analyses and functional assays of CD4+ T cells specific for human immunodeficiency virus (HIV) from HIV-infected people before and after initiation of antiretroviral therapy (ART). A follicular helper T cell (TFH cell)-like profile characterized HIV-specific CD4+ T cells in viremic infection. HIV-specific CD4+ T cells from people spontaneously controlling the virus (elite controllers) robustly expressed genes associated with the TH1, TH17 and TH22 subsets of helper T cells. Viral suppression by ART resulted in a distinct transcriptional landscape, with a reduction in the expression of genes associated with TFH cells, but persistently low expression of genes associated with TH1, TH17 and TH22 cells compared to the elite controller profile. Thus, altered differentiation is central to the impairment of HIV-specific CD4+ T cells and involves both gain of function and loss of function.

Activation Dynamics and Immunoglobulin Evolution of Pre-existing and Newly Generated Human Memory B cell Responses to Influenza Hemagglutinin.

Vaccine-induced memory B cell responses to evolving viruses like influenza A involve activation of pre-existing immunity and generation of new responses. To define the contribution of these two types of responses, we analyzed the response to H7N9 vaccination in H7N9-naive adults. We performed comprehensive comparisons at the single-cell level of the kinetics, Ig repertoire, and activation phenotype of established pre-existing memory B cells recognizing conserved epitopes and the newly generated memory B cells directed toward H7 strain-specific epitopes. The recall response to conserved epitopes on H7 HA involved a transient expansion of memory B cells with little observed adaptation. However, the B cell response to newly encountered epitopes was phenotypically distinct and generated a sustained memory population that evolved and affinity matured months after vaccination. These findings establish clear differences between newly generated and pre-existing memory B cells, highlighting the challenges in achieving long-lasting, broad protection against an ever-evolving virus.

T-cell receptor sequencing demonstrates persistence of virus-specific T cells after antiviral immunotherapy.

Viral infections are a serious cause of morbidity and mortality following haematopoietic stem cell transplantation (HSCT). Adoptive cellular therapy with virus-specific T cells (VSTs) has been successful in preventing or treating targeted viruses in prior studies, but the composition of ex vivo expanded VST and the critical cell populations that mediate antiviral activity in vivo are not well defined. We utilized deep sequencing of the T-cell receptor beta chain (TCRB) in order to classify and track VST populations in 12 patients who received VSTs following HSCT to prevent or treat viral infections. TCRB sequencing was performed on sorted VST products and patient peripheral blood mononuclear cells samples. TCRB diversity was gauged using the Shannon entropy index, and repertoire similarity determined using the Morisita-Horn index. Similarity indices reflected an early change in TCRB diversity in eight patients, and TCRB clonotypes corresponding to targeted viral epitopes expanded in eight patients. TCRB repertoire diversity increased in nine patients, and correlated with cytomegalovirus (CMV) viral load following VST infusion (P = 0·0071). These findings demonstrate that allogeneic VSTs can be tracked via TCRB sequencing, and suggests that T-cell receptor repertoire diversity may be critical for the control of CMV reactivation after HSCT.

Single-cell RNA sequencing identifies inflammatory tissue T cells in eosinophilic esophagitis.

T cell heterogeneity is highly relevant to allergic disorders. We resolved the heterogeneity of human tissue CD3+ T cells during allergic inflammation, focusing on a tissue-specific allergic disease, eosinophilic esophagitis (EoE). We investigated 1088 single T cells derived from patients with a spectrum of disease activity. Eight disparate tissue T cell subtypes (designated T1-T8) were identified, with T7 and T8 enriched in the diseased tissue. The phenotypes of T7 and T8 resemble putative Treg (FOXP3+) and effector Th2-like (GATA3+) cells, respectively. Prodigious levels of IL-5 and IL-13 were confined to HPGDS+ CRTH2+IL-17RB+FFAR3+CD4+ T8 effector Th2 cells. EoE severity closely paralleled a lipid/fatty acid-induced activation node highlighted by the expression of the short-chain fatty acid receptor FFAR3. Ligands for FFAR3 induced Th2 cytokine production from human and murine T cells, including in an in vivo allergy model. Therefore, we elucidated the defining characteristics of tissue-residing CD3+ T cells in EoE, a specific enrichment of CD4+ Treg and effector Th2 cells, confinement of type 2 cytokine production to the CD4+ effector population, a highly likely role for FFAR3 in amplifying local Th2 responses in EoE, and a resource to further dissect tissue lymphocytes and allergic responses.

Prolonged evolution of the memory B cell response induced by a replicating adenovirus-influenza H5 vaccine.

Induction of an antibody response capable of recognizing highly diverse strains is a major obstacle to the development of vaccines for viruses such as HIV and influenza. Here, we report the dynamics of B cell expansion and evolution at the single-cell level after vaccination with a replication-competent adenovirus type 4 recombinant virus expressing influenza H5 hemagglutinin. Fluorescent H1 or H5 probes were used to quantitate and isolate peripheral blood B cells and their antigen receptors. We observed increases in H5-specific antibody somatic hypermutation and potency for several months beyond the period of active viral replication that was not detectable at the serum level. Individual broad and potent antibodies could be isolated, including one stem-specific antibody that is part of a new multidonor class. These results demonstrate prolonged evolution of the B cell response for months after vaccination and should be considered in efforts to evaluate or boost vaccine-induced immunity.

The peripheral differentiation of human natural killer T cells.

The peripheral maturation of human CD1d-restricted natural killer T (NKT) cells has not been well described. In this study, we identified four major subsets of NKT cells in adults, distinguished by the expression of CD4, CD8 and CCR5. Phenotypic analysis suggested a hierarchical pattern of differentiation, whereby immature CD4+ CD8- CCR5- cells progressed to an intermediate CD4+ CD8- CCR5+ stage, which remained less differentiated than the CD4- CD8- and CD4- CD8+ subsets, both of which expressed CCR5. This interpretation was supported by functional data, including clonogenic potential and cytokine secretion profiles, as well as T-cell receptor (TCR) excision circle analysis. Moreover, conventional and high-throughput sequencing of the corresponding TCR repertoires demonstrated significant clonotypic overlap within individuals, especially between the more differentiated CD4- CD8- and CD4- CD8+ subsets. Collectively, these results mapped a linear differentiation pathway across the post-thymic landscape of human CD1d-restricted NKT cells.

T cell receptor sequencing of activated CD8 T cells in the blood identifies tumor-infiltrating clones that expand after PD-1 therapy and radiation in a melanoma patient.

PD-1-targeted therapy has dramatically changed advanced cancer treatment. However, many questions remain, including specificity of T cells activated by PD-1 therapy and how peripheral blood analysis correlates to effects at tumor sites. In this study, we utilized TCR sequencing to dissect the composition of peripheral blood CD8 T cells activated upon therapy, comparing it with tumor-infiltrating lymphocytes. We report on a nonagenarian melanoma patient who showed a prominent increase in peripheral blood Ki-67 + CD8 T cells following brain stereotactic radiation and anti-PD-1 immunotherapy. Proliferating CD8 T cells exhibited an effector-like phenotype with expression of CD38, HLA-DR and Granzyme B, as well as expression of the positive costimulatory molecules CD28 and CD27. TCR sequencing of peripheral blood CD8 T cells revealed a highly oligoclonal repertoire at baseline with one clonotype accounting for 30%. However, the majority of dominant clones-including a previously identified cytomegalovirus-reactive clone-did not expand following treatment. In contrast, expanding clones were present at low frequencies in the peripheral blood but were enriched in a previously resected liver metastasis. The patient has so far remained recurrence-free for 36 months, and several CD8 T cell clones that expanded after treatment were maintained at elevated levels for at least 8 months. Our data show that even in a nonagenarian individual with oligoclonal expansion of CD8 T cells, we can identify activation of tumor-infiltrating CD8 T cell clones in peripheral blood following anti-PD-1-based immunotherapies.

Structure and Diversity of the Rhesus Macaque Immunoglobulin Loci through Multiple De Novo Genome Assemblies.

The rhesus macaque is a critically important animal model in biomedical research, most recently playing a key role in the development of vaccines against human immunodeficiency virus-1. Nevertheless, the immunoglobulin (Ig) loci of macaques are as yet incompletely determined and our understanding of differences between human and macaque humoral immunity remains deficient. We completed a high-coverage, high-quality whole genome sequencing and assembly project with a single rhesus macaque of Indian origin, and partial genome assemblies using genomic molecular targeting of the Ig loci in nine other rhesus macaques of Indian origin. These data indicate that the macaque Ig loci are substantially more diverse than those in humans, including greater sequence diversity and copy-number variation between individuals. It appears likely that such copy-number variation even occurs between allelic loci within individuals. Different Ig gene families in the macaque show distinct relationships to the corresponding human gene families and appear to evolve under different mechanisms. These results raise intriguing questions about the evolution of antigen receptors in primates but also have important practical implications for the design and interpretation of biomedical studies.

Identification of a CD4-Binding-Site Antibody to HIV that Evolved Near-Pan Neutralization Breadth.

Detailed studies of the broadly neutralizing antibodies (bNAbs) that underlie the best available examples of the humoral immune response to HIV are providing important information for the development of therapies and prophylaxis for HIV-1 infection. Here, we report a CD4-binding site (CD4bs) antibody, named N6, that potently neutralized 98% of HIV-1 isolates, including 16 of 20 that were resistant to other members of its class. N6 evolved a mode of recognition such that its binding was not impacted by the loss of individual contacts across the immunoglobulin heavy chain. In addition, structural analysis revealed that the orientation of N6 permitted it to avoid steric clashes with glycans, which is a common mechanism of resistance. Thus, an HIV-1-specific bNAb can achieve potent, near-pan neutralization of HIV-1, making it an attractive candidate for use in therapy and prophylaxis.

Intrathecal T-cell clonal expansions in patients with multiple sclerosis.

OBJECTIVE: Analysis of the T-cell receptor (TCR) repertoire in the cerebrospinal fluid (CSF) of patients with multiple sclerosis (MS) can reveal antigen-specific immune responses potentially implicated in the disease process. We applied a new unbiased deep-sequencing method for TCR repertoire analysis to accurately measure and compare receptor diversity and clonal expansions within the peripheral and CSF-trafficking T-cell populations of patients with MS and control individuals with idiopathic intracranial hypertension (IIH). METHODS: Paired blood and CSF TCR ß-chain libraries from five MS patients and five IIH controls were sequenced, yielding a total of 80 million reads. RESULTS: Although TCR repertoire diversity was greater in the blood and CSF compartments of MS patients when compared with IIH controls, it is notable that the frequency of clonal expansions was also significantly higher in both compartments of MS patients. Highly expanded T-cell clones were enriched in the CSF compartment of MS patients compared to peripheral blood, very few of them were detected in both compartments. INTERPRETATION: Collectively, our data provide a proof of principle that private compartmentalized T-cell expansion exists in the intrathecal space of MS patients.

Vaccine-Induced Antibodies that Neutralize Group 1 and Group 2 Influenza A Viruses.

Antibodies capable of neutralizing divergent influenza A viruses could form the basis of a universal vaccine. Here, from subjects enrolled in an H5N1 DNA/MIV-prime-boost influenza vaccine trial, we sorted hemagglutinin cross-reactive memory B cells and identified three antibody classes, each capable of neutralizing diverse subtypes of group 1 and group 2 influenza A viruses. Co-crystal structures with hemagglutinin revealed that each class utilized characteristic germline genes and convergent sequence motifs to recognize overlapping epitopes in the hemagglutinin stem. All six analyzed subjects had sequences from at least one multidonor class, and-in half the subjects-multidonor-class sequences were recovered from >40% of cross-reactive B cells. By contrast, these multidonor-class sequences were rare in published antibody datasets. Vaccination with a divergent hemagglutinin can thus increase the frequency of B cells encoding broad influenza A-neutralizing antibodies. We propose the sequence signature-quantified prevalence of these B cells as a metric to guide universal influenza A immunization strategies.

Quality and quantity of TFH cells are critical for broad antibody development in SHIVAD8 infection.

Broadly neutralizing antibodies (bNAbs) protect against HIV-1 infection, yet how they are generated during chronic infection remains unclear. It is known that T follicular helper (TFH) cells are needed to promote affinity maturation of B cells during an immune response; however, the role of TFH during HIV-1 infection is undefined within lymph node germinal centers (GCs). We use nonhuman primates to investigate the relationship in the early stage of chronic SHIVAD8 (simian-human immunodeficiency virus AD8) infection between envelope (Env)-specific TFH cells, Env-specific B cells, virus, and the generation of bNAbs during later infection. We found that both the frequency and quality of Env-specific TFH cells were associated with an expansion of Env-specific immunoglobulin G-positive GC B cells and broader neutralization across HIV clades. We also found a correlation between breadth of neutralization and the degree of somatic hypermutation in Env-specific memory B cells. Finally, we observed high viral loads and greater diversity of Env sequences in rhesus macaques that developed cross-reactive neutralization as compared to those that did not. These studies highlight the importance of boosting high-quality TFH populations as part of a robust vaccine regimen aimed at eliciting bNabs.

Analysis of immunoglobulin transcripts and hypermutation following SHIV(AD8) infection and protein-plus-adjuvant immunization.

Developing predictive animal models to assess how candidate vaccines and infection influence the ontogenies of Envelope (Env)-specific antibodies is critical for the development of an HIV vaccine. Here we use two nonhuman primate models to compare the roles of antigen persistence, diversity and innate immunity. We perform longitudinal analyses of HIV Env-specific B-cell receptor responses to SHIV(AD8) infection and Env protein vaccination with eight different adjuvants. A subset of the SHIV(AD8)-infected animals with higher viral loads and greater Env diversity show increased neutralization associated with increasing somatic hypermutation (SHM) levels over time. The use of adjuvants results in increased ELISA titres but does not affect the mean SHM levels or CDR H3 lengths. Our study shows how the ontogeny of Env-specific B cells can be tracked, and provides insights into the requirements for developing neutralizing antibodies that should facilitate translation to human vaccine studies.

Epitope specificity delimits the functional capabilities of vaccine-induced CD8 T cell populations.

Despite progress toward understanding the correlates of protective T cell immunity in HIV infection, the optimal approach to Ag delivery by vaccination remains uncertain. We characterized two immunodominant CD8 T cell populations generated in response to immunization of BALB/c mice with a replication-deficient adenovirus serotype 5 vector expressing the HIV-derived Gag and Pol proteins at equivalent levels. The Gag-AI9/H-2K(d) epitope elicited high-avidity CD8 T cell populations with architecturally diverse clonotypic repertoires that displayed potent lytic activity in vivo. In contrast, the Pol-LI9/H-2D(d) epitope elicited motif-constrained CD8 T cell repertoires that displayed lower levels of physical avidity and lytic activity despite equivalent measures of overall clonality. Although low-dose vaccination enhanced the functional profiles of both epitope-specific CD8 T cell populations, greater polyfunctionality was apparent within the Pol-LI9/H-2D(d) specificity. Higher proportions of central memory-like cells were present after low-dose vaccination and at later time points. However, there were no noteworthy phenotypic differences between epitope-specific CD8 T cell populations across vaccine doses or time points. Collectively, these data indicate that the functional and phenotypic properties of vaccine-induced CD8 T cell populations are sensitive to dose manipulation, yet constrained by epitope specificity in a clonotype-dependent manner.

Quantification of HTLV-1 clonality and TCR diversity.

Estimation of immunological and microbiological diversity is vital to our understanding of infection and the immune response. For instance, what is the diversity of the T cell repertoire? These questions are partially addressed by high-throughput sequencing techniques that enable identification of immunological and microbiological "species" in a sample. Estimators of the number of unseen species are needed to estimate population diversity from sample diversity. Here we test five widely used non-parametric estimators, and develop and validate a novel method, DivE, to estimate species richness and distribution. We used three independent datasets: (i) viral populations from subjects infected with human T-lymphotropic virus type 1; (ii) T cell antigen receptor clonotype repertoires; and (iii) microbial data from infant faecal samples. When applied to datasets with rarefaction curves that did not plateau, existing estimators systematically increased with sample size. In contrast, DivE consistently and accurately estimated diversity for all datasets. We identify conditions that limit the application of DivE. We also show that DivE can be used to accurately estimate the underlying population frequency distribution. We have developed a novel method that is significantly more accurate than commonly used biodiversity estimators in microbiological and immunological populations.