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Summary: Upon resolution of an acute viral infection, during latent‐reactivating infection and during chronic active infections virus‐specific T‐cells differentiate into distinct subsets that differ in phenotype, longevity, transcriptional, metabolic, and epigenetic profiles, and effector functions. With recent advances in single‐cell profiling, this substantial heterogeneity has become apparent and new subsets of virus‐specific T cells, either of stable or transitory nature, are being identified. A unifying principle of T cells emerging in these different conditions is their precursor–progeny relationship. For acute and resolved viral infections, this relationship becomes apparent during re‐challenge, whereas a constant differentiation of progenitor T cells into more differentiated cells occurs during latent‐reactivating and active chronic viral infections. In this review, we summarize and discuss current knowledge about T‐cell heterogeneity and progenitor–progeny relationships in the setting of persistent viral infections. [ABSTRACT FROM AUTHOR]

Monoclonal antibodies (mAbs) are often selected from antigen-specific single B cells derived from different hosts, which are notably short-lived in ex vivo culture conditions and hence, arduous to interrogate. The development of several new techniques and protocols has facilitated the isolation and retrieval of antibody-coding sequences of antigen-specific B cells by also leveraging miniaturization of reaction volumes. Alternatively, mAbs can be generated independently of antigen-specific B cells, comprising display technologies and, more recently, artificial intelligence-driven algorithms. Consequently, a considerable variety of techniques are used, raising the demand for better consolidation. In this review, we present and discuss the major techniques available to interrogate antigen-specific single B cells to isolate antigen-specific mAbs, including their main advantages and disadvantages. Monoclonal antibodies (mAbs) are among the most important type of biologic drugs on the pharmaceutical market, as well as for diagnostic purposes. Presently, more than 100 mAbs have been approved by the US FDA against a variety of diseases such as cancer, infectious diseases, autoimmune diseases, and neurological disorders. Primary antigen-specific B cells are the main source for obtaining antigen-specific mAb sequences, particularly using human specimens such as peripheral blood mononuclear cells. Also, the humanization of mAbs derived from other species (e.g. mice, rats, and rabbits) has become easier and more efficient. Currently, single B cell screening systems bear multiple advantages over other systems, such as display technologies. Particularly, the in vivo development of mAbs favors the safety profile and the overall developability. It also has reduced off-target binding to the human proteome. Single B cell technologies have significantly evolved, becoming faster and higher throughput than before. Nonetheless, hybridoma technology, the first technique in this field, still represents an important methodology and is well known within the scientific community. At present no gold standard exists in the field, relying on a broad variety of different single B cell systems for mAb discovery – each with its advantages and disadvantages. [ABSTRACT FROM AUTHOR]

T cell responses are critical for controlling cytomegalovirus (CMV) infection. However, CMV expresses immune evasion genes promoting escape from T cell immunity. Furthermore, CMV persistence in form of latency, coupled with viral reactivation events, provokes two unique features of CMV-specific CD8 T cell responses: their size and phenotype. CMV-specific T cells with certain specificities respond to the infection by an initial expansion and thereafter a secondary increase to reach high and stably maintained frequencies of functional and widely dispersed CMV-specific CD8 T cells — in a process termed 'memory inflation'. Additionally, many of these 'inflated' CD8 T cells exhibit a particular phenotype, characterized by the expression of effector-memory and natural killer-associated markers. Here, we review and discuss insights into T cell responses elicited by CMV infection combined with cellular and molecular mechanisms explaining the scale and the phenotype of inflationary cells and their function in CMV infection. [ABSTRACT FROM AUTHOR]

The identification of T cell co-inhibition as a central mechanism in the regulation of adaptive immunity during infectious diseases provides new opportunities for immunotherapeutic interventions. However, the fact that T cell activity is frequently downregulated during pathogen-directed responses suggests a pivotal physiological role of co-inhibitory pathways during infectious disease. Reports of exacerbated immunopathology in conditions of impaired co-inhibition foster the view that downregulation of T cell activity is an essential negative feedback mechanism that protects from excessive pathogen-directed immunity. Thus, targeting co-inhibitory pathways can bear detrimental potential through the deregulation of physiological processes. Here, we summarize recent preclinical and clinical interventions that report immune-related adverse events after targeting co-inhibitory pathways. [ABSTRACT FROM AUTHOR]

The innate immune system recognizes invading microbes via conserved pattern recognition receptors and uses inflammatory signals to concert adaptive defense mechanisms. However, microbial and host parameters involved in CD4 Τ cell priming and direction of Th1, Th2, and Th17 differentiation in the context of infections with complex pathogens in vivo are incompletely understood. In this study, we used Legionella pneumophila, which triggers membrane-bound and cytosolic pattern recognition receptors, to study the innate instruction of adaptive immunity. Upon airway infection, Τ cells were primed exclusively in the lungdraining lymph nodes and differentiated into Th1/Th17 effector cells upon arrival in the lung. Although engagement of membrane-bound pattern recognition receptors was sufficient for initial Τ cell activation and proliferation, cytosolic pattern recognition was required for effector Τ cell differentiation. In the absence of cytoplasmic pattern recognition, My D88 was key for Τ cell priming, whereas, in its presence, My D88-mediated signals were crucial for Th17 differentiation. Specifically, cytosolic sensing of Legionella-derived flagellin, inflammasome activation, and IL-1 signaling contributed to Th17 development. In the absence of TLR signaling, a simultaneous Th1/Th2 response developed that was independent of the inflammasome-IL-1 axis. Collectively, these data illustrate the important role for various pattern recognition receptors triggered by complex pathogens and how they each instruct specific differentiation programs in responding CD4 Τ cells. [ABSTRACT FROM AUTHOR]

The generation of a functional memory T cell pool upon primary encounter with an infectious pathogen is, in combination with humoral immunity, an essential process to confer protective immunity against reencounters with the same pathogen. A prerequisite for the generation and maintenance of long-lived memory T cells is the clearance of antigen after infection, which is fulfilled upon resolution of acute viral infections. Memory T cells play also a fundamental role during persistent viral infections by contributing to relative control and immuosurveillance of active replication or viral reactivation, respectively. However, the dynamics, the phenotype, the mechanisms of maintenance and the functionality of memory T cells which develop upon acute/resolved infection as opposed to chronic/latent infection differ substantially. In this review we summarize current knowledge about memory CD8 T cell responses elicited during α-, β-, and λ-herpes viral infections with major emphasis on the induction, maintenance and function of virus-specific memory CD8 T cells during viral latency and we discuss how the peculiar features of these memory CD8 T cell responses are related to the biology of these persistently infecting viruses. [ABSTRACT FROM AUTHOR]

The outcome of human immunodeficiency virus type 1 (HIV-1) infection is related to the set-point plasma virus load (pVL) that emerges after primary HIV-1 infection (PHI). This set-point pVL generally remains stable but eventually increases with progression to disease. However, the events leading to loss of viremic control are poorly understood. Here, we describe an individual who presented with symptomatic PHI and subsequently progressed rapidly, after an initial period of 1 year during which viral replication was well controlled. Escalation of viral replication in this atypical case was preceded by the emergence of escape variants in many epitopes targeted by dominant CD8+ T cell responses and a marked decrease in HIV-1-specific CD4+ and CD8+ T cell frequencies. There were no changes in viral tropism, replication kinetics, or neutralizing antibody titers. These findings demonstrate the temporal relationship between viral escape from CD8+ T cell activity, decrease in HIV-1-specific T cell frequencies, and loss of control of viral replication. [ABSTRACT FROM AUTHOR]

The average time between infection with human immunodeficiency virus (HIV) and development of acquired immune deficiency syndrome is ∼8 years. However, progression rates vary widely, depending on several determinants, including HIV-specific immunity, host genetic factors, and virulence of the infecting strain. In untreated HIV-infected patients with different progression rates, we examined HIV-specific T cell responses in combination with host genetic markers, such as chemokine/chemokine-receptor (CCR) polymorphisms and human leukocyte antigen (HLA) genotypes. HIV-specific CD4+ T cell responses and, to a lesser extent, HIV-specific CD8+ T cell responses were inversely correlated with progression rate. Slower progression was not related to polymorphisms in CCR genes, HLA genotype, or GB virus C coinfection. These data suggest that HIV-specific T cell responses are involved in protecting the host from disease progression. [ABSTRACT FROM AUTHOR]

Background: According to the "autovaccination hypothesis," reexposure to human immunodeficiency virus (HIV) during treatment interruptions may stimulate the HIV-specific immune response and lead to low viremia after withdrawal of highly active antiretroviral treatment (HAART). Many patients who started HAART earlier in their disease course than is currently recommended would like to discontinue, but it is unknown whether it is safe to do so. Objectives: To determine whether repeated treatment interruptions of HAART (1) stimulated the cytotoxic HIV-specific immune response and whether such stimulation correlated with low viremia off treatment, and (2) were safe with respect to clinical complications, development of viral resistance, and decline in CD4 cell counts. Design: Interventional study with before-after comparison. Setting: Outpatient clinics of university hospitals in Switzerland and Spain. Patients: A total of 133 patients receiving HAART, with a median CD4 cell count of 740/μL, and whose viral load had been undetectable for a median of 21 months. Interventions: HAART was interrupted for 2 weeks, restarted, and continued for 8 weeks. After 4 such cycles, treatment was indefinitely suspended 40 weeks after study entry. Main Outcome Measures: HIV-specific cytotoxic T-cell responses were evaluated by interferon γ enzyme-linked immunospot analysis. The proportion of "responders" (viral load <5000 copies/mL) was measured at weeks 52 and 96. HIV-related diseases and CD4 cell counts were recorded. Results: Seventeen percent of patients (95% confidence interval, 11%-25%) were responders at week 52, and 8% at week 96. Low pre-HAART viral load and lack of rebound during weeks 0 to 40 predicted response. HIV-specific CD8[SUP+] T cells increased between week 0 (median, 343 spot-forming cells per million peripheral blood lymphocytes [SFC/10[SUP6] PBL]) and week 52 (median, 1930 SFC/10[SUP6] PBL), but there was an inverse correlation between... [ABSTRACT FROM AUTHOR]

Analyzes the impact of structured therapeutic interruptions (STI) on HIV-specific cellular immunity. Control of viral replication in the absence of antiretroviral therapy by STI; Increase in HIV-specific CD8[sup+] T lymphocyte frequencies induced by STI; Failure of STI to enhance viral control in chronic HIV infection.

Analyzes somatic variation of V[sub H]7183-positive vesicular stomatitis virus (VSV)-neutralizing monoclonal antibodies. V[sub H] and V[sub L] sequence comparison of VSV-specific monoclonal IgGs.

Presents information on a study which demonstrated the effect of early use of highly active antiretroviral therapy (HAART) during primary infection of HIV-specific T cells. Effectiveness of HAART in the management of HIV; Influence of delayed HAART initiation; Materials and methods used; Results and discussion.

Discusses research by H.D. Chen and colleagues, published in the November 2001 issue of 'Nature Immunology,' suggesting that pre-existing memory T cells specific for one type of virus can improve the disease outcome after infection with an unrelated virus. Protection afforded by lymphocytic choriomeningitis virus-specific memory cytotoxic T lymphocytes against heterologous virus challenge.

Memory T cell inflation is a process in which a large number of effector memory T cells accumulates in peripheral tissues. This phenomenon is observed upon certain low level persistent virus infections, but it is most commonly described upon infection with the β-herpesvirus Cytomegalovirus. Due to the induction of this large pool of functional effector CD8 T cells in peripheral tissues, the interest in using CMV-based vaccine vectors for vaccination purposes is rising. However, the exact mechanisms of memory T cell inflation are not yet fully understood. It is clear that repetitive exposure to antigen is a key determinant for memory inflation, and therefore the viral inoculum dose and the subsequent number of viral reactivation events strongly impact on the magnitude of the inflationary T cell pool. In addition, the number of CMV-specific CD8 T cells that is able to sense these reactivation events affects the size of the inflationary T cell pool. In the following, we will discuss factors that either promote or limit T cell inflation from both the virus and host perspective. These factors mostly operate by influencing the amount of available antigen or by affecting the T cell pool that is able to respond to the antigen. Furthermore, we will discuss the recent use of CMV-based vaccines in pre-clinical experimental settings, where these vectors have shown promising results by inducing prolonged effector memory T cell responses to foreign-introduced epitopes and thereby provided protection from subsequent virus or tumour challenges. [ABSTRACT FROM AUTHOR]

A response by the authors to a letter to the editor about their study titled "Nonhematopoietic Cells Are Key Players in Innate Control of Bacterial Airway Infection" is presented.

Antibody-cytokine complexes may offer new tools to treat cancer. Here, we show how TNF-linked antibodies, which recognize tumor-selective splice isoforms of fibronectin (F8-TNF), can be exploited to eradicate sarcomas in immunocompetent mice. We treated mice bearing WEHI-164 fibrosarcoma with a combination of F8-TNF and doxorubicin, curing the majority of treated animals (29/37). Notably, cured mice were resistant to rechallenge not only by WEHI-164 cells but also heterologous C51 or CT26 colorectal tumor cells in a CD8+ T-cell-dependent process. Mechanistic analyses revealed that each tumor cell line presented AH1, a common endogenous retroviral peptide. Numbers of AH1-specific CD8+ T cells exhibiting cytotoxic capacity were increased by F8-TNF plus doxorubicin treatment, arguing that cognate CD8+ T cells contributed to tumor eradication. Sequence analysis of T-cell receptors of CD8+ T cells revealed the presence of H-2Ld/AH1-specific T cells and an expansion of sequence diversity in treated mice. Overall, our findings provide evidence that retroviral genes contribute to tumoral immunosurveillance in a process that can be generally boosted by F8-TNF and doxorubicin treatment. [ABSTRACT FROM AUTHOR]

Legionella pneumophila is a facultative intracellular bacterium that lives in aquatic environments where it parasitizes amoeba. However, upon inhalation of contaminated aerosols it can infect and replicate in human alveolar macrophages, which can result in Legionnaires’ disease, a severe form of pneumonia. Upon experimental airway infection of mice, L. pneumophila is rapidly controlled by innate immune mechanisms. Here we identified, on a cell-type specific level, the key innate effector functions responsible for rapid control of infection. In addition to the well-characterized NLRC4-NAIP5 flagellin recognition pathway, tumor necrosis factor (TNF) and reactive oxygen species (ROS) are also essential for effective innate immune control of L. pneumophila. While ROS are essential for the bactericidal activity of neutrophils, alveolar macrophages (AM) rely on neutrophil and monocyte-derived TNF signaling via TNFR1 to restrict bacterial replication. This TNF-mediated antibacterial mechanism depends on the acidification of lysosomes and their fusion with L. pneumophila containing vacuoles (LCVs), as well as caspases with a minor contribution from cysteine-type cathepsins or calpains, and is independent of NLRC4, caspase-1, caspase-11 and NOX2. This study highlights the differential utilization of innate effector pathways to curtail intracellular bacterial replication in specific host cells upon L. pneumophila airway infection. [ABSTRACT FROM AUTHOR]

The article focuses on the diversity of responses and differentiation trajectories among naïve T cells during antigen responses, suggesting a potential role for both external factors and cell-intrinsic predeterminants. It systematically investigates the architectural heterogeneity of primary human and murine T cells and its influence on determining the strength of T cell receptor (TCR) signals.

The capacity of humoral B cell-mediated immunity to effectively respond to and protect against pathogenic infections is largely driven by the presence of a diverse repertoire of polyclonal antibodies in the serum, which are produced by plasma cells (PCs). Recent studies have started to reveal the balance between deterministic mechanisms and stochasticity of antibody repertoires on a genotypic level (i.e., clonal diversity, somatic hypermutation, and germline gene usage). However, it remains unclear if clonal selection and expansion of PCs follow any deterministic rules or are stochastic with regards to phenotypic antibody properties (i.e., antigen-binding, affinity, and epitope specificity). Here, we report on the in-depth genotypic and phenotypic characterization of clonally expanded PC antibody repertoires following protein immunization. We find that clonal expansion drives antigen specificity of the most expanded clones (top ∼10), whereas among the rest of the clonal repertoire antigen specificity is stochastic. Furthermore, we report both on a polyclonal repertoire and clonal lineage level that antibody-antigen binding affinity does not correlate with clonal expansion or somatic hypermutation. Last, we provide evidence for convergence toward targeting dominant epitopes despite clonal sequence diversity among the most expanded clones. Our results highlight the extent to which clonal expansion can be ascribed to antigen binding, affinity, and epitope specificity, and they have implications for the assessment of effective vaccines. [ABSTRACT FROM AUTHOR]

Type I interferons (IFNs) are pro-inflammatory cytokines that are rapidly induced in different cell types during viral infections. The consequences of type I IFN signalling include direct antiviral activity, innate immune cell activation and regulation of adaptive immune responses. In this Review, we discuss recent conceptual advances in our understanding of indirect and direct regulation of T cell immunity by type I IFNs, which can either promote or inhibit T cell activation, proliferation, differentiation and survival. This regulation depends, to a large extent, on the timing of type I IFN exposure relative to T cell receptor signalling. Type I IFNs also provide activated T cells with resistance to natural killer cell-mediated elimination. [ABSTRACT FROM AUTHOR]

Abs are able to mediate local protection from pulmonary infection with Legionella pneumophila, the causative agent of a severe form of pneumonia known as Legionnaires' disease. L. pneumophila is able to infect alveolar macrophages in the lung and replicates intracellularly in a vacuolar compartment with endoplasmic reticulum-like characteristics. However, Abs opsonize the bacteria and confer an FcR-mediated signal to phagocytic host cells that vetoes the bacterial evasion strategies, thereby efficiently targeting the bacteria to intracellular lysosomal degradation. In this study we analyzed the prevalence of pathogen-specific IgG subclasses present in immunized mice and found that the presence of IgG2c and IgG3 correlated with reduced bacterial titers after intranasal infection. We then isolated different IgG subclasses and compared their differential prophylactic potential in restricting airway L. pneumophila replication. We found that all IgG subclasses were effective in restricting pulmonary airway infection in mice when administered at high and equivalent doses. However, at limiting Ab concentrations we found a superior role of IgG2c in restricting L. pneumophila replication in a prophylactic setting. Furthermore, we assessed the therapeutic efficacy of administering an mAb during an established infection and found that bacterial titers could be reduced very efficiently with such a treatment. Thus, we propose the therapeutic use of Abs for the treatment of intracellular bacterial infections in situations where antibiotics might be ineffective. [ABSTRACT FROM AUTHOR]

Background: The continued spread of SARS-CoV-2 and emergence of new variants with higher transmission rates and/or partial resistance to vaccines has further highlighted the need for large-scale testing and genomic surveillance. However, current diagnostic testing (e.g., PCR) and genomic surveillance methods (e.g., whole genome sequencing) are performed separately, thus limiting the detection and tracing of SARS-CoV-2 and emerging variants. Results: Here, we developed DeepSARS, a high-throughput platform for simultaneous diagnostic detection and genomic surveillance of SARS-CoV-2 by the integration of molecular barcoding, targeted deep sequencing, and computational phylogenetics. DeepSARS enables highly sensitive viral detection, while also capturing genomic diversity and viral evolution. We show that DeepSARS can be rapidly adapted for identification of emerging variants, such as alpha, beta, gamma, and delta strains, and profile mutational changes at the population level. Conclusions: DeepSARS sets the foundation for quantitative diagnostics that capture viral evolution and diversity. DeepSARS uses molecular barcodes (BCs) and multiplexed targeted deep sequencing (NGS) to enable simultaneous diagnostic detection and genomic surveillance of SARS-CoV-2. Image was created using Biorender.com. [ABSTRACT FROM AUTHOR]

Genome mining and bioactivity studies suggested the sponge‐derived bacterium Aquimarina sp. Aq135 as a producer of new antibiotics. Activity‐guided isolation identified antibacterial peptides, named aquimarins, featuring a new scaffold with an unusual C‐terminal amino group and chlorine moieties. Responsible for the halogenation is the FeII/α‐ketoglutarate‐dependent chlorinase AqmA that halogenates up to two isoleucine residues in a carrier protein‐dependent fashion. Total syntheses of two natural aquimarins and eight non‐natural variants were developed. Structure–activity relationship (SAR) studies with these compounds showed that the synthetically more laborious chlorinations are not required for antibacterial activity but enhance cytotoxicity. In contrast, variants lacking the C‐terminal amine were virtually inactive, suggesting diamines similar to the terminal aquimarin residue as candidate building blocks for new peptidomimetic antibiotics. [ABSTRACT FROM AUTHOR]

Genome mining and bioactivity studies suggested the sponge‐derived bacterium Aquimarina sp. Aq135 as a producer of new antibiotics. Activity‐guided isolation identified antibacterial peptides, named aquimarins, featuring a new scaffold with an unusual C‐terminal amino group and chlorine moieties. Responsible for the halogenation is the FeII/α‐ketoglutarate‐dependent chlorinase AqmA that halogenates up to two isoleucine residues in a carrier protein‐dependent fashion. Total syntheses of two natural aquimarins and eight non‐natural variants were developed. Structure–activity relationship (SAR) studies with these compounds showed that the synthetically more laborious chlorinations are not required for antibacterial activity but enhance cytotoxicity. In contrast, variants lacking the C‐terminal amine were virtually inactive, suggesting diamines similar to the terminal aquimarin residue as candidate building blocks for new peptidomimetic antibiotics. [ABSTRACT FROM AUTHOR]

Motivation Single-cell sequencing now enables the recovery of full-length immune receptor repertoires [B cell receptor (BCR) and T cell receptor (TCR) repertoires], in addition to gene expression information. The feature-rich datasets produced from such experiments require extensive and diverse computational analyses, each of which can significantly influence the downstream immunological interpretations, such as clonal selection and expansion. Simulations produce validated standard datasets, where the underlying generative model can be precisely defined and furthermore perturbed to investigate specific questions of interest. Currently, there is no tool that can be used to simulate single-cell datasets incorporating immune receptor repertoires and gene expression. Results We developed Echidna, an R package that simulates immune receptors and transcriptomes at single-cell resolution with user-tunable parameters controlling a wide range of features such as clonal expansion, germline gene usage, somatic hypermutation, transcriptional phenotypes and spatial location. Echidna can additionally simulate time-resolved B cell evolution, producing mutational networks with complex selection histories incorporating class-switching and B cell subtype information. We demonstrated the benchmarking potential of Echidna by simulating clonal lineages and comparing the known simulated networks with those inferred from only the BCR sequences as input. Finally, we simulated immune repertoire information onto existing spatial transcriptomic experiments, thereby generating novel datasets that could be used to develop and integrate methods to profile clonal selection in a spatially resolved manner. Together, Echidna provides a framework that can incorporate experimental data to simulate single-cell immune repertoires to aid software development and bioinformatic benchmarking of clonotyping, phylogenetics, transcriptomics and machine learning strategies. Availability and implementation The R package and code used in this manuscript can be found at github.com/alexyermanos/echidna and also in the R package Platypus (Yermanos et al. , 2021). Installation instructions and the vignette for Echidna is described in the Platypus Computational Ecosystem (https://alexyermanos.github.io/Platypus/index.html). Publicly available data and corresponding sample accession numbers can be found in Supplementary Tables S2 and S3. Supplementary information Supplementary data are available at Bioinformatics Advances online. [ABSTRACT FROM AUTHOR]

Immune responses mediated by cytotoxic T lymphocytes (CTLs) have often been found to be functionally impaired in persistent infections. It is assumed that this impairment contributes to persistence of the infection. In this study, we compare the killing efficacy of CD8+ T-cell responses in mice acutely and persistently infected with the lymphocytic choriomeningitis virus, using an in vivo CTL killing assay. To infer the killing efficacy of CTLs, we developed a new mathematical model describing the disappearance of peptide-pulsed cells from the blood of the mice over time. We estimate a lower half-life for peptidepulsed cells in acute infection than in persistent infection, which indicates a higher killing efficacy of the CD8+ T-cell response in acute infection. However, by controlling for the different levels of CTLs in acutely and persistently infected mice, we find that CTLs in persistent infection are only two times less efficacious than CTLs in acute infections. These results strongly suggest that the in vivo cytotoxicity of CD8+ T-cell responses in persistent infection is modulated via the number of CTLs rather than their individual functionality. [ABSTRACT FROM AUTHOR]

Successful priming of adaptive immune responses is crucially dependent on innate activation signals that convert resting antigenpresenting cells (APCs) into immunogenic ones. APC5 expressing the relevant innate pattern recognition receptors can be directly activated by pathogen-associated molecular patterns (PAMPs) to become competent to prime T-cell responses. Alternatively, it has been suggested that APCs could be activated indirectly by promflammatory mediators synthesized by PAMP-exposed cells. However, data obtained with CD4+ T cells suggest that inflammatory signals often cannot substitute for direct pattern recognition in APC activation for the priming of T helper responses. To test whether the same is true for CD8+ T cells, we studied cytotoxic T lymphocyte development in vitro and in mixed chimeric mice in which coexisting APCs can either present a preprocessed model antigen or directly recognize a given PAMP, but not both. We show that indirectly activated APCs promote antigen-specific proliferation of naïve CD8+ T cells but fail to support their survival and cytotoxic T lymphocyte differentiation. Furthermore, CD8+ T cells primed by indirectly activated APCs are unable to reject tumors. Thus, inflammation cannot substitute for direct recognition of single PAMPs in CD8+ T-cell priming. These findings have important practical implications for vaccine design, indicating that adjuvants must be judiciously chosen to trigger the relevant pattern recognition receptors in APCs. [ABSTRACT FROM AUTHOR]

Certain virus infections depend on the presence of T cell help for the generation of primary CD8+ T cell responses. However, the mechanisms that render these particular viral infections T cell help dependent is largely unknown. In this study, we compared CD8+ T cell responses elicited by lymphocytic choriomeningitis virus infection, as prototype of a T cell help independent infection, with T cell help dependent CD8+ T cell responses induced by vaccinia virus infection. In this paper, we show that a key parameter decisive for T cell help independence is the ability of an infectious agent to stimulate early and robust production of type I IFN. Experimental provision of type I IFN during VV infection rendered the ensuing CD8+ T cell response completely T cell help independent. Our results support a model in which type I IFN has to be present during the first 3 d of Ag encounter and has to act directly on the responding CD8+ T cells to promote their survival and effector differentiation. We show that type I IFN signaling on responding CD8+ T cells induces profound upregulation of CD25 and increased IL-2 expression; however, neither this nor IL- 15 accounts for the type I IFN effects on responding CD8+ T cells. Thus, type I IFN can effectively replace the requirement of T cell help by directly promoting CD8+ T cell survival and differentiation independent of the type I IFN-induced cytokines IL-2 and IL-15. [ABSTRACT FROM AUTHOR]

Chronic viral infections are often characterized by CD8 T-cell responses with poor cytokine secretion potential and limited expansion of the CD8 T-cell pool, collectively referred to as CD8 T-cell exhaustion. Exhaustion of lymphocytic choriomeningitis virus (LCMV)-specific CD8 T cells was shown to be partially regulated by the inhibitory receptor programmed death 1 (PD-1). Here, we demonstrate that exhausted LCMV-specific CD8 T cells also express the negative regulatory receptor lymphocyte activation gene 3 (LAG-3) which is mainly expressed on cells co-expressing the negative regulatory receptors PD-1 and Tim-3. Expression levels of LAG-3 on anti-viral CD8 T cells remain stable over short-term in vitro stimulations in presence of antigenic peptide. Nevertheless, in vitro and in vivo blockade of LAG-3 did not rescue cytokine production by virus-specific CD8 T cells and did not alter the virus titer in various organs. Likewise, chronic LCMV infection of LAG-3−/− mice led to a comparable degree of T-cell exhaustion as observed in C57BL/6 controls and to similar virus titers. Further, LAG-3 did not influence T-cell activation or cell division during chronic LCMV infection. These data suggest that even though LAG-3 is continuously up-regulated on LCMV-specific exhausted CD8 T cells, it alone does not significantly contribute to T-cell exhaustion. [ABSTRACT FROM PUBLISHER]

Analyzes the dynamics of both HIV-1-specific CD4 and CD8 T cell responses during structured treatment interruptions (STI) in chronically HIV-1-infected (CHI) patients. Means of controlling viral replication in CHI patients; Changes in viral load set point following STI in CHI patients; Analysis of the evolution and dynamics of HIV-1-specific immune responses during STI.

T cells sense and respond to their local environment at the nanoscale by forming small actin-rich protrusions, called microvilli, which play critical roles in signaling and antigen recognition, particularly at the interface with the antigen presenting cells. However, the mechanism by which microvilli contribute to cell signaling and activation is largely unknown. Here, we present a tunable engineered system that promotes microvilli formation and T cell signaling via physical stimuli. We discovered that nanoporous surfaces favored microvilli formation and markedly altered gene expression in T cells and promoted their activation. Mechanistically, confinement of microvilli inside of nanopores leads to size-dependent sorting of membraneanchored proteins, specifically segregating CD45 phosphatases and T cell receptors (TCR) from the tip of the protrusions when microvilli are confined in 200-nm pores but not in 400-nm pores. Consequently, formation of TCR nanoclustered hotspots within 200-nm pores allows sustained and augmented signaling that prompts T cell activation even in the absence of TCR agonists. The synergistic combination of mechanical and biochemical signals on porous surfaces presents a straightforward strategy to investigate the role of microvilli in T cell signaling as well as to boost T cell activation and expansion for application in the growing field of adoptive immunotherapy. [ABSTRACT FROM AUTHOR]

Many individuals chronically infected with human immunodeficiency virus type 1 (HIV-1) experience a recrudescence of plasma virus during continuous combination antiretroviral therapy (ART) due either to the emergence of drug-resistant viruses or to poor compliance. In most cases, virologic failure on ART is associated with a coincident decline in CD4[sup +] T lymphocyte levels. However, a proportion of discordant individuals retain a stable or even increasing CD4[sup +] T lymphocyte count despite virological failure. In order to address the nature of these different outcomes, we evaluated virologic and immunologic variables in a prospective, single-blinded, nonrandomized cohort of 53 subjects with chronic HIV-1 infection who had been treated with continuous ART and monitored intensively over a period of 19 months. In all individuals with detectable viremia on ART, multiple drug resistance mutations with similar impacts on viral growth kinetics were detected in the poi gene of circulating plasma virus. Further, C2V3 env gene analysis demonstrated sequences indicative of CCR5 coreceptor usage in the majority of those with detectable plasma viremia. In contrast to this homogeneous virologic pattern, comprehensive screening with a range of antigens derived from HIV-1 revealed substantial immunologic differences. Discordant subjects with stable CD4[sup +] T lymphocyte counts in the presence of recrudescent virus demonstrated potent virus-specific CD4[sup +] and CD8[sup +] T lymphocyte responses. In contrast, subjects with virologic failure associated with declining CD4[sup +] T lymphocyte counts had substantially weaker HIV-specific CD4[sup +] T lymphocyte responses and exhibited a trend towards weaker HIV-specific CD8[sup +] T lymphocyte responses. Importantly the CD4[sup +] response was sustained over periods as long as 11 months, confirming the stability of the phenomenon. These correlative data lead to the testable hypothesis that the consequences of viral... [ABSTRACT FROM AUTHOR]

Nucleoprotein (N) is an immunodominant antigen in many enveloped virus infections. While the diagnostic value of anti‐N antibodies is clear, their role in immunity is not. This is because while they are non‐neutralising, they somehow clear infection by coronavirus, influenza and LCMV in vivo. Here, we show that anti‐N immune protection is mediated by the cytosolic Fc receptor and E3 ubiquitin ligase TRIM21. Exploiting LCMV as a model system, we demonstrate that TRIM21 uses anti‐N antibodies to target N for cytosolic degradation and generate cytotoxic T cells (CTLs) against N peptide. These CTLs rapidly eliminate N‐peptide‐displaying cells and drive efficient viral clearance. These results reveal a new mechanism of immune synergy between antibodies and T cells and highlights N as an important vaccine target. Synopsis: Cytosolic antibody receptor and ubiquitin ligase TRIM21 promotes antigen presentation and T cell activation by targeting immune complexes for efficient proteasomal degradation. Non‐neutralizing, anti‐nucleoprotein antibodies provide immune protection by stimulating cytotoxic T cell (CTL) activity.Anti‐nucleoprotein antibodies are dependent upon TRIM21 for their activity.TRIM21 and anti‐nucleoprotein antibodies help resolve LCMV infection in mice.TRIM21 promotes in vivo T cell killing. [ABSTRACT FROM AUTHOR]

Neuroinflammation plays a crucial role during ageing and various neurological conditions, including Alzheimer's disease, multiple sclerosis and infection. Technical limitations, however, have prevented an integrative analysis of how lymphocyte immune receptor repertoires and their accompanying transcriptional states change with age in the central nervous system. Here, we leveraged single-cell sequencing to simultaneously profile B cell receptor and T cell receptor repertoires and accompanying gene expression profiles in young and old mouse brains. We observed the presence of clonally expanded B and T cells in the central nervous system of aged male mice. Furthermore, many of these B cells were of the IgM and IgD isotypes, and had low levels of somatic hypermutation. Integrating gene expression information additionally revealed distinct transcriptional profiles of these clonally expanded lymphocytes. Our findings implicate that clonally related T and B cells in the CNS of elderly mice may contribute to neuroinflammation accompanying homeostatic ageing. [ABSTRACT FROM AUTHOR]

Viral infections are controlled, and very often cleared, by activated T lymphocytes. The inducible co-stimulator (ICOS) mediates its functions by binding to its ligand ICOSL, enhancing T-cell activation and optimal germinal center (GC) formation. Here, we show that ICOSL is heavily downmodulated during infection of antigen-presenting cells by different herpesviruses. We found that, in murine cytomegalovirus (MCMV), the immunoevasin m138/fcr-1 physically interacts with ICOSL, impeding its maturation and promoting its lysosomal degradation. This viral protein counteracts T-cell responses, in an ICOS-dependent manner, and limits virus control during the acute MCMV infection. Additionally, we report that blockade of ICOSL in MCMV-infected mice critically regulates the production of MCMV-specific antibodies due to a reduction of T follicular helper and GC B cells. Altogether, these findings reveal a novel mechanism evolved by MCMV to counteract adaptive immune surveillance, and demonstrates a role of the ICOS:ICOSL axis in the host defense against herpesviruses. [ABSTRACT FROM AUTHOR]

Introduction: Epidemiological data suggest that persistent viral infections impair immune homeostasis and immune responsiveness. Previous studies showed that chronic virus infections negatively impact bystander T‐cell differentiation and memory formation but there is limited knowledge of how chronic virus infections impinge on heterologous naive T‐cell populations. Methods: We used adoptive transfer of naive CD8 T cells with defined nonviral specificity into hosts, which were subsequently chronically infected with lymphocytic choriomeningitis virus, followed by analyses of numeric, phenotypic, and functional changes provoked in the chronically infected host. Results: We demonstrate that chronic virus infections have a profound effect on the number and phenotype of naive bystander CD8 T cells. Moreover, primary expansion upon antigen encounter was severely compromised in chronically infected hosts. However, when naive bystander CD8 T cells were transferred from the chronically infected mice into naive hosts, they regained their expansion potential. Conversely, when chronically infected hosts were supplied with additional antigen‐presenting cells (APCs), primary expansion of the naive CD8 T cells was restored to levels of the uninfected hosts. Conclusions: Our results document numeric, phenotypic, and functional adaptation of bystander naive CD8 T cells during nonrelated chronic viral infection. Their functional impairment was only evident in the chronically infected host, indicating that T‐cell extrinsic factors, in particular the quality of priming APCs, are responsible for the impaired function of naive bystander T cells in the chronically infected hosts. [ABSTRACT FROM AUTHOR]

Proteusins are a family of bacterial ribosomal peptides that largely remain hypothetical genome‐predicted metabolites. The only known members are the polytheonamide‐type cytotoxins, which have complex structures due to numerous unusual posttranslational modifications (PTMs). Cyanobacteria contain large numbers of putative proteusin loci. To investigate their chemical and pharmacological potential beyond polytheonamide‐type compounds, we characterized landornamide A, the product of the silent osp gene cluster from Kamptonema sp. PCC 6506. Pathway reconstruction in E. coli revealed a peptide combining lanthionines, d‐residues, and, unusually, two ornithines introduced by the arginase‐like enzyme OspR. Landornamide A inhibited lymphocytic choriomeningitis virus infection in mouse cells, thus making it one of the few known anti‐arenaviral compounds. These data support proteusins as a rich resource of chemical scaffolds, new maturation enzymes, and bioactivities. [ABSTRACT FROM AUTHOR]

Proteusins are a family of bacterial ribosomal peptides that largely remain hypothetical genome‐predicted metabolites. The only known members are the polytheonamide‐type cytotoxins, which have complex structures due to numerous unusual posttranslational modifications (PTMs). Cyanobacteria contain large numbers of putative proteusin loci. To investigate their chemical and pharmacological potential beyond polytheonamide‐type compounds, we characterized landornamide A, the product of the silent osp gene cluster from Kamptonema sp. PCC 6506. Pathway reconstruction in E. coli revealed a peptide combining lanthionines, d‐residues, and, unusually, two ornithines introduced by the arginase‐like enzyme OspR. Landornamide A inhibited lymphocytic choriomeningitis virus infection in mouse cells, thus making it one of the few known anti‐arenaviral compounds. These data support proteusins as a rich resource of chemical scaffolds, new maturation enzymes, and bioactivities. [ABSTRACT FROM AUTHOR]

Protection and neutralization of a vast array of pathogens is accomplished by the tremendous diversity of the B cell receptor (BCR) repertoire. For jawed vertebrates, this diversity is initiated via the somatic recombination of immunoglobulin (Ig) germline elements. While it is clear that the number of these germline segments differs from species to species, the extent of cross-species sequence diversity remains largely uncharacterized. Here we use extensive computational and statistical methods to investigate the sequence diversity and evolutionary relationship between Ig variable (V), diversity (D), and joining (J) germline segments across nine commonly studied species ranging from zebrafish to human. Metrics such as guanine-cytosine (GC) content showed low redundancy across Ig germline genes within a given species. Other comparisons, including amino acid motifs, evolutionary selection, and sequence diversity, revealed species-specific properties. Additionally, we showed that the germline-encoded diversity differs across antibody (recombined V-D-J) repertoires of various B cell subsets. To facilitate future comparative immunogenomics analysis, we created VDJgermlines, an R package that contains the germline sequences from multiple species. Our study informs strategies for the humanization and engineering of therapeutic antibodies. [ABSTRACT FROM AUTHOR]

Memory T cell inflation is a process in which a subset of cytomegalovirus (CMV) specific CD8 T cells continuously expands mainly during latent infection and establishes a large and stable population of effector memory cells in peripheral tissues. Here we set out to identify in vivo parameters that promote and limit CD8 T cell inflation in the context of MCMV infection. We found that the inflationary T cell pool comprised mainly high avidity CD8 T cells, outcompeting lower avidity CD8 T cells. Furthermore, the size of the inflationary T cell pool was not restricted by the availability of specific tissue niches, but it was directly related to the number of virus-specific CD8 T cells that were activated during priming. In particular, the amount of early-primed KLRG1- cells and the number of inflationary cells with a central memory phenotype were a critical determinant for the overall magnitude of the inflationary T cell pool. Inflationary memory CD8 T cells provided protection from a Vaccinia virus challenge and this protection directly correlated with the size of the inflationary memory T cell pool in peripheral tissues. These results highlight the remarkable protective potential of inflationary CD8 T cells that can be harnessed for CMV-based T cell vaccine approaches. [ABSTRACT FROM AUTHOR]

Besides their function in recognizing cancerous and virally infected cells, natural killer (NK) cells have the potential to shape adaptive immune responses. However, the mechanisms employed by NK cells to negatively regulate virus-specific CD8 T cell responses remain to be fully defined. Using activating receptor natural cytotoxicity receptor (NCR) 1 deficient (NCR1gfp/gfp) mice, we found increased numbers of virus-specific CD8 T cells, leading to enhanced virus control during acute LCMV infection. Furthermore, virus-specific CD8 T cells were more activated in the absence of NCR1, resulting in exacerbated immunopathology, documented by weight loss, and superior virus control early during chronic LCMV infection. Transfer experiments of virus-specific CD8 T cells into NCR1 deficient hosts revealed a direct cross talk between NK and CD8 T cells. Studies on the splenic microarchitecture revealed pronounced disorganization of T cells in infected NCR1gfp/gfp mice, resulting in enhanced immunopathology and disruption of the T cell niche upon chronic LCMV infection. Our data show a novel pathway employed by NK cells to regulate antiviral CD8 T cell responses, namely direct recognition and elimination of activated CD8 T cells via NCR1 early during infection to protect the host from an overshooting T cell response. [ABSTRACT FROM AUTHOR]

Summary: The induction of long‐lived populations of memory T cells residing in peripheral tissues is of considerable interest for T cell‐based vaccines, as they can execute immediate effector functions and thus provide protection in case of pathogen encounter at mucosal and barrier sites. Cytomegalovirus (CMV)‐based vaccines support the induction and accumulation of a large population of effector memory CD8 T cells in peripheral tissues, in a process called memory inflation. Tissue‐resident memory (TRM) T cells, induced by various infections and vaccination regimens, constitute another subset of memory cells that take long‐term residence in peripheral tissues. Both memory T cell subsets have evoked substantial interest in exploitation for vaccine purposes. However, a direct comparison between these two peripheral tissue‐localizing memory T cell subsets with respect to their short‐ and long‐term ability to provide protection against heterologous challenge is pending. Here, we discuss communalities and differences between TRM and inflationary CD8 T cells with respect to their development, maintenance, function, and protective capacity. In addition, we discuss differences and similarities between the transcriptional profiles of TRM and inflationary T cells, supporting the notion that they are distinct memory T cell populations. [ABSTRACT FROM AUTHOR]

Cytomegalovirus (CMV) infection induces an atypical CD8 T cell response, termed inflationary, that is characterised by accumulation and maintenance of high numbers of effector memory like cells in circulation and peripheral tissues—a feature being successfully harnessed for vaccine purposes. Although stability of this population depends on recurrent antigen encounter, the requirements for prolonged survival in peripheral tissues remain unknown. Here, we reveal that murine CMV-specific inflationary CD8 T cells are maintained in an antigen-independent manner and have a half-life of 12 weeks in the lung tissue. This half-life is drastically longer than the one of phenotypically comparable inflationary effector cells. IL-15 alone, and none of other common γ-cytokines, was crucial for survival of inflationary cells in peripheral organs. IL-15, mainly produced by non-hematopoietic cells in lung tissue and being trans-presented, promoted inflationary T cell survival by increasing expression of Bcl-2. These results indicate that inflationary CD8 T cells are not just simply effector-like cells, rather they share properties of both effector and memory CD8 T cells and they appear to be long-lived cells compared to the effector cells from acute virus infections. [ABSTRACT FROM AUTHOR]

Motivation: The evolution of antibody repertoires represents a hallmark feature of adaptive B-cell immunity. Recent advancements in high-throughput sequencing have dramatically increased the resolution to which we can measure the molecular diversity of antibody repertoires, thereby offering for the first time the possibility to capture the antigen-driven evolution of B cells. However, there does not exist a repertoire simulation framework yet that enables the comparison of commonly utilized phylogenetic methods with regard to their accuracy in inferring antibody evolution. Results: Here, we developed AbSim, a time-resolved antibody repertoire simulation framework, which we exploited for testing the accuracy of methods for the phylogenetic reconstruction of B-cell lineages and antibody molecular evolution. AbSim enables the (i) simulation of intermediate stages of antibody sequence evolution and (ii) the modeling of immunologically relevant parameters such as duration of repertoire evolution, and themethod and frequency of mutations. First, we validated that our repertoire simulation framework recreates replicates topological similarities observed in experimental sequencing data. Second, we leveraged Absim to show that current methods fail to a certain extent to predict the true phylogenetic tree correctly. Finally, we formulated simulation-validated guidelines for antibody evolution, which in the future will enable the development of accurate phylogenetic methods. [ABSTRACT FROM AUTHOR]

The decline in number and function of T cells is a hallmark of HIV infection, and preservation or restoration of HIV‐specific cellular immune response is a major goal of AIDS treatment. Dendritic cells (DCs) play a key role in the initiation and maintenance of the immune response, and their use as a vaccine vehicle is a promising strategy for enhancing vaccine efficacy. We evaluated the potential of DC‐mediated immunization with a DNA vaccine consisting of HIV‐1‐p55gag (gag, group‐specific antigen) associated to lysosomal associated protein (LAMP) sequence (LAMP/gag vaccine). Immunization of mice with mouse DCs transfected with LAMP/gag (Lg‐mDCs) stimulated more potent B‐ and T‐cell responses than naked DNA or DCs pulsed with inactivated HIV. Anti‐Gag antibody levels were sustained for at least 3 mo after immunization, and recall T‐cell responses were also strongly detected at this time point. Human DCs transfected with LAMP/gag (Lg‐hDCs) were also activated and able to stimulate greater T‐cell response than native gag‐transfected DCs. Coculture between Lg‐hDCs and T lymphocytes obtained from patients with HIV resulted in upregulation of CD38, CD69, HLA‐DR, and granzyme B by CD4+ and CD8+ T cells, and increased IFN‐γ and TNF‐α production. These results indicate that the use of LAMP/gag‐DC may be an efficient strategy for enhancing immune function in patients with HIV.—Lucas, C. G. D. O., Matassoli, F. L., Peçanha, L. M. T., Santillo, B. T., Oliveira, L. M. D. S., Oshiro, T. M., Marques, E. T. D. A., Jr., Oxenius, A., de Arruda, L. B. Dendritic cells primed with a chimeric plasmid containing HIV‐1‐gag associated with lysosomal‐associated protein‐1 (LAMP/gag) is a potential therapeutic vaccine against HIV. FASEB J. 30, 2970‐2984 (2016). www.fasebj.org [ABSTRACT FROM AUTHOR]

Protective CD8+ T cell-mediated immunity requires a massive expansion in cell number and the development of long-lived memory cells. Using forward genetics in mice, we identified an orphan protein named lymphocyte expansion molecule (LEM) that promoted antigen-dependent CD8+ T cell proliferation, effector function, and memory cell generation in response to infection with lymphocytic choriomeningitis virus. Generation of LEM-deficient mice confirmed these results. Through interaction with CR6 interacting factor (CRIF1), LEM controlled the levels of oxidative phosphorylation (OXPHOS) complexes and respiration, resulting in the production of pro-proliferative mitochondrial reactive oxygen species (mROS). LEM provides a link between immune activation and the expansion of protective CD8+ T cells driven by OXPHOS and represents a pathway for the restoration of long-term protective immunity based on metabolically modified cytotoxic CD8+ T cells. [ABSTRACT FROM AUTHOR]

Cytotoxic T lymphocytes (CTLs) are important agents in the control of intracellular pathogens, which specifically recognize and kill infected cells. Recently developed experimental methods allow the estimation of the CTL's efficacy in detecting and clearing infected host cells. One method, the in vivo killing assay, utilizes the adoptive transfer of antigen displaying target cells into the bloodstream of mice. Surprisingly, killing efficacies measured by this method are often much higher than estimates obtained by other methods based on, for instance, the dynamics of escape mutations. In this study, we investigated what fraction of this variation can be explained by differences in peptide loads employed in in vivo killing assays. We addressed this question in mice immunized with lymphocytic choriomeningitis virus (LCMV). We conducted in vivo killing assays varying the loads of the immunodominant epitope GP33 on target cells. Using a mathematical model, we determined the efficacy of effector and memory CTL, as well as CTL in chronically infected mice. We found that the killing efficacy is substantially reduced at lower peptide loads. For physiological peptide loads, our analysis predicts more than a factor 10 lower CTL efficacies than at maximum peptide loads. Assuming that the efficacy scales linearly with the frequency of CTL, a clear hierarchy emerges among the groups across all peptide antigen concentrations. The group of mice with chronic LCMV infections shows a consistently higher killing efficacy per CTL than the acutely infected mouse group, which in turn has a consistently larger efficacy than the memory mouse group. We conclude that CTL killing efficacy dependence on surface epitope frequencies can only partially explain the variation in in vivo killing efficacy estimates across experimental methods and viral systems, which vary about four orders of magnitude. In contrast, peptide load differences can explain at most two orders of magnitude. [ABSTRACT FROM AUTHOR]

Progressive quantitative and qualitative decline of CD4+ T cell responses is one hallmark of HIV-1 infection and likely depends on several factors, including a possible contribution by the HIV-1 envelope glycoprotein gp120, which binds with high affinity to the CD4 receptor. Besides virion-associated and cell-expressed gp120, considerable amounts of soluble gp120 are found in plasma or lymphoid tissue, predominantly in the form of gp120–anti-gp120 immune complexes (ICs). Because the functional consequences of gp120 binding to CD4+ T cells are controversially discussed, we investigated how gp120 affects TCR-mediated activation of human CD4+ T cells by agonistic anti-CD3 mAb or by HLA class II–presented peptide Ags. We show that the spatial orientation of gp120–CD4 receptor binding relative to the site of TCR engagement differentially affects TCR signaling efficiency and hence CD4+ T cell activation. Whereas spatially and temporally linked CD4 and TCR triggering at a defined site promotes CD4+ T cell activation by exceeding local thresholds for signaling propagation, CD4 receptor engagement by gp120-containing ICs all around the CD4+ T cell undermine its capacity in supporting proximal TCR signaling. In vitro, gp120 ICs are efficiently captured by CD4+ T cells and thereby render them hyporesponsive to TCR stimulation. Consistent with these in vitro results we show that CD4+ T cells isolated from HIV+ individuals are covered with ICs, which at least partially contain gp120, and suggest that IC binding to CD4 receptors might contribute to the progressive decline of CD4+ T cell function during HIV-1 infection. [ABSTRACT FROM AUTHOR]