Spaceflight validation of technology for point-of-care monitoring of peripheral blood WBC and differential in astronauts during space missions

During long duration orbital space missions, astronauts experience immune system dysregulation, the persistent reactivation of latent herpesviruses, and some degree of clinical incidence. During planned NASA 'Artemis' deep space missions the stressors that cause this phenomenon will increase, while clinical care capability will likely be reduced. There is currently minimal clinical laboratory capability aboard the International Space Station (ISS). The ability to monitor the white blood cell count (WBC) and differential during spaceflight has been an unmet NASA medical requirement, primarily due to a lack of capable hardware. We performed ground and flight validation of a device designed to monitor WBC and differential within minutes from a fingerstick blood sample. This device is miniaturized, robust, and generally compatible with microgravity operations. Ground testing for spaceflight consisted of vibration tolerance, power/battery and interface requirements, electromagnetic interference (EMI), and basic evaluation of sample preparation and operations in the context of spaceflight constraints. The in-flight validation performed aboard the ISS by two astronauts included assessment of three levels of control solution (blood) samples as well as a real time analysis of a fingerstick blood sample by one of the crewmembers. Flight and ground testing of the same lot of control solutions yielded similar total WBC values. There was some select discrepancy between flight and ground data for the differential analysis. However, the data suggest that this issue is due to compromise of the control solutions as a result of storage length before flight operations, and not due to a microgravity-associated issue with instrument performance. This evaluation also yielded lessons learned regarding crewmember training for technique-sensitive small-volume biosample collection and handling in microgravity. The fingerstick analysis was successful and was the first real-time hematology assessment performed during spaceflight. This device may provide an in-mission monitoring capability for astronauts thereby assisting Flight Surgeons and the crew medical officer during both orbital and deep space missions.

Attenuation of GARP expression on regulatory T cells by protein transport inhibitors

An integrated understanding of the functional capacities of cells in the context of their physical parameters and molecular markers is increasingly demanded in immunologic studies. Regulatory T cells (Tregs) are a subpopulation of T cells involved in immune response modulation and mediating tolerance to self-antigen with their absence leading to a loss of tolerance. Glycoprotein repetitions A predominant (GARP) is a key marker for activated Tregs, but its detection may also be useful in determining the functional capacities of the cell. This study aims to deduce the optimal stimulation period and the impact of protein transport inhibitors (PTIs), commonly used in the detection of intracellular cytokines, on GARP detection. Through flow cytometric analysis we analyzed different cell culture conditions for optimal GARP expression on activated Tregs. Healthy donor PBMCs were stimulated with either Staphylococcal Enterotoxin B (SEB) or PMA/Ionomycin (PMA/Iono), in the presence and absence of PTIs monensin and/or brefeldin A (BFA) and GARP expression was assessed on CD4+ CD25+ FOXP3+ Tregs. The optimal stimulation period for the detection of GARP was highest at 24-h. Furthermore, we determined that GARP expression on Tregs is significantly reduced when cells are treated with the PTIs monensin and/or BFA following PMA/Iono stimulation. This effect was not seen following SEB stimulation. Therefore, due to the effects of PTIs, alternative methods should be considered when performing simultaneous analysis for cytokine expression and GARP expression on Tregs.

An evaluation of cytokine and cellular immune responses to heterologous prime-boost vaccination with influenza A/H7N7-A/H7N9 inactivated vaccine

The immunologic mechanisms underlying the improved serologic responses to heterologous prime-boost avian influenza vaccination are unclear. An exploratory analysis of the immune responses following 1 dose of influenza A/H7N9 inactivated vaccine in subjects who received an influenza A/H7N7 inactivated vaccine (N = 17) 8 years earlier or who were influenza A/H7-naïve (10) was performed. Plasma IL-6 and IL-21 concentrations by ELISA, the frequency of A/H7N7-specific memory B cells and antibody secreting cells by ELISpot, the frequency of circulating T follicular helper cells and the frequency of T cells expressing IL-6 and IL-21 by flow cytometry were assessed at baseline (D1), and 8 days (D9) and 28 days (D29) after vaccination. We assessed the correlation between these measurements and the D29 serologic responses to the boost vaccine. Plasma IL-6 concentration on D9 significantly correlated with the H7N7 and H7N9 hemagglutination inhibition (HAI) antibody levels (P = .03 and 0.02 respectively); and the percentage of T cells expressing IL-21 on D9 significantly correlated with H7N9 HAI antibody seroconversion (P < .001). Significant associations with other immunologic markers were not detected. We detected an association between plasma IL-6 and intracellular IL-21 and serologic responses to heterologous prime-boost avian influenza vaccination. A clarification of the role of these and additional immunologic markers requires larger clinical trials.

SARS-CoV-2 Pandemic Impacts on NASA Ground Operations to Protect ISS Astronauts

NASA implements required medical tests and clinical monitoring to ensure the health and safety of its astronauts. These measures include a pre-launch quarantine to mitigate the risk of infectious diseases. During space missions, most astronauts experience perturbations to their immune system that manifest as a detectable secondary immunodeficiency. On return to Earth, after the stress of re-entry and landing, astronauts would be most vulnerable to infectious disease. In April 2020, a crew returned from International Space Station to NASA Johnson Space Center in Houston, Texas, during the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. Post-flight quarantine protocols (both crew and contacts) were enhanced to protect this crew from SARS-CoV-2. In addition, specific additional clinical monitoring was performed to determine post-flight immunocompetence. Given that coronavirus disease 2019 (COVID-19) prognosis is more severe for the immunocompromised, a countermeasures protocol for spaceflight suggested by an international team of scientists could benefit terrestrial patients with secondary immunodeficiency.

DNA hypermethylation during tuberculosis dampens host immune responsiveness

Mycobacterium tuberculosis (M. tuberculosis) has coevolved with humans for millennia and developed multiple mechanisms to evade host immunity. Restoring host immunity in order to improve outcomes and potentially shorten existing therapy will require identification of the full complement by which host immunity is inhibited. Perturbation of host DNA methylation is a mechanism induced by chronic infections such as HIV, HPV, lymphocytic choriomeningitis virus (LCMV), and schistosomiasis to evade host immunity. Here, we evaluated the DNA methylation status of patients with tuberculosis (TB) and their asymptomatic household contacts and found that the patients with TB have DNA hypermethylation of the IL-2/STAT5, TNF/NF-κB, and IFN-γ signaling pathways. We performed methylation-sensitive restriction enzyme-quantitative PCR (MSRE-qPCR) and observed that multiple genes of the IL-12/IFN-γ signaling pathway (IL12B, IL12RB2, TYK2, IFNGR1, JAK1, and JAK2) were hypermethylated in patients with TB. The DNA hypermethylation of these pathways was associated with decreased immune responsiveness with decreased mitogen-induced upregulation of IFN-γ, TNF, IL-6, CXCL9, CXCL10, and IL-1β production. The DNA hypermethylation of the IL-12/IFN-γ pathway was associated with decreased IFN-γ-induced gene expression and decreased IL-12-inducible upregulation of IFN-γ. This study demonstrates that immune cells from patients with TB are characterized by DNA hypermethylation of genes critical to mycobacterial immunity resulting in decreased mycobacteria-specific and nonspecific immune responsiveness.

Countermeasures-based Improvements in Stress, Immune System Dysregulation and Latent Herpesvirus Reactivation onboard the International Space Station - Relevance for Deep Space Missions and Terrestrial Medicine

The International Space Station (ISS) has continued to evolve from an operational perspective and multiple studies have monitored both stress and the immune system of ISS astronauts. Alterations were ascribed to a potentially synergistic array of factors, including microgravity, radiation, psychological stress, and circadian misalignment. Comparing similar data across 12 years of ISS construction and operations, we report that immunity, stress, and the reactivation of latent herpesviruses have all improved in ISS astronauts. Major physiological improvements seem to have initiated approximately 2012, a period coinciding with improvements onboard ISS including cargo delivery and resupply frequency, personal communication, exercise equipment and protocols, food quality and variety, nutritional supplementation, and schedule management. We conclude that spaceflight associated immune dysregulation has been positively influenced by operational improvements and biomedical countermeasures onboard ISS. Although an operational challenge, agencies should therefore incorporate, within vehicle design limitations, these dietary, operational, and stress-relieving countermeasures into deep space mission planning. Specific countermeasures that have benefited astronauts could serve as a therapy augment for terrestrial acquired immunodeficiency patients.

Zoster patients on earth and astronauts in space share similar immunologic profiles

BACKGROUND

On long-duration spaceflight, most astronauts experience persistent immune dysregulation and the reactivation of latent herpesviruses, including varicella zoster virus (VZV). To understand the clinical risk of these perturbations to astronauts, we paralleled the immunology and virology work-up of astronauts to otherwise healthy terrestrial persons with acute herpes zoster.

METHODS

Blood samples from 42 zoster patients - confirmed positive by PCR for VZV DNA in saliva (range from 100 to >285 million copies/mL) were analyzed for peripheral leukocyte distribution, T cell function, and plasma cytokine profiles via multi-parametric flow cytometry and multiplex bead-based immune-array assays. Patient findings were compared to normal value ranges specific for each assay that were defined in-house previously from healthy adult test subjects.

RESULTS

Compared to the healthy adult ranges, the zoster patients possess (1) a higher proportion of constitutively activated T-cells, (2) a T-cell population skewed towards a more experienced maturation state, (3) depressed general T-cell function, and (4) a higher concentration of 20 of 22 measured plasma cytokines.

DISCUSSION

The pattern of immune dysregulation in zoster patients is similar to that of astronauts during spaceflight who shed VZV DNA in their saliva. Because future deep space exploration missions will be of an unprecedented duration, prolonged immune depression and chronic viral reactivation threaten to manifest overt disease in exploration class astronauts.

Stress Induced Immune Dysregulation: A Continuum Spanning Antarctica Winterover, Spaceflight, and Terrestrial Patients

Spaceflight, a unique environment characterized by stress, microgravity, isolation, circadian misalignment, and radiation exposure, impacts immune health. This analysis compares various aspects of immune dysregulation in astronauts during long-duration orbital spaceflight to ground-analog populations, including hypoxic and normoxic Antarctic winterover. Astronaut data were also compared to a clinical immunodeficiency population, shingles patients, to help interpret clinical risks during deep space missions.

A comprehensive evaluation was performed across all platforms which included plasma and mitogen stimulated cytokine profiles, T cell function, and peripheral leukocyte distribution. A cross platform analysis was then performed to define in-flight immune alterations, determine analog appropriateness, and interpret clinical risk.

Astronauts manifest a distinct pattern of immune alterations, including unaltered leukocyte distribution, reduced T/NK cell function, and increases in plasma cytokines leading to the reactivation of latent herpesviruses. The pattern is similar to that observed in shingles patients, but reduced in magnitude. Immune alterations during interior Antarctic winterover were dissimilar from spaceflight, likely due to hypobaric hypoxia. Normoxic winterover, to date only cytokine data exist, appears more homologous to spaceflight.

Stress induced reductions in immunity can lead to clinical disease. This phenomenon may represent a continuum, where alterations in astronauts may represent more subtle variations which precede the development of disease. Antarctica data, at a magnitude between flight and disease, suggest that stress and circadian issues may be a primary contributor.

Epigenetic mediated immune exhaustion persists after successful Tuberculosis therapy

BACKGROUND

Chronic antigen stimulation from HIV, HPV, LCMV and schistosomiasis induce epigenetic-mediated immune exhaustion. Individuals with successful anti-TB therapy (ATT) have a thirteen-fold increased risk of developing recurrent TB.

METHODS

From a cohort of HIV infected and uninfected individuals with TB and their asymptomatic household contacts (n=32), genome-wide DNA methylation (DNA MethylEPIC) and epigenetic deconvolution (EDEC) identified cell-specific DNA methylation. Cell-specific results were validated with MSRE-PCR, gene expression and flow cytometry-based Mtb-specific multi-dimensional immune profiling.

RESULTS

Participants with TB had DNA hypermethylation in the IL-2, TCR and IFN-γ signalling pathways. The IFN-γ signalling pathway was affected in both innate (NK cells and monocytes) as well as adaptive (CD4 and CD8 T cells) lineages. Select DNA hyper-methylated differences were validated using MSRE-PCR. Pioneer and Transcription factors critical for cell-mediated immunity were also significantly differentially methylated with enrichment scores compatible with previous epigenetic-mediated immune exhaustion. After overnight stimulation with IFN-γ, TB patients have decreased IFN-γ-inducible gene expression. Six months after the completion of successful ATT, participants with TB have persistent DNA hypermethylation.

DISCUSSION

Persistent DNA hypermethylation may be a potential mechanism by which individuals with TB are at increased risk of recurrent disease. This may also assist in identifying potential new targets for host-directed therapy.

Recycling endosomes in human cytotoxic T lymphocytes constitute an auxiliary intracellular trafficking pathway for newly synthesized perforin

Although cytotoxic T lymphocytes (CTLs) store perforin within cytoplasmic secretory granules for immediate use, perforin is synthesized anew within hours of TCR stimulation. Previously, we observed new perforin protein at an immunologic synapse independent of secretory lysosomes; herein, we aimed to determine how new perforin transits to the synapse if not via lytic granules. We analyzed antigen-specific human CTLs via imaging flow cytometry and high-resolution confocal microscopy, with attention to intracellular trafficking components and new perforin. The recycling endosome compartments identified by rab8, rab11a, rab4, and rab37 co-localized with new perforin, as well as the SNAREs vti1b and VAMP4. After ablating the function of the recycling endosome pathway, we observed a relative accumulation of new perforin in rab8 vesicles. The recycling endosome pathway may serve as an auxiliary intracellular route for the delivery of new perforin to an immunologic synapse in order to perpetuate a cytotoxic response.

Immune System Dysregulation During Spaceflight: Potential Countermeasures for Deep Space Exploration Missions

Recent studies have established that dysregulation of the human immune system and the reactivation of latent herpesviruses persists for the duration of a 6-month orbital spaceflight. It appears certain aspects of adaptive immunity are dysregulated during flight, yet some aspects of innate immunity are heightened. Interaction between adaptive and innate immunity also seems to be altered. Some crews experience persistent hypersensitivity reactions during flight. This phenomenon may, in synergy with extended duration and galactic radiation exposure, increase specific crew clinical risks during deep space exploration missions. The clinical challenge is based upon both the frequency of these phenomena in multiple crewmembers during low earth orbit missions and the inability to predict which specific individual crewmembers will experience these changes. Thus, a general countermeasure approach that offers the broadest possible coverage is needed. The vehicles, architecture, and mission profiles to enable such voyages are now under development. These include deployment and use of a cis-Lunar station (mid 2020s) with possible Moon surface operations, to be followed by multiple Mars flyby missions, and eventual human Mars surface exploration. Current ISS studies will continue to characterize physiological dysregulation associated with prolonged orbital spaceflight. However, sufficient information exists to begin consideration of both the need for, and nature of, specific immune countermeasures to ensure astronaut health. This article will review relevant in-place operational countermeasures onboard ISS and discuss a myriad of potential immune countermeasures for exploration missions. Discussion points include nutritional supplementation and functional foods, exercise and immunity, pharmacological options, the relationship between bone and immune countermeasures, and vaccination to mitigate herpes (and possibly other) virus risks. As the immune system has sentinel connectivity within every other physiological system, translational effects must be considered for all potential immune countermeasures. Finally, we shall discuss immune countermeasures in the context of their individualized implementation or precision medicine, based on crewmember specific immunological biases.

Schistosomiasis Induces Persistent DNA Methylation and Tuberculosis-Specific Immune Changes

Epigenetic mechanisms, such as DNA methylation, determine immune cell phenotype. To understand the epigenetic alterations induced by helminth coinfections, we evaluated the longitudinal effect of ascariasis and schistosomiasis infection on CD4⁺ T cell DNA methylation and the downstream tuberculosis (TB)-specific and bacillus Calmette-Guérin-induced immune phenotype. All experiments were performed on human primary immune cells from a longitudinal cohort of recently TB-exposed children. Compared with age-matched uninfected controls, children with active Schistosoma haematobium and Ascaris lumbricoides infection had 751 differentially DNA-methylated genes, with 72% hypermethylated. Gene ontology pathway analysis identified inhibition of IFN-γ signaling, cellular proliferation, and the Th1 pathway. Targeted real-time quantitative PCR after methyl-specific endonuclease digestion confirmed DNA hypermethylation of the transcription factors BATF3, ID2, STAT5A, IRF5, PPARg, RUNX2, IRF4, and NFATC1 and cytokines or cytokine receptors IFNGR1, TNFS11, RELT (TNF receptor), IL12RB2, and IL12B (p < 0.001; Sidak-Bonferroni). Functional blockage of the IFN-γ signaling pathway was confirmed, with helminth-infected individuals having decreased upregulation of IFN-γ-inducible genes (Mann-Whitney p < 0.05). Hypomethylation of the IL-4 pathway and DNA hypermethylation of the Th1 pathway was confirmed by Ag-specific multidimensional flow cytometry demonstrating decreased TB-specific IFN-γ and TNF and increased IL-4 production by CD4+ T cells (Wilcoxon signed-rank p < 0.05). In S. haematobium-infected individuals, these DNA methylation and immune phenotypic changes persisted at least 6 mo after successful deworming. This work demonstrates that helminth infection induces DNA methylation and immune perturbations that inhibit TB-specific immune control and that the duration of these changes are helminth specific.

High self-reactivity drives T-bet and potentiates Treg function in tissue-specific autoimmunity

T cell receptor (TCR) affinity is a critical factor of Treg lineage commitment, but whether self-reactivity is a determining factor in peripheral Treg function remains unknown. Here, we report that a high degree of self-reactivity is crucial for tissue-specific Treg function in autoimmunity. Based on high expression of CD5, we identified a subset of self-reactive Tregs expressing elevated levels of T-bet, GITR, CTLA-4, and ICOS, which imparted significant protection from autoimmune diabetes. We observed that T-bet expression in Tregs, necessary for control of Th1 autoimmunity, could be induced in an IFNγ-independent fashion and, unlike in conventional T cells (Tconv), was strongly correlated with the strength of TCR signaling. The level of CD5 similarly identified human Tregs with an increased functional profile, suggesting that CD5hi Tregs may constitute an efficacious subpopulation appropriate for use in adoptive Treg therapies for treatment of inflammatory conditions. Overall, this work establishes an instrumental role of high TCR self-reactivity in driving Treg function.

High-resolution phenotyping identifies NK cell subsets that distinguish healthy children from adults

Natural killer (NK) cells are critical in immune defense against infected, stressed or transformed cells. Their function is regulated by the heterogeneous expression of a wide array of surface receptors that shape its phenotypic diversity. Although NK cells develop in the bone marrow and secondary lymphoid tissues, substantive differentiation is apparent in the peripheral blood including known age-related variation. In order to gain greater insight into phenotypic and functional variation within peripheral blood NK cells across age groups, we used multi-parametric, polyfunctional flow cytometry to interrogate the NK cell variability in 20 healthy adults and 15 5–10, 11–15 and 16–20 year-old children. We found that the normative ranges in both adults and children displayed great inter-individual variation for most markers. While the expression of several receptors did not differ, among those that did, the majority of the differences existed between adults and the three pediatric groups, rather than among children of different ages. Interestingly, we also identified variation in the individual expression of some markers by sex and ethnicity. Combinatorial analysis of NK cell receptors revealed intermediate subsets between the CD56^bright and CD56^dim NK cells. Furthermore, on examining the NK cell diversity by age, adults were discovered to have the lowest developmental diversity. Thus, our findings identify previously unappreciated NK cell subsets potentially distinguishing children from adults and suggest functional correlates that may have relevance in age-specific host defense.

Changes in Frequency and Activation Status of Major CD4+ T-Cell Subsets after Initiation of Immunosuppressive Therapy in a Patient with New Diagnosis Childhood-Onset Systemic Lupus Erythematosus

BACKGROUND

Several studies suggest that defects of regulatory T-cells (Tregs) and impaired cellular immunity are secondary to an imbalance between auto-aggressive T-cells and Tregs in lupus patients. Discrepancies in Tregs and effector T-cells (Teff) in active lupus patients are shown to be restored in patients upon receiving immunosuppressive therapy. Therefore, our main aim was to observe frequencies of these CD4⁺ T-cell subsets and Tregs/Teff ratio in a new diagnosis of childhood-onset systemic lupus erythematous (cSLE) before and after initiation of therapy. In addition, we monitored T-cell exhaustion status by examining responses to super-antigen staphylococcal enterotoxin B (SEB) and PD-1 expression in this patient.

METHODS

Phenotyping of CD4⁺ T-cell subsets was carried out under basal conditions and after SEB stimulation using flow cytometry in one inactive (I-cSLE) and one active cSLE (A-cSLE) patient, as well as a healthy control (HC). The A-cSLE patient was a new diagnosis. Variables were measured at three consecutive time points in the active patient, reflecting various stages of disease activity. Activation status of CD4⁺ T-cells in the A-cSLE patient was compared to that of the I-cSLE patient and HC. Disease activity was measured by calculating the systemic lupus erythematous disease activity index.

RESULTS

We found that the A-cSLE patient was not Tregs deficient. The patient had increased frequency of Tregs, and the Tregs/Teff ratio increased when the disease activity became less severe. CD4⁺ T-cells in the I-cSLE patient and in the A-cSLE patient with milder disease activity had heightened responsiveness to SEB, whereas T-cells were relatively hypo-responsive to SEB in the A-cSLE patient when disease activity was higher. The active patient exhibited higher frequencies of PD-1⁺ expressing Tregs, Teff, and Tnaïve/mem cells under basal conditions compared to the HC and I-cSLE patient.

CONCLUSION

In the A-cSLE patient, changes in Tregs/Teff ratio correlated better with clinical improvement compared to Tregs frequencies alone and might reflect the restoration of immune homeostasis with therapy. SEB hypo-responsiveness in the A-cSLE patient when disease activity was higher paralleled with findings of greater frequencies of PD-1⁺ expressing Tregs, Teff, and Tnaïve/mem cells, suggests a possible global exhaustion status of CD4⁺ T-cells in this patient.

STAT3 inhibition prevents lung inflammation, remodeling, and accumulation of Th2 and Th17 cells in a murine asthma model

BACKGROUND

STAT3 drives development of Th17 cells and cytokine production by Th2 and Th17 cells, which contribute to asthma. Alternative asthma treatments are needed, especially for the Th17 phenotype. We sought to determine whether C188-9, a small-molecule STAT3 inhibitor, can block Th2 and Th17 cell expansion and cytokine production to prevent house dust mite (HDM)-induced airway inflammation and remodeling.

METHODS

Three groups of C57BL/6 mice were treated intranasally (IN) and intraperitoneally (IP) daily for 3 weeks with the following: (i) vehicle 1 IN and vehicle 2 IP, (ii) HDM IN and vehicle 2 IP, or (iii) HDM IN and C188-9 IP. Sections of lung were stained with Alcian Blue/PAS and examined microscopically. Total (t) STAT3, STAT3 phosphorylated on Y705 (pSTAT3), IL-17, IL-13, IL-5, and IL-4 levels were measured in lung protein extracts and serum using Luminex beads. Frequencies of Th2-type and Th17-type lymphocytes were assessed in lungs and bronchoalveolar lavage fluid (BALF) by multiparametric flow cytometry.

RESULTS

HDM inhalation markedly increased airway goblet cell numbers and thickness of the epithelium and subepithelial smooth muscle layer, which was accompanied in the whole lung by increased pSTAT3, IL-4, IL-5, IL-13, and IL-17, and % CD4⁺ T cells that produce IL-5, IL-13, and IL-17. HDM inhalation also increased serum IL-4 and IL-17 levels and increased BALF % CD4⁺ T cells that produce IL-5 and IL-13. Remarkably, treatment with C188-9 normalized each endpoint.

CONCLUSION

HDM-induced airway inflammation, remodeling, and Th2/Th17-type cell accumulation involve STAT3 activation that can be prevented by C188-9 treatment.

Temporal Dynamics of CD8+ T Cell Effector Responses during Primary HIV Infection

The loss of HIV-specific CD8⁺ T cell cytolytic function is a primary factor underlying progressive HIV infection, but whether HIV-specific CD8⁺ T cells initially possess cytolytic effector capacity, and when and why this may be lost during infection, is unclear. Here, we assessed CD8⁺ T cell functional evolution from primary to chronic HIV infection. We observed a profound expansion of perforin⁺ CD8⁺ T cells immediately following HIV infection that quickly waned after acute viremia resolution. Selective expression of the effector-associated transcription factors T-bet and eomesodermin in cytokine-producing HIV-specific CD8⁺ T cells differentiated HIV-specific from bulk memory CD8⁺ T cell effector expansion. As infection progressed expression of perforin was maintained in HIV-specific CD8⁺ T cells with high levels of T-bet, but not necessarily in the population of T-bet^Lo HIV-specific CD8⁺ T cells that expand as infection progresses. Together, these data demonstrate that while HIV-specific CD8⁺ T cells in acute HIV infection initially possess cytolytic potential, progressive transcriptional dysregulation leads to the reduced CD8⁺ T cell perforin expression characteristic of chronic HIV infection.

Previous studies have demonstrated that HIV-specific CD8⁺ T cells are critical for the initial control of HIV infection. However, this control is typically incomplete, being able to neither clear infection nor maintain plasma viremia below undetectable levels. Mounting evidence has implicated CD8⁺ T cell cytotoxic capacity as a critical component of the HIV-specific response associated with spontaneous long-term control of HIV replication. CD8⁺ T cell cytotoxic responses are largely absent in the vast majority of HIV chronically infected individuals and it is unclear when or why this functionality is lost. In this study we show that HIV-specific CD8⁺ T cells readily express the cytolytic protein perforin during the acute phase of chronic progressive HIV infection but rapidly lose the ability to upregulate this molecule following resolution of peak viremia. Maintenance of perforin expression by HIV-specific CD8⁺ T cells appears to be associated with the expression level of the transcription factor T-bet, but not with the T-bet paralogue, Eomes. These findings further delineate qualitative attributes of CD8⁺ T cell-mediated immunity that may serve as targets for future HIV vaccine and therapeutic research.

Schistosome Soluble Egg Antigen Decreases Mycobacterium tuberculosis-Specific CD4+ T-Cell Effector Function With Concomitant Arrest of Macrophage Phago-Lysosome Maturation

Helminth-infected individuals possess a higher risk of developing tuberculosis, but the precise immunologic mechanism of Mycobacterium tuberculosis control remains unclear. We hypothesized that a perturbation of the M. tuberculosis-specific CD4(+) T-cell response weakens the ability of macrophages to contain M. tuberculosis We exposed peripheral blood mononuclear cells from M. tuberculosis-infected humans to schistosome soluble egg antigen (SEA) and then profiled M. tuberculosis-specific CD4(+) T cells via multiparametric flow cytometry. SEA decreased the frequency of cells producing interferon γ (6.79% vs 3.20%; P = .017) and tumor necrosis factor α (6.98% vs 2.96%; P = .012), with a concomitant increase in the median fluorescence intensity of interleukin 4 (IL-4; P < .05) and interleukin 10 (IL-10; 1440 vs 1273; P < .05). Macrophages polarized with SEA-exposed, autologous CD4(+) T-cell supernatant had a 2.19-fold decreased colocalization of lysosomes and M. tuberculosis (P < .05). When polarized with IL-4 or IL-10, macrophages had increased expression of CD206 (P < .0001), 1.5-fold and 1.9 fold increased intracellular numbers of M. tuberculosis per macrophage (P < .0005), and 1.4-fold and 1.7-fold decreased colocalization between M. tuberculosis and lysosomes (P < .001). This clarifies a relationship in which helminth-induced CD4(+) T cells disrupt M. tuberculosis control by macrophages, thereby providing a mechanism for the observation that helminth infection advances the progression of tuberculosis among patients with M. tuberculosis infection.

High resolution phenotyping identifies NK cell subsets that distinguish healthy children and adults

Natural killer (NK) cells possess an array of germline-encoded activating, inhibitory and adhesion receptors, the balance of which in concert with their developmental stage, determine their cytotoxic and cytokine-producing potential. Although NK cells develop in the bone marrow and secondary lymphoid tissues, substantive differentiation is apparent in the peripheral blood including known age-related variation. In order to gain greater insight into phenotypic and functional variation within peripheral blood NK cells across age groups, we used multi-parameter, polyfunctional flow cytometry to interrogate the NK cell variability in 20 healthy adults and 15 5–10, 11–15 and 16–20 year-old children. We found that the normative ranges in both adults and children displayed great inter-individual variation for most subsets. Children possessed &gt;76% unstimulated NK subsets coexpressing perforin and granzyme B as opposed to &gt;65% in adults. Children also had &gt;28% NK subsets expressing all adhesion receptors in our panel compared to half of that in adults. As examples, terminally differentiated CD16+CD57+CD11b+ NK cells were reduced after 16 years of age as well as NKp46, 2B4, CD107a and newly-synthesized perforin in adults. Although CD107a intensity and new perforin synthesis was lower in adults, induced levels of IFNγ (by intensity) was higher. Despite most receptors not differing in their overall expression levels, major phenotypic differences were revealed in the combinatorial expression of NK receptors between adults and children. Our findings identify previously unappreciated NK cell subsets potentially distinguishing children from adults and suggest functional correlates that may have relevance in age-specific host defense.

Utility of the Enzyme-Linked Immunospot Interferon-γ-Release Assay to Predict the Risk of Cytomegalovirus Infection in Hematopoietic Cell Transplant Recipients

The ability to distinguish allogeneic hematopoietic cell transplant (allo-HCT) recipients at risk for cytomegalovirus (CMV) reactivation from those who are not is central for optimal CMV management strategies. Interferon γ (IFN-γ) produced by CMV-challenged T cells may serve as an immune marker differentiating these 2 populations. We prospectively monitored 63 CMV-seropositive allo-HCT recipients with a CMV-specific enzyme-linked immunospot (ELISPOT) assay and for CMV infection from the period before transplantation to day 100 after transplantation. Assay results above certain thresholds (50 spots per 250 000 cells for immediate early 1 or 100 spots per 250 000 cells for phosphoprotein 65) identified patients who were protected against CMV infection as long as they had no graft-versus-host disease and/or were not receiving systemic corticosteroids. Based on the multivariable Cox proportional hazards regression model, the only significant factor for preventing CMV reactivation was a CMV-specific ELISPOT response above the determined thresholds (adjusted hazard ratio, 0.21; 95% confidence interval, .05-.97; P = .046). Use of this assay as an additional tool for managing allo-HCT recipients at risk for CMV reactivation needs further validation in future studies. Application of this new approach may reduce the duration and intensity of CMV monitoring and the duration of prophylaxis or treatment with antiviral agents in those who have achieved CMV-specific immune reconstitution.

Practical NK cell phenotyping and variability in healthy adults

Human natural killer (NK) cells display a wide array of surface and intracellular markers that indicate various states of differentiation and/or levels of effector function. These NK cell subsets exist simultaneously in peripheral blood and may vary among individuals. We examined variety among selected NK cell receptors expressed by NK cells from normal donors, as well as the distribution of select NK cell subsets and NK cell receptor expression over time in several individual donors. Peripheral blood mononuclear cells were evaluated using flow cytometry via fluorochrome-conjugated antibodies against a number of NK cell receptors. Results were analyzed for both mean fluorescence intensity (MFI) and the percent positive cells for each receptor. CD56(bright) and CD56(dim) NK cell subsets were also considered separately, as was variation in receptor expression in NK cell subsets over time in selected individuals. Through this effort, we provide ranges of NK cell surface receptor expression for a local adult population as well as provide insight into intra-individual variation.

Molecular mechanisms of functional natural killer deficiency in patients with partial DiGeorge syndrome

BACKGROUND

DiGeorge syndrome affects more than 3.5 million persons worldwide. Partial DiGeorge syndrome (pDGS), which is characterized by a number of gene deletions in chromosome 22, including the chicken tumor virus number 10 regulator of kinase (Crk)-like (CrkL) gene, is one of the most common genetic disorders in human subjects. To date, the role of natural killer (NK) cells in patients with pDGS remains unclear.

OBJECTIVE

We sought to define the effect of pDGS-related Crk haploinsufficiency on NK cell activation and cytotoxic immunological synapse (IS) structure and function.

METHODS

Inducible CrkL-silenced NK cells were used to recapitulate the pDGS, CrkL-haploinsufficient phenotype. Findings were validated by using NK cells from patients with actual pDGS. Ultimately, deficits in the function of NK cells from patients with pDGS were restored by lentiviral transduction of CrkL.

RESULTS

Silencing of CrkL expression inhibits NK cell function. Specifically, pDGS haploinsufficiency of CrkL inhibits accumulation of activating receptors, polarization of cytolytic machinery and key signaling molecules, and activation of β2-integrin at the IS. Reintroduction of CrkL protein restores NK cell cytotoxicity.

CONCLUSION

CrkL haploinsufficiency causes functional NK deficits in patients with pDGS by disrupting both β2-integrin activation and activating receptor accumulation at the IS. Our results suggest that NK cell IS quality can directly affect immune status, providing a potential target for diagnosis and therapeutic manipulation in patients with pDGS and in other patients with functional NK cell deficiencies.

Differential localization of T-bet and Eomes in CD8 T cell memory populations

In mice, two T-box transcription factors, T-box expressed in T cells (T-bet) and eomesodermin (Eomes), drive the differentiation of CD8 T cell lineages; however, little is known regarding their role in human CD8 T cell differentiation. In this study, we characterized T-bet and Eomes expression and localization within human CD8 memory T cell populations. We find that T-bet and Eomes are broadly expressed in human memory CD8 T cells, with increasing levels of T-bet and Eomes strongly correlating with differentiation from central memory to effector memory and effector subpopulations. In resting T cells, T-bet levels directly correlate to subcellular localization, with a higher propensity for nuclear expression of T-bet within T-bet(hi) cells and predominantly cytoplasmic expression in T-bet(lo) cells. In addition, Eomes is also localized to either the nucleus or the cytoplasm. Upon TCR stimulation, the percentage of T cells that express T-bet dramatically increases, whereas the percentage of cells expressing Eomes remains largely unchanged across all memory populations. Of interest, T-bet, but not Eomes, relocalizes to the nucleus in the majority of cells across all populations within 24 h post stimulation. These data indicate that T-bet and Eomes are likely regulated at the level of subcellular localization, potentially via different mechanisms. Together, these findings suggest a novel model for CD8 T cell differentiation in humans that is based on the localization of T-bet and Eomes.

Differential localization of T-bet and Eomes within distinct human CD8 T-cell memory populations (110.10)

In mice, two T-box transcription factors, T-bet and Eomes, drive the differentiation of CD8 T-cell lineages; however, little is known regarding their role in human CD8 T-cell differentiation. Here, we characterized T-bet and Eomes expression and localization within human CD8 memory T-cell populations. We find T-bet and Eomes are broadly expressed in human memory CD8 T cells, with increasing levels of T-bet and Eomes strongly correlating with differentiation from central memory to effector memory and effector subpopulations. Interestingly, T-bet levels directly correlate to subcellular localization, with a higher propensity for nuclear expression of T-bet within T-bethi cells and predominately cytoplasmic expression in T-betlo cells. In contrast, Eomes appears to be localized solely to the nucleus. In murine CD8 T cells, T-bet can be nuclear, cytoplasmic, or both; however, Eomes is detectable in both compartments suggesting differential regulation compared to humans. Additionally, in humans, Eomes tightly correlated with nuclear T-bet suggesting T-bet localization might impact Eomes expression. Together, our data provide a novel mechanism for CD8 T-cell differentiation in humans and mice based on subcellular localization of T-bet, and reveal the likely presence of previously unknown regulation mechanisms for these critical lineage defining transcription factors.

Living in a house of cards: re-evaluating CD8+ T-cell immune correlates against HIV

The Merck STEP and the Thai RV144 human immunodeficiency virus (HIV) vaccine trials confirmed that we still have a long way to go before developing a prophylactic HIV vaccine. The main issue at hand is that we have yet to identify an immunological correlate of protection against HIV. While many question the T-cell-based approach towards vaccine development, it is likely that T cells will be a necessary part of any vaccine strategy. CD8(+) T cells remain an attractive option because of their ability to specifically recognize and eliminate virally infected host cells. In this review, we recapitulate the evidence for CD8(+) T cells as an immunological correlate against HIV, but more importantly, we assess the means by which we evaluate their antiviral capacity. To achieve a breakthrough in the domain of T-cell-based HIV vaccine development, it has become abundantly clear that we must overhaul our system of immune monitoring and come up with a 'rational' tactic to evaluate the efficacy of HIV-specific CD8(+) T cells.

A polychromatic antibody cocktail to investigate phenotypic and functional markers on human myeloid and plasmacytoid dendritic cells (65.3)

Antigen presentation is a critical feature of adaptive immunity and essential in self versus nonself discrimination as well as in stimulating immune responses against pathogens. Dendritic cells (DCs) are considered to be the most potent antigen-presenting cells and have long been recognized as key regulators of the immune system. Because DCs are such crucial cells of the immune system, an extensive assessment of their quality in infected individuals is critical. Therefore, we have standardized a unique DC cocktail containing 12 different functional DC markers using an LSR II polychromatic flow cytometer. To this point, we have tested our newly standardized cocktail on the fresh, frozen, and cultured peripheral blood mononuclear cell (PBMCs) as well as on monocyte-derived DCs (MDDCs), a widely used surrogate system for primary blood DCs. This study emphasizes the practicality of utilizing frozen versus fresh cells, especially in rare disease states, wherein obtaining fresh material is virtually impossible. Furthermore, we focus on the feasibility of PBMCs compared to whole blood as starting material. To our knowledge this is the first comprehensive DC phenotyping protocol that uses an extensive list of functional markers (&gt;8). Collectively, these investigations possess great potential to enable investigators to perform immune cell monitoring and develop diagnostic and therapeutic strategies.

Perforin expression directly ex vivo by HIV-specific CD8 T-cells is a correlate of HIV elite control

Many immune correlates of CD8⁺ T-cell-mediated control of HIV replication, including polyfunctionality, proliferative ability, and inhibitory receptor expression, have been discovered. However, no functional correlates using ex vivo cells have been identified with the known ability to cause the direct elimination of HIV-infected cells. We have recently discovered the ability of human CD8⁺ T-cells to rapidly upregulate perforin—an essential molecule for cell-mediated cytotoxicity—following antigen-specific stimulation. Here, we examined perforin expression capability in a large cross-sectional cohort of chronically HIV-infected individuals with varying levels of viral load: elite controllers (n = 35), viremic controllers (n = 29), chronic progressors (n = 27), and viremic nonprogressors (n = 6). Using polychromatic flow cytometry and standard intracellular cytokine staining assays, we measured perforin upregulation, cytokine production, and degranulation following stimulation with overlapping peptide pools encompassing all proteins of HIV. We observed that HIV-specific CD8⁺ T-cells from elite controllers consistently display an enhanced ability to express perforin directly ex vivo compared to all other groups. This ability is not restricted to protective HLA-B haplotypes, does not require proliferation or the addition of exogenous factors, is not restored by HAART, and primarily originates from effector CD8⁺ T-cells with otherwise limited functional capability. Notably, we found an inverse relationship between HIV-specific perforin expression and viral load. Thus, the capability of HIV-specific CD8⁺ T-cells to rapidly express perforin defines a novel correlate of control in HIV infection.

While the majority HIV-infected individuals progress to AIDS, a fraction of these individuals—for reasons not completely understood—do not develop AIDS and also display sustained control over viral replication; these subjects are sometimes referred to as elite controllers (EC). Prior evidence has shown that HIV-specific CD8⁺ T-cells, a component of adaptive immunity against intracellular pathogens, from EC exhibit enhanced functionality compared to individuals with progressive disease. Therefore, HIV-specific CD8⁺ T-cells likely play an important role in the favorable clinical outcomes witnessed in EC. We show in this study that the ability to control HIV replication in EC is associated with the expression of a protein called perforin, a critical molecule that enables CD8⁺ T-cells to directly kill infected cells - thereby preventing the spread of HIV to previously uninfected cells. In infected subjects with nonprogressive disease, we show that HIV-specific CD8⁺ T-cells demonstrate a superior ability to express perforin upon antigen-specific stimulation, whereas in progressors this property is diminished. Thus, we identify a functional capability of CD8⁺ T-cells, readily measured by standard intracellular cytokine staining assays, that potentially has a direct impact on HIV replication in vivo. These findings may, therefore, provide an important qualifier for future HIV vaccine research.

Adenovirus-specific human T cells are pervasive, polyfunctional, and cross-reactive

Pre-existing immunity to adenovirus (Ad) reduces the efficacy of Ad-based vaccines. The goal of this study was to define the prevalence, magnitude, functionality and phenotype of Ad-specific human T cells directly ex vivo. To study the magnitude of T-cell responses to Ad, we developed a highly reproducible whole Ad vector stimulation assay for use with polychromatic flow cytometry. Ad-specific CD4(+) and CD8(+) T-cells were detected in all 17 human subjects tested and were capable of proliferating upon restimulation. Ad5-specific CD4(+) T cells were primarily monofunctional CD4(+) T cells that produced IL-2, IFN-gamma or TNFalpha and expressed the memory markers CD27 and CD45RO. In contrast, Ad5-specific CD8(+) T cells were more polyfunctional, expressing effector-like combinations of IFN-gamma, MIP1alpha and perforin, and generally lacked CD27 and CD45RO expression. Ad-specific CD4(+) and CD8(+) T-cell responses against chimpanzee-derived AdC6 and AdC7 were found in all subjects, indicating the commonality of cross-serotype reactivity of Ad-specific T cells. This cross-reactivity is due in part to extensive CD4(+) and CD8(+) T-cell recognition of hexon regions conserved between multiple Ad serotypes. The prevalence, cross-reactivity and effector-like functions of Ad-specific T cells in humans may affect the efficacy of Ad vector-based vaccines by eliminating vector infected cells even when rare serotype Ad vectors are employed.

Perforin and IL-2 upregulation define qualitative differences among highly functional virus-specific human CD8 T cells

The prevailing paradigm of T lymphocyte control of viral replication is that the protective capacity of virus-specific CD8⁺ T cells is directly proportional to the number of functions they can perform, with IL-2 production capacity considered critical. Having recently defined rapid perforin upregulation as a novel effector function of antigen-specific CD8⁺ T cells, here we sought to determine whether new perforin production is a component of polyfunctional CD8⁺ T cell responses that contributes to the control of several human viral infections: cytomegalovirus (CMV), Epstein-Barr virus (EBV), influenza (flu), and adenovirus (Ad). We stimulated normal human donor PBMC with synthetic peptides whose amino acid sequences correspond to defined CTL epitopes in the aforementioned viruses, and then used polychromatic flow cytometry to measure the functional capacity and the phenotype of the responding CD8⁺ T cells. While EBV and flu-specific CD8⁺ T cells rarely upregulate perforin, CMV-specific cells often do and Ad stimulates an exceptionally strong perforin response. The differential propensity of CD8⁺ T cells to produce either IL-2 or perforin is in part related to levels of CD28 and the transcription factor T-bet, as CD8⁺ T cells that rapidly upregulate perforin harbor high levels of T-bet and those producing IL-2 express high amounts of CD28. Thus, “polyfunctional” profiling of antigen-specific CD8⁺ T cells must not be limited to simply the number of functions the cell can perform, or one particular memory phenotype, but should actually define which combinations of memory markers and functions are relevant in each pathogenic context.

Although CD8⁺ T cells are thought to be largely responsible for the control of viral infections, exactly how they mediate protection is uncertain. One approach to assessing their protective capacity is to measure several of their functions simultaneously. Generally, it is believed the more functions a cell can perform, the better its potential to control viral replication. A multi-functional response including interleukin-2 (IL-2) production is currently valued as the key correlate of protection. We recently characterized a novel CD8⁺ T cell function: rapid perforin upregulation, which serves to contribute to and sustain the killing of virally infected host cells. In this study, we show that new perforin is abundant during adenovirus and cytomegalovirus infections, but scarcely detected in the context of influenza and Epstein-Barr virus. Importantly, perforin and IL-2 are rarely co-expressed. The significance of this relationship is that we can no longer assume the more functions a CD8⁺ T cell performs in response to a virus the better. Thus, when considering vaccine design, no single functional profile will likely be protective across all pathogens. Rather, vaccine-induced T cell responses may need to be “pathogen-specific”, as different T cell functional responses will be important for controlling different viral infections.

Vaccine-induced, simian immunodeficiency virus-specific CD8+ T cells reduce virus replication but do not protect from simian immunodeficiency virus disease progression

Our limited understanding of the interaction between primate lentiviruses and the host immune system complicates the design of an effective HIV/AIDS vaccine. To identify immunological correlates of protection from SIV disease progression, we immunized two groups of five rhesus macaques (RMs) with either modified vaccinia Ankara (MVA) or MVADeltaudg vectors that expressed SIVmac239 Gag and Tat. Both vectors raised a SIV-specific CD8(+) T cell response, with a magnitude that was greater in mucosal tissues than in peripheral blood. After challenge with SIVmac239, all vaccinated RMs showed mucosal and systemic CD8(+) T cell recall responses that appeared faster and were of greater magnitude than those in five unvaccinated control animals. All vaccinated RMs showed a approximately 1-log lower peak and early set-point SIV viral load than the unvaccinated animals, and then, by 8 wk postchallenge, exhibited levels of viremia similar to the controls. We observed a significant direct correlation between the magnitude of postchallenge SIV-specific CD8(+) T cell responses and SIV viral load. However, vaccinated RMs showed no protection from either systemic or mucosal CD4(+) T cell depletion and no improved survival. The observation that vaccine-induced, SIV-specific CD8(+) T cells that partially control SIVmac239 virus replication fail to protect from immunological or clinical progression of SIV infection underscores both the complexity of AIDS pathogenesis and the challenges of properly assessing the efficacy of candidate AIDS vaccines.

Rapid up-regulation and granule-independent transport of perforin to the immunological synapse define a novel mechanism of antigen-specific CD8+ T cell cytotoxic activity

CTL are endowed with the ability to eliminate pathogens through perforin-mediated cytotoxic activity. The mechanism for perforin-mediated Ag-specific killing has been solely attributed to cytotoxic granule exocytosis from activated CD8(+) T cells. In this study, we redefine this mechanism, demonstrating that virus-specific CD8(+) T cells rapidly up-regulate perforin in response to stimulation temporally with IFN-gamma and CD107a expression. Following Ag-specific activation, newly synthesized perforin rapidly appears at the immunological synapse, both in association with and independent of cytotoxic granules, where it functions to promote cytotoxicity. Our work suggests a novel mechanism of CTL cytotoxicity and identifies a novel correlate of CD8(+) T cell-mediated immunity.

Flow cytometric detection of perforin upregulation in human CD8 T cells

Perforin and granzymes work synergistically to induce apoptosis in target cells recognized by cytotoxic T lymphocytes. While perforin is readily detectable by flow cytometry in resting CD8 T cells, upregulation of perforin in activated cells is thought to require proliferation. However, perforin undergoes numerous conformational changes during its maturation, which may affect the ability of conventional antibodies to recognize newly synthesized perforin. Polychromatic flow cytometry was used to detect perforin and cytokine production following stimulation of ex vivo human CD8 T cells. Two different anti-perforin antibodies, clones B-D48 and deltaG9, were used to discriminate various forms of perforin after cellular activation. We provide evidence for the rapid upregulation of perforin protein, which may contribute to the ability of CD8 T cells to kill multiple targets over time. The deltaG9 clone recognizes the granule-associated conformation of perforin, while the B-D48 clone is able to detect perforin in multiple forms. Finally, we show there is variability in the ability of CD8 T cells to upregulate perforin. Human CD8 T cells are capable of new perforin production immediately following activation. This work defines a novel flow cytometric procedure that can be used to more completely assess the cytotoxic capacity of human CD8 T cells.

Activation drives PD-1 expression during vaccine-specific proliferation and following lentiviral infection in macaques

Recent data supports that increased expression of PD-1, a negative regulator of immune function, is associated with T cell exhaustion during chronic viral infection. However, PD-1 expression during acute infection and vaccination has not been studied in great detail in primates. Here, we examine PD-1 expression on CD3(+) T cells following DNA vaccination or lentiviral infection of macaques. Ex vivo peptide stimulation of PBMC from DNA-vaccinated uninfected macaques revealed a temporal increase in PD-1 expression in proliferating antigen-specific CD8(+) T cells. Following the initial increase, PD-1 expression steadily declined as proliferation continued, with a concomitant increase in IFN-gamma secretion. Subsequent examination of PD-1 expression on T cells from uninfected and lentivirus-infected non-vaccinated macaques revealed a significant increase in PD-1 expression with lentiviral infection, consistent with previous reports. PD-1 expression was highest on cells with activated memory and effector phenotypes. Despite their decreased telomere length, PD-1(hi) T cell populations do not appear to have statistically significant uncapped telomeres, typically indicative of proliferative exhaustion, suggesting a different mechanistic regulation of proliferation by PD-1. Our data indicate that PD-1 expression is increased as a result of T cell activation during a primary immune response as well as during persistent immune activation in macaques.

Comparison of HIV-specific CD8 T-cell responses among uninfected individuals exposed to HIV parenterally and mucosally

OBJECTIVE

To assess the influence of route of HIV exposure on the development of HIV-specific CD8 T-cell responses in exposed, uninfected (EU) individuals.

DESIGN

Two groups of EU exposed to virus through either sexual or intravenous contact were studied. Group I included subjects (n = 20) who had unprotected sexual contact with known HIV-infected partners and no intravenous HIV exposure; Group II included individuals (n = 27) who had shared needles with HIV-infected partners and had no sexual exposure to this virus. Between-group comparisons were made for the proportion of responders, breadth, magnitude, and specificity of HIV-specific responses.

METHODS

: The interferon-gamma ELISPOT assay was used to detect HIV-specific effector activity. Peripheral blood mononuclear cells (PBMC) from each subject were stimulated with a panel of HIV peptides restricted to the MHC class I alleles expressed by the individual.

RESULTS

A similar proportion of EU tested from each group (35.0% Group I versus 22.2% Group II) recognized at least one HIV peptide. Group I and II subjects recognized HIV peptides with a similar cumulative intensity of 130 +/- 67.5 and 182.9 +/- 184.2 spot forming cells/1 x 10 PBMC, respectively, and similar magnitude per stimulatory peptide of 82.7 and 78.4 SFC/1 x 10 PBMC, respectively. The proportion of stimulatory peptides derived from HIV Gag, reverse transcriptase, Env, and Nef was not significantly different between the two EU groups. HLA-A*0201 restricted HIV epitopes immunodominant in infected individuals are rarely stimulatory in EU subjects.

CONCLUSIONS

Both mucosal and parenteral exposure to HIV can elicit HIV-specific CD8 T-cell responses with similar characteristics.

HIV-specific CD8 T-cell activity in uninfected injection drug users is associated with maintenance of seronegativity

OBJECTIVES

To determine whether HIV-exposed, uninfected subjects (EUs) having HIV-specific effector activity are at a reduced risk for seroconverting compared with EUs with no HIV-specific effector responses.

DESIGN

Twenty-eight intravenous drug users (IVDU) with documented risk for HIV infection over a 1-year period were screened for the presence of HIV-specific CD8+ effector cell activity. Group I included 18 IVDUs who remained seronegative despite exposure to HIV through needle sharing with partner(s) known to be HIV infected. Group II included 10 IVDUs who seroconverted after similar HIV exposure.

METHODS

The enzyme-linked immunospot (ELIspot; Mabtech AB, Nacka, Sweden) assay was used to measure the frequency of HIV-specific interferon-gamma secreting cells. Peripheral blood mononuclear cells (PBMC) were stimulated with a panel of synthetic HIV peptides in a major histocompatibility complex class I antigen-restricted fashion. PBMC from group II were obtained from timepoints 7 months or less before seroconversion.

RESULTS

Twelve of 18 (66.7%) persistently seronegative subjects versus none of 10 seroconverters exhibited detectable HIV-specific effector responses at the sampling date (P < 0.001; Fisher's exact test). This represents an odds ratio of 40.38 (95% confidence intervals 2.95 to > 3000).

CONCLUSION

EUs who have developed HIV-specific effector responses are at a reduced risk for seroconversion compared with EUs who do not develop this type of immunity. This observation supports the hypothesis that HIV-specific effector responses are a correlate of immune protection from HIV infection.