Quantitative PET imaging of the CD4 pool in nonhuman primates.

PURPOSE: Previous SPECT and PET semi-quantitative in vivo imaging studies in monkeys have demonstrated specific uptake of radiolabeled rhesus recombinant anti-CD4 monoclonal antibody fragment CD4R1-F(ab΄)2 in the spleen and clusters of lymph nodes (LNs) but yielded conflicting results of imaging the gut CD4 + T-cell pool. Here, using PET dynamic imaging with kinetic analysis, we performed a fully quantitative CD4 imaging in rhesus macaques. METHODS: The biodistributions of [89Zr]Zr-CD4R1-F(ab΄)2 and/or of [89Zr]Zr-ibalizumab were performed with static PET scans up to 144 h (6 days) post-injection in 18 rhesus macaques with peripheral blood CD4 + T cells/µl ranging from ~ 20 to 2400. Fully quantitative analysis with a 4-h dynamic scan, arterial sampling, metabolite evaluation, and model fitting was performed in three immunocompetent monkeys to estimate the binding potential of CD4 receptors in the LNs, spleen, and gut. RESULTS: The biodistributions of [89Zr]Zr-CD4R1-F(ab΄)2 and [89Zr]Zr-ibalizumab were similar in lymphoid tissues with a clear delineation of the CD4 pool in the LNs and spleen and a significant difference in lymphoid tissue uptake between immunocompetent and immunocompromised macaques. Consistent with our previous SPECT imaging of [99mTc]Tc-CD4R1-F(ab΄)2, the [89Zr]Zr-CD4R1-F(ab΄)2 and [89Zr]Zr-Ibalizumab uptakes in the gut were low and not different between uninfected and SIV-infected CD4-depleted monkeys. Ex vivo studies of large and small intestines confirmed the in vivo images. CONCLUSION: The majority of specific binding to CD4 + tissue was localized to LNs and spleen with minimal uptake in the gut. Binding potential derived from fully quantitative studies revealed that the contribution of the gut is lower than the spleen's contribution to the total body CD4 pool.

Soccer-Specific Reactive Repeated-Sprint Ability in Elite Youth Soccer Players: Maturation Trends and Association With Various Physical Performance Tests.

Di Mascio, M, Ade, J, Musham, C, Girard, O, and Bradley, PS. Soccer-specific reactive repeated-sprint ability in elite youth soccer players: maturation trends and association with various physical performance tests. J Strength Cond Res 34(12): 3538-3545, 2020-Repeated-sprint ability is an important physical prerequisite for competitive soccer and deviates for players in various stages of growth and development. Thus, this study investigated reactive repeated-sprint ability in elite youth soccer players in relation to maturation (age at peak height velocity) and its association with performance of other physical tests. Elite male youth players from an English Premier League academy (U12, n = 8; U13, n = 11; U14, n = 15; U15, n = 6; U16, n = 10; and U18, n = 13) completed the reactive repeated-sprint test (RRST; 8 × 30-m sprints with 30-second active recovery), and other physical tests including the Yo-Yo intermittent recovery test level 2 (Yo-Yo IR2), arrowhead agility test, countermovement jump test with arms (CMJA), in addition to 10- and 20-m straight-line sprints. Reactive repeated-sprint test (RRST) performance (total time across 8 sprints) progressively improved from U12 to U16 (p < 0.01; effect size [ES]: 1.0-1.9), yet with no differences found between U16 and U18. No between-group differences in RRST performance were evident after accounting for age at peak height velocity (p > 0.05; ES: <0.3). Correlation magnitudes between performance on the RRST and other tests were trivial to moderate for the Yo-Yo IR2 (r = -0.15 to 0.42), moderate to very large for the arrowhead agility test (r = 0.48-0.90), moderate to large for CMJA (r = -0.43 to 0.66), and trivial to large for 10- and 20-m sprints (r = 0.05-0.61). The RRST was sensitive at tracking maturation trends in elite youth players, although performance improvements were not as marked from 15 to 16 years of age. RRST performance correlates with several physical qualities decisive for competitive soccer (agility, speed, power, and aerobic endurance).

Brain 18F-FDG PET of SIV-infected macaques after treatment interruption or initiation.

BACKGROUND: Although rates of severe HIV-associated neurocognitive disorders have declined in the post-antiretroviral treatment (ART) era, subtle deficits persist, possibly exacerbated by treatment non-adherence. The actual effects of ART interruption/initiation on brain glucose metabolism as a reflection of viral replication and neuroinflammation remain unclear. Our study investigates how treatment initiation and interruption alter brain glucose metabolism in SIV-infected macaques, using 18F-FDG PET in correlation with plasma and CSF viral loads (VL) and cytokine levels. METHODS: SIV-infected macaques (n = 7) underwent ART initiation only, ART interruption only, or both. Five uninfected animals served as controls. 18F-FDG PET imaging was performed at baseline and 1, 3, and 6 months after treatment modification. Mean and maximum standardized uptake values (SUV) for the whole-brain and subregions were calculated. Plasma and CSF VL and cytokine levels were measured. Paired t tests evaluated acute changes in whole-brain SUV from baseline to 1 month, while mixed-effect linear regression models evaluated changes over multiple timepoints and correlated SUV values with disease markers. RESULTS: ART interruption was associated with increased SUVmean and SUVmax acutely, after 1 month (SUVmean 95% CI [0.044-0.786 g/ml], p = 0.037; SUVmax 95% CI [0.122-3.167 g/ml], p = 0.041). The correlation between SUV and time, however, was not significant when evaluated across all timepoints. Increased SUVmean and SUVmax correlated with decreased CD4+ and CD8+ T-cell counts and increased plasma VL. SUVmax was positively associated with increases in CSF VL, and there were borderline positive associations between SUVmax and IL-2, and between SUVmean and IL-15. The treatment initiation group showed no associations between imaging and disease biomarkers despite viral suppression, reduced cytokine levels, and increased CD4+ and CD8+ T-cell counts. CONCLUSIONS: ART interruption is associated with increased brain glucose metabolism within 1 month of treatment cessation, which, in concert with increased levels of pro-inflammatory cytokines in the CSF, may reflect neuroinflammation in the setting of viral rebound. Although we cannot assert neurologic damage in association with cerebral hypermetabolism, it is a concerning outcome of ART non-adherence. Treatment initiation, meanwhile, did not result in significant changes in brain metabolism. HIV-induced neuroinflammation may require a longer period to abate than our follow-up period allowed.

Discordance in lymphoid tissue recovery following stem cell transplantation in rhesus macaques: an in vivo imaging study.

Ionizing irradiation is used routinely to induce myeloablation and immunosuppression. However, it has not been possible to evaluate the extent of ablation without invasive biopsy. For lymphoid recovery, peripheral blood (PB) lymphocytes (PBLs) have been used for analysis, but they represent <2% of cells in lymphoid tissues (LTs). Using a combination of single-photon emission computed tomography imaging and a radiotracer ((99m)Tc-labeled rhesus immunoglobulin G1 anti-CD4R1 (Fab')2), we sequentially imaged CD4(+) cell recovery in rhesus macaques following total body irradiation (TBI) and reinfusion of vector-transduced, autologous CD34(+) cells. Our results present for the first time a sequential, real-time, noninvasive method to evaluate CD4(+) cell recovery. Importantly, despite myeloablation of circulating leukocytes following TBI, total depletion of CD4(+) lymphocytes in LTs such as the spleen is not achieved. The impact of TBI on LTs and PBLs is discordant, in which as few as 32.4% of CD4(+) cells were depleted from the spleen. In addition, despite full lymphocyte recovery in the spleen and PB, lymph nodes have suboptimal recovery. This highlights concerns about residual disease, endogenous contributions to recovery, and residual LT damage following ionizing irradiation. Such methodologies also have direct application to immunosuppressive therapy and other immunosuppressive disorders, such as those associated with viral monitoring.

The reliability, validity and sensitivity of a novel soccer-specific reactive repeated-sprint test (RRST).

PURPOSE: The aim of this study was to determine the reliability, validity and sensitivity of a reactive repeated-sprint test (RRST). METHODS: Elite (n = 72) and sub-elite male (n = 87) and elite female soccer players (n = 12) completed the RRST at set times during a season. Total distance timed was 30 m and the RRST performance measure was the total time (s) across eight repetitions. Competitive match running performance was measured using GPS and high-intensity running quantified (≥ 19.8 km h(-1)). RESULTS: Test-retest coefficient of variation in elite U16 and sub-elite U19 players was 0.71 and 0.84 %, respectively. Elite U18 players' RRST performances were better (P < 0.01) than elite U16, sub-elite U16, U18, U19 and elite senior female players (58.25 ± 1.34 vs 59.97 ± 1.64, 61.42 ± 2.25, 61.66 ± 1.70, 61.02 ± 2.31 and 63.88 ± 1.46 s; ES 0.6-1.9). For elite U18 players, RRST performances for central defenders (59.84 ± 1.35 s) were lower (P < 0.05) than full backs (57.85 ± 0.77 s), but not attackers (58.17 ± 1.73 s) or central and wide midfielders (58.55 ± 1.08 and 58.58 ± 1.89 s; ES 0.7-1.4). Elite U16 players demonstrated lower (P < 0.01) RRST performances during the preparation period versus the start, middle and end of season periods (61.13 ± 1.53 vs 59.51 ± 1.39, 59.25 ± 1.42 and 59.20 ± 1.57 s; ES 1.0-1.1). Very large magnitude correlations (P < 0.01) were observed between RRST performance and high-intensity running in the most intense 5-min period of a match for both elite and sub-elite U18 players (r = -0.71 and -0.74), with the best time of the RRST also correlating with the arrowhead agility test for elite U16 and U18 players (r = 0.84 and 0.75). CONCLUSION: The data demonstrate that the RRST is a reliable and valid test that distinguishes between performance across standard, position and seasonal period.

Elite suppressors harbor low levels of integrated HIV DNA and high levels of 2-LTR circular HIV DNA compared to HIV+ patients on and off HAART.

Elite suppressors (ES) are a rare population of HIV-infected individuals that are capable of naturally controlling the infection without the use of highly active anti-retroviral therapy (HAART). Patients on HAART often achieve viral control to similar (undetectable) levels. Accurate and sensitive methods to measure viral burden are needed to elucidate important differences between these two patient populations in order to better understand their mechanisms of control. Viral burden quantification in ES patients has been limited to measurements of total DNA in PBMC, and estimates of Infectious Units per Million cells (IUPM). There appears to be no significant difference in the level of total HIV DNA between cells from ES patients and patients on HAART. However, recovering infectious virus from ES patient samples is much more difficult, suggesting their reservoir size should be much smaller than that in patients on HAART. Here we find that there is a significant difference in the level of integrated HIV DNA in ES patients compared to patients on HAART, providing an explanation for the previous results. When comparing the level of total to integrated HIV DNA in these samples we find ES patients have large excesses of unintegrated HIV DNA. To determine the composition of unintegrated HIV DNA in these samples, we measured circular 2-LTR HIV DNA forms and found ES patients frequently have high levels of 2-LTR circles in PBMC. We further show that these high levels of 2-LTR circles are not the result of inefficient integration in ES cells, since HIV integrates with similar efficiency in ES and normal donor cells. Our findings suggest that measuring integration provides a better surrogate of viral burden than total HIV DNA in ES patients. Moreover, they add significantly to our understanding of the mechanisms that allow viral control and reservoir maintenance in this unique patient population.

Decreases in IL-7 levels during antiretroviral treatment of HIV infection suggest a primary mechanism of receptor-mediated clearance.

IL-7 is essential for T-cell homeostasis. Elevated serum IL-7 levels in lymphopenic states, including HIV infection, are thought to be due to increased production by homeostatic feedback, decreased receptor-mediated clearance, or both. The goal of this study was to understand how immune reconstitution through antiretroviral therapy (ART) in HIV(+) patients affects IL-7 serum levels, expression of the IL-7 receptor (CD127), and T-cell cycling. Immunophenotypic analysis of T cells from 29 HIV(-) controls and 43 untreated HIV(+) patients (30 of whom were followed longitudinally for ≤ 24 months on ART) was performed. Restoration of both CD4(+) and CD8(+) T cells was driven by increases in CD127(+) naive and central memory T cells. CD4(+) T-cell subsets were not fully restored after 2 years of ART, whereas serum IL-7 levels normalized by 1 year of ART. Mathematical modeling indicated that changes in serum IL-7 levels could be accounted for by changes in the receptor concentration. These data suggest that T-cell restoration after ART in HIV infection is driven predominantly by CD127(+) cells and that decreases of serum IL-7 can be largely explained by improved CD127-mediated clearance.

Differential effects of HIV viral load and CD4 count on proliferation of naive and memory CD4 and CD8 T lymphocytes.

We previously showed that HIV infection leads to expansion of a rapidly proliferating pool (s(1)) of CD4 and CD8 T lymphocytes. In the current study, we used in vivo labeling with bromodeoxyuridine to characterize the kinetics of naive, memory, and activated (HLA-DR(+)/CD38(+)) subpopulations of CD4 and CD8 T lymphocytes, and to examine the relationship between kinetic parameters and baseline CD4 counts, HIV viral load, potential markers of microbial translocation, and cytokine levels. Activated cells showed the highest proliferation rates, followed by effector and central memory cells, with naive cells showing the lowest rates, for both CD4 and CD8 T cells. HIV viral load correlated with s(1) of CD4 and CD8 effector memory cells, as well as CD8 naive cells, whereas CD4 cell counts correlated inversely with naive CD4 s(1). Endotoxin levels showed a weak negative association with CD4 but not CD8 s(1). INF-γ and TNF-α were associated with s(1) for CD4 and CD8 cells, respectively. Thus, HIV is the primary driving force behind the activation and proliferation of most subsets of both CD4 and CD8 T lymphocytes, whereas naive CD4 cell proliferation likely represents a homeostatic response. Microbial translocation does not appear to play an important role in this proliferation.

Evaluation of the most intense high-intensity running period in English FA premier league soccer matches.

The aim of this study was to examine the most intense period of high-intensity running during elite soccer matches. Elite players (n = 100) were analyzed using a multicamera computerized tracking system. High-intensity running (speed >19.8 km·h) in 5-min periods were quantified during matches. High-intensity running was performed for approximately 3% of total time, but this doubled (F[1,99] = 9.179, p < 0.001, d > 1.2) during the most intense period (8.4 ± 2.7 vs. 16.4 ± 4.6 seconds). Recovery time between high-intensity efforts was approximately 30 seconds during the most intense period (33.3 ± 19.7 seconds). The work:rest ratio between high-intensity bouts increased (F[1,99] = 2.018, p < 0.001, d > 0.6) from 1:12 for the match average to 1:2 during the most intense period. The distance of each discrete high-intensity running bout increased (F[1,99] = 1.958, p < 0.001, d > 0.6) approximately 13% during the most intense period compared with that of the match average (6.7 ± 1.8 vs. 5.8 ± 0.6 m). Central defenders were running at high-intensity for less (F[4,95] = 4.907, p < 0.05, d > 0.6) time than full-backs, wide midfielders, and attackers (12.9 ± 2.4 vs. 17.9 ± 3.4, 18.3 ± 5.5, and 16.9 ± 3.8 seconds). Central defenders had a greater recovery time (F[4,95] = 3.083, p < 0.05, d > 0.6) between high-intensity efforts than wide midfielders. No differences were evident between playing positions for maximum running speed and average distances of high-intensity running. These results show that high-intensity running, work:rest ratios, and average high-intensity distances change markedly during the most intense period of matches and are highly dependent on positional role. Therefore, conditioning drills and performance tests should closely mimic distances, work:rest ratios, and recovery times of those found during the most intense period of matches.

Viral dissemination and immune activation modulate antiretroviral drug levels in lymph nodes of SIV-infected rhesus macaques.

Introduction and methods: To understand the relationship between immunovirological factors and antiretroviral (ARV) drug levels in lymph nodes (LN) in HIV therapy, we analyzed drug levels in twenty-one SIV-infected rhesus macaques subcutaneously treated with daily tenofovir (TFV) and emtricitabine (FTC) for three months. Results: The intracellular active drug-metabolite (IADM) levels (TFV-dp and FTC-tp) in lymph node mononuclear cells (LNMC) were significantly lower than in peripheral blood mononuclear cells (PBMC) (P≤0.005). Between Month 1 and Month 3, IADM levels increased in both LNMC (P≤0.001) and PBMC (P≤0.01), with a steeper increase in LNMC (P≤0.01). The viral dissemination in plasma, LN, and rectal tissue at ART initiation correlated negatively with IADM levels at Month 1. Physiologically-based pharmacokinetic model simulations suggest that, following subcutaneous ARV administration, ART-induced reduction of immune activation improves the formation of active drug-metabolites through modulation of kinase activity and/or through improved parent drug accessibility to LN cellular compartments. Conclusion: These observations have broad implications for drugs that need to phosphorylate to exert their pharmacological activity, especially in the settings of the pre-/post-exposure prophylaxis and efficacy of antiviral therapies targeting pathogenic viruses such as HIV or SARS-CoV-2 replicating in highly inflammatory anatomic compartments.

Noninvasive in vivo imaging of CD4 cells in simian-human immunodeficiency virus (SHIV)-infected nonhuman primates.

Since the earliest days of the HIV epidemic, the number of CD4(+) T cells per unit volume of blood has been recognized as a major prognostic factor for the development of AIDS in persons with HIV infection. It has also been generally accepted that approximately 2% of total body lymphocytes circulate in the blood. In the present study, we have used a nondepleting humanized anti-CD4 monoclonal antibody labeled with the gamma emitter indium-111 to visualize the CD4(+) T-cell pool in vivo in nonhuman primates with simian HIV infection. A strong correlation was noted between radiotracer uptake in spleen, tonsil, axillary lymph nodes, and peripheral blood CD4 T-cell counts (rho = 0.75, 0.93, and 0.85, respectively, P < .005). The relationship between radiotracer retention in lymphoid tissues and CD4(+) T-cell counts in the circulation was governed by an exponential law. These data provide an estimate for the total number of lymphocytes in the body as being between 1.9 and 2.9 x 10(12) and suggest that the partition between peripheral blood and lymphoid tissue is between 0.3% and 0.5%.

HIV infection-associated immune activation occurs by two distinct pathways that differentially affect CD4 and CD8 T cells.

HIV infection is characterized by a brisk immune activation that plays an important role in the CD4 depletion and immune dysfunction of patients with AIDS. The mechanism underlying this activation is poorly understood. In the current study, we tested the hypothesis that this activation is the net product of two distinct pathways: the inflammatory response to HIV infection and the homeostatic response to CD4 T cell depletion. Using ex vivo BrdU incorporation of PBMCs from 284 patients with different stages of HIV infection, we found that CD4 proliferation was better predicted by the combination of CD4 depletion and HIV viral load (R(2) = 0.375, P < 0.001) than by either parameter alone (CD4 T cell counts, R(2) = 0.202, P < 0.001; HIV viremia, R(2) = 0.302, P < 0.001). Interestingly, CD8 T cell proliferation could be predicted by HIV RNA levels alone (R(2) = 0.334, P < 0.001) and this predictive value increased only slightly (R(2) = 0.346, P < 0.001) when CD4 T cell depletion was taken into account. Consistent with the hypothesis that CD4 T cell proliferation is driven by IL-7 as a homeostatic response to CD4 T cell depletion, levels of phosphorylated STAT-5 were found to be elevated in naive subsets of CD4 and CD8 T cells from patients with HIV infection and in the central memory subset of CD4 T cells. Taken together these data demonstrate that at least two different pathways lead to immune activation of T cells in patients with HIV infection and these pathways differentially influence CD4 and CD8 T cell subsets.

The effect of playing formation on high-intensity running and technical profiles in English FA Premier League soccer matches.

The aim of this study was to examine the effect of playing formation on high-intensity running and technical performance during elite soccer matches. Twenty English FA Premier League games were analysed using a multiple-camera computerized tracking system (n = 153 players). Overall ball possession did not differ (P < 0.05) between 4-4-2, 4-3-3 and 4-5-1 formations (50%, s = 7 vs. 49%, s = 8 vs. 44%, s = 6). No differences were observed in high-intensity running between 4-4-2, 4-3-3 and 4-5-1 formations. Compared with 4-4-2 and 4-3-3 formations, players in a 4-5-1 formation performed less very high-intensity running when their team was in possession (312 m, s = 196 vs. 433 m, s = 261 vs. 410 m, s = 270; P 5 0.05) but more when their team was not in possession (547 m, s = 217 vs. 461 m, s = 156 vs. 459 m, s = 169; P < 0.05). Attackers in a 4-3-3 performed ~30% more (P < 0.05) high-intensity running than attackers in 4-4-2 and 4-5-1 formations. However, the fraction of successful passes was highest in a 4-4-2 (P < 0.05) compared with 4-3-3 and 4-5-1 formations. The results suggest that playing formation does not influence the overall activity profiles of players, except for attackers, but impacts on very high-intensity running activity with and without ball possession and some technical elements of performance.

Monitoring Immune Activation with Whole-Body Fluorodeoxyglucose-Positron-Emission Tomography in Simian Immunodeficiency Virus-Infected Rhesus Macaques.

This study aimed to assess immune activation in tissues by measuring glucose metabolism with 18F-fluorodeoxyglucose (FDG) and investigate the associations of various peripheral markers of disease progression with initiation and interruption of combination antiretroviral therapy in SIV-infected rhesus macaques (Macaca mulatta). Mixed-effect linear models revealed a significant inverse association of peripheral blood CD4+ T cell counts (p < 0.01) and a direct association of plasma viral load (p < 0.01) with the FDG uptake in the spleen, bone marrow, and most clusters of lymph nodes. In contrast, no significant associations were found for the liver and the bowel FDG uptake. We also found no association of the fraction of proliferating peripheral blood T and B lymphocytes with FDG uptake in any analyzed tissues. The bowel FDG uptake of uninfected animals was heterogeneous and reached levels as high as those seen in the bowel or the clusters of lymph nodes or the spleen of high viremic SIV-infected animals, suggesting that factors beyond SIV-induced immune activation dominate the gut FDG uptake.

Determination of virus burst size in vivo using a single-cycle SIV in rhesus macaques.

A single-cycle simian immunodeficiency virus (scSIV) that undergoes only one round of infection and replication was constructed to calculate the total number of virons produced by an SIV-infected cell in vivo. Four Mamu-A*01 rhesus macaques were inoculated on two occasions 11 weeks apart with the scSIV by ex vivo infection and i.v. reinfusion of autologous cells. After each inoculation, plasma viral loads peaked between 1 and 2.5 days and then declined exponentially in one or two phases to below detection limits within 2 weeks. Although higher levels of SIV-specific cytotoxic T lymphocytes and modest increases in antibody responses were observed for each animal after the second inoculation, decay rates of the infected cells were only minimally affected. Analyzing the viral load data with a mathematical model, the in vivo viral burst size averaged 4.0 x 10(4) and 5.5 x 10(4) virions per cell for the first and second inoculations, respectively, with no significant difference between the two inoculations. This estimate, in conjunction with our prior understanding of other quantitative viral and cellular parameters during SIV and HIV infection, provides critical insights into the dynamic process of viral production and its interplay with the infected host in vivo.

High-intensity activity profiles of elite soccer players at different performance levels.

The aims of the study were to (a) determine the high-intensity activity patterns of soccer players at different performance levels and playing positions, (b) investigate temporary and end game fatigue in elite domestic and international soccer matches, and (c) quantify acceleration and maximal running speed profiles of elite soccer players. Elite domestic (n = 100) and international (n = 10) soccer players were analyzed using a multicamera computerized tracking system. No differences were found for high-intensity running distance (2,520 +/- 678 vs. 2,745 +/- 332 m), mean recovery time (67 +/- 15 vs. 71 +/- 26 seconds), or maximal running speed (7.76 +/- 0.31 vs. 7.66 +/- 0.34 mxs-1). The distance covered in high-intensity running irrespective of playing level was 18% lower (p < 0.05) in the last than in the first 15-minute period of the game (391 +/- 117 vs. 478 +/- 141 m). The decline in high-intensity running immediately after the most intense 5-minute period was similar between international (222 +/- 33 vs. 109 +/- 37 m or 51% decline) and elite domestic (243 +/- 81 vs. 114 +/- 51 m or 53% decline) players. Wide midfielders, central midfielders, fullbacks, and attackers covered a greater (p < 0.01) distance in high-intensity running than central defenders (3,243 +/- 625, 2,949 +/- 435, 2,806 +/- 408, 2,618 +/- 745 vs. 2,034 +/- 284 m). Results demonstrate that high-intensity running is reduced during various periods of elite soccer matches, and high-intensity activity profiles and fatigue patterns are similar between international and elite domestic players but vary markedly between playing positions. These data provide valuable information to the fitness coach regarding the high-intensity active profile of elite soccer players that could be used to develop soccer-specific training drills.

Towards COVID-19 Prophylaxis: An AIDS Preclinical Research Perspective.

The success of an antiviral drug depends on its potency to neutralize the virus in vitro and its ability after administration in vivo to reach the anatomic compartments that fuel viral dissemination in the body. For instance, remdesivir, a potent SARS-CoV-2 antiviral drug based on studies in vitro, if administered orally would be poorly effective because low drug levels would reach the lungs due to its high first pass destruction in the liver. This is the reason remdesivir can only be administered intravenously, a requirement that clearly limits its use as a prophylactic agent for COVID-19, although novel formulations for its easier administration are under development. Whether an antiviral prophylaxis could further control or even stop the COVID-19 epidemic in synergy with other non-pharmacological based mitigation strategies is today unknown. Since the mid-1960s, pharmacologists have investigated the use of lipid-based nanoparticles for efficient delivery of antivirals to tissues, for example by transforming the route of administration from intravenous to oral, subcutaneous or aerosol administrations. These novel encapsulation strategies have also the potential to maintain high levels of the antiviral drugs in tissues, with reduced dose frequency compared to the non-encapsulated drug. Several lipid-based nanoparticles are today approved by the US Food and Drug Administration or being tested in clinical studies with favorable toxicity profiles. Nonhuman primate models of coronavirus infection offer unique platforms to accelerate the search for SARS-CoV-2 antiviral prophylaxis. Paradigms, to corroborate this claim, are borrowed from nonhuman primate research studies, some of which had a profound impact on global public health in the specific setting of the AIDS pandemic. Sharing information from nonhuman primate research programs, invoking principles of scientific transparency and bioethics similar to those universally agreed for human studies, would also likely significantly help our collective fight (as the human species) against this public health emergency.

Antiretroviral tissue kinetics: in vivo imaging using positron emission tomography.

Our current knowledge on the antiviral efficacy, dosing, and toxicity of available highly active antiretroviral therapy regimens is mostly derived from plasma or blood kinetics of anti-human immunodeficiency virus (anti-HIV) drugs. However, the blood comprises only 2% of the total target cells in the body. Tissue drug levels may differ substantially from corresponding plasma levels, and drug distribution processes may be characterized by high intertissue variability, leading to suboptimal target site concentrations and the potential risk for therapeutic failures. Positron emission tomography has greatly expanded the scope of the pharmacokinetic measurements that can be performed noninvasively in animal models or humans. We have prepared [18F]FPMPA, a fluorine-18-radiolabeled analogue of tenofovir, to study antiretroviral tissue kinetics in vivo noninvasively and tested the imaging probe in rats. The biodistribution of the fluorine-18 analogue closely follows that of nonfluorinated tenofovir. Compared to that in the blood, the levels of penetration of the antiretroviral drug were found to be significantly reduced in the spleen and submandibular lymph nodes (approximately 2-fold), in the mesenteric lymph nodes and the testes (approximately 4-fold), and in the brain compartment (approximately 25-fold). Intersubject variability of the trough drug concentration (measured at 120 min) in certain tissues, like the colon (coefficient of variation, >100%), is not reflected by the intersubject variability in the blood compartment (coefficient of variation, 24%). Positron emission tomography imaging of the fluorine-18 analogue revealed the accumulation of the antiretroviral drug in the cortex of the kidneys, a potential correlate of tenofovir-induced nephrotoxicity observed in HIV-1-infected treated patients. Thus, [18F]FPMPA is a promising radiotracer for evaluation of tenofovir biodistribution under carefully controlled drug administration protocols.

Dynamics of T- and B-lymphocyte turnover in a natural host of simian immunodeficiency virus.

Increased lymphocyte turnover is a hallmark of pathogenic lentiviral infection. To investigate perturbations in lymphocyte dynamics in natural hosts with nonpathogenic simian immunodeficiency virus (SIV) infection, the nucleoside analog bromodeoxyuridine (BrdU) was administered to six naturally SIV-infected and five SIV-negative sooty mangabeys. As a measure of lymphocyte turnover, we estimated the mean death rate by fitting a mathematical model to the fraction of BrdU-labeled cells during a 2-week labeling and a median 10-week delabeling period. Despite significantly lower total T- and B-lymphocyte counts in SIV-infected sooty mangabeys than in SIV-negative mangabeys, the turnover rate of B lymphocytes and CD4(+) and CD8(+) T lymphocytes was not increased in the SIV-infected animals. A small, rapidly proliferating CD45RA(+) memory subset and a large, slower-proliferating CD45RA(-) central memory subset of CD4(+) T lymphocytes identified in the peripheral blood of sooty mangabeys also did not show evidence of increased turnover in the context of SIV infection. Independently of SIV infection, the turnover of CD4(+) T lymphocytes in sooty mangabeys was significantly higher (P < 0.01) than that of CD8(+) T lymphocytes, a finding hitherto not reported in rhesus macaques or humans. The absence of aberrant T-lymphocyte turnover along with an inherently high rate of CD4(+) T-lymphocyte turnover may help to preserve the pool of central memory CD4(+) T lymphocytes in viremic SIV-infected sooty mangabeys and protect against progression to AIDS.

The amplitudes of viral blips in HIV-1 infected patients treated with antiretroviral therapy are power-law distributed.

We previously reported that in patients treated with highly active antiretroviral therapy (HAART) who achieve viral load (VL) suppression, low fluctuations of viral load over the threshold of detection (viral blips) more than 4 weeks apart occur at random, with a frequency that does not change with longer times of observation. The etiology of viral blips is currently unknown, but viral blip frequency inversely correlates with the decay of the latent reservoir, whose stability has been proposed as the major hurdle to HIV eradication. We show here that the distribution of viral blip amplitudes observed in a group of 272 patients successfully treated with highly active antiretroviral therapy appears to be power-law distributed. Such a distribution can be theoretically generated by randomly sampling the arrival of asynchronous and overlapping elementary pulses of viremia, with asymptotic exponential decay of kinetics, thus suggesting that the low fluctuations of viremia observed in patients during HAART treatment is, in part, a discrete phenomenon consistent with random activation of latently infected cells or release of virus and infected cells into the blood compartment from unknown sites of active viral replication.