Strategies for managing marine disease.

The incidence of emerging infectious diseases (EIDs) has increased in wildlife populations in recent years and is expected to continue to increase with global environmental change. Marine diseases are relatively understudied compared with terrestrial diseases but warrant parallel attention as they can disrupt ecosystems, cause economic loss, and threaten human livelihoods. Although there are many existing tools to combat the direct and indirect consequences of EIDs, these management strategies are often insufficient or ineffective in marine habitats compared with their terrestrial counterparts, often due to fundamental differences between marine and terrestrial systems. Here, we first illustrate how the marine environment and marine organism life histories present challenges and opportunities for wildlife disease management. We then assess the application of common disease management strategies to marine versus terrestrial systems to identify those that may be most effective for marine disease outbreak prevention, response, and recovery. Finally, we recommend multiple actions that will enable more successful management of marine wildlife disease emergencies in the future. These include prioritizing marine disease research and understanding its links to climate change, improving marine ecosystem health, forming better monitoring and response networks, developing marine veterinary medicine programs, and enacting policy that addresses marine and other wildlife diseases. Overall, we encourage a more proactive rather than reactive approach to marine wildlife disease management and emphasize that multidisciplinary collaborations are crucial to managing marine wildlife health.

Combination of CD8ß Depletion and Interleukin-15 Superagonist N-803 Induces Virus Reactivation in Simian-Human Immunodeficiency Virus-Infected, Long-Term ART-Treated Rhesus Macaques.

The "shock and kill" strategy predicates that virus reactivation in latently infected cells is required to eliminate the human immunodeficiency virus (HIV) reservoir. In a recent study, we showed robust and persistent induction of plasma viremia in antiretroviral therapy (ART)-treated simian immunodeficiency virus-infected rhesus macaques (RMs) undergoing CD8α depletion and treated with the interleukin-15 (IL-15) superagonist N-803 (J. B. McBrien et al., Nature 578:154-159, 2020, https://doi.org/10.1038/s41586-020-1946-0). Of note, in that study we used an antibody targeting CD8α, thereby depleting NK cells, NKT cells, and γδ T cells, in addition to CD8+ T cells. In the current proof-of-concept study, we tested whether virus reactivation can be induced by administration of N-803 to simian-human chimeric immunodeficiency virus-infected, ART-treated RMs that are selectively depleted of CD8+ T cells via the CD8ß-targeting antibody CD8b255R1. CD8ß depletion was performed in five SHIVSF162P3-infected RMs treated with ART for 12 months and with plasma viremia consistently below 3 copies/ml. All animals received four weekly doses of N-803 starting at the time of CD8b255R1 administration. The induction of detectable plasma viremia was observed in three out of five RMs, with the level of virus reactivation seemingly correlated with the frequency of CD8+ T cells following CD8ß depletion as well as the level of virus reactivation observed when the same animals underwent CD8α depletion and N-803 administration after 24 weeks of ART. These data indicate that CD8ß depletion and N-803 administration can induce virus reactivation in SHIVSF162P3-infected RMs despite suboptimal depletion of CD8+ T cells and profound ART-induced suppression of virus replication, confirming a critical role for these cells in suppressing virus production and/or reactivation in vivo under ART.IMPORTANCE The "shock and kill" HIV cure strategy attempts to reverse and eliminate the latent viral infection that prevents eradication of the virus. Latency-reversing agents tested in clinical trials to date have failed to affect the HIV viral reservoir. IL-15 superagonist N-803, currently involved in a clinical trial for HIV cure, was recently shown by our laboratory to induce robust and persistent induction of plasma viremia during ART in three in vivo animal models of HIV infection. These results suggest a substantial role for CD8+ lymphocytes in suppressing the latency reversal effect of N-803 by promoting the maintenance of viral latency. In this study, we tested whether the use of a CD8ß-targeting antibody, which would specifically deplete CD8+ T cells, would yield similar levels of virus reactivation. We observed the induction of plasma viremia, which correlated with the efficacy of the CD8 depletion strategy.

Author Correction: Robust and persistent reactivation of SIV and HIV by N-803 and depletion of CD8+ cells.

An Amendment to this paper has been published and can be accessed via a link at the top of the paper.

Robust and persistent reactivation of SIV and HIV by N-803 and depletion of CD8+ cells.

Human immunodeficiency virus (HIV) persists indefinitely in individuals with HIV who receive antiretroviral therapy (ART) owing to a reservoir of latently infected cells that contain replication-competent virus1-4. Here, to better understand the mechanisms responsible for latency persistence and reversal, we used the interleukin-15 superagonist N-803 in conjunction with the depletion of CD8+ lymphocytes in ART-treated macaques infected with simian immunodeficiency virus (SIV). Although N-803 alone did not reactivate virus production, its administration after the depletion of CD8+ lymphocytes in conjunction with ART treatment induced robust and persistent reactivation of the virus in vivo. We found viraemia of more than 60 copies per ml in all macaques (n = 14; 100%) and in 41 out of a total of 56 samples (73.2%) that were collected each week after N-803 administration. Notably, concordant results were obtained in ART-treated HIV-infected humanized mice. In addition, we observed that co-culture with CD8+ T cells blocked the in vitro latency-reversing effect of N-803 on primary human CD4+ T cells that were latently infected with HIV. These results advance our understanding of the mechanisms responsible for latency reversal and lentivirus reactivation during ART-suppressed infection.

Antibody-Mediated CD4 Depletion Induces Homeostatic CD4+ T Cell Proliferation without Detectable Virus Reactivation in Antiretroviral Therapy-Treated Simian Immunodeficiency Virus-Infected Macaques.

A major barrier to human immunodeficiency virus (HIV) eradication is the long-term persistence of latently infected CD4+ T cells harboring integrated replication-competent virus. It has been proposed that the homeostatic proliferation of these cells drives long-term reservoir persistence in the absence of virus reactivation, thus avoiding cell death due to either virus-mediated cytopathicity or immune effector mechanisms. Here, we conducted an experimental depletion of CD4+ T cells in eight antiretroviral therapy (ART)-treated, simian immunodeficiency virus (SIV)-infected rhesus macaques (RMs) to determine whether the homeostatically driven CD4+ T-cell proliferation that follows CD4+ T-cell depletion results in reactivation of latent virus and/or expansion of the virus reservoir. After administration of the CD4R1 antibody, we observed a CD4+ T cell depletion of 65 to 89% in peripheral blood and 20 to 50% in lymph nodes, followed by a significant increase in CD4+ T cell proliferation during CD4+ T cell reconstitution. However, this CD4+ T cell proliferation was not associated with detectable increases in viremia, indicating that the homeostatic activation of CD4+ T cells is not sufficient to induce virus reactivation from latently infected cells. Interestingly, the homeostatic reconstitution of the CD4+ T cell pool was not associated with significant changes in the number of circulating cells harboring SIV DNA compared to results for the first postdepletion time point. This study indicates that, in ART-treated SIV-infected RMs, the homeostasis-driven CD4+ T-cell proliferation that follows experimental CD4+ T-cell depletion occurs in the absence of detectable reactivation of latent virus and does not increase the size of the virus reservoir as measured in circulating cells.IMPORTANCE Despite successful suppression of HIV replication with antiretroviral therapy, current treatments are unable to eradicate the latent virus reservoir, and treatment interruption almost invariably results in the reactivation of HIV even after decades of virus suppression. Homeostatic proliferation of latently infected cells is one mechanism that could maintain the latent reservoir. To understand the impact of homeostatic mechanisms on virus reactivation and reservoir size, we experimentally depleted CD4+ T cells in ART-treated SIV-infected rhesus macaques and monitored their homeostatic rebound. We find that depletion-induced proliferation of CD4+ T cells is insufficient to reactivate the viral reservoir in vivo Furthermore, the proportion of SIV DNA+ CD4+ T cells remains unchanged during reconstitution, suggesting that the reservoir is resistant to this mechanism of expansion at least in this experimental system. Understanding how T cell homeostasis impacts latent reservoir longevity could lead to the development of new treatment paradigms aimed at curing HIV infection.

Characterization of damaged skin by impedance spectroscopy: chemical damage by dimethyl sulfoxide.

PURPOSE: To relate changes in the electrochemical impedance spectra to the progression and mechanism of skin damage arising from exposure to dimethyl sulfoxide (DMSO). METHODS: Electrochemical impedance spectra measured before and after human cadaver skin was treated with neat DMSO or phosphate buffered saline (control) for 1 h or less were compared with electrical circuit models representing two contrasting theories describing the progression of DMSO damage. Flux of a model lipophilic compound (p-chloronitrobenzene) was also measured. RESULTS: The impedance spectra collected before and after 1 h treatment with DMSO were consistent with a single circuit model; whereas, the spectra collected after DMSO exposure for 0.25 h were consistent with the model circuits observed before and after DMSO treatment for 1 h combined in series. DMSO treatments did not significantly change the flux of p-chloronitrobenzene compared to control. CONCLUSIONS: Impedance measurements of human skin exposed to DMSO for less than about 0.5 h were consistent with the presence of two layers: one damaged irreversibly and one unchanged. The thickness of the damaged layer increased proportional to the square-root of treatment time until about 0.5 h, when DMSO affected the entire stratum corneum. Irreversible DMSO damage altered the lipophilic permeation pathway minimally.

Characterization of damaged skin by impedance spectroscopy: mechanical damage.

PURPOSE: Electrochemical impedance spectroscopy is a convenient method that has been used to characterize skin barrier function, which affects drug delivery into and through the skin. The objective of this study was to relate changes in skin barrier function arising from mechanical damage to changes in the impedance spectra. These observations are compared in a companion paper to changes in chemically damaged skin. METHODS: Electrical impedance and the permeation of a non-polar compound were measured before and after human cadaver skin was damaged by needle puncture. RESULTS: The impedance responses of all skin samples were consistent with an equivalent circuit model with a resistor and constant phase element (CPE) in parallel. Pinhole-damaged skin exhibited a lower resistance pathway acting in parallel with the skin resistance without changing the CPE behavior. The characteristic frequency of the impedance scans determined after needle puncture increased by an amount that could be predicted. The flux of 4-cyanophenol increased by a small but significant amount that did not correlate with the hole resistance calculated under the assumption that the resistance of the surrounding skin did not change. CONCLUSIONS: Skin impedance measurements are sensitive to irreversible damage caused by exposure to puncture with a needle.

On the correlation between single-frequency impedance measurements and human skin permeability to water.

The objective of this study was to quantitatively compare measurements of tritiated water permeability with impedance determined at either 100 or 1000 Hz using an LCR databridge on the same pieces of skin. A previously published expression based on a simple circuit of a parallel resistor and constant phase element (CPE) was used to relate (RPARA) measured at different frequencies to the DC resistance (RskinA) and the steady-state skin permeability of tritiated water (kp). Using this analysis, kp and (RPARA) data from three laboratories were shown to be consistent with each other, and kp and (RskinA) estimated from (RPARA) were linearly correlated. Compared with urea and mannitol, which are known to permeate skin through a polar pathway, the value of kp for water was found to be about two times larger than expected for transport through only the polar pathway, suggesting an approximately equal contribution from the lipophilic pathway. Equations relating kp to (RPARA) and (RskinA) were used to compare on a consistent basis proposed tests for identifying and excluding damaged skin from chemical absorption studies. The criterion of 20 kΩ cm2 for (RskinA) corresponds to a tritiated water permeability of 3.2×10(-3) cm/h, which should exclude damaged skin without screening undamaged but higher permeability skin samples from study.

A critical analysis of single-frequency LCR databridge impedance measurements of human skin.

Testing whether the barrier of skin samples has sufficient integrity for meaningful measurements of in-vitro chemical permeability is usually required when data are generated for regulatory purposes. Recently, skin integrity has been assessed using LCR databridge measurements, which are reported as resistances determined in either series (SER) or parallel (PAR) modes at a single frequency, typically 100 or 1000Hz. Measurements made at different combinations of mode and frequency are known to differ, although the skin literature reveals confusion over the meaning of these differences and the impact on the interpretation of integrity test results. Here, the theoretical meanings of resistance and capacitance measurements in PAR and SER mode are described and confirmed experimentally. SER-mode resistances are equal to the real part of the complex impedance; whereas, PAR-mode resistances are the inverse of the real part of the admittance. Capacitance measurements reported in SER and PAR modes are similar manipulations of the imaginary parts of the complex impedance and admittance. A large body of data from human cadaver skin is used to show that the PAR-mode resistance and SER-mode capacitance measured at 100Hz are sensitive to skin resistivity, which is the electrical measurement most closely related to skin integrity.