Recovery scenario and immunity in COVID-19 disease: A new strategy to predict the potential of reinfection

Background

The recent ongoing outbreak of coronavirus disease 2019 (COVID-19), still is an unsolved problem with a growing rate of infected cases and mortality worldwide. The novel coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is targeting the angiotensin-converting enzyme 2 (ACE2) receptor and mostly causes a respiratory illness. Although acquired and resistance immunity is one of the most important aspects of alleviating the trend of the current pandemic; however, there is still a big gap of knowledge regarding the infection process, immunopathogenesis, recovery, and reinfection.

Aim of Review

To answer the questions regarding "the potential and probability of reinfection in COVID-19 infected cases" or "the efficiency and duration of SARS-CoV-2 infection-induced immunity against reinfection" we critically evaluated the current reports on SARS-CoV-2 immunity and reinfection with special emphasis on comparative studies using animal models that generalize their finding about protection and reinfection. Also, the contribution of humoral immunity in the process of COVID-19 recovery and the role of ACE2 in virus infectivity and pathogenesis has been discussed. Furthermore, innate and cellular immunity and inflammatory responses in the disease and recovery conditions are reviewed and an overall outline of immunologic aspects of COVID-19 progression and recovery in three different stages are presented. Finally, we categorized the infected cases into four different groups based on the acquired immunity and the potential for reinfection.

Key Scientific Concepts of Review

In this review paper, we proposed a new strategy to predict the potential of reinfection in each identified category. This classification may help to distribute resources more meticulously to determine: who needs to be serologically tested for SARS-CoV-2 neutralizing antibodies, what percentage of the population is immune to the virus, and who needs to be vaccinated.

Tumor cell lysates as immunogenic sources for cancer vaccine design

Autologous dendritic cells (DCs) loaded with tumor-associated antigens (TAAs) are a promising immunological tool for cancer therapy. These stimulate the antitumor response and immunological memory generation. Nevertheless, many patients remain refractory to DC approaches. Antigen (Ag) delivery to DCs is relevant to vaccine success, and antigen peptides, tumor-associated proteins, tumor cells, autologous tumor lysates, and tumor-derived mRNA have been tested as Ag sources. Recently, DCs loaded with allogeneic tumor cell lysates were used to induce a potent immunological response. This strategy provides a reproducible pool of almost all potential Ags suitable for patient use, independent of MHC haplotypes or autologous tumor tissue availability. However, optimizing autologous tumor cell lysate preparation is crucial to enhancing efficacy. This review considers the role of cancer cell-derived lysates as a relevant source of antigens and as an activating factor for ex vivo therapeutic DCs capable of responding to neoplastic cells. These promising therapies are associated with the prolonged survival of advanced cancer patients.

A commensal symbiotic factor derived from Bacteroides fragilis promotes human CD39(+)Foxp3(+) T cells and Treg function

Polysaccharide A (PSA) derived from the human commensal Bacteroides fragilis is a symbiosis factor that stimulates immunologic development within mammalian hosts. PSA rebalances skewed systemic T helper responses and promotes T regulatory cells (Tregs). However, PSA-mediated induction of Foxp3 in humans has not been reported. In mice, PSA-generated Foxp3(+) Tregs dampen Th17 activity thereby facilitating bacterial intestinal colonization while the increased presence and function of these regulatory cells may guard against pathological organ-specific inflammation in hosts. We herein demonstrate that PSA induces expression of Foxp3 along with CD39 among naïve CD4 T cells in vitro while promoting IL-10 secretion. PSA-activated dendritic cells are essential for the mediation of this regulatory response. When cultured with isolated Foxp3(+) Tregs, PSA enriched Foxp3 expression, enhanced the frequency of CD39(+)HLA-DR(+) cells, and increased suppressive function as measured by decreased TNFα expression by LPS-stimulated monocytes. Our findings are the first to demonstrate in vitro induction of human CD4(+)Foxp3(+) T cells and enhanced suppressive function of circulating Foxp3(+) Tregs by a human commensal bacterial symbiotic factor. Use of PSA for the treatment of human autoimmune diseases, in particular multiple sclerosis and inflammatory bowel disease, may represent a new paradigm in the approach to treating autoimmune disease.

During Stably Suppressive Antiretroviral Therapy Integrated HIV-1 DNA Load in Peripheral Blood is Associated with the Frequency of CD8 Cells Expressing HLA-DR/DP/DQ

Background

Characterising the correlates of HIV persistence improves understanding of disease pathogenesis and guides the design of curative strategies. This study investigated factors associated with integrated HIV-1 DNA load during consistently suppressive first-line antiretroviral therapy (ART).

Method

Total, integrated, and 2-long terminal repeats (LTR) circular HIV-1 DNA, residual plasma HIV-1 RNA, T-cell activation markers, and soluble CD14 (sCD14) were measured in peripheral blood of 50 patients that had received 1–14 years of efavirenz-based or nevirapine-based therapy.

Results

Integrated HIV-1 DNA load (per 10⁶ peripheral blood mononuclear cells) was median 1.9 log₁₀ copies (interquartile range 1.7–2.2) and showed a mean difference of 0.2 log₁₀ copies per 10 years of suppressive ART (95% confidence interval − 0.2, 0.6; p = 0.28). It was positively correlated with total HIV-1 DNA load and frequency of CD8⁺HLA-DR/DP/DQ⁺ cells, and was also higher in subjects with higher sCD14 levels, but showed no correlation with levels of 2-LTR circular HIV-1 DNA and residual plasma HIV-1 RNA, or the frequency of CD4⁺CD38⁺ and CD8⁺CD38⁺ cells. Adjusting for pre-ART viral load, duration of suppressive ART, CD4 cell counts, residual plasma HIV-1 RNA levels, and sCD14 levels, integrated HIV-1 DNA load was mean 0.5 log₁₀ copies higher for each 50% higher frequency of CD8⁺HLA-DR/DP/DQ⁺ cells (95% confidence interval 0.2, 0.9; p = 0.01).

Conclusions

The observed positive association between integrated HIV-1 DNA load and frequency of CD8⁺DR/DP/DQ⁺ cells indicates that a close correlation between HIV persistence and immune activation continues during consistently suppressive therapy. The inducers of the distinct activation profile warrant further investigation.

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Data from a homogenously treated population with consistent virological suppression

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Integrated HIV-1 DNA load did not vary significantly by duration of therapy

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Integrated HIV-1 DNA load was not associated with markers of recent virus replication

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Integrated HIV-1 DNA load and CD8+HLA-DR/DP/DQ+ frequency were positively associated

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Subjects with top quartile integrated HIV-1 DNA load showed high sCD14 levels

Integrated HIV-1 DNA load remains constant in the peripheral blood of individuals receiving long-term suppressive antiretroviral therapy (ART). However, the mechanisms preventing decay of the reservoir remain unclear. We studied a cross-sectional population, defined by the duration of suppressive ART. Integrated HIV-1 DNA load did not differ significantly according to the duration of suppressive ART, and showed no association with direct or indirect markers of ongoing virus replication. Rather, there was an independent, positive association between integrated HIV-1 DNA load and the frequency of CD8 cells expressing the activation marker HLA-DR/DP/DQ. These cells appear to have important regulatory and effector function. Our findings add to growing evidence that immune activation sustains the HIV-1 reservoir during long-term suppressive ART.