Long-term and short-term immunity to SARS-CoV-2: Why it matters

The adaptive immune system, regulated by CD4 T cells, is essential for control of many viral infections. Endemic coronavirus infections generally occur as short-term upper respiratory tract infections which in many cases appear to be cleared before adaptive immunity is fully involved, since adaptive immunity takes approximately 1.5-2 weeks to ramp up the response to a primary infection, or approximately 1 week for a recurrent infection. However, the adaptive immune response to SARS-CoV-2 infection will be critical to full recovery with minimal long-lasting effects, and to either prevention of recurrence of infection or at least reduced severity of symptoms. The detailed kinetics of this infection versus the dynamics of the immune response, including in vaccinated individuals, will largely determine these outcomes

Circulating gluten-specific, but not CMV-specific, CD39⁺ regulatory T cells have an oligoclonal TCR repertoire

Objectives: Understanding the T cell receptor (TCR) repertoire of regulatory CD4+ T-cell (Treg) populations is important for strategies aiming to re-establish tolerance in autoimmune diseases. We studied circulating deamidated gluten-epitope-specific CD39+ Tregs in patients with coeliac disease following an oral gluten challenge, and we used cytomegalovirus (CMV)-specific CD39+ Tregs from healthy controls as a comparator population. Methods: We used the OX40 assay to isolate antigen-specific Tregs by induced surface co-expression of CD25, OX40 and CD39. RACE PCR amplification and Sanger sequencing of the TCR β chain were used to analyse repertoire diversity. Results: We found that, following oral gluten challenge, circulating gluten-specific CD39+ Tregs had an oligoclonal TCR repertoire that contained public clonotypes. Conversely, the TCR repertoire of CMV-epitope-specific CD39+ Tregs from healthy controls was polyclonal. Discussion: These data indicate that a biased TCR repertoire is not inherent to CD39+ Tregs, and, in this case, is apparently driven by the HLA-DQ2.5-restricted deamidated gluten peptide in coeliac disease patients. Conclusion: This is the first assessment of the TCR repertoire within circulating human Tregs specific for foreign antigen. These data enhance our understanding of antigen-specific CD4+ responses in the settings of chronic inflammation and infection and may help guide immunomonitoring strategies for CD4+ T cell-based therapies, particularly for coeliac disease

Elevation of cell-associated HIV-1 transcripts in CSF CD4+ T cells, despite effective antiretroviral therapy, is linked to brain injury

Antiretroviral therapy (ART) can attain prolonged undetectable HIV-1 in plasma and cerebrospinal fluid (CSF), but brain injury remains prevalent in people living with HIV-1 infection (PLHIV). We investigated cell-associated (CA)-HIV-1 RNA transcripts in cells in CSF and blood, using the highly sensitive Double-R assay, together with proton Magnetic Resonance Spectroscopy (1H MRS) of major brain metabolites, in sixteen PLHIV. 14/16 CSF cell samples had quantifiable CA-HIV-1 RNA, at levels significantly higher than in their PBMCs (median 9,266 vs 185 copies /106 CD4+ T-cells; p<0.0001). In individual PLHIV, higher levels of HIV-1 transcripts in CSF cells were associated with greater brain injury in the frontal white matter (Std β=-0.73; p=0.007) and posterior cingulate (Std β=-0.61; p=0.03). 18-colour flow cytometry revealed that the CSF cells were 91% memory T-cells, equally CD4+ and CD8+ T-cells, but fewer B cells (0.4 %), and monocytes (3.1%). CXCR3+CD49d+integrin β7-, CCR5+CD4+ T-cells were highly enriched in CSF, compared with PBMC (p <0.001). However, CA-HIV-1 RNA could not be detected in 10/16 preparations of highly purified monocytes from PBMC, and was extremely low in the other six. Our data show that elevated HIV-1 transcripts in CSF cells were associated with brain injury, despite suppressive ART. The cellular source is most likely memory CD4+ T cells from blood, rather than trafficking monocytes. Future research should focus on inhibitors of this transcription to reduce local production of potentially neurotoxic and inflammatory viral products

Circulating gluten-specific FOXP3⁺CD39⁺ regulatory T cells have impaired suppressive function in patients with celiac disease

Background Celiac disease is a chronic immune-mediated inflammatory disorder of the gut triggered by dietary gluten. Although the effector T-cell response in patients with celiac disease has been well characterized, the role of regulatory T (Treg) cells in the loss of tolerance to gluten remains poorly understood. Objective We sought to define whether patients with celiac disease have a dysfunction or lack of gluten-specific forkhead box protein 3 (FOXP3)+ Treg cells. Methods Treated patients with celiac disease underwent oral wheat challenge to stimulate recirculation of gluten-specific T cells. Peripheral blood was collected before and after challenge. To comprehensively measure the gluten-specific CD4+ T-cell response, we paired traditional IFN-γ ELISpot with an assay to detect antigen-specific CD4+ T cells that does not rely on tetramers, antigen-stimulated cytokine production, or proliferation but rather on antigen-induced coexpression of CD25 and OX40 (CD134). Results Numbers of circulating gluten-specific Treg cells and effector T cells both increased significantly after oral wheat challenge, peaking at day 6. Surprisingly, we found that approximately 80% of the ex vivo circulating gluten-specific CD4+ T cells were FOXP3+CD39+ Treg cells, which reside within the pool of memory CD4+CD25+CD127lowCD45RO+ Treg cells. Although we observed normal suppressive function in peripheral polyclonal Treg cells from patients with celiac disease, after a short in vitro expansion, the gluten-specific FOXP3+CD39+ Treg cells exhibited significantly reduced suppressive function compared with polyclonal Treg cells. Conclusion This study provides the first estimation of FOXP3+CD39+ Treg cell frequency within circulating gluten-specific CD4+ T cells after oral gluten challenge of patients with celiac disease. FOXP3+CD39+ Treg cells comprised a major proportion of all circulating gluten-specific CD4+ T cells but had impaired suppressive function, indicating that Treg cell dysfunction might be a key contributor to disease pathogenesis

CD4(+) T follicular helper and IgA(+) B cell numbers in gut biopsies from HIV-infected subjects on antiretroviral therapy are similar to HIV-uninfected individuals

BACKGROUND: Disruption of gastrointestinal tract epithelial and immune barriers contribute to microbial translocation, systemic inflammation, and progression of HIV-1 infection. Antiretroviral therapy (ART) may lead to reconstitution of CD4(+) T cells in gut-associated lymphoid tissue (GALT), but its impact on humoral immunity within GALT is unclear. Therefore, we studied CD4(+) subsets, including T follicular helper cells (Tfh), as well as resident B cells that have switched to IgA production, in gut biopsies, from HIV(+) subjects on suppressive ART compared to HIV-negative controls (HNC). METHODS: Twenty-three HIV(+) subjects on ART and 22 HNC undergoing colonoscopy were recruited to the study. Single-cell suspensions were prepared from biopsies from left colon (LC), right colon (RC), and terminal ileum (TI). T and B lymphocyte subsets, as well as EpCAM(+) epithelial cells, were accurately enumerated by flow cytometry, using counting beads. RESULTS: No significant differences in the number of recovered epithelial cells were observed between the two subject groups. However, the median TI CD4(+) T cell count/10(6) epithelial cells was 2.4-fold lower in HIV(+) subjects versus HNC (19,679 versus 47,504 cells; p = 0.02). Similarly, median LC CD4(+) T cell counts were reduced in HIV(+) subjects (8,358 versus 18,577; p = 0.03) but were not reduced in RC. Importantly, we found no significant differences in Tfh or IgA(+) B cell counts at either site between HIV(+) subjects and HNC. Further analysis showed no difference in CD4(+), Tfh, or IgA(+) B cell counts between subjects who commenced ART in primary compared to chronic HIV-1 infection. Despite the decrease in total CD4 T cells, we could not identify a selective decrease of other key subsets of CD4(+) T cells, including CCR5(+) cells, CD127(+) long-term memory cells, CD103(+) tissue-resident cells, or CD161(+) cells (surrogate marker for Th17), but there was a slight increase in the proportion of T regulatory cells. CONCLUSION: While there were lower absolute CD4(+) counts in the TI and LC in HIV(+) subjects on ART, they were not associated with significantly reduced Tfh cell counts or IgA(+) B cells, suggesting that this important vanguard of adaptive immune defense against luminal microbial products is normalized following ART.John Zaunders, Mark Danta, Michelle Bailey, Gerald Mak, Katherine Marks, Nabila Seddiki, Yin Xu, David J. Templeton, David A. Cooper, Mark A. Boyd, Anthony D. Kelleher and Kersten K. Koelsc