Rapid, simplified whole blood-based multiparameter assay to quantify and phenotype SARS-CoV-2 specific T cells

Rapid tests to evaluate SARS-CoV-2-specific T cell responses are urgently needed to decipher protective immunity and aid monitoring vaccine-induced immunity. Using a rapid whole blood assay requiring minimal amount of blood, we measured qualitatively and quantitatively SARS-CoV-2-specific CD4T cell responses in 31 healthcare workers, using flow cytometry. 100% of COVID-19 convalescent participants displayed a detectable SARS-CoV-2-specific CD4T cell response. SARS-CoV-2-responding cells were also detected in 40.9% of participants with no COVID-19-associated symptoms or who tested PCR negative. Phenotypic assessment indicated that, in COVID-19 convalescent participants, SARS-CoV-2 CD4 responses displayed an early differentiated memory phenotype with limited capacity to produce IFNɣ. Conversely, in participants with no reported symptoms, SARS-CoV-2 CD4 responses were enriched in late differentiated cells, co-expressing IFNɣ and TNFα and also Granzyme B. This proof-of-concept study presents a scalable alternative to PBMC-based assays to enumerate and phenotype SARS-CoV-2-responding T cells, thus representing a practical tool to monitor adaptive immunity due to natural infection or vaccine trials.

Optimal CD4T Cell Priming in Lymph Nodes Requires Repertoire Scanning by CD301b+ Migratory cDC2 Cells

SummaryActivation of CD4T cells by conventional dendritic cells (cDC) is pivotal in adaptive immunity. However, while the activation mechanism of antigen-specific CD4T cells has been extensively studied, the cellular mechanism that leads to the selection of cognate CD4T cell clones out of the polyclonal pool is incompletely understood. Here, we show that, in the reactive lymph nodes, newly homed naive polyclonal CD4T cells are temporarily retained before leaving the lymph node. This stop-and-go traffic of CD4T cells provides an adequate time window for efficient scanning and timely priming of antigen-specific clones. Mechanistically, upon immunization, CD301b+ DCs, a major subset of migratory cDC2 cells, quickly migrate to the draining lymph node and settle in the areas near the high endothelial venules, where they retain incoming polyclonal CD4T cells through MHCII-dependent but antigen-independent mechanisms while concurrently providing cognate stimuli to prime antigen-specific CD4T cells. These results indicate that CD301b+ DCs function as an immunological “display window” for CD4T cells to efficiently scan their antigen specificity.Graphical AbstractHighlightsNewly homed polyclonal CD4T cells are temporarily retained in the reactive lymph nodes.Depletion of CD301b+ DCs results in shorter dwell time of CD4T cells in the draining lymph node and delayed priming of antigen-specific clones.The transient retention of polyclonal CD4T cells in the draining lymph node requires MHCII expression on CD301b+ DCs but not cognate antigen.CD301b+ DCs are required for robust expansion of rare antigen-specific CD4T cell clones and their skewing toward Th2 cells.

TLR7 Polymorphism (rs179008 and rs179009) in HIV-Infected Individual Naïve to ART

Toll-like receptors (TLRs) play an important role in the innate immune response to HIV infection. Single nucleotide polymorphism (SNP) in TLR7 (Gln11Leu) gene has been associated with a rapid decline of CD4T cell count. Hence, we assessed the TLR7 (rs179008, Gln11Leu (A/T) and rs179009, IVS2-151 (A/G)) polymorphism in 150 HIV-infected individuals naïve to ART and 158 healthy controls. The genotyping of TLR7 Gln11Leu (A/T) and IVS2-151 (A/G) polymorphisms was done using the PCR-RFLP method. In univariate analysis, none of the genotype and haplotype of TLR7 Gln11Leu (A/T) and IVS2-151 (A/G) polymorphism differed significantly between HIV-infected individuals and healthy controls. The occurrence of TLR7 rs179009AG genotype in the codominant model and rs179009 AG-GG genotype in the dominant model was significantly reduced in HIV-infected individuals as compared to healthy controls (18.0% vs. 29.1%, OR=0.42, P=0.016; 26.7% vs. 36.7%, OR=0.52, P=0.016). TLR7 rs179009AG genotype was significantly underrepresented in the intermediate HIV disease stage compared with healthy controls (OR=0.03, P=0.04). TLR7 rs179009AG genotype expressed higher in tobacco-consuming HIV-infected individuals compared with nonusers (OR=1.71, P=0.47). In conclusion, rs179009 AG-GG and AG genotypes were found reduced in HIV-infected individuals as compared to healthy controls; their higher prevalence in health individuals clearly support that they are associated with reduced risk of acquisition of HIV-1 infection.