Early T Follicular Helper Cell Responses and Germinal Center Reactions Are Associated with Viremia Control in Immunized Rhesus Macaques

Abstract

T follicular helper (TFH) cells are fundamental in germinal center (GC) maturation and selection of antigen-specific B cells within secondary lymphoid organs. GC-resident TFH cells have been fully characterized in human immunodeficiency virus (HIV) infection. However, the role of GC TFH cells in GC B cell responses following various simian immunodeficiency virus (SIV) vaccine regimens in rhesus macaques (RMs) has not been fully investigated. We characterized GC TFH cells of RMs over the course of a mucosal/systemic vaccination regimen to elucidate GC formation and SIV humoral response generation. Animals were mucosally primed twice with replicating adenovirus type 5 host range mutant (Ad5hr)-SIV recombinants and systemically boosted with ALVAC-SIVM766Gag/Pro/gp120-TM and SIVM766&CG7V gD-gp120 proteins formulated in alum hydroxide (ALVAC/Env) or DNA encoding SIVenv/SIVGag/rhesus interleukin 12 (IL-12) plus SIVM766&CG7V gD-gp120 proteins formulated in alum phosphate (DNA&Env). Lymph nodes were biopsied in macaque subgroups prevaccination and at day 3, 7, or 14 after the 2nd Ad5hr-SIV prime and the 2nd vector/Env boost. Evaluations of GC TFH and GC B cell dynamics including correlation analyses supported a significant role for early GC TFH cells in providing B cell help during initial phases of GC formation. GC TFH responses at day 3 post-mucosal priming were consistent with generation of Env-specific memory B cells in GCs and elicitation of prolonged Env-specific humoral immunity in the rectal mucosa. GC Env-specific memory B cell responses elicited early post-systemic boosting correlated significantly with decreased viremia postinfection. Our results highlight the importance of early GC TFH cell responses for robust GC maturation and generation of long-lasting SIV-specific humoral responses at mucosal and systemic sites. Further investigation of GC TFH cell dynamics should facilitate development of an efficacious HIV vaccine. IMPORTANCE The modest HIV protection observed in the human RV144 vaccine trial associated antibody responses with vaccine efficacy. T follicular helper (TFH) cells are CD4+ T cells that select antibody secreting cells with high antigenic affinity in germinal centers (GCs) within secondary lymphoid organs. To evaluate the role of TFH cells in eliciting prolonged virus-specific humoral responses, we vaccinated rhesus macaques with a combined mucosal prime/systemic boost regimen followed by repeated low-dose intrarectal challenges with SIV, mimicking human exposure to HIV-1. Although the vaccine regimen did not prevent SIV infection, decreased viremia was observed in the immunized macaques. Importantly, vaccine-induced TFH responses elicited at day 3 postimmunization and robust GC maturation were strongly associated. Further, early TFH-dependent SIV-specific B cell responses were also correlated with decreased viremia. Our findings highlight the contribution of early vaccine-induced GC TFH responses to elicitation of SIV-specific humoral immunity and implicate their participation in SIV control.

TFH Cells Induced by Vaccination and Following SIV Challenge Support Env-Specific Humoral Immunity in the Rectal-Genital Tract and Circulation of Female Rhesus Macaques

“…PD-1 upregulation is required for positioning T FH cells within GCs ( 49 ). GC-T FH cells were identified as PD-1 hi CXCR5 + CD4 + T cells as previously described ( 30 , 43 ) ( Figure 1A ). The transcription factor BCL6 (B-cell lymphoma protein 6) supports the differentiation of T cells into T FH cells by activating upregulation of PD-1 and defines GC-committed T FH cells ( 50 ).…”

“…B cells in LN were detected as previously reported ( 30 ) with antibodies described in Table 1 . Envelope protein staining was carried out by incubating cells with biotinylated gp120 proteins (2 µg/sample) at 4°C, following incubation with streptavidin-APC at 4°C.…”

“…However, vaccine-induced T FH cells have also been correlated with higher acute viral loads following SIV challenge ( 18 ). We recently reported that early induction of T FH cells in GCs of immunized rhesus macaques was important for robust GC maturation associated with viremia control following SIV infection ( 30 ). Here, using female rhesus macaques immunized mucosally with replicating Adenovirus type 5 host range mutant (Ad5hr)-SIV recombinants followed by intramuscular gp120 protein boosting ( 31 ), we expanded our investigations of T FH cells and their role in development of SIV-specific humoral responses in different mucosal and systemic tissue compartments.…”

Th2-like T Follicular Helper Cells Promote Functional Antibody Production during Plasmodium falciparum Infection

“…This is consistent with an important role for the early activation of cTfh cells in initial phases of GC formation, as previously reported for HIV vaccination in rhesus macaques. 40 To assess the impact of individual subsets at this early day 8 time point, the change in ICOS + cTfh for each subset was calculated; activation was moderately correlated across subsets ( Figure S4 A). The positive association between antibody score and ICOS + cTfh cells at day 8 was restricted to the Th2-cTfh cell subset, suggesting that Th2-cTfh activation is the most important factor in antibody development ( Figures 7 C and S4 C).…”

How could we forget immunometabolism in SARS-CoV2 infection or COVID-19?

“…The patients with mild to moderate COVID-19 show the increased number of antibody (Ab)-secreting plasma cells, which secrete IgM and IgG Abs, circulating follicular helper T cells (cTFHs), CD38 and HLA-DR expressing activated CD4 þ , and CD8 þ T cells ( Figure 1) [26]. The early TFHs and germinal center (GC) reactions control viremia and clear the infection (Figure 1) [27]. The circulating CD8 þ T cells do not show an exhaustion phenotype in mild to moderate COVID-19 patients [28].…”