Figure 3. Blood CXCR5⁺ CD4⁺ T cells predict germinal center T_FH cell and B cell responses.

(A) Higher frequency of Ki-67⁺ CD4⁺ T cells after 2^nd MVA in DDMM-Pro group (****, p < 0.0001 at week 1 with a two-tailed, non-parametric t test). (B) To determine if gp140 boost resulted in higher Env-specific CD4⁺ T cells, responses were compared using a one-tailed t test, which showed increased Env IFN-γ⁺, IL-21⁺, and IL-4⁺ frequencies in DDMM_gp140 group at week 1 post 2^nd MVA immunization and no change in (C) Gag responses. (D) Inguinal lymph nodes were biopsied from the lymph node non-draining to immunization site at 2 weeks post-2^nd MVA immunization (E) Flow plot shows presence of distinct subsets of CXCR5⁺ CD4⁺ T cells in lymph node ; PD-1⁺⁺GC T_FH (red) , PD-1⁺, (blue) , and PD-1 cells. Middle panel shows GC B cells identified by Bcl-6 and scatter lot shows correlation between GC B cells and GC T_FH cells. (D) Inclusion of gp140 boost did not alter frequencies of GC T_FH cells, CXCR5⁺PD-1⁺, and GC B cells. (F) To determine if responses in blood (at week 1 post 2^nd MVA) were positively correlated with magnitude of GC responses, these indices were correlated using a one-tailed Spearman correlation (*, p < 0.05). Blood Ki-67⁺ CXCR5⁺ cells correlated with GC T_FH cells (R² = 0.21), CXCR5⁺ PD-1⁺ T_FH cells (R² = 0.24), and GC B cells (R² = 0.20) in lymph node.