Figure 1. T_FH differentiation is not the default pathway.

a, Schematic of the SMARTA cell transfer system used for KLH-gp₆₁ immunization. wild-type, Bcl6^f/f, Prdm1^f/f, and Bcl6^f/fPrdm1^f/f Cre^CD4 SMARTA CD4⁺ T cells were transferred to C57BL/6 host mice, followed by immunization of the host mice with KLH-gp₆₁ in alum + cGAMP adjuvant, and analyzed 8 days later. See Fig. 1b and Extended Data Fig.1c–d.

b, Representative flow cytometry of GC-T_FH, T_FH and non-T_FH SMARTA cell subsets from draining LNs (dLNs) of KLH-gp₆₁ immunized mice. Three independent experiments were performed; each dot represents one mouse (n = 4). Data are mean ± s.d., unpaired two-tailed Student’s t-test.

c, wild-type, Bcl6^f/f, Prdm1^f/f, and Bcl6^f/fPrdm1^f/f Cre^CD4 SMARTA CD4⁺ T cells were transferred to C57BL/6 host mice, followed by infection of the host mice with LCMV_Arm, and analyzed 7 days later. Relative protein expression of GC-T_FH core signature markers, gated on CXCR5⁺ T_FH cells. gMFI value of each gene was normalized to wild-type. Three independent experiments were performed; each dot represents one mouse (n = 4). Data are mean ± s.d., unpaired two-tailed Student’s t-test. See Extended Data Fig.1e.

d, Schematic of the SMARTA cell transfer system used for LCMV_Arm infection or KLH-gp₆₁ immunization. Wild-type, Bcl6^f/f, Prdm1^f/f, and Bcl6^f/fPrdm1^f/f Cre^CD4 SMARTA CD4⁺ T cells were transferred to Bcl6^f/fPrdm1^f/f Cre^CD4 host mice, followed by infection or immunization of the host mice with LCMV_Arm or KLH-gp₆₁ in alum + cGAMP adjuvant, and analyzed 8 days later. See Fig.1e–i and Extended Data Fig.1h–i.

e, Representative flow cytometry gate of B_GC cells from spleens of LCMV_Arm infected mice. Three independent experiments performed; each dot represents one mouse (n = 4). Data are mean ± s.d., unpaired two-tailed Student’s t-test.

f, Representative flow cytometry of B_GC cells and B_PC from dLNs of KLH-gp₆₁ immunized mice. Two independent experiments were performed; each dot represents one mouse (n = 4). Data are mean ± s.d., unpaired two-tailed Student’s t-test.

g, Histology of dLNs at d8 after KLH-gp₆₁ immunization in Fig.1f. Magnified images from Extended Data Fig.1g are shown. Blue, TCRβ; red, GL7; green, IgD; white, CD45.1 SMARTA. SMARTA cells were presented with large dots for clarity. Scale bar, 200 μm.

h, Quantification of results in Fig. 1i. Total counted number of SMARTA cells were indicated.

i, Serum antigen-specific IgG endpoint titers at d8 after KLH-gp₆₁ immunization in Fig.1f. Two independent experiments were performed; each dot represents one mouse (n = 4). Data are mean ± s.d., unpaired two-tailed Student’s t-test.