Hypothesis: Germline‑like telomerase and epigenetic reprogramming of follicular dendritic cells reverses germinal center aging

Core idea – Aged germinal centers fail because follicular dendritic cells (FDCs) lose germline‑grade maintenance mechanisms: telomerase activity, efficient base‑excision repair, and epigenetic resetting. Restoring these germline traits in FDCs should re‑establish antigen trapping, revive Tfh help, and rescue somatic hypermutation in old mice.

Mechanistic proposal – Deliver a transient, FDC‑specific expression cassette encoding TERT (telomerase reverse transcriptase) together with TET2 and Blimp1 via an adjuvant‑targeted nanoparticle. TERT will elongate telomeres and reduce DNA‑damage signaling, TET2 will mediate 5‑mC oxidation to promote chromatin openness at FcγRIIb and Cr2 loci, and Blimp1 will drive a transcriptional program akin to germline epigenetic resetting. Together they are predicted to:

• Increase FDC numbers and network expansion after immunization
• Restore FcγRIIb and complement receptor (CR1/CR2) surface levels
• Lower γH2AX foci and senescence‑associated β‑galactosidase in FDCs
• Boost AID expression in germinal center B cells via improved antigen depot
• Enhance Tfh CD40L and ICOS production while reducing IL‑10
• Elevate germinal center size, somatic hypermutation load, and high‑affinity antibody titers in aged mice

Experimental plan – 1) Treat aged (≥18 mo) mice with FDC‑targeted nanoparticles carrying the TERT‑TET2‑Blimp1 cassette or control empty vector. 2) Immunize with NP‑OVA in alum. 3) At day 7 and day 14 post‑immunization quantify:

• FDC frequency (CD35⁺ staining) and network area (confocal)
• FcγRIIb and CR1/CR2 mean fluorescence intensity on FDCs
• Telomere length (Q‑FISH) and γH2AX foci in sorted FDCs
• AID mRNA in GC B cells (RT‑qPCR)
• Tfh phenotype (CXCR5⁺PD‑1⁺, CD40L, ICOS, IL‑10) by flow
• GC size (GL7⁺Fas⁺ B cells) and SHM frequency in VH186.2 sequencing
• Serum OVA‑specific IgG affinity (ELISA with decreasing antigen concentrations)

Predictions – If germline‑like maintenance is sufficient, the treated aged mice will show FDC numbers and function comparable to young controls, rescued GC kinetics, and antibody affinities that are not significantly different from young mice. Conversely, if the microenvironment is not the limiting factor, the intervention will fail to improve any readout despite efficient transgene expression.

Falsifiability – A lack of improvement in any of the listed parameters, despite verified FDC‑specific expression and telomere elongation, would falsify the hypothesis. Moreover, rescuing telomerase alone without TET2/Blimp1 should yield only partial recovery, indicating the necessity of combined germline‑like mechanisms.

Broader impact – Success would suggest that stromal rejuvenation, modeled on germline immortality strategies, can be a general approach to revive age‑dependent adaptive immune responses, informing vaccine design for the elderly.

[1] https://academic.oup.com/jimmunol/article/214/5/862/8064672 [2] https://pmc.ncbi.nlm.nih.gov/articles/PMC12293126/ [3] https://doi.org/10.1073/pnas.0913125107 [4] https://pubmed.ncbi.nlm.nih.gov/17561442/ [5] https://doi.org/10.1002/bies.202200208