Pulsed mTOR Inhibition Combined with B Cell Depletion Rejuvenates Humoral Immunity by Creating Space for mTOR‑Dependent Naïve Output
Hypothesis
Transient, intermittent mTOR inhibition paired with periodic B cell depletion will restore naïve B cell production and repertoire diversity more effectively than either intervention alone, because depletion opens homeostatic niches while pulsed rapamycin windows allow mTORC1‑driven AID expression and germinal cell recovery during refeeding phases.
Mechanistic Rationale
mTORC1 signaling is required for AID induction, class switch recombination and plasma cell differentiation[[https://pmc.ncbi.nlm.nih.gov/articles/PMC5559228/]]. Continuous rapamycin blocks these steps, suppressing humoral responses[[https://www.jci.org/articles/view/86504]]. In contrast, B cell depletion removes long‑lived memory cells that crowd the niche, relieving homeostatic suppression and reactivating bone‑marrow output[[https://www.aging-us.com/article/100313/text]]. If mTOR inhibition is applied only during short nutrient‑scarcity mimics, the cell experiences a hormetic stress that boosts autophagy and reduces translation without chronically starving the AID‑machinery. During the intervening refeeding periods, mTORC1 activity rebounds, permitting the transient surge of AID needed for effective affinity maturation while the depleted niche still favors naïve cell output.
This creates a cyclical environment where scarcity signals improve cellular housekeeping, and abundance signals permit the lymphocyte‑specific reparative program that constant rapamycin prevents.
Testable Predictions
- Mice receiving a regimen of three‑day rapamycin pulses every two weeks combined with monthly anti‑CD20 depletion will show higher frequencies of bone‑marrow pro‑B cells and greater serum IgG diversity after 6 months than mice receiving either treatment alone.
- Following immunization with a T‑dependent antigen, the pulsed‑combination group will generate higher affinity antibodies and more robust germinal center B cell populations than depletion‑only or continuous‑rapamycin groups.
- If the hypothesis is wrong, the combination will not improve naïve B cell output or vaccine response beyond depletion alone, and may even worsen outcomes due to added mTOR suppression.
Experimental Design
- Groups: (1) Control, (2) Continuous rapamycin (2 mg/kg diet), (3) Monthly anti‑CD20 depletion, (4) Pulsed rapamycin (3‑day 2 mg/kg every 14 days) + monthly anti‑CD20 depletion.
- Readouts: Flow cytometry of bone‑marrow B cell subsets, spleen germinal center B cells, serum immunoglobulin sequencing for diversity and affinity, ELISPOT for antigen‑specific plasma cells.
- Timeline: Treat 12‑month‑old mice for 6 months, then immunize with NP‑OVA; analyze at days 7, 14, and 28 post‑immunization.
A statistically significant increase in naïve B cell frequency and antibody affinity in group 4 versus groups 2 and 3 would falsify the claim that mTOR inhibition merely impersonates a harder life and instead support the idea that strategic, intermittent mTOR modulation can cooperate with niche renewal to genuinely rejuvenate humoral immunity.