Methotrexate Inhibits T Cell Proliferation but Not Inflammatory Cytokine Expression to Modulate Immunity in People...

Area of Science:

• Immunology
• Pharmacology
• HIV Medicine

Background:

• Chronic inflammation persists in people living with HIV (PWH) despite combination antiretroviral therapy (ART), increasing comorbidity risk.
• A prior trial indicated low-dose methotrexate (MTX) decreased T cell counts in PWH.

Purpose of the Study:

• To investigate the effects of low-dose MTX on T cell phenotypes and inflammatory markers in PWH.
• To elucidate the in vitro mechanisms of MTX action on T cells.

Main Methods:

• Analysis of T cell phenotypes (Ki67+, Bcl-2) and plasma inflammatory cytokines from a placebo-controlled MTX trial in PWH.
• In vitro experiments assessing MTX effects on T cell cytokine production, proliferation, mTOR signaling, mitochondrial function, and cell cycle.

Main Results:

• MTX reduced cycling T cells lacking Bcl-2 but did not significantly alter plasma inflammatory cytokines.
• In vitro, MTX inhibited T cell proliferation downstream of mTOR activation and cell cycle entry, without affecting effector cytokine production.
• Folinic acid reversed MTX's inhibitory effects in vitro, suggesting dihydrofolate reductase inhibition as the primary mechanism.

Conclusions:

• Low-dose MTX exerts anti-inflammatory effects in PWH primarily by inhibiting T cell proliferation via dihydrofolate reductase.
• Daily folic acid supplementation did not rescue the observed T cell reduction in the trial.
• Findings clarify MTX's mechanism in PWH and may inform its use in other inflammatory conditions.