Cyclosporine: Non‑Cytotoxic Immunosuppression – Evidence Summary

Mechanism of Action

Cyclosporine forms a complex with cyclophilin that inhibits calcineurin phosphatase, preventing NFAT nuclear translocation and thereby blocking transcription of interleukin‑2 and other cytokines; T‑cells remain viable but functionally suppressed in the G0/G1 phases of the cell cycle【1】.
By suppressing IL‑2 production, cyclosporine indirectly reduces B‑cell activation without exerting direct cytotoxic effects【1】.
The drug functionally impairs antigen‑presenting cells such as Langerhans cells and dendritic cells, without causing cell death【1】.

Cyclophosphamide’s active metabolite phosphoramide mustard creates DNA cross‑links that trigger apoptosis of proliferating cells【2】.
Cyclophosphamide is associated with bone‑marrow suppression, infertility, secondary malignancies, and hemorrhagic cystitis due to its direct cellular toxicity【2】.
In contrast, cyclosporine’s principal toxicities (nephrotoxicity, hypertension) arise from functional tissue effects rather than cell‑destructive mechanisms【2】.

Reported major adverse effects of cyclosporine include nephrotoxicity (~6–7 %), hypertension (~11 %), and gingival hyperplasia (~6 %); none are linked to cytotoxicity【2】.
Unlike azathioprine, cyclosporine does not increase the risk of cytopenias, indicating preservation of bone‑marrow function【2】.
Clinical experience shows that patients can sustain therapeutic responses while on cyclosporine without accumulating cellular damage【2】.

The absence of bone‑marrow toxicity, alopecia, and heightened malignancy risk distinguishes cyclosporine from cytotoxic agents, supporting its use when non‑destructive immunosuppression is desired【2】.

Cyclosporin A is a calcineurin inhibitor that suppresses the immune response by down-regulating the transcription of various cytokine genes, with interleukin-2 (IL-2) being the most significant target 3
The drug binds to cytoplasmic cyclophillin (a cis-trans isomerase) and inhibits calcineurin phosphatase, which prevents the dephosphorylation of nuclear factor of activated T cells (NFAT) 4, 5
This inhibition prevents NFAT from entering the nucleus and promoting the transcription of lymphokines, most notably IL-2 4

Cyclosporin A most potently inhibits IL-2 production, which serves as the major activation factor for T-cells in numerous immunological processes 3
While cyclosporin can affect other cytokines to varying degrees, its primary and most significant effect is on IL-2 4

It can inhibit cytokine production from both T-helper 1 (Th1) and T-helper 2 (Th2) cells 3
It has some inhibitory effects on tumor necrosis factor-α (TNF-α) production, but this is not its primary mechanism 4, 6

The inhibition of IL-2 by cyclosporin A leads to reduced T-helper cell function, which is the main target of the drug's immunosuppressive action 3
A further effect of IL-2 inhibition is a reduction in B-cell activation and subsequent antibody production 3
IL-2 levels are known to increase during proteinuria and normalize during remission in adults with idiopathic nephrotic syndrome, making cyclosporin's IL-2 inhibition clinically relevant in these conditions 3