topical cyclosporin wasn’t very effective…only grew hair about 20 percent of the time.
For immunosuppressants to be effective, they need to be internal because of how the immune system works. The immune system is a body-wide phenomenon with travelling cells that constantly look for foreign bodies to mark, while others go back and “tell” other immuno cells to come attack, etc. It simply can’t be just suppressed topically and be really effective.
According to Peter Proctor (look at his site), cyclosporin regrows more hair than any anti-androgen when used internally.
Here is what is on Proctor’s site about cyclosporin:
Emerging Model for Pattern Balding (after Kligman, others )
Balding begins when male sex hormones do "something " to the scalp hair follicle which causes it to be read as a “foreign body”. Your immune system then mounts an attack on the hair folllicle. The main damage in pattern hair loss is probably immunologically-mediated. Damage to lining of blood vessels, which produces hair growth factors, makes the balding process worse.
Castration, lack of DHT-receptors/enzymes (testicular feminization) , feminine status block the progression of balding and hair loss. However, women and castrated males have other sources of androgens and can still experience pattern loss.
Microscopically, balding looks like organ rejection. That is, increased number of immune system cells clustor round the base of the scalp hair follicle. Interestingly, lessor numbers of immune system cells normally cluster around the hair follicle. These may have a role in the normal hair cycle.
Organ rejection drugs ( e.g., cyclosporin ) reverse balding better than antiandrogens. This gives a rough indication of the relative importance of hormonal verses immunological factors in maintaining the balding state. Conversely, cyclosporin and similar agents may also have a “phenytoin-like” action on follicles which induces hair regrowth, separate from their immunosuppressive properties. Antibodies to hair follicles are also present in blood in some cases of pattern hair loss