Phototherapy-Induced Immunosuppressive Effects

Topical photodynamic therapy is immunosuppressive in humans.

Matthews YJ, Damian DL

Br J Dermatol 2009 Oct 26

In this Australian study, investigation of immunosuppression after photodynamic therapy was done with the Mantoux test (delayed-type hypersensitivity responses to tuberculin purified protein derivative)

Introduction: Visible light irradiation following application of a photosensitizer (topical photodynamic therapy; PDT) is more and more used to treat nonmelanoma skin cancers and premalignant actinic keratoses. PDT can achieve cosmetically better results than surgery, but failure rates range from 10% to 40%. Studies done in mice suggest immunostimulation following treatment, wheras other studies suggest an immunosuppressive effect, which increases the risk of recurrence. An example would be the increase after immunosuppressive treatment introduced following organ transplantation.

Aim of the study: This study tried to determine the in immune effects of PDT in humans.

Methodology: Using healthy, Mantoux-positive volunteers, areas of the back were irradiated with narrowband red light (630 nm; 37 J cm(-2)):

-in one group there was prior application of 5-aminolaevulinic acid (ALA) or methyl aminolaevulinate (MAL).

-in the other group there was NO application of ALA nor MAL

Areas of skin surrounding the irradiated zone were considered as immunologically preserved (control areas)

Adjacent, untreated areas served as immunologically intact control sites.

Mantoux were then elicited in each of the irradiated, unirradiated and control areas, and the intensity of the reactions was quantitated with an erythema meter and by measurement of Mantoux diameter. By comparing Mantoux intensity at treated and control sites, immunosuppression was determined in each volunteer for each intervention.

Results: The authors found that both MAL-PDT and ALA-PDT significantly suppressed Mantoux erythema (by 30% and 50%, respectively) and diameter (41% and 38%). Red light alone significantly suppressed diameter (22%) but not erythema (13%).

Conclusion of the authors: Topical PDT induced decreased Mantoux test reactions, suggesting significant immune suppression, which could hamper local antitumour immune responses and this may be part of the explanation of why a relatively high number of treatments are not as succesful as would be expected. Therefore, this PDT should be used with immunostimulative treatments (such as imiquimod) to improve long term results. Additional research at the molecular level could provide additional credance to the interesting results of this study.

Contributors:

Dr Christophe HSU – dermatologist. Geneva, Switzerland