Skin Associated Staphylococcus Aureus Contributes to Disease Progression in CTCL

It has been proposed that bacteria play a direct role in progression of cutaneous T cell lymphoma (CTCL), although definitive evidence is missing, and the underlying mechanism of how microbes contribute to disease progression remains unknown. The skin of CTCL patients is frequently colonized with Staphylococcus aureus (S. aureus) strains and infections with hospital and community associated strains of S. aureus are a frequent cause of morbidity and mortality among patients with advanced CTCL. Here we provide a comprehensive analysis of the association between CTCL and S. aureus colonization, and use our unique pre-clinical animal model of CTCL to determine the cause-effect relationship between skin-associated S. aureus and CTCL progression.

To understand the relationship between bacterial colonization and CTCL we collected skin swabs from active lesions, unaffected skin and nares of CTCL patients to perform S. aureus cultures and 16S rRNA gene sequencing. Skin swabs of psoriasis patients and healthy donors served as controls. The frequency of S. aureus colonization determined by culture based techniques revealed that >65% of advanced stage patients had S. aureus present at lesional/tumor sites, while corresponding sites in patients with psoriasis and in healthy controls rarely had detectable S. aureus. Colonization rates correlated positively with the disease stage. Unbiased, 16s sequencing based analysis of the skin microbiome from advanced CTCL patients revealed that the overall skin microbiome of these patients is distinct from that of healthy individuals and patients with psoriasis. A lower phylogenetic diversity and significantly higher relative abundance of Staphylococcus species was found in CTCL patients.

To determine the causal relationship between skin flora and progression of CTCL we used our mouse model of CTCL and assessed disease progression in both conventionally housed specific-pathogen-free (SPF) conditions and in germ free (GF) isolators using a standardized clinical score. The CD4CreSTAT3^stopfl/+ mice express a hyper-active STAT3C mutant protein selectively in T lymphocytes and virtually all mutant mice develop T cell infiltration in the epidermis causing skin lesions resembling CTCL, by eight months of age. In contrast to the SPF housed animals, GF mice remained disease free or developed only a mild phenotype (clinical score 1 out of 5) after 11 months of follow-up. Notably, when GF CD4CreSTAT3^stopfl/+ mice were transitioned to SPF conditions they all developed advanced disease.

Finally, we examined the role of T cell antigen receptor (TCR) signaling in mediating the transformation of T lymphocytes. R26STAT3C^stopfl/+CD4Cre Rag2KO OTII mice express only OVA-specific TCRs. T cells from R26STAT3C^stopfl/+ CD4Cre Stim1^fl/fl mice express a normal TCR repertoire, but exhibit defective T cell receptor signaling due to compromised calcium influx. Both strains failed to develop typical skin lesions, suggesting an essential role for TCR interaction with tumor microenvironment and microbial antigens in the pathogenesis of CTCL.

In conclusion, we demonstrate a strong correlation between CTCL staging and rates of S. aureus colonization. Our study supports a cause-effect relationship between skin flora and CTCL oncogenesis. We propose that CTCL represents an antigen driven malignancy. Further studies using mono-colonization with single bacterial strains are needed to further interrogate the role of specific bacteria.