atients with cutaneous T-cell lymphomas (CTCLs) may go months or even decades without a proper diagnosis and treatment, experiencing debilitating itch and progression to fungating weeping wounds as they cycle through ineffective therapies. Diagnosis is just one of the many clinical challenges patients face. Fortunately, dynamic partnerships between patients, physicians, and researchers have led to significant advances in the diagnosis and management of this life-threatening disease.

In this article, we highlight how the application of a basic and robust tool to characterize the T-cell repertoire, enabled by next-generation sequencing, is making headway in the diagnosis and management of CTCL and how investigation into an orphan disease can translate into insights that extend far beyond treating CTCL.

T-cells and the Skin

The skin is more than a physical barrier, keeping us warm and protecting us from injury. Because it is visible and accessible, it is the perfect host for cutting-edge translational research, allowing clinicians and scientists to observe, biopsy, and interrogate skin diseases, moving seamlessly from the bedside to the bench and back. The skin is also a rich immune organ with roughly 20 billion T-cells, more than twice as many as the peripheral blood. Resident immune cells and other T-cells programmed to traffic to the skin may undergo malignant transformation, giving rise to a rare group of non-Hodgkin’s lymphomas, termed cutaneous T-cell lymphomas (CTCLs). Clinically and pathologically, these diseases can mimic benign inflammatory conditions like eczema.

Research Insights Advance Care Across the Full Spectrum of Disease Management

Cooperation between clinicians and researchers has been integral in applying technological innovations from the laboratory to improve diagnosis, develop prognostic indicators, and optimize treatment for CTCL patients.

Diagnosis and Monitoring

T-cell lymphomas are fundamentally a monoclonal disease. However, within skin lesions of CTCL, clonal malignant T-cells are admixed with benign reactive T and other immune cells, obfuscating the malignant process. Distinguishing benign from malignant eruptions can be clinically and pathologically challenging, with lesions of lymphoma often resembling eczema, psoriasis, or other inflammatory rashes. Luckily, given that T-cells each carry a genetically unique T-cell receptor (TCR), like a fingerprint, molecular assays based on sequencing of the TCR can be used to identify and quantify clonal T-cell populations. The most widely used method to detect a dominant T-cell clone relies on traditional polymerase chain reaction (PCR), which identifies the relative abundance of unique clones based on the size of PCR amplicons (i.e., DNA or RNA fragments that are the product of amplification events such as PCR). This technique has limited sensitivity and high false negative rates.

One significant advancement in the accurate diagnosis of these cancers has been the application of high-throughput sequencing (HTS) of the TCR, a technology that greatly increases the amount of DNA that can be sequenced. Assays based on HTS can provide the exact TCR sequence of each T-cell and can precisely quantify each T-cell population. Our colleagues led by Clark have used HTS to develop a metric to quantify the dominant clone and distinguish CTCL from clinical mimics.

While this technology is now available to clinicians to help diagnose disease, the US Food and Drug Administration’s approval of this assay for this indication is sorely needed to enable insurance coverage and wider adoption of this powerful tool. Once the malignant clone has been identified and quantified, HTS can be repeated over time to assess response to therapy.

Prognosis

In early-stage mycosis fungoides (MF), the most common subtype of CTCL, most patients have great outcomes. A subset of patients, however, will develop more aggressive disease. One major clinical challenge is to predict which patients are at risk of disease progression and who may benefit from more definitive or aggressive therapy upfront. The quantification of the cancer cell populations by HTS, introduced above, may also be used as a prognostic tool. The measured frequency of tumor clones may predict which patients are at a higher risk for disease progression; work from our team led by Kupper and colleagues found that a tumor clone frequency (the percentage of T-cells that are malignant) greater than 25% was associated with a higher risk for disease progression in MF patients. We then showed that treatment of high-risk MF patients (based on TCF > 25%) with definitive radiation led to improved overall survival.

Treatment

Much research has been conducted into the genomic landscape of CTCL, with the hopes of furthering personalized medicine by targeting mutations specific to an individual’s cancer. Unfortunately, there are no broadly druggable mutations across CTCL patients. Responses to JAK (Janus kinase) and Pi3K (phosphoinositide 3-kinase) inhibitors from phase 1/2 studies have been underwhelming, and targetable fusion proteins or structural variants are rare. In other words, despite all the genetic information we have gathered, there have been few success stories in applying this to successfully treat patients.

Excitingly, there are growing efforts to develop therapies that target the TCR of the malignanT-cell itself, taking advantage of the fact that CTCL is a monoclonal disease. Development of therapies based on antibody recognition of the most evident TCR molecular families, work demonstrated in in vivo models to date, is an attractive method to specifically target malignant T-cells, which otherwise exhibit vast genomic and transcriptional heterogeneity. This more selective targeting of T-cells would also be less immunosuppressive than therapies that broadly destroy cells, such as alemtuzumab, an anti-CD52 antibody.

Pathophysiology

Identification of the TCR Vβ families used by CTCL has also helped advance our understanding of possible contributors to cancer development, specifically supporting the chronic antigen stimulation theory; expansion of clonal T-cells due to antigen or superantigen binding leads to proliferation and increased susceptibility to malignant transformation. Patients are frequently observed to have malignancy derived from T-cells using the TCRBV20 family, which is associated with activation by Staphylococcus aureus. This is supported by several clinical observations, made as early as the 1980s, when physicians observed that bacterial infections of the skin drove disease flares in patients with CTCL and oral antibiotics can reduce skin disease severity and itch in CTCL patients.

The efficacy of oral antibiotics in CTCL has led to the investigation of how bacteria, particularly S. aureus, not only play a role in disease pathophysiology, but may also be targeted with novel antimicrobial therapies. Ødum and colleagues have shown that certain proteins of S. aureus suppress antitumor immunity and directly promote the proliferation of cancerous cells. Excitingly, this has led to the development of a novel protein (endolysin) which has been shown to effectively reduce S. aureus colonization on CTCL skin, decreasing activation and proliferation of cancerous T-cells. Planning has begun for clinical investigation of this novel topical. This is another prime example of the fluidity that defines the collaboration between clinicians and scientists in the study of skin disease: clinicians provided an observation regarding infection-induced flares, and scientists then pursued targeted research to understand the mechanism and eventually develop a drug that clinicians can bring back to patients.

Beyond CTCL

Understanding basic T-cell biology, namely TCR genetic recombination, has allowed clinicians to apply a basic tool of bench immunology scientists, TCR sequencing, to better study, diagnose, and clinically manage T-cell lymphomas. In turn, using CTCL as a model disease for T-cell survival led scientists to identify a novel fusion protein, which could be engineered into chimeric antigen receptor (CAR)-T-cells to increase proliferation, persistence, and function, creating a superior T-cell anticancer therapy. CAR-T-cells have become a transformative therapeutic modality to treat hematologic malignancies and are under investigation in T-cell lymphomas as well as diverse solid tumors. In a clever twist, clinician scientists have exploited T-cell lymphoma biology, hopefully, to its own end if we can engineer a superior CAR-T directed against T-cell lymphomas.

Conclusion

The open communication between dermatologists, oncologists, and basic scientists is enhancing patient care, through innovation in diagnosis, prognosis, and management. This collaboration between the bench and bedside is advancing the field of CTCL and is a prototype for how translational research can be conducted and applied to other diseases.

References available upon request.