CSF TACI and BAFF levels in patients with primary CNS lymphoma as novel diagnostic biomarkers

Updates of primary central nervous system lymphoma

Lymphoma occurring in the central nervous system is considered primary central nervous system lymphoma (PCNSL), usually without systematic lesions. Over the last few decades, a deep understanding of PCNSL has been lacking due to the low incidence rate, and the overall survival and progression-free survival of patients with PCNSL are lower than those with other types of non-Hodgkin lymphoma. Recently, there have been several advancements in research on PCNSL. Advances in diagnosis of the disease are primarily reflected in the promising diagnostic efficiency of novel biomarkers. Pathogenesis mainly involves abnormal activation of nuclear factor kappa-B signaling pathways, copy number variations, and DNA methylation. Novel therapies such as Bruton's tyrosine kinase inhibitors, immunomodulatory drugs, immune checkpoint inhibitors, and phosphoinositide 3-kinase/mammalian target of rapamycin inhibitors are being evaluated as possible treatment options for PCNSL, especially for relapsed/refractory (R/R) cases. Several clinical trials also indicated the promising feasibility and efficacy of chimeric antigen receptor T-cell therapy for selected R/R PCNSL patients. This review focuses on discussing recent updates, including the diagnosis, pathogenesis, and novel therapy of PCNSL.

The BAFF-APRIL System in Cancer

B cell-activating factor (BAFF; also known as CD257, TNFSF13B, BLyS) and a proliferation-inducing ligand (APRIL; also known as CD256, TNFSF13) belong to the tumor necrosis factor (TNF) family. BAFF was initially discovered as a B-cell survival factor, whereas APRIL was first identified as a protein highly expressed in various cancers. These discoveries were followed by over two decades of extensive research effort, which identified overlapping signaling cascades between BAFF and APRIL, controlling immune homeostasis in health and driving pathogenesis in autoimmunity and cancer, the latter being the focus of this review. High levels of BAFF, APRIL, and their receptors have been detected in different cancers and found to be associated with disease severity and treatment response. Here, we have summarized the role of the BAFF-APRIL system in immune cell differentiation and immune tolerance and detailed its pathogenic functions in hematological and solid cancers. We also highlight the emerging therapeutics targeting the BAFF-APRIL system in different cancer types.

APRIL and BAFF play a key role in differentiating vitreoretinal lymphoma from uveitis

BACKGROUND

Early diagnosis of vitreoretinal lymphoma (VRL) is critical for the successful treatment of this rare intraocular malignancy. However, fast and reliable diagnosis of VRL in patients presenting with intermediate or posterior non-infectious uveitis remains a challenge. A proliferation-inducing ligand (APRIL) and B-cell activating factor (BAFF) are vital factors in the pathophysiology, diagnosis, and prognosis of primary central nervous system lymphoma (PCNSL) and systemic autoimmune diseases. However, their utility as biomarkers for the diagnosis of VRL and uveitis remains unclear.

METHODS

In this retrospective study, we analyzed APRIL and BAFF levels in the aqueous humor (AH) of 43 eyes of 40 patients, including 23 eyes of 20 patients with VRL, eight eyes of eight patients with uveitis, and 12 eyes of 12 patients with other ocular diseases (OODs). Additionally, we measured their levels after induction of chemotherapy in five eyes of five patients with VRL.

RESULTS

AH levels of APRIL reliably distinguished VRL from uveitis, with a specificity of 78.3% and sensitivity of 75%. BAFF also showed similar potential. Serial AH analysis of patients with VRL during chemotherapy demonstrated a corresponding decline in AH levels of APRIL and BAFF.

CONCLUSION

This study extends the spectrum of valuable diagnostic biomarkers for VRL and uveitis. In patients with uveitis, the assessment of AH APRIL may help accelerate the diagnosis of VRL. Moreover, our results underline the important role of APRIL and BAFF in therapeutic monitoring of VRL.

Novel insights into the biomarkers and therapies for primary central nervous system lymphoma

Primary central nervous system lymphoma (PCNSL) is a rare and highly aggressive extranodal type of non-Hodgkin lymphoma. After the introduction and widespread use of high-dose-methotrexate (HD-MTX)-based polychemotherapy, treatment responses of PCNSL have been improved. However, long-term prognosis for patients who have failed first-line therapy and relapsed remains poor. Less invasive diagnostic markers, including the circulating tumor DNAs (ctDNAs), microRNAs, metabolomic markers, and other novel biomarkers, such as a proliferation inducing ligand (APRIL) and B-cell activating factor of the TNF family (BAFF), have shown potential to distinguish PCNSL at an early stage, and some of them are related with prognosis to a certain extent. Recent insights into novel therapies, including Bruton tyrosine kinase (BTK) inhibitors, immunomodulatory drugs, immune checkpoint inhibitors, PI3K/mTOR inhibitors, and chimeric antigen receptor (CAR) T cells, have revealed encouraging efficacy in treatment response, whereas the duration of response and long-term survival of patients with relapsed or refractory PCNSL (r/r PCNSL) need further improvement. In addition, the diagnostic efficiency of novel markers and the antitumor efficacy of novel therapies are needed to be assessed further in larger clinical trials. This review provides an overview of recent research on novel diagnostic markers and therapeutic strategies for PCNSL.

Endogenous soluble receptors sBCMA and sTACI: biomarker, immunoregulator and hurdle for therapy in multiple myeloma

BAFF and APRIL regulate B cell homeostasis by binding to their three receptors BAFFR, BCMA and TACI. The complexity of this system is further increased by shedding of these three receptors; this reduces signaling due to the display of less surface receptors. Further, soluble forms, sBCMA and sTACI, were detected in body fluids and serve as biomarker in malignancies, autoimmune diseases and immunodeficiencies. sBCMA and sTACI function as decoys blocking BAFF and APRIL. BCMA is a promising therapeutic target in multiple myeloma, but sBCMA may reduce therapeutic activity of CAR T cells, bispecific antibodies, and antibody-drug conjugates. Insights into the biochemical mechanism of shedding of BCMA can be harnessed to improve BCMA-directed therapy by blocking its shedding with a γ-secretase inhibitor.

Alteration of BAFF and APRIL in the cerebrospinal fluid based on the therapeutic response in primary central nervous system B-cell lymphoma

We evaluated the cerebrospinal fluid (CSF) levels of the B-cell activating factor of the tumor necrosis factor family (BAFF) and A proliferation-inducing ligand (APRIL) in two cases of primary central nervous system B-cell lymphoma (PCNSBL) before and after treatment. One patient achieved clinical remission, and demonstrated decrease in the CSF levels of both BAFF and APRIL after treatment. Meanwhile, the other patient with insufficient therapeutic response showed increase in the BAFF levels despite decrease in APRIL levels. This report suggests that the combination of BAFF and APRIL levels could be useful in estimating the therapeutic efficacy in treating PCNSBL as reliable CSF markers.

The Role of BAFF-R Signaling in the Growth of Primary Central Nervous System Lymphoma

Primary CNS lymphoma (PCNSL) is an aggressive brain tumor. Despite improvements in therapeutic algorithms, long-term survival remains rare, illustrating an urgent need for novel therapeutic targets. BAFF-R is a pro-survival receptor expressed on most malignant B cells, including PCNSL. To date, its role in PCNSL growth remains elusive. Here, we have created a BAFF-R knockout lymphoma cell line (BAFF-R-KO) using CRISPR-Cas9. In serum-starved conditions, BAFF-R-KO cells exhibit decreased viability in vitro compared to BAFF-R⁺ cells. Combining an orthotopic mouse model of PCNSL with chronic cranial windows and intravital microscopy, we have demonstrated a significant delay in tumor growth in mice inoculated with BAFF-R-KO cells compared to BAFF-R⁺ PCNSL. Additionally, median survival of BAFF-R-KO mice was significantly prolonged. Altogether, our results indicate the high potential of BAFF-R as a novel treatment target for PCNSL.

Cerebrospinal fluid biomarkers for brain tumor detection: clinical roles and current progress

Brain tumors include those that originate within the brain (primary tumors) as well as those that arise from other cancers (metastatic tumors). The fragile nature of the brain poses a major challenge to access focal malignancies, which certainly limits both diagnostics and therapeutic approaches. This limitation has been alleviated with the advent of liquid biopsy technologies. Liquid biopsy represents a highly convenient, fast and non-invasive method, which allows multiple sampling and dynamic pathological detection. Biomarkers derived from liquid biopsies can promptly reflect changes on the gene expression profiling of tumors. Biomarkers derived from tumor cells contain abundant genetic information, which may provide a strong basis for the diagnosis and the individualized treatment of brain tumor patients. A series of body fluids can be assessed for liquid biopsy, including peripheral blood, cerebrospinal fluid (CSF), urine or saliva. Interestingly, the sensitivity and specificity of biomarkers from the CSF of patients with brain tumors is typically higher than those detected in the peripheral blood and other sources. Hence, here we describe and properly discuss the clinical roles of distinct classes of CSF biomarkers, isolated from patients with brain tumors, such as circulating tumor DNA (ctDNA), microRNA (miRNA), proteins, and extracellular vesicles (EVs).

APRIL and BAFF: novel biomarkers for central nervous system lymphoma

Background

Early diagnosis of CNS lymphoma (CNSL) is essential for successful therapy of this rapidly progressing brain tumor. However, in patients presenting with focal brain lesions, fast and reliable diagnosis of PCNSL remains a challenge. A proliferation-inducing ligand (APRIL) and B cell activating factor (BAFF) are important factors in the pathophysiology, diagnosis, and prognosis of systemic B cell malignancies. However, their utility as biomarkers for the diagnosis of CNSL and their effects on CNSL cells remain unclear.

Methods

In this prospective study, we analyzed the levels of APRIL and BAFF in the cerebrospinal fluid (CSF) of 116 patients with suspected focal brain lesions, including 53 CNSL patients. Additionally, we serially measured their levels during chemotherapy and relapse. Furthermore, we analyzed the effect of APRIL and BAFF on two B cell lymphoma cell lines using proliferation, viability, and chemotaxis assays.

Results

CSF levels of APRIL and BAFF reliably differentiated CNSL from other focal brain lesions (including primary and metastatic brain tumors, autoimmune-inflammatory lesions, and neuroinfectious lesions) with a specificity of 93.7% (APRIL, BAFF) and a sensitivity of 62.3% (APRIL) and 47.1% (BAFF). Serial CSF analysis of CNSL patients during chemotherapy and relapse demonstrates a close correlation of APRIL CSF levels and the course of this disease. In vitro, APRIL and BAFF showed anti-apoptotic effects during MTX treatment and mediated chemotaxis of malignant B cells.

Conclusion

This study extends the spectrum of valuable diagnostic biomarkers in CNSL. In patients with focal brain lesions, measurement of APRIL in CSF could help accelerating the diagnosis of CNSL. Moreover, our results highlight an important role of APRIL and BAFF in the pathophysiology of CNSL.