Dangerous clones with complex ties to AL amyloidosis Free

In this issue of Blood, Gort-Freitas et al¹ present a pilot study on multimodal analysis of transcriptional and proteomic profiles of clonal plasma cells (PCs) and bone marrow microenvironment in amyloid light chain (AL) amyloidosis. Their findings reveal that amyloidogenic PCs experience proteotoxic stress and engage in complex interactions with nonclonal cells in the bone marrow. This study provides further insights into the pathogenesis of AL amyloidosis, identifies possible novel therapeutic targets and might enable new biomarker discovery.

AL amyloidosis arises from a typically small but highly pathogenic PC clone that produces unstable, toxic light chains (LCs) prone to misfolding and aggregation that form amyloid fibrils.² This disease is the prototype of monoclonal gammopathies of clinical significance, manifesting as progressive organ dysfunction and damage that can be fatal if treatment is delayed or ineffective. The deceptive clinical manifestations, which depend on symptoms and signs of organ involvement that often appear at late stages and mimic more common disorders, make early diagnosis a critical unmet need. Efforts are underway to detect AL amyloidosis at a presymptomatic stage using biomarkers of organ dysfunction and damage or characteristics of the amyloidogenic PC clone, such as preferential LC germ line gene usage and N-glycosylation of kappa LCs at specific regions.^3-5 Current therapies aim to eliminate the amyloidogenic clone, halting the production of toxic LCs. Successful suppression can enable organ recovery, and patients achieving deep hematologic and organ responses experience prolonged survival comparable to age-matched general population.⁶ However, fostering early diagnosis, improving treatment efficacy, and increasing the proportion of patients achieving organ recovery require laboratory and translational research to deepen our understanding of the amyloid clone’s biology and the mechanisms of organ targeting and toxicity.⁷ 

Gort-Freitas et al report that clonal amyloidogenic PCs have unique transcriptional states distinct from nonmalignant PCs and multiple myeloma PCs, consistent with previous studies. They found substantial interpatient transcriptional heterogeneity in clonal PCs, driven by chromosomal abnormalities, particularly t(11;14), the most common translocation in AL amyloidosis.⁸ Notably, t(11;14) confers exquisite sensitivity to B-cell lymphoma 2 inhibitors such as venetoclax, suggesting these findings could guide personalized treatment strategies.⁹ They also found increased expression of genes involved in proteostasis, which are implicated in the pathogenesis of other protein-folding disorders, such as Alzheimer disease. Moreover, they observed upregulation of proteostasis-related proteins in the bone marrow plasma of patients with AL amyloidosis, suggesting that proteotoxic stress from amyloidogenic LC production affects both clonal PCs and the bone marrow microenvironment. Previous studies have shown that amyloidogenic LC production is associated with ultrastructural signs of cellular stress, abundant stress-related transcripts, and heightened sensitivity to proteasome inhibition in PCs.¹⁰ These findings support targeting the unfolded protein response through proteasome inhibitors or alternative approaches as a key strategy in AL amyloidosis.

The authors extended their investigation beyond clonal PCs, revealing complex interactions between the amyloidogenic clone and the bone marrow microenvironment. By analyzing CD138^– cells to represent the non-PC components of the bone marrow microenvironment, they found that normal hematopoiesis was suppressed, accompanied by expanded monocytes and CD4⁺ T cells. Amyloid deposits were detected in some bone marrow biopsies, suggesting the bone marrow can be both the source and a target of amyloid deposition and this may be reflected by microenvironment findings. The absence of clonal expansion in B or T cells suggests immune tolerance to amyloidogenic PCs or their antigens. Surprisingly, an expansion of transcriptionally distinct, nonmalignant PCs was observed in the bone marrow of these patients. These nonmalignant PCs exhibit elevated expression of Cysteine-Rich Intestinal Protein 1 (CRIP1), a multifunctional protein that modulates proteasome and autophagy activities in clonal multiple myeloma PCs, fostering resistance to proteasome inhibitors. By analyzing public data sets as another resource, Gort-Freitas et al detected CRIP1-positive, nonclonal PCs in patients with monoclonal gammopathy of undetermined significance as well, suggesting this may be a shared feature of PC dyscrasias. The unexpected expansion of nonmalignant PCs expressing CRIP1 raises questions about their role in supporting the amyloidogenic clone or even modulating therapy responses. This finding challenges the traditional focus on clonal PCs alone and suggests broader dysregulation of PC populations in AL amyloidosis and possibly other PC dyscrasias. Elucidating the role of nonclonal PCs could uncover novel therapeutic targets or strategies to enhance the efficacy of existing treatments.

A notable finding is an inflammatory transcriptional signature in the bone marrow microenvironment of patients with AL amyloidosis, characterized by tumor necrosis factor alpha signaling, upregulated complement and phagocytosis-related proteins, interferon responses, and elevated soluble CD276 (B7-H3). This protein inhibits T-cell activation, promotes tumor immune evasion, modulates cytokine production, enhances cancer cell proliferation and survival, and supports angiogenesis, fostering an immunosuppressive and protumorigenic bone marrow niche.

These multifaceted findings were enabled by a meticulous and comprehensive methodological framework, significantly bolstering the depth and validity of the results. The integration of single-cell RNA sequencing, proteomic profiling via tandem mass tag mass spectrometry, and multiplex immunofluorescence staining captures both cellular and soluble elements of the bone marrow microenvironment in AL. However, the small sample size and use of CD138^– cells for microenvironment analysis necessitate validation in larger, standardized cohorts. Functional experiments are also needed to clarify the role of these findings in disease pathogenesis. Finally, dynamic, longitudinal studies could uncover mechanisms of resistance or relapse associated with these findings, paving the way for more long-term effective therapeutic strategies.

The findings of Gort-Freitas et al offer intriguing hypotheses for future translational research in AL amyloidosis. Validating and deepening these insights could lead to diagnostic biomarkers that distinguish potentially amyloidogenic PC clones, enabling early diagnosis to address the critical need for screening tests. Therapeutically, targeting unfolded protein response, the interplay with nonclonal PCs, and the inflammatory microenvironment offers promising new treatment strategies. By unraveling the complex interplay between amyloidogenic and nonamyloidogenic PCs and their inflammatory bone marrow microenvironment, Gort-Freitas et al provide a roadmap for transforming AL amyloidosis management, paving the way for earlier diagnosis, personalized therapies, and improved outcomes for this devastating disease.

Conflict-of-interest disclosure: G.P. received honoraria from AbbVie, Alexion, Bayer, Janssen, Life Molecular Science, Neurimmune, Protego, Pfizer, Prothena, and Regeneron. S.S. received honoraria from Janssen, Pfizer, Sobi, Prothena, Neurimmune, Alexion, and Teli and financial support of scientific projects from Prothena, Janssen, Neurimmune, and Protego.