Single nucleotide variants in cytokine genes alter the susceptibility and aggressiveness for follicular lymphoma

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Follicular lymphoma (FL) is the most common indolent non-Hodgkin lymphoma subtype. The discovery of susceptibility factors for this disease, as well as for other cancers, is of utmost importance. Not only it helps to elucidate the mechanisms of lymphomagenesis, but it may also allow a closer follow-up of susceptible individuals.

It is increasingly evident that the neoplastic cells in FL (illustrated as the follicular structures in the cover image) depend on stromal signals to grow, including the signaling performed by cytokines. A normal balance of cytokines is important to regulate physiological immune responses. These molecules allow the shifting between immune networks, such as Th1, Th2, and Th17, depending on the environmental stimulus. It is already known that there is a disruption of the cytokine balance in FL patients, as the serum profiles of these molecules in patients are different than the ones of healthy persons1. However, little is known about the genetic regulation of these molecules and its role in lymphomagenesis.

In our study, we opted to study key immune-response genes from Th1 (IL12A, IL2), Th2 (IL10, TGFB1, TGFBR1, TGFBR2) and Th17 (IL17A, IL17F) pathways, which are still underexplored in FL despite their pivotal roles in immunity. We asked the question of whether single nucleotide variants (SNVs) within these genes were responsible for an altered susceptibility for FL. SNVs encompass single-nucleotide substitutions in a gene sequence that may or may not cause a downstream functional alteration (figure 1). Because of our goal in potentially targetable pathways, we focused mainly on SNVs that could alter immune responses (the so-called candidate-marker approach), following previous evidences in various biological contexts. Therefore, we selected 16 SNVs distributed in the 8 genes of interest and compared allelic and genotypic frequencies between FL cases and controls (healthy blood donors). We found that 4 SNVs were associated with increased FL risk: rs1800469 (TGFB1), rs3087465 (TGFBR2), rs3748067 (IL17A) and rs763780 (IL17F). The wild-type alleles of all SNVs were detected in higher frequencies among cases, compared to controls. We also found that the wild-type allele of rs1800469 (TGFB1) was associated with more aggressive FL; CC or CT genotypes were more frequent in patients with Ann Arbor stages III or IV than in those with I or II stages. For TGFB1, this was an expected result, as the wild-type allele (“C”) of rs1800469 is known to decrease the production of TGFβ2. As TGFβ is generally responsible for immunosuppression, less levels of this cytokine may favor excessive immunological stimuli, immune exhaustion, and FL onset. However, it will be necessary to confirm the functional role of this SNV in FL patients, as the original functional study was performed only in healthy individuals2. On the other hand, although the remaining 3 SNVs have postulated functional roles3,4,5, it was never tested whether they have the ability to shift circulating cytokine levels in patients, so this is an interesting hypothesis to be tested in other studies.

Our results complement the seminal investigation of serum cytokines in FL patients. We showed that the genetic variations in cytokine genes also present differences between FL patients and controls. Future approaches may integrate both the genetic data and the protein data. It is clinically feasible to prospectively collect serum samples from patients. Therefore, we recommend a joint approach in further studies, to compare SNV genotypes with the respective cytokine levels from pre-treatment samples. It will be particularly important to address if these susceptibility markers have real functional consequences that lead to FL and to more aggressive disease. However, we may consider that the protein endpoint is not the only one; other possibilities exist (figure 1). Are the SNVs responsible for an alteration of the transcript? Or post-translational modifications (such as miRNA binding)? Do they modulate specific immunological aspects (e.g. T-cell anergy?). The answer to these questions will bring even deeper insights into lymphomagenesis from the immunological point of view.

Finally, future validations of our results, in other populations, will be important to stress the role of these candidate SNVs in FL, tailoring a personalized approach in individuals with increased risks.

Our article can be read in the following link: https://www.nature.com/articles/s41408-020-00365-4.

 

Immune responses in germinal centers encompass adequate levels of Th1, Th2 and Th17 cytokines, which act on B-cell maturation (left panel). We have observed that single nucleotide variants (SNVs) in 4 cytokine genes (TGFB1, TGFBR1, IL17A and IL17F) are responsible for an increased susceptibility for follicular lymphoma (middle panel). These SNVs were previously implicated in the modulation of immune responses in contexts other than lymphomas. We hypothesize that these SNVs may also alter the immune balance to favor lymphomagenesis. However, this was not a specific question of this study. Further investigations, either in silico or experimental, may elucidate the specific step (transcription, translation, post-translational modifications) by which the SNVs act on the respective pathways (right panel).

References:

1) Calvo KR, et al. IL-4 protein expression and basal activation of Erk in vivo in follicular lymphoma. Blood. 2008;112(9):3818-26.

2) Grainger DJ, et al. Genetic control of the circulating concentration of transforming growth factor type beta1. Hum Mol Genet. 1999;8(1):93-7.

3) Seijo ER, et al. Identification of genetic alterations in the TGFbeta type II receptor gene promoter. Mut Res. 2001;483:19-26.

4) Kawaguchi M, et al. IL-17F sequence variant (His161Arg) is associated with protection against asthma and antagonizes wild-type IL-17F activity. J Allergy Clin Immunol. 2006; 117:795-801.

5) Dong K, et al. Associations of functional microRNA binding site polymorphisms in IL23/Th17 Inflammatory pathway genes with gastric cancer risk. Mediators Inflamm. 2017; 2017:6974696. doi: 10.1155/2017/6974696.

Guilherme Rossi Assis-Mendonça

MD, University of Campinas

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