Like trying to find a lit match in a room full of burning furniture, isolating Hodgkin’s lymphoma cancer cells from within an inflamed tumor is a challenge that has hampered efforts to better understand the genes and biology of cancer. Now, a group of researchers has isolated cancerous cells from non-cancerous ones, but for the first time they have sequenced their entire genome.
Reported in Discovery of blood cancer, the study revealed a number of previously unknown genetic changes, including mutations in genes that drive cancer progression (1). By reconstructing a timeline of how these changes occurred, the researchers highlighted how cancer goes from a seemingly harmless match lit on the table, to the burning dining room, to the burning room.
“Identifying these changes allows us to build a catalog of possible targets that we can use to develop new treatments,” said cancer geneticist and co-author Francesco Maura of the University of Miami. “It also helps us understand why some existing drugs work so well.”
Maura and her colleagues isolated the elusive Hodgkin and Reed Sternberg (HRS) tumor cells from the tumors of 25 patients with Hodgkin’s lymphoma using optimized fluorescence-activated cell sorting. HRS cells are notoriously difficult to study because they make up only about one percent of a tumor’s mass.
Once isolated, the researchers amplified the cells’ DNA and sequenced it. When Mauro’s team looked at the data, they found a variety of changes in the genomes of HRS cells, including specific mutations, whole genome duplication in some cases, and structural changes such as chromothripsis, which the researchers described as the chromosomes damaged that appear to have been hit by sledgehammers. Some of these changes were unsurprising and had been discovered previously, but others were new (2).
Tomohiro Aoki, a hematologist and oncologist at Princess Margaret Cancer Center who was not involved in the study, said in an email that “this study has significantly improved our understanding of the pathogenesis of Hodgkin’s lymphoma in a sophisticated way,” adding that the workflow of the researchers described could be used to understand how other types of cancer progress.
One particularly intriguing finding was changes to the guide genes that help tumors grow. An example is file changes MSL2 gene, in which a mutation contributes to impaired DNA repair. Ninety-five percent of the patients studied by Mauro’s team had at least one mutated driver gene; some had as many as 14.
“If we are to use the information to develop any personalized treatment strategy, then we need to understand tumor heterogeneity and key drivers,” said Maura. At this stage, researchers don’t yet know exactly what each change in the DNA contributes to the symptoms patients experience or the severity of their tumors.
The researchers also figured out which of the genetic changes happened before the others. They saw that deletions of sections of DNA and some genetic mutations occurred early in tumor development, while genome doubling or major structural changes occurred later.
The prevailing theory on how Hodgkin lymphoma develops is that B cells mutate into cancerous HRS cells within a germinal center (3). Instead, the timeline reconstructed by Maura and her team suggests that the first genomic event may occur in B cells before the germinal center forms.
Knowing the order in which mutations occur could mean that, in the future, it will be possible to target treatments at those early driver events and halt the progression of the cancer. “Step by step, we hope to understand which drivers and in what order need to be acquired for these cells to transform into Hodgkin’s lymphoma,” said Maura.
Aoki said the timeline shows how unique the progression of Hodgkin’s lymphoma is compared to other blood cancers.
The study established a proof of concept that includes a relatively small number of patients. Next, Maura and her collaborators hope to apply similar techniques to a larger pool of samples to help them identify biomarkers of Hodgkin’s lymphoma that could be found using less invasive and complicated means than whole genome sequencing, such as through the blood sample.
- Maura, F., Ziccheddu, B., Xiang, JZ, Bhinder, B., Rosiene, J., Abascal, F., Maclachlan, KH, et al. Molecular evolution of classical Hodgkin lymphoma revealed through whole genome sequencing of Hodgkin and Reed Sternberg cells. Discovery of blood cancer BCD-22-0128 (2023).
- Wienand K., Chapuy B., Stewart C., Dunford AJ, Wu D., Kim J., Kamburov A., et al. Genomic analyzes of flux-ordered Reed-Sternberg Hodgkin cells reveal complementary mechanisms of immune evasion. Blood advances 3 (2019).
- Piris, MA, Medeiros, LJ, Chang, KC. Hodgkin’s lymphoma: a review of pathological features and recent advances in pathogenesis. Pathology 52 (2020).
#Hodgkins #lymphoma #sequencing