Pieter Van Der Velden, Principal Investigator, Leiden University Medical Center. Nelleke Gruis, Associate Professor at Leiden University Medical Center, presented a biomarker for lung cancer treatment using immune therapy. Their novel biomarker is based on counting lymphocytes in DNA samples.
Van Der Velden explained that their technology involves analysing DNA dispersed into droplets and counting and analysing alleles after amplification. The assay was validated with flow cytometry, the gold standard in lymphocyte counting, and an adequate correlation was observed between the 2 approaches. They were able to conclude that DNA-based cell counting with digital PCR is as accurate as flow cytometry and only requires minimal amounts of DNA instead of fresh cells.
To take their technology to new heights, Van der Velden combined all his assays in one multiplex assay called the D4BST which can quantify B cells, switch B cells, and T cells in DNA samples. It is also capable of providing absolute quantification with minimal sample requirements.
Gruis outlined how the group implemented the D4BST in lung cancer stratification. She began her presentation by explaining that the number of lung cancer cases is on the rise with roughly 2.2 million incident cases worldwide and 1.8 million deaths per year. The majority of these patients are non-small cell lung cancer patients that present progressive disease meaning their five-year survival rate is around 5%.
Research has shown that compared to chemotherapy, immunotherapy performs much better in the presence of PD-L1 expression. However, this effect is typically observed in cases where PD-L1 expression is 50% or more. Yet, there are many non-responders in the high PD-L1 expression groups which is puzzling and proves that there is a demand for a more sensitive biomarker.
A few years later, research conducted by Patil et al., which compared gene expression of 800 tumours from long-term survivors compared to short-term survivors showed that groups of genes differentially expressed being to a group of B cells rather than T cells.
Gruis elaborated: “Plasma cells showed the strongest predictive association with overall survival in this study in patients on immunotherapy and the benefit of the plasma cells was independent of the presence of CD8 positive T cells or the PD-L1 expression.” Therefore, B cells specifically plasma cells became more predictive biomarkers in the treatment of non-small cell lung cancer patients.
Based on this new evidence, Gruis and Van der Velden wanted to investigate whether the D4BST test could discriminate between responders and non-responders on immunotherapy. They conducted a pilot study with 34 lung cancer patients on progression-free survival over a year or less than six months. The D4BST test was good at predicting immune checkpoint inhibitor treatment response in lung cancer patients and achieved a sensitivity of 82%. Gruis also noted that T cell levels did not differ significantly between responders and non-responders, reinforcing the focus on plasma cells.
In summary, the D4BST corroborated the research from Patil et al. that suggests that plasma cells are useful biomarkers for the stratification of lung cancer patients. Gruis added that they will follow up on their pilot research using the D4BST test in a larger cohort and focus on applying it across other immune-related diseases.
