We were interested in acute lymphoblastic leukaemia patients who are treated with CD-19 directed immunotherapy and we focussed on patients who relapsed after this treatment and they lost the target antigen. That means that they were CD-19 negative at relapse. We were interested in the mechanism, how this CD-19 negative phenotype is caused so we performed exome sequencing to identify mutations which could be responsible for the immunophenotype. We checked the CD-19 gene in 17 patients which we had in our cohort. We expected to find quite some mutations but surprisingly we only found mutations in five out of the 17 patients. I say surprisingly because in quite a similar cohort of patients who were treated with CAR T-cells, which is also a CD-19 directed therapy they identified CD-19 mutations in all of them. So the fact that we only found mutations in less than one-third of the patients surprised us.

So we looked into other genes because exome sequencing makes it possible and what we discovered was that some groups of genes which are responsible for the calcium transport and for cholesterol synthesis were mutated in quite some patients, I think it was five or six patients from the cohort. So we made a hypothesis that maybe this could be responsible for the CD-19 negative loss but of course we don’t know it, we have to investigate it further, probably on a bigger patient cohort or do some knockout experiments to confirm that these mutations which we discovered can cause that phenotype.

It would be really great to explain that because we need to understand the mechanism of the CD-19 loss because we, of course, need to prevent that. Maybe that would help to prevent the relapses as well.

What are the next steps?

Next is probably those knockout experiments. We unfortunately don’t have RNA from the patients so we cannot confirm that it’s not expressed. So we will probably do the knockout experiments and we are planning to include more patients to see if it’s true also in the other ones.