According to the Robert-Koch-Institute, the number of leukemia cases in Germany will increase to around 16.000 in 2020. Besides classical therapy modalities of this diverse disease, a relatively new tool appeared: Cellular Immunotherapies. Currently, one of the most exciting treatment modalities in tumor therapy is the application of genetically modified T-cells which detect tumor cells specifically by their chimeric antigen receptor (CAR). CD19-specific CAR-T-cells have proven effective e.g. in B-cell leukemias (B-ALL), Non-Hodgkin-Lymphoma (NHL) or Chronic Lymphatic Leukemia (CLL). However, the development of highly efficient and persistent CAR-T-cells is a challenge since up to date there is no in vitro-test system which is able to determine the specificity and efficacy of CAR-T-cells in bone marrow.

We have therefore developed the model of the microcavity array based healthy hematopoietic niche further to a leukemic niche model in which human mesenchymal stromal cells (hMSC) and CD19-positive cells can be co-cultured (Fig. 1).

Fig.1: Model of the leukemic niche with human mesenchymal stromal cells from bone marrow, NALM-6-cells and the addition of CAR-T-cells.

On the basis of the methods developed in our group to detect and quantify single cells in microcavities, we are able to determine the CAR-T-cell efficacy in a bone marrow surrogate (Fig. 2).

Fig. 2: Detection and reconstruction of CD19-positive cells in microcavities.

An impression of CAR-T-cell mediated ALL-cell lysis in a microcavity array is shown in the video sequence. CAR-T-cells are the small cells attached to larger ALL-cells via an immunologic synapse.

These approaches will lead to the development of a new assay that will be able to determine CAR-T-cell-efficacy in the bone marrow.