Towards predicting response to daratumumab therapy in relapsed/refractory multiple myeloma
Daratumumab (DARA), an anti-CD38 IgG1-κ monoclonal antibody, has become a mainstay in multiple myeloma (MM) therapy regimens. Unfortunately, there is great interpatient variability in its efficacy. Here, we set out to develop a patient-specific sensitivity test for DARA therapy.
Both cell lines and primary MM samples were cultured in a PuraMatrix hydrogel-based three-dimensional culture system, supplemented with pro-survival cytokines IL-6 and APRIL. To measure the in vitro response to DARA by MM cells, we performed both complement-dependent cytotoxicity (CDC) and antibody-dependent cellular cytotoxicity (ADCC) assays. We added 10% pooled human serum or allogeneic PBMCs to the culture system, for CDC and ADCC, respectively. After 24h, specific lysis was measured with flow cytometry using ToPro3 stain and absolute counting beads. Responses to DARA by primary MM in the culture model were compared to the clinical responses of the corresponding patients.
Conventional two-dimensional CDC and ADCC assays were reproduced in a 3D culture with human MM cell lines (HMCL) and Daudi cells. The latter were very sensitive to both CDC and ADCC and functioned as a positive control. HMCL showed varying levels of sensitivity to ADCC, but very little to no sensitivity to CDC. DARA assays were then successfully carried out with primary MM samples, with great interpatient differences in DARA efficacy. Incubation of samples with ATRA resulted in an increased efficacy of DARA treatment. In a preliminary analysis, we found an association between the in vitro results and the clinical response to DARA.
Here we demonstrate that the use of the therapeutic monoclonal antibody DARA in a 3D hydrogel-based culture system is feasible and in line with prior work on DARA. The response to DARA by primary MM cells seems to be congruent with the clinical response to DARA by the corresponding patient. Further work should prove whether these data are robust enough to allow for a prediction of DARA sensitivity prior to the start of therapy by a relapsed/refractory MM patient.