Identifying clinical response to daratumumab therapy in relapsed/refractory multiple myeloma using a patient-derived in vitro model

Abstract

Response to daratumumab in patients with relapsed/refractory multiple myeloma is heterogeneous, and a reliable biomarker of response is lacking. We aimed to develop a method that identifies response to daratumumab therapy. Patient-derived MM cells were collected before start of daratumumab treatment and were cultured in a hydrogel-based culture system. The extent of antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity in vitro was associated with both clinical response and progression-free survival in corresponding patients. Together, our results demonstrate that in vitro sensitivity to daratumumab therapy in a hydrogel culture with primary MM cells might be used to identify patients most likely to benefit from treatment.

Keywords: daratumumab; multiple myeloma; patient‐derived plasma cells; relapsed/refractory multiple myeloma; response to therapy.

FIGURE 1

CD38 mean fluorescent intensity (MFI), antibody‐dependent cellular cytotoxicity (ADCC), and complement‐dependent cytotoxicity (CDC) associate with clinical response to daratumumab therapy. (A) Comparison of CD38 mean fluorescent intensity (MFI) in plasma cells from patients with relapsed/refractory multiple myeloma (RRMM) that either did not respond clinically (<partial response [PR], n = 5) or that did respond clinically (≥PR, n = 8). Dots denote individual patient samples, while the dashed line (MFI 15015) corresponds with the optimal cut‐off value as determined by the Youden's index in (B). Statistical difference between these groups was calculated using a two‐tailed Mann–Whitney test. Horizontal bar represents the median and error bars indicate the interquartile range. (B) Receiver operating characteristics (ROC) curve of data in (A). The dashed line represents an AUC_ROC of 0.5 and indicates no predictive value. Green dot identifies the Youden's index. (C) Confusion matrix comparing clinical responses of patients with predicted responses based on the cut‐off value of a CD38 MFI of 15,015, as established in (B). (D) Results of in vitro ADCC assays. RRMM patient‐derived bone marrow mononuclear cells were treated with daratumumab or isotype control and incubated for 24 h with healthy‐donor PBMCs at an effector‐to‐target ratio of 10:1. Samples were derived from nine patients that achieved a clinical response and five patients that did not achieve a measurable response. ADCC was calculated on the absolute number of surviving CD138+CD38+ plasma cells in the treated versus isotype conditions, as measured by flow cytometry. Dotted line (38.5% cell death) corresponds with the optimal cut‐off value. (E) ROC curve of ADCC results in (D). Method similar to (B). (F) Confusion matrix comparing clinical responses of patients with predicted responses based on the cut‐off value of 38.5% specific cell death after ADCC, as established in (E). (G) Results of in vitro CDC assays, similar to (D), with RRMM patients that did not obtain a PR (n = 4) and patients that obtained a PR or better (n = 8). CDC was measured by adding pooled healthy‐donor non‐heat inactivated serum. The dotted line (11.7% cell death) corresponds with the optimal cut‐off value. (H) ROC curve of CDC data in (G). Method similar to (B) and (E). (I) Confusion matrix comparing clinical responses of patients with predicted responses based on the cut‐off value of 11.7% specific cell death after CDC, as established in (H). (J) Comparison of the clinical response of each included patient with the classification of the response according to ADCC, CDC, and CD38 MFI. Each column represents an individual patient. Blue color denotes a PR for the clinical response or a positive response prediction for each of the respective tests, while red denotes a negative response. Grey square indicates no test result available.

FIGURE 2

Progression‐free survival is higher in patients with antibody‐dependent cellular cytotoxicity (ADCC) or complement‐dependent cytotoxicity (CDC) above the cut‐off value. (A) Kaplan–Meier curve of the progression‐free survival (PFS) of daratumumab treatment, comparing patients with CD38 mean fluorescent intensity (MFI) above and below the cut‐off value of 15015 MFI. Statistical difference between groups was calculated with the Wilcoxon Test. Incorrectly classified patient samples are marked with a circle. Sample MM13 was incorrectly classified as a response, with CD38 expression above the cut‐off value. Sample MM5 was incorrectly classified as a non‐responder, with CD38 expression below the cut‐of value. (B) Comparison of PFS of relapsed/refractory multiple myeloma (RRMM) patients with in vitro ADCC above or below cut‐off value of 38.5% cell death as established previously. Incorrectly classified patient samples are marked with a circle. Sample MM2 was incorrectly classified as a non‐responder, as in vitro ADCC was below 38.5% (C) PFS of RRMM patients of which in vitro CDC was above or below cut‐off value of 11.7% cell death, as established previously. Incorrectly classified patient samples are marked with a circle. Sample MM5 was incorrectly classified as a non‐responder based on an in vitro CDC below 11.7%.