A sequential cohort study evaluating single-agent KappaMab and KappaMab combined with lenalidomide and low-dose dexamethasone in relapsed and/or refractory kappa light chain-restricted multiple myeloma (AMaRC 01-16).

KappaMab (KM; formerly MDX-1097) is a monoclonal antibody specific for the kappa myeloma antigen (KMA), a cell-surface antigen expressed on malignant plasma cells in kappa-restricted multiple myeloma (κMM), some lymphomas, occasional tonsillar B cells and in vitro activated B cells, but not on normal B cells in bone marrow. Phase I/IIa studies of single-agent KM confirmed a favourable toxicity profile and evidence of anti-myeloma activity. Ex-vivo studies demonstrating upregulation of KMA by lenalidomide, and enhanced effector-cell cytotoxicity provided the rationale for this phase IIb study where KM or KM in combination with lenalidomide and dexamethasone (KM-Rd) was administered in relapsed, refractory κMM patients. In addition, outcomes for a real-world matched case-control cohort from the Australian and New Zealand Myeloma and Related Diseases Registry (MRDR) who received Rd were compared to the KM-Rd cohort. KM-Rd demonstrated an overall response rate of 82.5% which compared favourably to the Rd-MRDR cohort of 45.1%. Both single-agent KM and KM-Rd regimens were well tolerated, with the KM-Rd safety profile similar to patients given only Rd in other clinical settings. Based on the excellent safety profile and significant efficacy, further clinical trials escalating the KM dose and pairing KM with other standard-of-care treatments are planned.

Changes in immune cell populations following KappaMab, lenalidomide and low-dose dexamethasone treatment in multiple myeloma.

Objectives: Lenalidomide (LEN) is used to treat multiple myeloma (MM) and shows in vitro synergy with KappaMab (KM), a chimeric antibody specific for Kappa Myeloma antigen, an antigen exclusively expressed on the surface of kappa-restricted MM cells. Lenalidomide, dexamethasone (DEX) and KM control MM via multiple immunomodulatory mechanisms; however, there are several additional effects of the drug combination on immune cells. Lenalidomide can increase T cell and NKT cell cytotoxicity and dendritic cell (DC) activation in vitro. We investigated the immune cell populations in bone marrow of patients treated with KM, LEN and low-dose DEX in kappa-restricted relapsed/refractory MM ex vivo and assessed association of those changes with patient outcome. Methods: A cohort (n = 40) of patients with kappa-restricted relapsed/refractory MM, treated with KM, LEN and low-dose DEX, was analysed using a mass cytometry panel that allowed identification of immune cell subsets. Clustering analyses were used to determine significant changes in immune cell populations at time periods after treatment. Results: We found changes in five DC and 17 T-cell populations throughout treatment. We showed an increase in activated conventional DC populations, a decrease in immature/precursor DC populations, a decrease in activated CD4 T cells and an increase in effector-memory CD4 T cells and effector CD8 T cells, indicating an activated immune response. Conclusion: These data characterise the effects of LEN, DEX, and KM treatment on non-target immune cells in MM. Treatment may support destruction of MM cells by both direct action and indirect mechanisms via immune cells.