CD319 (SLAMF7) an alternative marker for detecting plasma cells in the presence of daratumumab or elotuzumab

Abstract

Background: Daratumumab is an anti-CD38 immunotherapeutic drug that has increasingly been used to treat patients with heavily pre-treated and relapsed/refractory multiple myeloma. In so doing, the detection of CD38 antigen on plasma cells by flow cytometry is impeded. We hypothesized that alternative markers can be used in place or in addition to CD38 when detecting plasma cells post-treated with daratumumab.Methods: A total of 16 alternative markers were tested using 22 bone marrow aspirates from patients with plasma cell neoplasm. The ability of selected markers to discern plasma cells from other hematopoietic cells were evaluated. The stability of tested markers when stored at 4 or 25 C after T = 0, 24, 48, and 72 h was also established. Finally, selected markers were incorporated into a panel used for monitoring multiple myeloma measurable residual disease to test their utility to identify plasma cells in the presence of daratumumab and/or elotuzumab (anti-CD319) drugs.Results: Out of the 16 tested markers, CD319, CD54, CD229, CD317, and p63 were expressed by >90% of the plasma cells. Only CD319, CD54, and CD229 achieved 100% detection sensitivity. Further analysis showed that CD319 was better than CD229 and CD54 at resolving plasma cells from background hematopoietic cells, with CD54 being the worst (resolution metric, mean ± SD: CD319 [2.04 ± 0.86]; CD229 [1.47 ± 0.45]; and CD54 [1.22 ± 0.60]). CD229 was expressed by >90% of T lymphocytes, whereas CD319 was expressed preferentially by the CD8+ T cells and less frequently in CD4+ T cells. Additionally, CD229 was found on >60% of B and NK cells, as well as minor subsets of monocytes and granulocytes. CD319 was expressed on most NK cells and a minor subset of B cells, granulocytes, and monocytes. Even though CD229 and CD319 were expressed by different leukocyte subsets, their expression levels were highest on plasma cells. The expression of CD138 on plasma cells was significantly lower after storage at 4 C, while the expression levels of CD38, CD229, and CD319 remained stable at 4 or 25 C. Using limiting dilution experiments, the treatment of cells with daratumumab severely impeded the detection of CD38 antigen on plasma cells, whereas elotuzumab treatment did not block detection of CD319 on plasma cells.

Evaluation of measurable residual disease in multiple myeloma by multiparametric flow cytometry: Current paradigm, guidelines, and future applications

“…Complicating the situation further, the other primary gating marker, CD138, can be heterogeneously expressed on PCs and shed from the cell surface under unfavourable storage conditions and/or with cell ageing. 49,50 Currently, there are no recommendations as to how one should circumvent the issue with PCs detection when CD38 and/or CD138 is compromised. Multiple alternative markers have been explored, such as CD54, CD229, and CD319 which are expressed by most PCs.…”

“…Multiple alternative markers have been explored, such as CD54, CD229, and CD319 which are expressed by most PCs. 50 These markers, however, are not PC-specific as they can be expressed at the same intensities by other leucocyte subsets as PCs, limiting their potential to completely replace CD38 and/or CD138 for detecting PCs. The expression of CD269 was found to be more PC-specific but not all PCs express this particular marker.…”

“…The CD38 multiepitope reagent, however, only partially restores the detection of CD38 in the presence of daratumumab, and the intensity remains diminished, with more than 50% loss in fluorescence intensity when compared to an untreated samples. 50 VS38, which is a mouse mAb that recognizes CLIMP-63…”

“…We and others have shown that while VS38 is highly expressed in most PCs, it is also expressed by other haematopoietic cells including monocytes, myeloid cells, and a subpopulation of B cells. 50,52…”

Elotuzumab for the treatment of extramedullary myeloma: a retrospective analysis of clinical efficacy and SLAMF7 expression patterns

“…However, the emergence of antigen loss variants during therapy with BCMA-directed CAR T cells has been documented, leading to fulminant recurrence of the disease [5]. Interestingly, antigen reduction under therapeutic selection pressure has so far not been reported for SLAMF7 [36]. Thus, we have generated a SLAMF7-directed CAR equipped with an antigen-binding domain derived from elotuzumab [15].…”