Case report: serological testing interference of daratumumab (anti-CD38) therapy in multiple myeloma

We report the case of a 54 years old patient monitored for a monoclonal IgG kappa light chain refractory relapsed multiple myeloma and receiving daratumumab immunotherapy. Daratumumab (DARA), a monoclonal anti-CD38 antibody, belongs to the new generation of immunotherapy in refractory relapse multiple myeloma which the medical pathologist should be aware of to avoid misinterpretation of biological tests performed for patients followed for this disease. By its IgG1K humanized monoclonal antibody backbone, DARA interferes in both serum protein electrophoresis and immunofixation by the presence of an alternate IgGK monoclonal peak, leading to a possible difficulty to assess treatment's response in monoclonal IgG kappa light chain myeloma. By its intrinsic anti-CD38 activity DARA also interferes in the screening and identification of red blood cells alloantibodies, due to stabilized red cells reagent expressing weakly the CD38 molecule. We manage to overcome this last interference by using dithiotreitol.

Release of biologically active kinin peptides, Met-Lys-bradykinin and Leu-Met-Lys-bradykinin from human kininogens by two major secreted aspartic proteases of Candida parapsilosis

In terms of infection incidence, the yeast Candida parapsilosis is the second after Candida albicans as causative agent of candidiases in humans. The major virulence factors of C. parapsilosis are secreted aspartic proteases (SAPPs) which help the pathogen to disseminate, acquire nutrients and dysregulate the mechanisms of innate immunity of the host. In the current work we characterized the action of two major extracellular proteases of C. parapsilosis, SAPP1 and SAPP2, on human kininogens, proteinaceous precursors of vasoactive and proinflammatory bradykinin-related peptides, collectively called the kinins. The kininogens, preferably the form with lower molecular mass, were effectively cleaved by SAPPs, with the release of two uncommon kinins, Met-Lys-bradykinin and Leu-Met-Lys-bradykinin. While optimal at acidic pH (4-5), the kinin release yield was only 2-3-fold lower at neutral pH. These peptides were able to interact with cellular kinin receptors of B2 subtype and to stimulate the human endothelial cells HMEC-1 to increased secretion of proinflammatory interleukins (ILs), IL-1β and IL-6. The analysis of the stability of SAPP-generated kinins in plasma suggested that they are biologically equivalent to bradykinin, the best agonist of B2 receptor subtype and can be quickly converted to des-Arg(9)-bradykinin, the agonist of inflammation-inducible B1 receptors.

Potent and long-lasting inhibition of human P2X2 receptors by copper

P2X receptors are ion channels gated by ATP. In rodents these channels are modulated by zinc and copper. Zinc is co-released with neurotransmitter at some synapses and can modulate neuronal activity, but the role of copper in the brain is unclear. Rat P2X2 receptors show potentiation by 2-100 μM zinc or copper in the presence of a submaximal concentration of ATP but are inhibited by zinc or copper at concentrations above 100 μM. In contrast, human P2X2 (hP2X2) receptors show no potentiation and are strongly inhibited by zinc over the range of 2-100 μM. The effect of copper on hP2X2 is of interest because there are human brain disorders in which copper concentration is altered. We found that hP2X2 receptors are potently inhibited by copper (IC50 = 40 nM). ATP responsiveness recovered extremely slowly after copper washout, with full recovery requiring over 1 h. ATP binding facilitated copper binding but not unbinding from this inhibitory site. A mutant receptor in which the first six extracellular cysteines were deleted, C(1-6)S, showed normal copper inhibition, however reducing agents dramatically accelerated recovery from copper inhibition in wild type hP2X2 and the C(1-6)S mutant, indicating that the final two disulfide bonds are required to maintain the high affinity copper binding site. Three histidine residues required for normal zinc inhibition were also required for normal copper inhibition. Humans with untreated Wilson's disease have excess amounts of copper in the brain. The high copper sensitivity of hP2X2 receptors suggests that they are non-functional in these patients.