Daratumumab (Darzalex) is an IgG1k monoclonal antibody directed against CD38, which is over expressed on the plasma cells in patients with multiple myeloma. Daratumumab binds to CD38 and causes apoptosis through antibody-dependent cellular cytotoxicity or complement-dependent cytotoxicity. In 2015 the FDA approved daratumumab for the treatment of refractory multiple myeloma. Refractory meaning that patients have received at least three previous treatment protocols that failed to show sustained efficacy or any efficacy at all. Recently in May of 2018, the FDA approved daratumumab for first line therapy in combination with bortezomid, melphalan, and prednisone. The names of the drugs aren’t important, what is important is that this monoclonal antibody approach has become more common and now has moved into first line therapy meaning that more patients are going to receive this treatment. Its no secret that patients with multiple myeloma when undergoing treatment and throughout the course of the disease progression need blood component transfusions.
Typing and screening patients that are receiving daratumumab is extremely difficult and time consuming. The daratumumab not only binds to the CD38 on the malignant lymphoma cells, but it also binds to the red cells who express CD38. This causes interference in transfusion testing. Part of normal pre-transfusion testing is an antibody screen. An antibody screen is important as it tells the transfusion team if there are any alloantibodies. Alloantibodies are antibodie directed towards red cell antigens on the donor cells. If a patient has an alloantibody, it makes selecting red cells for transfusion difficult. Additional testing must be done to select antigen negative donor cells for the antibody that the recipient or the patient has. Daratumumab causes the antibody screen and corresponding antibody panel panreactive, including a positive autocontrol. This may mask any additional clinically significant alloantibody that the patient may have.
The blood bank team must perform testing prior to the patient receiving this daratumumab. The clinical team must be in communication with the blood bank. Before the patient receives the medication, the team must get a baseline type and screen. Normally they are negative, but in the off chance that they have an alloantibody, the blood bank can identify the antibody before daratumumab interferes with testing. Other testing must include a complete phenotype of the patients cell. A complete phenotype will identify all the antigens that are present on the patients cells. This tells the blood bank and clinician vital information. If the patient does NOT have the antigen present on their red cells, there is a chance that they can produce an antibody towards that antigen on donor cells making it hard to find correct donors for transfusion. For example, if the patient is negative for the E antigen, they may or may not develop an antibody towards the E antigen, so in the event that the donor red cells have the E antigen present, the patients antibody will attack those cells and cause a transfusion reaction. For the characteristics of different transfusion reactions, reference transfusion reactions.
Once the daratumumab has been given there are techniques that must be followed to obtain a sample that is suitable for testing. An enzyme called dithiothreitol (DTT) is used to negate the binding of DARA-T to CD38 on the red cell surface. This will allow for an antibody screen to be run. Unfortunately, DTT destroys the Kell antigen on the red cell surface. Kell is a clinically significant antibody in transfusions so its important to know whether or not if the patient has the antigen or not. Patients treated with DTT, MUST have Kell negative donor units, because of the risk of developing an anti-K antibody and not being able to identify it.