PBMC and product characterization
PBMC used for ide-cel manufacturing and DP characteristics were evaluated from cryopreserved samples produced during the ide-cel clinical manufacturing process. PBMC or DP samples were thawed, washed and stained with cocktails of fluorescently labeled antibodies targeting T cell differentiation, exhaustion and senescence markers as described below. Flow cytometry was performed to assess phenotypic characteristics of PBMC and DP T cells based on surface expression of CD45RA (BD Biosciences, HI100-BV605; volume per test = 5, final staining concentration = 1.25 µg mlTo evaluate antigen-specific function (IFN-γ secretion) of ide-cel, DPs were thawed, washed and cultured in the presence of recombinant human BCMA. After 22–24 h, culture supernatants were collected, and the concentration of IFN-γ secretion was assessed via automated immunoassay (Protein Simple, Human IFNγ Single Plex).Prior therapy washout was calculated for six common drug classes (HSCT, alkylating agents, anti-CD38 agents, corticosteroids, IMiDs and proteasome inhibitors) and was defined as the date of last known exposure until the date of apheresis for CAR T. The washout time was transformed as 1 per washout for patients with a recorded prior exposure; nonexposure was represented by a value of 0. A Spearman correlation was then used to test for a relationship between PBMC attributes and time-since-last-exposure for each drug class.