A Randomized Phase II Study of Xcellerated T Cells™ with or without Prior Fludarabine Therapy in Patients with Relapsed or Refractory Multiple Myeloma.

Background: T cells from myeloma subjects can be activated and expanded ex vivo using the Xcellerate™ Process, in which peripheral blood mononuclear cells are incubated with anti-CD3 and anti-CD28 antibody-coated magnetic beads (Xcyte™-Dynabeads®). In a previous study (Borrello et al., ASCO 2004), Xcellerated T Cells administered to myeloma subjects following high dose chemotherapy and autologous stem cell transplantation led to accelerated lymphocyte recovery and restoration of the T cell receptor repertoire. In the current study, subjects with relapsed or refractory myeloma were randomized to Xcellerated T Cells with or without one cycle of fludarabine prior to Xcellerated T Cells. Fludarabine is being used to assess the influence of lymphoablation on the anti-tumor and immune reconstitution effects of T cell therapy; it has previously been reported to have no significant activty in myeloma (Kraut et al., Invest. New Drugs, 1990).

Methods: Approximately 30 subjects are planned to receive treatment. Each receives a single dose of 60–100 x 10⁹ Xcellerated T Cells. Subjects on the fludarabine arm receive a single cycle (5 days at 25 mg/m²), completed 4 days prior to the Xcellerated T Cell infusion.

Results: 17 subjects have been enrolled and 13 treated to date, with median last f/u visit of 28 days (range 0–140). Xcellerated T Cells were successfully manufactured in all subjects, with T cell expansion 136 ± 61 fold (mean ± SD), with 79.2 ± 13.8 x 10⁹ cells infused, and final product 98.0 ± 2.0% T cells (n=13). There have been no reported serious adverse events related to Xcellerated T Cells. In the fludarabine arm, lymphocytes decreased from 1,228 ± 290/mm³ (mean ± SEM) to 402 ± 164 following fludarabine, and then increased to 1,772 ± 278 on Day 14 following T cell infusion (n=7). In the non-fludarabine arm, lymphocyte counts increased from 1,186 ± 252 to 3,204 ± 545 on Day 14 (n=4). Lymphocytes were comprised of both CD4⁺ and CD8⁺ T cells. Increases were observed in NK cells from 77 ± 26 to 121 ± 25, monocytes from 166 ± 44 to 220 ± 30 and platelets from 218 ± 16 to 235 ± 24 by Day 14 (n=11). In the non-fludarabine arm, neutrophils increased from 3.6 ± 0.9 to 4.8 ± 0.6 on Day 1. On the fludarabine arm, 3 of 6 subjects developed Grade 4 neutropenia and one developed Grade 3 thrombocytopenia. Seven subjects were evaluable for serum M-protein measurements to Day 28. One of three fludarabine treated subjects had an M-protein decrease of 38%.

Conclusions: Xcellerated T Cells were well-tolerated and led to increased lymphocytes, including T cells and NK cells. Increases in other hematologic parameters, including neutrophils and platelets were also observed. In this patient population, fludarabine is lymphoablative and also can cause neutropenia and thrombocytopenia. The fludarabine schedule has been decreased from 5 to 3 days. A decrease in M-protein has been observed in one of three fludarabine-treated subjects; data on additional subjects will be presented.