Induction Of Anti-Myeloma Cellular and Humoral Immunity By Pre-Targeting Clonogenic Myeloma Cells Prior To Stem Cell Transplant With T Cells Armed With Anti-CD3 x Anti-CD20 Bispecific Antibody Leads To Transfer Of Cellular and Humoral Anti-Myeloma Immunity

A phase Ib trial was conducted in standard and high risk multiple myeloma (MM) patients to determine whether infusions of anti-CD3 x anti-CD20 bispecific antibody (CD20Bi) armed activated T cells (aATC) prior to autologous stem cell transplant (ASCT) were safe and would induce anti-myeloma (anti-MM) immunity that could be detected after ASCT. We hypothesized that targeting CD20⁺/CD138^- myeloma clonogenic cells with aATC would release “MM antigens” including anti-Sry-HMG-box 2 (SOX-2). Engagement of target cells by aATC also induces release of Th₁ cytokines by aATC creating an environment conducive for in situ immunization against MM antigens. Twelve patients received two infusions of 10¹⁰ one week apart and within 4 weeks prior to ASCT. Four patients received a 10 x 10⁹ aATC booster infusion between 6 and 18 months after ASCT. There were significant increases in the fraction of patients who developed IFN-g EliSpots directed at CD20+ Daudi lymphoma cells (p<0.06), CD20 negative RPMI 8226 multiple myeloma cells (p<0.02), and K562 natural killer cell targets (p<0.01) from 6 to 12 months after ASCT. Specific cytotoxicity directed at Daudi (p<0.03), K562 (p<0.009), and RPMI 8226 (p<0.02) targets increased significantly after aATC infusions and post ASCT compared to pre infusion baseline cytotoxicity. SOX-2 IgG antibody levels increased above baseline after aATC infusions (p<0.002) and post ASCT (p<0.02) (Fig. 1A). There was no significant difference observed between pre and 1 month post ASCT in anti-SOX-2 levels or between pre and 3 month post ASCT serum samples from control ASCT patients who did not receive IT (Fig. 1B). In order to determine whether there was an association between the level of anti-SOX-2 antibodies and clinical outcome, anti-SOX-2 antibody levels were plotted in patients who progressed and those who did not progress. The box plots show the clear separation between two groups. The median anti-SOX-2 antibody levels at 3 months after ASCT in patients who relapsed was 19.7 ng/ml (25-75%, 8.6 - 40.3) and in patients who remained in remission was 48.1 ng/ml (37.5 - 73.3), these data suggest that anti-SOX-2 levels may predict clinical outcomes (Fig. 1C). There were no dose-limiting toxicities. In summary, aATC infusions pre ASCT induced anti-myeloma IFN-g EliSpot and anti-SOX-2 IgG responses that could be detected at 6-12 months after ASCT and these responses were boosted in 4 of 4 patients after ASCT. Data suggest that infusions of targeted T cells given prior to ASCT could induce cellular and humoral anti-myeloma immunity that could be transferred, detected, and boosted after ASCT. These results have implications for the design of immunotherapy in combination with ASCT.