Presentation Details
| Chimeric Antigen Receptor (CAR) T Cell Treatment in Very High Titer Inhibitor Murine Model Requires CD19 and BCMA Targeting Julia Q.Chau2, Caroline Markmann1, Zheng Zhang1, Michael C.Milone1, Bhavya S.Doshi2, 3, Vijay G.Bhoj1, Benjamin J.Samelson-Jones2, 3. 1Department of Pathology and Laboratory Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.2The Raymond G.Perelman Center for Cellular and Molecular Therapeutics, The Children's Hospital of Philadelphia, Philadelphia, PA, USA.3Department of Pediatrics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA |
Abstract
Background: The development of anti-factor VIII (FVIII) antibodies is the major complication of FVIII replacement therapy in hemophilia A (HA). Though the consequences of neutralizing anti-FVIII antibodies for HA patients has been improved by the development of non-factor therapies for HA, inhibitors remain a challenging clinical problem. The anti-FVIII immune response continues to be incompletely understood. Immunosuppression has historically been used as second-line therapy if inhibitors are resistant to ITI regimens, with anti-CD20 monoclonal antibody being the recommended agent (Valentino et al. Haemophilia 2015). As it is an antibody-mediated process, B and plasma cells must participate in the inhibitor response. We hypothesized that targeting CD19+ cells is advantageous to selective depletion of CD20+ B cells, as the former is expressed on plasmablasts and some plasma cell populations that may contribute to FVIII antibody production. Objective: We tested if administration of murine (m) T cells expressing chimeric antigen receptors (CARs) composed of an anti-mCD19 single-chain variable fragment (scFv) extracellular targeting domain (CART-19) or a B-cell maturation antigen (BCMA) ligand (mAPRIL) extracellular targeting domain (CART-BCMA) could eradicate very high-titer inhibitors in HA mice. Methods: HA mice on the C57BL/6-129 background were immunized with 1.5 IU of intravenous recombinant human FVIII protein weekly for 4-6 weeks to achieve very high-titer inhibitors. After lymphodepletion with 5 Gray total-body radiation, 4 x 106 unmodified (NTD negative control) or CAR T cells per mouse were intravenously administered. This degree of lymphodepletion is necessary for sustained T cell engraftment in immunocompetent animals and does not by itself eradicate FVIII inhibitors. Results: We initially compared administration of unmodified T cells and CART-19 in inhibitor mice (5-9/cohort) with median and interquartile range (IQR) of 340 (280-750) BU and 310 (140-370) BU, respectively. At 2 weeks, both cohorts had peripheral B cell depletion, though the CART-19 cohort was lower at 3.5 (0-6.9) compared to 14 (55-180) cells/μL for NTD (p <0.005). However, by 6 weeks, the NTD cohort had recovered (2,600 (1,600-3,900) cells/μL), while the CART-19 cohort had sustained B cell aplasia (4.4 (1.4-5.5) cells/μL). Despite this sustained B cell aplasia, the NTD and CART-19 mice retained similar persistent very high-titer inhibitors: 250 (220-320) and 240 (0-300). These results suggest that very high-titer FVIII inhibitors in the HA mice model are resistant to sustained CD19+ B cell depletion. We then compared administration of unmodified T cells, CART-BCMA, and concomitant CART-BCMA and CART-19 (CART-COMBO) in inhibitor mice (5-14 cohort) with 310 (150-440) BU, 250 (170-260) BU, and 440 (120-510) BU respectively. At 7 weeks, the mice that received CART-COMBO had a significantly lower inhibitor titer of 0 (0-3) BU compared to either the CART-BCMA (12 (2-62) BU, p <0.05) and NTD (50 (6-120) BU, p <0.005), as shown in Figure 1. Conclusions: These results indicate that very high-titer neutralizing antibodies to FVIII requires the elimination of both mature B cells and plasma cells, which can be accomplished by concomitant treatment with CART-19 and/or CART-BCMA; CD19+ B cell depletion alone is likely insufficient for eradication of very high-titer inhibitors.
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No part of this publication may be reproduced, distributed, or transmitted in any form or by any means, including photocopying, recording, or other electronic or mechanical methods, without the prior written permission of the author.