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3514 Mechanisms of Immunosuppression By FVIII-Specific TCR Engineered Human Regulatory T Cells

Disorders of Coagulation or Fibrinolysis
Program: Oral and Poster Abstracts
Session: 322. Disorders of Coagulation or Fibrinolysis: Poster III
Monday, December 7, 2015, 6:00 PM-8:00 PM
Hall A, Level 2 (Orange County Convention Center)

Yong Chan Kim, PhD1*, Ai-Hong Zhang, MS, PhD2*, Jeong Heon Yoon, PhD1* and David William Scott, PhD1

1Department of Medicine, Uniformed Services University of the Health Sciences, Bethesda, MD
2Department of Medicine, Uniformed Services university of the Health Sciences, Bethesda, MD

Expanded antigen-specific engineered regulatory T cells (Tregs) have been proposed for potential clinical application for the treatment of undesirable immune responses, such as inhibitor responses in hemophilia A patients and autoimmune diseases.  By providing an antigen-specific T-cell receptor (TCR) to polyclonal natural Tregs, we suggested that antigen-specific engineered Tregs would migrate specifically to particular target tissues and induce antigen-specific immune tolerance in the local milieu. Previously, we developed FVIII C2-specific Tregs using a long-term stabilization protocol in vitro and demonstrated that these stabilized engineered Tregs successfully modulated FVIII-specific T-cell- and B-cell immune responses. Herein, we examined the mechanism of suppression by antigen-specific engineered Tregs compared to polyclonal normal natural Tregs.

Initially, we tested whether these FVIII-specific engineered Tregs were able to suppress neighboring activated T-cell effectors locally.  We found that FVIII C2-specific Tregs strongly suppressed myelin basic protein (MBP)-specific T effectors by presentation of both specific antigens in same APC population.  However, we also observed that C2-specific Tregs could suppress MBP-specific T effectors presented on different APCs. These results imply contactless suppressive function of C2-specific engineered Tregs.  Using a modified trans-well suppression assay, in which physical distance and clear separation between Tregs and a set of T effectors was created, we found that C2-specific activated Tregs showed significant contactless suppression only when T effectors were also present.  In addition, and confirming previous studies with polyclonal Tregs, suppression by FVIII-specific engineered Tregs could be overcome by increasing the dose of IL-2 in co-culture media.  This suggests that Tregs act, in part, by usurping IL-2 needed by T effectors to proliferate. Surprisingly, neutralization of CTLA-4 did not interfere with FVIII C2-specific suppression of engineered Tregs in contrast to the reversal seen with anti-CD3e-driven non-specific immunosuppression. 

Our data strongly suggest that suppressive function of FVIII-specific engineered Tregs is not restricted to cell-to-cell contact. Rather cross-talk of engineered Tregs and T effectors potentially generate a contactless suppressive mechanism to suppress other FVIII-specific multiple effector cells in the local milieu for effective immune tolerance. Understanding the mechanism of contactless suppression mechanism should provide critical clues to develop more effective engineered Tregs as a therapeutic tool in hemophilia A.

(Supported by NIH grants HL061883 and HL126727)

Disclosures: Kim: Henry Jackson Foundation: Other: patent filed . Zhang: Henry Jackson Foundation: Other: patent filed . Scott: Henry Jackson Foundation: Other: patent filed .

*signifies non-member of ASH