Cardiac Xenotransplantation: Reconstituted B Cells After Rituxan Treatment Maintain Their Repertoire But Have a Muted Response to Xenoantigens

A. Singh,¹ P. Corcoran,¹ B. Lewis,² M. Thomas,² D. Ayers,³ K. Horvath,¹ M. Mohiuddin.¹

¹CSRP/NIH/NHLBI, NIH, Bethesda, MD
²DVR/ORS, NIH, Bethesda, MD
³Revivicor Inc, Blacksburg, VA.

Meeting: 2015 American Transplant Congress

Abstract number: B292

Keywords: B cells, CD20, Xenotransplantation

Session Information

Session Name: Poster Session B: Vascularized Composite Tissue Allografts and Xenotransplantation

Session Type: Poster Session

Date: Sunday, May 3, 2015

Session Time: 5:30pm-6:30pm

Presentation Time: 5:30pm-6:30pm

Location: Exhibit Hall E

Background: Xentoranplantation (XTx) remains an option for end stage organ failure. Recently we have reported cardiac xenograft survival of over one year pig to baboon hetertotopic transplatation model. One major component of the modified immunosuppression (IS) included depletion of B cells by Rituxan (anti-CD20 antibody). In this study we have investigated the effect of Rituxan treatment on the infection rate in the recipient baboon and also evaluated the repertoire and function of re-emerging (RE) B cells.

Methods: Heterotopic cardiac XTx was performed from GTKOhCD46Tg (n=8) and GTKOhCD46TBM (n=5) pig to baboons using IS regimen that included anti thymocyte globulin, Rituxan on days -7, 0, 7, 14, mycophenolate mofitel, cobra venom factor, and co-stimulation blockade (anti-CD154 or anti-CD40) antibody. Baboon peripheral blood lymphocytes (PBLs) were collected twice a week for the first two months after cardiac XTx and then monthly thereafter. FACS analysis was done on PBLs with fluorescence conjugated anti-human CD3, CD4, CD5, CD19, CD20, CD24, CD38, IgD and IgM monoclonal antibodies to analyze the percentages of the B cells repertoire (plasma, naive, transitional and memory). Antibody secretion was also measured by ELISA from the supernatant of stimulated PBLs with anti IgM antibody.

Results: The Rituxan treatment depleted B cells completely at the time of XTx. Recipient baboons tolerated IS very well and there was no significant increase in infection rate while the B cells were depleted. B cells re-emerged after 8-10 weeks of last dose of Rituxan. There was no significant difference found in relative percentages of RE- naive (CD20+CD24loCD38lo), transitional (CD20+CD24++CD38++) and memory (CD20+ CD27+) B cells as compared to naive animals. However, plasma cells (CD19loCD20neg and CD38++) were slightly increased in RE- B cells. We have also found that antibody secretion (IgG and IgM) by RE- B cells from XTx baboons were significantly lower compared to naive baboon.

Conclusion: Transient B cell depletion by Rituxan treatment in cardiac XTx does not increase the risk of infection rate. The RE- B cells were not significantly different from the normal B cells. With recovery, immune response returned to normal, while the antibody secretion from RE- B cells was significantly reduced .

To cite this abstract in AMA style:

Singh A, Corcoran P, Lewis B, Thomas M, Ayers D, Horvath K, Mohiuddin M. Cardiac Xenotransplantation: Reconstituted B Cells After Rituxan Treatment Maintain Their Repertoire But Have a Muted Response to Xenoantigens [abstract]. Am J Transplant. 2015; 15 (suppl 3). https://atcmeetingabstracts.com/abstract/cardiac-xenotransplantation-reconstituted-b-cells-after-rituxan-treatment-maintain-their-repertoire-but-have-a-muted-response-to-xenoantigens/. Accessed June 5, 2025.

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