High-dose porcine hematopoietic cell transplantation combined with CD40 ligand blockade in baboons prevents an induced anti-pig humoral response.
BACKGROUND
In pig-to-primate organ transplantation, hyperacute rejection can be prevented, but the organ is rejected within days by acute vascular rejection, in which induced high-affinity anti-Gal alpha1-3Gal (alphaGal) IgG and possibly antibodies directed against new porcine (non-alphaGal) antigenic determinants are considered to play a major role. We have explored the role of an anti-CD40L monoclonal antibody in modifying the humoral response to porcine hematopoietic cells in baboons pretreated with a nonmyeloablative regimen.


METHODS
Porcine peripheral blood mobilized progenitor cells obtained by leukapheresis from both major histocompatibility complex-inbred miniature swine (n=7) and human decay-accelerating factor pigs (n=3) were transplanted into baboons. Group 1 baboons (n=3) underwent whole body (300 cGy) and thymic (700 cGy) irradiation, T cell depletion with ATG, complement depletion with cobra venom factor, short courses of cyclosporine, mycophenolate mofetil, porcine hematopoietic growth factors, and anti-alphaGal antibody depletion by immunoadsorption before transplantation of high doses (2-4 x 10(10)/cells/kg) of peripheral blood mobilized progenitor cells. In group 2 (n=5), cyclosporine was replaced by eight doses of anti-CD40L monoclonal antibodies over 14 days. The group 3 baboons (n=2) received the group 1 regimen plus 2 doses of anti-CD40L monoclonal antibodies (on days 0 and 2).


RESULTS
In group 1, sensitization to alphaGal (with increases in IgM and IgG of 3- to 6-fold and 100-fold, respectively) and the development of antibodies to new non-alphaGal porcine antigens occurred within 20 days. In group 2, no sensitization to alphaGal or non-alphaGal determinants was seen, but alphaGal-reactive antibodies did return to their pre- peripheral blood mobilized progenitor cells transplant levels. In group 3, attenuated sensitization to alphaGal antigens was seen after cessation of cyclosporine and mycophenolate mofetil therapy at 30 days (IgM 4-fold, IgG 8-30-fold), but no antibodies developed against new porcine determinants. In no baboon did anti-CD40L monoclonal antibodies prevent sensitization to its own murine antigens.


CONCLUSIONS
We believe these studies are the first to consistently demonstrate prevention of a secondary humoral response after cell or organ transplantation in a pig-to-primate model. The development of sensitization to the murine elements of the anti-CD40L monoclonal antibodies suggests that nonresponsiveness to cell membrane-bound antigen (e.g., alphaGal) is a specific phenomenon and not a general manifestation of immunological unresponsiveness. T cell costimulatory blockade may facilitate induction of mixed hematopoietic chimerism and, consequently, of tolerance to pig organs and tissues.
Bühler
L
L
Transplantation Biology Research Center, Massachusetts General Hospital, Harvard Medical School, Boston 02129, USA.
Awwad
M
M
Basker
M
M
Gojo
S
S
Watts
A
A
Treter
S
S
Nash
K
K
Oravec
G
G
Chang
Q
Q
Thall
A
A
Down
J D
JD
Sykes
M
M
Andrews
D
D
Sackstein
R
R
White-Scharf
M E
ME
Sachs
D H
DH
Cooper
D K
DK
D000818:Animals; D000911:Antibodies, Monoclonal / Q000097:blood / Q000276:immunology / Q000494:pharmacology; D000917:Antibody Formation / Q000187:drug effects; D001769:Blood / Q000276:immunology; D023201:CD40 Ligand; D003602:Cytotoxicity, Immunologic; D018380:Hematopoietic Stem Cell Transplantation; D006801:Humans; D008562:Membrane Glycoproteins / Q000037:antagonists & inhibitors* / Q000276:immunology; D051379:Mice; D009017:Morbidity; D009026:Mortality; D010215:Papio / Q000276:immunology*; D013552:Swine; D013556:Swine, Miniature / Q000276:immunology*; D019172:Transplantation Conditioning / Q000379:methods; D014183:Transplantation, Heterologous / Q000276:immunology* / Q000401:mortality
D000911:Antibodies, Monoclonal; D008562:Membrane Glycoproteins; D023201:CD40 Ligand