Association of natural killer cell depletion with induction of mixed chimerism and allograft tolerance in non-human primates

BACKGROUND

Nonmyeloablative T cell depletion followed by donor bone marrow infusion has proved to be an effective approach to induction of mixed chimerism and tolerance of organ allografts in non-human primates. To help define the mechanisms involved we have compared T cell depletion with ATG versus anti-CD2 monoclonal antibody with respect to establishment of mixed chimerism and induction of tolerance.

METHOD

Both nonmyeloablative regimens included low dose total body irradiation (1.5 Gy x 2), thymic irradiation (7 Gy), splenectomy and kidney plus donor bone marrow transplantation, followed by a 4-week posttransplant course of cyclosporine. In addition, the ATG group (13 recipients) received antithymocyte globulin, although the LOCD2b group (10 recipients) were treated with an anti-CD2 monoclonal antibody (LOCD2b).

RESULTS

In the ATG group, 11 of 13 monkeys developed multilineage chimerism and 9 survived for more than 100 days without kidney allograft rejection. In contrast, 0/10 monkeys in the LOCD2b group developed chimerism, 5 died of infection and 5 suffered progressive rejection; only 1 recipient survived beyond 100 days. Sequential monitoring of peripheral blood mononuclear cells revealed greater T cell (CD3+) depletion in the LOCD2b-treated animals compared to those receiving ATG. However, NK cells (CD16+CD8+) were significantly more depleted in the ATG group and NK function remained abrogated longer after ATG than LOCD2b treatment (3 weeks vs. <5 days).

CONCLUSION

Despite excellent T cell depletion by LoCD2b, ATG was more effective in inducing chimerism and tolerance. This difference correlated with anti-NK activity of the two reagents. These data suggest that NK cells may also resist engraftment of allogeneic bone marrow cells in this model.

Long-term outcome and alloantibody production in a non-myeloablative regimen for induction of renal allograft tolerance

BACKGROUND

Multilineage chimerism and long-term acceptance of renal allografts has been produced in non-human primates conditioned with a nonmyeloablative regimen. Our study was undertaken to evaluate the immunological and pathological status of long-term survivors and to define the role of splenectomy and of the primarily vascularized kidney in the regimen.

METHOD

Monkeys were treated with the basic regimen, including: total body irradiation, thymic irradiation, antithymocyte globulin, donor bone marrow transplantation, and a 4-week course of cyclosporine after which no further immunosuppression was given. They were divided into four groups according to the timing of kidney transplantation (KTx) and splenectomy as follows; group A (n=13): KTx and splenectomy on the day of donor bone marrow transplantation (day 0); group B (n=3): KTx on day 0 without splenectomy; group C (n=7): splenectomy on day 0 but delayed KTx until 3 to 16 weeks post-donor bone marrow transplantation; group D (n=3): both splenectomy and KTx delayed until day 120 post-donor bone marrow transplantation.

RESULTS

In group A, 11 of 13 monkeys developed chimerism and 9 monkeys achieved long-term survival of 4 to 70 months without evidence of chronic vascular rejection. Alloantibodies were detected in only one long-term survivor. In contrast, all three monkeys in group B developed alloantibodies and rejected their allografts. In group C, long-term survival without alloantibody production was observed in two of three monkeys that had developed chimerism. In group D, all three recipients were sensitized and rejected the kidney allografts rapidly after transplantation.

CONCLUSIONS

1) Production of anti-donor antibody was prevented in most recipients that developed mixed chimerism in the regimens with splenectomy at the time of donor bone marrow transplantation. 2) If splenectomy is not included in the initial conditioning regimen, induction of B cell tolerance is less likely and the result is late onset of alloantibody production and allograft rejection. 3) Immediate transplantation of the kidney at the time of recipient conditioning is not essential for induction of donor specific hyporesponsiveness by bone marrow transplantation.

The interaction of (1-4)-fragment of thymosin beta 4 with calmodulin-sensitive cAMP phosphodiesterase from hypothalamus

Evidence was accumulated indicating that cyclic nucleotides are involved in regulation of growth, differentiation and function of lymphoid cells. It was previously shown that the N-fragment (1-4) of thymosin beta 4 (Ac-Ser-Asp-Lys-Pro-OH) inhibits in vivo the entry of cell populations into S-phase. In the course of the study of the interrelationship between the immune and neuroendocrine systems we have found that the tetrapeptide caused incomplete competitive inhibition of hypothalamic calmodulin (CaM)-dependent phosphodiesterase (PDE) stimulated by CaM. In the presence of the peptide, the 20-fold increase of the constant for PDE activation by CaM was accompanied by an insignificant rise in the maximum rate of cAMP hydrolysis. The value of the inhibition constant (Ki) amounted to 600 nM. In the absence of CaM, the peptide at saturating concentrations reduced the basal activity of PDE nearly 2- to 3-fold. The effect of the peptide on PDE was noncompetitive with respect to cAMP. The results support our suggestion that the tetrapeptide realizes its effects in the immuno-neuroendocrine system by the mechanism of cyclic nucleotide metabolism.