Chimerism and the facilitating cell

Quantitative polymerase chain reaction assessment of chimerism in non-human primates after sex-mismatched islet and bone marrow transplantation

BACKGROUND

Accurate assessment of chimerism in recipients of islet and bone marrow transplantation (BMT) may allow for a clearer assessment of the role of chimerism in islet engraftment or rejection. A quantitative polymerase chain reaction (PCR) assay was developed for the detection of the sex-determining region of the Y chromosome (SRY) in peripheral blood samples from female non-human primate recipients of allogeneic male islets and vertebral body marrow (VBM) from the same donor.

METHODS

The assay incorporates a synthetic internal standard (IS) containing the same primer template sequences as the target to compete for primer annealing and amplification. Each DNA sample was coamplified with a constant amount of IS. The concentration of male DNA in the test samples was calculated from the regression equation of a standard curve that was generated by plotting the logarithm of the ratio of the intensities of SRY to IS PCR products versus the logarithm of known percentages of input male DNA.

RESULTS

This method allows for a correction of the variability of efficiency of the PCR technique and also overcomes the drawback of time-consuming competitive PCR. Using this assay, we quantitated the amount of male DNA in samples taken from female baboon recipients of male islets and VBM. There was detectable male donor DNA in the samples taken one day after BMT; pre-BMT samples were negative. This technique works well for samples obtained from rhesus and cynomogus monkeys as well.

CONCLUSIONS

It is a practical method for accurately evaluation of chimerism after sex-mismatched allogeneic BMT in non-human primate models.

Cardiac xenotransplantation

Heart failure is an important medical and public health problem. Although medical therapy is effective for many people, the only definitive therapy is heart transplantation, which is limited severely by the number of donors. Mechanical devices presently are used as "bridges" to transplantation. Their widespread use may solve the donor shortage problem, but at present, mechanical devices are limited by problems related to blood clotting, power supply, and foreign body infection. Cardiac xenotransplantation using animal donors is a potential biologic solution to the donor organ shortage. The immune response, consisting of hyperacute rejection, acute vascular rejection, and cellular rejection, currently prevents clinical xenotransplantation. Advances in the solution of these problems have been made using conventional immunosuppressive drugs and newer agents whose use is based on an understanding of important steps in xenoimmunity. The most exciting approaches use tools of molecular biology to create genetically engineered donors and to induce states of donor and recipient bone marrow chimerism and tolerance in xenogeneic organ recipients. The successful future strategy may use a combination of a genetically engineered donor and a chimeric recipient with or without nonspecific immunosuppressive drugs.

Donor-specific unmodified bone marrow transfusion does not facilitate intestinal engraftment after bowel transplantation in a porcine model

BACKGROUND

The immunosuppression required to prevent rejection of intestinal transplants causes a high rate of infection and lymphoma. It is crucial that immunomodulatory strategies be developed to facilitate intestinal engraftment.

METHODS

We prospectively examined the effect of unpurified donor-specific bone marrow transfusions (DSBMTs) on rejection, infection, graft-versus-host disease (GVHD), and survival after intestinal transplantations in 44 Yorkshire Landrace pigs. Four groups that differed according to presence or abscence of treatment with FK506 and DSBMT were analyzed.

RESULTS

In nonimmunosuppressed pigs, DSBMTs had no effect on survival (8 days versus 9 days in controls; p = 0.9). In FK506 pigs, DSBMTs tended to reduce survival (21 days versus 37 days in FK506 controls; p = 0.1); no difference was seen between two bone marrow dosages 5 x 10(7) or 5 x 10(8) bone marrow cells/kg. No difference in the incidence of death caused by rejection was seen between DSBMTs and controls, but there was a marked tendency toward more deaths caused by rejection in DSBMTs + FK506 versus FK506-only pigs (p = 0.09). Daily stomal assessment showed a higher rate of moderate and severe interstitial rejection in DSBMT + FK506 versus FK506-only pigs; DSBMT was also associated with increased vascular rejection. Finally, groupwise comparison showed an order of susceptibility to lethal GVHD and infection as follows: DSBMT + FK506 > FK506 > DSBMT > controls.

CONCLUSIONS

Rather than promoting engraftment, DSBMT can sensitize recipients and cause rejection after intestinal transplantation. It aggravates the risks of generalized GVHD and infection and tends to reduce graft and recipient survival. Before being applied clinically, DSBMT needs to be refined to increase its tolerogenic potential without causing GVHD.

Fetal surgery

Although most fetal defects are best managed after birth, a few with predictable, life-threatening developmental consequences have been successfully corrected in utero. Many technical problems have been solved, but preterm labor remains a significant risk to mother and fetus. Less invasive interventional techniques and fetal stem cell transplantation promise to extend the indications for intervention.