Engraftment of quiescent progenitors and conversion to full chimerism after nonmyelosuppressive conditioning and hematopoietic cell transplantation in miniature swine

Our laboratory has previously reported a nonmyelosuppressive preparative regimen for hematopoietic cell transplantation that leads to mixed chimerism and allograft tolerance in miniature swine across minor and major histocompatibility disparities. Stable chimerism persisted in most of these animals but was restricted to T cells and confined to peripheral blood. Because of the importance of myeloid and erythroid progenitors for the treatment of hematologic disorders, the objective of this study was to assess whether such cells existed in the bone marrow of these lymphoid chimeras as an indication of functional engraftment. Colony-formation assays were performed on donor inocula before infusion and on bone marrow cells harvested from the transplant recipients. Donor-origin myeloid/erythroid progenitor colonies were detected in bone marrow from 6 of 7 lymphoid chimeric recipients. A delayed donor leukocyte infusion successfully converted a stable lymphoid chimera to full multilineage chimerism within 2 weeks. Donor-origin myeloid/erythroid progenitors could be detected in the bone marrow of a host-matched recipient after myeloablation and adoptive transfer of mobilized cells from one of the engrafted lymphoid chimeras. These data suggest that even when only lymphoid chimerism is readily detected by flow cytometry, dormant myeloid/erythroid progenitors can exist and subsequent conversion to full donor chimerism can be achieved. The ability to establish multilineage engraftment and chimerism without significant toxicity may have important clinical implications for the management of nonmalignant hematopoietic disorders and hematologic malignancies.

A simple method to calculate the influence of dose inhomogeneity and fractionation in normal tissue complication probability evaluation

PURPOSE

Since volumetric dose distributions are available with 3-dimensional radiotherapy treatment planning they can be used in statistical evaluation of response to radiation. This report presents a method to calculate the influence of dose inhomogeneity and fractionation in normal tissue complication probability evaluation.

METHODS

The mathematical expression for the calculation of normal tissue complication probability has been derived combining the Lyman model with the histogram reduction method of Kutcher et al. [14] and using the normalized total dose (NTD) instead of the total dose.

RESULTS

The fitting of published tolerance data, in case of homogeneous or partial brain irradiation, has been considered. For the same total or partial volume homogeneous irradiation of the brain, curves of normal tissue complication probability have been calculated with fraction size of 1.5 Gy and of 3 Gy instead of 2 Gy, to show the influence of fraction size. The influence of dose distribution inhomogeneity and alpha/beta value has also been simulated: considering alpha/beta = 1.6 Gy or alpha/beta = 4.1 Gy for kidney clinical nephritis, the calculated curves of normal tissue complication probability are shown.

CONCLUSION

Combining NTD calculations and histogram reduction techniques, normal tissue complication probability can be estimated taking into account the most relevant contributing factors, including the volume effect.