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BACKGROUND Organ procurement organizations (OPOs) are currently evaluated on donation rates and number of organs per donor. However, there is significant variability in market characteristics which affect transplant programs' donor organ acceptance practices and OPOs' ability to successfully place higher risk organs. The impact of transplant market characteristics on OPO performance metrics has not been evaluated. METHODS The OPO performance measures were correlated annually with the Herfindahl Hirschman Index, a standard measure of market competition for centers within the OPO donor service areas from 2003 to 2011. RESULTS More competitive donor service areas were associated with increased number of donors (P = 0.01) and eligible deaths (P < 0.001). Market competition was associated with increased use of high Donor Risk Index for kidney (P = 0.03) and liver (P = 0.01) allografts. The OPOs with increased competition in liver transplant also were noted to have a higher donor conversion rate (P < 0.001), more donors per million population (P < 0.001), and a higher utilization rate for liver allografts (P = 0.007). CONCLUSIONS These data suggest that proposals to increase district size to increase competition among transplant programs could result in improved organ utilization over time by incentivizing the use of marginal donor organs and increasing access to transplantation.

BACKGROUND Kidney transplant centers are distributed unevenly throughout 58 donor service areas (DSAs) in the United States. Market competition and transplant center density may affect transplantation access and outcomes. We evaluated the role of spatial organization of transplant centers in conjunction with market competition in the conduct of kidney transplantation. METHODS The Scientific Registry of Transplant Recipients was queried for market characteristics associated with kidney transplantation between 2003 and 2012. Market competition was calculated using the Herfindahl Hirschman Index. Kidney transplant centers were geocoded to measure spatial organization by the average nearest neighbor (ANN) method. Kidney quality was assessed by kidney donor risk index. A hierarchical negative binomial mixed effects model tested the relationship between market characteristics and annual kidney transplants by DSA. RESULTS About 152,071 kidney transplants were performed at 229 adult kidney transplant centers in 58 DSAs. Greater market competition was associated with kidney transplant center spatial clustering (P < 0.001). In multivariable analysis, more kidney transplant centers (incidence rate ratio [IRR], 1.04; P = 0.005), 100 more new listings (IRR, 1.02; P = 0.003), 100 more deceased donors (IRR, 1.23; P < 0.001), 100 more new dialysis registrants (IRR, 1.01; P < 0.001), and higher kidney donor risk index (IRR, 1.98; P < 0.001) were associated with increased kidney transplants. CONCLUSIONS After controlling for market characteristics, larger numbers of kidney transplant centers were associated with more kidney transplants and increased utilization of deceased donor kidneys. This underlines the importance of understanding geography as well as competition in improving access to kidney transplantation.

In an effort to produce stable, long-term, complete hematopoietic chimerism in unrelated RLA-matched adult rabbits, the maximum dose of total-body irradiation (TBI) tolerated both with and without autologous marrow support was defined, and it was then determined whether the maximum tolerated dose was sufficiently immunosuppressive and myeloablative to allow engraftment of allogeneic marrow. Forty rabbits received TBI at 4.8 cGy/min at doses from 525-925 cGy. All rabbits receiving 525, 625, 725 and 825 cGy survived without marrow transplantation. At 875 cGy 50% of animals died and at 925 cGy all animals died within 96 hr of TBI. Survival was not changed with autologous marrow support, with all animals receiving 825 cGy surviving, while 50% survived at 875 cGy, and none at 925 cGy. Two RLA-matched, sex and immunoglobulin allotype-mismatched pairs were transplanted following 825 cGy and were given posttransplant cyclosporine. Both recipients survived beyond 200 days posttransplant, with cytogenetic and immunoglobulin allotype evidence of complete, or nearly complete, hematopoietic engraftment. Thus, stable, long-term complete chimerism can be achieved in adult RLA-matched unrelated rabbits prepared by TBI, and this animal model can be used for bone marrow transplantation studies.

Chimeras established by transferring spleen or lymph node cells from primed donors use donor-derived B lymphocytes in responses to the antigen used in priming of the donor, whereas cells of the recipient are used in responses to other antigens. Clonal dominance by donor cells lasts for at least 9 months. Treatment of newborn rabbits with the antigen used in priming the donors elicits copious production of antibody bearing the donor's allotypic markers in chimeras, but tolerance is induced in nonchimeric controls. Lasting and effective memory is also established in chimeras in the absence of immediate antigenic stimulation. This model for transplantation of allogeneic lymphoid cells into recipients matched with the donor for major histocompatibility antigens shows that priming of the donor facilitates the specific, effective, and enduring acquisition of immunocompetence in the recipient for the antigen used in priming the donor.

Stable and lasting B lymphocyte chimerism induced in newborn rabbits through the introduction of spleen or lymph node cells from adult donors matched with the recipients for major histocompatibility antigens, is characterized by an apparent immunodeficiency of donor-derived cells. However, priming of the donor with an antigen that is subsequently used to immunize the recipients results in the selective and effective participation of donor cells in the chimera's antibody response to this antigen. These findings are ascribed to limitations in the repertoire of cells from the unprimed donor that colonize the recipients. Polyclonal stimulation secondary to allogeneic effects has been suggested as an explanation for the participation of donor-derived B cells noted in occasional recipients of cells from unprimed donors matched with recipients with respect to major but not minor histocompatibility antigens, and seen more regularly in surviving recipients of unmatched or mismatched donor cells.

In the course of experiments designed to demonstrate an active mechanism of allotype suppression in rabbits, spleen cells from adult donors were transferred to newborn recipients. Among 23 rabbits that received injections, 4 stable chimeras were formed, as determined by the production of serum immunoglobulins marked with light and heavy chain allotypes. The other rabbits that survived the immediate postinjection period displayed a temporary chimeric state lasting up to several weeks, after which they either succumbed to graft-versus-host disease or rejected the donor cells. One chimeric animal was apparently repopulated by the hemopoietic cells of the donor's spleen. Insofar as could be determined, the recipient's blood cells became phenotypically identical to those of the donor. This condition manifested itself as a loss of the recipient gene products associated with both lymphocyte and erythrocytes, accompanied by a seemingly total replacement with those of the donor.

Stable and lasting B lymphocyte chimerism induced in newborn rabbits through the introduction of spleen or lymph node cells from adult donors matched with the recipients for major histocompatibility antigens, is characterized by an apparent immunodeficiency of donor-derived cells. However, priming of the donor with an antigen that is subsequently used to immunize the recipients results in the selective and effective participation of donor cells in the chimera's antibody response to this antigen. These findings are ascribed to limitations in the repertoire of cells from the unprimed donor that colonize the recipients. Polyclonal stimulation secondary to allogeneic effects has been suggested as an explanation for the participation of donor-derived B cells noted in occasional recipients of cells from unprimed donors matched with recipients with respect to major but not minor histocompatibility antigens, and seen more regularly in surviving recipients of unmatched or mismatched donor cells.

Transfer of adult spleen, lymph node, or bone marrow cells to newborn recipients matched with the donor with respect to the major histocompatibility antigen or antigens, but mismatched with regard to immunoglobulin allotypes results in lasting B cell chimerism. Using such chimeras as donors for secondary recipients, the persistence of B cells from the original donor and the ability of such cells to propagate in the secondary recipient have been demonstrated. In contrast to the effective establishment of donor B cells in primary and secondary recipients, functional T cells of donor origin were not demonstrable among lymphocytes of primary recipients.

Chimeras established by transferring spleen or lymph node cells from primed donors use donor-derived B lymphocytes in responses to the antigen used in priming of the donor, whereas cells of the recipient are used in responses to other antigens. Clonal dominance by donor cells lasts for at least 9 months. Treatment of newborn rabbits with the antigen used in priming the donors elicits copious production of antibody bearing the donor's allotypic markers in chimeras, but tolerance is induced in nonchimeric controls. Lasting and effective memory is also established in chimeras in the absence of immediate antigenic stimulation. This model for transplantation of allogeneic lymphoid cells into recipients matched with the donor for major histocompatibility antigens shows that priming of the donor facilitates the specific, effective, and enduring acquisition of immunocompetence in the recipient for the antigen used in priming the donor.