Leukemia virus activation during homograft rejection.

Activation of murine leukemia viruses, as detected by the mixed culture cytopathogenicity (XC) assay, followed the transplantation of A/J skin onto immunosuppressed BALB/c mice. Virus was found in most of the mice receiving both skin grafts and antilymphocyte serum, but not in animals receiving either the serum alone, skin graft alone, or no treatment.

Antiserum to lymphocytes: prolonged survival of canine renal allografts.

A horse immunized with dog lynmphocytes produced an antiserum which agglutinated canine lymphocytes in vitro and caused prolonged lymphopenia in dogs in vivo. Renal transplants in dogs treated with this antiserum survived for long periods, two of the grafts surviving beyond 350 days with normal function and histologic appearance.

Structural characterization of the major adducts obtained after reaction of an ultimate carcinogen aflatoxin B1-dichloride with calf thymus DNA in vitro.

The major adduct formed on acid hydrolysis of calf thymus DNA which has been reacted with 8,9-dichloro-8,9-dihydroaflatoxin B1, a chemical model of the ultimate carcinogen 8,9-dihydro-8,9-epoxyaflatoxin B1 (AFB1-epoxide), has been characterized by proton nuclear magnetic resonance and fast atom bombardment mass spectroscopy. This adduct has been identified as an N7-substituted guanine adduct analogous to that formed on reaction of AFB1-8,9-epoxide with DNA in vivo and in vitro, namely trans-8,9-dihydro-8-(7-guanyl)-9-hydroxy AFB1. This 8,9-dichloro-8,9-dihydroaflatoxin B1 adduct in DNA, like its equivalent B1 adduct in DNA, like its equivalent AFB1-epoxide adduct, is prone to quantitative imidazole ring opening of the substituted guanine in mildly alkaline conditions and to substantial depurination under mildly acidic conditions.

Induction of unresponsiveness to skin allografts in adult mice disparate at defined regions of the H-2 complex. I. Effect of donor-specific bone marrow in ALS-treated mice.

The induction of unresponsiveness to skin allografts was studied in adult congenic B10 mice disparate either at isolated K, I, or D regions of the H-2 complex or at combined K/D and I regions. Recipient mice were treated with antilymphocyte serum (ALS) and injected with donor bone marrow after skin grafting. Unresponsiveness to antigens of the isolated K or D regions (class I) could not be induced, as shown by the inability of bone marrow to prolong graft survival in these mice compared with ALS-treated controls. Significant unresponsiveness to antigens of the isolated I region could be induced by ALS immunosuppression alone, and it was not possible to determine the additive effects of bone marrow. Unresponsiveness to antigens of the K or D regions, or both, could be induced when they were presented with antigens of the I region. This indicates that the I region exerts a tolerogenic effect on the K and D regions. The requirement for the concomitant presentation of antigens of the K/D and I regions to achieve unresponsiveness is consistent with our previous observations that active suppression is one of the mechanisms of the induction of unresponsiveness in ALS-treated, marrow injected mice.

Induction of unresponsiveness to skin allografts in adult mice disparate at defined regions of the H-2 complex. II. Effect of pre-graft donor-specific blood transfusions in ALS-treated mice.

The effect of pretransplant donor-specific blood transfusions on the survival of subsequent skin allografts was studied in adult congenic B10 mice disparate at various regions of the H-2 complex. Donor-host combinations were used that were disparate either at isolated K or I regions or at combined K/D and I regions. Recipient mice were given a single donor-specific blood transfusion ten days before antilymphocyte serum (ALS) treatment and skin grafting. A beneficial effect of donor-specific blood transfusions on skin graft survival was observed only in donor-recipient combinations that differed at the K and I regions. Disparity at the IA and IJ subregions appeared to be particularly important in obtaining the transfusion effect. Donor-specific transfusion had no effect on graft survival in donors and recipients disparate at only the K region, the D region plus part of the I region, or the entire H-2 complex. Pregraft transfusion in mice disparate at the I region sensitized the recipients to subsequent skin grafts from the blood donor. These results indicate that both antibody and suppressor cells play a role in the induction of the beneficial effect obtained from pretransplant donor specific transfusions.

Suppressor cells in specific unresponsiveness to skin allografts in ALS-treated, marrow-injected mice.

Lymphoid cells from ALS-treated (C57BL/6 x A/J)F1 (B6AF1) mice bearing enhanced C3H/He grafts were assayed for their ability to suppress the response to C3H/He grafts after transfer to syngeneic B6AF1 recipients. Cells were transferred from ALS-treated B6AF1 mice that had received either a C3H/He graft alone, C3H/He marrow alone, or both a graft and marrow. Suppressor cells appeared in the spleens of ALS-treated B6AF1 mice that had received either a graft alone or both graft and marrow as early as day +13. They persisted only in the spleens of mice that had received both a graft and marrow, i.e., mice whose grafts showed significant prolongation. Suppressor cells did not appear in the lymph nodes of mice bearing enhanced grafts until day +42. Thymocytes and bone marrow cells were unable to transfer unresponsiveness. The cells which transferred unresponsiveness were specific for the graft donor strain as they did not transfer unresponsiveness to third-party grafts. The ability of cells to transfer suppression was abrogated by treatment with anti-theta serum.

The effect of timing of skin grafts on subsequent survival in ALS-treated, marrow-infused mice.

It has previously been shown that the survival of C3H/He skin grafts can be prolonged on ALS-treated (C57 x A)F1 mice by the injection of C3H/He bone marrow cells 7 days after grafting. Experiments have now been done to study the influence of timing of the skin graft on its subsequent survival. Single grafts were placed either before or after marrow was given. Paired grafts on the same animal were also studied, one placed before and one after marrow was given. Grafts placed before marrow was given, whether single or paired, showed equal and significant prolongation while grafts placed after marrow was given showed only slight prolongation compared with ALS controls. Paired grafts showed distinctly different survival curves depending on their time of placement in relation to injection of marrow. The pattern of graft survival suggests that the graft prolongation achieved is attributable to a mechanism similar to enhancement. Experiments were also done to see whether a state of preexisting immunity to the skin graft donor induced by the injection of marrow could be manipulated to achieve prolonged graft survival. (C57 x A)F1 mice were treated with ALS, given injections of C3H/He marrow, and grafted 56 days later with C3H/He skin either with or without additional ALS at the time of grafting. If no ALS was given grafts were rejected in accelerated fashion, indicating that the previous injection of marrow had sensitized the recipient. With additional ALS, the prolongation of graft survival achieved far exceeded that seen using our standard protocol of skin grafting a week before marrow is given. This represents one of the first demonstrations of positive alteration of a preexisting state of immunity to achieve graft prolongation which exceeds that expected by giving ALS immunosuppression alone to a presensitized animal.

Effect of blood transfusion on IL-2 production.

Spleen cells from B10.A mice transfused with B10.D2 blood suppress the immune responses of normal B10.A to B10.D2 in coculture as early as 2 days posttransfusion. In addition, the ability of B10.A mice to respond in cell-mediated lymphocytotoxicity (CML) is significantly impaired as early as 2 days after B10.D2 transfusion. Experiments were performed to characterize the cells mediating the suppressive effect and to determine whether the inability of transfused mice to generate a cytotoxic response is due to an inhibition of IL-2 production. To characterize the suppressor cells, spleen cells from B10.A mice were assayed 2 or 16 days after B10.D2 transfusion for the ability to suppress mixed lymphocyte culture (MLC) and CML responses of normal B10.A mice in coculture. The putative suppressor cells were either passed over a Sephadex G-10 or nylon wool column, treated with anti-Thy antibody or left untreated before addition to the coculture. Untreated cells from transfused mice suppressed the CML response of normal B10.A both 2 and 16 days posttransfusion, while the effect on the MLC response was inconsistent. Passage of the cells over Sephadex G-10 or nylon wool before assaying abrogated the suppressive effect, while treatment with anti-Thy antibody had no effect. These results suggest that the suppressor cells appearing shortly after blood transfusion have the characteristics of macrophages and not T lymphocytes. To determine the effect of transfusion on IL-2 production, cells from transfused mice were assayed for their ability to produce IL-1 and IL-2 and for the formation of IL-2 receptors. In addition, the effect of exogenous IL-1 and IL-2 on restoring the CML response of transfused mice to normal was assayed. The production of IL-1 by transfused mice was normal, while the production of IL-2 was significantly suppressed both 2 and 16 days posttransfusion. Activated cells from normal and transfused mice showed equal ability to absorb IL-2, indicating that IL-2 receptor formation is normal after transfusion. The addition of exogenous IL-2, but not IL-1, to CML cultures containing cells from transfused mice as responders restored the response to normal. These results indicate that the inability of transfused mice to respond in CML is due, at least in part, to an inability to produce IL-2. This could be mediated by prostaglandins released by activated macrophages.

Suppressor cells in specific unresponsiveness to skin allografts in thymectomized, ALS-treated, marrow-injected mice.

Spleen cells from thymectomized antilymphocyte serum (ALS)-treated B6AF1 mice bearing enhanced C3H/He grafts after the infection of C3H/He marrow were assayed for their ability to suppress the response to C3H/He grafts after transfer to syngeneic B6AF1 recipients. Cells were transferred from thymectomized ALS-treated B6AF1 mice that had received either a C3H/He graft alone, C3H/He marrow alone, or both a graft and marrow. Cells were removed from donors and transferred at either day +13, +42, +62, +100, or +150. Spleen cells from thymectomized mice were unable to transfer unresponsiveness regardless of donor treatment or time of transfer.

Effect of splenectomy on specific unresponsiveness to skin allografts induced in ALS-treated, marrow-injected mice.

The role of the spleen in the induction and maintenance of unresponsiveness to skin allografts and in the generation of suppressor cells has been studied in ALS-treated B6AF1 mice grafted with C3H/He skin and injected with C3H/He marrow. B6AF1 mice were splenectomized either before the induction of unresponsiveness or on day +13, +28, or +42 after unresponsiveness was induced. Graft survival in the splenectomized mice was compared to that observed in nonsplenectomized ALS-treated, marrow-injected controls. Graft survival was prolonged equally in all splenectomized groups and the nonsplenectomized controls. To study the effect of the spleen on the generation of suppressor cells, lymph node cells were removed at day +42 from splenectomized ALS-treated, marrow-injected B6AF1 mice bearing C3H/He skin grafts and transferred to ALS-treated B6AF1 recipientso ALS-treated BTAF1 recipients grafted with C3H/He skin. Graft survival in the secondary recipients receiving lymph node cells from splenectomized donors was compared to that observed in ALS-treated B6AF1 mice that received lymph node cells transferred from nonsplenectomized enhanced donors. Suppressor cell activity could be detected in the nodes of splenectomized mice, but a higher dose of lymph node cells was required to transfer unresponsiveness from splenectomized donors compared to nonsplenectomized donors. These results indicate that the spleen is not necessary for the induction or maintenance of unresponsiveness to skin allografts in ALS-treated, marrow-injected mice. In addition, suppressor cells can be generated in the lymph nodes of unresponsive mice in the absence of the spleen, although the production of suppressor cells appears to be less effective in splenectomized mice than in mice with intact spleens.

Characterization of spleen cells capable of inducing unresponsiveness in ALS-treated mice.

C3H/He skin allografts are significantly prolonged in ALS-treated B6AF1 mice by the injection of 50 x 10(6) C3H/He spleen cells 1 week postgrafting. To identify and characterize the spleen cell active in promoting graft survival, C3H/He spleen cells were separated on a discontinuous Percoll gradient and the various fractions were assayed for the ability to prolong skin graft survival in ALS-treated B6AF1 mice. In addition, unfractionated spleen and spleen fractions were depleted of specific cell populations before injection to determine the effect of various cell populations on graft prolongation. The active cell was recovered primarily in the 52.5% Percoll fraction. Cells in the 60% fraction also had a graft-prolonging effect, but not as significant as that of the 52.5% fraction. Depletion of Thy 1, Ia and Ig-positive cells from unfractionated spleen or spleen fractions did not decrease the graft-prolonging effect. Both Fc gamma R-positive and Fc gamma R-negative cells prolonged graft survival, but the Fc gamma R- cells were the most effective. In contrast to the effect of spleen cells, lymph node cells and thymocytes are relatively ineffective in prolonging graft survival in ALS-treated mice. When lymph node lymphocytes and thymocytes were separated on a Percoll gradient, the cell population active in prolonging graft survival was recovered primarily in the 52.5% fraction. Treatment of the 52.5% fraction of lymph node lymphocytes or thymocytes with monoclonal antibody to Thy 1 before injection abrogated the graft-prolonging effect. These results indicate that the spleen cell(s) active in prolonging graft survival in ALS-treated mice is a non-T, non-B cell, as it lacks Thy 1, Ia, and Ig surface markers. Both Fc gamma R+ and Fc gamma R- spleen cells are effective in prolonging grafts, but Fc gamma R- cells are the most effective. In contrast, the active cell in lymph node and thymus is Thy 1-positive, indicating that it is a T lymphocyte.

Immune reactivity in congenic mice after allogeneic or isogeneic transfusion.

Pretransplant donor-specific blood transfusion has a beneficial effect on subsequent skin graft survival in B10 congenic mice when donor and recipient differ at both the K and I regions of the H-2 complex, but has no effect on graft survival in donor-recipient combinations differing at the K region alone. Immune reactivity was studied in B10.A recipients after a single allogeneic transfusion from B10 donors differing either at both K and I regions or at K alone, or after a transfusion of isogeneic B10.A blood. Spleen cells were assayed for the ability to respond in mixed lymphocyte culture (MLC) and cell mediated lymphocytotoxicity (CML) assays against blood donor and third-party at 2, 9, 16, and 30 days after transfusion. MLC and CML responses were nonspecifically suppressed in recipients transfused with allogeneic blood from K or K and I region disparate donors. The responses of mice receiving K region disparate blood were partially recovered by 9 days posttransfusion and had returned to normal 16 days posttransfusion. Responses of mice receiving K and I region disparate blood remained suppressed 30 days post transfusion. Isogeneic transfusion induced a suppression of the MLC response. Two days posttransfusion, the MLC response was suppressed to a variety of stimulators representing disparity at K alone; K and I; or K, I, and D. The response to K region disparate stimulators had recovered 9 days after isogeneic transfusion, but the response to K and I or K, I, and D region disparate stimulators remained suppressed 30 days after transfusion. The suppression observed after allogeneic or isogeneic transfusion was not due to a shift in the day of peak response in the transfused mice. Kinetic studies showed that the day of peak MLC and CML responses in the transfused mice corresponded to that of normal controls, but the level of response was significantly lower in the transfused mice.

The effect of timing of multiple donor-specific or nonspecific blood transfusions on skin allograft survival in ALS-treated mice.

The effect of timing of multiple transfusions on skin allograft survival in antilymphocyte serum (ALS)-treated mice was studied using donor-specific or nonspecific transfusions. Transfusions were given every 4, 7, 14, or 21 days and skin grafting was done 10 days after the last transfusion. To study the effect of donor-specific transfusion, four DBA/2 transfusions were given to ALS-treated B6AF1 recipients followed by grafting with DBA/2 skin. To study the effect of nonspecific transfusions, five CF1 transfusions were given to ALS-treated B6AF1 mice, followed by grafting with C3H/He skin. Transfusions of both donor-specific and nonspecific blood every 4 days had no effect on prolonging graft survival, compared with ALS-treated controls. Transfusions of both types of blood every 7, 14, or 21 days significantly prolonged graft survival, with maximum survival observed in the group receiving transfusions every 14 days. The effect of varying the interval between the last transfusion and skin grafting was studied using multiple transfusions of nonspecific blood. Five weekly CF1 blood transfusions were given to ALS-treated B6AF1 mice. Skin grafting with C3H/He skin was done 2, 5, 10, 30, or 60 days after the last (5th) transfusion. Maximum graft prolongation was achieved when grafting was done 2 days after the last transfusion. Significant graft prolongation was also achieved when grafting was done 5, 10, or 30 days after the last transfusion. Of the mice grafted 60 days after the last transfusion, 60% showed no graft prolongation compared with controls, and survival of 40% of the grafts in this group was prolonged.

The effect of injection of donor bone marrow on the frequency of donor-reactive CTL in antilymphocyte serum-treated, grafted mice.

The survival of C3H/He skin grafts can be prolonged on B6AF1 mice immunosuppressed with ALS by the injection of C3H/He marrow 1 week postgrafting. The precursor frequencies of donor-reactive CTL in the spleen and lymph nodes of ALS-treated, grafted mice given donor marrow were compared with CTL frequencies observed in ALS-treated, grafted controls. Spleens and nodes were removed from experimental and control mice on days +8, +14, +21, +58, and 1 year postgrafting, and used as effectors in the LDA. Donor-reactive CTL in the marrow-injected group remained suppressed as long as the recipients maintained their grafts. The frequency of CTL to third-party antigens was normal in mice bearing long-term C3H/He grafts. When marrow-injected mice rejected their grafts, the total donor-reactive CTL frequency returned to normal. In contrast, in ALS-treated controls that did not receive marrow, the total number of donor-reactive CTL returned to normal levels with recovery from the immunosuppressive effects of ALS. These results suggest that donor marrow suppresses the regeneration of donor-reactive CTL in the lymphoid tissues of ALS-treated mice, possibly by veto cell activity.

Suppressor cells in mice bearing intact skin allografts after blood transfusions.

Evidence for the presence of suppressor cells in B6AF1 mice bearing long-term C3H skin grafts after multiple blood transfusions and antilymphocyte serum (ALS) treatment is described. Transfer of spleen cells from these mice into secondary B6AF1 recipients given ALS and C3H skin grafts resulted in marked prolongation of graft survival. The spleen cells were also capable of specifically inhibiting the proliferative response of normal B6AF1 responders to C3H stimulator cells in coculture mixed lymphocyte culture (MLC) experiments.

Effect of granulocyte-macrophage colony-stimulating factor on the induction of unresponsiveness by lymphoid cells.

Skin grafts can be significantly prolonged in ALS-treated mice by the injection of 25 x 10(6) donor bone marrow cells or 50 x 10(6) spleen cells. Lymph node cells and thymocytes are only minimally effective in prolonging grafts. The effect of a hematopoietic growth factor, granulocyte-macrophage colony stimulating factor (GM-CSF) was studied in this model of unresponsiveness. C3H/He lymphoid cell donors were treated with GM-CSF. Either normal or GM-CSF-treated cells were injected into ALS-treated B6AF1 mice grafted with C3H/He skin. GM-CSF treatment significantly augmented the effect of marrow in prolonging graft survival at doses of 1 to 25 x 10(6) cells. In contrast, GM-CSF had no effect on the graft-prolonging effect of spleen cells when 50 x 10(6) cells were given. When the dose of cells was reduced to 25 x 10(6), graft survival in the group given GM-CSF-treated cells was prolonged compared with survival in the group given normal cells. Grafts in the group given GM-CSF-treated lymph node cells were rejected in sensitized fashion. When marrow and spleen are separated on a Percoll gradient, the cell active in promoting graft survival is recovered primarily in the 52.5% fraction. The graft-prolonging effect of the 52.5% marrow fraction was not affected by GM-CSF treatment. In contrast, GM-CSF-treated marrow cells in the 60% fraction significantly prolonged graft survival, while normal marrow cells in this fraction had no effect on graft survival. GM-CSF-treated spleen cells in the 52.5% and 60% fractions significantly decreased graft survival compared with normal cells when given at a dose equal to the number of cells recovered from 50 x 10(6) cells. When the dose of fractionated spleen cells was reduced, GM-CSF-treated spleen cells were more effective than normal cells in prolonging graft survival. These results indicate that GM-CSF activates a cell in marrow that promotes graft survival. This cell is recovered in the 60% Percoll fraction. In contrast, GM-CSF appears to affect two cell populations in spleen, one beneficial and one detrimental to graft survival. The predominant effect depends on the dose of spleen cells that is given.

Induction of tolerance to skin allografts by intrathymic injection of donor splenocytes. Effect of donor-recipient strain combination and supplemental rapamycin.

The effect of donor-recipient strain combination and supplemental rapamycin (Rapa) on tolerance induction by intrathymic (IT) injection of donor splenocytes was examined in a mouse skin allograft model. In an MHC class I-mismatched C3H/He skin to (C57BL/6 x A)F1 (B6AF1) mouse combination, IT injection of 50 x 10(6) donor splenocytes with transient immunosuppression by rabbit anti-mouse lymphocyte serum (ALS) induced significant prolongation of skin allograft survival with a median survival time (MST) of 115 days versus an MST of 24.5 days in controls given ALS alone. With an additional short course of supplemental Rapa treatment at a dose of 1.5 mg/kg i.p. every other day from day 0 to 12, all C3H/He skin allografts survived indefinitely (> 350 days) in ALS-treated, donor splenocyte intrathymically injected B6AF1 recipient mice. Tolerance was antigen-specific, since the second donor-type skin allografts were accepted while third-party skin allografts were acutely rejected in these mice bearing long-term C3H/He skin allografts. In MHC class I- and II-disparate (DBA/2 to B6AF1) and fully MHC-incompatible (AKR to B6) strain combinations, IT injection of donor splenocytes and ALS treatment failed to prolong skin allograft survival over ALS controls. When supplemental Rapa was used, long-term skin allograft acceptance was observed with an MST of 127 days for the DBA/2 to B6AF1 combination and 70 days for the AKR to B6 combination. In contrast, supplemental treatment with cyclosporine was not effective in these combinations, which suggests that supplemental Rapa may have a unique effect in augmenting IT tolerance induction. Thymectomy within 7 days after IT injection significantly shortened the allograft survival, which suggests that interaction of the host thymus and the injected donor splenocytes, which takes place early after IT injection, plays an important role in the induction of allograft tolerance in this model.

Superiority of sirolimus (rapamycin) over cyclosporine in augmenting allograft and xenograft survival in mice treated with antilymphocyte serum and donor-specific bone marrow.

BACKGROUND: Sirolimus is a potent immunosuppressive agent with great therapeutic potential. The objective of our study was to evaluate the efficacy of sirolimus versus cyclosporine in augmenting the unresponsiveness induced by an antilymphocyte serum (ALS)/donor-specific bone marrow (BM)-based regimen across three levels of histoincompatibility: class I and II disparate (DBA/2 to B6AF1), complete mismatch (AKR to C57BL/6), and xenograft (ACI rat to B6AF1). METHODS: Full-thickness skin grafts were taken from donors and placed on recipients in standard fashion. Seven groups of recipient mice (n=10-28) received various combinations of the following treatment protocols: sirolimus, 1.5 mg/kg (3.0 mg/kg for xenografts) every other day from day 0 to day 12; cyclosporine, 50 mg/kg every other day from day 10 through 22; ALS, 0.5 ml on days -1 and 2 for allografts and days -1, 2, and 4 for xenografts; and BM, 25 million donor-specific cells IV on day 7. RESULTS: The administration of ALS or ALS/BM resulted in modest but significant prolongation of skin graft survival in all combinations tested. Cyclosporine combined with ALS or ALS/BM significantly extended allograft survival compared with ALS or ALS/BM alone (P<0.05) but had no effect on xenograft survival. In contrast, the combination of sirolimus with ALS or ALS/BM resulted in a two- to threefold increase in allograft survival and over a fourfold increase in xenograft survival when compared with the comparable cyclosporine-based regimen. Additionally, lymphocytes isolated from class I and II incompatible mice with skin grafts surviving >100 days demonstrated markedly reduced interleukin 2 and interferon-gamma secretion in response to irradiated donor-specific lymphocytes in culture. CONCLUSIONS: In the regimens tested, sirolimus was superior to cyclosporine in augmenting donor BM-induced skin graft prolongation in ALS-treated mice across all levels of histoincompatibility.

Prolongation of skin allograft survival in H-2 K and I region-incompatible mice by pretransplant blood transfusion.

The effect of donor specific and nonspecific pretransplant blood transfusion on skin allograft survival was studied in a mouse model, using skin donor-recipient combinations that differed at the K and I regions of the H-2 complex. In the first series of experiments, B6AF1 mice were treated with antilymphocyte serum (ALS) and grafted with DBA/2 skin. This donor-recipient combination differs in the K and I regions of the H-2 complex. Recipients were transfused 10 days before grafting with donor-specific DBA/2 blood or blood from various donors which were either completely incompatible at the H-2 complex with DBA/2 or shared various H-2 specificities with DBA/2. Only donor-specific DBA/2 blood or blood from donors sharing the K and I regions of the H-2 with DBA/2 prolonged DBA/2 skin graft survival. Donor-specific blood was effective over a wide interval between transfusion and grafting (days -50 to -10). In a second series of experiments using congenic strains of mice, the effect of pretransplant transfusions was studied in the B10.D2 to B10.A combination. These strains differ at the K and I region of the H-2, but share the same minor histocompatibility antigens. ALS-treated B10.A recipients were transfused either with donor-specific B10.D2 blood or blood from B10.BR which shares the minor histocompatibility antigens with B10.D2, but differs in the major antigens or DBA/2 blood which shares the majority histocompatibility antigens with B10.D2, but differs in the minor antigens. Only donor-specific blood or blood from the DBA/2 donor sharing the major antigens with the skin donor prolonged graft survival.

Marked prolongation of rat skin xenografts induced by intrathymic injection of xenogeneic splenocytes and a short course of rapamycin in antilymphocyte serum-treated mice.

The effect of intrathymic (IT) injection of donor splenocytes and a short course of rapamycin (Rapa) treatment on rat to mouse skin xenograft survival was investigated. ACI rat skin xenografts were transplanted to (C57BL/6 x A)F1 mice treated with rabbit anti-mouse lymphocyte serum (ALS) on days -1, +2, and +4 relative to skin grafting on day 0. Fifty million donor-type splenocytes were injected intrathymically on day 7 after transplantation. Rapa was given intraperitoneally every other day from day 0 to day 12 at a dose of 3.0 mg/kg. Prolonged skin xenograft survival was observed in ALS- and Rapa-treated recipients (no IT injection) with a median survival time of 47 days. However, skin graft survival was markedly more prolonged in the group treated with ALS, Rapa, and IT injection of donor splenocytes did not have a beneficial effect on skin xenograft survival in ALS-treated recipients. An increased presence of donor-type cells was observed in the thymus of the ALS- and Rapa-treated recipients for 7 days after IT injection of donor splenocytes. In conclusion, a short course of Rapa markedly augments rat skin xenograft survival in ALS-treated mice injected intrathymically with donor-type splenocytes.