Retinoic acid-producing, ex-vivo-generated human tolerogenic dendritic cells induce the proliferation of immunosuppressive B lymphocytes.

While much is known about tolerogenic dendritic cell effects on forkhead box protein 3 (FoxP3)⁺ regulatory T cells, virtually nothing is known about their effects on another arm of immunoregulation that is mediated by a subpopulation of immunosuppressive B cells. These cells suppress rheumatoid arthritis, lupus and inflammatory bowel disease in mice, and functional defects have been reported in human lupus. We show that co-stimulation-impaired tolerogenic dendritic cells that prevent and reverse type 1 diabetes mellitus induce the proliferation of human immunosuppressive B cells in vitro. We also show that the suppressive properties of these B cells concentrate inside the CD19⁺ CD24⁺ B cell population and more specifically inside the CD19⁺ CD24⁺ CD38⁺ regulatory B cell population. We discovered that B cell conversion into suppressive cells in vitro is partially dependent on dendritic cell production of retinoic acid and also that CD19⁺ CD24⁺ CD38⁺ B regulatory cells express retinoic acid receptors. Taken together, our data suggest a model whereby part of the immunosuppressive properties of human tolerogenic dendritic cells could be mediated by retinoic acid which, in addition to its known role in favouring T cell differentiation to FoxP3⁺ regulatory T cells, acts to convert B cells into immunosuppressive cells.

Interleukin-7 matures suppressive CD127(+) forkhead box P3 (FoxP3)(+) T cells into CD127(-) CD25(high) FoxP3(+) regulatory T cells.

We have identified a novel interleukin (IL)-7-responsive T cell population [forkhead box P3 (FoxP3(+) ) CD4(+) CD25(+) CD127(+) ] that is comparably functionally suppressive to conventional FoxP3(+) CD4(+) CD25(+) regulatory T cells (T(regs) ). Although IL-2 is the most critical cytokine for thymic development of FoxP3(+) T(regs) , in the periphery other cytokines can be compensatory. CD25(+) CD127(+) T cells treated with IL-7 phenotypically 'matured' into the known 'classical' FoxP3(+) CD4(+) CD25(high) CD127(-) FoxP3(+) T(regs) . In freshly isolated splenocytes, the highest level of FoxP3 expression was found in CD127(+) CD25(+) T cells when compared with CD127(-) CD25(+) or CD127(+) CD25(-) cells. IL-7 treatment of CD4(+) CD25(+) T cells induced an increase in the accumulation of FoxP3 in the nucleus in vitro. IL-7-mediated CD25 cell surface up-regulation was accompanied by a concurrent down-regulation of CD127 in vitro. IL-7 treatment of the CD127(+) CD25(+) FoxP3(+) cells also resulted in up-regulation of cytotoxic T lymphocyte antigen 4 without any changes in CD45RA at the cell surface. Collectively, these data support emerging evidence that FoxP3(+) T cells expressing CD127 are comparably functionally suppressive to CD25(+) CD127(-) FoxP3(+) T cells. This IL-7-sensitive regulation of FoxP3(+) T(reg) phenotype could underlie one peripheral non-IL-2-dependent compensatory mechanism of T(reg) survival and functional activity, particularly for adaptive T(regs) in the control of autoimmunity or suppression of activated effector T cells.

Application of recipient-derived dendritic cells to induce donor-specific T-cell hyporesponsiveness.

Administration of donor-derived immature dendritic cells (DC) treated with NF-kappaB oligodeoxyribonucleotides (ODN) prevents allograft rejection. We attempted to explore the use of recipient-derived DC pulsed with donor antigens, in which the donor antigens were presented to host T cells via an indirect pathway (cross-priming). Expression of CD40, CD80, and CD86 on DC was significantly inhibited by treatment with NF-kappaB ODN, whereas MHC class I and II were minimally affected. Normal C3H DC pulsed with B10 antigens stimulated proliferative responses and donor-specific CTL activity in C3H T cells, both of which were, however, markedly inhibited when DC were treated with NF-kappaB ODN. This manipulation was associated with reduced IFN-gamma and increased IL-10 production in the supernate, suggesting a Th2 bias. More frequent apoptotic T cells were observed in cultures with NF-kappaB ODN DC. In contrast to administration of normal DC pulsed with donor antigens that accelerated rejection of B10 cardiac allografts (median survival time [MST] 7 days versus 10 days in no-DC treatment control, P < .05), a single injection of 2 x 10(6) NF-kappaB ODN DC significantly prolonged allograft survival (MST 50 days, P < .05 compared with no-DC treatment control). The anti-donor CTL activity in infiltrating T cells isolated from cardiac grafts in recipients that received NF-kappaB ODN DC was significantly suppressed. These data indicate that vaccination with immature DC, propagated from recipient BM is an attractive approach to induce T-cell hyporesponsiveness.

Prolongation of cardiac allograft survival using dendritic cells treated with NF-kB decoy oligodeoxyribonucleotides.

Dendritic cells (DC) classically promote immune responses but can be manipulated to induce antigen-specific hyporesponsiveness in vitro. The expression of costimulatory molecules (CD40, CD86, CD80) at the DC cell surface correlates with their capacity to induce or suppress immune responses. Expression of these molecules is associated with NF-kB-dependent transcription of their genes. DC tolerogenicity has been associated with impaired NF-kB-dependent transcription of costimulatory genes as well as NF-kB translocation to the nucleus. In this report, we demonstrate that double-stranded oligodeoxyribonucleotides containing binding sites for NF-kB (NF-kB ODN) are efficiently incorporated by bone marrow-derived DC and specifically inhibit NF-kB-dependent transcription of a reporter gene. Moreover, exposure of DC to the oligonucleotide decoys inhibited lipopolysaccharide (LPS)-induced nitric oxide production, a marker of DC maturation. Treatment of bone marrow-derived DC progenitors with NF-kB ODN selectively suppressed the cell-surface expression of costimulatory molecules without interfering with MHC class I or class II expression. Furthermore, NF-kB ODN DC induced allogeneic donor-specific hyporesponsiveness in mixed leukocyte cultures, and this was associated with inhibition of Th1-type cytokine production. Finally, infusion of NF-kB ODN-modified bone marrow-derived DC into allogeneic recipients prior to heart transplantation resulted in significant prolongation of allograft survival in the absence of immunosuppression. Specific interference with NF-kB and other transcriptional pathways involved in immune stimulation in DC using ODN decoy approaches could be one means to promote tolerance induction in organ transplantation.

Cardiac transplantation in the rat. II. Alteration of the severity of donor graft arteriosclerosis by modulation of the host immune response.

Cardiac transplantation between inbred rat strains that differ for weak histocompatibility antigens is associated with the development of arteriosclerosis in the arteries of the donor graft myocardium. The lesions are seen in donor/recipient pairs that differ for both MHC and non-MHC histocompatibility antigens that apparently stimulate a low-level, chronic rejection of the donor heart graft. The arteriosclerosis associated with this chronic rejection consists of a diffuse, concentric proliferation of the intima and pathologically resembles the lesions observed in the coronary arteries of long-term human cardiac graft recipients. We have recently examined the influence of positive and negative manipulation of the host immune response on the development of the graft arteriosclerosis. Our results demonstrate that delayed harvest of the cardiac grafts or immunization with donor skin grafts or splenic lymphocytes increases the sensitivity of the recipient to the donor heart grafts--and, under conditions that allow for the long-term survival of the graft--increases the severity of the arteriosclerotic lesions. Alternatively, suppression of the host immune responses with cyclosporine or FK506, substantially reduces the arteriosclerotic changes. These results suggest that control of accelerated graft arteriosclerosis in long-term human cardiac recipient may require more careful and effective immunosuppression of the allograft reaction.

Lymphokine-activated killer (LAK) cell purging of leukemic bone marrow: range of activity against different hematopoietic neoplasms.

Natural killer cells activated in vitro by incubation with IL-2 display a broad range of cytolytic activity against neoplastic cells. These lymphokine-activated killer (LAK) cells can discriminate between neoplastic and normal bone marrow cells and may represent a useful means of purging bone marrow prior to autologous transplantation. We demonstrate that LAK cells can successfully remove four distinctly different malignant hematopoietic cell types from normal bone marrow grafts. The LAK purging technique is capable of a 2-3 log10 reduction in tumor cells in the bone marrow graft without compromising hematological recovery or survival. Our results also suggest, however, that an inhibitory effect on stem cell function by allogeneic LAK cells exists, and this form of purging may be used only if greater levels of bone marrow are transferred in an allogeneic setting. The ability to detect and eliminate malignant cells in bone marrow prior to use for autologous transplantation suggests that LAK cells, alone or in conjunction with current methods of bone marrow purging, could be useful for the in vitro treatment of bone marrow in patients who require high-dose chemotherapy and autologous bone marrow transplantation.

Cardiac transplantation in the rat. I. The effect of histocompatibility differences on graft arteriosclerosis.

The development of arteriosclerosis is the most serious and common complication in long-term survivors of cardiac transplantation. We have used a variety of inbred rat strains with selected histocompatibility differences to examine the influence of prolonged, mild rejection reactions on the development of pathological changes in long-term cardiac allografts. Heterotopic cardiac allografts were exchanged between rat strains that differed for MHC class I (RT1.A and/or RT1.E) antigens or groups of minor, non-MHC antigens in MHC-compatible congenic combinations. Our results demonstrate that in strain combinations in which the allograft reaction is mild and prolonged, the donor hearts exhibit pathological changes that include a diffuse, interstitial myocardial fibrosis, perivascular fibrosis, and intimal proliferation in arteries of the graft myocardium. The lesions were less prominent in animals with more active rejection and infrequent in strains that differ for class I histocompatibility antigens or syngeneic controls. These results suggest that the comparable pathological changes seen in long-term human cardiac survivors may reflect low-level, persistent allograft reactions rather than factors associated with graft anoxia or effects of immunotherapy to prevent graft rejection.

Lymphokine-activated killer cell purging of leukemia cells from bone marrow prior to syngeneic transplantation.

We have studied the effect of using lymphokine-activated killer (LAK) cells as an in vitro means for eliminating leukemic cells from normal bone marrow prior to transplantation of experimental animals. Rat LAK cells exhibit broad cytolytic activity against a variety of hematopoietic neoplasms, but do not kill normal bone marrow cells or lectin-stimulated blasts. Bone marrow was harvested from normal Fischer 344 rats, combined with increasing numbers of CRNK-16 tumor cells, and then incubated with LAK cells. The BM/tumor/LAK mixture was then administered to untreated Fischer rats, and the ability of the LAK cells to purge the bone marrow of neoplastic cells and prevent the transmission of the leukemia to recipient animals monitored. Our results demonstrate that LAK cells are capable of efficiently purging the bone marrow of neoplastic cells. Treatment of the BM/tumor mixtures with LAK cells is associated with significant prolongation of survival in the higher tumor doses (10(5) tumor cells/recipient) and complete elimination of the tumor in a high percentage of recipients at lower tumor levels (10(3)-10(4) tumor cells/recipient). At levels of BM transfer comparable to that used in humans, there was no evidence of a failure of LAK-treated bone marrow to reconstitute lethally conditioned recipient animals. However, with lower numbers of BM cells, there was an increased mortality in animals receiving LAK-treated BM, suggesting a minimal inhibition of pluripotent hematopoietic stem cell function when suboptimal numbers of BM cells are used for reconstitution. These experiments demonstrate that LAk cells are capable of eliminating neoplastic cells in bone marrow without significant destruction of immature syngeneic stem cells. LAK cells display a broad range of cytolytic activity against hematopoietic and solid tissue tumors, and are therefore capable of eliminating small numbers of tumor cells from a wide variety of neoplastic diseases of the marrow. The ability to detect and eliminate malignant cells, without interfering with reconstitution with donor marrow, suggests that immune therapy with LAK cells can be a relatively simple and efficient method to purge bone marrow prior to autologous transplantation in patients following high-dose chemotherapy for neoplastic diseases.

Heterogeneity of murine mammary adenocarcinoma cell subpopulations. In vitro and in vivo resistance to macrophage cytotoxicity and its association with metastatic capacity.

Properties of Ts, a long-term tissue culture line of T1699 mammary adenocarcinoma of DBA/2 mice, and two of its sublines - TR2 and TLI-1-were comparatively studied. Ts tumors produced no spontaneous metastases, nor did i.v. injection of up to 1 X 10(6) Ts cells produce a lung tumor nodule. Ts cells were susceptible to macrophage cytotoxicity in vitro and i.v. injected cells were rapidly destroyed in the lungs. TLI-1 tumors spontaneously metastasized to the lungs, and i.v. injection of 1 X 10(3) TLI-1 cells produced approximately 15 lung nodules per animal. TLI-1 cells were least susceptible to both macrophage-mediated cytolysis in vitro and in vivo host antitumor mechanisms. TR2 cells were intermediate with respect to all these properties. Differences in their susceptibility to macrophage cytotoxicity were recognized not only by normal peritoneal macrophages but also by murine macrophage lines. On the other hand, all the subpopulations were uniformly resistant to NK activity in vitro. These findings suggest that resistance of tumor cells in vitro to macrophage cytotoxicity corresponds with their in vivo metastatic potential.

Dose, route, and time dependence of serum lysozyme and antitumor activity following administration of glucan, Corynebacterium parvum, pyran, or lipopolysaccharide to mice.

Following the administration of Di Luzio particulate glucan, Corynebacterium parvum, pyran (maleic anhydride vinyl ether 6), and lipopolysaccharide (Shigella) to inbred C57BL/6J mice, dose, route, and time-dependent studies were undertaken on antitumor activity and serum lysozyme levels to explore the possible relevance of serum lysozyme as a useful index of antitumor activity. Antitumor activity was assessed by measurement of the extent of loss of iv injected 125I-labeled 5-iodo-2'-deoxyuridine-labeled B16 tumor cells. Increases in serum lysozyme levels were dose-, route-, and time-dependent and varied greatly from one agent to another. The peak levels of antitumor activity were similar for all agents but were also critically dose- and time-dependent. Correlations of serum lysozyme levels and antitumor activity were inexact. The doses for peak lysozyme level increases were higher than those for peak antitumor activity. Antitumor activity peaked earlier and lasted longer than serum lysozyme level increases.

Collaboration between specific anti-tumor immunity and chemotherapeutic agents.

Treatment of DBA/2J mice bearing a T1699 syngeneic mammary adenocarcinoma (Ts) with a single intraperitoneal (i.p.) injection of 100 ug melphalan produced complete tumor regression in about 65% of the animals treated; however, tumors recurred in about 85% of these regressors after 15-25 days' remission. The drug regimen was ineffective against Ts tumors growing in immunosuppressed or immunodeficient animals. Stimulation of immunologically intact Ts tumor-bearers with bacterial lipopolysaccharide (LPS) or with phytohemagglutinin (PHA) 3 days prior to melphalan therapy, on the other hand, produced not only higher rates of tumor regression but also significant increases in the number of permanent cures. A tumor induced by T1699 subline TR2 was resistant to the same regimen, although Ts and TR2 cells were equally susceptible to the cytotoxic and growth-inhibiting activities of the drug in vitro. In contrast, the combination of specifically armed monocytes and melphalan in vitro produced enhanced killing of Ts cells but not of TR2 cells. Analysis of the collaborative cytotoxicity between immune effector cells and melphalan indicated that exposure of tumor cells to killer cells increased the drug susceptibility of the tumor cells, but not the reverse. These results suggest a possible mechanism for in vivo resistance of tumors to chemotherapeutic agents that is not directly associated with the drug resistance of the tumor cells in vitro.

Establishment of heteroploid cell lines from mouse peritoneal exudate cells.

Proliferation was observed during in vitro cultivation of peritoneal exudate cells that had been educed from a C3H mouse with Freund's incomplete adjuvant. These cells were successfully subcultured by release with trypsin-EDTA solution and are now at passage 108 after 22 months in culture. Using this technique, 12 other rapidly growing peritoneal exudate cultures were obtained, whereas 10 cultures not educed with adjuvant did not proliferate. Characteristics of four adjuvant-induced cell lines established in culture include: rapid attachment to glass, doubling time in culture of 18 to 19 hr, phagocytosis of colloidal carbon, enhanced phagocytosis of specifically sensitized bacteria, epithelium-like morphology, and retention of C3H histocompatible specificities. These cell lines had widely varying chromosome distributions with modes from 37.3 +/- 2.4 to 82.6 +/- 2.30, but inoculation of 10(7) cultured cells into syngeneic animals did not produce tumors. Procedures described for the reproducible establishment of peritoneal exudate cell lines did not require use of conditioned media or exogenous viral infection.