Natural killer activity by spleen, lymph node, and thymus cells during the graft-versus-host reaction

Responses of regulatory and effector T-cells to low-dose interleukin-2 differ depending on the immune environment after allogeneic stem cell transplantation

CD4⁺Foxp3⁺ regulatory T cells (Tregs) play a central role in the maintenance of immune tolerance after allogeneic hematopoietic stem cell transplantation (HSCT). Tregs promptly respond to low concentrations of IL-2 through the constitutive expression of high-affinity IL-2 receptors. It has been reported that low-dose IL-2 therapy increased circulating Tregs and improved clinical symptoms of chronic GVHD. Clinical studies of IL-2 therapy so far have mainly targeted patients in the chronic phase of transplantation when acute immune responses has subsided. However, the biological and clinical effects of exogenous IL-2 in an acute immune environment have not been well investigated. In the current study, we investigated the impact of exogenous IL-2 therapy on the post-transplant homeostasis of T cell subsets which influence the balance between GVHD and GVL in the acute phase, by setting the various immune environments early after HSCT in murine model. We initially found that 5,000 IU of IL-2 was enough to induce the active proliferation of Treg without influencing other conventional T cells (Tcons) when administered to normal mice. However, activated Tcons showed the response to the same dose of IL-2 in recipients after allogeneic HSCT. In a mild inflammatory environment within a threshold, exogenous IL-2 could effectively modulate Treg homeostasis with just limited influence to activated T cells, which resulted in an efficient GVHD suppression. In contrast, in a severely inflammatory environment, exogenous IL-2 enhanced activated T cells rather than Tregs, which resulted in the exacerbation of GVHD. Of interest, in an immune-tolerant state after transplant, exogenous IL-2 triggered effector T-cells to exert an anti-tumor effect with maintaining GVHD suppression. These data suggested that the responses of Tregs and effector T cells to exogenous IL-2 differ depending on the immune environment in the host, and the mutual balance of the response to IL-2 between T-cell subsets modulates GVHD and GVL after HSCT. Our findings may provide useful information in the optimization of IL-2 therapy, which may be personalized for each patient having different immune status.

Analysis of Cell Subsets in Donor Lymphocyte Infusions from HLA Identical Sibling Donors after Allogeneic Hematopoietic Cell Transplant

Donor lymphocytes infusions (DLIs) are a major therapeutic approach to treat relapse and mixed chimerism after allogeneic hematopoietic cell transplant (alloHCT). The impact of the composition regarding different cell subsets in the development of graft-versus-host disease (GVHD) is not fully understood. We performed a cell subsets analysis of 56 DLIs from fully HLA-compatible identical matched sibling donors (MSDs) in 36 alloHCT patients and studied its association with GVHD. A median of one DLI was infused per patient. Fourteen patients (38%) developed GVHD. The cell composition analysis of the first DLI (DLI1) showed that a high dose of B cells (P = .03) and CD27⁺ B cells (P < .01) was associated with GVHD. We identified DLI dose cutoff points for several cell populations above which GVHD was more frequent (CD8⁺ T_N >3 × 10⁶ cells/kg, CD27⁺ B cells >2.6 × 10⁶/kg, CD27⁺ NK >0.35 × 10⁶ cells/kg, and mononuclear cells >0.83 × 10⁸/kg). Noteworthy, the proportion of CD4⁺ naive T cells (T_N) or unselected T_N was not linked with GVHD and a DLI1 containing a higher dose of regulatory T cells was not protective for GVHD. We studied several transplant clinical variables and did not find any association with GVHD. Altogether, this study provides a comprehensive analysis of the cell populations in a DLI from MSDs and identifies potential key cell subsets, which provides insight for the understanding of GVHD after DLI.

Alpha-1 Antitrypsin-Expressing Mesenchymal Stromal Cells Confer a Long-Term Survival Benefit in a Mouse Model of Lethal GvHD

Acute graft-versus-host disease is a frequent complication associated with allogeneic hematopoietic stem cell transplantation. Patients that become refractory to initial steroid treatment have a poor prognosis. apceth-201 consists of human allogeneic mesenchymal stromal cells, engineered by lentiviral transduction to express the protease inhibitor alpha-1 antitrypsin, to augment the anti-inflammatory potential of the mesenchymal stromal cells. We show that apceth-201 mesenchymal stromal cells efficiently suppress T cell proliferation and polarize macrophages to an anti-inflammatory M2 type, in vitro. To assess the in vivo efficacy of apceth-201, it was tested in two different mouse models of acute graft-versus-host disease. Control animals in a humanized model succumbed quickly to disease, whereas median survival was doubled in apceth-201-treated animals. The product was also tested in a graft-versus-host disease model system that closely mimics haploidentical hematopoietic stem cell transplantation, an approach that is now being evaluated for use in the clinic. Control animals succumbed quickly to disease, whereas treatment with apceth-201 resulted in long-term survival of 57% of the animals. Within 25 days after the second injection, clinical scores returned to baseline in responding animals, indicating complete resolution of graft-versus-host disease. These promising data have led to planning of a phase I study using apceth-201.

Natural Killer Cells in Graft-versus-Host-Disease after Allogeneic Hematopoietic Cell Transplantation

Allogeneic hematopoietic cell transplantation (HCT) is a well-established therapeutic modality effective for a variety of hematological malignancies but, unfortunately, is associated with significant morbidity and mortality related to cancer relapse as well as to transplant-related complications including graft-versus-host-disease (GvHD). Natural killer (NK) cells are the first donor-derived lymphocyte subset to recover after HCT, and their crucial role in protection against cancer relapse and infections is well established. Conversely, the role played by NK cells in GvHD is still controversial. Early studies suggested a participation of NK cells in GvHD induction or exacerbation. Subsequently, experimental evidence obtained in mice as well observational studies performed in humans led to a model in which NK cells play a regulatory role in GvHD by repressing alloreactive T cell responses. This widely accepted model has been recently challenged by clinical evidence indicating that NK cells can in some cases promote GvHD. In this review, we summarize available knowledge about the role of NK cells in GVHD pathogenesis. We review studies uncovering cellular mechanisms through which NK cells interact with other immune cell subsets during GvHD leading to a model in which NK cells naturally suppress GvHD through their cytotoxic ability to inhibit T cell activation unless exogenous hyperactivation lead them to produce proinflammatory cytokines that can conversely sustain T cell-mediated GvHD induction.

Early intestinal Th1 inflammation and mucosal T cell recruitment during acute graft-versus-host reaction

Little is understood about the earliest cytokine responses and the role(s) of donor CD4 T cells in the intestine during the induced graft-vs-host reaction (GVHR). We investigated the activation and mucosal homing phenotype of the donor CD4 cells and the kinetics of cytokine responses within the intestine and associated lymphoid tissues during early GVHR. Significant frequencies of donor CD4 cells accumulated within recipient Peyer's patches (PP), mesenteric lymph nodes (MLN), lamina propria (LP), and spleen (SP), during the first 9 days of GVHR. Many donor CD4 cells in SP, MLN, and LP expressed CD44 and also expressed de novo the mucosal homing integrin alpha(4)beta(7) (LPAM-1). A large IFN-gamma response occurred by day 3 in cells from PP and MLN, but much later (day 9) in SP and LP cells. IL-10 production by SP and MLN cells was elevated initially but declined substantially by day 9. IL-4 production by SP, MLN, and PP cells was low on day 3 and showed gradual decline in LP by day 9. IL-5 production by LP cells gradually increased in direct contrast to IL-5 production by MLN cells. The MLN CD4 cells showed the most dynamic changes, with high numbers of activated/effector donor CD4 cells and altered cytokine production consistent with a developing Th1 response. The IFN-gamma responses in PP and MLN preceded that of the SP, suggesting an intestinal origin for some Th1 effector cells in GVHR. Donor CD4 T cells apparently acquire the ability to home to the LP during early GVHR.

Cell surface markers and circulating cytokines in graft versus host disease

Graft versus host disease (GVHD) remains the major obstacle to the widespread application of allogeneic bone marrow transplantation (BMT) despite improvement in drug prophylaxis. T cells in the donor bone marrow recognize and react against host alloantigens and thereby initiate GVHD, but the precise mechanisms by which host tissues are damaged remain unclear. In the current study, we determined the cytokine secretion, cell population distribution, and cell surface markers expression by ELISA and flow cytometer, to understand further the pathophysiology of GVHD. Our results demonstrated that there was no significant change in the cell ratio of B-and T- lymphocytes, and helper/suppressor cells during GVHD development when compared to the condition before transplantation. Furthermore, the percentage of natural killer cells, the interleukin-2 receptor (IL-2R) or the HLA-DR antigen on both CD4 and CD8 positive cells presented no significant difference between pre-transplantation and during GVHD. The serum cytokine secretion of IL-1, TNF-alpha, IL-2, ICAM-1, endothelin, TGF-beta showed no difference before BMT and during GVHD. However, when patients in the developing of GVHD, there was significant difference in the serum levels of soluble IL-2R (slL-2R), epidermal growth factor (EGF), and platelet derived growth factor (PDGF). In addition, with patients who develop GVHD, the mixed lymphocyte reaction also presented a significant difference. This study indicated that some serum cytokines such as sIL-2R, growth factors, and the mixed lymphocyte reaction may be used as parameters for the early detection of the development of GVHD.

Involvement of both donor cytotoxic T lymphocytes and host NK1.1+ T cells in the thymic atrophy of mice suffering from acute graft-versus-host disease

It has been reported that a dramatic decrease in the number of thymocytes (thymic atrophy) in mice suffering from acute graft-versus-host disease (GVHD) is ascribed to glucocorticoids. In this study, we examined the possibility that cellular immune responses may thus be involved in thymic atrophy. In contrast to chronic GVHD mice, acute GVHD (C57BL/6 X DBA/2) F1 (BDF1) hybrid mice, which were injected intravenously with both spleen and lymph node cells from C57BL/6 mice, showed a dramatic decrease in the number of CD4 CD8 double-positive thymocytes 2 or 3 weeks after the induction of GVHD. A flow cytometric analysis revealed the donor-derived T cells with either CD4 or CD8 molecules to infiltrate the thymus of the mice undergoing acute GVHD for 10 days. In a cytolytic assay, such thymus-containing cells exhibited a cytolytic activity specific to the host cells. In addition, anti-H-2d cytolytic T cells showed a high level of cytolytic activity against BDF1 (H-2bXd) thymocytes, whereas they also showed a low level of cytolytic activity against C57BL/6 (H-2b) thymocytes, thus suggesting that the thymus-infiltrating donor-derived T cells killed the host thymocytes through both anti-H-2d-specific and non-specific mechanisms. Interestingly, a flow cytometric analysis revealed both the percentage and the absolute cell number of host-derived NK1.1+ CD3+ cells to increase in the thymus of mice suffering from acute GVHD for 10 days. In addition, they also showed the cytolytic activity against YAC-1 cells and the mRNA expression of interleukin-12 (IL-12) in the thymus to be also significantly augmented on day 7 after the induction of acute GVHD. Collectively, our results indicate that the cellular immune responses such as donor cytotoxic T lymphocytes and host NK1.1+ T cells are therefore involved in the thymic atrophy of mice suffering from acute GVHD.

Clinical relevance of serum soluble interleukin-2 receptor levels in acute and chronic graft-versus-host disease

Soluble interleukin-2 receptor (sIL-2R) levels were analyzed in the sera from 27 patients who underwent allogeneic bone marrow transplantation (BMT) in order to to examine whether there was any correlation between sIL-2R levels and graft-versus-host disease (GVHD). The sIL-2R levels markedly increased at the engraftment period, mainly due to cytokine administration shortly after BMT. Although the sIL-2R levels increased at the onset of acute GVHD, the subsequent development of GVHD could not be predicted by the sIL-2R levels documented before acute GVHD. As acute GVHD improved, the sIL-2R levels decreased, thus showing that the sIL-2R levels correlated with the disease status. In patients without acute GVHD, the sIL-2R levels gradually decreased with time and returned to the pretransplant levels after about 12 weeks post BMT. The sIL-2R levels were higher in unrelated allogeneic BMT patients with acute GVHD when compared with related allogeneic BMT patients. There was a significant increase in the sIL-2R levels at the engraftment period and at the onset of acute GVHD. At the onset of chronic GVHD, the sIL-2R levels once again increased and then decreased as chronic GVHD improved. Prolonged increase in sIL-2R levels was followed by subsequent development of chronic GVHD. Patients with a poor prognosis had higher sIL-2R levels than those with a good prognosis. Therefore, it seems that sIL-2R is a useful marker for monitoring the disease status of acute and chronic GVHD.

Graft-versus-leukemia effect and its clinical implications

Graft-versus-leukemia (GVL) effect is an immunologically important phenomenon which decreases the relapse rate of leukemia after allogeneic bone marrow transplantation. GVL effect is sometimes associated with the occurrence of graft-versus-host disease (GVHD). Analyses of GVL effect and GVHD showed that these two phenomena were separable in some conditions. Although we cannot yet completely control the development of the GVL effect without inducing GVHD in humans, basic analyses using animal models show potential benefits of the GVL effect for clinical applications. Autologous GVHD is another important phenomenon which can help to eradicate minimal residual disease. Interleukin 2 and/or cyclosporin A are extensively used in animal models and in humans to induce autologous GVHD, showing beneficial effects. In the future, cytokine usage and allogeneic stem cell transplantation or leukocyte infusion appear to be promising in the control of minimal residual disease. Further studies on the mechanisms of GVL effects and GVHD may well open a new era for cell transplantation.

Novel approaches to the control of graft versus host disease

Graft versus host disease (GVHD) remains the major obstacle to the application of bone marrow transplantation across HLA barriers. Recent advances in our understanding of GVHD pathophysiology have resulted in the evaluation in animal models and in clinical trials of some novel approaches to avoiding and treating GVHD. Continued advances in our knowledge are likely to result in the clinical application of biological therapies to maximize graft versus leukemia effects and alloengraftment, while avoiding GVHD.

Postoperative infection and natural killer cell function following blood transfusion in patients undergoing elective colorectal surgery

The frequency of infection in 197 patients undergoing elective colorectal surgery and having either no blood transfusion, transfusion with whole blood, or filtered blood free from leucocytes and platelets was investigated in a prospective randomized trial. Natural killer cell function was measured before operation and 3, 7 and 30 days after surgery in 60 consecutive patients. Of the patients 104 required blood transfusion; 48 received filtered blood and 56 underwent whole blood transfusion. Postoperative infections developed in 13 patients transfused with whole blood (23 per cent, 95 per cent confidence interval 13-32 per cent), in one patient transfused with blood free from leucocytes and platelets (2 per cent, 95 per cent confidence interval 0.05-11 per cent) and in two non-transfused patients (2 per cent, 95 per cent confidence interval 0.3-8 per cent) (P less than 0.01). Natural killer cell function was significantly (P less than 0.001) impaired up to 30 days after surgery in patients transfused with whole blood. These data provide a strong case against the use of whole blood transfusion in patients undergoing elective colorectal surgery.

Induction, specificity and elimination of asialo-GM1+ graft-versus-host effector cells of donor origin

In previous studies we demonstrated that an induced asialo-GM1 positive (ASGM1+) cell of donor origin that exerts natural killer cell-like activity (NK activity+) plays a crucial role in the development of graft-versus-host (GVH)-associated tissue damage and severe immunosuppression. This study examined whether the ASGM1+ (NK activity+) GVH effector cells were activated by non-specific signals or whether these cells were triggered by specific alloantigens and displayed antigenic specificity. C57B1/6 (B6) donor mice were treated with either B6 x AF1 (B6AF1) lymphoid cells and anti-asialo GM1 antibodies (anti-ASGM1) to induce and eliminate specifically activated B6-anti-B6AF1 ASGM1+ (NK activity+) cells or with polyinosinic: polycytidylic acid (poly I:C), and anti-ASGM1 to eliminate non-specifically activated ASGM1+ (NK activity+) cells. Donor spleen and lymph node cells depleted of the specific allo-induced ASGM1+ NK reactive cells showed near normal numbers of L3T4+ and Lyt-2+ cells and retained T- and B-cell functions as measured by mitogen responses (to PHA, Con A and LPS), mixed lymphocyte responses (MLR) (to B6AF1) and the generation of cytotoxic T cells (CTL) (to B6AF1 blasts). Anti-ASGM1 treatment almost completely abrogated NK activity in all donor inocula. GVH reactions were induced by injecting treated donor cells into B6AF1, B6 x C3HejF1 (B6C3HF1) and B6 x SJLF1 (B6SJLF1) hybrids and monitored by splenomegaly, suppression of T-cell mitogen responses and the development of histopathological lesions in the thymus, liver and pancreas. Cells from donors depleted of non-specifically (poly I:C) induced ASGM1+ cells induced severe histological lesions, marked immunosuppression and splenomegaly in all three F1 hybrid combinations. When the donor cells were depleted of specifically induced (B6-anti-B6AF1) ASGM1+ cells and injected into the three F1 combinations they induced splenomegaly in all three but caused severe tissue injury and intense immunosuppression only in B6C3HF1 and B6SJLF1 mice and not in B6AF1 mice. Genetic analysis suggests that the H-2D (or a closely related) region of the H-2 complex plays an important role in the activation of the specific GVH effector cells. These results suggest that the cell(s) responsible for splenomegaly are different from the ones that cause severe GVH-associated tissue damage and immunosuppression although there may be cells and/or lymphokines common to both processes.(ABSTRACT TRUNCATED AT 400 WORDS)

Natural killer (NK) cell activity in mice with acute graft-versus-host reactions: characterization of a Thy-1+ NK-like cell with a broadened spectrum of lytic activity in the spleen and lymph nodes

We have shown that acute (GVH) reactions produced in the parental-F1 hybrid combination, A/J----(C57BL/6 x A/J)F1 result in the activation of two cytotoxic cell populations: a host-derived Thy-1+/- natural killer (NK) cell with a lytic spectrum confined to YAC-1 targets, and a donor-derived Thy-1+ NK-like cell that has the ability to lyse target cells that are normally insensitive to lysis by NK cells. Cold-target inhibition (CTI) experiments have shown that the greater range of target cell killing seen in the NK-like population is mediated by a single effector cell with a broadened lytic repertoire. Percoll density fractionation studies have revealed that NK and NK-like cells co-fractionate, suggesting that both are large granular lymphocytes. We we have also shown that NK-like cells do not express either Lyt-2 or L3T4 markers. We have also observed that there is a close temporal relationship between elevated levels of interleukin-2 (IL-2) secretion by spleen cell cultures from mice with GVH disease and the subsequent emergence of splenic NK activity in both acute [A/J----(C57BL/6 x A/J)F1] and chronic (A/J----CBA x A/J)F1 GVH reactions. We have also noted that, despite high levels of IL-2 secretion, mice with chronic GVH reactions do not generate NK-like activity. Interferon (IFN) measurements have shown that, although increased IFN activity can be detected in both acute and chronic models, a preponderance of IFN-alpha/beta and some IFN-gamma is produced in the acute reaction, whereas only IFN-gamma can be detected in the chronic model. These results suggest that, although IL-2 may participate in augmenting conventional NK activity, IL-2 by itself does not generate NK-like activity. We suggest that IFN-alpha/beta may be the cytokine that, either alone or in concert with IL-2, triggers the NK-like cell response. The NK-like cell described in our study resembles a phenotypically identical, donor-derived large granular lymphocyte, identified by others, in close proximity to dead or dying epithelial cells in mice with GVH disease [14]. It has been suggested that these cells may mediate tissue injury. If in fact these graft-derived NK-like cells are involved in the pathogenesis of acute GVH disease, our present findings suggest that they must first be activated by an appropriate complement of cytokines that includes IFN-alpha/beta.(ABSTRACT TRUNCATED AT 400 WORDS)

Augmented natural killer cell activity during neonatal graft-versus-host disease is of predominantly donor origin

Natural killer cells have been postulated to play a role in the immunopathogenesis of graft-versus-host disease (GVHD). This is based on reports of augmented natural killer (NK) activity, both in animal models and in humans. It has not been elucitated from previous reports, however, whether the cells mediating this activity are of donor or recipient origin. We have investigated the origin of the effector cells using highly specific antisera. Our results indicate that the augmented lytic activity seen during the course of GVHD is mediated primarily by donor lymphocytes. Depletion with anti-Class I antisera followed by immuno-staining with anti-asialo GM-1 indicate that the effector cells are also asialo GM-1 positive. We report here that the augmented non-specific lytic activity seen during GVHD is mediated by asialo GM-1 positive lymphocytes predominantly of donor origin.

The effect of oral retinoid therapy on the normal human immune system

Twenty four patients were studied prior to and after 6 and 12 weeks therapy with isotretinoin (17 patients) for acne and related disorders, or with etretinate (7 patients) for psoriasis and related disorders. Patients treated with isotretinoin had a significant reduction in natural killer cell activity at an effector: target cell ratio of 100: 1 at 12 weeks and also a reduction in natural killer cell numbers at this time. Patients treated with etretinate had elevated natural killer cell activity and a significant elevation of natural killer cell numbers at 12 weeks. Other tests which were performed and showed no significant change at 6 or 12 weeks compared with starting levels included lymphocyte transformation in response to phytohaemagglutinin, pokeweed mitogen and concanavalin A, total numbers of circulating T lymphocytes, B lymphocytes and T helper and T suppressor subsets, numbers of epidermal Langerhans cells and serum levels of IgA, IgM and IgE. In view of the involvement of natural killer cells in the initial phase of organ rejection, these results suggest that isotretinoin is the safer of the two retinoids if administration to renal transplant recipients is considered, particularly in the immediate post-transplant period.

Association between the degree of thymic dysplasia and the kinetics of thymic NK cell activity during the graft-versus-host reaction

In this study, by employing different cell doses and parent into F1 hybrid combinations, we have investigated the relationship between the severity of thymic medullary dysplasia and the kinetics of thymic natural killer (NK) cell activity after the induction of graft-versus-host (GVH) reactions. GVH reactions were induced by injecting different doses (30, 20, 10 X 10(6] of C57BL/6 (B6) of A parental lymphoid cells (PLC) into non-X-irradiated adult B6xAF1 (B6AF1) mice. On different days after the induction of GVH reactions, the thymuses were examined histologically and thymocyte NK cell activity was tested by using YAC targets. Our results show that, depending upon the genotype and dose of PLC injected, various degrees of thymic medullary dysplasia (mild, moderate, or severe) can be induced. Furthermore, severe to moderate thymic medullary dysplasia is observed only in those groups of GVH-reactive mice in which thymic NK cell activity occurs early and increases rapidly. In contrast, when mild thymic medullary dysplasia or no thymic alterations was observed, thymic NK cell activity peaked later and was of lower intensity than that of the groups with moderate to severe lesions. These results suggest an association between the degree of thymic medullary dysplasia and the kinetics of NK cell activity in the thymus. Furthermore, the different degrees of thymic medullary dysplasia as described here may serve as a powerful tool to study the role of thymic medullary dysplasia in determining the duration of T-cell immunodeficiency associated with the GVH reactions.

Enhanced interferon-alpha/beta (IFN-alpha/beta) and defective IFN-gamma production in chronic graft versus host disease: a potential mechanism for immunosuppression

Immunosuppression is a well-characterized consequence of chronic graft-versus-host disease (GVHD). We have previously shown that interferon (IFN) is produced in high levels during acute GVHD. Our objective in this study was to determine if IFN, as a cytokine with known immunosuppressive qualities, could be detected in mice experiencing chronic GVHD-induced immunosuppression. Two different experimental models were used to induce chronic GVHD. The first model involved the injection of parental strain spleen cells into adult F1 hybrids (AJ----B6AF1), while the second model utilized GVHD induced across minor histocompatibility barriers (B10.D2----BALB/c). Results indicated that significant levels of serum IFN-alpha/beta are present in mice undergoing chronic GVHD. Spleen cells from chronic GVHD mice were also shown to produce significant levels of IFN-alpha/beta upon in vitro culture in medium only. This IFN-alpha/beta production was greatly increased when GVHD spleen cells were cultured with either concanavalin A (Con A) or IL-2. In contrast, IFN-gamma production was undetectable in these Con A- or IL-2-containing cultures. Additionally, these same spleen cells which produced high levels of IFN-alpha/beta were immunosuppressed as measured by mitogen-induced cell proliferation. These results suggest that IFN-gamma production is defective in GVHD spleen cells, and that the presence of high IFN-alpha/beta production by GVHD mice may contribute to the immunosuppression associated with chronic GVHD.

Immunoregulation by natural killer cells

Polyinosinic-polycytidilic acid (poly (I:C], a synthetic analog of viral double-stranded RNA (dsRNA), activates natural killer (NK) cells and inhibits induction or promotes termination of the primary IgM response in vivo. Suppression of responses was reproduced in vivo by interferons (IFN) which activate NK cells and in vitro by cells enriched for NK cells. The likelihood that NK cells may be involved in the normal regulation of IgM responses is supported by the following observations: immunization itself induces NK activity at times appropriate to account for termination, NK cells activated by immunization suppress in vitro, mice with high NK activity induced by immunization with one antigen have reduced responses to immunization with a second antigen, and mice with induced loss of NK activity fail to down-regulate IgM antibody responses normally.

The effects of polyinosinic: polycytidylic acid (pI:C) on the GVH reaction: immunopathological observations

The effects of polyinosinic: polycytidylic acid (pI:C) on the graft-versus-host (GVH) reaction were studied. The drug pI:C rapidly and markedly induces interferon and augments natural killer (NK) cell activity. GVH reactions were induced by injecting parental lymphoid cells intravenously into F1 hybrid mice. The development of a GVH reaction was monitored by measuring the plaque-forming cell (PFC) response to sheep red blood cells (SRBC) and by histological examination. When 30 X 10(6) B6 lymphoid cells were injected into B6AF1 mice, the recipients developed profound immunosuppression by 10-12 days post-GVH induction. In addition, pathological changes indicative of GVH reactions were seen in the spleen, lymph nodes, thymus, liver, lung, pancreas, and salivary gland of these mice. However, the treatment of B6AF1 recipients with pI:C prior to parental cell transfer markedly reduced the degree of suppression of the immune response, as measured by the PFC response to SRBC. Also, such mice failed to demonstrate the histological lesions of GVH disease. Treatment of donor mice with pI:C had no effect in preventing either GVH-induced immunosuppression or pathological changes. This study suggests that a pI:C-induced mechanism, possibly involving NK cells, is capable of regulating the GVH reaction.

The functional and histological basis for graft-versus-host-induced immunosuppression

The GvH reaction resulting from the injection of parental strain cells into adult F1 hybrids suppresses both cell-mediated and humoral immune responses and is dependent on the donor-host combination and the number of parental cells used to induce the GvH reaction. The early suppression is due, at least in part, to the increased number of macrophages and the activation of suppressor macrophages which act directly on the T-helper cell and perhaps the B-cell as well. The macrophage suppression is associated with an increase in PGE production. The long-term T-cell immunodeficiency is mediated by GvH-induced thymic dysplasia resulting in a block or an arrest in T-cell differentiation and deficient IL-2 production. The B-cell immunodeficiency is associated with both a decrease in B-cell production from lymphoid progenitors and a decrease in CFU-s production. The GvH reaction induces 2 types of thymic lesion, a stress-related effect causing atrophy of the thymic cortex and a cytolytic process causing severe-to-moderate lesions in the thymic medulla as a consequence of injury to medullary epithelial cells and a loss of Hassall's corpuscles (thymic dysplasia). By employing the NK-cell-deficient beige mutation, it was shown that the severe-to-moderate thymic medullary lesions occurred in F1 mice only in those transplant situations in which the donor inoculum was of the +/bg genotype, regardless of the genotype of the recipient. It is proposed that activation of parental T cells may contribute to the early immunosuppressive events; however, the relatively permanent immunosuppression appears to be associated with NK-like effector cells which are capable of causing injury to lymphoid and epithelial tissue, especially epithelium of the thymic medulla. These studies raise the possibility that the GvH reaction may contribute to some T- and B-cell immunodeficiencies observed in the SCID and AIDS syndromes, as well as in patients following bone marrow transplantation.

Augmentation of natural killer cell activity by anti-host delayed-type hypersensitivity during the graft-versus-host reaction in mice

During a graft-versus-host (GVH) reaction in unirradiated F1 hybrid mice there is a generalized activation of natural killer (NK) cells. We have examined whether the enhanced NK activity is due to an F1 resistance mechanism directed at the parental cells used to induce the GVH reaction. Spleen cells of C57BL/10 origin induce much more NK cell activation in B10F1 hybrids than the opposite parental type, despite a similar intensity of systemic GVH reactions. However, this does not correlate with in vivo resistance of mice with GVH reaction to a local challenge dose of B10 cells. NK cell activation in (CBA X BALB/c)F1 mice with GVH reaction involves both host and donor cells and is preceded by an anti-host delayed-type hypersensitivity (DTH) response. B10 cells have a greater ability to induce DTH in B10F1 mice than cells from the opposite parent. We propose that NK cells are one group of non-specific effector cells recruited by DTH in a GVH reaction and may contribute to the tissue pathology.

The organization of cell populations within lymph nodes: their origin, life history and functional relationships

The normal lymph node comprises a superficial cortex, a deep cortex or paracortex and a medulla. In each of these regions there are three kinds of spaces: an intralymphatic space, an intravascular space and an extravascular space or interstitium. Both the vascular endothelium and the lymphatic endothelium are specialized in these different regions. The cell types in lymph nodes comprise lymphoid cells, accessory or non-lymphoid cells and stromal cells, and within these cell types a number of different sub-types can now be identified by means of enzyme- and immunocytochemistry. Based predominantly on experimental studies, the origin, migratory patterns, localization, inter-relationships and interactions between these various cells are reviewed.

Rationale for a novel immunotherapy of cancer with allogeneic lymphocyte infusion

A simple method of cancer immunotherapy has been developed which achieves marked objective response in 20-30% of patients with disseminated disease. Each course consists of a low dose of chemotherapy followed two days later by intravenous infusion of allogeneic lymphocytes. Courses are repeated on a monthly basis as needed. The function of the chemotherapy--too mild to significantly influence tumor growth directly--appears to be depletion of suppressor T cells, which sensitizes the patient to the immunostimulant action ("allogeneic effect") of the subsequently infused lymphocytes. The rationale for this method is discussed in the context of a review of past attempts at lymphocyte immunotherapy. We are now attempting to improve response rates by combatting anergy with nutritional immunopotentiators, and by preventing prostaglandin-mediated or -dependent immunosuppression with prostaglandin synthetase inhibition. By understanding and counteracting the various specific and general means by which a growing tumor induces host tolerance, it should prove possible to achieve immune-mediated tumor regression in a high proportion of patients. Best results may be seen when allogeneic lymphocyte therapy is initiated at an earlier stage of the disease, and is used in conjunction with surgery, radiotherapy, short-course intensive chemotherapy, or hyperthermia-based methods.

Homeostasis of the antibody response: immunoregulation by NK cells

When injected into mice, the synthetic double-stranded polynucleotide poly(inosinic) X poly(cytidylic) acid induces high natural killer (NK) cell activity within 4 to 12 hours. Induction of NK activity in mice immunized 2 or 3 days previously, or the addition of NK cells to cultures immunized in vitro 2 or 3 days previously, promotes early termination of the ongoing primary immunoglobulin M antibody response. A target for NK cells is a population of accessory cells that has interacted with antigen and is necessary for sustaining the antibody response. The inference is strong that NK cells induced normally by immunization also terminate the usual antibody response in vivo by elimination of antigen-exposed accessory cells.

Natural killer activity in (C57BL/6 X DBA/2)F1 hybrids undergoing acute and chronic graft-vs.-host reaction

The present findings demonstrate that a total i.v. transfer of 100 X 10(6) C57BL/6 (B6) parental spleen cells into untreated (C57BL/6 X DBA/2)F1 hybrids (B6D2F1) resulted in acute runting, which was associated with a significantly elevated graft-vs.-host (GVH) index over a one-month period following GVH induction. Furthermore, this B6-induced acute GVH disease was associated with a marked depression of natural killer (NK) cell activity (spleen and peripheral blood) (with or without addition of mouse fibroblast interferon), which correlated with lymphoid cell hypocellularity, prominent splenic extramedullary hematopoiesis (EMH), and parallel depressions of both concanavalin A- and lipopolysaccharide-induced mitogenesis. Significantly increased killing by antibody-dependent cellular cytotoxicity of antibody-coated chicken red blood cells, as well as increased T cell killing of the NK-insensitive cell line P815 (as compared to the significantly decreased killing of the NK-sensitive cell line YAC-1) was also observed in the spleens of this 100 X 10(6) B6-injected F1 group. In marked contrast to this 100 X 10(6) B6-injected acute GVH group, untreated mice injected i.v. with the same or greater numbers of parental DBA/2 spleen cells (100 X 10(6)-150 X 10(6) DBA/2 spleen cells) exhibited a milder and more chronic form of GVH disease, which was not associated with a significant decrease of NK activity. It was of considerable interest that a total i.v. transfer of 50 X 10(6) B6 spleen cells (i.e. one-half of that required to produce acute GVH, markedly depressed NK, and prominent splenic EMH) into B6D2F1 hybrids also resulted in a more chronic form of GVH disease, but was associated with significantly increased levels of NK activity at two weeks post GVH induction.

Level and temporal pattern of naturally cytolytic cells during acute Graft-versus-Host Disease (GVHD) in the rat

The purpose of the present study was to determine the level of nonadherent lymphoid cells from Graft-verus-Host Disease (GVHD) rats able to naturally kill (NK/NC cells) various solid tumor or lymphoma cells in vitro. Acute lethal GVHD was produced in either newborn or adult (DA x LEW)F1 rats by iv injection of LEW spleen and lymph node (LN) cells. Controls received the same dose of syngeneic cells. At 7, 14, and 21 days after cell injection, the ability of non-adherent mononuclear cells from the LN, spleen, peripheral blood lymphocytes (PBL), marrow, and thymus to kill 51Cr-labeled dog (DT-5) lymphoma, and undifferentiated sarcoma (11031) or human (HUS-2) sarcoma cells in vitro was determined. Only spleen and marrow of controls caused significant 51Cr release from the target cell lines. However, LN, spleen, marrow, PBL, and thymus from neonates and adults with GVHD of 7 days duration caused greater release from all targets than controls (P less than 0.05-0.001). By Day 14 the level of 51Cr released was significantly less than controls except for the values from LNs and thymus which remained elevated. By Day 21 all lymphoid compartments exhibited a decrease in NK/NC cells. Thus, early during acute GVHD, there is an activation and/or expansion of NK/NC cells while later-stage GVHD rats have depressed NK/NC levels.