Isolated limb perfusion for extremity soft-tissue sarcomas, in-transit metastases, and other unresectable tumors: credits, debits, and future perspectives

Isolated limb perfusion (ILP) with melphalan is effective against melanoma in-transit metastases but has failed in the treatment of limb-threatening extremity sarcomas. Tumor necrosis factor-alpha (TNF) has changed this situation completely. Now, ILP with TNF + melphalan is a very successful treatment to prevent amputation. In a multicenter European trial, ILP with TNF + melphalan resulted in a 76% response rate and a 71% limb salvage rate in patients with limb-threatening soft-tissue sarcomas, deemed unresectable by independent review committees, leading to approval of TNF in Europe. We have also reported on the success of this regimen against bulky melanomas, multifocal skin cancers, and drug-resistant bony sarcomas. High-dose TNF destructs tumor vasculature, and, most importantly, it enhances tumor-selective drug uptake (ie, melphalan and doxorubicin) by threefold to sixfold. Similar synergy is observed in well-vascularized liver metastases after isolated hepatic perfusion with TNF and melphalan. New (vasoactive) drugs and mechanisms of action and interaction with chemotherapy are in development. ILP is also a promising treatment modality for adenoviral vector-mediated gene therapy. Many clinical phase I/II evaluations in ILP are now underway.

Adenovirus-mediated interleukin 3 beta gene transfer by isolated limb perfusion inhibits growth of limb sarcoma in rats

Cytokine gene transfer using (multiple) intratumoral injections can induce tumor regression in several animal models, but this administration technique limits the use for human gene therapy. In the present studies we describe tumor growth inhibition of established limb sarcomas after a single isolated limb perfusion (ILP) with recombinant adenoviral vectors harboring the rat IL-3 beta gene (IG.Ad.CMV.rIL-3 beta). In contrast, a single intratumoral injection or intravenous administration did not affect tumor growth. Dose-finding studies demonstrated a dose-dependent response with a loss of antitumor effect below 1 x 10(9) IU of IG.Ad.CMV.rIL-3 beta. Perfusions with adenoviral vectors bearing a weaker promoter (MLP promoter) driving the rIL-3 beta gene did not result in antitumor responses, suggesting that the rIL-3 beta-mediated antitumor effect depends on the amount of rIL-3 beta protein expressed by the infected cells. Furthermore, it was shown by direct comparison that ILP with IG.Ad.CMV.rIL-3 beta in the ROS-1 osteosarcoma model is at least as efficient as the established therapy with the combination of TNF-alpha and melphalan. Treatment with IG.Ad.CMV.rIL-3 beta induced a transient dose-dependent leukocytosis accompanied by an increase in peripheral blood levels of histamine. Leukocyte infiltrations were also histopathologically demonstrated in tumors after perfusion. These results demonstrate that ILP with recombinant adenoviral vectors carrying the IL-3 beta transgene inhibits tumor growth in rats and suggest that cytokine gene therapy using this administration technique might be beneficial for clinical cancer treatment.

Isolated limb perfusion for local gene delivery: efficient and targeted adenovirus-mediated gene transfer into soft tissue sarcomas

OBJECTIVE

To evaluate the potential of isolated limb perfusion (ILP) for efficient and tumor-specific adenovirus-mediated gene transfer in sarcoma-bearing rats.

SUMMARY BACKGROUND DATA

A major concern in adenovirus-mediated gene therapy in cancer is the transfer of genes to organs other than the tumor, especially organs with a rapid cell turnover. Adjustment of the vector delivery route might be an option creating tumor specificity in therapeutic gene expression.

METHODS

Rat hind limb sarcomas (5-10 mm) were transfected with recombinant adenoviruses. Intratumoral luciferase expression after ILP was compared with systemic administration, regional infusion, or intratumoral injection using a similar dose of adenoviruses carrying the luciferase marker gene. Localization studies using lacZ as a marker gene were performed to evaluate the intratumoral distribution of transfected cells after both ILP and intratumoral injection.

RESULTS

Intratumoral luciferase activity after ILP or intratumoral administration was significantly higher compared with regional infusion or systemic administration. After ILP, luciferase gene expression was minimal in extratumoral organs, whether outside or inside the isolated circuit. Localization studies demonstrated that transfection was confined to tumor cells lying along the needle track after intratumoral injection, whereas after ILP, lacZ expression was found in viable tumor cells and in the tumor-associated vasculature.

CONCLUSIONS

Using ILP, efficient and tumor-specific gene transfection can be achieved. The ILP technique might be useful for the delivery of recombinant adenoviruses carrying therapeutic gene constructs to enhance tumor control.

Nitric oxide synthase inhibition results in synergistic anti-tumour activity with melphalan and tumour necrosis factor alpha-based isolated limb perfusions

Nitric oxide (NO) is an important molecule in regulating tumour blood flow and stimulating tumour angiogenesis. Inhibition of NO synthase by L-NAME might induce an anti-tumour effect by limiting nutrients and oxygen to reach tumour tissue or affecting vascular growth. The anti-tumour effect of L-NAME after systemic administration was studied in a renal subcapsular CC531 adenocarcinoma model in rats. Moreover, regional administration of L-NAME, in combination with TNF and melphalan, was studied in an isolated limb perfusion (ILP) model using BN175 soft-tissue sarcomas. Systemic treatment with L-NAME inhibited growth of adenocarcinoma significantly but was accompanied by impaired renal function. In ILP, reduced tumour growth was observed when L-NAME was used alone. In combination with TNF or melphalan, L-NAME increased response rates significantly compared to perfusions without L-NAME (0-64% and 0-63% respectively). An additional anti-tumour effect was demonstrated when L-NAME was added to the synergistic combination of melphalan and TNF (responses increased from 70 to 100%). Inhibition of NO synthase reduces tumour growth both after systemic and regional (ILP) treatment. A synergistic anti-tumour effect of L-NAME is observed in combination with melphalan and/or TNF using ILP. These results indicate a possible role of L-NAME for the treatment of solid tumours in a systemic or regional setting.

An overview on the use of TNF-alpha: our experience with regional administration and developments towards new opportunities for systemic application

Tumor necrosis factor-alpha is a multifunctional cytokine and its potential as antitumor agent has been extensively investigated for the treatment of cancer: Initial enthusiasm was tempered when systemic treatment with TNF-alpha was found to cause severe toxic side effects in phase I/II studies. Other applications were sought and a revival of the drug was its application in combination with the cytotoxic drug melphalan in isolated limb perfusion (ILP). Here we discuss the pre-clinical and clinical studies which led to the success in treatment of patients with irresectable extremity soft tissue sarcoma and multiple melanoma in-transit metastases confined to the limb. This achievement may herald the development of new applications of TNF-alpha in isolated organ perfusion settings. An extension of its use may be found in the application of less toxic TNF-mutants or encapsulated in sterically stabilized liposomes. The review concludes with the possible application of low dose TNF-alpha, which can be given systemically, to enhance the anti-tumor potency of formulated drugs (such a liposomal doxorubicin) by increasing solid tumor targeting.

Synergistic antitumour effect of TNF-SAM2 with melphalan and doxorubicin in isolated limb perfusion in rats

An isolated limb perfusion model (ILP) using soft tissue sarcoma bearing rats (BN175) was used to study antitumour activity of a tumour necrosis factor alpha mutant (TNF-SAM2) in combination with melphalan and doxorubicin. Progressive disease was demonstrated after ILP without agents (sham) or with 50 micrograms TNF-SAM2. ILP with 40 micrograms melphalan or 400 micrograms doxorubicin resulted in no change of tumour volume or progressive disease five days after perfusion. Partial and complete response rates were demonstrated in 76% of rats when the combination of TNF-SAM2 and melphalan was used. TNF-SAM2 in combination with doxorubicin was synergistic as well with a 70% response rate. Histopathologically these responses consisted of hemorrhagic necrosis of the coagulative type. 2 In conclusion, TNF-SAM2 has similar antitumour activity in combination with melphalan or doxorubicin as rHuTNF in sarcoma-bearing rats and is eligible to be tested in clinical ILP or organ perfusion settings because of its potential decreased toxicity.

Tumor necrosis factor-alpha augments tumor effects in isolated hepatic perfusion with melphalan in a rat sarcoma model

Isolated hepatic perfusion (IHP) is an attractive approach to treating nonresectable liver tumors, because the effects of systemic chemotherapy are poor and its application is hampered by severe general toxicity. In clinical and experimental settings, the efficacy of isolated limb perfusion (ILP) with tumor necrosis factor-alpha (TNF alpha) in combination with melphalan to treat melanoma in transit and soft-tissue sarcoma has been well established. In an ILP model in rats, the authors previously observed synergistic anti-tumor effects of TNF and melphalan on BN 175 soft-tissue sarcoma extremity tumors. The aim of the current study was to determine whether similar synergy in anti-tumor effects could be achieved by treating experimental BN 175 soft-tissue sarcoma liver tumors by IHP using these agents. The authors found that IHP with TNF and melphalan resulted in a dramatic increase in regional concentrations of perfused agents with virtually no concomitant systemic leakage. Isolated hepatic perfusion with only carrier solution resulted in a significantly diminished growth rate of BN 175 liver tumors compared with the growth rate of tumors in nonperfused rats. Perfusion with melphalan alone resulted in minimal anti-tumor effects. Perfusion with only TNF had a slight growth-stimulatory effect on the BN 175 liver tumors, but no negative effects on tumor growth were observed. When TNF was added to melphalan, a dramatic anti-tumor effect was observed. Thus, as in the rat ILP setting, the anti-tumor effect is augmented when TNF is added to IHP with melphalan to treat BN 175 soft-tissue sarcoma tumor-bearing rats. Strikingly, the tumor response was potentiated at relatively low concentrations of TNF compared with concentrations that elicited synergy with melphalan in ILP.

Isolated hypoxic hepatic perfusion (IHHP) using balloon catheter techniques: from laboratory to the clinic towards a percutaneous procedure

BACKGROUND/AIMS

The success of and our extensive experience with TNF alpha-based isolated limb perfusions in patients with unresectable extremity soft tissue sarcomas made us explore the possibilities for a similar approach for the treatment of hepatic metastases. After experience with the classic surgical isolated hepatic perfusion in pigs and in patients, we concluded that the classic surgical approach was associated with serious drawbacks i.e., magnitude of the procedure with morbidity, lack of repeatability of the procedure, complexity and costs. These problems were addressed in a program aimed at developing a repeatable method of isolated perfusion of the liver with minimally invasive techniques.

METHODOLOGY

We validated the methodology of isolated hypoxic hepatic perfusion using balloon catheter techniques in pigs.

RESULTS

The excellent pharmacokinetic profile of the procedure, resulting in very high regional drug concentrations and negligible systemic drug concentrations, allowed us to move on to the clinic and start to study and further develop this method in a phase I-II study using the drug melphalan, in patients with irresectable hepatic metastases.

CONCLUSIONS

We aim to develop step by step a fully percutaneous approach for isolated hypoxic hepatic perfusion.

Systemic toxicity and cytokine/acute phase protein levels in patients after isolated limb perfusion with tumor necrosis factor-alpha complicated by high leakage

BACKGROUND

Since the introduction of high-dose tumor necrosis factor-alpha (TNFalpha) in the setting of isolated limb perfusion (ILP) in the clinic, prevention of leakage to the body of the patient is monitored with great precision for fear of TNF-mediated toxicity. That we observed remarkably little toxicity in patients with and without leakage prompted us to determine patterns of cytokines and acute phase proteins in patients with high leakage and in patients without any leakage.

METHODS

TNFalpha, interleukin (IL)-6, IL-8, C-reactive protein, and secretory (s)-phospholipase A2 were measured at several time points during and after (until 7 days) ILP in 10 patients with a leakage to the systemic circulation varying in percentage from 12% to 65%. As a control, the same measurements, both in peripheral blood and in perfusate, were performed in nine patients without systemic leakage.

RESULTS

In patients with systemic leakage, levels of TNFalpha increased during ILP, reaching values to 277 ng/ml. IL-6 and IL-8 peaked 3 hours after ILP with values significantly higher compared with patients without systemic leakage. C-reactive protein and s-phospholipase A2 peaked at day 1 in both patient groups, s-phospholipase A2 with significant higher levels and C-reactive protein, in contrast, with lower levels in the leakage patients.

CONCLUSIONS

High leakage of TNFalpha to the systemic circulation, caused by a complicated ILP, led to 10-fold to more than 100-fold increased levels of TNFalpha, IL-6, and IL-8 in comparison with patients without leakage. The increase of the acute phase proteins was limited. Even when high leakage occurs, this procedure should not lead to fatal complications. The most prominent clinical toxicity was hypotension (grade III in four patients), which was easily corrected. No pulmonary or renal toxicity was observed in any patient. It is our experience that, even in the rare event of significant leakage during a TNFa-based ILP, postoperative toxicity is usually mild and can be easily managed by the use of fluid and, in some cases, vasopressors.

Tumour necrosis factor alpha increases melphalan concentration in tumour tissue after isolated limb perfusion

Several possible mechanisms for the synergistic anti-tumour effects between tumour necrosis factor alpha (TNF-alpha) and melphalan after isolated limb perfusion (ILP) have been presented. We found a significant sixfold increase in melphalan tumour tissue concentration after ILP when TNF-alpha was added to the perfusate, which provides a straightforward explanation for the observed synergism between melphalan and TNF-alpha in ILP.

TNF-alpha augments intratumoural concentrations of doxorubicin in TNF-alpha-based isolated limb perfusion in rat sarcoma models and enhances anti-tumour effects

We have shown previously that isolated limb perfusion (ILP) in sarcoma-bearing rats results in high response rates when melphalan is used in combination with tumour necrosis factor alpha (TNF-alpha). This is in line with observations in patients. Here we show that ILP with doxorubicin in combination with TNF-alpha has comparable effects in two different rat sarcoma tumour models. The addition of TNF-alpha exhibits a synergistic anti-tumour effect, resulting in regression of the tumour in 54% and 100% of the cases for the BN175-fibrosarcoma and the ROS-1 osteosarcoma respectively. The combination is shown to be mandatory for optimal tumour response. The effect of high dose TNF-alpha on the activity of cytotoxic agents in ILP is still unclear. We investigated possible modes by which TNF-alpha could modulate the activity of doxorubicin. In both tumour models increased accumulation of doxorubicin in tumour tissue was found: 3.1-fold in the BN175 and 1.8-fold in the ROS-1 sarcoma after ILP with doxorubicin combined with TNF-alpha in comparison with an ILP with doxorubicin alone. This increase in local drug concentration may explain the synergistic anti-tumour responses after ILP with the combination. In vitro TNF-alpha fails to augment drug uptake in tumour cells or to increase cytotoxicity of the drug. These findings make it unlikely that TNF-alpha directly modulates the activity of doxorubicin in vivo. As TNF-alpha by itself has no or only minimal effect on tumour growth, an increase in local concentrations of chemotherapeutic drugs might well be the main mechanism for the synergistic anti-tumour effects.

Prerequisites for effective isolated limb perfusion using tumour necrosis factor alpha and melphalan in rats

An isolated limb perfusion (ILP) model using soft tissue sarcoma-bearing rats was used to study prerequisites for an effective ILP, such as oxygenation of the perfusate, temperature of the limb, duration of the perfusion and concentration of tumour necrosis factor (TNF). Combination of 50 microg TNF and 40 microg melphalan demonstrated synergistic activity leading to a partial and complete response rate of 71%. In comparison to oxygenated ILP, hypoxia was shown to enhance anti-tumour activity of melphalan alone and TNF alone but not of their combined use. Shorter perfusion times decreased anti-tumour responses. At a temperature of 24-26 degrees C, anti-tumour effects were lost, whereas temperatures of 38-39 degrees C or 42-43 degrees C resulted in higher response rates. However, at 42-43 degrees C, local toxicity impaired limb function dramatically. Synergy between TNF and melphalan was lost at a dose of TNF below 10 microg in 5 ml perfusate. We conclude that the combination of TNF and melphalan has strong synergistic anti-tumour effects in our model, just as in the clinical setting. Hypoxia enhanced activity of melphalan and TNF alone but not the efficacy of their combined use. For an optimal ILP, minimal perfusion time of 30 min and minimal temperature of 38 degrees C was mandatory. Moreover, the dose of TNF could be lowered to 10 microg per 5 ml perfusate, which might allow the use of TNF in less leakage-free or less inert perfusion settings.

Isolated hypoxic hepatic perfusion with tumor necrosis factor-alpha, melphalan, and mitomycin C using balloon catheter techniques: a pharmacokinetic study in pigs

OBJECTIVE

To validate the methodology of isolated hypoxic hepatic perfusion (IHHP) using balloon catheter techniques and to gain insight into the distribution of tumor necrosis factor-alpha (TNF), melphalan, and mitomycin C (MMC) through the regional and systemic blood compartments when applying these techniques.

SUMMARY BACKGROUND DATA

There is no standard treatment for unresectable liver tumors. Clinical results of isolated limb perfusion with high-dose TNF and melphalan for the treatment of melanoma and sarcoma have been promising, and attempts have been made to extrapolate this success to the isolated liver perfusion setting. The magnitude and toxicity of the surgical procedure, however, have limited clinical applicability.

METHODS

Pigs underwent IHHP with TNF, melphalan, and MMC using balloon catheters or served as controls, receiving equivalent dosages of these agents intravenously. After a 20-minute perfusion, a washout procedure was performed for 10 minutes, after which isolation was terminated. Throughout the procedure and afterward, blood samples were obtained from the hepatic and systemic blood compartments and concentrations of perfused agents were determined.

RESULTS

During perfusion, locoregional plasma drug concentrations were 20- to 40-fold higher than systemic concentrations. Compared with systemic concentrations after intravenous administration, regional concentrations during IHHP were up to 10-fold higher. Regional MMC and melphalan levels steadily declined during perfusion, indicating rapid uptake by the liver tissue; minimal systemic concentrations indicated virtually no leakage to the systemic blood compartment. During isolation, concentrations of TNF in the perfusate declined only slightly, indicating limited uptake by the liver tissue; no leakage of TNF to the systemic circulation was observed. After termination of isolation, systemic TNF levels showed only a minor transient elevation, indicating that the washout procedure at the end of the perfusions was fully effective.

CONCLUSIONS

Complete isolation of the hepatic vascular bed can be accomplished when performing IHHP using this balloon catheter technique. Thus, as in extremities, an ideal leakage-free perfusion of the liver can now be performed, and repeated, without major surgery. The effective washout allows the addition of TNF in this setting.

Differential nitric oxide and TNF-alpha production of murine Kupffer cell subfractions upon priming with IFN-gamma and TNF-alpha

AIMS/BACKGROUND

We have previously shown a striking heterogeneity of naive murine Kupffer cells (KC) that depends on cell size.

METHODS

In the present study, we demonstrate a shift in response of KC fractions separated on cell size by countercurrent elutriation upon priming with tumor necrosis factor-alpha (TNF-alpha) or interferon-gamma (IFN-gamma).

RESULTS

Whereas unprimed large KC are most active in the production of TNF-alpha and nitric oxide (NO), after priming of KC with TNF-alpha predominantly small and intermediate sized KC produce TNF-alpha in response to bacteria. Priming with IFN-gamma enhanced NO production in all KC. A strong synergy, with respect to production of NO, was observed when KC subfractions were exposed to a combination of TNF-alpha and IFN-gamma. Concerning TNF-alpha production, priming of KC subfractions seemed to induce a shift of activity from large KC to smaller KC.

CONCLUSIONS

The present data demonstrate a clear heterogeneity among murine KC with respect to immunologic response to stimuli. These results demonstrate that KC have different functions in immunologic reactions that seem to be related to size.

Biodistribution and tumor localization of stealth liposomal tumor necrosis factor-alpha in soft tissue sarcoma bearing rats

The blood residence half-life and organ distribution of recombinant human tumor necrosis factor-alpha (TNF-alpha) encapsulated in sterically stabilized liposomes, were investigated in rats bearing a soft tissue sarcoma in the hind leg. We studied the decay in blood concentration of "empty" liposomes using the aqueous marker 67gallium-desferal, as well as the blood concentration of soluble TNF-alpha and liposome encapsulated TNF-alpha using l25I. Encapsulation efficacy of TNF-alpha was 24%. The pharmacokinetics of TNF-alpha were markedly altered after encapsulation in liposomes, with a 33-fold increase in mean residence time of TNF-alpha in the blood, and a concomitant 14-fold increase in the area under the plasma concentration vs. time curve for liposomal TNF-alpha. Although the liposomes exhibit Stealth characteristics, uptake by mononuclear phagocyte-rich organs (e.g., liver and spleen) was noticeable, especially at later time points. Encapsulation of TNF-alpha in sterically stabilized liposomes resulted in a marked increase in localization of the cytokine in tumor measured as total uptake over time. However, peak TNF-alpha concentration levels in tumor were not significantly enhanced compared with free TNF-alpha. Besides the augmented localization of TNF-alpha after encapsulation in sterically stabilized liposomes, a diminished toxicity was observed.

Involvement of T cells in enhanced resistance to Klebsiella pneumoniae septicemia in mice treated with liposome-encapsulated muramyl tripeptide phosphatidylethanolamine or gamma interferon

We have previously shown that prophylactic administration of the liposome-encapsulated immunomodulating agents muramyl tripeptide phosphatidylethanolamine (MTPPE) and gamma interferon (IFN-gamma) results in strongly increased survival of mice from a normally lethal septicemia with Klebsiella pneumoniae. It was anticipated that the treatment acts on macrophages and nonspecifically augments host resistance to various infections. In the present study, we provide evidence for a key role for T cells in host defense potentiation by the liposomal immunomodulators toward K. pneumoniae septicemia. It is shown that both CD4 and CD8 cells are important in immunomodulation, most likely due to production of IFN-gamma. Depletion of circulating IFN-gamma resulted in strong reduction of the antimicrobial host defense activation. Administration of interleukin-10 resulted in decreased antimicrobial host defense activation by liposomal immunomodulators. Moreover, administration of liposomal immunomodulators was shown to induce predominantly T-helper type 1 (Th1) cell populations in the spleen. These findings indicate that immunomodulation with liposomal MTPPE and IFN-gamma favors Th1 and NK cell activation.

Isolation and characterization of murine Kupffer cells and splenic macrophages

A method is described using counterflow centrifugation elutriation to isolate macrophages from murine liver and spleen. In this study three, size fractionated, macrophage populations were collected. Isolation resulted in a high yield of pure Kupffer cells (total of 10 x 10(6) /g liver) and enrichment of splenic macrophages to 20%. In addition to standard methods such as non-specific esterase staining, the isolated macrophages were also characterized by flow cytometry using specific monoclonal antibodies. In addition, a rapid flow cytometry method was introduced to determine the percentage of macrophages based on autofluorescence. A strong correlation was found between the percentages of macrophages found by non-specific esterase staining and autofluorescence. Functional tests revealed differences between the isolated macrophages in terms of tumor necrosis factor-alpha (TNF-alpha) production, oxygen metabolism and the production of nitric oxide. However, no significant differences in phagocytic activity was observed between the fractions. After two weeks of culture without the addition of antibiotics the cells still exhibited the above mentioned functions.

Enhancement of nonspecific resistance by liposome-encapsulated immunomodulators does not affect skin graft rejection in mice

Administration of liposome-encapsulated immunomodulating agents muramyl tripeptide phosphatidyl ethanolamine (LE-MTPPE) or interferon-gamma (LE-IFN-gamma), or co-encapsulated MTPPE and IFN-gamma (LE-(MTPPE/IFN-gamma)) resulted in a dramatic increase of the nonspecific antimicrobial resistance in mice, as shown before. This kind of treatment is especially of use in immunocompromised hosts who are prone to severe infections. Application of these immunomodulators might protect these patients, e.g., transplant recipients, from opportunistic infections. However, accelerated rejection of the graft, resulting from augmentation of the antimicrobial defense in a nonspecific way, has to be avoided. In this study, the effect of treatment with LE-MT-PPE, LE-IFN-gamma, or LE-(MTPPE/IFN-gamma) on skin graft rejection in mice was investigated. It was found that prophylactic treatment of skin-grafted mice with immunomodulating formulations did not influence rejection of the graft. Moreover, in T cell-depleted mice, which showed a prolonged graft survival compared with immunocompetent recipients, the administration of immunomodulators did not change the survival time of the grafts compared with T cell-depleted mice that did not receive immunomodulators. The results clearly show that, in this experimental setting, application of the antimicrobial resistance-enhancing formulations (LE-MTPPE, LE-IFN-gamma, and LE-(MTPPE/IFN-gamma)) is allowed in graft-bearing recipients, without influencing graft survival.

Modulation of nonspecific antimicrobial resistance of mice to Klebsiella pneumoniae septicemia by liposome-encapsulated muramyl tripeptide phosphatidylethanolamine and interferon-gamma alone or combined

Activation of the host defense system in a nonspecific way might provide tools to support failing antibiotic treatment in certain infectious diseases. The antimicrobial effect was investigated of liposome-encapsulated muramyl tripeptide phosphatidylethanolamine (MTPPE) and interferon (IFN)-gamma and liposome-coencapsulated MTPPE and IFN-gamma on Klebsiella pneumoniae septicemia in mice. Prophylactic treatment of mice with five doses of liposomal MTPPE or IFN-gamma increased survival from 0 to 65%. Administration of MTPPE and IFN-gamma coencapsulated in liposome resulted in 100% survival. In vitro, peritoneal macrophages by themselves were stimulated by these agents but were unable to kill K. pneumoniae. However, production of both oxygen and nitrogen intermediates increased when immunomodulators were added to macrophages. These results indicate that effective prophylactic treatment of septicemia due to K. pneumoniae with coencapsulated MTPPE and IFN-gamma is not solely due to activation of the resident macrophages.

Liposomes as delivery systems in the prevention and treatment of infectious diseases

Research on the potential application of liposomes in the prevention and treatment of infectious diseases has focussed on improvement of the therapeutic index of antimicrobial drugs and immunomodulators and on stimulation of the immune response to otherwise weak antigens in vaccines composed of purified micro-organism subunits. In this review current approaches in this field are outlined. The improved therapeutic index of antimicrobial drugs after encapsulation in liposomes is a result of enhanced drug delivery to infected tissue or infected cells and/or a reduction of drug toxicity of potentially toxic antibiotics. Liposomal encapsulation of immunomodulators that activate macrophages aims at reducing the toxicity of these agents and targeting them to the cells of the mononuclear phagocyte system in order to increase the nonspecific resistance of the host against infections. Studies on the immunogenicity of liposomal antigens have demonstrated that liposomes can potentiate the humoral and cell mediated immunity to a variety of antigens.

Role of adjuvants in the modulation of antibody isotype, specificity, and induction of protection by whole blood-stage Plasmodium yoelii vaccines

Mice were immunized with whole killed blood stage Plasmodium yoelii parasites in 15 adjuvant formulations then boosted and challenged with parasitized blood. Five of six groups immunized with the Ag in oil-in-water emulsions or formulations without oil were protected. Formulations that induced protection contained saponin, pertussis, copolymer P1004, and detoxified RaLPS. In contrast, none of nine groups of animals immunized with Ag in water-in-oil emulsions were protected. Ineffective adjuvants included CFA and water-in-squalene emulsions with copolymer L141 plus detoxified RaLPS, dimethyldioctadecyl ammonium bromide, and mycobacterial cell wall skeletons. Antibody was measured by ELISA against disrupted parasites and by indirect fluorescent antibody (immunofluorescence) using intact parasites. Protection was associated with antibody of the IgG2a isotype detected by immunofluorescence but not with other isotypes detected by immunofluorescence or any type antibody detected by ELISA. The water-in-oil adjuvants induced high titers by ELISA but low titers by immunofluorescence. These results, together with Western blot analyses, suggested that adjuvant vehicles control the specificity of antibody and that this, in turn, is essential for induction of protective immune responses in this model.

Role of adjuvants in the modulation of antibody isotype, specificity, and induction of protection by whole blood-stage Plasmodium yoelii vaccines

Mice were immunized with whole killed blood stage Plasmodium yoelii parasites in 15 adjuvant formulations then boosted and challenged with parasitized blood. Five of six groups immunized with the Ag in oil-in-water emulsions or formulations without oil were protected. Formulations that induced protection contained saponin, pertussis, copolymer P1004, and detoxified RaLPS. In contrast, none of nine groups of animals immunized with Ag in water-in-oil emulsions were protected. Ineffective adjuvants included CFA and water-in-squalene emulsions with copolymer L141 plus detoxified RaLPS, dimethyldioctadecyl ammonium bromide, and mycobacterial cell wall skeletons. Antibody was measured by ELISA against disrupted parasites and by indirect fluorescent antibody (immunofluorescence) using intact parasites. Protection was associated with antibody of the IgG2a isotype detected by immunofluorescence but not with other isotypes detected by immunofluorescence or any type antibody detected by ELISA. The water-in-oil adjuvants induced high titers by ELISA but low titers by immunofluorescence. These results, together with Western blot analyses, suggested that adjuvant vehicles control the specificity of antibody and that this, in turn, is essential for induction of protective immune responses in this model.