Treatment of experimental rabbit liver tumours by selectively targeted hyperthermia.

Experimental rabbit liver tumours were preferentially heated to therapeutic temperatures without compromising the surrounding normal hepatic parenchyma. This was achieved by the use of hepatic arterially infused ferromagnetic microspheres that heat as a result of magnetic hysteresis loss when exposed to an alternating magnetic field. Treatment sessions involving a single 20-min exposure to the alternating field resulted in total suppression of tumour growth at 14 days compared to controls, in which tumour sizes increased dramatically over the same period. Histopathological examination of treated tumour sections showed total tumour destruction in some cases. Separate animal groups used to control for the effects of the embolized microspheres alone and for the effect of the applied magnetic field yielded similar tumour growth responses to a control group with no intervention whatsoever. The achievement of positive temperature differentials between tumour and normal liver and the consequent therapeutic responses encourages further development of this technology for the treatment of liver cancer in humans.

Experimental examination of a targeted hyperthermia system using inductively heated ferromagnetic microspheres in rabbit kidney.

It is known that significant heating can be generated by magnetic hysteresis effects in small ferromagnetic particles exposed to a rapidly alternating magnetic field. If such particles can be made to infiltrate the vascular bed surrounding a tumour by intravascular infusion then it may be possible to generate sufficient heating to destroy the tumour by hyperthermia. One of the constraints on such a technique is the limited amount of magnetic material that can be delivered to a tumour via the intravascular route and the consequent heating that can be induced by this material. Here, we report on a series of experiments in which doses of microspheres containing different amounts of ferromagnetic material were infused into rabbit kidneys via the renal artery with the aim of testing whether adequate tissue heating could be achieved using realistic concentrations of the embolised material. Heating rates were measured for each infused quantity under similar conditions with the animal alive and dead to examine the role of blood flow in the heating process. The results show that tissue temperatures above the therapeutic threshold of 42 degrees C can be readily achieved using this method with clinically relevant concentrations of microspheres in living tissue.

Inflammatory and immunological responses to murine cytomegalovirus in resistant CBA mice.

The resistance of CBA mice to MCMV is associated with the resistance of H-2k cells to infection in vitro, high NK and virus-specific DTH responses, and minimal accumulation of cytostatic peritoneal macrophages. This study investigates the functional capacity of lymphoid cells from infected CBA mice, using this strain as a model for successful control of CMV. Splenic viral replication was high 1-3 days p.i. and cell numbers were depressed, but T and B cells frequencies were maintained. The remaining spleen cells were hyporesponsive in culture and accessory cell function was marginally deficient. By 7 days p.i., virus titres declined, responsiveness increased and the residual defect was associated with cytostatic macrophages. The lymph nodes did not atrophy, exhibited low levels of viral replication and proliferative capacity was retained. The beige mutation did not affect the local response to intraperitoneal infection, but spleen cell numbers and responsiveness declined progressively. The results suggest the spleen may contribute to CMV disease by the replication of virus in susceptible cells until the NK response reduces virus titres and hence limits acute virus-induced immunosuppression. Macrophage-mediated suppression persisted in the spleen during recovery so clonal expansion of protective virus-primed T cells may occur predominantly in the lymph nodes.

The inflammatory macrophage response to murine cytomegalovirus in genetically susceptible mice.

Adherent suppressor cells have often been implicated in the depression of immunocompetence following CMV infections. We have reported that high levels of cytostatic macrophages in the peritoneal cavities of infected mice correlate with genetically-based sensitivity to CMV disease, suggesting they may modulate protective immune responses. This study investigates the properties and kinetics of such cells. Genetically-susceptible BALB/c mice infected with MCMV accumulated activated peritoneal macrophages, 7 days post-infection. These cells suppressed 3H-thymidine-incorporation and lymphokine production in syngeneic lymphocyte cultures and hence appeared to have depressed accessory cell function, although interleukin-1 production and the capacity to take up colloidal gold were enhanced. The cytostatic activity was located in a low density fraction (1.05 g/ml), which was expanded by MCMV infection. The lowest density cells had higher frequencies of infection but the proportion of cells releasing virus (less than 0.2%) was below the proportion activated, as shown by the shift in the density profile or enhanced colloidal gold uptake. A comparable accumulation of cytostatic activated peritoneal macrophages occurred in mice treated with cyclosporine A, but nude mice showed macrophage activation without cytostasis, so the role of T cells is not resolved. The spleens of infected mice maintaining high levels of virus in this organ atrophied, and the remaining cells were unable to proliferate in culture. In contrast, mice clearing the virus developed splenomegaly and restricted responsiveness, which may be governed by cytostatic cells equivalent to those in the peritoneal cavity. The spread of virus to the lymph nodes was limited and MCMV-primed cells were readily demonstrable.

Genetically determined resistance to murine cytomegalovirus: a role for lymphocytostatic macrophages.

Sensitivity to lethal infection with murine cytomegalovirus depends on the H-2 and background phenotype. H-2d appears to confer sensitivity in isolated cells, but sensitive BALB/c (H-2d) mice also exhibit non-specific immunosuppression which may indicate an impaired protective immune response. To determine the significance and mechanism of this immunosuppression, genetic factors controlling the activation, lymphocytostatic potential and accessory cell function of peritoneal macrophages were analysed after sub-lethal infection. In BALB/c mice, the number of peritoneal cells declined by 20% on day 3 post-infection and increased threefold over normal levels by day 7 with a progressive increase in macrophage activation and differentiation. Cells collected on day 7 exhibited lymphocytostatic activity which was not influenced by indomethacin and depressed their ability to act as accessory cells in a proliferative assay. Similar changes in the numbers of activated mature macrophages occurred in moderately resistant BALB.K (H-2k) mice showing an association with the background phenotype. In contrast peritoneal cell counts from resistant CBA (H-2k) mice were depressed by 80% on day 4 and the remaining cells enhanced the proliferation of syngeneic lymphocytes. However, later in the infection the percentage of peritoneal cells releasing virus declined rapidly and fewer cells became lymphocytostatic in both H-2k strains.

Functional changes in murine macrophages infected with cytomegalovirus relate to H-2-determined sensitivity to infection.

Peritoneal macrophages were infected with murine cytomegalovirus in vitro, and indices of infection and macrophage function were monitored over 4 days. When the cells were assessed for the expression of viral antigen or for cytopathic effects, infection was found to be solely determined by the H-2 phenotype. Less than 10% of the macrophages from resistant H-2k strains were affected, whereas 90% of H-2d cells and approximately 80% of H-2b and H-2a cells became infected. Similar trends were demonstrable by the measurement of viral DNA. In H-2a cells (B10.A), Dd conferred sensitivity despite the resistant K and class II phenotype. The findings suggest a critical association between the class I antigens and an early stage in the infectious process. Indices of infection were paralleled by a loss of Fc receptor expression and optimal colloidal gold uptake, whereas most cells remained trypan blue negative, retained dehydrogenase and acid phosphatase activities, and did not release infectious virus during the period of study. This is consistent with a role for macrophages in the persistence of cytomegalovirus in the host.