RECENT STUDIES ON THE MECHANISMS OF THE ALLOGENEIC INHIBITION PHENOMENON*

Acute leukaemia: development, remission/relapse pattern, relationship between normal and leukaemic haemopoiesis, and the 'sleeper-to-feeder' stem cell hypothesis

Attention has been focused on two problems of acute leukaemia: (1) the origin of normal-appearing haemopoietic cells during relapse, and (2) the inverse relationship between leukaemic blast cell proliferation and useful haemopoietic cell production. The available evidence suggests that the normal-appearing cells during relapse may not all be remnants of normal haemopoiesis but may at least in part be derived from leukaemic cells. Although a differentiation defect is a major characteristic of acute leukaemia, it seems as if this defect is not absolute: some cells may succeed in differentiating more or less normally in spite of their descent from a leukaemic stem cell. Acute leukaemia is usually considered to be a primary white cell disorder which indirectly affects the other haemopoietic cell lines. It appears more likely, however, that acute leukaemia, at least the myeloid type, is a disorder of a stem cell common to granulocytopoiesis, erythropoiesis, and probably thrombocytopoiesis. Most descendants from the diseased stem cell fail to differentiate and remain at the blast cell level where they proliferate for some time; however, at a certain point proliferation ceases and the cells ultimately die. Another fraction of the progeny of the leukaemic stem cells may differentiate to some extent and may give rise to functionally useful cells. This is analogous to chronic myeloid leukaemia. The mechanism by which useful haemopoiesis apparently is suppressed in the presence of leukaemic blast cells has remained enigmatic so far. Previously suggested explanations which all assume some kind of cell-cell interaction by which normal haemopoietic cells succumb have neither been proved nor disproved. In this chapter, a new hypothesis is presented. It is assumed that some normal haemopoietic stem cells enter a dormant state at various distances in lineage from the fertilized ovum ('sleepers'). Another fraction of haemopoietic stem cells ('feeders') are actively proliferating and serve to feed the differentiating haemopoietic cell lines and to maintain the 'feeder' pool. When the 'feeder' pool is exhausted, a 'sleeper' cell is activated and sets up a new 'feeder' clone. Otherwise, 'sleepers' are protected against acting as 'feeders' in order to keep 'sleeper' divisions at a minimum and thus preserve their genetic information as intact as possible. It is suggested that the leukaemic event initially takes place in one or a few 'sleepers'. If the leukaemic 'sleeper' never succeeds in setting up a 'feeder' clone, clinical leukaemia will not develop. Clinical leukaemia will result if a leukaemic 'sleeper' establishes a leukaemic 'feeder' pool.(ABSTRACT TRUNCATED AT 400 WORDS)

Ultrastructural findings in the mouse exocrine pancreas during graft-versus host reaction

12- to 36-hours-old newborn CBA mice were intraperitoneally injected each with 10 X 10(6) allogeneic spleen cells of adult C57Bl mice. Control mice received syngeneic spleen cells of adult CBA mice either in the same way or remained untreated. The animals were killed 1, 3, 7, 14 or 21 days after the spleen cell injection. The pancreas was studied histologically and electron microscopically by common methods. Together with an interstitial lymphohistiocytic infiltration of the pancreas different acinar cell alterations were observed in the mice treated with allogeneic spleen cells: 1. Acute lethal pancreatic cell damages on the day after the intraperitoneal injection of allogeneic spleen cells. 2. Membrane-lined inclusion vacuoles between the 7th and 21st experimental day. 3. Atrophy of pancreatic acinar cells in the terminal stage of a severe graft-versus-host disease. The pathogenesis of the observed pancreatic changes seems to be due to nonimmunological and immunological processes. The membrane-lined inclusion vacuoles of the acinar cells could be the consequence of a cell-mediated immune process in the graft-versus-host reaction.

Inhibition of intracellular multiplication of adenovirus by interaction between infected and uninfected cells

The possibility that virus multiplication may be inhibited by interaction of infected cells with uninfected cells was tested by experiments, using human adenovirus type 12 (Ad12). Permissive human cells (human embryonic kidney-HEK,KB or HeLa) were infected and seeded on uninfected or infected "nonpermissive" cell (human embryonic lung=HEL) monolayers, and virus yields or proportions of viral antigen-synthesizing cells were compared with each other. Both the virus yields and the proportions of viral antigen-positive cells were not reduced significantly when seeded on infected HEL cells, while they seeded on uninfected HEL cells both of them were reduced remarkably, compared with the yield and the proportion of controls seeded on glass. Similar results were obtained regardless of the type of permissive cells, HEK, KB, or HeLa. Similar reduction of the yield was observed when seeded on HEL cells infected with Ad12 inactivated by heat or by antiserum, and partial reduction was observed when seeded on HEL cells infected with UV-inactivated Ad12, depending on the extent of UV dosis. These experiments showed that intracellular virus multiplication may be inhibited by interaction of infected cells with uninfected cells, and this may be due to the difference in the cell surface structure.