Thymosine, a thymus hormone, restores the thymectomy induced deterioration of the routine pathways of migration and differentiation ofhemopoietic stem cells in mice. Administration of thymosine together with bone marrow cells from thymectomized mice to irradiated recipients also restores the level of migration and differentiation of hemopoietic stem cells. The inducing effect of thymosine on the maturation of T-lymphocyte precursors, which in their turn restore the usual rate of migration and differentiation of hemopoietic stem cells, has been suggested.

A research was made to study the dynamics of the proliferative, colony-forming and migration capacity of stem hemopoietic cells in (CBA X C57Bl) F1 hybrid mice under the influence of testosterone propionate, 10 mg/100 g, as well as the migration of immunocompetent B lymphocytes from the bone marrow to the spleen and the accumlation of their progeny, antibody-producing cells, in the spleen. The immunodepressive effect of testosterone was manifested by a decrease in the migration of B cells and the number of antibody-producing cells in the spleen. On the contrary, testosterone had a stimulating effect on the functional activity of stem hemopoietic cells, increasing their proliferation and migration. Under conditions of the suppressed erythropoietic differentiation of multipotent stem hemopoietic cells the injection of testosterone resulted in an increase in the number of antibody-producing cells in the spleen. This suggests that the stimulation of erythropoiesis and immunosuppression, induced by testosterone, are interconnected and determined by the direct action of the hormone on the cellular cycle of the stem cells, as well as by their prevailing differentiation towards the erythroid series, resulting in the decrease of their differentiation into B cells.

The analysis of NA-5 and NA-6, copolymers of acrylic acid and N-vinylpyrrolidone obtained by the method of radical copolymerization, indicated that these copolymers, while having no toxicity characteristic of polyacrylic acid known to be a powerful agent for stimulating immunogenesis, increased the migration of stem cells, and the processes of T and B lymphocyte spreading, as well as sharply enhanced the effect of interaction between T and B lymphocytes and partially replaced the helper function of T cells; all these actions finally enhanced immune response in the body. A decrease in the toxicity of copolymers was found to be in linear relationship with the percentage of the links of acrylic acid, whereas the adjuvant activity of the copolymers remained unchanged.

"Phodomos", a biostimulator of the "Biomos" group of metal complexes, considerably increases (2-3-fold) antibody production and the phagocytic ability of micro- and macrophages in experimental animals. The preparation has no essential influence on the ability of the bone marrow stem cells for colony formation in the body of irradiated animals.

An ascite variant of spontaneous mammary gland tumor of C3H/Sn mice was transplanted subcutaneously into syngenic mice. During the tumor growth (150 days) some alterations occur in the genetical structure of the tumor population: a change in the stem line, the increase and a further decrease of nearoctaploid cells.

The hemopoietic cell cloning in the spleen of irradiated mice showed that thymectomy in mature animals produced no significant changes either in the CFU count or in their self-maintenance ability.

Decreased self-maintenance ability of the migrating stem cells (CFU) from the peripheral blood or ectopic focus of hemopoiesis in comparison to the settled bone marrow CFU, as measured by the spleen colony method or by means of chromosomal markers, has been studied. The competence for myeloid and lymphoid differentiation was essentially the same for migrating and settled stem cells.

A mixed transplantation of bone marrow cells, and lymph nodes or thymic cells of mice CBA strain into lethally irradiated hybrid recipients (CBAXC57B1)F1 is accompanied with changes in the differentiation pattern from a mainly erythroid to a mainly granuloid way. Thymectomy of either donor of bone marrow cells or recipients, or both, destroys the stem cell differentiation in the direction of granulopoieseis. Intact syngeneic lymphocytes normalize differentiation of the stem cells, but in the presence of tissue antigens these provide for the stem cell differentiation mainly in the direction of granulopoiesis. The differentiation of stem haemopoietic cells is accomplished under the thymic and lymphocyte control. T-differentiating lymphocytes (Td) are the lymphocytes controlling the stem cell differentiation.