The manifestation of age-related changes of the immune system is one of the key factors of the whole organism aging. In contrast to many other organs and systems, the immune system aging begins in an early age and has more pronounced changes. The immune function decrease is explained by many factors, including thymus dysfunction, decrease in the proportion and function of T cells, changes in hematopoietic stem cell pool, etc. To prevent these changes we used various model approaches. The model of heterochronic parabiosis demonstrated that: i) age changes of the immune system are not passive, and regular interchange by blood factors, circulating lymphocytes and stem cells between heterochronic partners does not lead to the old system rejuvenation; ii) the main age changes relate to the cells of lymphoid organ microenvironment, which provoke disturbance of the T-cell peripheral differentiation and, consequently, decrease of the immune functions and life expectancy in young heterochronic partners. The model of neonatal lymphoid organ transplantation, allowing form a lymphoid niches with young donor origin, demonstrated that the optimal development of the neonatal spleen occurs only in the absence of its own spleen in young recipients. Additional thymus graft is capable of greater stimulation of the functional activity of splenocytes from neonatal graft versus own organ in old animals. The report discusses the possible mechanisms capable to improve immunological functions in aged animals which depend on a combination of transplanted organs and age-related interaction between them.