**1. Introduction**

The authors of this chapter have been dealing with programmed cell death in T1DM for many years. The area of scientific interests is the assessment of apoptosis of peripheral blood lymphocytes in the closest relatives of DM1 patients with a high risk of developing DM1. The risk group for DM1 was included by the first author of this chapter in her thesis on "Apoptosis of peripheral blood mononuclear cells in patients with type 1 diabetes mellitus."

The study of the mechanisms and significance of genetically programmed cell death began in the 1960s. The authorship of the term "apoptosis" belongs to the

English scientists—J. Kerr, E. Wylie and A. Kerry, who first put forward and substantiated the concept of a fundamental difference between physiological cell death (apoptosis) and their pathological death (necrosis). To date, tens of thousands of scientific papers have been devoted to the theory of apoptosis, revealing the main mechanisms of its development at the physiological, genetic, and biochemical levels. There is an active search for its regulators. Of particular interest are studies that allow the practical use of apoptosis regulation in the treatment of oncological, autoimmune, and neurodystrophic diseases.

Apoptosis (from the Greek άπόπτωσις—fall), the process of self-destruction or "leaf fall". However, not everything is so clear. Recent studies convincingly show that the processes of apoptosis and regeneration can be strongly interrelated. The removal of non-functioning cells by apoptosis can simultaneously serve as a signal for regenerative processes through the transmission of information through apoptotic bodies. The need for a clear coordination of tissue regeneration processes raises the question of the coordinators of this regulation and the signaling pathways through which different types of cells perform their functions in this process.

And since there is only one step from cell death to regeneration, the authors of the chapter are working hard to unravel the mystery: what molecules and what mechanisms can coordinate these processes? The issues of pancreatic cell regeneration in T1DM are the subject of research that we are currently doing in our laboratory.
