Biology and postnatal development of organ systems of cynomolgus monkeys ( <i>Macaca fascicularis</i> )

Background The cynomolgus macaque has become the most used non-human primate species in nonclinical safety assessment during the past decades. Methods This review summarizes the biological data and organ system development milestones of the cynomolgus macaque available in the literature. Results The cynomolgus macaque is born precocious relative to humans in some organ systems (e.g., nervous, skeletal, respiratory, and gastrointestinal). Organ systems develop, refine, and expand at different rates after birth. In general, the respiratory, gastrointestinal, renal, and hematopoietic systems mature at approximately 3 years of age. The female reproductive, cardiovascular and hepatobiliary systems mature at approximately 4 years of age. The central nervous, skeletal, immune, male reproductive, and endocrine systems complete their development at approximately 5 to 9 years of age. Conclusions The cynomolgus macaque has no meaningful developmental differences in critical organ systems between 2 and 3 years of age for use in nonclinical safety assessment.