Preventive vaccination is a crucial strategy for controlling and preventing infectious diseases, offering both effectiveness and cost-efficiency. However, despite the widespread success of vaccination programs, there are still certain population groups who struggle to mount adequate responses to immunization. These at-risk groups include but are not restricted to the elderly, overweight individuals, individuals with chronic infections and cancer patients. All of these groups are characterized by persistent chronic inflammation. Recent studies have demonstrated that one of the key players in immune regulation and the promotion of chronic inflammation are myeloid-derived suppressor cells (MDSCs). These cells possess a wide range of immunosuppressive mechanisms and are able to dampen immune responses in both antigen-specific and antigen-nonspecific manner, thus contributing to the establishment and maintenance of an inflammatory environment. Given their pivotal role in immune modulation, there is growing interest in understanding how MDSCs may influence the efficacy of vaccines, particularly in vulnerable populations. In this narrative review, we discuss whether MDSCs are able to regulate vaccine-induced immunity and whether their suppression can potentially enhance vaccine efficacy in vulnerable populations.
Keywords: Aging; cancer; chronic infection; myeloid-derived suppressor cell; obesity; vaccination.
Preventive vaccines have long been considered essential for controlling infectious diseases. By stimulating T and B cell responses, successful vaccination can provide robust protection against pathogens. However, not everyone responds equally to vaccination, and certain groups face challenges in mounting adequate immune responses, leaving them more vulnerable to vaccine-preventable diseases. Among these at-risk groups are aged individuals, individuals with excess body mass and patients battling cancer and chronic infections. What ties these groups together is the presence of chronic inflammation - a sustained and prolonged inflammatory response in the body that lingers for an extended period, typically weeks, months, or even years. Recent research has shed light on the role of so-called myeloid-derived suppressor cells (MDSCs) in driving and sustaining chronic inflammation. These MDSCs can inhibit the activity of T and B cells through various mechanisms and, therefore, these cells may be one of the reasons why the above-mentioned at-risk groups cannot develop a normal response after vaccination. In this study, we reviewed the available information on the role of MDSCs in controlling vaccine-induced immune responses and discussed the strategies that may enhance vaccination outcomes in at-risk groups.