Il3, also known as interleukin-3, is a hemopoietic growth factor involved in the survival, proliferation, and differentiation of multipotent hemopoietic cells [3]. It is associated with the regulation of various hematopoietic lineages, including neutrophilic, eosinophilic, basophilic granulocytes, monocytes, red cells, and platelets. IL3-related pathways can impact inflammation, immunity, and hematopoiesis, making it biologically important. Genetic models, such as gene knockout (KO) mouse models, are valuable for studying its functions.

In cancer research, IL3-driven T cell-basophil crosstalk has been found to enhance antitumor immunity. Intratumoral CTLs show a decline in IL3 production, correlating with impaired cytotoxic function. Augmenting IL3 supplementation, via various means, protects against tumor progression by increasing CTL activity. CTLs are crucial for this effect as IL3 has no impact on tumor growth in Rag1 knockout mice or after CD8+ T-cell depletion. Instead, CTL-derived IL3 acts on basophils, amplifying antitumor immunity within CTLs. Basophil-derived IL4, induced by IL3, further elevates CTL IFNγ production and viability, as seen by the lack of benefits of IL3 supplementation in IL4 knockout tumor-bearing mice [1].

In transplantation settings, IL3 has a detrimental effect on hematopoietic stem cell self-renewal. Using the commonly used cytokine combination with or without IL3 for CD34+ cell expansion and transplanting into NSG mice, it was found that IL3 leads to lower human cell engraftment and repopulating capacity, suggesting a negative effect on HSC self-renewal [2].

In conclusion, Il3 is essential in regulating hematopoietic cell functions, inflammation, and immunity. The use of KO mouse models in cancer and transplantation research has revealed its significant roles. In cancer, it can enhance antitumor immunity through T cell-basophil crosstalk, while in transplantation, it negatively impacts hematopoietic stem cell self-renewal, providing insights into potential therapeutic strategies and limitations in these disease areas.