IL-3-driven T cell-basophil crosstalk enhances anti-tumor immunity
Cytotoxic T lymphocytes (CTLs) are pivotal in combating cancer, yet their efficacy is often hindered by the immunosuppressive tumor microenvironment, resulting in exhaustion. This study investigates the role of interleukin (IL)-3 in orchestrating anti-tumor immunity through CTL modulation. Intratumoral CTLs undergo a progressive decline in IL-3 production, which is correlated with impaired cytotoxic function. Augmenting IL-3, through intraperitoneal administration, IL-3-expressing melanoma cells, or IL-3-engineered CD8+ T cells, confers protection against tumor progression, concomitant with increased CTL activity. CTLs are critical in this therapeutic efficacy as IL-3 demonstrates no impact on tumor growth in RAG1 knockout mice or following CD8+ T cell-depletion. Rather than acting directly, CTL-derived IL-3 exerts its influence on basophils, synergistically amplifying anti-tumor immunity within CTLs. Introducing IL-3-activated basophils retards tumor progression, whereas basophil depletion diminishes the effectiveness of IL-3 supplementation. Furthermore, IL-3 prompts basophils to produce IL-4, which subsequently elevates IFN-{gamma} production and viability of CTLs. Notably, the importance of basophil-derived IL-4 is evident from the absent benefits in IL-3-supplementated, IL-4 knockout tumor-bearing mice. Overall, this research unveils IL-3-mediated CTL-basophil crosstalk in regulating anti-tumor immunity and offers the prospect of harnessing IL-3 sustenance as a promising approach for optimizing and enhancing cancer immunotherapy. Significance StatementThis study elucidates the critical role of IL-3 in orchestrating anti-tumor immunity, particularly within the context of CTLs and melanoma growth. It reveals a progressive decline in CTL-derived IL-3 during tumor progression, correlated with CTL exhaustion--a formidable barrier in cancer immunotherapy. Intriguingly, augmentation of IL-3, achieved through diverse means, effectively impedes tumor progression by enhancing CTL activity. This research unveils a novel mechanism: IL-3-mediated crosstalk between CTLs and IL-4-producing basophils, resulting in the rejuvenation of CTLs and amplifying their anti-tumor ability. These insights hold promise for the advancement and optimization of cancer immunotherapeutic strategies, deepening our comprehension of CTL dynamics within the tumor microenvironment, and advancing our ability to combat cancer effectively.