Murine splenic CD4⁺ T cells, induced by innate immune cell interactions and secreted factors, develop antileukemia cytotoxicity.

Inciting the cellular arm of adaptive immunity has been the fundamental goal of cancer immunotherapy strategies, specifically focusing on inducing tumor antigen-specific responses by CD8(+) cytotoxic T lymphocytes (CTL). However, there is an emerging appreciation that the cytotoxic function of CD4(+) T cells can be effective in a clinical setting. Harnessing this potential will require an understanding of how such cells arise. In this study, we use an IL12-transduced variant of the 70Z/3 leukemia cell line in a B6D2F1 (BDF1) murine model system to reveal a novel cascade of cells and soluble factors that activate anticancer CD4(+) killer cells. We show that natural killer T cells play a pivotal role by activating dendritic cells in a contact-dependent manner; soluble products of this interaction, including MCP-1, propagate the activation signal, culminating in the development of CD4(+) CTLs that directly mediate an antileukemia response while also orchestrating a multipronged attack by other effector cells. A more complete picture of the conditions that induce such a robust response will allow us to capitalize on CD4(+) T-cell plasticity for maximum therapeutic effect.